5 - Final recommendation on the Stormwater Strategic Plan
CITY OF BOULDER
WATER RESOURCES ADVISORY BOARD
AGENDA ITEM
MEETING DATE:April 16, 2007
AGENDA TITLE:
Final Recommendation on the Stormwater Strategic Plan
PREPARING DEPARTMENT:
Robert E. Williams – Director of Public Work for Utilities
Robert J. Harberg – Utilities Planning and Project Management Coordinator
Douglas Sullivan – Engineering Project Manager – Presenter
Jeff Arthur – Engineering Review Manager
Donna Scott – Stormwater Quality Specialist
Brett Hill – Information Resources GIS specialist
FISCAL IMPACT:
None
PURPOSE:
This agenda item presents the Stormwater Strategic Plan dated April 2007
ATTACHMENT A
(). Utilities staff recommend that the Water Resources Advisory Board (WRAB)
accept the Stormwater Strategic Plan as presented including the priorities assigned to the various
projects and provide any other recommendations concerning the allocation of Capital Improvement
Program (CIP) funding to these projects and other funding options that the WRAB would like
Utilities staff to consider.
EXECUTIVE SUMMARY:
The Stormwater Strategic Plan (SSP) is a comprehensive analysis of the city’s storm sewers and
local drainage systems, and is intended to guide future Stormwater and Flood Management Utility
(Utility) decisions. The SSP serves to update the 1984 Stormwater Collection System Master Plan
(1984 Plan). The SSP goals include the following:
Efficiently manage stormwater runoff
Protect water quality
Minimize localized flooding impacts
The SSP involved the development of a hydrologic and hydraulic model to evaluate the stormwater
collections system’s ability to convey the flow associated with the 2-year and 5-year storm events.
The SSP identifies a recommended CIP project list for storm sewer conveyance and water quality
improvements throughout the city. This project list includes 51 conveyance water quality projects
which are organized into three categories (Tier 1, Tier 2, and Tier 3). Tier 1 projects represent major
Agenda Item V, Page 1
system deficiencies; Tier 2 projects represent moderate system deficiencies; and Tier 3 projects
represent nuisance system deficiencies. There are four Tier 1 problems, 16 Tier 2 problems and 31
Tier 3 problems identified. These potential projects range in cost from $63,000 to $11,000,000. A
map of the recommended CIP is shown in Figure ES-3.
In the report’s presentation, the water quality problems are integrated with the conveyance problems
when they are located in the same vicinity. Additionally, the SSP identifies 12 Water Quality Areas
of Concern, which represent the areas of the city responsible for the largest volume of pollutant
loading to the drainageways. The Water Quality Areas of Concern represent potential small capital
projects, ranging in cost between $51,000 and $157,000. The 12 projects have an estimated total
cost of approximately $1,000,000. The total cost associated with the conveyance and water quality
projects is listed below:
Tier 1 = $20,000,000
Tier 2 = $22,000,000
Tier 3 = $17,000,000
WQ = $1,000,000
Total = $60,000,000
A map of the Water Quality Areas of Concern is shown in Figure ES-2.
BACKGROUND:
The SSP has been a 16-month project, begun in January 2006, which involved numerous analytical
tasks necessary to develop a recommended projects list. An overview of these tasks was presented
ATTACHMENT B
in the February 26, 2007 WRAB Agenda Item ().
FISCAL IMPACTS:
There are no fiscal impacts at this time. Staff will evaluate the allocation of CIP funding to projects
identified in the SSP and other funding options as part of the 2008 budget process.
ANALYSIS:
A detailed analysis summarizing the key components in the SSP was provided in the February 26,
ATTACHMENT B
2007 WRAB Agenda Item ().
The SSP identifies a CIP of approximately $60,000,000 in potential storm sewer related projects.
Cash funding for projects in the current Utility CIP is $2-2.5 million per year (see
ATTACHMENT C
: 2007-2012 Stormwater and Flood Management CIP.) The funding rate for
stormwater management projects is $300,000 over the next few years and escalates to $800,000
in 2012. The number one Tier 1 project is the Upper Goose Creek drainage basin, located in the
th
vicinity of 9 Street and Balsam Avenue. Improvements associated with this project are
estimated at $11,000,000, and would likely be completed in numerous phases. Therefore, the
current funding allocated to stormwater management is inadequate to complete this project in the
near future.
Based on an analysis of the CIP budget expenditures between 1990 and 2006, 80 percent of the
funding has been allocated to major drainage way corridors. Two of the marquee major
Agenda Item V, Page 2
drainageway projects competed in the last 20 years include Bear Canyon Creek and Goose
Creek. Below is a breakdown of the expenditure allocation for the last 17 years. During this
period, only 10 percent of the total CIP funds were allocated to storm sewer improvements:
Major drainage ways = $14,000,000 (37%)
Property acquisition = $16,400,000 (43%)
Storm sewers = $3,800,000 (10%)
Greenways = $1,300,000 (6%)
Miscellaneous = $2,300,000 (4%)
Total = $37,800,000 (100%)
The focus on the major drainage way improvements has been to address the threats to life safety and
property along the major drainage way corridors as well as the opportunity to collaborate under the
city’s Greenways Program goals which include improvements for flood mitigation, alternative
transportation, recreation, wildlife habitat and water quality. There are still many identified threats to
life safety and property as well as opportunities to collaborate on projects through the Greenways
Program such that continued emphasis on major drainage way corridors is likely. These corridors
include South Boulder Creek, Wonderland Creek, Fourmile Canyon Creek, and Elmer’s Two-mile
Creek as listed in the current Utility CIP.
Modern development standards call for urban drainage systems to convey the flow associated with
the 2-year and 5-year storm events. Major areas of the city were developed prior to these standards
being established and so there are numerous deficiencies. However, these deficiencies do not pose
the same level of threat to life safety and property damage as those posed along the city’s major
drainage ways by storm events. As a result or these considerations, it is unlikely that major changes
to the current funding allocations or new funding options will be recommended by staff as part of the
2008 budget process. Staff will continue to evaluate these issues each year as part of the annual
budget process.
OTHER IMPACTS:
None
OTHER BOARD AND COMMISSION FEEDBACK:
None
PUBLIC FEEDBACK:
None
STAFF RECOMMENDATION:
Utilities staff recommends that the WRAB accept the Stormwater Strategic Plan recommendations
including the priorities assigned to the various projects and provide any other recommendations
concerning the allocation of Capital Improvement Program (CIP) funding to these projects and other
funding options that the WRAB would like Utilities staff to consider.
ATTACHMENTS:
A.Stormwater Strategic Plan Report dated April 2007
B.February 26, 2007 Water Resources Advisory Board Agenda Item (memo only)
C.2007-2012 Stormwater and Flood Management Utility CIP
Agenda Item V, Page 3
9ROXPH²'UDIW5HSRUW
City of Boulder
Stormwater Strategic Plan
Prepared for
City of Boulder
April 2007
Prepared by
HDREngineering
Supporting Documents
Several technical memorandums (TMs) were developed through the course of this project.
These TMs provide supporting information for the analysis, improvement alternatives and
recommendations contained in this report. The supporting documents are summarized below
for reference and bound in separate volumes for future use by the City and the engineering
community.
Volume 2 – Technical Appendices
Appendix A: Model Input Data Tables, Results Tables and XPSWMM output.
Appendix B: Model Network Mapping
Appendix C: Detailed Cost Estimates
Volume 3 – Hydraulic Technical Memoranda
TM 3.2 Design Storm
TM 4.2 Groundwater Mapping and Future Tasks
TM 5.1 Hydraulic Conceptual Alternatives
TM 5.1b Storm Drain and Canal Separation Alternatives
TM 5.1c Goose Creek Alternatives
TM 5.1d Broadway Improvement Alternatives
Volume 3 – Water Quality Technical Memoranda
TM 3.5 Water Quality Model and Construction Results
TM 3.6.1 Water Quality Analysis Results
TM 3.6.3 Water Quality Recommendations
TM 4.3 BMP Toolbox
Contents
Section Page
Executive Summary............................................................................................................................1
Introduction...............................................................................................................................7
1.1Goals and Objectives......................................................................................................7
1.2Stormwater Planning Process........................................................................................7
1.3Previous Studies..............................................................................................................8
1.4Stormwater Management Principles and Policies......................................................8
1.4.1Guiding Principles................................................................................................9
1.4.2Stormwater Management Policies......................................................................9
Analysis and Problem Identification Criteria...................................................................17
2.1Study Area......................................................................................................................17
2.1.1Topography.........................................................................................................17
2.1.2Land Use..............................................................................................................17
2.1.3Soils.......................................................................................................................17
2.1.4Climate.................................................................................................................18
2.2System Analysis Criteria..............................................................................................18
2.2.1Design Storms.....................................................................................................18
2.2.2Continuous Simulation Modeling....................................................................19
2.2.3Stormwater Conveyance Elements..................................................................19
2.2.4Landuse and Imperviousness...........................................................................19
2.3Problem Identification Criteria...................................................................................20
2.3.2Water Quality......................................................................................................21
Model Development..............................................................................................................23
3.1Modeling Approach......................................................................................................23
3.1.1Data and Basis of Model Construction............................................................23
3.2Hydrologic and Hydraulic Model..............................................................................24
3.2.1Existing Condition Model Construction.........................................................24
3.2.2Model Validation Parameters and Results......................................................28
3.2.3Future Condition Model Construction............................................................31
3.3Water Quality Model....................................................................................................31
3.3.1Model Construction............................................................................................32
System Analysis and Results...............................................................................................35
4.1System Description.......................................................................................................35
4.1.1Major Drainageways..........................................................................................35
4.1.2Irrigation Canals.................................................................................................35
4.1.3Storm Drains........................................................................................................35
4.2Storm Drain Problem Identification...........................................................................35
4.3Storm Drain Problem Prioritization...........................................................................36
4.3.1Criteria and Definitions.....................................................................................36
III
CONTENTS, CONTINUED
Section Page
4.3.2Criteria Weights and Ranking..........................................................................37
4.3.3Problem Area Priorities......................................................................................38
4.4Irrigation Canal Problem Identification.....................................................................40
4.5Water Quality Areas of Concern.................................................................................40
4.5.1Catchments..........................................................................................................40
4.5.2Outfalls.................................................................................................................41
System Improvement Recommendations..........................................................................43
5.1Hydraulic Alternatives.................................................................................................43
5.1.1Alternative Development Process....................................................................43
5.1.2Alternative Evaluation Process.........................................................................44
5.1.3Upper Goose Creek ² Alternative Analysis....................................................44
5.1.4Canal Separation Conceptual Alternatives.....................................................45
5.2Water Quality Alternatives..........................................................................................46
5.2.1Alternative Development 3URFHVV² Water Quality Areas of Concern.......46
5.2.2Alternative Development Process ² Boulder Creek Outfalls.......................46
5.2.3Alternative Evaluation and Recommendations.............................................47
5.3Recommended Plan......................................................................................................50
5.3.1Recommendations ² Bear Canyon Creek Subbasin.......................................51
5.3.2Recommendations ² Dry Creek Subbasin.......................................................52
5.3.3Recommendations ² Dry Creek No. 2 Subbasin............................................52
5.3.4Recommendations ² Elmers Twomile Creek Subbasin.................................53
5.3.5Recommendations ² Fourmile Canyon Creek Subbasin...............................53
5.3.6Recommendations ² Goose Creek Subbasin...................................................53
5.3.7Recommendations ² Kings Gulch Subbasin...................................................54
5.3.8Recommendations ² Lower Boulder Creek Subbasin...................................55
5.3.9Recommendations ² Middle Boulder Creek Subbasin..................................55
5.3.10Recommendations ² Skunk Creek Subbasin...................................................57
5.3.11Recommendations ² Viele Channel Subbasin................................................57
5.3.12Recommendations ² Wonderland Creek Subbasin.......................................58
Capital Improvement Program............................................................................................59
6.1Cost Estimating.............................................................................................................59
6.2Implementation Plan....................................................................................................59
6.3Recommended Plan Fact Sheets..................................................................................64
6.3.1Tier 1 Priority Improvements............................................................................64
6.3.2Tier 2 Priority Improvements............................................................................69
6.3.3Tier 3 Priority Improvements............................................................................88
6.3.4Water Quality Specific Projects.........................................................................90
IV
CONTENTS, CONTINUED
Section Page
/LVWRI)LJXUHV²5HFRPPHQGHG3ODQ)DFW6KHHWs
GC_01:UPPERGOOSECREEK...................................................
E!B.
RROR OOKMARK NOT DEFINED
GC_02:.............................................................................................65
BROADWAY,IRISTOBALSAM
MBC_10:18ANDSPRUCESTREET.................................................................................................66
TH
MBC_14:ARAPAHOEAND28STREET.........................................................................................67
TH
DC_01:GUNBARREL²SPINEROAD,LOOKOUTAND63SYSTEMS.....................................68
RD
SC_01:MOORHEADANDMOORHEADFRONTAGE...................................................................69
MBC_04:LINCOLN................................................................................................................................71
WC_03:VAILANDINDEPENDENCE................................................................................................72
MBC_22:ARAPAHOE,COMMERCE,ANDRANGE.......................................................................73
MBC_20:PARKINGSTRUCTUREBETWEENFOOTHILLSAND38.........................................74
TH
DC2_02:THUNDERBIRD,OSAGE,ANDFOOTHILLS....................................................................75
GC_08:FOOTHILLSANDVALMONT...............................................................................................77
GC_09:INDUSTRIALAREANEARPEARLPARKWAYANDWONDERLANDCREEK.........78
ETC_01:BROADWAYANDIRIS.........................................................................................................79
MBC_23:ACCESSRDAND55ST/PEARLANDBOULDERCREEK.........................................80
TH
DC2_06:ARAPAHOE/56THSTREETANDDRYCREEK................................................................81
SC_02:EUCLIDAND30.....................................................................................................................82
TH
MBC_09:16ST......................................................................................................................................83
TH
GC_04:FOLSOM,GLENWOOD,&FLORAL.....................................................................................84
BCC_03:GILLASPIEANDSHOPPINGCENTERPARKING..........................................................87
MBC_18:ARAPAHOEAND30STREET.........................................................................................88
TH
MBC_19:MARINEAVENUEANDBOULDERCREEK....................................................................89
LBC_02:BOULDERCREEK1,4·EASTOF75STREET...............................................................90
TH
MBC_16:BOULDERCREEK&28STREET......................................................................................90
TH
LBC_01:BOULDERCREEK&75STREET.......................................................................................91
TH
MBC_06:BOULDERCREEK&EASTBROADWAYSTREET&ARAPAHOEAVENUE............91
MBC_11:BOULDERCREEK·WESTOFFOLSOMSTREET.......................................................92
MBC_12:BOULDERCREEK&FOLSOMSTREET.............................................................................92
MBC_03:BOULDERCREEK&9STREET........................................................................................93
TH
KG_01:BROADWAY&SKUNKCREEK.............................................................................................93
MBC_07:BOULDERCREEK&13STREET......................................................................................94
TH
MBC_05:BOULDERCREEK&11STREET......................................................................................94
TH
V
CONTENTS, CONTINUED
Section Page
List of Tables
Table ES-1: Tier 1 Hydraulic and Combined Hydraulic/Water Quality CIP Projects.....................5
Table ES-2: Water Quality Improvement CIP Projects.........................................................................5
Table 2.2-1 Rainfall Depth-Duration-Frequency Values, NOAA Atlas II........................................18
Table 3.2-1 Horton Infiltration Parameters...........................................................................................25
Table 3.2-2 Comparison of Impervious Percentages...........................................................................26
7DEOH0DQQLQJ·V5RXJKQHVV9DOXHV............................................................................................27
Table 3.2-4 CUHP Validation Subcatchment Parameters..................................................................29
Table 3.2-5 Validation Results: 5-yr, 1-hr, Peak Flow Summary......................................................30
Table 3.2-6 Validation Results: 5-yr, 1-hr, Peak Flow Summary......................................................30
Table 3.2-7 Future Condition Imperviousness by Landuse...............................................................31
Table 3.3-1 Event Mean Concentrations (EMC) Values......................................................................33
Table 3.3-2 BMP Pollutant Removal Efficiencies.................................................................................34
Table 3.3-3 Proprietary BMP Locations.................................................................................................34
Table 4.3-1 Problem Prioritization Criteria and Definitions..............................................................37
Table 4.3-2 Weighting Criteria...............................................................................................................38
Table 4.3-3 Summary of Problem Area Ranking Results..................................................................38
Table 4.5-1 Top 12 Pollutant Contributing Outfalls............................................................................41
Table 5.2-1. Common Water Quality Area of Concern and Boulder Creek Outfalls....................47
Table 5.2-2 TSS Removal and Costs for Recommended BMPs........................................................48
Table 5.2-3 Recommended Water Quality Sites..................................................................................49
Table 5.3-1 Summary of Recommended Improvements - Bear Canyon Creek Subbasin..............51
Table 5.3-2 Summary of Recommended Improvements - Dry Creek Subbasin.............................52
Table 5.3-3 Summary of Recommended Improvements - Dry Creek No. 2 Subbasin...................52
Table 5.3-4 Summary of Recommended Improvements - Elmers Twomile Creek Subbasin.......53
Table 5.3-5 Summary of Recommended Improvements - Fourmile Canyon Creek Subbasin.....53
Table 5.3-6 Summary of Recommended Improvements - Goose Creek Subbasin.........................54
Table 5.3-7 Summary of Recommended Improvements - Kings Gulch Subbasin..........................55
Table 5.3-8 Summary of Recommended Improvements - Lower Boulder Creek Subbasin..........55
Table 5.3-9 Summary of Recommended Improvements - Middle Boulder Creek Subbasin........55
Table 5.3-10 Summary of Recommended Improvements - Skunk Creek Subbasin.......................57
Table 5.3-11 Summary of Recommended Improvements - Viele Channel Subbasin.....................57
Table 5.3-12 Summary of Recommended Improvements - Wonderland Creek Subbasin............58
Table 6.2-1 Tier 1, Tier 2 and Tier 3 CIP Projects Implementation Plan...........................................59
Table 6.2-2 Water Quality Improvements Implementation Plan......................................................63
VI
GLOSSARY OF TERMS
ac-ftacre-feet
BMPsbest management practices
BTVBoulder Transit Village
BVCPBoulder Valley Comprehensive Plan
CFSComprehensive Flood and Stormwater Utility Master Plan
cfscubic feet per second
CIPCapital Improvement Plan
Citythe city of Boulder
Cucopper
CUHPColorado urban hydrograph procedure
DCSdesign and construction standards
DTMdigital terrain model
EMCeventmeanconcentration
HGLhydraulic grade line
lbs/ac/yrpounds per acre per year
LIDlow impact development practices
MDCIAminimum of directly connected impervious area
mg/Lmilligrams per liter
µg/Lmicrograms per liter
mslmean sea level
NOAANational Oceanic & Atmospheric Administration
NPDESNational pollutant discharge elimination system
Natural Resources Conservation Service (formerly the Soil
NRCS
Conservation Service)
Pphosphorous
Pblead
Qratio of peak flow capacity to full flow capacity
Ratio
Q(wq)water quality design storm peak flow (cfs)
SSPStormwaterStrategicPlan
SSURGOSoil Survey Geographic (database)
SWMMStormwaterManagementModel
TMCCTwo Mile Canyon Creek
TMstechnicalmemorandums
TSStotal suspended solids
UDFCDUrban Storm Drainage Criteria Manual
USGSU.S. Geological Survey
WQIMPwater quality improvement projects
Znzinc
VII
Executive Summary
The original 1984 City of Boulder Storm Water Collection System Master Plan is being updated
to reflect changes in land use, infrastructure and the regulatory climate as well as anticipated
redevelopment within the community. The revised Stormwater Strategic Plan (SSP) provides
the City of Boulder with the necessary planning tools and capital improvement projects to
address flood management and water quality within the collector portion of the storm drainage
system for the next decade.
The Boulder SSP was developed to replace the 1984 plan with a document that is more inline
with present-day problems and opportunities and the City’s overarching environmental,
economic and social goals. The goal of the Boulder SSP is to proactively manage stormwater
runoff to protect water quality and to minimize impacts of localized and downstream flooding by
identifying infrastructure improvements for the collection, conveyance and treatment of
stormwater runoff from within the City. The SSP prioritizes storm drain and water quality
improvements within the City and provides an implementation plan for the construction of
conveyance and water quality improvements
Major activities undertaken in the development of the plan include the following:
Develop system analysis and problem identification criteria,
Develop hydrologic, hydraulic and water quality models,
Evaluate the system and rank problem areas,
Perform alternatives analysis and develop a recommended plan,
Prepare a capital improvement plan.
Study Area Characterization
The City of Boulder, with a population of approximately 100,000 and an area of nearly 25.5
square miles, is locatedalong the front range of the Rocky Mountains, northwest of Denver,
Colorado. Within the City, there are 12 subbasin and 15 major creeks (a.k.a. major
drainageways) that generally flow from west to east as they converge on Boulder Creek, which
is the main tributary flowing through the City. Runoff from within the City is conveyed to these
major drainageways by the City’s collector storm drain system and the irrigation canal system.
At present, Boulder is nearly fully built-out withmuch of the future development expected to
occur as site redevelopment. Collectively, the current impervious percentage, assuming 2006
land use conditions,is 32% and is projected to be 34% under the Boulder Valley
Comprehensive Plan. However, considering the City’s Design and Construction Standards
(DCS), the net future condition imperviousness used for this analysis was determined to be
33%,
Planning and Analysis Criteria
A master planning analysis was performed to identify potential collector system stormwater and
associatedwater quality improvements within the City of Boulder. The evaluation was guided
by a set of system analysis criteria used to identify conveyance and water quality problem areas
and to evaluate potential improvements. These criteria included quantitative assessments of
storm drain surcharging, culvert overtopping, channel/canal flooding, structure flooding
(buildings, etc) and pollutant loadings. Other system analysis criteria used to support the study
1
included design storms (2-year, 5-year and water quality), landuse (existing and future
conditions)and model boundary conditions.
Analysis Approach
A key element in the master planning process is the development of a hydrologic, hydraulic and
water quality model of the natural and man-madestormwater system within the City. The model
should be capable of analyzing runoff conditions; predicting flooding risk; estimating
comparative pollutant loadings; evaluating existing facilitiesand infrastructure; and designing
proposed improvements. To these ends, the primary objectives of the stormwater analysis were
to:
Construct a model that accurately represents the existing stormwater system within the
City’s collector system.
Validate the model to previous studies and regional rainfall-runoff statistics.
Utilize a land use-based method to estimate runoff under current conditions and incorporate
the Boulder Valley Comprehensive Plan to represent future development conditionswithin
the City.
Evaluate the existing stormwater infrastructure with respect to the system analysis criteria
and rank each problem in terms of severity.
Locate, size and assess the performance of new stormwater management facilities
including pipes, detention ponds, surface channel and irrigation canals.
Locate, size and assess the performance of new water quality facilities based on areas
identified in the model that exhibit elevated pollutant concentrations and/or loads.
Limits of Analysis
The focus of the Boulder SSP is the collector storm drainage system, which includes pipe 18” in
diameter and larger and primary open channel systems that are not part of the City’s major
drainageways. To further refine the stormwater conveyance system, two levels of service are
provided based on landuse and roadway category. For areas that are mainly residential in land
use, the 2-year recurrence interval design storm was used to identify problems in the
downstream conveyance system. For areas draining mainly commercial, industrial and collector
and arterial roadways, the 5-year event was used. Areas within the city that experience
localized flooding (e.g., undersizedpipes that are less than 18 inches in diameter; roadside
ditches; and clogged catch basins) were not considered as part of this study unless they have
been identified by the City as known flooding locations.
Modeling Approach
The modeling approach for the Boulder SSP integrated GIS as a pre- and post-processing tool
with an EPA-based Storm Water Management Model (SWMM) as the hydrologic, hydraulic and
water quality analysis tool. The analysis software used for the project was XPSWMM which is a
proprietary version of EPA-SWMM software that provided an efficient GIS interface that EPA-
SWMM does not have at this date.Workflow began in GIS, where the input parameters for the
SWMM model were developed. This data was transferred out of GIS to SWMM, for the
evaluation of the system hydraulics and water quality. Model results were ultimately brought
back into GIS for post processing and storage for future reference by the City.
Landuse and CityDevelopment Criteria
Land use is a key factor in assessing stormwater runoff because it affectsboth the quantity
(volume and peak) and quality of water being routed through the stormwater system and natural
channels. The effect land use has on water quantity can be generally linked to the amount of
2
impervious area for a particular land use category. The more impervious the area, the faster the
water will be routed to the storm water collection system due to the lower surface roughness of
the ground. It will also have an increase in volume since infiltration can not occur through
impervious surfaces. Consequently, an area with a higher percentage of impervious surfaces
will produce higher peak flows over a shorter period of time than will a similar area with a lower
percentageof impervious surfaces.
The future conditions scenario represents a fully developed urban area according to the Boulder
Valley Comprehensive Plan, 2006 (BVCP). This scenario represents a worst case scenario
from a stormwater perspective because it encompasses the highest level of imperviousness.
However, this scenario has also incorporated the City’s DCS, which require detention and water
quality treatment for all new impervious areas associated with new and re-development
projects. As discussed in later sections of this report, the City performed an inventory of
existing detention and treatment facilities and it was identified that roughly 78% of all current
facilities are adequately functioning (22% have failed). Consequently, to incorporate the DCS,
this same facility performance level (78%) was also assumed to occur under future development
conditions.To accomplish this, thechange in impervious percentage between existing and
future conditions was reduced by 78% to account for the detention and treatment facilities that
will collectively be built as the city develops and/or re-develops.
Problem Identification
Utilizing the verified SWMM model, runoff, hydraulic, and water quality calculations were
completed for two different land use scenarios: existing conditions and future conditions, and
three different design storms: the 2- and 5-yr events and the water quality storm. These results
were then evaluated with respect the previously noted system analysis criteria to identify
specific system deficiencies within the City’s collector storm drain system.
Hydraulic Problem Areas and Ranking
Model results for existing conditions indicate that 572 nodes out of 1635 nodes within the model
violate one or more of the noted criteria. To better understand the cause and affect of each
problem area, a number of these deficient nodes and links were combined together into
individual problem locations. This resulted in a total of 51 hydraulic problem locations. Irrigation
canal segments were also added to the problem identification list if the correspondingdesign
storm causes the channel to overtop its banks and flood the surroundingarea.
Due to the relatively large number of problem locations identified through the modeling and GIS
analysis, and due to limitations within the City’s capital budget, a ranking was performed on the
problem areas to prioritize the conveyance problems. This process resulted in identifying three
problem priority levels; Tier 1, Tier 2 and Tier 3 indicatingsevere, major or minor problem areas,
respectively. The process of ranking system problems into tiers utilized a point-basedmatrix
using a weighted criteria approach.Six criteria were used to rank the problem areas. These
criteria include: 1) the extent of the problem, 2) the flooded volume, 3) the impact to neighboring
structures, 4) the length of under capacity pipe, 5) the confidence in the underlying data and 6)
the proximately of the hydraulic problem to waterquality areas of concern. The problem
prioritization process resulted in five Tier 1 problem areas, 17 Tier 2 problem areas, and 31 Tier
3 problem areas. These problem locations are shown on Figure ES-1.
Water Quality Analysisand Problem Areas
The water quality analysis included two separate approaches to identify problem locations within
the collector system: 1) a buildup-washoff analysis using the XPSWMMmodel to identify water
quality areas of concern that produce high pollutant loads and 2) targeted outfall approach
focusing on the collector system outfalls to Boulder Creek. The water quality area of concern
3
approach used the XPSWMMmodel to identify areas within the City having comparatively
higher pollutant concentrations and/or loads. This approach identified 12 locations within the
City that were characterized as water quality areas of concern. The Boulder Creek outfall
approach identified 17 collector system outfalls that do not currently receive pollution reduction
through regional water quality facilities. The water quality areas of concern and Boulder Creek
outfall sites are shown on Figure ES-2.
System Improvement Alternatives and Recommendations
Improvement alternatives were developed for the Tier 1 and Tier 2 problem areas and a
qualitative assessment identified the preferred alternative for each problem area. The Tier 3
problem areas did not receive an evaluation of different alternatives due to the limited severity of
the conveyance problems. Instead, improvements to resolve the Tier 3 problem areas consisted
of pipe replacement to increase the system capacity and resolve the conveyance problem.
For the water quality area of concern sites, improvement alternatives were developed to
evaluate the optimum improvement for a give site or location. Improvements for the Boulder
Creek outfall sites were developed based on the use of proprietary BMPs (a.k.a. water quality
manholes) since these types of facilities are best suited for highly urbanized areas as typically
found near the collector system outfall top Boulder Creek. A cost/benefit analysis was
performed for the improvement water quality improvementsat each of the water quality area of
concern and Boulder Creek outfall sites. This process identified 18 water quality improvement
projects to address the address the water quality area of concern site and the Boulder Creek
outfall sites that favorable cost/benefit ratios or that did not rely on future development for
project implementation.
The recommended plan for addressing the conveyance and water quality problem areas is a
compilationof all hydraulic and water quality improvements developed in this study.Figure ES-
3 provides an overview of the recommended plan improvements with corresponding
improvement projects IDs. In some instances, the recommended water quality improvements
were in close proximity to a hydraulic improvement location and were combined into a single
project. Other recommended improvements consist of improvements that separately address
water quality or conveyance problems.
Capital Improvement Plan
The goal for this strategic plan is to manage stormwater, by minimizing impacts on localized and
downstream flooding and improving water quality. To these ends, the recommended system
improvements were categorized as 1) Hydraulic and Combined Hydraulic/Water Quality projects
or 2) Water Quality Improvement projects. These two project categories form the collector
system Capital Improvement Plan (CIP).
The implementation plan for the Hydraulic and Combined Hydraulic/Water Quality CIP projects
follows the Tier 1, 2 and 3 problem areas. Tier1 CIP projects are considered high priority
improvements as they resolve severe conveyance system problems and in some instances
address stormwater quality problems. Tier 1 projects areas are anticipated to a) have a high
social benefit by resolving street and property flooding issues,b) have a high economic benefit
by reducing flooding risk and property damage, and c) provide an environmental benefit by
addressingstormwaterquality issues at identified problem locations. Note that not all Tier 1
locations included a water quality problem site and that the overriding criterion for prioritization
was resolving flooding issues. Table ES-1 identifies the Tier 1 CIP projects; Tier 2 and 3
projects are identified in Sections 5 and 6 of the main report.
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Table ES-1: Tier 1 Hydraulic and Combined Hydraulic/WaterQuality CIP Projects
RankingImprovementLocationImprovement TypeCapital
IDCost
$10,701,000
1GC_02Upper Goose CreekPipe Replacement
New Storm Drain
Channel Improvement
$1,577,000
th
2MBC_1018 and Spruce Street Pipe Replacement
Storm Drain Re-Routing/Extension
$1,659,000
th
3MBC_14Arapahoe and 28Pipe Replacement
Street
Storm Drain Re-Routing/Extension
Proprietary BMP
$5,694,000
4DC_01Gunbarrel–SpinePipe Replacement
rd
Road, Lookout and 63
Storm Drain Re-Routing/Extension
Systems
Constructed Wetland
The implementation plan for the Water Quality Improvement (WQIMP) projects were prioritized
based on problem severity as identified by pollutant load. The WQIMP category was developed
since many of the water quality project sites were not adjacent to hydraulic problem and
improvement locations.In addition, many of these WQIMP projects could be defined as a small
capital projects since the estimated construction costs are less than $100,000.
Table ES-2: Water QualityImprovement CIP Projects
Location
ImprovementAnnualCapital
IDTSSCost
Load
(pounds)
$104,000
61,900 th
WQIMP 2 Boulder Creek 1,400’ East of 75 Street
$81,000
th
56,500
WQIMP 3 Boulder Creek & 28 Street
$76,000
th
WQIMP 5 46,200Boulder Creek & 75 Street
$157,000
WQIMP 6 & 45,700Boulder Creek & East Broadway Street & Arapahoe
WQIMP 9 & 38,400Avenue
WQIMP 8 $84,000
41,500Boulder Creek 200’ West of Folsom Street
WQIMP 12 $78,000
29,000Boulder Creek & Folsom Street
WQIMP 14 $73,000
24,200 th
Boulder Creek & 9 Street
WQIMP 15 $73,000
22,800
Broadway & Skunk Creek
WQIMP 16 $81,000
20,300 th
Boulder Creek & 13 Street
WQIMP 18 $51,000
th
15,000Boulder Creek & 11 Street
Estimates of capital construction costs included in this plan are considered planning level
estimates to be used in developing stormwater capital budget requirements.
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6
Introduction
The primary goal of the Boulder SSP is to provide the City with a guide to proactively address
existing and future flooding and water quality problem areas through a series of recommended
improvements to the City’s stormwater collection system. In 1984, the City developed a
stormwatercollection system master plan to guide upgrades and expansion to the system
through a capital improvement program. While this plan has been a useful document, new data
and analysis tools have become available, landuse conditions have changed and new
environmental regulations now need to be addressed. With this in mind, the Boulder SSP was
developed to replace the 1984 plan with a document that is more inline with present-day
problems and opportunities and the City’s overarching environmental, economic and social
goals.
1.1Goals and Objectives
The goal of the Boulder SSP is to proactively manage stormwater runoff to protect water quality
and to minimize impacts of localized and downstream flooding by identifying infrastructure
improvements for the collection, conveyance and treatment of stormwater within the city limits.
The plan prioritizes storm drain improvements based on problem severity including flooding
extent, stormwater pollutant loads, and an assessment of potential property damage risk. The
analyses performed in development of this plan expanded and built upon the City’s goals to
address environmental, economic andsocial issues. Each of these was addressed through the
following planning objectives:
Develop a stormwater infrastructureplan for the collectorsystem that alleviates current
capacity and flooding problems that can also manager addition runoff generated from future
development or redevelopment.
Identify site specific improvements that address stormwater quality to improve receiving water
quality for environmental and recreational benefit.
Identify implementable engineering solutions thatare context sensitive and cost effective.
Incorporatesocialimplications in the prioritization of recommended projects by focusing on
problem locations that impacts key community facilities, major transportation corridors and
protection of private property.
Recommended improvements that provide the greatest community benefit.
Recommend improvements that are sustainable from and operations and maintenance
perspective.
1.2Stormwater Planning Process
The planning process used in preparing the Boulder SSP involved a series of steps as generally
described below. Additionally, through a progression of workshops at the onset and completion
of the key step, input from City staff was gathered and incorporated into the plan to ensure the
overall goals and objectives were being met.
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Collect and review existing information, including previous studies, design, survey information
(including new survey), drainage reports and other data to support development of the plan
(Section 1)
Establish a set of goals, policies and analysis criteria that will guide the analysis and
development of a recommended plan (Section 1 and 2)
Develop and verify a hydrologic, hydraulic and water quality model of the collector storm
drainage system (Section 3)
Evaluate the existing stormwater infrastructure with respect to the system analysis criteria and
rank each problem in terms of severity (Section 4)
Develop alternatives for each problem area (Section 5)
Prepare a recommended plan, documenting the preferred alternatives, detailed cost
estimates significantimplementation issues (large utility conflicts,permitting, mitigation, etc),
(Section 6).
The format of the SSP report was based on the project workflow starting with project goals and
ending with recommended plan. The City of Boulder’s Project Planning and Approval Process
Handbook for Capital Improvement Program Projects (July 2003) presents a general framework
for master plans. The SSP report modified the suggested framework to accommodate the
project scope, purpose and needs. The content of the SSP is in agreement with that identified
in the City’s master plan framework.
1.3Previous Studies
Previouslywritten documents that address collector system stormwater management or overall
stormwatergoals and policies include the BVCP, the Comprehensive Flood and Stormwater
Utility Master Plan (CFS, written by the City of Boulder and URS Corporation, 2004), the
StormwaterCollection SystemMaster Plan (written by WRC Engineering, Inc, 1984) and the
City’s DCS. Other studies and documents that were also used in the developmentof the
Boulder SSP are listed in the bibliography of this report.
1.4Stormwater Management Principles and Policies
As series of guiding principles, policies, and implementation measures were used to define the
Boulder SSP approach. There are other principles and policies in the City’s overall drainage,
stormwatermanagement, and environmental programs that complement the stormwater facility
planning process but are not integral to achieving the primary goals of the StormwaterStrategic
Plan. As such, these overarching principles andpolicies are not included in this summary. For
example,managing constructionsite runoff is a component of the National Pollutant Discharge
Elimination System (NPDES) Phase II permit and has a direct impact on stormwater quality but
is not included in the scope of the Boulder SSP as it is a construction related program. While
this section primarily refers to specific planningprinciples and policies, the overarching guiding
document was the Design and Construction Standards (DCS). The SSP follows the criteria and
policies outlined in the DCS.
The approach of this report section is to present the general guiding principles, narrow these to
policies, and then present the more specific aspects, the implementation measures. Note this
document does not attempt to repeat previous principles, policies, and implementation
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measures word for word from previous documents, but rather to capture the general intent and
to include the most relevant specifics within the SSP.
1.4.1Guiding Principles
In the CFS, guiding principles for stormwater drainage and water quality were presented in the
respective chapters. These are listed below by topic and will also be included in the SSP, along
with additional guiding principles.Guiding principles from the CFS are italicized.
1.4.1.1Stormwater Drainage
1.Maintain and preserve existing andnatural drainage systems.
2.Reduce and manage developed runoff.
3.Eliminate drainage problems and nuisances.
1.4.1.2Stormwater Quality
1.Protect public health and the environment.
2.Manage pollution at the source.
3.Protect and enhance natural resources associated with the stream environment.
4.Prevent significant erosion resulting from stormwater outfalls and their adverse effects
on water quality.
1.4.1.3Multi-Objective Stormwater Planning
1.Integrate stormwater quantity and stormwater quality solutions.
2.Provide a regional approach to stormwater management that is consistent with other
communitygoals and plans.
3.Assure an orderly implementation of improvements to the storm drainage system to
serve existing and future development,both new development and redevelopment.
1.4.1.4Irrigation Ditches
1.Address irrigation ditch issues relating to the stormwater collection system, water quality,
conveyance of urban stormwater runoff, and contributions to groundwater conditions.
1.4.2Stormwater Management Policies
Policies and implementation measures for stormwater management were developed in the
BVCP, and additional ones were developed in the CFS. Those that are applicableto the SSP
are presented below along with policies and implementation measures to be adopted in the
SSP. Some of the policies and implementation measures to be adopted in the SSP are based
on those in the previous documents; others were developed by the project team to help guide
the master planning process.
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1.4.2.1Stormwater Drainage Systems
Policies and implementation measures for stormwater drainage systems address the
conveyance of stormwater runoff to the major drainageway system.
Policies fromthe Boulder ValleyComprehensive Plan
Policy 4.28Drainage Utility Plans
The City shall prepare and maintain drainage utility plans that define maintenance needs,
priorities for improvements, funding requirements, the character of necessary structural
improvements, and water quality issues.
Design Storm Frequency (BVCP Section 3.c - Urban Service Standards)
All local collection systems shall be designed to transport the following storm frequency:
Single family residential: 2-year storm
All other areas: 5-year storm
Policies and ImplementationMeasures from the CFS
Update the City’s Stormwater Collection System Master Plan
Update hydrology/hydraulic models from the 1984 Stormwater Collection System Master
Plan
Prioritize projects with a focus on known problems and future development areas.
Re-evaluate detention including the possibility of regional detention and increasing
existing detention.
Focus on smaller storms (less than1-inch) because of the greater hydrologic impact of
these storms.
SSP Policies and Implementation Measures
The policies or implementation measures that are a significant divergence from the BVCP, CFS
or the Design and Construction Standards are highlighted in italics.
Policy 1 – Stormwater Collection System Infrastructure
The City will provide an adequate stormwater collection andconveyance system for existing and
future development within the City.
Implementation Measures:
Update the collection system hydrologic and hydraulic models. Use appropriate land
use projections and associated imperviousness values to estimate the future stormwater
runoff.
Focus on problems areas created by smaller storms because of the greater hydrologic
impact of these storms.
Develop cost effective improvements to the existing storm drainage system resulting in a
continuousdrainage system that provides service to the upstream users.
Size the storm sewer system to convey the runoff from 2-year storm events in residential
areas and runoff from 5-year storm events in commercial areas. At a minimum,
collector and arterial roadways are to convey the 5-year storm event.
Prioritize CIP projects to develop a financing strategy to fund capital projects that
improve the storm drainage system. Financing strategies will be in accordance with
existing laws, rules and regulations,and may include an increase in the stormwater
utility fee.
10
Policy 2 – Maximize Existing Infrastructure
The City will maximize the use of existing storm drainage infrastructure and optimize the size of
required drainage system improvements.
Implementation Measures:
Allow limited surcharging in the existing storm drain piped system to increase
conveyance system capacity. These minimum levels of surcharging will provide a
sufficient safety factor as to prevent flooding under the design storm conditions by
limiting the hydraulic grade line to be approximatelyone foot below the ground surface.
Incorporateexisting private facilities and the one public detention facility in the system
analysis.
Utilize appropriate analysis and planning tools to evaluate the system capacity and
identify system improvements.
Policy 3– Open ChannelDrainage Systems
The City will strive to minimize flooding, stream bank and channel erosion within the open
channel storm drainage system by controlling the rate and volume of stormwater runoff from
development and redevelopment projects.
Implementation Measures:
Infiltrate storm runoff where site conditions allow as a means of reducing post
development runoff volumes and associated flow rates.
Continue to provide detention facilities that limit post-development runoff rates to
previous development rates.
Continue to require the minimization of directly connected impervious area (MDCIA),as
well as other development practicesto reduce discharges from storm sewer systems
into the receiving waters of the City, as specified in the city’s DCS.
1.4.2.2Stormwater Quality
Policies and implementation measures for stormwater quality address the reduction of pollutants
and runoff volume inherent in urban stormwater runoff to help mitigate their negative impacts on
the receiving waters.
Policies fromthe Boulder ValleyComprehensive Plan
Policy 4.19Protection of Water Quality
Water quality is a critical health, economic and aesthetic concern. The City and County shall
protect, maintain and improve water quality within the Boulder Creek basin and the Boulder
Valley watersheds as a necessary component of existing ecosystems and as a critical resource
for the human community. The City and County shall seek to establish comprehensive goals for
water quality, to maintain full compliance with federal and state water quality standards, and to
reduce point and non-point sources of pollutants. Special emphasis shall be placed on regional
efforts such as watershed planning and protection. Efforts shall be made to take an integrated
approach to the protection of groundwater, surface water and stormwater and to plan for future
needs.
Policy 4.22Stormwater
The City and County shall protect the quality of its surface water, meet all state and federal
regulations for stormwater quality, and evaluate additional voluntary standards as appropriate.
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Policy4.25 Pollution Control
The City and County shall seek to control both point and non-point sources of water through
pollution prevention, improved land use configurations, wetland detention areas, standards to
control degradation of streams and lakes caused by storm runoff in urban and rural areas, and
control and monitoring of direct sources of discharge, including those of gravel extraction and
wastewater treatment facilities.
Policies and ImplementationMeasures from the CFS
Update the Stormwater Management Plan to incorporate a watershed management approach
Balance quantity and quality issues
Prevention first, mitigation second – Prevent stormwater excessive runoff and pollution
at the source using techniques tailored to each sub-basin.
Apply conservation principles. Shift the focus from stormwater disposal to prevention
and conservation. Approach stormwater management as a resource to enhance natural
systems and processes
SSP Policies and Implementation Measures
The policies or implementation measures that are a significant divergence from the BVCP, CFS
or the Design and Construction Standards are highlighted in italics.
Policy 4 – Stormwater Quality CIP Projects
The City will strive to protect the quality of water in the storm drainage system and receiving
waters, including Boulder Creek, to maintain and enhance the environment, quality of life, and
economic well-being of the City of Boulder by identifying and implementing stormwater quality
CIP projects.
Implementation Measures:
Identify and implement regional, post-construction stormwater quality facilities (best
management practices or BMPs) that will reducepollutants from existing impervious
areas.
Emphasize the use of surface oriented BMPs to manage stormwater quantity and quality
in the City’s CIP projects.
Develop BMP Toolbox and user-friendly selection process, which will leverage other City
capital projects (e.g., water, transportation,parks) to assist in implementing stormwater
quality solutions.Include identification of practical low impact development practices
(LID) on a parcel level tomitigate impervious areas, runoff volume and associated
pollutants.
1.4.2.3Multi-Objective Planning
Policies and implementation measures for multi-objective planning are intended to identify
opportunities for including stormwater projects with other capital improvements in the City. This
will improve the efficiency of implementing stormwater improvements.
Policies fromthe Boulder ValleyComprehensive Plan
Policy 3.04ChannelingDevelopment to Areas with Adequate Infrastructure
In order to protect and use past investmentsin capital improvements, new development and
redevelopment shall be located in areas where adequate public servicesand facilities presently
exist or are planned to be provided under the City’s Capital Improvements Program.
Policy 3.07 Multi-purposeUse of Public Lands
Multi-purpose use of public lands, facilities, and personnel services shall be emphasized.
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Policy 3.10Utility Provision to Implement Community Goals
The City shall consider the importance of the other objectives of the Comprehensive Plan in the
planning and operation of the water, wastewater and stormwater management/drainage utilities.
These other objectives include in-stream flow maintenance, enhancement of recreational
opportunities, water quality management, preservation of natural ecosystems, open space and
irrigated agricultural land, and implementation of desired timing and location of growth patterns.
Policy 4.20 Water Resource Planning
Land use patterns that reduce water pollution and promote water conservation shall be
encouraged. Local development plans shall be reviewed for their impact on water quality.
Policies and Implementation Measures from the CFS
Update the Stormwater Management Plan by incorporating the following approaches:
Integrate water quality and other multi-objective issues.
Use multiple objectives approach. Develop solutions that coordinate management of
peak rates and volume, water quality, and maintenance.
Integrate BMPs into site design process. Determine appropriate application of BMPs in
prioritizedsub-basins in order to integrate BMPs into the first stages ofsite planning and
overall sub-basin planning.
SSP Policies and Implementation Measures
The policies or implementation measures that are a significant divergence from the BVCP, CFS
or the Design and Construction Standards are highlighted in italics.
Policy 5 – Stormwater Planningand Coordination
The City will continue to integrate the quantity and quality aspects of stormwater in the planning,
design, and construction of development and redevelopment projects, and will look for
opportunities to address stormwater issues when planning and designing other capital projects
in the City, including projects involving water, wastewater, transportation, and parks.
Implementation Measures:
Emphasize the use of surface oriented BMPs to manage stormwater quantity and quality
in private development projects through revisions to City ordinances and the
development code.
Identify and implement regional, multi-use drainage and stormwater quality facilities that
combine stormwater function with public and natural resource enhancements.
Investigateopportunities to removepollutants and reduce runoff volume by identifying
surface oriented BMPs in conjunction with acquisition of floodplain hazard properties.
Identify opportunities for drainage and water quality improvements related to
transportation, water, and wastewater projects.
Investigate an achievable level for implementation of low impact development practices
for new development that would reduce the size and extent of required improvements to
the existing storm drainage system.
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1.4.2.4Irrigation Ditches
Policies and implementation measures associated with irrigation ditchesaddress the quantity of
stormwater runoff discharged to the irrigation systems within the City and problems associated
with ditch over-topping.
Policies fromthe Boulder ValleyComprehensive Plan
Stormwaterand Flood Management (BVCPSection3.c - Urban Service Standards)
Storm runoff quantity greater than the ‘historical’ amount shall not be discharged into irrigation
ditches without the approval of the flood regulatory authority or the appropriate irrigation ditch
company.
Policies and Implementation Measures from the CFS
Update the City’s Stormwater Collection System Master Plan
The Stormwater Management Plan should address separating stormwater drainage from
the irrigation ditches.
SSP Policies and Implementation Measures
The policies or implementation measures that are a significant divergence from the BVCP, CFS
or the Design and Construction Standards are highlighted in italics.
Policy 6 – Separation of Stormwater Outfalls from Irrigation Ditches
Storm sewer outfalls (point discharges) are to be separated from irrigation ditches within the
City limits.
Implementation Measures:
Continue to allow surface runoff from undeveloped areas within the City to enter the
irrigation ditches via overland flow.
Identify near-term opportunities for removing storm sewer outfalls from irrigation ditches
that alleviate known ditch over-topping problem locations.
Identify a time schedule for separating the storm sewer system from irrigation ditches.
1.4.2.5Groundwater
Policies and implementation measures for groundwater are associated with the identification of
high groundwater areas and associated water quality issues.
Policies fromthe Boulder ValleyComprehensive Plan
Policy 4.24 Groundwater.
The City and County shall continueto evaluate aquifers, groundwater recharge and discharge
areas, and sources of groundwater pollution within the Boulder Creek watersheds and shall
formulate appropriate pollution and source protection programs. Impacts to groundwater shall
be considered in land use planning, development review and public land management
practices.
SSP Policies and Implementation Measures
The policies or implementation measures that are a significant divergence from the BVCP, CFS
or the Design and Construction Standards are highlighted in italics.
Policy 7 – Groundwater Impacts Resulting from Development
The City will continue to address groundwater issues related to development proposals and the
associateddischarge locations of pump groundwater flows including water quality impacts due
to potential groundwater quality issues at registered locations.
14
Implementation Measures:
The Stormwater Management Plan will not include pumpedgroundwater discharge into
the storm sewer system in the capacity analysis due to the level of complexity in
determining actual pumped flow rates and discharge locations.
Collect more accurate data on groundwater levels in potential problemareas, including
seasonal fluctuations.
Develop requirements,including groundwater quality, for disposal of pumped
groundwater into the stormwater collection system from dewatering activities.
Develop requirements formitigation plans for problem areas such as areas where
dewatering will impact wetlands and well levels.
At relevant sites, incorporate groundwater sampling into an overall water quality
monitoring plan.
Address problems related to the interaction of irrigation ditches and groundwater,
including groundwater contamination.
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Analysis and Problem Identification Criteria
The Boulder SSP was performed to identify improvements to the City’s collector storm drainage
system. The evaluation was guided by a set of system analysis criteria used to identify
conveyance and water quality problem areas and to evaluate potential improvements. These
criteria included quantitative assessments of storm drain surcharging, culvert overtopping,
channel/canal flooding, structure flooding (buildings, etc) and pollutant loadings.
This section presents a descriptionof the study area, the criteria used in the analysis of the
storm drainage system and the criteria used for identifying problems within the system.
2.1Study Area
The City of Boulder, with a population of approximately 100,000 and an area of nearly 25.5
square miles, is locatedalong the front range of the Rocky Mountains, northwest of Denver,
Colorado. Within the City, there are 12 subbasin and 15 major creeks (a.k.a. major
drainageways) that generally flow from west to east as they converge on Boulder Creek, which
is the main tributary flowing through the City (Figure 2-1). Runoff from within the City is
conveyed to these major drainageways by the City’s collector storm drain system and the
irrigation canal system.
2.1.1Topography
Topographically, Boulder sits roughly 5,430 feet above sea level. Elevations in the city range
from over 6,400 feet mean sea level (msl) aboveWonderland Lake on the west side of the city
to approximately 5,100 feet (msl) near Boulder Reservoir in the northeast corner of town.
Surface slopes within the city are relatively flat with few areas exceeding 5% except for the
western foothills, where slopes nearing 1:1 are not uncommon (Figure 2-2).
2.1.2Land Use
The City of Boulder is nearly fully “built-out” with the majority of the landuse in the basin as
residential.The highest density commercial areas are located along Boulder Creek in the
th
central downtown core area and along 28 Avenue and Foothills Highway. The University of
Colorado is also located within Boulder and occupies roughly 1 square mile of land in the
southwestern portion of the city. At present, because the city is almost fully developed,
anticipated future landuse is not expected to substantially change with construction activities
mainly involving site redevelopment.
2.1.3Soils
The City of Boulder is located at the foothillsof the Rocky Mountains. Its underlying geologic
unit is classified as young Quaternary deposits of stream gravels and sand, slope wash, terrace
gravels and landslides and was deposited approximately 65 million years ago. The surface
soils are mainly composed of poorly cemented and unconsolidated sands and gravels.
Hydrologically speaking, the soils are largely classified as Type C according to the Natural
ResourcesConservation System (NRCS, formerly the Soil Conservation Service), however all
other hydrologic soils type classifications can be found in the City.
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2.1.4Climate
The climate of the Boulder Valley area is typical of the Front Range. During the summer
months, the average temperature is approximately 66 F; during the winter months, the average
temperature is about 35 F but freezing temperatures are not uncommon. The average annual
precipitation in Boulder is approximately 20 inches with nearly 60% occurring as rain between
March and July. Significant summer rainfall events are typically thunderstorms and are
characterized as high in intensity and short in duration. On average, 54 thunderstorms occur
annually between April and September (NOAA, 2005).
2.2System Analysis Criteria
Stormwaterplanning was accomplished using a set of planning and design criteria.The
following information summarizes these criteria,including design storms, modeling assumptions
and other system analysis criteria that were used for the Boulder SSP.
2.2.1Design Storms
Foremost of the system analysis criteria is the design storm. In general terms, the design storm
involves two elements; the recurrence interval (2- and 5-year events; water quality event) and
the temporal distribution(the rainfall pattern); both of which influence pipe capacity
requirements, volumes and water quality treatment. Table 2.2-1 summarizes the 1-hour
precipitation depths for the Boulder area for the 2- and 5-year recurrence interval events and the
water quality storm. As noted in the UDFCD Volume 1 criteria manual, very intense rainfall in
the Denver/Boulder area results from convective storms or frontal stimulated convective storms.
These types of storms often have their most intense periods that are less than one or two hours
in duration and can produce brief periods of high rainfall intensities. Thus, the UDFCD criteria
manual recommended design a 2-hour storm duration for the Boulder SSP.
Table 2.2-1 Rainfall Depth-Duration-Frequency Values, NOAAAtlas II
Return Frequency (yr)1-Hour Precipitation (in)
WQ0.43
21.05
51.48
In terms of a temporal distribution, the UDFCD criteria manual recommends a front weighted
distributionwith peak precipitation occurring 25 minutes after the onset of the storm event
(Figure 2-3 and 2-4). This distribution was compared to the recently completed South Boulder
Creek design storm evaluation, which is based on 12-years of actual thunderstorm radar
records. Due to the relatively small drainage area within the city as compared to typical
convective cell sizes, the South Boulder Creek design storm confirmed the approached used in
this project by closely matching the UDFCD distribution over the City.
For the water quality design storm, the UDFCD criteria manual recommends a total depth of
0.43 inches, which represents the average runoff producing storm in the Boulder area (Figure
SQ-3, Volume 3 of UDFCD). This precipitation was distributed into 5-minute increments using
the 2-year rainfall distribution noted above. The resulting hyetograph for this storm is shown on
Figure 2-5.
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2.2.2Continuous Simulation Modeling
In addition to the event-based design storms discussed above, a year-long continuous rainfall
design storm was also developed. This event was used to estimate annual pollutant loadings at
key locations throughout the City as identified during the water quality analysis phase of the
project. This rainfall pattern is based on the hourly 2003 rainfall record from a rain gauge
located in the north part of the City of Boulder. For this station, data was available for 57 years
of record (1949 – 2005), and the data for 2003 was selected because it best represents a typical
rainfall year in terms of total depth during the wet months of April through September (10.4
inches) and the total number of storms with more than an inch of precipitation during a 6-hour
period (two events). The hyetograph for this storm is shown below in Figure 2-6.
2.2.3Stormwater Conveyance Elements
The focus of the Boulder SSP is the collector storm drainage system, which includes pipe
diameters of 18-inches and larger and primary open channel systems that are not part of the
City’s major drainageways. To further refine thestormwater conveyance system, two levels of
service are provided based on landuse and roadway category. For areas that are mainly
residentialin land use, the 2-year recurrence interval design storm was used to identify
problems in the conveyance system. For areasdraining mainly commercial, industrial and
collector and arterial roadways, the 5-year event was used. Figure 2-7 illustrates the recurrence
interval used throughout the City’s storm drain system.
Irrigation ditches throughout the City play a major role in the conveyance of stormwater runoff.
Many ditches receive stormwater from storm drains that outfall directly to the ditch system and
from overland flow. Being that many of these ditches meander through all landuse types within
the City and cross collector and arterial roadways, a 5-year event was used as the design storm
for the system analysis.
Areas within the city that experience localized flooding (e.g., undersizedpipes, which are less
than 18 inches in diameter; roadside ditches; and clogged catch basins) were not considered as
part of this study unless they have been identified by the City as known flooding locations.
2.2.4Landuse and Imperviousness
Landuse affects both the quantity (volume and peak rate) and quality of water running off and
routed through the City’s storm drainage system. The effect landuse has on water quantity is
generally linked to the amount of impervious area for a particular land use category. The more
impervious the area, the faster the water will be routed to the storm water collection system due
to the lower surface roughness of the ground. It will also increase the total volume of runoff
since infiltration can not occur through impervious surfaces.Consequently, an area with a
higher percentage of impervious surfaces will produce higher peak flows and large volumes
over a shorter period of time than will similar area with a lower percentage of impervious
surfaces. In order to identify problem areas within the minor storm drainage system, two
representative scenarios were used in this planning study.
2.2.4.1Existing Conditions
The existing conditions scenario represents 2006 landuse (Figure 2-8) within the city limits and
reflects present-day problems within the system. To supplement the landuse data within the
City’s GIS database, an actual impervious surfaces layer based on recent aerial photography
was also incorporated into this scenario.
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2.2.4.2Future Conditions
The future conditions scenario represents a fully developed urban area according to the Boulder
Valley Comprehensive Plan (Figure 2-9). This scenario represents a worst case scenario from
a stormwater perspective because it encompasses the highest level of imperviousness.
However, this scenario has also incorporated the City’s DCS, which require detention and water
quality treatment for all new impervious areas associated with new and re-development
projects. As discussed in later sections of this report, the City performed an inventory of
existing detention and treatment facilities and it was identified that roughly 78% of all current
facilities are adequately functioning (22% have failed). Consequently, to incorporate the DCS,
this same facility performance level (78%) was also assumed to occur under future development
conditions.To accomplish this, thechange in impervious percentage between existing and
future conditions was reduced by 78% to account for the detention and treatment facilities that
will collectively be built as the city develops and/or re-develops.
2.3Problem Identification Criteria
The Boulder SSP was guided by a set of problem identification criteria used to locate and
categorizeconveyanceand water quality problem areas and to evaluate potential
improvements. These criteria included quantitative assessments of storm drain surcharging,
culvert overtopping, channel/canal flooding, structure flooding (buildings, etc) and pollutant
loadings. This section describes each of the problem identification criteria.
2.3.1.1Hydraulic Problem Identification Criteria
Hydraulic deficiencies are generally related to insufficientsystem storage, excessive runoff
generated from highly impervious land covers or flooded backwater conditions from the major
drainageways; however they can also result from an undersized or poorly designed conveyance
system. To identify these deficiencies, results from the hydraulic model were incorporated into
the project GIS and compared to a set of problem identification criteria, which are described
below. Other problem areas were also added to the system deficiency list if they are known
flooding locations as provided by the City.Depending on the type of the conveyance element
being investigated, the following criteria were used.
Storm Drains
Surcharge conditions for the piped system are acceptable only for demonstrating the adequacy
of the system to convey the peak runoff for the corresponding design storms, provided that the
hydraulic grade line (HGL) is one foot lower than the manhole rim elevation. If the HGL is
within, or higher, than one foot below the manhole rim elevation, that particular section of pipe
was identified as undersized.
Culverts
There are several locations within the City where open channel flow is conveyed through a
culvert under a public roadway. Culverts at locations where the estimated HGL will inundate the
road sub-grade were classified as undersized.The roadway sub-grade elevation was
determined by subtracting one foot from the roadway crown elevation as determined from the
DTM coverage supplied by the City.Culverts were evaluated to the 2-year event for residential
drainage systems and the 5-year event for commercial and industrial systems.
Irrigation Canals and Open Channels
Open channel conveyance elements, including primary irrigation ditches,were added to the
problem identification list if the corresponding design storm causes the channel to overtop its
20
banks and flood the surrounding area. It should be noted that it was outside the scope of this
project to complete a detailed capacity analysis of the primary irrigation canals.
Structure Flooding
Buildings or other structures that are within 100 feet of a flooded manhole and whose ground
elevation is at or below the adjacent water surface elevation of that flooded manhole or open
channel were added to the problem identification list. Areas within the city that exhibit
significant potential structural flooding risk areconsidered high priority areas in terms of
conveyance system improvements.
2.3.2Water Quality
In addition to evaluating localized flooding potential, the modeling analysis was used to evaluate
stormwaterpollutant loading at outfalls throughout the City. The primary goal of the water
quality model development and analysis is to identify drainage basins and the associated
outfalls within the city where relatively high pollutant loads are expected. These locations of
high pollutant loads were identified as Water Quality Area of Concern. In addition to the model
results, other factors were considered during the evaluation included:
Recent development and construction of water quality BMPs
Areas where development is likely in the near future
Areas where property ownership will likely preclude BMP construction
Proximity to Boulder Creek.
Using the model resultsand these other factors, specific outfalls were identified for further
analysis including recommendations for water quality BMPs.These BMPs can be integrated
into the capital program, and projects can be targeted throughout the city to maximize the
system-wide water quality benefit.
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22
Model Development
A key element in the stormwater planning process is the development of a robust hydrologic,
hydraulic and water quality model of the watershed and it s natural and man-made stormwater
system. The model should be capable of analyzing controlstrategies for basin master planning;
predicting flooding risk; evaluating existing facilities and infrastructure; assessing pollutant
loadings and designing proposed facilities.
This section presents the development and verification of the Boulder stormwatermodel.
Included are a description of the XPSWMM model, the data requirements, the data sources, the
model setup and the model verification.
3.1 Modeling Approach
A comparative software review between EPA-SWMM and XPSWMM was performed to
determine the appropriate model to use in SSP. It was determined that XPSWMM provided a
more efficient means for pre- and post-processing of data for integration with GIS, better water
quality analysis tools and compatibilities for 2-dimensional analysis. As a result XPSWMMwas
selected as the system model for the SSP.
The modeling approach for the Boulder SSP integrates GIS as a pre- and post-processing tool
with XPSWMM (an EPA-based Storm Water Management Model) as the hydrologic and
hydraulic tool. Workflow began in GIS, where the input parameters for the XPSWMM model
were developed. This data were transferred out of GIS to XPSWMM, for the evaluation of the
system hydraulics and potentialimprovements.Model results were ultimately brought back into
GIS for post processingand storage for future reference by the City. The following section
describesthis process in more detail.
3.1.1Data and Basis of Model Construction
The primary sources of data used in this master plan originated from 1) the City’s GIS database,
2) the City’s 2’ contour data and associated digital terrain model (DTM), 3) supplemental field
survey data collected in 2006 by Merrick & Company, 4) previous storm drain and flood studies
completed for the City (see references) and 5) direct discussion with City staff.
The following is a list of data that were not available. All of the items listed below were
consideredpreferable data used to enhance the model results, but not critical to theoverall
master planning analysis and goals.
The city’s original manhole database was missing invert or ground elevation measurements
for 541 manholes: 383 of the 541 data gaps were address through supplemental survey
performed by Merrick & Company.
Of the remaining 158 data gaps, interpolation from the surrounding manholes was required
to populate invert elevations, and rim elevation were extracted from the city’s DTM.
All other elevation data used in the analysis was derived from the City’s 2’ contour data. This
included manhole rim elevations; canal, channel and drainageway cross-sections; and
pond/lake area-volume relationships. Due to the lack of actual field survey information for these
areas, City staff visually compared several cross-sectionsas a means to confirm the contour
data’s accuracy for the purposes of this study. Therefore, it should be note the data used for
23
the open channel analysis is relatively coarse as compared to the storm drain pipe and manhole
data.
3.2Hydrologic and Hydraulic Model
This section presents the hydrologic and hydraulic model inputs. Because of the nature and
analysis capabilities of XPSWMM, data requirements are extensive. Numerous inputs are
required for both the hydrologic (rainfall-runoff) and hydraulic (routing) portions of the analysis
and are individually summarized in the following sections.
3.2.1Existing Condition Model Construction
The existing conditionsmodel was developed to represents 2006 land use conditions within the
Boulder Urban Growth Boundary. The results from the model represent present-day problems
within the system.
3.2.1.1Hydrologic Parameters
Modeling the rainfall-runoff process in XPSWMM involves a series of steps to determine
appropriatemodel parameters in GIS prior to model execution. The follow sections describe
this sequential process.
Subcatchment Boundaries
One of the key tasks in building a hydrologic model is to allocate flows from individual
subcatchments to their respective conveyance element. In addition, the spatial arrangement
between these subcatchments in the model must represent actual ground conditions. Gridded
elevation data, (provided by the City as a DTM), was processed using GIS software to initially
examine the topography of each catchment. For areas with significant relief, the GIS
delineationwas used directly. In addition, irrigation ditchesand roadways were used to
delineate subcatchment boundaries. For areas where topography alone could not accurately
delineate the subcatchment boundary, aerial photos and the existing drainage network map
were also reviewed and the subcatchment boundaries were adjusted manually. Ultimately, 700
subcatchments were used to delineate the storm drain collector system (Figure 3-1). It should
be noted that some of these subcatchments were redefined as a part of the recommended
system improvements based on storm drain system extensions or other similar
recommendations.
Basin Width
Basin width, which represents the physical width of overland flow and essentially determines the
time lag between peak precipitation and peak runoff, was determined by dividing the length of
the longest flow path by the subbasin size. This length was determined by measuring the
distance from the upper-most point in the subbasin, through the overland and stormwater
conveyance path, to the most downstream point in the subbasin.
Slope
Subbasin slope also influences the runoff travel time and resulting hydrograph shape. Subbasin
slopes were determined by intersecting the longest flow path noted above with the City’s DTM
data at the end points and dividing the total elevation difference by the flow length.
Infiltration
Infiltrationis the process by which surface water percolates into the subsurface soil and
groundwater column. Infiltration is an important hydrologic process because it governs
groundwater recharge, soil moisture storage, and surface water runoff volume. As modeled in
the XPSWMM runoff block, infiltration is one of several processes that represent a withdrawal of
24
a portion of total storm precipitation that could otherwise generate surface runoff. Each of the
surface infiltration parameters were calculated in GIS by co-analyzing soils, landuse(impervious
area), topography, and other subbasin characteristics.
Soils
Information on soil types and characteristics within the city were compiled and grouped from the
NRCSSSURGO dataset (Figure 3-2). Using GIS, the predominant hydrologic soil type in each
subcatchment was identified. For each soil group, a set of Horton infiltration parameters
including Max Infiltration Rate, Asymptotic Infiltration Rate and Decay Rate of Infiltration were
assigned (Table 3.2-1) based on UDFCD guidance. The Horton infiltration method was used
because parameters can be estimated from existing soil surveys without extensive field testing.
Table 3.2-1 Horton Infiltration Parameters
Infiltration
NRCS HydrologicDecay
(in/hr)
Soil Group Coefficient
InitialFinal
A5.01.00.0007
B4.50.60.0018
C3.00.50.0018
D3.00.50.0018
Impervious Percentage (Existing Conditions)
The existing impervious percentages for each subcatchment were determined by overlaying the
subcatchments with the City’s impervious area database (Figure 3-3) and determining a
weighted average for each subcatchment. A list of the resulting impervious percentages for
each subcatchment is provided in the Volume 2 of this report. City-wide, the impervious area
database revealed the existing impervious percentage to be approximately 32.3% and is
graphically shown by subcatchment on Figure 3-4.
In addition to developing individual impervious percentages for each subcatchment, it was also
necessary to estimate impervious percentagesby land use to be used as a baseline for the
future conditions analysis. This was accomplished by combining 1) the city and county parcel
maps, 2) a set of lookup Tables that link buildingand land classification with nine generalized
land use categories and 3) the impervious area database provided by the city. The process is
outlined as follows:
1.The city and county parcel maps were combined, with the city parcels taking precedence in
areas of overlap.
2.The new project parcel layer was joined with the previously noted Tables to spatially
describe the existing land use in terms of the nine generalized land use categories;Rural
Residential (RR), Low Density Residential (LDR), Medium Density Residential (MDR), High
Density Residential (HDR), Commercial (COM), Industrial (IND), Educational/College (EDU),
Open space (OPEN) and Transportation Right-of-Way (TRANS).
3.The impervious area layer was intersected with the parcels layer to determine cumulative
averages for each land use category.
The results of this analysis are listed below in Table 3.2-2 and compared to the original 1984
StormwaterMaster Plan as well as the published impervious percentages recommended in the
UDFCD Urban Storm Drainage Criteria Manual.
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Table 3.2-2 Comparison of Impervious Percentages
Impervious Percentages
Land Use
Distribution
1984 MasterUDFCD2005 Aerial
Land Use Description
w/in City
PlanManualData
1.3%
RRRuralResidential34.0%*30.2%
31.5%24.2%
LDRLowDensityResidential39.0%*
47.4%4.8%
MDRMediumDensityResidential43.0%67.5%
57.6%1.8%
HDRHighDensityResidential58.0%80.0%
64.5%9.6%
COMCommercial88.0%90.0%
44.9%8.7%
INDIndustrial70.0%85.0%
38.5%5.3%
EDUEducational/College25.0%50.0%
7.3%29.7%
OPENOpenSpace5.0%2.0%
TRANSTransportationRight-of-Wayn/a100.0%70.3%14.6%
* Variable depending on acreage and home type
In general, the impervious area database results are uniformly lower as compared to the other
references.This may provide evidence as to why a number of flooding and under capacity
problem areas in the previous master plan have not been observed to be real-world problems.
Consequently, this update to the master plan should provide a more accurate evaluation of the
systems existing capacity and more appropriaterecommendations where improvements are
needed.
Other Hydrologic Parameters
In addition to the soil infiltration rates, XPSWMMalso requires surface parameters that control
the amount of immediate runoff and the rate of runoff from overland areas. There are three
parameters required: depression storage, zero detention and Manning’s “n”.
Depression Storage
Depressionstorage defines the amount of rain that must fall before runoff can occur in a
subcatchment. These values were assigned for pervious areas (0.35 inches) and impervious
areas (0.1 inches) respectively, based on UDFCD guidance.
Zero Detention
The zero detention parameter controls the amount (area) of a subcatchment that has immediate
runoff, or the area that has no depression storage. Based on guidance in the XPSWMM users
manual, this parameter was uniformly set to 10%.
Manning’s Roughness
Manning’s roughness, or “n”, is used to calculate the time it takes for precipitation to be
transformed to runoff. Higher values of Manning’s “n” represent rougher surfaces like grass
where runoff times will be delayed. Low values represent impervious areas such as roads or
parking lotsand produce higher peak flows with little or no runoff delay. These values were
assigned for pervious areas (0.2) and impervious areas (0.03) respectively, based on guidance
in the XPSWWM user’s manual.
3.2.1.2Hydraulic Parameters
The collector storm drain system within the City includes natural and manmade conveyance and
storage elements (Figure 3-5). XPSWMM models each of these features together as a
completed hydraulic system as described below.
26
StormDrain and Manhole Data
The storm drain pipe and manhole data used for model construction were developed from two
sources. At the planimetric level, the City’s GIS storm drain and manhole data layers were used
to develop a system schematic map. With this in hand, the existing manhole database,
supplemented by additional field surveysmade at each key manhole within the system, was
used to determine manhole invert and rim elevations as well as pipe invert elevations.
Generally, pipes less than 18” in diameter were excluded from the XPSWMMmodel in order to
strike a balance between accurately representing the drainage system and model complexity.
Open Channels
Open channel data, including major roadside ditches, irrigation canals and major drainageways
were extracted from the City’s DTM. The DTM data was used to determine channel cross-
sections as well as overall reach slopes. Roughness estimates for each open channel element
were derived from the city’s high resolution aerial photography. The stormwater model includes
the major drainageways for model connectivity and definitionof outfall hydraulics only; major
drainageway capacities were not analyzed in this study.
Roughness
Roughnesscharacteristics for each model segment were assigned based on material and its’
associatedManning’s roughness coefficient, “n” according to Table 3.2-3.
Table 3.2-3 Manning’s Roughness Values
IDDescriptionManning’s “n” Description
Variable (0.025 – Chapter 7 (UDFCD Storm Drain Criteria
NATNaturalChannel
0.08)Manual)
Assume Concrete: From Section 7.08 in
BOXBoxCulvert0.015
Boulder D&C Standards
Assume Concrete: From Section 7.08 in
CIPCast In Place0.015
Boulder D&C Standards
Corrugated Metal
th
CMP0.026Handbook of Hydraulics, 7 Edition (Table 6.4)
Pipe
CONCConcrete Pipe0.015From Section 7.08 in Boulder D&C Standards
th
DIPDuctile Iron Pipe0.014Handbook of Hydraulics, 7 Edition (Table 6.4)
NJPUnknown0.015AssumeConcrete
Polyvinyl Chloride
PPVC0.013From Section 7.08 in Boulder D&C Standards
Pipe
Polyvinyl Chloride
PVC
0.013From Section 7.08 in Boulder D&C Standards
Pipe
Reinforced
RCP0.015From Section 7.08 in Boulder D&C Standards
Concrete Pipe
th
VCPVitrified Clay Pipe 0.015Handbook of Hydraulics, 7 Edition (Table 6.4)
UNKUnknown Material0.015Assume Concrete
Boundary Conditions
Boundary conditions are an important part of the system analysis criteria because they establish
flows and water levels at the upstream and downstream limits of the City-wide hydraulic model.
Upstream Boundary Conditions
Upstream boundary conditions include inflows for Boulder Creek and South Boulder Creek
where they enter the city. These flows were set to the maximummeanmonthly discharge as
per USGS gauge records. These flows rates were deemed appropriate because it was
27
assumed that 2- and 5-year rainfall events within the city would not occur simultaneously with
large flow events in Boulder and South Boulder Creeks.
Interior Boundary Conditions(Irrigation Canals)
Interior boundary conditions are represented in the Boulder SWMM model as constant diversion
flows into the primary irrigation canals within thecity. The actual flow rates are based on five
years of measured diversions (recorded as ac-ft over the irrigation season and converted to an
average flow in cfs) in the canals and representa typical condition during the irrigation season.
These interior boundary conditionswere provided by the City for use in the system analysis.
Downstream BoundaryConditions
The upstream and interior boundary conditionsalso effect the piped collector system at outfall
locations to major the noted drainageways and irrigation ditches. By routing flows from the
major drainageways and ditches in the hydraulic model, boundary conditions at each storm
drain outfall are included in the model simulation and do not require an individual boundary
condition.
At the downstream limit of the model, normal depth boundary conditions were applied. This
condition establishes a variable depth based on the channel slope, geometry and roughness
and the contributing discharge.
Detention Ponds
According to the City’s GIS database, 713 detention facilitiesexist within the city limits (Figure
3-6. To account for this additionalstorage during the SWMM analysis two methods were used;
1) for subcatchments with a relatively small storage volume as compared to the subcatchments
area, the depression storage parameter was adjusted to account for the additional volume and
2) for individually larger facilities, or subcatchments that have a significantcumulative storage
as compared to their area, a synthetic pond approach was used. Each method is described
below.
For both scenarios the total storage volume within each subcatchment was calculatedby
intersectingthe detention pond and subcatchment layers and summing the total storage
volumes. This volume was then compared to the total subcatchment area. If the ratio of the
storage volume to the subcatchment area was less than 1815 cu-ft/acre (0.5 in/acre), then
scenario 1 was used; otherwise, scenario 2 was used. For scenario 1, the total storage volume
was converted to an average depth across the subcatchment and added to the depression
storage parameter. For scenario 2, the total storage volume was explicitly included as a
detention pond and modeled with appropriate outlet conditions and stage-storage relationships
derived from average conditions within the city.
In addition to incorporating the detention storage volume into the XPSWMM analysis, the
performance of each facility has also been included. Based on a recent detention pond
inventory completed by the City, it was determined that 22% of all the existing facilities are
either failing to the point of needing major rehabilitation (9%) or completely failed (13%) and
requiring total replacement (Figure 3-7). To account for this trend under existing conditions, the
volume of any facility within these two categories was removed from the total subcatchment
storage. Under future conditions, any new storage volume being added to a subcatchment will
be uniformly reduced by 22%.
3.2.2Model Validation Parameters and Results
Development of hydrologic and hydraulic models typically relies on validation to verify that
model results represent actual conditions within the study area. Calibration consists of adjusting
a set of model parameters so that measured data(e.g., pipe flow, streamflow, rainfall) match the
predicted runoff or flows from the corresponding model calculation. The calibration process
28
relies on measured data within the conveyancesystem, typically obtained from stream gauges
or flow meters but also from other sources such as anecdotal evidence.For the storm drain
system modeled for the SSP, flow measurement data does not exist, and calibration could not
be performed.
In lieu of calibration, a validation process was used to verify model accuracy in simulating
hydrologic conditions within the basin. Validation of the Boulder XPSWMMmodel consisted of
comparing the calculated peak flow and runoff volume results from the model at six selected
locations within the city (Figure 3-8) to results from other analytical models. The analytical
models used for validation were:
The Colorado Urban Hydrograph Procedure (CUHP method)
The USGS regional regression equations
The City of Boulder 1984 Storm Water Master Plan SWMM model results.
3.2.2.1CUHP Method
The CUHP is a method of hydrologic analysis based upon the unit hydrograph principle. It has
been developed and calibrated using rainfall-runoff data collected in Colorado (mostly in the
Denver/Boulder metropolitan area) and is a standard procedure outlined in the Urban Drainage
and Flood Control District (UDFCD) stormwater manual.
The CUHP computer program requires the input of a design storm and a set of hydrologic
parameters that describe the subcatchment characteristics.The design storm used for the
validation of the Boulder model was the 5-year (frequency), 1-hour (duration) synthetic event as
described in Section 2.The subcatchment characteristics include: area, flow path length,
centroid flow path link, impervious percentage, basin slope,pervious and impervious depression
storage and infiltration rates (Horton initial and final infiltration rate and the Horton decay rate).
Table 3.2-4 summarizes these parameters for each of the six validation subcatchments.
Table 3.2-4 CUHP Validation Subcatchment Parameters
Flow
AreaCentroidImperviousSlopeDepressionHorton
Basin ID Length
12
(sq-mi)Length (mi)Percent (%)(ft/ft)Storage (in) Infiltration
(mi)
VAL_10.0810.4830.17741.80.06270.35 / 0.1
5.0 / 1.0 / 0.0007
VAL_20.1400.7290.36547.30.04780.35 / 0.1
4.75 / 0.8 / 0.0007
VAL_30.2411.0520.4541.40.15590.35 / 0.1
4.75 / 0.8 / 0.0007
VAL_40.1200.7020.33334.90.00840.35 / 0.1
3.0 / 0.5 / 0.0018
VAL_50.1110.6270.34141.50.01690.35 / 0.1
3.0 / 0.5 / 0.0018
VAL_60.0890.7260.28749.20.01120.35 / 0.1
3.0 / 0.5 / 0.0018
1. (A / B) A is pervious depression storage, B is impervious depression storage
2. (A / B / C) A is initial infiltration rate (in/hr), B is final infiltration rate (in/hr),C is decay rate
Table 3.2-5 compares the XPSWMM model results with the CUHP method for the 5-year event.
The XPSWMM peak flow results are similar to the CUHP values for all catchments with the
largest difference being approximately 14%. In terms of runoff volume, the average difference
between the two calculation procedures for all six catchments is less than 2%. Such small
differencesbetween the two methods suggest the parameters used within the XPSWMMmodel
are appropriate as validated by CUHP (i.e. Colorado-specific) hydrology.
29
Table 3.2-5 Validation Results: 5-yr,1-hr, Peak Flow Summary
Runoff Volume (ac-ft)Peak Flow(cfs)
Basin
ID
XPSWMM Model CUHPXPSWMM Model CUHP
VAL_12.872.3957.262.8
VAL_25.975.23105.6115.0
VAL_30.490.7511.713.6
VAL_44.914.5474.873.5
VAL_54.414.9890.496.0
VAL_63.984.4269.979.9
3.2.2.2Regional Regression
In addition to the CUHP validation approach, the USGS regional regression equations present
another method for verifying peak discharges in the Boulder storm drain system. The Colorado
Plains region-specific regression equations wereselected to provide a statistical approximation
of peak runoff from the selected subcatchment within the city. It should be noted that because
the regional regression equations are intended for subcatchments significantly larger that those
within the Boulder city limits, the following results should be considered for comparison
purposes only.
Table 3.2-6 compares the XPSWMM model results with the regional regression method for the
5-year event. In general, the two methods compare reasonably well to one another. With the
exception of basin VAL_3, which has nearly no impervious cover and very permeable soils,
peak flow results from the remaining five basins are within 20% for the two methods. This is
well within the standard error range of the regional regression equations (± 34%) and supports
the validation of the XPSWMM model.
Table 3.2-6 Validation Results: 5-yr,1-hr, Peak Flow Summary
Peak Flow(cfs)
Basin ID
XPSWMM Model Regional Regression
VAL_157.271.8
VAL_2105.689.4
VAL_311.7111.0
VAL_474.884.0
VAL_590.481.5
VAL_669.974.6
3.2.2.31984 City of Boulder SWMP
The 1984 City of Boulder Storm Water Collection System Master Plan modeled runoff for
Boulder using EPA SWMM software. The 1984 EPA-SWMMmodel results were calibrated
using the CUHP program to produce SWMM flood peaks to within 15% of the CUHP results.
The results from the XPSWMM model and the 1984 SWMP are similar, but because the
contributingareas vary between the two studies, a direct comparison of peak flows is not
possible. Rather, a unit dischargecomparison was also performed using data referenced in the
appendix of the 1984 SWMP. Figure 3-9 displays the unit discharge vs. percent impervious for
the 5-year, 1-hour event with the data points from the XPSWMMmodel plotted to show their
30
conformance to the established discharge/impervious area relationship. The XPSWMMvalues
are similar to the 1984 EPA-SWMM result, illustrating the similarity between the two data sets.
3.2.3Future Condition Model Construction
The future conditions model represents a fully developed urban area according to the Boulder
Valley Comprehensive Plan. This scenario represents the worst case from a stormwater
perspectivebecause it encompasses the maximum planned level of development and the
corresponding highest level of imperviousness.
Impervious Percentage (Future Conditions)
In a similar method to that outlined above in Section 3.1, a unique impervious percentage was
assigned for each catchment. Instead of directly calculating an impervious percentage from the
impervious area database, the individual percentages were determined by joining the project
parcels dataset with the average impervious percentage for each general land use and
intersectingthat with the subcatchment coverage to establish a future net impervious
percentage for each subcatchment (Figure 3-10). City-wide, the future impervious percentage
was estimated to be approximately 33%. Table 3.2-7 provides a summary of future condition
imperviousness percentages by landuse.
Table 3.2-7 Future Condition Imperviousness by Landuse
Land Use
%
Distribution
Impervious
Land Use Description
w/in City
1.3%
30.2%
31.5%24.2%
LDRLow DensityResidential
47.4%4.8%
MDRMedium DensityResidential
57.6%1.8%
HDRHigh DensityResidential
64.5%9.6%
COMCommercial
44.9%8.7%
INDIndustrial
38.5%5.3%
EDUEducational/College
7.3%29.7%
OPENOpen Space
TRANSTransportation Right-of-Way 70.3%14.6%
* Variable depending on acreage and home type
Detention Ponds
In order to incorporate the City’s Design and Construction Standard requirements for detention
facilities in the future conditions model, the same level of performance determined by the City’s
recent facility inventory (78% of all detention and water quality ponds were performing) was
used. This was incorporated for each subcatchment by reducing the net change in impervious
percentagebetween existing and future conditions by 78%.
3.3Water Quality Model
The primary goal of the water quality model development and analysis was to identify areas
within the City having comparatively high pollutant concentrations and/or loads. With this
information, locations of BMPs or capital projects were targeted throughout the city to maximize
the system-wide water quality benefit. The following section describes in more detail the
development of the water quality model in XPSWMM.
31
3.3.1Model Construction
The water quality analysis was incorporated into the XPSWMM model by estimating the washoff
and transport of pollutants in stormwater runoff, pollutant removal by existing BMPs, and
calculationsof annual pollutant loadings into the City’s receiving waters.For estimating annual
pollutant loads, the XPSWMMmodel was run as a continuous time series for an entire year
using 1-hour recorded precipitation data.
Existing water quality BMPs include over 700 detention ponds, and these were incorporated into
the model. Except for the largest 20 ponds, the remaining facilities were not included as
individual features but grouped together within each basin using the depression storage
parameter as describedin Section 3.2.1. Other existing features integrated into the model
th
include proprietary BMPs at the City building north of Boulder Creek, the 29 Street
development, and the Target store.
3.3.1.1Model Parameters
The stormwater quality analysis modeled five water quality constituents: total suspended solids
(TSS), total phosphorus (P), and three metals – lead (Pb), copper (Cu), and zinc (Zn).
Total Suspended Solids
Total Suspended Solids (TSS) represents the amount of suspended organic and inorganic
matter in the runoff. It includes all sediments and other constituents that are attached to the
sediments or suspended in the water column itself. TSS is also a frequently reported parameter
as a surrogate for other stormwaterpollutants,including metals, nutrients, and various organic
compounds.
Total Phosphorus
Phosphorus (P) is a relatively common element that is found uniformly throughout land uses as
it is widely used in fertilizers and pesticides and as a cleanser. Phosphorus is also found to
occur naturally in soils and groundwater.
Metals
Metals such as Lead (Pb), Copper (Cu) and Zinc (Zn) are relatively common in urban storm
runoff. Lead is often found in paints used on older homes. Zinc is found on roadways due to its
use as a galvanizing agent on automobiles and metal structures and is also used in tires and oil.
Copper is a commonly used metal in electrical wires, paints, and in several automobile
applications(such as brakes and wires).
3.3.1.2Event Mean Concentrations
Event mean concentration (EMC) values are the typical concentrationsin stormwater runoff for
a particular land use and provide a means to model land-use-based water quality constituents in
XPSWMM.EMCvalues were determined for industrial, commercial, residential, undeveloped
and transportation land use categories through a review of the UDFCD Drainage Design Criteria
Manual and other applicable reference documents (Table 3.3-1).
To incorporate these parameters into XPSWMM, the percentage of each land use category was
determined using GIS for each individual subcatchment, and the model determined the
corresponding net pollutant concentration for each subcatchment.
32
Table 3.3-1 Event Mean Concentrations (EMC) Values
Land Use
Constituent
IndustrialCommercialResidentialUndevelopedTransportation
Total Suspended
399225240400150
Solids, TSS(mg/L)
Total Phosphorus, P
0.430.420.650.400.376
(mg/L)
8443294028
Copper, Cu (g/L)
13059531008
Lead, Pb (g/L)
520240180100197
Zinc, Zn (g/L)
1.Data source for all land uses except transportation: UDFCD Drainage Design Criteria, Volume 3.
2.Data source for transportation: Analysis of OregonWater Quality Monitoring Data (ACWA, 1997).
3.mg/L = milligrams per liter.g/L = micrograms per liter.
3.3.1.3Existing Water Quality Facilities
Within the City of Boulder, there are generally two different categories of water quality facilities.
The most predominate facility type is the detention pond; there are numerous detention ponds
located throughout the city. The other common facility type is the proprietary BMP, which is
often referred to as a “water quality manhole.” Each is described below.
Detention and Water Quality Ponds
According to the City’s current stormwater facility database, over 700 detention ponds exist
within Boulder. Although not all off these ponds were originally designed with water quality
treatment in mind, some level of pollution reduction can be expected at nearly all functioning
facilities. This is due to storage volume and drawdown time, and the tendency for pollutants to
settle out of suspension in this environment.
Because the City’s stormwater facility database does not readily indicate whether water quality
was a consideration during design of these ponds, a consistent approach was employed. This
approach assumed that regardless of the original design intent, water quality treatment is
occurring to some degree at each facility during the water quality design event. Within SWMM,
this assumption was applied as follows.
For all but the largest detention ponds, the depression storage concept was used. Depression
storage reduces the net runoff and pollutant loads from each catchment by uniformly subtracting
the total storage volume and associated pollutant loads within that catchment from the runoff
hydrograph. Further discussion of depressionstorage is provided in Section 3.2.1.1. For the
largest facilities, each was modeled explicitly, with as-built stage-storage-volume curves, actual
outlet structure configurations, and pollutant removal percentages as shown below in Table 3.3-
2. Although the approach used draws upon the significant data within the stormwater facility
database, the lack of detailed information regarding the design of individual detention ponds is a
limiting factor.
Structural Pollution Reduction Facilities
Within the City of Boulder, four sites existwhere proprietary BMPs have been installed as a
water quality treatment device. Each PRF was modeled explicitly in XPSWMM to account for
pollutant removal efficiency as well as treatment and bypass flow capacities. The type, size and
location of each PRF is described below in Table 3.3-3 with their associated pollutant removals
listed in Table 3.3-2.
33
Table 3.3-2 BMP Pollutant RemovalEfficiencies
Removal Efficiency (%)
Design Flow
Metals (Lead,
BMP Type
Total SuspendedTotal
Rate (cfs)
; Zinc ;
PbZn
Solids ()Phosphorus ()
TSSP
Copper,)
Cu
1
Detention Pondsn/a50%30%30%
Vortechs 30004.580%50%25%
Stormceptor 6000 1.880%50%50%
Stormceptor 110003.577%50%50%
Stormceptor 130003.571%50%50%
1. Removal efficiencies are for synthetic ponds. All other detentionponds remove pollutants through depression storage,which
completelyremoves runoff volume in the simulation.
Table 3.3-3 Proprietary BMP Locations
LocationDescription
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14 Street at Fourmile
Two Vortechnics Vortechs 3000 units.
Canyon Creek
Two Stormceptor units.
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29 Street Mall One locatedat the north end of the 29Street Mall (STC 13000) and one
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located at the south side of the 29 Street Mall (STC 11000).
A single Stormceptor 6000 unit locatedat Broadway and BoulderCreek.
Broadway at Boulder Cr
34
System Analysis and Results
This section presents a characterization of the existing and future hydraulic and water quality
problem areas that will be used as a baseline for the development of a recommended plan and
stormwaterCIP program for the City of Boulder.
4.1 System Description
As previously noted, the focus of the Boulder SSP is the collector storm drainage system, which
includes pipe 18” in diameter and larger and primary open channel systems that are not part of
the City’s major drainageways. The following sections provide an overview of those portions of
the City’s storm drainage system that were included in the model and analyzed as part of this
project.
4.1.1Major Drainageways
From a storm drainage perspective, the City of Boulder is generally split east-west by Boulder
Creek, which is the ultimate discharge point for much of the City’s stormwater runoff. In addition
to Boulder Creek, the City’s other major creeks include Gregory Creek, Bluebell Creek, Skunk
Creek, Bear Canyon Creek and South Boulder Creek to South and Goose Creek, Twomile
Canyon Creek, Elmer’s Two Mile Creek, Wonderland Creek and Fourmile Canyon Creek to the
North. Although the major drainageways and creeks within the City were not evaluated as part
of this plan, they were still incorporated into the hydraulic analysis to provide system
connectivity and serve as boundary conditions at outfalls and other points of discharge. Figure
4.1 illustrates the major drainageways.
4.1.2Irrigation Canals
The presence of irrigation canals within the City plays an important role in the collection and
conveyance of stormwater runoff. Because the canals tend to run perpendicular to the
surroundingground slope, they can often intercept a substantial portion of runoff and transfer it
to neighboring basins.The major irrigation canals within the city, including Farmers Ditch, Silver
Lake Ditch, Boulder White Rock Ditch, North Boulder Farmers Ditch, Anderson Ditch and
Wellman Ditch were included in the hydraulic analysis and evaluated for flooding problems.
Figure 4-1 illustrates the primary irrigation canals as included in the hydraulic analysis.
4.1.3Storm Drains
The existing storm drain system within the City includes nearly 160 miles feet of pipe ranging in
size from less than 12” to 72” in diameter. Of that, approximately 52 miles of 18” in diameter
and larger pipe was included in the hydraulic model and evaluated for system problems. Figure
4-1 identifies the modeled and non-modeled storm drains.
4.2Storm Drain Problem Identification
Utilizing the XPSWMMmodel, runoff, hydraulic, and water quality calculations were completed
for two different land use scenarios: existing conditions and future conditions, and three different
design storms: the 2- and 5-yr events and the water quality storm. These results were then
evaluated with respect the problem identification criteria presented in Section 2 to identify
specific system deficiencies within the City’s storm drain system.
35
Initially, a comparison of hydraulic system problems for the existing and future landuse condition
scenario was performed. Model results indicated no additional problems areas resulted from
the slight increase in imperviousness between the existing and future condition landuse
scenarios.However, it was observed that there was a slight increase in problem severity.As a
result, the collector system problemidentification used only the future condition landuse
scenario.
Model results indicate that 572 nodes out of 1635 nodes within the City violate one or more of
the noted criteria. In most cases, a number of these deficient nodes and links were grouped
together into a single problem area. This resulted in 50 hydraulic problem locations as shown
on Figure 4-2. To provide additional detail on the locations of the storm drain problem locations
and identify model node and link ID, three E-sized maps are included in the back pocket of the
report. The model IDs from these hard copy maps can be referenced to printed model results in
Appendix A for future reference.
In general, the areas that were identified as most severely undercapacity or the areas that flood
the most include
Upper Goose Creek between North Boulder Park and Folsom St,
rd
Spine Road and N. 63 Street in the Gunbarrel part of town,
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Spruce St between 18 St and Boulder White Rock Ditch, and
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28 St. between Arapahoe Ave and Boulder Creek.
4.3Storm Drain Problem Prioritization
Due to the large number of problem locations and limitations within the City’s capital budget, a
ranking was performed on the problem areas to group the conveyance problems into three tiers
defined as: Tier 1 = severe problem area, Tier 2 = major problem area, and Tier 3 = minor
problem area. Detailed alternativesand design solutions were developed for the Tier 1 and Tier
2 priority problems areas. However, pipe sizes and design criteria are also provided for the Tier
3 problem area based on a pipe replacement improvement.The following paragraphs
summarize the criteria used to identify and rank the high priority conveyance problems within
the City’s collector system.
As noted above, model results identified 572 problem nodes that were either surcharged or
flooding based on the project hydraulic criteria.Further investigation of the problem nodes
showed locations where the hydraulic criteria were violated by matter of inches and/or for a
relatively short duration. Considering those nodes that were only slightly exceeding the project
hydraulic criteria were not identified as system problem locations by the City, an additional
screeningcriterion was developed to remove these minor capacity restrictions from the problem
identification list.
Prior to ranking and identification each problem area, a problem override criterion was applied
to nodes that were either 1) flooded or surcharged for less than 15 minutes and/or 2) only
violated the HGL surcharge criteria by less than two tenths of a foot and were isolated with
respect to other flooded problem areas. The problem override criterion and removed 60 model
nodes, or 4% of the total model nodes, from the problem identification process.
4.3.1Criteria and Definitions
The process of prioritizing system problems intotiers utilized a point-based matrix using a
weighted criteria approach. The problem prioritization criteria and their definitions are presented
in Table 4.3-1. The process of prioritizing the identified hydraulic problem locations assigned a
36
relative score of 1 to 10 to each of the prioritization criterion. The following sectionsdescribe
the criteria scoring process and graphically compare the relative score for each problem
location. The criteria scoring process, graphicalcomparisons and a complete set of raw data
and scores for each criterion is included in the Appendix, Volume 2.
Table 4.3-1 Problem PrioritizationCriteria and Definitions
CriterionDefinition
Length of the storm drainsystem that is identified as a hydraulic problem. This is
intended to be a measure of the extent of the street andassociated inlets that are
Problem Extentimpacted by the surcharged hydraulic gradeline. This criterion is determined for
each problem location by calculating thelength of the storm drainsystem between
surcharged and/or floodednodes.
Volume of flow that exceeds the rim elevation. This is intended to be a measure of
the problem severity by evaluating the volume of runoff that could potentially
escape the storm drain system into the street and result in localized flooding. This
Flooded Volume
criterion is determined as direct output from XPSWMM summed for all flooded
nodes with in a problem location. Note this does not include surcharged nodes
(HGL within 1-ft of the rim) and identifies locations with severe flooding potential.
Number of buildings or structures potentially impacted by system flooding. This
measures the problem severity for flooded nodes by differentiating node flooding in
Structure Impactdensely developed areas or where development is well above the rim of the storm
drainsystem. This criterion is calculated using flooded node HGL elevations
intersected with the surrounding building elevations in the project GIS.
The Q is defined as the peak system flow divided by the manning’s full flow
Ratio
capacity of the pipe. The higher the Q the more severe the capacity problem is
Ratio
in the pipe segment. This is intended to be another measure of problem severity for
Length of High Qa surchargedor flooded system and typically identifies the cause of the flooded
Ratio
volume and problem extent criterion. This criterion is calculated as direct output
from XPSWMM by multiplying the Qby length for each pipesegment where the
Ratio
Q is greater than 1.1.
Ratio
General ranking of the amount of data gaps remainingthat are adjacent to a
problem node or pipe. This would be a measure of the level of confidence in how
the model is predicting actual system hydraulics with respect to the best available
Data Confidence
data. For example, if a problem locationis a result or partial result of a model
element that was not able tobe surveyed, it would rank as a less severe issue. A
resulting recommendationwould be for additional data collection in that area.
Identifies problem locations that may have multi-objective solutions. This identifies
Water Quality Area of
if the hydraulic problem area is adjacent to or contains a Water Quality Area of
Concern
Concern.
4.3.2Criteria Weights and Ranking
Weighting factors were used to identify those criteria that are of a higher concern with respect to
basin characteristics and the level of service provided by the City’s collector system. For
example, theLength of Q criterion is a representation of amount of under-capacity pipe
Ratio
within a problem location but does not necessarily indicate a problem. Therefore, this criterion
37
would be weighted less thanFlooded Volumeor Structural Flooding for example, which
represent the severity of a system deficiency and the potential impacts created by system
flooding. Weighting factors were developed on a percentage basis for each of the six criteria
such that the sum of all the weights totaled 100%. The ranking scoresfor each problem
location were calculated by multiplying the criteria scores by the criteria weight percentages and
converted to a percentage. In theory, the maximum rank a problem area could attain would be
100% thus attaining the maximum score for all of the criteria. Table 4.3-2 provides a summary
of the weighting criteria.
Table 4.3-2 Weighting Criteria
Scoring Criteria Weight
Problem Extent13%
Flooded Volume25%
Structure Impact31%
Q
6%
Length of High
Ratio
Data Confidence9%
Water Quality Area of Concern16%
4.3.3Problem Area Priorities
The process of identifying the Tier 1, 2 and 3 priority locations was developed to identify the
severe, major and minor problems within the City’s collector system. This approach was
necessitated due to the large number of problem locations, the anticipated high cost associated
by addressing all problems and the limited budget available within the City’s stormwater utility.
It should be noted these problem categories do not address local drainage problems as this was
outside the scope of the SPP.
Identifying the breakpoint between the Tier 1, 2 and 3 problem locations was intended to identify
the point of diminishingreturns with respect to capital expenditures and problem severity. A
comparison of the ranking score for each of the problem locations was made to identify if there
were natural breakpoints in the distribution problem location score. This comparison of ranking
score for each problem location was made graphically using a histogram. It can be seen there
is a natural break between the problem locations scores around 25% thus indicating the
problem severity significantly decreases past a 25% score. In addition, there is another
grouping of scores above the 45% point indicating a series of very severe problem locations.
With those naturally occurring breakpoints, Table 4.3-3 was used to identify the Tier 1, 2 and 3
problem locations. This is also shown on Figure 4-3.
Table 4.3-3 Summary of Problem Area Ranking Results
Problem ID ScoreRankTier 1 Tier 2 Tier 3
HYD#1673.11
HYD#3450.02
HYD#5549.73
HYD#848.84
HYD#4240.65
HYD#4140.06
HYD#1939.17
HYD#2435.98
38
Table 4.3-3 Summary of Problem Area Ranking Results
Problem ID ScoreRankTier 1 Tier 2 Tier 3
HYD#2935.09
HYD#4735.09
HYD#2733.411
HYD#2132.512
HYD#931.313
HYD#1530.614
HYD#2030.614
HYD#2229.716
HYD#3829.418
HYD#3527.819
HYD#1827.520
HYD#4927.221
HYD#4826.322
HYD#5025.923
HYD#3021.625
HYD#4620.926
HYD#719.427
HYD#2319.427
HYD#3219.129
HYD#218.830
HYD#318.830
HYD#3318.830
HYD#1718.133
HYD#5218.133
HYD#1117.835
HYD#116.936
HYD#516.936
HYD#1216.936
HYD#1416.936
HYD#2816.936
HYD#3716.936
HYD#4516.936
HYD#5116.936
HYD#5316.936
HYD#5416.936
HYD#1316.348
HYD#3115.949
HYD#3915.050
HYD#4015.050
HYD#4415.050
HYD#3614.153
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Table 4.3-3 Summary of Problem Area Ranking Results
Problem ID ScoreRankTier 1 Tier 2 Tier 3
HYD#2513.154
HYD#48.455
4.4Irrigation Canal Problem Identification
Irrigation canal segments were added to the problem identification list if the corresponding
design storm causes the channel to overtop its banks and flood the surrounding area. These
processes identified approximately13 locations where canal flooding might occur. Figure 4-4
illustrates these canal flooding locations graphically.
4.5Water Quality Areas of Concern
The primary goal of the water quality model development and analysis was to identify areas
within the city having comparatively higher pollutant concentrations and/or loads. With this
information, specific capital projectsor BMPs could be selected and located within the city to
maximize their system-wide water quality benefit. A detailed presentation of the water quality
analysis approach and problem identification process is included in TM 3.5 Water Quality Model
and Construction Results, located in the Appendix, Volume 4.
Initially, the pollutant loadings for both the existing and future land use conditions were
evaluated. However, by considering the limitedamount of new development or redevelopment
expected within the city, and by acknowledging that the City’s Design and Construction
Standards tend to mitigate pollutant loading from new impervious surfaces, it was recognized
that both scenarios would produce similar water quality results. This conclusion was supported
by the model, which indicated a difference of less than 2 percent in city-wide total pollutant
washoff between the two scenarios. Consequently, it was determined that a single scenario
would provide an appropriate basis for comparison in the subsequent analysis.Therefore, all
water quality problem area identifications and improvementsutilize the future conditions land
use scenario.
4.5.1Catchments
Identifying the catchments that generate the highest pollutant loadings per acre was an
important first step in selecting specific sites where water quality treatment would be most
beneficial.Figure 4.-5 illustrates the normalized pollutant loads (per acre) for each of the 700
subcatchments used in the SWMM model.
In general, the highest pollutant loadings are located in the central core of the city, between
thth
Valmont Road and Arapahoe Avenue (north-south) and 28Street and 55 Street (east-west).
This area includes significant industrial developments, high-traffic-volume roadways, and the
proposed Boulder Transit Village site. In addition to this central core area, two other areas were
rd
identified as having comparatively high pollutant loads. These include 63 Street and the
Diagonal Highway in the Gunbarrel area and Broadway and Fourmile Creek in the northwestern
corner of the city.
40
4.5.2Outfalls
Although identifying the catchments with the highest comparative washoff load is important from
a source control standpoint, identifying the specific outfalls that are discharging these high
concentration pollutants can help to identify site-specific locations where water quality treatment
facility would be most beneficial and could be included in the City’s capital improvement
program. The outfalls with the highest pollutant load concentrations were identified as the
Water Quality Areas of Concern and are shown on Figure 4-6 and summarized in table 4.5-1
listed by outfall location.
Table 4.5-1 Top 12 Pollutant Contributing Outfalls
Pollutant Load (lbs/ac/yr)
RankLocation
TSSPCuPbZn
1Broadway & Fourmile Canyon Creek1,9703.160.350.522.13
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249 Street & Goose Creek1,2491.390.250.391.55
3Foothillsand Wonderland Creek1,3341.770.170.330.71
4Pearl Parkway & Wonderland Creek9801.290.200.291.22
5Diagonal Highway & Boulder Creek9571.300.200.281.18
6Arapahoe and Range Street9121.550.160.240.99
7Pearl Street & Goose Creek8060.960.170.241.05
8Broadway & Skunk Creek7630.850.160.240.99
9Broadway at Boulder Creek7301.660.110.140.68
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1056 Street & Dry Creek7121.200.130.190.81
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1128 Street & Boulder Creek6871.320.130.170.75
rd
1263 Street & Boulder White RockDitch6820.840.150.220.94
The existing 36-inch storm drain running south along Broadway and discharging into Fourmile
Canyon Creek was predicted to have the highest pollutant loadings with 1,970 pounds of TSS
per acre per year. The next six highest contributing outfalls are all located in the central
downtown area of the City, and discharging into Goose Creek, Boulder Creek, and North
Boulder Farmer’s Ditch.
The model results and problem identification process originally identified the Boulder Transit
Village (BTV) redevelopment area as a water quality area of concern. The BTV site was ranked
as the fourth highest contributing outfall, and the proposed redevelopment project offers an
excellent opportunity to attain a significant reduction in urban stormwater pollution. However,
since a separate stormwater quality analysis for the redevelopment options was prepared in
parallel with the SSP, this location was removed from the water quality area of concern list. A
separate, more detailed analysis of this site is included in the Appendix, Volume D.
41
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42
System Improvement Recommendations
This section summarizes the development and evaluation of various alternatives intended to
resolve the system deficiencies identified in the previous section. In addition, this section
presents the recommended plan for storm drain and water quality improvements as well as
methods and factors considered in developing and screening the various alternatives.
5.1Hydraulic Alternatives
Improvement alternatives were developed for theTier 1 and Tier 2 priority problem areas and
the identified irrigation canal problem areas. Detailed summaries of the alternatives are
included in the Appendix, Volume 4, which includes improvement descriptions, design data,
benefits and issues.
5.1.1Alternative Development Process
Conceptualalternativesfor the hydraulic problem areas were developed and evaluated using a
combination of the project GIS and the XPSWMM model. Conceptual alternatives include pipe
replacement, hydraulically parallel storm drain pipes, flow diversions and detention. The
alternativesfor each of the Tier 1 and 2 problem areas were summarized in a fact sheet format.
Alternatives for the Tier 3 problem areas were not developed; rather, the Tier 3 problem areas
were resolved via pipe replacement.
Multiple factors were considered in developing each alternative. Although each problem area
had unique constraintsand required a different set of improvements, a number of common
themes were followed:
To minimize capital expenditures, the existing infrastructurewas used to the maximum
extent possible.
Land acquisition, in terms of size and ownership and potential development pressures, was
consideredwhen locating system improvements.
Where feasible, system improvements were located in public property, right-of-way.
Where canal capacity problems exist, storm drain flows entering the canal system were
eliminated if practical.
For problem areas that discharge to a canal, alternatives were investigated that remove the
outfall to the canal by diverting flow to a major drainageway or storm drain with sufficient
capacity.
Tier 1 problem areas received a more detailed analysis at this concept alternative stage as the
problems are generally more severe. Alternatives for Tier 1 problem areas were modeled using
XPSWMM and mapped in GIS to more clearly define the alignments of the alternatives. The
Upper Goose Creek problem area (Tier 1) was further analyzed using a 2-dimensional model to
optimize the system improvementwith respect to major drainageway conveyance issues as
noted in Section 5.1.4 below. Alternatives for Tier 2 problem areas were sized based on normal
depth calculations using future base condition model resultsstored in the GIS with the
alignmentsdescribed in the fact sheets.
43
5.1.2Alternative Evaluation Process
Alternative fact sheets were used to summarize information regarding each alternative and then
to used that information to qualitatively evaluate the alternatives. Each fact sheet includes the
problem area identification code that can be referenced to TM 4.1b. Fact sheets also include
the information regarding the following topics:
Problem Location. Summarizes the location and extent of the problem with respect to city
streets and other key landmarks.
Problem Summary. Summarizes the system problems as developed using the problem
identification criteria.
Alternative Summary. Provides a narrative of the components for each alternative
developed. This includes a description of alignment corridors, pipe diameters and lengths,
and other improvement-related information needed to implement the project.
Technical Data. Summarizes the hydraulic data needed to evaluate the viability of the
conceptualalternative. This includes design flows, pipe slopes, pipe diameters and storage
volumes.
Benefits. Identifies if the problems are resolved. Also identifies the benefits relative to
another alternative described for the same problem location.
Land Ownership. Summarizes existing land ownership and any land acquisition required
to implement the alternative.
Permitting. Summarizes any permitting or mitigation issues likely to be associated with the
alternative.
Issues. Identifies issues that would affect construction and maintenance for each
alternative. Examples include major utility relocations, high groundwater, significant
roadway closures, etc.Also identifies special construction techniques necessary to
implement the alternatives. Also identifies if the alternative does not alleviate deficiencies
within a problem area.
The identification of the preferred alternative was based a qualitative assessment of the
information presented in the fact sheets. In addition, factors including alignment opportunities,
utility constraints, land ownership, perceived cost and whether the project could be connected
with other planned City capital improvements were also considerations in identifying the
preferred alternative.
5.1.3Upper Goose Creek – Alternative Analysis
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The Upper Goose Creek collector system extends west of 19 Avenue in Alpine Avenue and
then branches near Broadway south toward Dewey Street and north toward North Boulder Park.
Collector system improvement alternatives were developed, as described in Section 5.1.1, to
address the hydraulic problems within the Upper Goose Creek collector system. The alternative
evaluation process, as described inSection 5.1.2, identified the preferred alternative of tying
into the future major drainageway improvement as defined in the 1988 Major Drainageway Plan
(Greenhorne and O’mara, Inc). The 1988 Major Drainageway Plan also required capacity
th
improvements downstream in Goose Creek between 19 Avenue and Folsom, along Edgewood
th
Avenue. The improvements along this 19 to Folsom reach present many challenges including
property acquisition and lack public support. As a result, a more detailed analysis of potential
collectorsystem improvements was required.The goals of the Upper Goose Creek alternative
analysis were as follows:
44
th
Develop collector system improvement alternatives upstream of 19 that are located within
the ROW.
th
Develop alternatives that minimize constructionimpacts in Goose Creek between 19 and
Folsom.
Identify collector system improvementsthat maximize storm conveyance and balances
constructability, capital cost, private property concerns, and flooding risk.
Minimize and reduce major storm flooding depths within the collectorsystem upstream of
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19 Avenue for storm events greater than the 5-yr collector system design storm
requirement.
A 2-dimensional hydraulic model was developed to efficiently evaluate surface flow in
conjunctionwith collector system improvement alternatives.The XP-2Dmodule was added
onto the XPSWMM collector system model as the analysis tool to assist in the alternative
thth
development and evaluation. The 2-D limits of the model extended from 19 Avenue 6
Avenue. Alternatives were developed and modeled using the 2-year, 5-year, 10-year and 100-
year design storms to evaluate the flooding depths and downstream impacts. In addition,
estimates of construction costs were developed for two alternatives.
The alternative evaluation process resulted in theleast cost alternative that did not increase
flooding risk to residents along the Edgewood reach of Goose Creek. Details regarding the
model development, results, alternatives are included in TM 5.1c Goose Creek 2-D Analysis
located the Appendix, Volume 3.
5.1.4Canal Separation Conceptual Alternatives
In addition to the alternatives discussed in the previous section, potential locations to separate
the storm drain system from the irrigation canals were also evaluated. The areas investigated
were canal reaches that are know system problem locations and/or that were identified in the
hydraulic model as under capacity sections. In addition to identifying potential sites, a process
of ranking each storm drain outfall that discharges to a canal with respect to relocating the
outfall to a neighboringmajor drainageway was also investigated.
Identifying the outfalls that discharge directly to the canal system was accomplished in GIS by
intersectingthe storm drain (pipe) layer with the canal layer. The resulting point database
included 24 outfalls, had diameters greater than 18” and represents the collector system
stormwaterpipes that discharge directly into the canal system.
The process used to identify the most opportune sites for separation involved four criteria. Each
criterion was estimated using GIS, with the highest ranking sites identified qualitatively. The
criteria includeDistance to majordrainageway,existing problem area,contributing drainage
area and known canal flooding. Each is described in more detail in the Appendix, Volume 4.
By applying the criteria noted above in GIS to each of the outfalls, a thematic map was created
to illustratewhich outfalls represent the best opportunity for separate from the canal system.
th
This GIS mapping process indicated the top four site are: 1) Iris Ave and Farmer’s Ditch, 2) 9
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Street and Anderson Ditch, 3) Mapleton Ave and Boulder White Rock Ditch, and 4) 5 St and
Farmers Ditch.
Two example fact sheets shown in the Appendix, Volume 4 were developed to provide
thth
conceptualalternativesfor improvements at 9 Street and Anderson Ditch (#2) and 5 Street
and Farmers Ditch (#4). Conceptual alternatives were developed for these two sites as they
provided the best opportunity for system improvements. Alternatives for the other site locations
become more problematic to implement and have a reduced system benefit. However, the
thth
conceptualalternative fact sheets for the 9 Street and Anderson Ditch (#2) and 5 Street and
45
Farmers Ditch (#4) sites provide an illustration of the general approach that could be applied to
other sites if needed.
5.2Water Quality Alternatives
The water quality analysis identified twelve (12) locations asWater Quality Areas of Concern
(Figure 5-1). For these locations, improvement alternatives were developed to evaluate the
most appropriate solution considering the contributing area and site constraints.
In addition to the Water Quality Areas of Concern, HDR performed an analysis of the 18
collectorsystem outfalls on Boulder Creek, focusing on the use of proprietary BMPs (a.k.a.
water quality manholes) that utilize hydrodynamic forces to remove TSS and associated
pollutants from stormwater runoff. This secondapproach to addressingstormwaterquality was
developed to evaluate the potential benefit of focusing on a single, highpriority stream system
instead of a City-wide approach.
A summary of the key elements of the water quality alternatives analysis and recommendations
is presented below. The analysis is described in more detail in TM 3.6.2 Water Quality
Alternatives and Recommendations and in TM 3.6.3 Water Quality Improvement
Recommendations. These TMs are located in the Appendix, Volume 4.
5.2.1Alternative Development Process – Water Quality Areas of Concern
HDR developed fact sheets summarizing a series of conceptual alternatives. Conceptual
alternativeswere developed to address the modeled stormwater pollutants were initially
developed using aerial photography and GIS data, includingexisting stormwater infrastructure
and land ownership. The BMP Toolbox developed for this project (TM 4.3, Appendix Volume 4)
was used as a “menu” of potential BMPs. The primary BMPs included in the recommendations
in the fact sheets include constructed wetland detention ponds, grass swales with check
structures, and proprietary BMPs. Constructed wetland detention ponds are recommended
because they are large enough to provide water quality treatment for an entire basin. Grass
swales with check structures are recommended for situations where the available area is a long,
thin strip of land. Proprietary BMPs are listed as alternatives for each of the sites because of
their ability to be constructed in a retro-fit application with minimal site impacts or land
acquisition requirements.
The fact sheets include the problem location (illustrated with a map), problem summary,
benefits, technical data, land ownership, implementation issues, and capital costs.
For the twelve (12) Water Quality Areas of Concern, there are six particular basins that are
expected to undergo significant redevelopment: sites1, 2, 6, 8, 9, and 10. In these basins, HDR
accounted for the possibility of stormwater BMPs being built as part of the development
process, and, in some cases, these sites were given lower priority for City-constructed BMPs
due to their potential for re-development.
5.2.2Alternative Development Process – Boulder Creek Outfalls
In addition to the twelve (12) sites identified as Water Quality Areas of Concern by the XP-
SWMM model, HDR conducted an analysis of eighteen (18) proprietary BMPs at outfalls on
Boulder Creek (Figure 5-1). Two of these outfalls overlap with the water quality area of concern
approach; these are listed in Table 5.2-1. Note there is an existing proprietary BMP located
Broadway and Boulder Creek and was identifies as site BC3.
46
Table 5.2-1 Common Water Quality Area of Concern and Boulder Creek Outfalls
WQ Area of Concern ID WQ Area of Concern DescriptionBoulderCreek Site Number
WQ4Broadway and Boulder Creek BC6
th
WQ528 Street and Boulder Creek BC11
Fact sheets were developed for each site and are included in TM 3.6.6 located in the Appendix,
Volume 4. The fact sheets show conceptual locations for the water quality manholes. Siting
these facilities assumed the water quality manhole would be an off-line system and therefore
would require a diversion manhole and connecting influent and effluent pipes.
5.2.3Alternative Evaluation and Recommendations
Alternatives for the 27 sites (12 Water Quality Areas of Concern and 15 Boulder Creek outfalls)
were further evaluated and recommendations for each site were developed. The recommended
BMPs are the result of a field visit as well as workshops with City Staff.
The next step of the process was to evaluate each of the two stormwater quality approaches
(the Water Quality Areas of Concern and the Boulder Creek outfalls) and identify a
recommended plan to be incorporated into the City’s CIP. To assist in this effort, a cost/benefit
analysis was performed for the Water Quality Areas of Concern as well as the Boulder Creek
outfalls.
Each of the 27 sites and the respective recommended BMPs were analyzed in terms of
pollutant loading at the outfall and pollutant removal by the BMP. TSS was used as the
representative pollutant for the analysis. Annual loading of TSS to each of the sites was
determined using the XPSWMMmodel and the annual rainfall series identified in Section 2 of
this report.Removal of TSS by recommendedwater quality BMPs was determined using the
model results and an Excel spreadsheet tool.
The spreadsheet tool evaluated the water quality storm peak flow being diverted to a facility and
then applied a removal effectivenessto arrive at a load reduction. Some of the BMPS were not
sized for the entire water quality peak due to site constraintsor other facility sizing issues. If the
water quality peak flow in the system was greater than the size of the BMP, the spreadsheet
tool accounted for the peak of the pollutographnot receiving pollution reduction through the
BMP. The following quantities of removal effectiveness were used in the analysis through the
spreadsheet tool as determined from a literature search,
80 percent removal of TSS for detention ponds and constructed wetland ponds.
50 percent removal of TSS for proprietary BMPs.
50 percent removal of TSS for vegetated swales with check structures.
For comparison purposes, conceptual construction costs for the recommended BMPs at each of
the sites were estimated. Table 5.2-2 lists the TSS removal and costs for the recommended
BMPs for the Water Quality Areas of Concern and the Boulder Creek Outfalls approaches. It
should be noted that WQ4 is the same as BC6 and WQ5 is the same as BC11. All four rows
are listed in this table to develop a cost/benefit for each approach; however, this redundancy is
removed in the Recommended Plan in the following section.The results indicate the cost per
pound of removal is comparable for the two approaches – approximately $5 per pound of TSS
per year.
47
Table 5.2-2 TSS Removaland Costsfor Recommended BMPs
Annual
TSS RemovalConceptual Cost
Outfall(pounds)Capital Costper Pound
Water QualityArea of Concern
WQ114,831 $ 54,000 $ 3.64
WQ2124,805 $ 635,000 $ 5.09
WQ314,970 $ 54,000 $ 3.61
WQ49,770 $ 81,000 $ 8.29
WQ515,854 $ 92,000 $ 5.80
WQ658,009 $ 289,000 $ 4.98
WQ77,924 $ 98,000 $ 12.37
WQ89,846 $ 137,000 $ 13.91
WQ920,128 $ 81,000 $ 4.02
WQ1041,004 $ 54,000 $ 1.32
WQ1125,472 $ 77,000 $ 3.02
WQ1211,024 $ 73,000 $ 6.62
353,637 $ 1,725,000 $ 4.88
Boulder Creek Outfalls
BC111,690 $ 73,000 $ 6.24
BC27,242 $ 51,000 $ 7.04
BC421,749 $ 84,000 $ 3.86
BC517,956 $ 73,000 $ 4.07
BC69,770 $ 81,000 $ 8.29
BC719,530 $ 84,000 $ 4.30
BC813,503 $ 78,000 $ 5.78
BC92,542 $ 73,000 $ 28.72
BC1026,193 $ 81,000 $ 3.09
BC1115,854 $ 92,000 $ 5.80
BC1213,215 $ 104,000 $ 7.87
BC131,391 $ 47,000 $ 33.79
BC144,830 $ 47,000 $ 9.73
BC155,438 $ 61,000 $ 11.22
BC168,628 $ 39,000 $ 4.52
BC1722,036 $ 76,000 $ 3.45
BC1829,036 $ 104,000 $ 3.58
230,604 $ 1,248,000 $ 5.41
Based on the Cost/Benefit Analysis, neither the Boulder Creek approach nor the Water Quality
Areas of Concern approach is significantly better than the other approach in terms of reducing
TSS loading to Boulder Creek and its tributaries. However, there are specific outfalls in each
approach that have a comparatively high cost per pound ratio which include Sites WQ7, WQ8,
BC9, BC13 and BC15. These high cost per pound sites do not provide a cost effective
approach to addressingstormwaterquality.
48
Several of the Water Quality Area of Concern sites have the potential to undergo significant
redeveloped as identified by City Staff. When redevelopment occurs, stormwater quality
improvements would be required by the City’s DCS which would address a majority of the
subcatchment contributing pollutants to the Water Quality Area of Concern outfall. The potential
redeveloped sites were identified as WQ1, WQ6 and WQ10. These site locations are shown on
Figure 5-1.As a result, it is recommended that a subset of these sites be included in the
Recommended Plan. The recommended sites include WQ2, WQ3, WQ4, WQ5, WQ9, WQ11,
and WQ12. Of note, WQ2 is considered a high priority because the project routes stormwater
flow away from an irrigation ditch and is part of a larger project, which is a solution to a hydraulic
problem. WQ9 is considered a high priority because it is an excellent spot for a wetland pond
on open City property.An additional benefit is that both of these high priority projects may
provide wetlands mitigation credits.
The project team recognizes that water quality in Boulder Creek itself is of primary importance,
and treating stormwaterat outfalls that flow directly into Boulder Creek may be the most direct
way to improve water quality in the most heavily used and regulated creek in the City.
Furthermore, the proprietary BMPs identified for the Boulder Creek Outfall approach tend to be
easier to site in an urban environment than ponds and swales. Therefore, it is recommended
that the BMPs for the Boulder Creek outfalls be constructed with the exception of Sites BC9 and
BC13. These exceptions are identified as the Cost/Benefit analysis shows sites BC9 and BC13
have very high costs per pound of TSS removal.
Considering the site constraints for the BMPs analyzed and the cost/benefit analysis, Table 5.2-
3 summarizes the following sites for incorporation into the Recommended Plan.
Table 5.2-3 Recommended Water Quality Sites
ImprovementOutfall ID ImprovementAnnualDetailed
Annual
Site ID DescriptionTSS Load Capital
TSS Removal
(pounds)Cost
(pounds)
WQIMP 1 WQ2ConstructedWetland166,516124,805$635,000
$104,000
WQIMP 2 BC18Proprietary BMP 61,92829,036
$81,000
WQIMP 3 BC10Proprietary BMP 56,51726,193
$77,000
WQIMP 4 WQ11Proprietary BMP 54,46725,472
$76,000
WQIMP 5 BC17Proprietary BMP 46,15222,036
$84,000
WQIMP 6 BC4Proprietary BMP 45,71221,749
$81,000
WQIMP 7 WQ9ConstructedWetland27,44420,128
$84,000
WQIMP 8 BC7Proprietary BMP 41,53319,530
$73,000
WQIMP 9 BC5Proprietary BMP 38,41817,956
$92,000
WQIMP 10 WQ5Proprietary BMP 34,24215,854
$54,000
WQIMP 11 WQ3Proprietary BMP 31,79714,970
$78,000
WQIMP 12 BC8Proprietary BMP 29,03913,503
$104,000
WQIMP 13 BC12Proprietary BMP 27,77013,215
$73,000
WQIMP 14 BC1Proprietary BMP 24,18311,690
$73,000
WQIMP 15 WQ12Proprietary BMP 22,81411,024
$81,000
WQIMP 16 WQ4Proprietary BMP 20,3189,770
$39,000
WQIMP 17 BC16Proprietary BMP 18,2958,628
$51,000
WQIMP 18 BC2Proprietary BMP 14,9887,242
$47,000
WQIMP 19 BC14Proprietary BMP 10,5604,830
49
5.3Recommended Plan
The recommended plan is a compilation of all hydraulic and water quality improvements
developed in this study. Figure 5-1 provides an overview of the recommended plan
improvements with corresponding improvement projects IDs.Project IDs were assigned based
on the subbasin the project was located in and a numerical identifier. Note the numerical
identifiers within each subbasin were assigned spatially from upper left to lower right and do not
indicate the improvement priority. To provide additional detail on the locations of the storm drain
improvements and identify model node and link ID, three E-sized maps are included in the back
pocket of the report. The model IDs from these hard copy maps can be referenced to printed
model results in Appendix A for future reference.
The process for developing the recommended plan involved refining the hydraulic alternative
recommendations for the Tier 1 and 2 problems area to resolve conflicts with existing water and
sewer utilities. Potential conflicts with sanitary sewers were resolved by identifying locations
where storm drain improvements cross sanitary sewers. At these sewer crossings, the
proposed storm drain was graded to provide a minimum of 18” of vertical clearance.There
were several locations where this storm/sanitarysewer clearance could not be obtained and the
existing sewer was re-graded and lowered to accommodate the proposed storm drain
improvement. Waterline lowerings were identified for locations where the new storm drain
crosses a water transmission line (16” diameter and greater) where the proposed storm drain
was within 4’ of the ground surface.The focus on the transmission mains were identified as the
larger lines are more problematic and expensive to relocate than smaller diameter water
distribution lines.
In addition to resolving utility conflicts, development of the recommended plan included addition
of Tier 3 hydraulic improvements and water quality improvements.
The following tables are intended to be a summary of the recommended plan for each subbasin
and include a Project ID, along with a description of the project improvement and capital cost. A
more thorough analysis for each project is presented in Section 6 of this report along with a
descriptionof how the capital costswere developed.
50
5.3.1Recommendations – Bear Canyon Creek Subbasin
The recommended plan for the Bear Canyon Creek Subbasin includes seven individual CIP
projects, which are summarized in Table 5.3-1.All of the projects are hydraulic improvement
projects.
Table 5.3-1 Summary of Recommended Improvements- Bear Canyon Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 3
BCC_01
Hydraulic Improvement $863,000
Storm Drain: Pipe Replacement
Tier 3
BCC_02Hydraulic Improvement $153,000
Storm Drain: Pipe Replacement
Tier 2 and 3
Hydraulic Improvement
BCC_03
Storm Drain: $1,183,000
Pipe Replacement
o
Storm Drain Re-Routing/Extension
o
Tier 3
BCC_04
Hydraulic Improvement $397,000
Storm Drain: Pipe Replacement
Tier 3
BCC_05
Hydraulic Improvement $156,000
Storm Drain: Pipe Replacement
Tier 3
BCC_06
Hydraulic Improvement $656,000
Storm Drain: Pipe Replacement
Tier 3
BCC_07Hydraulic Improvement $337,000
Storm Drain: Pipe Replacement
Total$3,745,000
51
5.3.2Recommendations – Dry Creek Subbasin
The recommended plan for the Dry Creek Subbasin includes two individual CIP projects, which
are summarized in Table 5.3-2. One project isacombined hydraulic/water quality improvement
project and the other is a hydraulic improvement project.
Table 5.3-2 Summary of Recommended Improvements- Dry Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 1 and 2
Combined Hydraulic/Water Quality Improvement
Storm Drain:
DC_01
$5,964,000
Pipe Replacement
o
Storm Drain Re-Routing/Extension
o
Constructed Wetland
Tier 3
DC_02
Hydraulic Improvement $334,000
Storm Drain: Pipe Replacement
Total$6,298,000
5.3.3Recommendations – Dry Creek No. 2 Subbasin
The recommended plan for the Dry Creek No. 2 Subbasin includes six individual CIP projects,
which are summarized in Table 5.3-3. Five of the projects are hydraulic improvement projects
and one is a combined hydraulic/water quality improvement project.
Table 5.3-3 Summary of Recommended Improvements- Dry Creek No. 2 Subbasin
IDImprovement Category Capital Cost ($)
Tier 3
DC2_01Hydraulic Improvement $982,000
Storm Drain: Pipe Replacement
Tier 2
DC2_02Hydraulic Improvement $4,381,000
Storm Drain: Pipe Replacement
Tier 3
DC2_03
Hydraulic Improvement $482,000
Storm Drain: Pipe Replacement
Tier 3
DC2_04
Hydraulic Improvement $504,000
Storm Drain: Pipe Replacement
Tier 3
DC2_05
Hydraulic Improvement $588,000
Storm Drain: Pipe Replacement
Tier 2
Combined Hydraulic/Water Quality Improvement
DC2_06
$547,000
Storm Drain: Pipe Replacement
Proprietary BMP
Total$7,484,000
52
5.3.4Recommendations – Elmers Twomile Creek Subbasin
The recommended plan for the Elmers Twomile Creek Subbasin includes three individual CIP
projects, which are summarized in Table 5.3-4.All of the projects are hydraulic improvements
projects.
Table 5.3-4 Summary of Recommended Improvements- Elmers Twomile Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 2
Hydraulic Improvement
ETC_01
Storm Drain:$526,000
Pipe Replacement
o
Diversion to Major Drainageway
o
Tier 3
ETC_02
Hydraulic Improvement $143,000
Storm Drain: Pipe Replacement
Tier 3
ETC_03
Hydraulic Improvement $881,000
Storm Drain: Pipe Replacement
Total$1,550,000
5.3.5Recommendations – Fourmile Canyon Creek Subbasin
The recommended plan for the Fourmile Canyon Creek Subbasin includes one individual CIP
project, which is summarized in Table 5.3-5. It is a hydraulic improvement project.
Table 5.3-5 Summary of Recommended Improvements- Fourmile Canyon Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 3
FCC_01
Hydraulic Improvement $718,000
Storm Drain: Pipe Replacement
Total$718,000
5.3.6Recommendations – Goose Creek Subbasin
The recommended plan for the Goose Creek Subbasin includes nine individual CIP projects,
which are summarized in Table 5.3-6. Seven of the projects are hydraulics improvement
projects and two are combined hydraulic/water quality projects.
53
Table 5.3-6 Summary of Recommended Improvements- Goose Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 2
GC_01
Hydraulic Improvement $6,227,000
Storm Drain: New System
Tier 1
Hydraulic Improvement
Storm Drain:
GC_02
$10,701,000
Pipe Replacement
o
New, Hydraulically Parallel Storm Drain
o
Channel Improvement
Tier 3
GC_03
Hydraulic Improvement $637,000
Storm Drain: Pipe Replacement
Tier 2
Hydraulic Improvement
GC_04
Storm Drain:$1,360,000
Pipe Replacement
o
Diversion to Major Drainageway
o
Tier 3
GC_05
Hydraulic Improvement $648,000
Storm Drain: Pipe Replacement
Tier 3
GC_06
Hydraulic Improvement $740,000
Storm Drain: Pipe Replacement
Tier 3
GC_07Hydraulic Improvement $154,000
Storm Drain: Pipe Replacement
Tier 2
Combined Hydraulic/Water Quality Improvement
GC_08
$397,000
Storm Drain: Pipe Replacement
Proprietary BMP
Tier 2
Combined Hydraulic/Water Quality Improvement
GC_09
$814,000
Storm Drain: Pipe Replacement
Constructed Wetland
Total$21,678,000
5.3.7Recommendations – Kings Gulch Subbasin
The recommended plan for the Kings Gulch Subbasin includes one individual CIP project, which
is summarized in Table 5.3-7. It is a water quality improvement project.
54
Table 5.3-7 Summary of Recommended Improvements- Kings Gulch Subbasin
IDImprovement Category Capital Cost ($)
WQIMP_15
Water Quality Improvement
$73,000
(KG_01)
Proprietary BMP
Total$73,000
5.3.8Recommendations – Lower Boulder Creek Subbasin
The recommended plan for the Lower Boulder Creek Subbasin includes two individual CIP
projects, which are summarized in Table 5.3-8.Both of the projects are water quality
improvement projects.
Table 5.3-8 Summary of Recommended Improvements- Lower Boulder Creek Subbasin
IDImprovement Category Capital Cost ($)
WQIMP_05Water Quality Improvement
$76,000
(LBC_01)
Proprietary BMP
WQIMP_02
Water Quality Improvement
$104,000
(LBC_02)
Proprietary BMP
Total$180,000
5.3.9Recommendations – Middle Boulder Creek Subbasin
The recommended plan for the Middle Boulder Creek Subbasin includes twenty three individual
CIP projects, which are summarized in Table 5.3-9. Twelve of the projects are hydraulic
improvement projects, seven are water quality improvement projects, and four are combined
hydraulic/water quality improvement projects.
Table 5.3-9 Summary of Recommended Improvements- Middle Boulder Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 3
MBC_01
Hydraulic Improvement $149,000
Storm Drain: Pipe Replacement
Tier 3
MBC_02
Hydraulic Improvement $204,000
Storm Drain: Pipe Replacement
WQIMP_14Water Quality Improvement
$73,000
(MBC_03)
Proprietary BMP
Tier 2
MBC_04Hydraulic Improvement $543,000
Storm Drain: Pipe Replacement
WQIMP_18
Water Quality Improvement
$51,00
(MBC_05)
Proprietary BMP
WQIMP_06Water Quality Improvement
$157,000
WQIMP_09
Proprietary BMP
55
Table 5.3-9 Summary of Recommended Improvements- Middle Boulder Creek Subbasin
IDImprovement Category Capital Cost ($)
(MBC_06)
WQIMP_16
Water Quality Improvement
$81,000
(MBC_07)
Proprietary BMP
Tier 3
MBC_08
Hydraulic Improvement $1,018,000
Storm Drain: Pipe Replacement
Tier 2
MBC_09Hydraulic Improvement $1,004,000
Storm Drain: Pipe Replacement
Tier 1
Hydraulic Improvement
MBC_10
Storm Drain:$1,577,000
Pipe Replacement
o
Storm Drain Re-Routing/Extension
o
WQIMP_08Water Quality Improvement
$84,000
(MBC_11)
Proprietary BMP
WQIMP_12
Water Quality Improvement
$78,000
(MBC_12)
Proprietary BMP
Tier 3
MBC_13
Hydraulic Improvement $624,000
Storm Drain: Pipe Replacement
Tier 1
Combined Hydraulic/Water Quality Improvement
Storm Drain:
MBC_14$1,659,000
Pipe Replacement
o
Storm Drain Re-Routing/Extension
o
Proprietary BMP
Tier 3
MBC_15
Hydraulic Improvement $125,000
Storm Drain: Pipe Replacement
WQIMP_03
Water Quality Improvement
$81,000
(MBC_16)
Proprietary BMP
Tier 3
MBC_17Hydraulic Improvement $411,000
Storm Drain: Pipe Replacement
Tier 3
Combined Hydraulic/Water Quality Improvement
MBC_18
$1,422,000
Storm Drain: Pipe Replacement
Proprietary BMP
Tier 3
Combined Hydraulic/Water Quality Improvement
MBC_19
$408,000
Storm Drain: Pipe Replacement
Proprietary BMP
Tier 2
MBC_20
$63,000
Hydraulic Improvement
56
Table 5.3-9 Summary of Recommended Improvements- Middle Boulder Creek Subbasin
IDImprovement Category Capital Cost ($)
Storm Drain: Pipe Replacement
Tier 3
MBC_21
Hydraulic Improvement $184,000
Storm Drain: Pipe Replacement
Tier 2
MBC_22
Hydraulic Improvement $1,740,000
Storm Drain: Pipe Replacement
Tier 2
Combined Hydraulic/Water Quality Improvement
MBC_23$380,000
Storm Drain: Pipe Replacement
Proprietary BMP
Total$12,116,000
5.3.10Recommendations – Skunk Creek Subbasin
The recommended plan for the Skunk Creek Subbasin includes two individual CIP projects,
which are summarized in Table 5.3-10. Both of the projects are hydraulic improvement projects.
Table 5.3-10 Summary of Recommended Improvements - Skunk Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 2
Hydraulic Improvement
SC_01
Storm Drain:$968,000
Pipe Replacement
o
Diversion to Major Drainageway
o
Tier 2
SC_02
Hydraulic Improvement $931,000
Storm Drain: Pipe Replacement
Total$1,899,000
5.3.11Recommendations – Viele Channel Subbasin
The recommended plan for the Viele Channel Subbasin includes two individual CIP projects,
which are summarized in Table 5.3-11. Both of the projects are hydraulic improvement projects.
Table 5.3-11 Summary of Recommended Improvements - Viele Channel Subbasin
IDImprovement Category Capital Cost ($)
Tier 3
VC_01
Hydraulic Improvement $941,000
Storm Drain: Pipe Replacement
Tier 3
VC_02$1,284,000
Hydraulic Improvement
57
IDImprovement Category Capital Cost ($)
Storm Drain: Pipe Replacement
Total$2,225,000
5.3.12Recommendations – Wonderland Creek Subbasin
The recommended plan for the Wonderland Creek Subbasin includes three individual CIP
projects, which are summarized in Table 5.3-12. All three of the projects are hydraulic
improvement projects.
Table 5.3-12 Summary of Recommended Improvements - Wonderland Creek Subbasin
IDImprovement Category Capital Cost ($)
Tier 3
WC_01
Hydraulic Improvement $239,000
Storm Drain: Pipe Replacement
Tier 3
WC_02
Hydraulic Improvement $333,000
Storm Drain: Pipe Replacement
Tier 2
WC_03Hydraulic Improvement $644,000
Storm Drain: Pipe Replacement
Total$1,216,000
58
Capital Improvement Program
6.1 Cost Estimating
Itemized cost estimates were developed for each CIP project with an anticipated level of
accuracy of +50% to –30% (order-of-magnitude cost estimates). The cost estimate worksheets
are included in the appendix for reference. The estimates include capital construction costs and
estimates land acquisition. Unit costs were obtained from recent bid tabs andSite Work and
LandscapeCost Data, RSMeans®, and equipment suppliers. Unit costs for pipeline
construction, manholes and inlets include material, excavation, and backfill. Surface restoration
was developed as a separate cost item. Utility relocation cost were developed as a separate
item for sewer line relocations and for watermain lowerings 16” in diameter and greater. Minor
utility relocations including, water and sewer service laterals, were accounted for as an
allowance of the total constructioncost. Quantities were for pipes, inlets, manholes, and water
quality facilities were obtained from the project GIS.
The cost estimates also include a 30% construction contingency and an 18% allowance for
engineeringand administration. All estimates are in 2006 dollars and equate to an Engineering
News Record, Construction Cost Index of 7880
6.2Implementation Plan
The goal for this strategic plan is to manage stormwater, by minimizing impacts on localized and
downstream flooding and improving water quality. To these ends, the recommended system
improvements were categorized as 1) Hydraulic and Combined Hydraulic/Water Quality projects
or 2) Water Quality Improvement projects. These two project categories form the collector
system CIP.
The implementation plan for the Hydraulic and Combined Hydraulic/Water Quality CIP projects
follows the Tier 1, 2 and 3 problem areas. Tier1 CIP projects are considered high priority
improvements as they resolve severe conveyance system problems and in some instances
address stormwater quality problems. Tier 1 projects areas are anticipated to a) have a high
social benefit by resolving street and property flooding issues,b) have a high economic benefit
by reducing flooding risk and property damage, and c) provide an environmental benefit by
addressingstormwaterquality issues at identified problem locations. Note that not all Tier 1
locations included a water quality problem site and that the overriding criterion for prioritization
was resolving flooding issues. Table 6.2-1 identifies the Tier 1, Tier 2 and 3 CIP projects.
Table 6.2-1 Tier 1, Tier 2 and Tier 3 CIP Projects Implementation Plan
ProblemRankingImprovementLocationImprovement TypeCapital
PriorityIDCost
$10,701,000
Tier 1 1GC_02Alpine Avenue , west of
Pipe
th
19 Avenue, in and near
Replacement
Broadway south towards
NewStorm
Dewey Street and north
Drain
towardsNorth Boulder Park
Channel
Improvements
59
Table 6.2-1 Tier 1, Tier 2 and Tier 3 CIP Projects Implementation Plan
RankingLocationImprovement Type
ProblemImprovementCapital
PriorityIDCost
$1,577,000
th
Tier 1 2MBC_1018 and Spruce Street
Pipe
Replacement
Storm DrainRe-
Routing/Extensi
on
$1,659,000
th
Tier 1 3MBC_14Arapahoe and 28 Street
Pipe
Replacement
Storm DrainRe-
Routing/Extensi
on
Proprietary BMP
$5,964,000
Tier 1/2 4/13DC_01Gunbarrel – Spine Road,
Pipe
rd
Lookout and 63 Systems
Replacement
Storm DrainRe-
Routing/Extensi
on
Constructed
Wetland
$968,000
Tier 2 5SC_01Moorhead and Moorhead
Pipe
frontage
Replacement
Diversion to
Major
Drainageway
$543,000
Tier 2 6MBC_04Lincoln
Pipe
Replacement
$644,000
Tier 2 7WC_03Vail and Independence
Pipe
Replacement
$1,740,000
Tier 2 8MBC_22Arapahoe, Commerce, and
Pipe
Range
Replacement
$63,000
Tier 2 9MBC_20Parking structure between
Pipe
th
Foothills and 38
Replacement
$4,381,000
Tier 2 9DC2_02Thunderbird,Osage, and
Pipe
Foothills
Replacement
$397,000
Tier 2 11GC_08Foothills and Valmont
Pipe
Replacement
Proprietary BMP
$814,000
Tier 2 12GC_09Industrial area near Pearl
Pipe
Parkway and Wonderland
Replacement
Creek
Constructed
Wetland
$526,000
Tier 2 14ETC_01Broadway and Iris
Pipe
Replacement
60
Table 6.2-1 Tier 1, Tier 2 and Tier 3 CIP Projects Implementation Plan
RankingLocationImprovement Type
ProblemImprovementCapital
PriorityIDCost
Diversion to
Major
Drainageway
$380,000
th
Tier 2 14MBC_23Access roadand 55
Pipe
St/Pearl and Boulder Creek
Replacement
Proprietary BMP
$547,000
Tier 2 16DC2_06Arapahoe/56th Street and
Pipe
Dry Creek
Replacement
Proprietary BMP
$931,000
th
Tier 2 18SC_02Euclid and 30
Pipe
Replacement
$1,004,000
th
Tier 2 19MBC_0916 St.
Pipe
Replacement
$1,360,000
Tier 2 20GC_04Folsom, Glenwood, &
Pipe
Floral
Replacement
Diversion to
Major
Drainageway
$6,227,000
Tier 2 SeeGC_01Broadway, Iris to Balsam
NewStorm
Note 1
Drain System
$1,183,000
Tier 2/3 21/23BCC_03Gillaspie and Darley
Pipe
Replacement
Storm DrainRe-
Routing/Extensi
on
$941,000
Tier 3 22VC_01Gillaspie and Heidelberg
Pipe
Replacement
$1,284,000
Tier 3 23VC_02Broadway and Viele
Pipe
Channel
Replacement
$1,422,000
th
Tier 3 25MBC_18Arapahoe and 30 Street
Pipe
Replacement
Proprietary BMP
$982,000
Tier 3 26DC2_01Baseline and Inca
Pipe
Replacement
$397,000
Tier 3 27BCC_04Broadway and Bear Creek
Pipe
Replacement
$588,000
th
Tier 3 27DC2_0555 and Dry CreekNumber
Pipe
2
Replacement
$740,000
th
Tier 3 29GC_06Pearl and 30
Pipe
Replacement
$504,000
Tier 3 30DC2_04Pennsylvania and Crescent
Pipe
Replacement
61
Table 6.2-1 Tier 1, Tier 2 and Tier 3 CIP Projects Implementation Plan
RankingLocationImprovement Type
ProblemImprovementCapital
PriorityIDCost
$624,000
Tier 3 30MBC_13Folsom and Walnut
Pipe
Replacement
$637,000
rd
Tier 3 30GC_0323 and Mapleton
Pipe
Replacement
$333,000
Tier 3 33WC_02Island and Kalmia
Pipe
Replacement
$863,000
Tier 3 33BCC_01Lehigh and Bear Creek
Pipe
Replacement
$718,000
th
Tier 3 35FCC_01Hoya, Corriente and 30
Pipe
Replacement
$334,000
Tier 3 36DC_02Clubhouse and Augusta
Pipe
Replacement
$154,000
th
Tier 3 36GC_0730 and Corona
Pipe
Replacement
$239,000
Tier 3 36WC_01WonderlandHill and Poplar
Pipe
Replacement
$143,000
Tier 3 36ETC_02Cloverleaf and Kalmia
Pipe
Replacement
$408,000
Tier 3 36MBC_19Marine Avenue and
Pipe
Boulder Creek
Replacement
Proprietary BMP
$204,000
th
Tier 3 36MBC_024 and Canyon
Pipe
Replacement
BCC_07$337,000
th
Tier 3 3636 and Baseline
Pipe
Replacement
BCC_02$153,000
Tier 3 36Hartford and Darley
Pipe
Replacement
BCC_06$656,000
nd
Tier 3 3642 and Moorhead
Pipe
Replacement
BCC_05$156,000
Tier 3 36Martin and Ash
Pipe
Replacement
ETC_03$881,000
th
Tier 3 4826 and Kalmia
Pipe
Replacement
GC_05$648,000
th
Tier 3 4927 and Spruce
Pipe
Replacement
MBC_15$125,000
th
Tier 3 5028 and Colorado
Pipe
Replacement
MBC_08$1,018,000
th
Tier 3 5013 and Broadway
Pipe
Replacement
DC2_03$482,000
Tier 3 50Manhattan and Baseline
Pipe
Replacement
MBC_01$149,000
th
Tier 3 535 and Mountain View
Pipe
62
Table 6.2-1 Tier 1, Tier 2 and Tier 3 CIP Projects Implementation Plan
RankingLocationImprovement Type
ProblemImprovementCapital
PriorityIDCost
Replacement
MBC_21$184,000
th
Tier 3 5448 and Arapahoe
Pipe
Replacement
MBC_17$411,000
th
Tier 3 5528, 500’ north of Canyon
Pipe
Replacement
Notes:
1. Broadway, Iris to Balsam problem area has no existing storm drain system. As a result, the problem
improvement ranking process does not apply. However, no flooded structures were predictedby the
model.
The implementation plan for the WQIMP projects were prioritized based on problem severity as
identified by pollutant load. The WQIMP category was developed since many of the water
quality project sites were not adjacent to hydraulic problem and improvement locations. In
addition, many of these WQIMP projects could be defined as a small capital projectssince the
estimated construction costs are less than $100,000.
Table 6.2-2 Water QualityImprovements Implementation Plan
ImprovementAnnualLocationCapital
IDTSSCost
Load
(pounds)
$104,000
61,900 th
WQIMP 2 Boulder Creek 1,400’ East of 75 Street
$81,000
56,500 th
WQIMP 3 Boulder Creek & 28 Street
$76,000
th
WQIMP 5 46,200Boulder Creek & 75 Street
$157,000
WQIMP 6 45,700Boulder Creek & East Broadway Street & Arapahoe Avenue
WQIMP 9 & 38,400
WQIMP 8 $84,000
41,500Boulder Creek 200’ West of Folsom Street
WQIMP 12 $78,000
29,000Boulder Creek & Folsom Street
WQIMP 14 $73,000
24,200 th
Boulder Creek & 9 Street
WQIMP 15 $73,000
22,800
Broadway & Skunk Creek
WQIMP 16 $81,000
20,300 th
Boulder Creek & 13 Street
WQIMP 18 $51,000
th
15,000Boulder Creek & 11 Street
63
6.3Recommended Plan Fact Sheets
Fact sheets were developed to provide details regarding each of the Tier 1 and Tier 2 problem
priority areas. In addition, fact sheets were also developed for three Tier 3 problem priority
areas that have associated WQIMP projects. These fact sheets provide the problem ID,
improvement location and alignment, technical data for initiating the design process, land
ownership and acquisition needs, implementation issues, and an estimate of the capital
construction costs. Theproblem ID can be used with the technical memorandums in the
Appendix, Volume 3, to research the problem causes and severity. The improvement plan view
map shown in the fact sheets identify the recommended pipe size and model link ID. The model
link ID can be used to query the GIS to determine other design data and evaluate model results
as the projects progress into the design phase.
6.3.1Tier 1 Priority Improvements
This section includes fact sheets that provide details for each of the Tier 1 problem priority areas
in the Recommended Plan.
64
GC_02: UPPER GOOSE CREEK
Discussion
Subbasin/Outfall:
Goose Creek Subbasin, Outfall to Goose Creek
Problem ID:
HYD#16 (Tier 1 Priority Level)
Improvement
See TM 5.1c located in Volume 3 of the Appendices for a detailed discussion and
Description
improvement phasing recommendations.
Replace existing system in Phases 1, 4, and 5
Channel improvements in Phase 2
Construct a parallelsystem in Phases 3 and 4
Technical Data:
The system is required to convey the 5-yr storm
th
Land
All construction west of 19 Avenue would be within Public ROW.
Ownership:
Constructionalong the Edgewood reach of Goose Creek will require land aquisition
Implementation
Restricted construction access for Edgewood reachchannel improvements
Issues:
Large storm drain sizes in an urbanizedareawill create traffic control and utility issues
Phased construction due to high capital cost
Potential for high groundwater
Capital Cost:
$10,700,000
65
MBC_10:18 TH AND SPRUCE STREET
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin, Outfall to Boulder White RockDitch
Problem IDs:
HYD#34 (Tier 1 Priority Level)
Improvement
Extension of Existing Storm Drains at 18th/Spruce & 20th/Spruce Intersections to Walnut
Description
Extend the existing storm drain system at 18th/Spruce to the 18th/Walnut intersection. At
18th/Walnut, extend storm drain down the southsideof Walnut (water and sewer utilities
exist on the north side) to a discharge point at Boulder White Rock Ditch.
thth
Extend the existing storm drain system at 20/Sprucedown the east side of 20 to the
th
newstorm drain at 20 and Walnut.
The system is required to convey the 5-yr storm
Technical Data:
Land
All construction would be within Public ROW.
Ownership:
Implementation
Potential for relocating privateutilities on 18th and 20th Streets.
Issues:
Constructionon 18th, 20th and Walnut would require traffic control and short-term
closures.
Potential for high groundwater
Capital Cost:
$1,577,000
66
MBC_14: ARAPAHOE AND 28 TH STREET
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin, Outfall to Boulder Creek
Problem ID:
HYD#55 (Tier 1 Priority Level), WQIMP 10 (Boulder Creek Outfall)
Improvement
Construct a new diversion manhole on Folsom St, south of Arapahoe to tie the western
Description
storm drainsystem into the existing 48” system along the west side of Folsom (with
th
availablecapacity). Replace existing under capacity storm drain along 26, Arapahoe and
thth
28 and construct a new 36” to 42” pipe along 28 Street between Arapahoe and Boulder
Creek to convey both the eastern and westernsystems.
th
Install a proprietary BMP along 28 Street near the outfall to Boulder Creek.
The system is required to convey the 5-yr storm
Technical Data:
Q(wq) – 7.32 cfs
Size of manhole: 10-foot
Size of connector pipe: 30-inch
Land
Public ROW and private property.
Ownership:
th
Implementation
Easement acquisition, approximately 500 ft, may be needed on the west side of 28,
Issues:
south of the super market.
Capital Cost:
$1,659,000
67
DC_01: GUNBARREL – SPINE ROAD, LOOKOUT AND 63 RD SYSTEMS
Discussion
Subbasin/Outfall:
Dry Creek Subbasin, Outfall to Dry Creek east of the Diagonal Highway
Problem ID:
HYD#8 (Tier 1 Priority Level)HYD#9 (Tier 2 PriorityLevel), WQIMP 01 (Hot Spot)
,
Improvement
Replace the existing under capacity storm drain system with pipe diameters that range
Description
from 30” to 60“. Minor changes to existing pipe slopes are required to optimize the
proposed diameters. The new storm drain is typically located lower than the sanitary
sewer to avoid conflicts with sewer mains and service laterals.
Construct storm sewer along Lookout Rd to connectwith system to east alongSpine
Road. Constructed wetland pond with discharge to Dry Creek.
System is required to convey the 5-year storm.
Technical Data:
Pond Volume = 347,000 cu ft (8 acre feet)
Pond surface area: 69,000 square feet
Land
All construction would be within Public ROW south of Odel Road. North of Odel Road it is
Ownership:
assumed the existing pipe is in an easement and no additional permanent easement
acquisition would be required.
Implementation
Traffic control and business impacts (shipping/truck traffic) for construction in Spine Road
Issues:
and Lookout Road.
Possible conflicts with existing sanitary sewers and 16 inch water main.
Capital Cost:
$5,964,000
68
6.3.2Tier 2 Priority Improvements
This section includes fact sheets that provide details for each of the Tier 2 problem priority areas
in the Recommended Plan.
SC_01:MOORHEAD AND MOORHEAD FRONTAGE
Discussion
Subbasin/Outfall:
Skunk Creek Subbasin, Outfall to Skunk Creek
Problem ID:
HYD#42 (Tier 2 Priority Level)
Improvement
Diversion to Bear Creek Ditch
Description
st
Construct a diversion manhole in the Moorhead/31St. intersection to divert flow to a new
storm drainrunning northeast to discharge into the Bear CreekDitch adjacent to Highway
36. Install a piped storm drain to replace the ditch. The alignment between the homes is
stnd
to follow the existing storm drains between 31 and 32. The existing ditch along
Highway 36 could also be used insteadof installing the 36” storm drain. The ditch would
need to be re-graded to flow consistently toward the north and the cross-section improved
to convey the design flow.
The system is required to convey the 5-yr storm
Technical Data:
Land
Constructionthrough possible residential area
Ownership:
69
SC_01:MOORHEAD AND MOORHEAD FRONTAGE
Discussion
Implementation
Potential for relocating private utilities along Bear Creek Ditch.
Issues:
Constructionon private property, betweenexisting homes would require easement
acquisition, approximately 160 ft. Limited space/width between the homes could also
create difficulties during construction.
Potential for high groundwater.
Capital Cost:
$968,000
70
MBC_04:LINCOLN
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin; Outfall to Anderson Ditch
Problem ID:
HYD#41 (Tier 2 Priority Level)
Improvement
Replace the existing under capacity storm drain system betweenCollege and the
Description
Anderson Ditch and match existing grades.
The system is required to convey the 2-yr storm
Technical Data:
Land
All construction would be within Public ROW.
Ownership:
Implementation
Construction in Lincoln would require traffic control.
Issues:
Limited cover north of College requires parallel pipes for the short connection to the
Anderson Ditch.
th
A transportation (road widening/bike lane) project is planned along 9, west of Lincoln.
Capital Cost:
$543,000
71
WC_03: VAIL AND INDEPENDENCE
Discussion
Subbasin/Outfall:
WonderlandCreek Subbasin; Outfall to Boulder & Lefthand Ditch
Problem ID:
HYD#19 (Tier 2 Priority Level)
Improvement
Abandon the existing system that is routedunder the existing trailers/mobile home and
Description
construct a new system in the street.
The reservoir outlet needs to be confirmed prior to final design development.
The reservoir was assumed to be full and therefore rainfall would spill into the outlet/storm
drain system.
The system is required to convey the 2-yr storm
Technical Data:
Land
Constructionwould be within Public ROW.
Ownership:
Implementation
Probable water and sewer utility relocations andpotential for relocating private utilities.
Issues:
A transportation (road widening/bike lane) project is planned adjacent to the existing storm
drain on the east side of Independence.
Potential for high groundwater
Capital Cost:
$644,000
72
MBC_22: ARAPAHOE, COMMERCE, AND RANGE
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin, Outfall to a unknown tributary to Boulder Creek
Problem ID:
HYD#24 (Tier 2 Priority Level)
Improvement
Range Street System: Replace the existingunder capacity storm drain system along
Description
Range.
Commerce Street System: Replace the existing under capacity storm drain system along
Commerce. As the 36” pipe crosses under therailroad embankment and is only slightly
surcharge, it is recommended this pipe not be replaced.
The system is required to convey the 5-yr storm
Technical Data:
Land
All construction would be within Public ROW.
Ownership:
Implementation
Potential for high groundwater
Issues:
Capital Cost:
$1,740,000
73
MBC_20: PARKING STRUCTURE BETWEEN FOOTHILLS AND 38 TH
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin, Outfall to Boulder Creek
Problem ID:
HYD#29 (Tier 2 Priority Level)
Improvement
Replace the existing under capacity stormdrain system and match existing grades.
Description
The system is required to convey the 5-yr storm
Technical Data:
Land
Private. Potential for pipe to be within a drainage easement.
Ownership:
Implementation
Potential for high groundwater
Issues:
Capital Cost:
$63,000
74
DC2_02: THUNDERBIRD, OSAGE, AND FOOTHILLS
Discussion
Subbasin/Outfall:
Dry Creek Subbasin, Outfall Dry Creek No. 2 Ditch
Problem ID:
HYD#47 (Tier 2 Priority Level)
Improvement
(1) System Replacement - Along Foothills, Osage, and Qualla to Highway 36.
Description
Replace the under capacity and severely under capacity pipes.
(2) System Replacement - Foothills to Thunderbird Lake.
(3) System Replacement – Sioux between Iroquois & Seminole.
(4) System Replacement – Across Foothills at Cherokee.
Replace the existing under capacity storm drain systems.
(1) Foothills,5-Year system.
Technical Data:
(2) Thunderbird Lake, 2-year system
(3) Sioux, 2-Year system
(4) Cherokee, 2 & 5-Year systems
Land
Constructionwould be within Public ROW and someprivate/public lawn areas.
Ownership:
75
DC2_02: THUNDERBIRD, OSAGE, AND FOOTHILLS
Discussion
Implementation
Potential for high groundwater.
Issues:
Boringwill be required to cross foothills.
Thunderbird Lake system has shallow cover issues and may require a parallel HERCP
system.
Possible conflicts with existing sanitary sewers and 16 inch water main.
Final designprocessshould consider an alternative alignment evaluation to remove the
upstreamcrossing under Foothills Parkway as this will be a bore crossing. Consider
routing flow north to the Foothills crossing at Sioux.
Capital Cost:
$4,381,000
76
GC_08: FOOTHILLS AND VALMONT
Discussion
Subbasin/Outfall:
Goose Creek Subbasin, Outfall to Goose Creek
Problem ID:
HYD#27 (Tier 2 Priority Level), WQIMP 11 (Hot Spot)
Improvement
Replace the existing under capacity 18” diameter storm drain in Foothills, under Valmont
Description
and 36” diameter storm drain in Foothills and matchexisting grades.
Install a proprietary BMP southwest of the intersection of Foothills and Valmont.
The system is required to convey the 5-yr storm
Technical Data:
Q(wq) – 5.54 cfs
Size of manhole: 8-foot
Size of connector pipe: 24-inch
Land
All construction would be within Public ROW.
Ownership:
Implementation
Construction in Valmont would require traffic control and closing of the east and
Issues:
westbound lanes.
A transportation (multi-use path) project is planned along the west side of Foothills
Highway from Valmont to the Federal facility.
Capital Cost:
$397,000
77
GC_09: INDUSTRIAL AREA NEAR PEARL PARKWAY AND WONDERLAND CREEK
Discussion
Subbasin/Outfall:
Goose Creek Subbasin, Outfall to Goose Creek
Problem ID:
HYD#21 (Tier 2 Priority Level), WQIMP 07 (Hot Spot)
Improvement
Construct a new system that abandons the system that is routed under the existing
Description
building. The new pipe system would berouted in the middle of the accessroad.
Constructedwetland pond in the City Yards(to be redesigned). Flow would be diverted
from the collectorsystems to the pond via a diversionmanhole and storm drain.Flow from
the water quality pond would be discharged to Wonderland Creek via the collector system.
Flows in excess of the WQ stormwould not be routed through the pond.
The system is required to convey the 5-yr storm
Technical Data:
Pond volume = 40,800 cubic feet (0.9 acre feet)
Pond surface area: 14,000 square feet
Land
Private property. Being the system goes under a building it is doubtful an easement exists.
Ownership:
Implementation
Probable water and sewer utility relocations andpotential for relocating private utilities.
Issues:
Little to no room may be available for relocation.
An easement, approximately 220 ft, for Link 1748 will be needed.
Capital Cost:
$814,000
78
ETC_01: BROADWAY AND IRIS
Discussion
Subbasin/Outfall:
Elmers TwoMile Canyon CreekSubbasin, Outfall to Farmers Ditch
Problem ID:
HYD#15 (Tier 2 Priority Level)
Improvement
Diversionto Major DrainagewayImprovement
Description
Construct a diversion manhole at the Broadway/Iris intersection to divert excessflow from
the collectorsystemsouth into the planned Two Mile Canyon Creek (TMCC) major
drainagewayimprovement. The TMCC improvement consists on a 54” storm drain the
runs south of Iris in Broadway then turnseast on Hawthorne and continues to eventually
outfall to Goose Creek as shown in GC_04.
The system is required to convey the 5-yr storm
Technical Data:
Increase in 5-year flow to the TMCC project is approximately 20 cfs totaling about
a 10% in the original design capacity. This would require 2,640’ of 24” RCP to be
increased to 60” RCP.
Land
All construction would be within Public ROW with the exception of a drainage easement
Ownership:
identified in the TMCC major drainageway project.
Implementation
Construction in Broadwaywould require significant traffic control.
Issues:
Potential for high groundwater
Capital Cost:
$526,000
79
MBC_23: ACCESS RD AND 55 TH ST/PEARL AND BOULDER CREEK
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin & 100-year flood zone, Outfall to Boulder Creek
Problem ID:
HYD#20 (Tier 2 Priority Level), WQIMP 17 (Boulder Creek Outfall)
Improvement
Replace the existing under capacity stormdrain system and match existing grades.
Description
h
Install a proprietary BMP along 55 Street near the outfall.
The system is required to convey the 5-yr storm
Technical Data:
Q(wq) – 2.95 cfs
Size of manhole: 8-foot
Size of connector pipe: 24-inch
Land
Some constructionwould be within Public ROW;
Ownership:
Otherconstruction may be within an assumed drainage easement across private property
within the industrial area.
Implementation
Potential for high groundwater
Issues:
Capital Cost:
$380,000
80
DC2_06: ARAPAHOE/56TH STREET AND DRY CREEK
Discussion
Subbasin/Outfall:
Dry Creek No.2 Subbasin and 100-year Flood Zone, Outfall to Dry Creek
Problem ID:
HYD#22 (Tier 2 Priority Level),WQIMP 04 (Hot Spot)
Improvement
Replace the existing under capacity stormdrain system and match existing grades.
Description
Install a proprietary BMP at northeast corner of the basin. Requires two diversion
structures from two systems.
The system is required to convey the 5-yr storm
Technical Data:
Q(wq) – 6.5 cfs
Size of manhole: 8-foot
Size of connector pipe: 24-inch
Land
All construction would be within Public ROW.
Ownership:
Implementation
Construction in Arapahoewould require traffic control and closing of the lane(s).
Issues:
A transportation (road widening/multi-use path) project is planned along Arapahoe.
Capital Cost:
$547,000
81
SC_02: EUCLID AND 30 TH
Discussion
Subbasin/Outfall:
Skunk CreekSubbasin, Outfall to Wellman Ditch
Problem ID:
HYD#38 (Tier 2 Priority Level)
Improvement
Replace the existing under capacity storm drain system.
Description
The system is required to convey the 5-yr storm
Technical Data:
Land
Assumed located within drainage easement(s) through private property. May need to
Ownership:
increase easement width as pipe diametersat downstream end are significantly larger.
Implementation
Confined construction behind condos and impacts to existing trees and landscaping would
Issues:
increase project costs and public involvement issues.
Capital Cost:
$931,000
82
MBC_09:16 TH ST.
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin, Outfall to North Boulder FarmersDitch
Problem ID:
HYD#35 (Tier 2 Priority Level)
Improvement
System Replacement.
Description
th
Replace the existing under capacitystorm drain system in Pine and 16 Street,.
The system is required to convey the 5-yr storm
Technical Data:
Land
All construction would be within Public ROW.
Ownership:
th
Implementation
Construction in 16 St. would require traffic control
Issues:
Capital Cost:
$1,004,000
83
GC_04: FOLSOM, GLENWOOD, & FLORAL
Discussion
Subbasin/Outfall:
Goose Creek Subbasin; Outfall to Goose Creek
Problem ID:
HYD#18 (Tier 2 Priority Level)
Improvement
Diversionto Major Drainageway
Description
Replace the Folsom system betweenHawthorne and Glenwood and the Glenwood
system. Construct a diversion manhole near the Folsom/Glenwood intersection to divert
flow to a new storm drain that runs in to Glenwood and east of Folsom. This new storm
drainwould connect the existing storm drain (on the west side of Folsom) to a discharge
point at Elmers Two-MileCreek.
The storm drain that runs to the northwest is part of the TMCC major drainage way
improvement that ties in with the system shown in ETC_01.
The system is required to convey the 5-yr storm
Technical Data:
Land
All construction would be within Public ROW.
Ownership:
Implementation
Potential for high groundwater.
Issues:
Capital Cost:
$1,360,000
84
BROADWAY, IRIS TO BALSAM
GC_01:
Discussion
Subbasin/Outfall:
Goose Creek Subbasin, Outfall to Goose Creek andTwo Mile Creek
Problem ID:
Not assigned – no existing storm drain in Broadway
GC-02
GC-02
Improvement
See TM 5.1d located in Volume 3 of the Appendices for a detailed project and
Description
improvement phasing discussion.
New Storm Drain System.
Extend a new storm drain in Broadway from Two Mile Creek/Iris to Elder Street, then
easterly to the confluenceof Two Mile Creek and Goose Creek. This system would
convey street runoff and major drainageway flows from Two Mile Creek, upstream of
Broadway.
Extend a new storm drain in Broadway from Delwood to a connection with Upper Goose
Creek storm drain system near Balsam.
The system is required to convey the 5-yr storm
Technical Data:
Land
All construction would be within Public ROW.
Ownership:
85
BROADWAY, IRIS TO BALSAM
GC_01:
Discussion
Implementation
Approximately 1.8-miles of new storm drain in an urbanized area.
Issues:
Water line replacements are probable.
Numeroussewer main and service lateral crossings. No conflicts with sewer mains are
anticipated as identified using the City’s GIS data.
Crossing the Farmer Ditchstructure may require a siphon or partialsiphon depending on
the ditch depth.
Capital Cost:
$6,227,000
86
BCC_03: GILLASPIE AND SHOPPING CENTER PARKING
Discussion
Subbasin/Outfall:
Bear Canyon Creek Subbasin,Outfall to Bear Canyon Creek
Problem ID:
HYD#49 (Tier 2 Priority Level), HYD#50 (Tier 3 Priority Level)
Improvement
System Replacement/Diversion.
Description
Replace the existing under capacity storm drain along Darley from Edinboro to Gillaspie.
Construct a diversion manhole near the Darley/Gillaspie intersection to divert flow to a new
storm drain that continuesnortheast in Darley. This new storm drain would connect with
the existing storm drain at the Darley/Toedtli intersection where it would eventually
discharge into Viele Creek.
Technical Data:
The system is required to convey the 2 and 5-yr storms
Land
All construction would be within Public ROW.
Ownership:
Implementation
Construction in Darley and Broadwaywould require minor traffic control.
Issues:
Potential for high groundwater
Capital Cost:
$1,183,000
87
6.3.3Tier 3 Priority Improvements
This section includes fact sheets that provide details for each of the Tier 3 problem priority areas
in the Recommended Plan that have WQIMP associated with them. The remaining Tier 3
improvements are shown on the E-sized maps in the back pocket of this report.
MBC_18: ARAPAHOE AND 30 TH STREET
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin, Outfall to Boulder Creek
Problem ID:
HYD#30 (Tier 3 Priority Level), WQIMP 13 (Boulder Creek Outfall)
Improvement
System Replacement.
Description
Replace the existing under capacity storm drain system.
th
Install a proprietary BMP along 30 Street near the outfall.
The conveyancesystem is required to convey the 5-yr storm
Technical Data:
Q(wq) – 9.84 cfs, Size of manhole:10-foot, Size of connector pipe: 30-inch
Land
Land ownedby University of Colorado
Ownership:
Implementation
Easement acquisition
Issues:
Capital Cost:
$1,422,000
88
MBC_19: MARINE AVENUE AND BOULDER CREEK
Discussion
Subbasin/Outfall:
Middle Boulder Creek Subbasin, Outfall to Boulder Creek
Problem ID:
HYD#28 (Tier 3 Priority Level)
- Existing storm drainpipe diameters are 18”. Future
condition 5-yr runoff peaksrange from 8.2 to 12.2 cfs. Storm drain pipes from Boulder
Creek to about Marine are under capacity with a Q ranging from 1.3 to 1.9.
Ratio
WQIMP 19 (Boulder Creek Outfall)
- The basin for WQIMP 19 extends east of 30th
approximately 1,600 feet and straddlesMarine about 200 ft north and south.
Improvement
Replace the existing under capacity storm drain system.
Description
th
Install a proprietary BMP along 30 Street near the outfall.
The system is required to convey the 5-yr storm
Technical Data:
Q(wq) – 1.95 cfs
Size of manhole: 6-foot
Size of connector pipe: 18-inch
Land
Land ownedby University of Colorado.
Ownership:
Implementation
Easement acquisition
Issues:
Capital Cost:
$408,000
89
6.3.4Water Quality Specific Projects
This section includes fact sheets for areas in the Recommended Plan that have only water
quality improvements.
LBC_02: BOULDER CREEK 1,400’ EAST OF 75 STREET
TH
Improvement
The basin for WQIMP 02 consists of
Location:
the east half of the area
encompassed by Heatherwood Dr
th
and 75.
-
WQIMP 02 (Boulder Creek Outfall)
Improvement
th
I
nstall a proprietary BMP east of 75
Description:
near Aberdeen and Heatherwood
Q(wq) – 19.41cfs
Technical Data:
Size of manhole: 10-foot
Size of connector pipe: 30-inch
City of Boulder
Land Ownership:
Maintenance access maybe
Implementation
problematic.
Issues:
Capital Cost:
$104,000
MBC_16: BOULDER CREEK & 28 TH STREET
Improvement
The basin for WQIMP 03 includes
Location:
the area south of Boulder Creek
th
along 28 to Colorado.
-
WQIMP 03 (Boulder Creek Outfall)
Improvement
th
I
nstall a proprietary BMP west of 28
Description:
near Boulder Creek
Q(wq) – 14.49cfs
Technical Data:
Size of manhole: 10-foot
Size of connector pipe: 30-inch
PublicROW
Land Ownership:
CDOTROW
Implementation
Issues:
Capital Cost:
$81,000
90
LBC_01: BOULDER CREEK & 75 STREET
TH
Improvement
The basin for WQIMP 05 includes
th
Location:
the area about 450 ft wide along 75
from BoulderCreek north to
Clubhouse.
-
WQIMP05 (Boulder Creek Outfall)
Improvement
th
I
nstall a proprietary BMP along 75.
Description:
Q(wq) – 11.72cfs
Technical Data:
Size of manhole: 10-foot
Size of connector pipe: 30-inch
Construction wouldbe within
Land Ownership:
Public ROW.
Propertyacquisition
Implementation
Issues:
Capital Cost:
$76,000
MBC_06: BOULDER CREEK & EAST BROADWAY STREET & ARAPAHOE AVENUE
Improvement
The basins for WQIMP 06 and
Location:
WQIMP 09 include a large area
south of Boulder Creek to Cascade
about 1,200 ft wide on the east side
of Broadway.
WQIMP 06 and WQIMP 09 (Boulder
Improvement
- I
Creek Outfalls)
nstall a proprietary
Description:
BMPwest of Broadway near Boulder
Creek and a second south of Arapahoe
near Boulder Creek
Broadway BMP
Technical Data:
Q(wq) – 22.48cfs
Size of manhole: 10-foot
Size of connector pipe: 30-inch
Arapahoe BMP
Q(wq) – 23.91cfs
Size of manhole: 10-foot
Size of connector pipe: 30-inch
City of Boulder
Land Ownership:
Construction in Broadway
Implementation
Issues:
Capital Cost:
$157,000
91
MBC_11: BOULDER CREEK 200’ WEST OF FOLSOM STREET
Improvement
The basin for WQIMP 08 includes
Location:
the area south of Boulder Creek
along Folsom to Colorado.
-
WQIMP 08 (Boulder Creek Outfall)
Improvement
I
nstall a proprietary BMP west of Folsom
Description:
south of Boulder Creek
Q(wq) – 10.13cfs
Technical Data:
Size of manhole: 10-foot
Size of connector pipe: 30-inch
UniversityofColorado
Land Ownership:
Propertyacquisition
Implementation
Issues:
Capital Cost:
$84,000
MBC_12: BOULDER CREEK & FOLSOM STREET
Improvement
The basin for WQIMP 12 includes
Location:
the area north of Boulder Creek
along Folsom to Arapahoe.
-
WQIMP 12 (Boulder Creek Outfall)
Improvement
I
nstall a proprietary BMP west of Folsom
Description:
north of Boulder Creek
Q(wq) – 6.32 cfs
Technical Data:
Size of manhole: 8-foot Size of
connector pipe: 24-inch
UniversityofColorado
Land Ownership:
Propertyacquisition.
Implementation
Issues:
Capital Cost:
$78,000
92
MBC_03: BOULDER CREEK & 9 STREET
TH
Improvement
The basin for WQIMP 14 includes
th
Location:
the area 200ft wide along 9 from
Boulder Creek to Walnut and east
th
from 9 about 1,100 ft.
-
WQIMP 14 (Boulder Creek Outfall)
Improvement
th
I
nstall a proprietary BMP near 9 and
Description:
Canyon.
Q(wq) – 10.71cfs
Technical Data:
Size of manhole: 10-foot
Size of connector pipe: 30-inch
City of Boulder
Land Ownership:
Noneidentified
Implementation
Issues:
Capital Cost:
$73,000
KG_01: BROADWAY & SKUNK CREEK
Improvement
The basin for WQIMP 15
Location:
encompasses the NIST facility west
of Broadway and south of Bluebell
Ave.
WQIMP 15 (Hot Spot)
- Install a
Improvement
proprietary BMP along Broadway.
Description:
Q(wq) – 5.34 cfs
Technical Data:
Size of manhole: 8-foot
Size of connector pipe: 24-inch
Construction wouldbe within
Land Ownership:
the ROW.
NoneIdentified
Implementation
Issues:
Capital Cost:
$73,000
93
MBC_07: BOULDER CREEK & 13 STREET
TH
Improvement
The basin for WQIMP 16 includes
Location:
the area encompassed by
thth
Arapahoe, 16, Canyon, and 13.
-
WQIMP 16 (Boulder Creek Outfall)
Improvement
th
I
nstall a proprietary BMP west of 13.
Description:
Q(wq) – 7.59 cfs
Technical Data:
Size of manhole: 10-foot
Size of connector pipe: 30-inch
City of Boulder
Land Ownership:
NoneIdentified
Implementation
Issues:
Capital Cost:
$81,000
MBC_05: BOULDER CREEK & 11 TH STREET
Improvement
The basin for WQIMP 18
Location:
encompasses an area about 750 ft
wide from Boulder Creek north to
Pine St.
-
WQIMP 18 (Boulder Creek Outfall)
Improvement
th
I
nstall a proprietary BMP near 11 and
Description:
Canyon.
Q(wq) – 6.40 cfs
Technical Data:
Size of manhole: 8-foot
Size of connector pipe: 24-inch
City of Boulder
Land Ownership:
Noneidentified
Implementation
Issues:
Capital Cost:
$51,000
94
Appendices
Volume 2
Appendix A: Model Input Data Tables, Results Tables and XPSWMM output.
Appendix B: Model Network Mapping
Appendix C: Detailed Cost Estimates
Volume 3
TM 3.2 Design Storm
TM 4.2 Groundwater Mapping and Future Tasks
TM 5.1 Hydraulic Conceptual Alternatives
TM 5.1b Storm Drain and Canal Separation Alternatives
TM 5.1c Goose Creek Alternatives
TM 5.1d Broadway Improvement Alternatives
Volume 3
TM 3.5 Water Quality Model and Construction Results
TM 3.6.1 Water Quality Analysis Results
TM 3.6.3 Water Quality Recommendations
TM 4.3 BMP Toolbox
1
CITY OF BOULDER
WATER RESOURCES ADVISORY BOARD
AGENDA ITEM
MEETING DATE:February 26, 2007
AGENDA TITLE:
Update on the Draft Stormwater Strategic Plan
PREPARING DEPARTMENT:
Robert E. Williams – Director of Public Work for Utilities
Robert J. Harberg – Utilities Planning and Project Management Coordinator
Douglas Sullivan – Engineering Project Manager – Presenter
Jeff Arthur – Engineering Review Manager
Donna Scott – Stormwater Quality Specialist
Brett Hill – Information Resources GIS specialist
FISCAL IMPACT:
None
PURPOSE:
This memorandum presents an update on the draft Stormwater Strategic Plan (SSP).
EXECUTIVE SUMMARY:
The SSP is a comprehensive analysis of the city’s storm sewers and local drainage systems and is
intended to guide future Stormwater and Flood Management Utility (Utility) decisions. The SSP
serves to update the 1984 Stormwater Collection System Master Plan (1984 Plan). The SSP goals
include:
Efficiently manage stormwater runoff
Protect water quality
Minimize localized flooding impacts
Key tasks integral to the SSP included the following:
Data Collection – to update the city’s GIS stormwater collections system database
Model Development – to define hydrologic, hydraulic and water quality parameters
Subbasin Characterization – to identify hydraulic and water quality problem areas
Alternatives Analysis – to develop and evaluate alternatives to produce a recommended plan
Capital Improvements Plan (CIP) – to develop projects cost and an implementation plan
The SSP will produce a recommended Capital Improvements Plan (CIP) project list for storm sewer
conveyance and water quality improvements throughout the city. The SSP has identified 55
potential hydraulic and combined hydraulic/water quality projects which are organized into three
AGENDA ITEM # V Page 1
categories (Tier 1, Tier 2 and Tier 3). Tier 1 projects represent major system deficiencies; Tier 2
projects represent moderate system deficiencies; and Tier 3 projects represent nuisance system
deficiencies. There are four Tier 1 problems, 17 Tier 2 problems and 34 Tier 3 problems identified.
These potential projects range in cost from $15,000,000 to less than $100,000. A map of the
recommended CIP is shown in Figure ES-3.
In the study, the water quality problems were integrated with the hydraulic problems when they were
located in the same vicinity. Additionally, the SSP identified 12 Water Quality Areas of Concern.
These projects are small capital projects. The total cost associated with the hydraulic and water
quality projects is listed below:
Tier 1 = $30,000,000
Tier 2 = $17,000,000
Tier 3 = $14,000,000
WQ = $1,000,000
Total = $62,000,000
A map of the Water Quality Areas of Concern is shown in Figure ES-2.
Background:
The 1984 Plan included a comprehensive analysis of the city’s stormwater collection system. This
analysis included subbasin characterization, hydrologic and hydraulic modeling, and a prioritization
of potential improvements projects. The study included a recommended CIP project list which
prioritized projects in four categories (Priority A through D) at a total cost of $15,000,000. Several
of the recommended projects have been constructed over the last 22 years, many in conjunction with
roadway improvements constructed by the city’s Transportation division. The following is a list of
projects, identified in the 1984 plan, which have been constructed:
Priority A
C-4: Pennsylvania Avenue
DC-5: East Euclid Avenue and Sycamore Avenue
BC-1: Lehigh Street at Bear Canyon Creek
DC-2: Folsom Street From Colorado to Boulder Creek
BC-3: Kohler Drive and Dartmouth Avenue to Broadway and Lashley Lane
(partial)
Priority B
BC-5: Moorhead Drive from Martin Drive to Bear Creek (partial)
WC-1: Broadway/Cherry Avenue and Silver Lake Ditch to Broadway and
Wonderland Creek (partial)
SC-1: Sunnyside Lane from Baseline to Skunk Creek (partial)
Priority C
FM-1: Colorado State Highway No. 7 to Fourmile Creek along Broadway
(partial)
WC-2: North Broadway from Poplar to Wonderland Creek (partial)
GC-1: Foothill Parkway
Priority D
AGENDA ITEM # V Page 2
WC-5: Valmont Road from Sterling Drive to Wonderland Creek (partial)
Some of the recommended projects were eventually found to be unnecessary because various major
drainage way improvements projects (i.e. Goose Creek) constructed in the vicinity of the
recommended localized drainage projects rendered the projects obsolete.
Many projects were never constructed, primarily because the Utility has historically allocated the
majority of its CIP funds to major drainage way improvements and associated property
acquisition. Based on an analysis of the CIP budget between 1990 and 2002, 80 percent of the
utility funding was allocated to major drainage way corridors. Below is a breakdown of the
expenditure allocation for the years between 1990 and 2002. Only 10 percent of the total CIP
funds were allocated to storm sewer work:
Major drainage ways = $14,000,000 (37%)
Property acquisition = $16,400,000 (43%)
Storm sewers = $3,800,000 (10%)
Greenways = $1,300,000 (6%)
Miscellaneous = $2,300,000 (4%)
Total = $37,800,000 (100%)
The reason for allocated funds in this manner has been because of threats to life safety and property
along the major drainage way corridors as well as the opportunity to collaborate under the stated
goals of the city’s Greenways Program which include improvements for flood mitigation, alternative
transportation, recreation, wildlife habitat and water quality.
Fiscal Impacts:
There are no fiscal impacts at this time. However, the Utilities division will need to decide how
to allocate future CIP funding associated with the projects identified in the SSP.
Cash funding for projects in the current Utility CIP is $2-2.5 million per year (see Attachment G:
2007-2012 Stormwater and Flood Management CIP.) The funding rate for stormwater
management projects is only $300,000 over the next few years and escalates to $800,000 in
th
2012. The number one Tier 1 project is Upper Goose Creek, located in the vicinity of 9 and
Balsam streets. Improvements associated with this project are estimated at $15,000,000.
Therefore, the current funding allocated to stormwater management is inadequate to complete
even the first phase of the number one Tier 1 project in the near future.
There are still many identified threats to life safety and property as well as opportunities to
collaborate as part of the Greenways Program such that continued emphasis on major drainage
way corridors is likely. These corridors include South Boulder Creek, Wonderland Creek,
Fourmile Canyon Creek, and Elmer’s Two-mile Creek as listed in the current Utility CIP.
Staff will evaluate funding options as part of the 2008 budget process and report on these options
to the Water Resources Advisory Board (WRAB) in the near future.
Analysis:
AGENDA ITEM # V Page 3
The SSP involved numerous tasks in order to develop a recommended CIP projects list. The study’s
major tasks included the following:
Data Collection
Analysis and Problem Identification
Model Development
System Analysis and Results
System Improvement Recommendations
Capital Improvements Plan
The following is a brief summary of the work associated with the project tasks:
Data Collection
In reviewing the city’s GIS storm sewer database, HDR (the design engineer) discovered that there
were significant system data gaps (missing storm sewer manhole data). Utilities staff added a
supplemental surveying task to the project’s Scope of Work to collect data for several hundred
missing manholes. This information has since been added to the city’s Storm Sewer GIS Dataset.
Analysis and Problem Identification
This task analyzed various criteria specific to the city of Boulder to help construct the hydrologic
model. These criteria included topography, land use, imperviousness, design storms, and the
stormwater collection system infrastructure. The effect land use has on water quality is generally
linked to the amount of impervious area for a particular land use category. The more impervious the
area, the faster the water will be routed to the stormwater collection system. Impervious surfaces
will also increase the total amount of runoff because infiltration does not occur through impervious
surfaces. An area with higher percentage of impervious surfaces will produce higher peak flows and
large volumes over a shorter period of time than will a similar sized area with a lower percentage of
impervious surfaces. A map of the city’s impervious percentages is shown in Figure 3-4.
Model Development
The hydrologic model analyzes stormwater as it is conveyed throughout the system, from rainfall to
overland flow in the western reaches on the basin throughout the collection system to the major
drainage ways. All pipe sections 18-inches and larger were modeled.
The city’s GIS database currently includes updated impervious coverage data for the entire city.
This information was developed using aerial photography and creating a polygon mapping the
impervious areas of the city. These areas include street, sidewalks, parking lots, building, etc. In
previous studies, the impervious coverage was estimated based on Urban Drainage and Flood
Control District (UDFCD) figures which may not have been representative of the actual conditions.
The actual impervious coverage figures used in this study were found to be, in some cases,
significantly different that the figures previously used. A summary of these figures is shown in
Table 3.2-2.
System Analysis and Results
The model was used evaluate three different design storms including: the 2-yr, 5-yr, and the water
quality storm. The water quality storm is a smaller storm event which will still produce runoff and
AGENDA ITEM # V Page 4
can be expected to occur several times per year. Due to the large number of problem locations (55)
identified within the city, a ranking was performed to group the conveyance problems according to
priority. Six criterions were utilized to assist in the problem prioritization. These criteria included:
Problem Extent
Flooded Volume
Structure Impact
Length of High Q ratio
Data confidence
Water Quality Area of Concern
These criteria are defined in Table 4.3-1.
System Improvement Recommendations
Conceptual alternatives were developed for the hydraulic problem areas in Tier 1 and Tier 2 and fact
sheets were developed summarizing the alternatives. Conceptual alternatives include pipe
replacement, parallel storm systems, flow diversions and detention.
The water quality analysis identified 12 locations representing Water Quality areas of Concern.
These Water Quality Ares of Concern represented the highest pollutant load contributors to the
storm water system. The pollutant loading totals were based on the contribution of five pollutants
including total suspended solids (TSS), phosphorus, copper, lead, and zinc. In addition to the Water
Quality Areas of Concern, the study included an analysis of 18 collector system outfalls to Boulder
Creek. HDR analyzed 15 proprietary BMP’s (best management practices) at the Boulder Creek
outfalls.
Capital Improvements Plan
The goal for the SSP was to manage stormwater, by minimizing impacts from localized flooding,
and to improve water quality. The Capital Improvements Plan (CIP) summarizes the recommended
improvements. The improvements are organized by two categories. The first category represents
Hydraulic and combined Hydraulic/Water Quality problems. The second category represents Water
Quality problems alone. The first category includes 55 problems divided into three Tiers and is
presented in Table 6.2-1. The second category includes 11 Water Quality problems listed by their
TSS contribution. TSS concentration is considered a good indicator of stream health and BMP
performance because it acts as a surrogate pollutant, whereby other nutrients and metals bond to the
solids. A Table of TSS concentration is presented in table 6.2-2.
Other Impacts:
None
Other Board and Commission Feedback:
None
Public Feedback:
None
Staff Recommendation:
Utilities staff will be returning to WRAB at the April 16, 2007 meeting with a final report and will
be asking for a Board recommendation to accept the Stormwater Strategic Plan.
AGENDA ITEM # V Page 5
Attachments:
A.Stormwater Strategic Plan Draft Report
B.Executive Summary Figures – Three maps
C.Section 2 Figures – Six maps
D.Section 3 Figures – Ten maps
E.Section 4 Figures – Six maps
F.Section 6 Figures – One map
G.2007-2012 Stormwater and Flood Management Utility CIP
AGENDA ITEM # V Page 6
ABCDEFGHIJK
1
CITY OF BOULDER20-Nov-06
2
2007-2012 CAPITAL IMPROVEMENT PROGRAM - Draft -
3
STORMWATER AND FLOOD MANAGEMENT UTILITY FUND
4
5
6
20052006200720082009201020112012
7
PROJECT NAMEACTUALREVISEDRECOMMENDEDPROJECTEDPROJECTEDPROJECTEDPROJECTEDPROJECTEDTOTAL
8
9
Major Drainageways
10
Elmer's Two-mile Creek 431332 $147,023$1,352,977$500,000$500,000$500,000$0$0$0$3,000,000
11
Goose Creek 431710 $4,417$0$0$0$0$0$0$0$4,417
12
South Boulder Creek431202 $154,213$103,760$100,000$150,000$300,000$0$0$0$807,973
13
South Boulder Creek - Bond Proceeds$0$0$0$0$0$3,000,000$0$0$3,000,000
14
Bond Issuance Costs$0$0$0$0$0$120,800$0$0$120,800
15
Four Mile Canyon Creek431729 $517,581$820,964$250,000$250,000$500,000$500,000$500,000$500,000$3,838,545
16
Bear Cree431010 $300,000$0$0$0$0$0$0$0$300,000
k
17
Gregory Creek431702 $0$0$0$0$0$0$0$0$0
18
Boulder Creek431015 $0$0$100,000$0$0$0$0$0$100,000
19
Wonderland Creek421003 $0$100,000$250,000$250,000$250,000$500,000$500,000$250,000$2,100,000
20
Wonderland Creek - Diagonal Highway Under431009 $667,885$100,615$0$0$0$0$0$0$768,500
21
Subtotal - Major Drainageway Improvements$1,791,119$2,478,316$1,200,000$1,150,000$1,550,000$4,120,800$1,000,000$750,000$14,040,235
22
23
Miscellaneous
24
Preflood Acquisition431622 $5,292$764,708$500,000$500,000$500,000$500,000$500,000$500,000$3,770,000
25
Greenways Program431630 $162,073$518,166$150,000$150,000$150,000$150,000$150,000$150,000$1,580,239
26
Wolff Fountain Grant431631 $3,150$0$0$0$0$0$0$0$3,150
27
Yards Master Plan Implementation431039 $362$250,000$0$110,000$0$0$0$0$360,362
28
Utility Billing Computer System Replacement431453 $88,579$281,931$0$0$0$0$0$0$370,510
29
Subtotal - Miscellaneous Drainage Improvements$259,456$1,814,805$650,000$760,000$650,000$650,000$650,000$650,000$6,084,261
30
31
Stormwater Management
32
Mapleton Hill Drainage431709 $0$0$0$0$0$50,000$250,000$250,000$550,000
33
Upper Goose Creek Drainage431459 $0$0$0$0$0$50,000$250,000$250,000$550,000
34
Stormwater Quality Demonstration431775 $0$50,000$50,000$50,000$50,000$50,000$50,000$50,000$350,000
35
Broadway Storm Sewer431013 $0$0$0$0$0$0$0$0$0
36
BVRC Redevelopment431704 $1,016$1,296,396$0$0$0$0$0$0$1,297,412
37
Transportation Coordination431780 $250,000$250,000$250,000$250,000$250,000$250,000$250,000$250,000$2,000,000
38
Subtotal - Localized Drainage Improvements$251,016$1,596,396$300,000$300,000$300,000$400,000$800,000$800,000$4,747,412
39
40
TOTAL CAPITAL USES OF FUND$2,301,591$5,889,517$2,150,000$2,210,000$2,500,000$5,170,800$2,450,000$2,200,000$24,871,908
S
41