HomeMy WebLinkAbout4 - Information Item: Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Plan and Critical Facilities Code Update
CITYOFBOULDER
WATER RESOURCES ADVISORY BOARD
INFORMATION ITEM
MEMO DATE: June 2, 2009
INFORMATION ITEM: Fourmile Canyon Creek and Wonderland Creek Flood
Mitigation Plan and Critical Facilities Code Update
FROM: Ned Williams, Director of Public Works for Utilities
Bob Harberg, Utilities Planning and Project Management Coordinator
Christie Coleman, Engineering Project Manager
EXECUTIVE SUMMARY:
This information item is intended to present the information regarding the April 28, 2009 Flood
Management and Mitigation Program Study Session. This study session focused on the
proposed Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Plan and potential
regulation of critical facilities in flood hazard areas. Attachment B is the Study Session
Summary from the meeting and was approved by city council on June 2, 2009.
BACKGROUND:
The purpose of the April 28, 2009 study session was to present information and discuss issues
raised during the Nov. 10, 2008 public hearing with City Council regarding the Fourmile Canyon
Creek and Wonderland Creek Flood Mitigation Plan. At that public hearing, concerns were
raised regarding:
1. the intent and interpretation of current city flood policies,
2. vulnerable populations to flooding, especially Crestview Elementary School,
3. the cost of the proposed property acquisition and flood mitigation plan, and
4. the priority of the proposed work compared to other flood hazard areas in Boulder
The attached study session agenda packet provides the information presented to City Council
regarding these issues. Specific issues and analysis related to the city's property acquisition and
flood mitigation program were presented to provide additional information for council in
consideration of whether to approve, at a future city council meeting, the Fourmile Canyon
Creek and Wonderland Creek flood mitigation plan. Information on the city's proposed critical
facilities code update was also presented. The power point presentation from the study session is
provided, as well as the study session summary which documents the feedback received from the
City Council.
PAGE 1
NEXT STEPS:
As part of this study session, staff presented information regarding the issues raised by council at
the Nov. 10, 2008 public hearing and will proceed with the following:
1. A WRAB agenda item and public hearing for the proposed Fourmile Canyon Creek and
Wonderland Creek Flood Mitigation Plan in August. Planning Board consideration
would follow in October, and City Council consideration in November.
2. Agenda items and public hearing concerning the critical facilities ordinance scheduled
with the WRAB in October, Planning Board in November, and City Council by February
of 2010.
ATTACHMENTS:
Attachment A: Flood Management and Mitigation Program and Fourmile Canyon Creek and
Wonderland Creek Flood Mitigation Plan CCSS Agenda Packet
Attachment A-A: Map of Major Drainageways in Boulder
Attachment A-B: Map of Floodplains in Boulder
Attachment A-C: Fourmile Canyon Creek and Wonderland Creek, Council Agenda
item dated Nov. 10, 2008
Attachment A-D: Map of Residential Structures Located in the High Hazard Zone
Attachment A-E: Critical Facility Information
Attachment A-F: Map of Critical Facilities Located in the High Hazard Zone
Attachment B: April 28, 2009 Study Session Summary on Flood Management and Mitigation
Program and Fourmile Canyon Creek and Wonderland Creek Flood Mitigation
Plan.
Attachment C: City Council Study Session Power Point Presentation
PAGE 2
Attachment A
City of Boulder, CO
April 28, 2009
6:00 PM
City Council Study Session
Flood Management and Mitigation Program
and
Fourmile Canyon Creek and Wonderland Creek
Flood Mitigation Plan
TABLE OF CONTENTS
Page
Introduction 3
Questions for City Council 3
Flood Management Work Program 4
1. Overview 4
II. Flood Mitigation Planning 4
III. Property Acquisition and Flood Mitigation Work Program 7
A. Current Policies and Guidance 8
a. Preservation of Floodplains 8
b. Flood Management 8
c. Non-Structural Approach 9
d. Protection of High Hazard Areas 12
e. Larger Flooding Events 15
f. Flood Hazard Land Use Analysis 15
B. Critical Facilities and Vulnerable Populations 16
C. Property Damage and Other Cost Issues 19
D. Collaboration with Greenways Program Objectives 22
IV. Next Steps 24
Attachments:
A - Map of Major Drainageways in Boulder
B - Map of Floodplains in Boulder
C - Fourmile Canyon Creek and Wonderland Creek, Council Agenda Item dated Nov. 10, 2008
D - Map of Residential Structures Located in the High Hazard Zone
E - Critical Facility Information
F - Map of Critical Facilities Located in the High Hazard/Conveyance Zones
Introduction
The purpose of this study session is to present information and discuss issues raised during the
Nov. 10, 2008 public hearing regarding the Fourmile Canyon Creek and Wonderland Creek
Flood Mitigation Plan. At that public hearing, concerns were raised regarding:
1. the intent and interpretation of current city flood policies,
2. vulnerable populations to flooding, especially Crestview Elementary School,
3. the cost of the proposed property acquisition and flood mitigation plan, and
4. the priority of the proposed work compared to other flood hazard areas in Boulder
This document provides City Council with information regarding these issues in preparation for
the April 28, 2009 study session discussion. Specific issues and analysis related to the city's
property acquisition and flood mitigation program are presented to provide additional
information for council in considering whether to approve, at a future city council meeting, the
Fourmile Canyon Creek and Wonderland Creek flood mitigation plan.
Questions for City Council
Staff is suggesting the following questions to guide City Council's discussion at the study
session:
1. Does council agree with staff's approach to flood mitigation planning and the role it plays
in Capital Improvement Program (CIP) project prioritization?
2. Does council have questions about current flood policies how they are being applied in
the proposed Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Plan?
3. What feedback does council have regarding the development and analysis of preliminary,
draft regulations pertaining to critical facilities and vulnerable populations located within
the 100-year and 500-year floodplains?
4. What feedback does council have regarding the proposed Fourmile Canyon Creek and
Wonderland Creek flood mitigation plan regarding costs, benefits and priorities?
5. Does council have questions regarding the proposed next steps for either the Fourmile
Canyon Creek and Wonderland Creek flood mitigation plan or the draft regulations
pertaining to critical facilities and vulnerable populations?
Flood Management Work Program
1. Overview
Boulder is located at the base of the foothills where there is high potential for flash flood events
that allow little time for warning. Including Boulder Creek, there are 15 major drainageways
that pass through the city of Boulder - see Attachment A, with the 100-year floodplains from
these drainageways occupying 15 percent of the land area of the city of Boulder - see
Attachment B. A major flood event could result in substantial loss of life and property damage.
Because the threat to life and property damage is so great, the need to monitor, regulate and
mitigate the impacts of flooding is critical.
The flood management program was most recently defined in the Comprehensive Flood and
Stormwater Master Plan, which was accepted by City Council in 2004. Five guiding principles
and work program elements were defined in the master plan as follows:
1. Preserve Floodplains (floodplain mapping)
2. Be Prepared for Floods (flood education and insurance)
3. Help People Protect Themselves from Flood Hazards (flood preparedness)
4. Prevent Adverse Impacts and Unwise Uses in the Floodplain (floodplain regulations)
5. Seek to Accommodate Floods, not Control Them (property acquisition and flood
mitigation)
This study session packet format includes specific sections of a description and analysis of the
topic (as shown in the Table of Contents), directly followed by a brief description of how the
proposed Fourmile Canyon and Wonderland Creek mitigation plan responds to the topic, along
with a re-statement of the respective "Questions for City Council."
II. Flood Mitigation Planning
Each year in the United States, natural disasters take the lives of hundreds of people and injure
thousands more. Floods are America's #1 natural disaster and can happen anytime, anywhere. In
fact, 90 percent of all natural disasters in the U.S. involve flooding. Nationwide, billions of
dollars are spent annually to help communities, organizations, businesses and individuals recover
from these disasters. This money only partially reflects the true cost of disasters because
additional expenses to insurance companies and non-governmental organizations are not
reimbursed by tax dollars. Many natural disasters are predictable, and much of the damage
caused by these events can be alleviated or even eliminated through proper planning.
The city of Boulder first adopted floodplain regulations in 1969, in response to Front Range
flooding events that demonstrated the flood potential and need for protective measures within the
city. The city's Stormwater and Flood Management Utility was established in 1974. The current
floodplain regulations were adopted in 1989 and established three specific flood zones used to
manage and regulate development and uses within the floodplain. These zones are the 100-year
floodplain, conveyance zone and high hazard zone and are described as follows:
• The 100-year Floodplain is defined as all land areas subject to inundation by flood
waters that have a one percent (1%) chance of occurring.
• The Conveyance Zone represents a corridor within the floodplain that should be
preserved to pass the flood water, anticipating that debris will create blockages during a
large storm event.
• The High Harzard Zone is an area of the floodplain where the combination of water
depth and water velocity are expected to be too great for some people (e.g., young
children and elderly) to maintain their balance should they be caught in a flash flood or
attempt to cross a flood area.
Proactive mitigation planning helps reduce the cost of disaster response and recovery to the city
and its property owners by protecting critical community facilities, reducing liability exposure,
and minimizing overall community impacts and disruption. Boulder has been affected by natural
hazards in the past and is committed to reducing future disaster impacts and maintaining
eligibility for federal funding.
The city's Comprehensive Flood and Stormwater Master Plan outlines the overarching policy
issues for the Stormwater and Flood Management Utility, while specific flood mitigation plans
are developed for each drainageway.
Flood mitigation plans, such as the one for Fourmile Canyon and Wonderland creeks, provide a
long-range plan that can be used to prioritize capital improvement projects in the context of the
overall flood Capital Improvement Program (CIP) and are similar to subcommunity and area
plans, which inform development standards and zoning in certain areas of the city. Mitigation
plans are updated periodically to address new information related to flood mapping and
modeling, as well as physical modifications in the drainageway, and they provide information
that allows staff, private property owners and the development community to plan and coordinate
activities in recognition of the flood hazards and potential mitigation strategies.
In most cases, the drainageway mitigation studies and plans are developed in cooperation with
the Urban Drainage and Flood Control District (UDFCD). In doing so, the city is eligible to
receive funding from the UDFCD to assist with the design, construction and maintenance of
improvements to its major drainageways. The studies and plans are typically developed in two
stages:
• Phase A - Alternatives Analysis, and
• Phase B - Prel. Design and Community and Environmental Assessment Process (CEAP).
Once the Phase B work has been accepted, projects are prioritized in the CIP to implement the
plan within the budget constraints of the Stormwater and Flood Management Utility Fund.
Priority is based primarily on the following factors:
1. Life safety (high hazard) mitigation
2. Flood emergency response capability
3. Critical facility (vulnerable population) hazard mitigation
4. Property damage mitigation
5. Collaboration with other Greenways Program Objectives
Last November, City Council considered accepting the proposed flood mitigation plan for
Fourmile Canyon and Wonderland creeks. Acceptance of the plan does not obligate the city to
fund any portion of the plan within any specific timeline since specific funding requests would
be made through the annual budget process. One of the primary motivations for updating this
particular plan was the significant changes in the city's understanding of flood hazards for the
Fourmile Canyon and Wonderland creeks, based on the 2007 flood mapping changes. These
changes rendered previous flood mitigation plans obsolete. Another motivation for updating the
mitigation plan was the rapid development and redevelopment changes occurring within the
North Boulder areas. The proposed flood mitigation plan would help guide future development
and redevelopment activities in this area. The mitigation plan also allows the city to identify
properties that might need to be acquired to reasonably mitigate life safety hazards associated
with flooding.
The flood mitigation studies and plans also allow city staff to look for opportunities to leverage
limited city funding with other funding sources, such as through the city's Greenways Program.
For example, if the city's Transportation Division decides that a bridge or culvert needs to be
replaced, then the flood mitigation plan provides information regarding the size of the bridge or
culvert that is needed to pass the designated flood event. The upgrades to the bridge then are
made in cooperation with the Transportation Division on a timeline that allows for the most
efficient use of resources.
Funds are available through the Stormwater and Flood Management Utility Fund and, if the
associated mitigation projects are deemed to be of high priority, the city may decide to actively
pursue components of a flood mitigation plan. This is done through the annual budget process.
Proposed projects and expenditures are reviewed by the Water Resources Advisory Board
(WRAB), Planning Board and City Council. Because projects typically have a significant cost
that exceeds annual revenue, it is likely that flood mitigation plans will require decades to fully
accomplish. There is the potential that a major flood will occur before all of the mitigation
improvements are implemented, which is why prioritization of projects within a plan and among
all the city's mitigation plans is so important.
Boulder has its share of success stories.
Even when a flood mitigation plan is not
fully implemented, whenever any mitigation rr3 f'^'
project is completed, the community
benefits from the results. Previously 4
constructed improvements have already
provided significant benefits to Boulder. For
example, a significant storm event on Aug.
15, 2007 along Bear Canyon Creek would'
have likely flooded a day care center located
immediately adjacent to the creek if flood'
mitigation work had not been previously
accomplished.
Bear Canyon Creek - August 15, 2007
The recent federal economic stimulus funding provides another incentive for the city to develop
plans and designs so that projects may qualify for these funds by becoming "shovel ready" in the
near future. Although none of the projects associated with the proposed Fourmile Canyon and
Wonderland creeks plan are considered shovel ready for this round of stimulus funding, there
may be additional stimulus funding or other federal funding programs through which projects
could be qualified.
City Council adopted the multi-hazard mitigation plan (MHMP) in August 2008 in order to make
the city and its residents less vulnerable to future natural hazard events. The plan was prepared
pursuant to the requirements of the Disaster Mitigation Act of 2000 in order for the city to be
eligible for the Federal Emergency Management Agency's (FEMA) Pre-Disaster Mitigation and
Hazard Mitigation grant programs. It is anticipated that projects identified in the Fourmile
Canyon and Wonderland creeks plan would be eligible for these pre-disaster mitigation grants.
Fourmile Canyon and Wonderland Creeks
The Fourmile Canyon and Wonderland creeks flood mitigation plan, including the Phase A
report developed by Love & Associates, analyzed various alternatives designed to mitigate flood
hazards along these creeks. The work was jointly sponsored by the Urban Drainage and Flood
Control District and the city. This plan was presented to City Council on Nov. 10, 2008 during a
public hearing and a copy of the agenda item and selected attachments is presented as
Attachment C.
Staff considered the cost and priority of the proposed work compared to other flood hazards in
the city and based on five prioritization factors mentioned above on page 5. The public process
included two open houses and several public hearings with the Water Resources Advisory Board
(WRAB) and Planning Board. Based on the feedback received during this process, several flood
mitigation alternatives were evaluated and refined. Staff considered this feedback in formulating
the recommendations made to City Council in November 2008.
Question #1: Does council agree with staff's approach to flood mitigation
planning and the role it plays in CIP project prioritization?
III. Property Acquisition and Flood Mitigation Work Program
During the Nov. 10, 2008 public hearing regarding the Fourmile Canyon Creek and Wonderland
Creek flood mitigation plan, concerns were raised regarding:
1. the intent and interpretation of the non-structural approach policy,
2. vulnerable populations to flooding, especially Crestview Elementary School,
3. the cost of the proposed property acquisition and flood mitigation plan, and
4. the priority of the proposed work compared to other flood hazard areas in Boulder
Specific policies and analysis related to the city's property acquisition and flood mitigation
program are presented as follows:
A. Current Policies and Guidance
Flood related policies were last reviewed as part of the 2005 major update to the Boulder Valley
Comprehensive Plan (BVCP). The current plan lists several policies related to flood management
as follows:
a. BVCP Policy 4.20 - Preservation of Floodplains
"Undeveloped floodplains will be preserved or restored where possible through public
land acquisition of high hazard properties, private land dedication and multiple
program coordination. Comprehensive planning and management of floodplain lands
will promote the preservation of natural and beneficial functions of floodplains
whenever possible. "
This policy is being implemented in part through the city's Greenways Program that
encompasses and integrates the protection and restoration of habitat, enhancement of
water quality, flood mitigation and drainage, alternative transportation routes for
pedestrians and bicyclists, recreation and protection of cultural resources. The city's
floodplain and wetland regulations that work to preserve the natural and beneficial
function of floodplains and associated riparian areas also serve to implement this policy
as well as on-going review of annexation and development proposals. However, when
public land acquisition is not economically feasible or possible, current city floodplain
regulations do not prevent redevelopment of these properties but require suitable flood
protection measures and allow structural mitigation of high hazard and conveyance zone
impacts.
Fourmile Canyon and Wonderland Creeks
The recent update of the floodplain mapping for Fourmile Canyon and Wonderland
Creek as well as the guidance provided in the proposed flood mitigation plan promotes
the effective implementation of this policy. For example, previously unknown flood
hazard areas are now being addressed through the city's floodplain regulations that limit
development in flood prone areas. The dedication of private land along Fourmile Canyon
or Wonderland Creek to preserve the natural and beneficial function of the floodplain is a
normal condition for county parcels whose property owners wish to annex to the city.
b. BVCP Policy 4.21 - Flood Management
"The city will protect the public and property from the devastating impacts of flooding
in a timely and cost-effective manner while balancing community interests with public
safety needs. The city will manage the potential for floods by implementing the
following guiding principles:
a) Preserve floodplains
b) Be prepared for floods
c) Help people protect themselves from flood hazards
d) Prevent unwise uses and adverse impacts in the floodplain
e) Seek to accommodate floods, not control them"
This policy was adopted in consideration of the Comprehensive Flood and Stormwater
Master Plan guiding principles and work program elements that form the basis for the
city's flood management and mitigation program.
Fourmile Canyon and Wonderland Creeks
These policies have been considered as part of the proposed flood mitigation plan. Staff
balanced community interests and modified the final recommendations for flood
mitigation in several areas. For example, along Fourmile Canyon - Reach 4 initial
recommendations called for containment of the 100-year flood event but because of
aesthetic and cost concerns the recommendation were modified to contain the high hazard
zone only.
c. BVCP Policy 4.22 - Non-Structural Approach
The city will seek to preserve the natural and beneficial functions of floodplains by
emphasizing and balancing the use of non-structural measures with structural
mitigation. Where drainageway improvements are proposed, a non-structural approach
should be applied wherever possible to preserve the natural values of local waterways
while balancing private property interests and associated cost to the city.
This policy was modified during the 2005 major revision to the BVCP to revise the
previous policy statement. Between 1978 and 1995, the BVCP reflected a policy that
required a "non-containment approach to flood management on Boulder Creek and a
generally non-structural approach to flood control on all major water courses and
drainageways." This approach and policy originated in 1978 when the work of the city's
Boulder Creek Subcommittee evaluated the U.S. Army Corps of Engineers' Committee
on Environmental Planning report. The city's subcommittee submitted an 11-point plan
concentrating on non-structural approaches to flood management. In 2005, the policy
was revised to reflect a more consistent manner to floodplain management.
City staff is now implementing this policy for Boulder Creek and other major
drainageways by interpreting the meaning of the non-structural approach in the following
manner:
Non-structural: A non-structural approach is flexible in allowing modifications to the
creeks and adjacent landscape that provide containment of flood waters. It emphasizes
that such modifications have a natural appearance, avoiding the use of hardened
structures, and provide water quality and wildlife habitat enhancements.
Because of the large volume of water associated with a Boulder Creek flood (100-year
flood flow equals nearly 12,000 cubic feet per second at the mouth of the canyon), full or
partial containment of the 100-year flood event would require either 1) a massive
conveyance structure incompatible with Boulder's existing character or 2) significant
land area requiring the removal of existing structures that currently support Boulder's
economy. Since either of these approaches would be very costly, the current focus is on
the containment of the high hazard flood flows through selected property acquisition and
excavation outside of the main Boulder Creek channel.
Excavation outside of the main channel of the creek is called "overbank" excavation. The
most notable project along Boulder Creek occurred in 1993 and was accomplished in
collaboration with the Boulder Valley School District. Nine properties were purchased in
the vicinity of Boulder High School and 13d' Street. The structures were removed and the
overbank area on the north side of the creek, south of Arapahoe, was excavated and
graded to provide for additional flood conveyance and the construction of park and
athletic fields, as shown in the photo below.
IF
Boulder Creek Overbank Excavation Mitigation West of Boulder High School
Other private structures along Boulder Creek that have been acquired and removed since
1989 include:
• City Tree House (Parks and Recreation) office structure on the south side of
Boulder Creek, east of the Library
• Residence at 1234-18th St., along the north side of Boulder Creek
• 18-unit apartment complex at 299 Arapahoe Ave., just east of the Eben G. Fine
Park, on the south side of Boulder Creek
• Residences at 1228 and 1230-17th St., along the north side of Boulder Creek
Other flood mitigation improvements that have been implemented along Boulder Creek
since 1989 include:
• Lower Arapahoe Avenue Bridge structure replaced just east of Broadway
• 17th Street Bridge replaced with a 100-year structure
• Conveyance/detention storage improvements through CU's Research Park
• Railroad underpass structure at Cottonwood Grove
• Upper Arapahoe Bridge structure replaced above Eben Fine Park
• 55th Street Bridge replaced with 100-year structure
• Replacement of the Broadway Bridge with 100-year structure
• Elimination of 29d' St. shopping area from 100-year floodplain based on fill
Because the volume of water associated with floods on other major drainageways is not
as significant as Boulder Creek (Fourmile Canyon Creek 100-year flood flow equals
about 3,000 cubic feet per second at the mouth of the canyon), full or partial containment
of 100-year flood flows is feasible using a combination of property acquisition,
excavation and limited structural solutions. The acquisition of property allows for fewer
structural approaches to be implemented.
The city has implemented many flood containment and mitigation projects along major
drainageways, most notably Goose Creek and Bear Canyon Creek. These projects have
used a combination of non-structural approaches that emphasize a natural appearance and
some structural solutions where the expense of purchasing existing structures was
deemed too great.
Bear Creek and Goose Creek are examples of this combined approach, as shown in the
following photos
-Ioi P,
Lfl x'71 w'^
~tzx 1t
b - - ~y
Bear Canyon Creek flood mitigation improvements in Martin Park
'iivr(mea_F
Goose Creek flood mitigation west of 28tL St.
Fourmile Canyon and Wonderland Creeks
It is staff's opinion that the proposed flood mitigation plan for Fourmile Canyon and
Wonderland Creeks complies with the non-structural approach policy. In most cases,
there would be limited excavation in or near existing low-flow channels. Exceptions
would be in areas where 100-year flood containment is deemed desirable because of the
extensive property damage that would otherwise occur during flood events.
In all situations, the use of concrete would be minimized and there would be extensive
revegetation effort for any improvement project. There are also opportunities to improve
habitat and water quality through the creation of wetland areas that do not exist today.
d. BVCP Policy 4.23 - Protection of High Hazard Areas
"The city will prevent redevelopment of significantly flood-damaged properties in high
hazard areas. The city will prepare a plan for property acquisition of flooddamaged
and undeveloped land in high hazard flood areas. Undeveloped high hazard flood
areas will be retained in their natural state whenever possible. Compatible uses of
riparian corridors, such as natural ecosystems, wildlife habitat and wetlands will be
encouraged wherever appropriate. Trails or other open recreational facilities may be
feasible in certain areas."
Life safety is a significant concern along Boulder's major drainageways. Many structures
have been built in the designated high hazard flood zone, the area that poses the greatest
risk to life safety. Life safety (high hazard zone) mitigation is a primary issue in
prioritizing flood mitigation capital improvement projects.
Because of the large number of structures in the high hazard zone, a rating system was
developed in 1997 by staff and a consultant based on potential threats to the safety of
building occupants as well as the potential for damage to structures during the 100-year
flood. Criteria (listed from most important to least important) included the following:
1. Overall safety of individuals within flood water near the structure
2. Ability of occupants to climb above flood water within the structure
3. Structural stability during flooding
4. Impact of rapid velocity flows
5. Possibility that occupants living in below-grade units may be trapped
6. Ability of occupants to leave or enter the building during a flood
7. Use of the structure
8. Site specific hydraulic conditions
Because evacuation during a flood event will be more difficult for people living in
residential structures (for instance during the middle of the night when people are
sleeping), it is appropriate to place a higher priority on the mitigation of life safety
hazards for these structures than on commercial or industrial structures.
Based on an analysis performed in 1997, there were a total of 279 structures located
completely or partially in the high hazard zone. Of the 279 structures in the high hazard
zone, 41 structures received the highest rating.
Since 1997, several projects and acquisitions have either physically removed structures
from the high hazard flood zone or changed the flood waters so that the high hazard zone
boundaries changed to no longer impact certain structures. Recent improvements along
Bear Canyon Creek have eliminated all structures from the high hazard flood zone.
Improvements along Goose Creek, through the Mapleton Mobile Home Park, eliminated
all structures (mobile homes) that received the highest rating based on potential threat.
These same improvements also removed the two structures associated with Elmer's
Twomile Creek. The city acquired and removed all residential structures that received the
highest rating along Boulder Creek. The number of structures along Fourmile Canyon
Creek has been reduced because of the 2007 flood mapping study update, but two
structures were added along Wonderland Creek for this same reason. A structure along
Twomile Canyon Creek has been added and it is unknown why this structure was not
included in the analysis performed in 1997.
As of 2009, the total number of structures located in or partially in the high hazard zone
has been reduced from 279 (in 1979) to 178 structures. Of the 178 total structures, 132 of
them are residential structures that are completely or partially in the high hazard zone.
Based on this information, 17 residential structures are associated with Fourmile Canyon
and Wonderland creeks. Please refer to Attachment D for a map of the general location
of residential structures in the high hazard zone.
Total number of residential structures in high hazard zone (2009)
Maior Drainageway
Boulder Creek/Boulder Slough 2
Fourmile Canyon 7
Wonderland 10
Twomile Canyon 21
Goose 37
Elmer's Two-mile 0
Sunshine Canyon 4
Gregory Canyon 29
South Boulder/Dry Creek No. 2 3
Skunk 13
Bluebell/King's Gulch 5
Bear Canyon 1
Viele Channel 0
Total 132
The following information presents the most vulnerable structures based on potential
threat. Gregory Canyon Creek has the highest number of most vulnerable structures.
Most vulnerable residential structures in high hazard zone
Ma.ior Drainneway 1997 2009
Boulder Creek/Boulder Slough 5 0
Fourmile Canyon 5 2
Wonderland 0 2
Twomile Canyon 0 1
Goose 22 0
Elmer's Two-mile 2 0
Sunshine Canyon 0 0
Gregory Canyon 7 7
South Boulder /Dry Creek No. 2 0 0
Skunk 0 0
Bluebell/King's Gulch 0 0
Bear Canyon 0 0
Viele Channel 0 0
Total 41 12
Note: the increase in most vulnerable residential structures for Wonderland Creek in 2009
is due to recognition of the spill flow from Fourmile Canyon subsequent to 1997.
The anticipated capability of emergency management personnel to warn residents prior to
a flash flood event is a significant consideration in determining the appropriate extent and
priority of flood mitigation capital improvement project work.
Boulder and South Boulder creeks are by far the largest drainageways that flow through
the city of Boulder. For these drainageways, the Urban Drainage and Flood Control
District (UDFCD) early flood detection system called ALERT is available to provide
real-time information that would aid in providing advance warning to residents of flash
floods. This system is comprised of numerous rainfall and stream level gauges that
provide data to assess flash flood potential in the foothills and canyons west of Boulder
and is expected to provide up to 20-40 minutes of lead time prior to a flash flood event on
these two creeks. (Longer warning times may be available under other types of flood
events that develop more slowly due to extended periods of lower intensity rainfall.)
These gauges are not installed on the other drainageways as this type of system would not
provide adequate notice of flash flooding along these drainageways, which are tributary
to Boulder and South Boulder creeks. These tributary drainageways are relatively small
and can develop runoff that produces flash flood affects in a very short period of time. It
is unlikely that an early warning system could be designed for these drainageways that
would provide adequate notice (20 minutes or more) to aid warning and evacuation
efforts. In these cases, emergency response is likely to be confined to rescue efforts and
sheltering in place methods
Another consideration is the ability of emergency response personnel to access and egress
the flooded areas. The city has evaluated the affect of flooding on major roadways in
Boulder and numerous roadways would be inundated during a major flood event.
For these reasons, the focus of high hazard (life safety) mitigation efforts on vulnerable
residential structures along tributary drainageways that do not have an early warning
system capability should be a higher priority.
Fourmile Canyon and Wonderland Creeks
From a high hazard (life safety) perspective, four of the city's 12 most vulnerable
residential structures are located along Fourmile Canyon and Wonderland creeks. The
proposed property acquisition and flood mitigation plan would mitigate the high hazard
vulnerability of all these structures.
The proposed plan would also improve ability of emergency response personnel to access
and egress the flooded areas along Fourmile Canyon and Wonderland creeks including
those associated with Crestview Elementary School. This would be accomplished by
containing the high hazard portion of the flood flows within a defined area and improving
the conveyance of water underneath intersecting roadways including Upland Avenue and
191h Street.
e. BVCP Policy 4.24 - Larger Flooding Events
"Flood management has historically focused on and primarily addresses the impacts of
a 100 year flood event. The city recognizes that larger flooding events will occur
resulting in greater risks and flood damage that will affect even improvements
constructed with standard flood protection measures. The city will seek to better
understand the impact of larger flood events and consider necessary floodplain
management strategies."
The city currently maps the floodplain area associated with the 500-year flood event. The
affect of this larger flood event is currently being assessed and considered for critical
facilities as discussed below.
f. Flood Hazard Land Use Analysis (possible future policy)
Another flood management policy issue relates to the potential conflict between the
BVCP community design and flood management policies and regulations. The primary
concern is that a significant number of parcels with redevelopment potential have more
than 50% of their land area in some portion of the floodplain. Several commercial and
industrial parcels in particular have more than 50% of their land area in the high hazard
zone or conveyance zones. The CFS Master Plan recommended a Flood Hazard Land
Use Analysis which will assess the future development potential in the floodplain,
explore various tools to reduce this risk and assess the long term ramifications of
mitigation and regulatory changes.
Current city floodplain regulations do not prevent redevelopment of these properties but
require suitable flood protection measures and allow structural mitigation of high hazard
and conveyance zone impacts. Although redevelopment of these properties would secure
flood protection under the 100-year flood event, these properties would still be subject to
flood damage from larger flood events. Redevelopment of some of these properties could
also result in further structural mitigation of high hazard and conveyance zone impacts or
reduce the likelihood of redevelopment in key commercial areas such as the North
Boulder Village Center. The Flood Hazard Land Use Analysis will explore a range of
strategies to reduce the flood risk in flood prone areas and clarify and strengthen the
city's flood management policies.
The analysis will inform recommendations to changes in flood plain policies and
regulations. This study effort will likely begin in 2010 or 2011.
Question #2: Does council have questions about current flood policies
and how they are tieing applied in the Fourmile Canyon Creek and
Wonderland Creek Flood Mitigation Plan?
B. Critical Facilities and Vulnerable Populations
Prevention and mitigation of flood damages to critical facilities and life safety issues associated
with at-risk populations are important issues in prioritizing flood mitigation capital improvement
projects. In an effort to reduce the damages to infrastructure and strengthen life safety responses,
city staff is developing and analyzing preliminary, draft regulations pertaining to critical
facilities and vulnerable populations located in the 100-year and 500-year floodplains. These
preliminary, draft regulations include the following definition of critical facilities:
"Critical facility, " for floodplain purposes, means a facility, including without limitation,
a structure, infrastructure, property, equipment or service, that if flooded may result in
severe consequences to public health and safety or interrupt essential services and
operations for the community at any time before, during and after a flood. A critical
facility is classified by the following categories: (1) Essential Services, (2) Hazardous
Materials, (3) At-risk Populations, and (4) Vital to Restoring Normal Services.
In addition to attempting to define critical facilities, staff is also developing management
strategies for these facilities that will strengthen life safety emergency preparedness and reduce,
over time, the type and number of facilities exposed to flood risk. Staff anticipates completing
the analysis of the preliminary, draft regulations, along with identifying the impacts, and
initiating a public review and comment process within the next six months. Please see
Attachment E for more information on the development of the critical facility regulation.
Staff conducted research on the number and locations of facilities that would be classified as
critical. The following table presents the number of critical facilities along each drainageway for
the high hazard zone, conveyance zone, and 100- year floodplain.
Critical Facilities Located in the High Hazard and Conveyance Zones
High Hazard Zone Facilities
Name Address Prima Category Second Subcategory
Cottage School 1301 North Street At-risk Population Day Care
Dream Makers Preschool 1345 28th Street At-risk Population Day Care
Crestview Christian Reformed 3545 Madison Ave At-risk Population Church
*New Britain Building 1101 Arapahoe Ave Essential Services Warning Systems
*Boulder Fire Station # 3 30th & Arapahoe Essential Services Warning Systems
*Boulder Fire Station # 3 30th & Arapahoe Essential Services Fire
*New Britain Building 1101 Arapahoe Ave Vital Normal Services Administration and Management
Atrium Building 1300 Canyon Blvd Vital Normal Services Administration and Management
Boulder Building Maintenance 1720 13th St Vital Normal Services Maintenance and Equipment
Park Central Building 1739 Broadway Vital Normal Services Permitting and Inspection
Conveyance Zone Facilities
Name Address Primary Category Second Subcategory
Elm Tree 1330 Alpine Ave. At-risk Population Day Care
Wynwood at Ridge Point 3375 34th St. At-risk Population Senior Housing
Millennium Harvest House 1345 28th St At-risk Population Hotel
Alandi Ashram 1705 14th St At-risk Population Church
St. Andrew Church 3700 Baseline At-risk Population Church
Cottage School Day Camp 805 30th Street At-risk Population Day Care
CU Married Student Housing Marine St At-risk Population Student Housing
Boulder Medical Center 2750 Broadway Essential Services Clinic
Crossroads AMOCO 3005 Arapahoe Ave Hazardous Materials Service Station
Grizzly Gasoline and Store 3200 Arapahoe Ave Hazardous Materials Service Station
Conoco 601 S. Broadway Hazardous Materials Service Station
Boulder Municipal Building 1777 Broadway Vital Normal Services Administration and Management
Downtown Public Library 900 Canyon Blvd Vital Normal Services Library
*In the table above, some structures may include more than one type of critical facility category.
For example, the New Britain Building includes both a flood warning system and city
administration and management services. The general location of critical facilities located in the
high hazard zone and conveyance zones is shown on the map of Attachment F.
Critical Facilities Located in Flood Hazard Areas
Major High Hazard and 100 Year Floodplain Drainageway
Drainageway Conveyance Zone Structures Structures Total
Boulder Creek 13 35 48
Fourmile Canyon Creek 0 2 2
Twomile Canyon Creek 0 4 4
Goose Creek 3 4 7
Elmer's Twomile Creek 0 2 2
Gregory Canyon Creek 0 3 3
Skunk Creek 2 4 6
Bear Canyon Creek 2 2 4
South Boulder Creek 0 4 4
Wonderland Creek 1 4 5
Sunshine Canyon Creek 0 0 0
Bluebell Canyon Creek 0 0 0
King's Gulch 0 0 0
Dry Creek 0 0 0
Totals 21 64 85
These high hazard and conveyance zone critical facilities are further identified as follows:
Fourmile Canyon and Wonderland Creeks
There are currently seven critical facilities located in the Wonderland and Fourmile Canyon
Creek 100-year floodplains. Five of these facilities house vulnerable populations. The proposed
flood mitigation plan would remove three critical facilities from the 100-year floodplain and one
facility from the conveyance zone.
Critical Facilities - Fourmile Canyon and
Wonderland Creeks Relationship to Flood Condition
Existin Conditions Phase A Mitigation Measures
Name Address Drains ewa 100 Con HHZ 100 Con HHZ
Crestview Elements 1897 Sumac Ave Fourmile Within outside outside no change no change no chan e
Shining Mountain Waldorf School 999 Violet Ave Fourmile within outside outside no change no change no change
Boulder Waldorf Kindergarten 4072 N. 19th Wonderland within outside outside no change no change no change
The Atrium: Brookdale Senior-Living 3350 30th St. Wonderland within outside outside removed no change no change
W nwood at Ridge Point 3375 34th St. Wonderland within within outside removed removed no chan e
Diagonal AMOCO Gas 2990 Diagonal H Wonderland within outside outside removed no change no change
N. Broadway Silco Gas 4501 N Broadway Fourmile within outside outside no chan a no change no change
Key to above table: "100" means within the 100-year floodplain
"Con" means within the conveyance zone
"HHZ" means within the high hazard zone
With respect to these facilities the proposed critical facilities regulation management strategies
will regulate facilities that provide care for 12 or more children/students/residents. Upon change
of use, new use or expansion, these facilities will develop an emergency management plan that
will at a minimum include either an evacuation plan or a shelter in place plan. For the two
facilities that store hazardous chemicals, upon change of use, new use, or substantial
modification or improvement, all hazardous material must be stored such that they are located
above the 500-year flood elevation or are floodproofed.
Staff was asked to investigate the specific emergency plan for Crestview Elementary School.
The proposed flood mitigation plan for this school would not eliminate it from the 100-year
floodplain. City staff have contacted Boulder Valley School District (BVSD) staff and discussed
the best way to deal with a flood emergency for schools in Boulder. Evacuation may be the best
approach in cases where there is adequate advanced warning of certain types of flood events that
develop slowly due to extended periods of low-intensity rainfall. However, advanced warning
may be too short or not possible for flash flood events. The existing Crestview Elementary
School building structure would provide substantial protection during a flood event, so shelter in
place should be considered versus the risk of exposing evacuees directly to flood waters. During
a major flood event, it is likely that the first floor of the building would be partially flooded.
Evacuation to the roof is a possibility but problematic during inclement weather conditions. It
has been recommended to the BVSD staff that they consider flood proofing the existing structure
to minimize the entry of water. As indicated previously, the proposed plan would improve the
ability of emergency response personnel to access and egress the flooded areas along Fourmile
Canyon and Wonderland creeks including those associated with Crestview Elementary School.
This information has been discussed with BVSD/Central Administration staff and Crestview
Elementary School administration staff, but a full and complete resolution and consensus
regarding the best action has not been reached. City staff, Boulder County Emergency
Management staff and BVSD staff will continue the conversations so that ultimately, the BVSD
can implement an emergency management and response plan for the students, faculty and
parents.
In addition, city stormwater/flood education staff has been in contact with Crestview faculty and
are sharing flood preparedness education information with teachers and students. The Stn graders
from Crestview will be attending the city's annual Children's Water Festival in May, which will
contain a flood education component. Outreach materials are being shared with other schools in
Boulder as well.
Question #3: What feedback does council have regarding the development and
analysis ofpreliminary, draft regulations pertaining to critical facilities and
vulnerahle populations located within the 100 year and 500 year floodplains?
C. Property Damage and Other Cost Issues
In the event of a significant flood, property damage will be considerable. In addition, a major
flood on Boulder Creek may have a major impact on Boulder's economy since much of
Boulder's commercial and industrial property is located in the Boulder Creek floodplain. For
these reasons, mitigation of potential property damage due to floods is also considered in
prioritizing flood mitigation capital improvement projects.
The following information is presented concerning the number of structures and assessed value
for each major drainageway. Based on this information, approximately 11 percent of the
structures representing eight percent of the assessed value in the 100-year floodplain are
associated with Fourmile Canyon and Wonderland creeks.
Number and assessed value of structures located in the 100-year floodplain
Number of
Drainageway Structures Assessed Value
Boulder Creek/Boulder Slough 935 $ 590,684,000
Fourmile Canyon 144 $ 38,362,200
Wonderland 361 $ 109,125,900
Two-mile Canyon 208 $ 52,874,400
Goose 210 $ 101,439,300
Elmer's Twomile 150 $ 44,415,100
Sunshine Canyon 87 $ 30,387,500
Gregory Canyon 127 $ 47,789,200
South Boulder/Dry Creek No. 2 1,063 $ 429,561,100
Skunk 200 $ 65,842,900
Bluebell/Kings Gulch 43 $ 13,003,400
Bear Canyon 93 $ 34,744,400
Viele 0 $ 0
Totals 3,621 $ 1,558,229,400
Flood insurance provides a mechanism for private property owners to mitigate some of the
potential property damage due to flooding. However, the maximum insurable value under
FEMA's National Flood Insurance Program (NFIP) is $250,000.
Economic impacts from floods to property and business owners may also be mitigated to some
degree by federal disaster assistance programs. These programs provide relief funding to
communities who suffer a major disaster so that the community can rebuild its economy and tax
base.
In determining whether to acquire property and/or use other flood mitigation alternatives, a
traditional cost-benefit analysis is used to compare the current value of future flood losses with
the cost of project improvements. For example, along certain segments of Fourmile Canyon and
Wonderland creeks, the estimated benefit-cost ratio of implemented pre-flood improvements is
greater than five. In these cases, staff is recommending that the city initiate improvements that
would alleviate damages caused by a 100-year flood. An alternative approach would be for the
private property owners to continue to bear the cost of maintaining flood insurance through the
NFIP.
There is also the potential of property damage to city infrastructure such as roadways and utility
pipes.
Fourmile Canyon and Wonderland Creeks
From a property damage perspective, 11 percent of the structures representing eight percent of
the assessed value in the 100-year floodplain are associated with Fourmile Canyon and
Wonderland creeks. The proposed flood mitigation plan would significantly mitigate the
potential for property damage. The current value of mitigating future property damage due to
flooding has been estimated to be greater than $90 million.
The overall cost of the proposed property acquisition and flood mitigation plan is significant, but
would be implemented over a period of several decades depending on the ability of the city to
fund the improvements. Acceptance of the study does not obligate the city to fund the proposed
flood mitigation improvements. Specific funding requests are prioritized and submitted through
the annual budget process.
The following chart summarizes the city's Stormwater and Flood Management Utility capital
expenditures from 1990 through 2008 in units of 2008 dollars. Over $24 million has been spent
on pre-flood property acquisition and nearly $38 million on major drainageway (flood
mitigation) improvements. The largest expenditures were associated with Goose Creek ($19
million) and Boulder Creek ($15 million).
Summary of Capital Expenditures (in 2008 Dollars)
S22.000.0--Z
$15.1100,.7-- -
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Localized drainage improvements include small storm sewers (up to 36-inch diameter) and street
inlets to convey small quantities of stormwater.
The estimated costs associated with the proposed flood mitigation plan recommended by staff
are as follows:
Proposed Present Worth Costs in 2008 dollars
City Capital Costs
Property acquisition $4 to 6 million
Channel improvement $10 to 12 million
Roadway crossing $8 to 10 million
City On-going Operation and Maintenance $5 to 6 million
Private Property Owner Costs
Floodproofing $15 to 20 million
In many cases, the cost of the proposed improvements can be shared with other agencies
including the UDFCD and the city's Transportation Division. The plan proposes significant
capital improvement expenditures associated with combination flood conveyance and pedestrian
underpasses at major roadways. Typically, these costs have been split between the city's Utilities
and Transportation divisions. In some cases, these projects have been partially funded by the
Federal Transportation Improvement Program.
The level of capital expenditure needed to accomplish the flood mitigation along Fourmile
Canyon and Wonderland creeks is deemed reasonable, considering the length of time over which
the work would be accomplished. The suggested improvements are consistent with the level of
previous flood mitigation expenditures by the city's Stormwater and Flood Management Utility.
D. Collaboration with Greenways Program Objectives
The initial Tributary Greenways Master Plan that was developed in 1989 described the purpose
of the program as providing a unique opportunity for creating a comprehensive greenways
system for the community that could be creatively developed to function as storm drainage and
flood channels, efficient bicycle and pedestrian transportation systems, open space and wildlife
corridors and attractive recreation areas. The Greenways Master Plan was updated in December
2001. At that time, the purpose of the program was re-evaluated and a purpose statement was
developed, which is:
"To extend the stewardship of the city of Boulder to the important
riparian areas along the tributaries of Boulder Creek to integrate the
following six objectives: protect and restore habitat, enhance water
quality, facilitate storm drainage and mitigate floods, provide alternative
transportation routes for pedestrians and bicyclists, provide recreational
opportunities and protect cultural resources. "
The Greenways Program provides an opportunity to collaborate on various city interests, as well
as leverage funding sources. The Greenways Program has adopted an opportunistic approach to
achieve multiple objectives throughout the system. Frequently, specific efforts within a
greenway corridor can be completed in conjunction with a transportation, flood hazard
mitigation, park or private development project. Major outside funding from such sources as the
UDFCD and the Colorado Department of Transportation (CDOT) has allowed the Greenways
system to expand and complete projects at an accelerated rate, with a much lower direct cost to
the city (nearly 50 percent less). Cooperation with the University of Colorado and the Boulder
Valley School District has resulted in extension of greenways facilities through properties owned
and managed by those entities. Through the site review process, private developers may provide
conservation easements to the city along the program tributaries, as well as fund and construct
trail links, park connections and underpass installations.
The Elmer's Twomile Greenways project provides a current example of an opportunity to meet
multiple objectives through leveraged funding. The Elmer's Twomile project includes:
• A transportation component that provides a missing link between the Goose Creek Path
and Glenwood Drive by constructing a grade-separated path with an underpass at
Valmont Road, and
• Flood mitigation improvements that address flooding that occur south of Glenwood Drive
during a 100-year storm event. Several properties are currently in the 100-year
conveyance zone and portions of these properties are also in the high hazard zone.
The Elmer's Twomile project will result in approximately 50 properties no longer being in the
100-year floodplain. Commercial properties along 28th Street will be removed from the
floodplain allowing greater redevelopment potential and providing economic vitality to the city.
For example, the Rayback property was purchased and is being redeveloped to take into
consideration the improvements made possible by the Elmer's Twomile project.
In addition to providing flood and transportation improvements, the project also includes an
enhancement to water quality. As part of this project, the city purchased a one-acre easement
that will allow for an open channel and a constructed wetland in a narrow urbanized corridor.
The total cost for the Elmer's Twomile Greenways project from Goose Creek to Glenwood Drive
including design, property acquisition and construction is estimated to be $9 million. The
Elmer's Twomile project is being funded through the city's Stormwater and Flood Management
Utility ($3.47 million) and Greenways CIP ($1 million), with additional funding contributions
from outside sources including the Federal Transportation Improvement Program ($3.25 million)
and the Urban Drainage and Flood Control District ($1.28 million). By collaboratively
constructing projects like the Elmer's Twomile Greenways project, the city can leverage outside
funding and share in costs that would be required if the projects were bid out separately.
Fourmile Canyon and Wonderland Creeks
The proposed flood mitigation plan for Fourmile Canyon and Wonderland Creeks provides many
opportunities to collaborate with other Greenways Program projects including transportation,
recreation, environmental and water quality enhancements. The Greenways Master Plan ranked
the opportunity for improvements for each of the Greenways' objectives by stream reach. For
the reaches of Fourmile Canyon Creek west of 28th Street, the need for a path connection ranked
high, primarily as it serves as a "safe route to school" for the Crestview Elementary School
students. Habitat and water quality improvements received a medium ranking throughout
Fourmile Canyon Creek based on opportunities to improve the quality of the habitat in these
areas. Along Wonderland Creek, between Foothills and 28th Street, the transportation objective
received a medium ranking. Habitat and water quality opportunities received a medium to high
ranking for the most part along Wonderland Creek. These improvements were considered and
incorporated as part of the proposed flood mitigation plan.
Question #4: What feedback does council have regarding the proposed
Fourmile Canyon Creek and Wonderland Creek flood mitigation plan
regarding costs, benefits and priorities?
IV. Next Steps
As part of this study session packet, staff has presented additional information regarding the
issues raised by council in the previous Nov. 10, 2008 public hearing. As next steps, staff will:
1. Prepare an agenda item to accept the Study Session summary,
2. Prepare an agenda item to consider acceptance of the proposed Fourmile Canyon Creek
and Wonderland Creek flood mitigation plan, and
3. Continue the development and analysis of the preliminary, draft regulations pertaining to
critical facilities and vulnerable populations located within the 100-year and 500-year
floodplains, along with identifying the impacts, and initiating a public review and
comment process within the next six months.
4. Develop a Flood Hazard Land Use Analysis to explore a range of strategies for reducing
the flood risk in flood prone areas. The analysis will inform recommendations to
changes in flood plain policies and regulations and will likely begin in 2010 or 2011.
Question #5: Does council have questions regarding the proposed next steps for
either the Fourmile Canyon Creek and Wonderland Creek flood mitigation plan or
the draft regulations pertaining to critical facilities and vulnerable populations?
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Attachment B
CITY OF BOULDER
CITY COUNCIL AGENDA ITEM
MEETING DATE: November 10, 2008
AGENDA TITLE: Consideration of a Motion accepting the Fourmile Canyon and
Wonderland Creeks Flood Mitigation Plan as documented in the Phase A Report and as
Modified by Staff
PRESENTERS
Jane S. Brautigam, City Manager
Stephanie Grainger, Deputy City Manager/Operations
Maureen Rait, Executive Director for Public Works
Ned Williams, Director of Public Works for Utilities
Bob Harberg, Utilities Planning and Project Management Coordinator
EXECUTIVE SUMMARY:
The purpose of this agenda item is for City Council's review and consideration of a flood
mitigation plan for Fourmile Canyon and Wonderland creeks in north Boulder.
The Fourmile Canyon Creek and Wonderland Creek Major Drainageway Planning - Phase A
Report - Alternatives Analysis was developed by Love & Associates, dated June 2007. The
Phase A Report focuses on the development, evaluation, and recommendations of flood
mitigation alternatives along both creeks. The work was jointly sponsored by the Urban Drainage
and Flood Control District (UDFCD) and the city. The executive summary of the Phase A Report
is presented as Attachment A.
City staff has coordinated this flood mitigation planning effort with the objectives of the city's
Greenways Program. A public process that included two open houses and several public
hearings with the Water Resources Advisory Board (WRAB) and Planning Board was
conducted. Based on the feedback received during this process, several flood mitigation
alternatives were evaluated and refined. A chronology of the flood mitigation planning, including
the public process, is presented as Attachment B. A map of the study area is included as
Attachment C.
The complete Fourmile Canyon Creek and Wonderland Creek Phase A Report is available at the
City Council Office and the main branch of the Boulder Public Library and on the city's Web
site at www.boulderwater.net under "Projects & Programs."
AGENDA ITEM 9 PAGE 1
STAFF RECOMMENDATION:
Sugp_ested Motion Lanpua2e:
Staff requests council consideration of this matter and action in the form of the
following motion:
Motion to accept the Fourmile Canyon Creek and Wonderland Creek Flood
Mitigation Plan as documented in the Phase A Report (Attachment A) and as
modified by the staff recommendations documented in this agenda item.
Staff recommendations for each of the various sections of the creeks can be found in the
"Analysis" section of this memo and a summary table of the staff recommendations is found at
the end of the section.
COMMUNITY SUSTAINABILITY ASSESSMENTS AND IMPACTS:
Economic: A land use analysis associated with the recommended mitigation plan shows that the
proposed mitigation work allows for redevelopment consistent with the North Boulder
Subcommunity Plan. Thus, mitigation work should help enhance the economic viability of the
north Boulder community.
Environmental: Flood mitigation work is intended to create as little environmental disturbance
as possible. In particular, through discussions with residents during the public process, the
Githens Acres riparian corridor was re-studied in order to minimize environmental impacts from
flood mitigation work. Additionally, as seen with redevelopments such as the Violet Crossing on
Fourmile Canyon Creek, flood mitigation work can result in the expansion of wetlands and
provide water quality enhancements.
Social: In addition to environmental upgrades, mitigation work also includes Greenways
Program objectives such as improved trails and educational opportunities in the riparian corridor
that provide benefit to the entire community.
OTHER IMPACTS:
Fiscal: The flood mitigation plan recommended by staff is estimated to have a total cost of
$49,253,000 of which $33,926,000 would be a public expense and $15,327,000 would be borne
by private property owners. The city's project funding would be supplemented by the Urban
Drainage and Flood Control District (UDFCD), who routinely participates in flood mitigation
efforts. Property owners would not be required to bear their expense unless they proposed new
development or redevelopment on their property, in which case, they would be required to meet
current flood-proofing regulations. Rather, property owners would be encouraged to protect their
property from future flood damages through voluntary efforts by flood proofing their individual
structures.
The plan will likely take several decades to implement by the city. Significant total benefits of
over $90,000,000 are estimated based on a reduction in total property damage due to future
flooding. The following Table summarizes the cost and benefit information based on a present
worth cost analysis (2007 dollars) using a 50-year period and a discount rate of 3 percent. The
cost analysis does not consider insurance premium, life safety or greenways benefits.
AGENDA ITEM 9 PAGE 2
Wonderland Creek
Staff Recommended B/C
Reach Alternate Ratio Benefits Costs
Total Total Public Private
1 Maintain Existing 0.00 $0 $618,000 $618,000 $0
2 Flood roofm 0.60 $326,000 $539,000 $332,000 $207,000
HHZ Containment/
3 Floodproofmg 0.47 $4,803,000 $10,237,000 $7,307,000 $2,930,000
4 100-Year Channel 5.34 $37,970,500 $7,110,000 $7,110,000 $0
5 100-Year Channel 4.75 $19,279,300 $4,058,000 $4,058,000 $0
HHZ Containment/
6 Floodproofmg 0.37 $1,601,200 $4,365,000 $2,509,000 $1,856,000
7 Maintain Existing 0.00 $0 $807,000 $807,000 $0
8 Maintain Existing 0.00 $0 $289,000 $289,000 $0
Total 2.28 $63,980,000 $28,023,000 $23,030,000 $4,993,000
Fourmile Canyon
Creek
Staff Recommended B/C
Reach Alternate Ratio Benefits Costs
Total Total Public Private
HHZ Containment/
la Flood roofm 0.50 $785,600 $1,584,000 $1,025,000 $559,000
lb Maintain Existing 0.00 $0 $1,188,000 $1,188,000 $0
2a Maintain Existing 0.00 $0 $442,000 $442,000 $0
2b 100-Year Channel 2.15 $3,402,400 $1,580,000 $1,580,000 $0
HHZ Containment/
3 Flood roofm 0.65 $585,400 $900,000 $741,000 $159,000
HHZ Containment/
4 Flood roofm 1.22 $11,160,000 $9,113,000 $4,468,000 $4,645,000
HHZ Containment/
5 Flood roofm 4.02 $3,209,000 $798,000 $394,000 $404,000
HHZ Containment/
6a Floodproofmg 1.12 $5,274,000 $4,689,000 $290,000 $4,399,000
HHZ Containment/
6b Flood roofm 3.62 $2,761,000 $763,000 $595,000 $168,000
6c Maintain Existing 0.00 $0 $173,000 $173,000 $0
Total 1.28 $27,177,400 $21,230,000 $10,896,000 $10,334,000
Combined Total 1.85 $91,157,400 $49,253,000 $33,926,000 $15,327,000
AGENDA ITEM 9 PAGE 3
Funding has been budgeted for the proposed flood mitigation work in the 2009-2014 Utilities
Division Capital Improvement Program (CIP) budget. The proposed work is comprised of
multiple individual projects that allow funding to be spread out over the next 20-30 years. The
city will prioritize those projects that have the most significant benefit from either a life safety or
property damage mitigation perspective and are within the incorporated city limits. Projects that
provide multiple benefits and allow the city to leverage funding with private developers or other
agencies such as the Denver Regional Council of Governments (DRCOG) Transportation
Improvement Project (TIP) funding will also be prioritized. One of these projects is envisioned
to be a new culvert and pedestrian underpass at the Burlington Northern and Santa Fe Railroad
and Boulder White Rocks Ditch just upstream of Foothills Parkway on Wonderland Creek. The
city applied for TIP funding for this project and it is possible the city will receive matching
funds. All projects will be closely coordinated with the city's Greenways Program and
Transportation Division.
As a result of some of the recommended mitigation alternatives, there are a significant number of
flood insurance policy holders who in the future would no longer be required to hold flood
insurance with their mortgages. It is estimated that a combined property owner premium savings
of approximately $225,000 per year would be realized if the outlined mitigation
recommendations were implemented. In addition, a primary goal has been to remove structures
from the high hazard zone (HHZ) to eliminate life-safety risk. The implementation of the
improvements would remove all structures along both creeks from the HHZ with the exception
of a few storage sheds and garages. Below is a table listing the total annual premium savings for
each reach.
AGENDA ITEM 9 PAGE 4
Wonderland Creek
# Structures Total Annual Savings after
# Structures Removed Premium under Implementation
in 100-year from 100-year Existing of Selected
Reach Floodplain Floodplain Conditions Alternate
1 0 0 $0 $0
2 16 0 $20,800 $0
3 82 82 $77,800 $77,800
4 5 5 $8,700 $8,700
5 70 70 $67,300 $67,300
6 19 3 $17,600 $735
7 3 0 $2,600 $0
8 1 0 $200 $0
Total 196 160 $195,000 $154,535
Fourmile Canyon Creek
# Structures
Removed Total Annual Savings after
# Structures from 100- Premium under Implementation
in 100-year year Existing of Selected
Reach Floodplain Floodplain Conditions Alternate
Lower 18 0 $8,100 $0
1 0 0 $0 $0
2 7 7 $3,700 $3,700
3 4 0 $4,200 $0
4 29 29 $40,400 $40,400
5 59 0 $66,600 $0
6 22 14 $34,500 $26,315
Total 139 50 $157,500 $70,415
AGENDA ITEM 9 PAGE 5
Staff time:
Staff is intending to work with consultants to development future phases of this mitigation
project. This will be built into yearly work programs.
BOARD AND COMMISSION FEEDBACK:
Greenways Staff and Greenways Advisory Committee (GAC):
Project staff met with Greenways staff and the Greenways Advisory Committee (GAC) on
Sept. 19, 2007. The proposed flood mitigation plan followed the recommendations of the
Greenways Master Plan with regard to all of the objectives of the Greenways Program including
the use and location of multi-use paths, as well as habitat restoration recommendations. The
GAC concluded that there should be continued focus on minimizing the HHZ, including perhaps
considering property damage as a less important factor for Reach 4 of Fourmile Canyon Creek in
exchange for fewer impacts on the drainage area. Top priorities identified by the GAC were:
high hazard mitigation and undersized culvert replacement and flood protection. Greenways staff
were directed to work to establish environmental criteria for flood project construction.
Water Resource Advisory Board (WRAB):
Discussions with the WRAB occurred on Oct. 15, 2007, Dec. 17, 2007 and Jan. 28, 2008.
WRAB recommended that City Council accept the flood mitigation plan based on the following
motion:
Motion: Recommend approval of the Phase A plan as modified by staff with the following
recommendations and guiding principles as this project continues to future phases and more
detailed concept review (Approved vote 4-0, 1 absent).
The complete WRAB recommendations and guiding principles, along with staff responses, is
presented as Attachment D.
Planning Board:
The proposed flood mitigation plan was presented to the Planning Board on Feb. 21 and March
20, 2008. The purpose was to provide Planning Board with information regarding the land use
implications of the proposed flood mitigation plan. Planning Board recommended that City
Council accept the flood mitigation plan based on the following motion:
Motion: The Planning Board recommended (5-1, A. Sopher opposed, R. Soso absent) that City
Council accept the proposed flood mitigation plan outlined in the March 20, 2008 staff
memorandum including the following additional recommendations:
1. That City Council approve the staff's recommendation with prioritization, to the extent
feasible from an engineering perspective, favoring city improvements over county improvements;
2. That public education on life safety issues as to flooding, particularly as to critical facilities,
be given a high priority;
3. And that discussion with the affected property owners in the Village Center take place with the
feasibility of moving forward with flood mitigation.
AGENDA ITEM 9 PAGE 6
The dissenting vote from Sopher was based on his request that the report contain additional
physical flood protection for access and egress to Crestview Elementary and Waldorf Elementary
school. Staff has met with the Waldorf School officials and is working with Crestview to
educate them on flood awareness and response. Sopher felt that education was not enough to
ease flood concerns. Staff indicated the plan does call out replacement of underpasses at Violet,
Upland, 19th at Fourmile and 19th at Wonderland. Through the increase in conveyance of flood
flows, these underpasses would allow passage on roadways over the creeks in a 100-year flood.
PUBLIC FEEDBACK:
The public process for this study has included a presentation to the GAC, WRAB and Planning
Board. At each event, the public had an opportunity to give input and their comments have been
noted and responded to as follows:
During the December 2007 WRAB meeting, a question was raised whether detention storage
was feasible for upstream Fourmile Canyon Creek in order to mitigate the spill to Wonderland
Creek. The consultant was asked to consider this option and provide an analysis. The consultant
determined that a 30-acre footprint multi-staged reservoir would be required in addition to
significant channel work. The cost was estimated at $55,000,000. Because of the significant
environmental impacts of this approach and the excessive project costs, staff does not
recommend this option.
Also during the December 2007 WRAB meeting, a suggestion by several members of the public
was made to use the area of undeveloped land north of Violet to direct flood flows east to the
U.S. 36 corridor and then over to Boulder Creek. Such an alignment could remove water from
the main stem of Fourmile Canyon Creek, including the spill flow under the 100-year flood
event, and redirect this flow to Boulder Creek through a man-made conveyance structure. The
estimated cost of this alternative is approximately $53 million. This project would present
substantial property acquisition issues as well as other impacts along the corridor, many of which
would impact city Open Space land.
A question that has come up numerous times is why the Fourmile Canyon Creek flood flows are
not contained in the channel, thereby lessening the impact to Wonderland Creek. An underlying
issue with regard to the conceptual analysis is how to mitigate the historic spill flows that move
from Fourmile Canyon Creek to Wonderland Creek in events exceeding the 50-year recurrence
interval. The spill from Fourmile is due to the topography and has historically occurred.
Changing historical flow patterns has enormous implications and is traditionally avoided. If
containment was initiated, a great deal of mitigation work would have to be completed on
Fourmile since the existing facilities and flood protection is sized for the historical lower flow
rates. All of these costly projects would have to be completed before any diversion could occur.
Additionally, there are a number of legal issues associated with changing flood patterns of this
magnitude and UDFCD has indicated that they would not support this concept. The UDFCD
legal opinion is available as Attachment E.
AGENDA ITEM 9 PAGE 7
Even with the great deal of flood mitigation improvements suggested with this study, there will
still be areas of shallow flooding, most notably in the spill area between Fourmile Canyon and
Wonderland creeks. Citizens living within these areas have raised concerns with regard to
property damage and the cost of flood insurance. However, these areas do not pose the same life
safety and property damage threats that are posed by the flood hazard zones along the main
channels of Fourmile Canyon and Wonderland creeks. It is proposed that the city's resources be
directed towards flood mitigation work that addresses the most significant life safety and
property damage issues. A limited amount of funding is available to address other repetitive loss
drainage issues, and citizens will be encouraged to come forward with drainage concerns in order
for the city to prioritize and attempt to mitigate these problems.
Finally, a comment was received regarding completing the plan but questioning why
implementation of mitigation projects has to occur before a flood event. Staff feels that the risk
to life safety and property compels the city to attempt to pursue mitigation projects prior to an
actual flood event.
ANALYSIS:
The study area includes the Fourmile Canyon Creek floodplain from the mouth of the canyon to
its confluence with Boulder Creek, and the Wonderland Creek floodplain from downstream of
Wonderland Lake to its confluence with Goose Creek. Additionally, the Fourmile Canyon Creek
spill floodplain, located between Fourmile Canyon Creek and Wonderland Creek, upstream of
Broadway approximately to 19th Street, is also included.
Background:
Major drainageway planning documents were previously developed for Fourmile Canyon Creek
and Wonderland Creek in the mid 1980s. Due to development that occurred in the floodplain
and better floodplain information, the city of Boulder commissioned a re-study of the Fourmile
Canyon Creek floodplain and the Wonderland Creek flood hazards. The study is based on
detailed 2003 aerial mapping and new hydrologic analysis techniques. Love & Associates was
retained by the city to prepare a Letter of Map Revision (LOMR) submittal to FEMA for these
two streams. The LOMR was developed during 2004-2005 and approved by various city boards
and the City Council in early 2006. The LOMR was submitted to FEMA in March 2006 and
approved in November 2006. The new flood hazard areas became official following the end of
the public appeal period in late March 2007.
The initial flood mitigation planning effort began in June 1999. Both a Phase A and Phase B
study were completed for Fourmile Canyon Creek. However, it became apparent that the
topography has historically caused a wide shallow spill from Fourmile Canyon Creek to
Wonderland Creek. It was decided that historic flows should not be altered and UDFCD
advocated there be no changes to existing drainage patterns. Following the review and input
from an Independent Review Panel (IRP) comprised of floodplain experts in 2000, it was
recommended that due to the interaction of the creeks, a combined Phase A alternate analysis
report should be undertaken for both Fourmile Canyon and Wonderland creeks. Subsequent to
the completion of the LOMR, the combined alternate analysis began in fall 2006. The final Phase
A report was published in June 2007.
AGENDA ITEM 9 PAGE 8
The flood analysis of Fourmile Canyon and Wonderland creeks indicated significant differences
from the original regulatory studies, resulting in additional properties being located within the
two floodplains. Of particular importance, the re-study identified reaches of Fourmile Canyon
Creek west of 19th Street, where, once the channel capacity is exceeded, flood flows overtop the
south bank of the creek and flow in a southeasterly direction towards Wonderland Creek. These
"spill flows" result in a reduction of flows in Fourmile Canyon Creek downstream of 19th Street
but also result in an increase in the flows in Wonderland Creek. During the 100-year flood
event, Fourmile Canyon Creek near the mouth of the canyon would experience approximately
3,300 cubic feet per second (cfs) of water. Of this amount, approximately 1,600 cfs will overtop
the south bank spill and flow toward Wonderland Creek. The remaining 1,700 cfs will remain in
the Fourmile Canyon Creek channel. Likewise, the 100-year discharge in Wonderland Creek
significantly increases downstream of the spill inflow. Some of the spill returns to Fourmile
Canyon Creek near 19th Street, but the majority remains in the Wonderland Creek floodplain.
Early in the study, a broad range of alternates were identified. These alternates were screened
following an analysis of each stream and detailed discussions held during progress meetings on a
reach-by-reach basis for each stream. A wide array of options were looked at as potentials for
mitigation of the flooding, ranging from a status quo alternate to construction of a 100-year
storm event containment alternate for each stream, thereby confining the spill from Fourmile
Canyon Creek.
Legal Opinion:
There has been some discussion whether the spill from Fourmile Canyon Creek to Wonderland
Creek should be contained. This approach would not maintain historic flow patterns. A legal
opinion was issued by the Urban Drainage and Flood Control District (UDFCD) recommending
against any changes to the historic flow pattern of Fourmile Canyon and Wonderland creeks.
Based in part on this legal opinion, containment of 100-year storm event flood water in Fourmile
Canyon Creek is not considered a desirable option. Therefore, the flood mitigation plan
anticipates that flood water will continue to flow into Wonderland Creek. The legal opinion is
presented as Attachment E.
Alternatives:
The conceptual alternates considered for both streams included "High Hazard Containment" and
"Floodproofing of Structures" alternates. Original alternates considered in the initial Fourmile
Canyon Creek Major Drainageway Master Plan also included both a "50- year channel alternate"
and "100-year channel alternate."
1) The 100-year flood mitigation alternate for Fourmile Canyon and Wonderland Creek
would be designed by an inter-disciplinary team of engineers, geomorphologists and
biologists to emulate a natural channel. This alternate would eliminate various spills
from either channel during the 100-year or smaller flood event. The channel would be
designed to UDFCD and city criteria with FEMA and city-required freeboard. (Freeboard
is the additional elevation built into flood protection as an additional factor of safety.)
AGENDA ITEM 9 PAGE 9
2) The 50-year flood mitigation alternate for the study would contain the 50-year flows
but would not have freeboard built into the design, in the event of a 100-year flood. The
50-year flood has a 2 percent chance of occurring in any given year.
3) The HHZ containment alternate would remove all habitable structures identified in
either stream from the city's HHZ through direct purchase of the property and physical
removal of the building, the enlargement of road crossing structures, channel excavation,
and/or floodproofing or a combination thereof. The HHZ is defined as those areas where
the product number of velocity (measured in feet per second) times flow depth (measured
in feet) equals or exceeds four, or where flow depths equal or exceed four feet. These
portions of the 100-year floodplain pose an unacceptably high hazard to human safety. In
the HHZ, the construction, expansion or enlargement of any structure intended for human
occupancy or establishment of a new parking lot is prohibited. This alternate does not
entirely eliminate the out-of-channel bank floodplain; however, it reduces flood levels for
structures in the HHZ to increase the safety people who may not be evacuated during a
flood. Also, there is increased safety during an evacuation because water levels would be
reduced for access and egress. This alternative will also remove the majority of structures
from the conveyance zone as indicated in the following table. The table on the following
page shows the number of structures removed from the HHZ and Conveyance zone
through implementation of the recommended improvements.
WONDERLAND CREEK FOURMILE CANYON CREEK
HHZ AFTER RECOMMENDED IMPROVEMENTS HHZ AFTER RECOMMENDED IMPROVEMENTS
CITY OF CITY OF
BOULDER OUT OF HHZ STILL IN HHZ BOULDER OUT OF HHZ STILL IN HHZ
Sub-Total 13 0 Sub-Total 22 1
BOULDER BOULDER
COUNTY OUT OF HHZ STILL IN HHZ COUNTY OUT OF HHZ STILL IN HHZ
Sub-Total 3 0 Sub-Total 21 3
TOTAL 16 0 TOTAL 43 4
CONVEYANCE ZONE AFTER IMPROVEMENTS CONVEYANCE ZONE AFTER IMPROVEMENTS
CITY OF OUT OF STILL IN CITY OF OUT OF STILL IN
BOULDER CONV. CONV. BOULDER CONY. CONV.
Sub-Total 17 0 Sub-Total 4 3
BOULDER OUT OF STILL IN BOULDER OUT OF STILL IN
COUNTY CONV. CONY. COUNTY CONV. CONY.
Sub-Total 0 0 Sub-Total 11 3
TOTAL 17 0 TOTAL 15 6
AGENDA ITEM 9 PAGE 10
4) The floodproofing alternate would minimize flood damages by either keeping
floodwaters away from damageable property or making the property less susceptible to
damages when floodwaters reach the structure. The floodproofing of structures alternate
is a combination of adjustments and/or additions of physical features installed in, on or
around individual structures and designed to eliminate or reduce the potential for flood
damage to the structure. Floodproofing consists of the techniques and approaches for
preventing or minimizing flood damages to a structure and its contents in flood hazard
areas. Floodproofing techniques include:
• The construction of levees and flood walls around a structure
• Installing water-tight doors and windows
• Physically raising the structure elevation using fill or piers
• Measures designed to reduce water seepage and/or resist lateral pressure from
flood water in the structure
Floodproofing measures may be applied to new structures as well as retrofitting existing
structures, which may allow for development within the floodplain in low hazard areas.
Floodproofing does not eliminate all flood damages but can, if done correctly,
significantly reduce damages from flooding. The city may offer guidance and
disseminate information regarding various floodproofing techniques; however, it would
be the responsibility of the individual property owner to implement this alternate for their
own individual properties.
5) Alternates proposed were compared to the "Status Quo" alternate. Maintaining the
existing floodplain configuration would mean adopting the new floodplain mapping
without proposing mitigation improvements. Additional non-structural methods,
including flash flood forecasting, warning systems and evacuation plans would be
recommended for implementation. Flood insurance and floodproofing of structures
would also be recommended (at the individual property owner's expense). Floodplain
regulations would be strictly enforced. Post flood relief would be provided. This
alternate requires no new city funding, but may sacrifice opportunities to greatly improve
Fourmile Canyon Creek and mitigate flooding in the future.
Financial Considerations:
Reach-by-reach cost estimates were prepared for each of the alternates analyzed. The estimate
of future flood damage to a property decreases as the level of pre-flood mitigation improvements
increase.
One method commonly used to compare alternatives is the benefit/cost (B/C) ratio. In general,
the higher the B/C ratio, the more cost effective the alternate. In this study, the benefit/cost ratio
compares the total cost to implement a flood control alternate with the benefits that would be
realized if that flood control alternate were implemented.
A B/C ratio greater then one (1) indicates the benefit received is greater than the cost to
implement the alternative. A B/C ratio equal to one (1) indicates the benefit received is the same
as the cost to implement the alternative. A B/C ratio less then one (1) indicates the benefit
AGENDA ITEM 9 PAGE 11
received is less than the cost to implement the alternative. The financial analysis is summarized
in the executive summary of the Phase A report, Attachment A.
Consultant Recommendation:
Love & Associates, Inc. recommended a combination alternate for both Fourmile Canyon Creek
and Wonderland creeks. For each creek, the recommended alternate consisted of a combination
of the 100-Year Channel, High Hazard Containment, Floodproofing and Status Quo alternatives.
The recommendation was developed utilizing a reach-by reach approach.
The Love & Associates' recommendation also made the point that it is important to realize the
Fourmile Canyon Creek and Wonderland Creek floodplains are hydraulically connected. Due to
topography and the limited channel capacity of Fourmile Canyon Creek, spills from Fourmile
Canyon Creek flow into the Wonderland Creek floodplain. Decisions made on floodplain
management and mitigation within the Fourmile Canyon Creek floodplain have a direct impact
on the Wonderland Creek floodplain. All development within the existing floodplain should be
in accordance with the city, county and federal permitting requirements. The UDFCD developed
a draft selected plan that endorses the Love & Associates recommendations and provides
additional direction to be considered. The UDFCD Selection Plan is presented as Attachment F.
Intangible Benefits (Greenways Objectives):
There are numerous intangible benefits that would arise from the implementation of flood
mitigation improvements. Many of these intangible benefits are related to other Greenways
Program objectives. The intangible benefits that may be realized through flood mitigation
include the following:
• Improved traffic movement during floods
• Improved emergency response
• Improved recreation and alternative transportation
• Improved public health and safety, including life safety due to flash flooding
• Improved environment, water quality and riparian habitat
• Lower flood insurance rates for private property owners
• Increased property values
• Creation of urban open land
• Creation of cultural, educational, and scientific resources
These benefits have not been quantified from a monetary perspective and included in the
benefit/cost analysis. As a result, the benefit/cost ratios are lower than what would be realized if
dollar values were placed upon the intangible benefits.
AGENDA ITEM 9 PAGE 12
Other Considerations:
Bigger floods can and will occur. This statement holds true whether you are talking about a 10-
year, 100-year or 500-year flood event. The Fourmile Canyon Creek and Wonderland Creek
drainageways have not had a significant flood since the early part of the last century. The public
awareness of the significance of the flood situation is low since many of the residents in the
floodplain have not seen the results of a disaster in their neighborhood. For this reason, staff
recommends continued emphasis on public education and awareness as well as flood
preparedness. These activities are funded as part of the city's overall flood management
program.
Staff Modifications that differ from the Consultant Recommendations:
Attachments G and H are maps that integrate the consultant and staff recommendations for
flood mitigation along Fourmile Canyon and Wonderland creeks respectively. Staff
modifications are generally consistent with both the consultant recommendations and
the UDFCD selected plan, with three modifications.
As part of the public process, a number of additional ideas and flood mitigation alternatives were
evaluated. Based on these ideas and evaluations, staff is recommending the following three
changes to the recommendations provided in the Phase A Report:
1. Wonderland Creek - Reach 6
On Reach 6 of Wonderland Creek, three structures were determined to be in the HHZ (HHZ) at
Poplar Avenue, east of 19th Street, and recommended for city purchase. Additional evaluation
has indicated there is a more cost effective and desirable way to mitigate the HHZ on this reach.
This alternative eliminates the need to purchase the properties and helps mitigate flooding near
the Centennial Middle School. This alternate has a cost of $933,500 versus the anticipated cost
of $1,593,200 for the alternative that requires the acquisition of existing residences. Staff is
recommending this new option instead of the consultant's recommendation.
2. Fourmile Canyon Creek - Reach 6a
On Reach 6a of Fourmile Canyon Creek west of Broadway, there is currently significant
commercial/industrial property within the HHZ. Although the commercial/industrial property
does not pose the same level of life safety risk as residential property within the HHZ, there is
still a basis for concern. Also, the HHZ designation would preclude extensive re-development in
this area as called for in the North Boulder Subcommunity Plan. Staff asked the consultant to
develop an additional alternate in order to contain the HHZ and floodway, allowing for
redevelopment in this area. In the new recommended strategy, the channel would be excavated
to contain the overbank flooding and the Yarmouth and Rosewood road crossings would be
improved. The cost for this option would be $2,350,000. Because there are numerous flood
mitigation project competing for limited funds, implementation of this alternate would be
contingent on redevelopment proposals that provide for significant private financing of the flood
mitigation improvements.
3. Fourmile Canyon Creek - Reach 4
On Reach 4 of Fourmile Canyon Creek, comments were received indicating that some property
owners would be willing to accept some risk and tolerate mild flooding along Fourmile Canyon
AGENDA ITEM 9 PAGE 13
Creek. In particular, the residents of Githens Acres have voiced their concern on the impact of
flood mitigation work to the riparian corridor vegetation and associated wildlife habitat. The
consultant has recommended 100-year channel improvements in this area based in part on the
fact that the estimated benefit cost ratio is greater than 1.
Staff recommends the combined Floodproofing/High Hazard Containment alternate for Fourmile
Canyon Creek - Reach 4. Although the benefit/cost ratio for this alternate is somewhat less, the
public expense is dramatically reduced. This is the least invasive flood mitigation strategy that
still addresses life-safety concerns. In addition, excavation work required by this alternate will
allow the city to minimize impacts to riparian corridor vegetation and associated wildlife habitat.
This alternate is also intended to secure a continuous maintainable drainageway corridor through
Fourmile Canyon Creek - Reach 4.
The following tables summarize the type of improvement recommended for each reach of the
creek, with the three modifications in bold as recommended by city staff:
AGENDA ITEM 9 PAGE 14
Wonderland Creek
Reach Staff Recommendation Consultant Recommendation
1 - Valmont to
Goose Creek Maintain Existing Maintain Existing
2 - Foothills Pkwy
to Valmont Flood roofin Flood roofin
3-SH119to
Foothills Pkwy HHZ Containment & Floodproofing HHZ Containment & Floodproofmg
4 - 28th St. to SH
119 100-Year Channel 100-Year Channel
5 - 26th St. to 28th
St. 100-Year Channel 100-Year Channel
HHZ Containment &
6 - 19th St. to 26th Floodproofing without acquisition HHZ Containment & Floodproofmg with
St. of existing residences property acquisition
7 - Broadway to
19th St. Maintain Existing Maintain Existing
8 - Wonderland
Lake to Broadway Maintain Existing Maintain Existing
Fourmile Canyon Creek
Reach Staff Recommendation Consultant Recommendation
la-SH119 to
Boulder Creek HHZ Containment & Floodproofmg HHZ Containment & Floodproofmg
lb - Savannah to
SH 119 Maintain Existing Maintain Existing
2a - 30th St. to
Savannah Maintain Existing Maintain Existing
2b - 28th St. to
30th St. 100-Year Channel 100-Year Channel
3 - 26th St. to 28th
St. HHZ Contaimment & Flood roofin HHZ Containment & Flood roofm
4 - 19th St. to 26th HHZ Containment &
St. Flood roofin 100-Year Channel
5 - Broadway to
19th St. HHZ Contaimnent & Floodproofmg HHZ Containment & Floodproofmg
6a - 7th St. to HHZ Containment &
Broadway Flood roofin Flood roofing
6b - 4th St. to 7th
St. HHZ Containment & Flood roofm HHZ Containment & Flood roofing
6c - Foothills to 4th
St. Maintain Existing Maintain Existing
AGENDA ITEM 9 PAGE 15
NEXT STEPS:
Following the consideration and acceptance of the Fourmile Canyon Creek and Wonderland
Creek mitigation plan by council, staff will formally present the plans to UDFCD.
Representatives from the UDFCD have seen the staff recommendations and are supportive of the
changes. After the adoption by UDFCD, the next phase includes preliminary design and a
Community and Environmental Assessment Process (LEAP).
MATRIX OF OPTIONS:
1. Accept the Fourmile Canyon and Wonderland Creek Flood Mitigation Plan, as modified
by staff (staff recommendation).
2. Accept the Fourmile Canyon and Wonderland Creek Flood Mitigation Plan, with
additional changes and conditions.
3. Reject the Fourmile Canyon and Wonderland Creek Flood Mitigation Plan, and provide
direction to staff.
Approved By:
Jane S. Brautigam,
City Manager
ATTACHMENTS:
Attachment A - Phase A Report Executive Summary
Attachment B - Chronology
Attachment C - Study Area Map
Attachment D - WRAB Motion and Utilities Division Staff Comments
Attachment E - Legal Opinion
Attachment F - UDFCD Selected Plan
Attachment G - Fourmile Canyon Creek Flood Delineation
Attachment H - Wonderland Creek Flood Delineation
AGENDA ITEM 9 PAGE 16
Attachment A
FOURMILE CANYON CREEK AND
WONDERLAND CREEK
MAJOR DRAINAGEWAY PLANNING
PHASE A REPORT Background Information
ALTERNATIVES ANALYSIS
The study area includes the Fourmile Canyon Creek floodplain from the mouth of the canyon to its
confluence with Boulder Creek and the Wonderland Creek floodplain from downstream of Wonderland
EXECUTIVE SUMMARY Lake to its confluence with Goose Creek. The Fourmile Canyon Creek spill floodplain, which is located
between the Fourmile Canyon Creek and Wonderland Creek floodplains from upstream of Broadway to
The development, evaluation, and recommendation of floodplain alternatives to mitigate existing approximately 19th Street, is included in the study area.
flooding in both the Fourmile Canyon Creek and Wonderland Creek floodplains within the City of
Boulder (City) and Boulder County are presented in this report. This effort is jointly sponsored by the Major drainageway planning documents were previously developed
for Fourmile Canyon Creek and
Urban Drainage and Flood Control District (UDFCD) and the City of Boulder, Colorado. Wonderland Creek by Greenhorne & O'Mara, Inc in 1984 and 1987 and for Wonderland Creek
by Boyle
Engineering in 2002. Due to recent development that has occurred in the floodplain and inaccuracies in
Purpose and Objectives the original studies, the City of Boulder commissioned a re-study of the Fourmile Canyon Creek
floodplain in 1997 and the Wonderland Creek floodplain in 2005. Love & Associates was retained by
The purpose of the study is to analyze the existing and future drainage conditions within both the the City to prepare a Letter of Map Revision (LOMR) submittal
to FEMA for these two streams and the
Fourmile Canyon and Wonderland Creek floodplains, develop alternate drainageway planning concepts LOMR was approved by various City Boards and the City Council
in early 2006. The LOMR was
to mitigate existing flood damages taking into consideration the impacts of the spill flows from Fourmile submitted to FEMA in March, 2006 and approved by FEMA in November, 2006.
The new floodplains
Canyon Creek to Wonderland Creek, and prepare a preliminary design of an alternative selected by the became regulatory following the appeal period in late March, 2007.
Project Sponsors. The study is divided into two phases. The first phase (Phase A) of which this report is
a part covers the hydrologic, hydraulic, and alternate evaluation aspects of the project. The second phase The LOMR submittal for these two creeks indicated significant
problems with the original FEMA
(Phase B) will cover the preliminary design of the selected alternate(s). regulatory studies, resulting in additional properties being located within the two
floodplains. Of
particular importance, the re-study identified reaches of Fourmile Canyon Creek west of 19'h Street,
Planning Process where, once the channel capacity is exceeded, flood flows overtop the south bank of the creek and flow in
a southeasterly direction towards Wonderland Creek. These "spill flows" result in a reduction of flows in
The initial planning effort began in June of 1999 and both a Phase A and Phase B study were completed Fourmile Canyon Creek downstream of 19th Street but also result
in an increase in the flows in
for Fourmile Canyon Creek. Following the review and input from the Independent Review Panel (IRP) Wonderland Creek. During the 100-year flood event, approximately 3,300 cubic
feet per second (cfs) is
comprised of floodplain experts in 2000, it was recommended that in order to develop a more complete in Fourmile Canyon Creek near the mouth of the Canyon, of this amount
approximately 1,600 cfs will
solution for flooding on Fourmile Canyon Creek, a combined Phase A Alternate Analysis report should overtop the south bank spill and flow toward Wonderland Creek. The remaining
1,700 cfs will remain in
be undertaken as a combined study of both Fourmile Canyon and Wonderland Creeks. This combined the Fourmile Canyon Creek Channel. Likewise, the 100-year discharge
in Wonderland Creek
Alternate Analysis began in the Fall of 2006. Since that time, a series of progress meetings have taken significantly increases downstream of the spill inflow. Some
of the spill flows return to Fourmile
place to exchange information and discuss ideas and findings of the combined study. The progress Canyon Creek near 19t" Street but the majority of the spill remains
in the Wonderland Creek floodplain.
meetings were regularly attended by representatives of the sponsoring agencies. Concurrent with the
progress meetings, a series of public meetings were conducted to discuss the planning effort and solicit Damage Analysis
public input.
All property, structures and infrastructure within the 500-year floodplain were included in the damage
The Project Sponsors will review the Phase A report and make a decision on the alternative that is to be analysis which was undertaken as a part of this master planning
effort. The damage analysis was
studied in greater detail in Phase B of this planning effort. In Phase B, the consultant will prepare a calculated using the UDFCD Methodology for Evaluation
of Feasibility: Multi-Jurisdictional Urban
preliminary design of the alternative(s) selected by the Project Sponsors for both streams. The type, size, Drainage and Flood Control Projects. Flood damages were calculated
for the 2-, 5-, 10-, 50-, 100-, and
location of various improvements will be developed in greater detail. In the process, cost estimates will 500-year flood events. For the economic analysis, a 50-year project
life was chosen, which corresponds
be refined and the relative priorities and phasing of these facilities will be identified. A final Phase B to a typical structure life. A 6% annual interest rate
was selected, which corresponds to the cost of
report will be published following selection of the preferred alternative. The Phase B report will serve as borrowed capital for the entities involved and a 3% annual
rate of inflation was assumed. The net
a planning tool for the Project Sponsors and private development within the Fourmile Canyon Creek and discount rate used in present value calculations was 3%.
Wonderland Creek floodplains.
ES-1
Attachment A
Identification of Potential Flood Mitigation Alternates and/or resist lateral pressure from flood water in the structure, etc. Floodproofing measures
may be
applied to new structures as well as retrofitting existing structures which may allow for development
Early in the study, a broad range of alternates were identified. These alternates were screened following within the floodplain in low hazard areas. The purpose of floodproofing
is to minimize flood damages by
an analysis of each stream and detailed discussions held during progress meetings on a reach by reach either keeping floodwaters away from damageable property or making
the property less susceptible to
basis for each stream. A wide array of options were looked at as potentials for mitigation of the flooding damages when floodwaters reach the structure. Floodproofing does not
eliminate all flood damages but
ranging from a `do-nothing' status quo alternate to construction of a 100-year flood channel for each can, if done correctly, significantly reduce damages from
flooding. The City may offer guidance and
stream confining the spill from Fourmile in its own channel. disseminate information regarding various floodproofing techniques; however, it would be the
responsibility of the individual property owner to implement this alternate for their own individual
Alternates Analysis properties.
A number of alternates were reviewed as a part of this study. The damage analysis and alternate costs for Alternates proposed are compared to the Status Quo or Maintain Existing
Conditions alternate. Maintain
the previous Fourmile Canyon Creek (2000) and Lower Fourmile Canyon Creek (2002) reports were existing floodplain configuration would adopt the new floodplain mapping
without proposing mitigation
updated and benefits and costs for two additional alternates were developed. The two additional improvements at this time. Additional non-structural methods
including flash flood forecasting and
alternates considered for both streams included a High Hazard Containment and Floodproofing of warning systems and evacuation plans would also be recommended for implementation.
Flood insurance
Structures in the spill area between Fourmile Canyon and Wonderland Creeks alternate. Original and floodproofing of structures would also be recommended (at
the individual property owner's
alternates considered in the initial Fourmile Canyon Creek Major Drainageway Master Plan also expense). Floodplain regulations would be strictly enforced. Post flood
relief would be provided. This
included both a 50- year and 100-year channel alternate. alternate requires no new funding, but may sacrifice opportunities to greatly improve Fourmile Canyon
Creek and mitigate flooding in the future. A "Do Nothing" solution would offer no opportunity to
The 100-year channel would be designed by an inter-disciplinary team of engineers, geomorphologists mitigate spills and flooding to the south of Fourmile Canyon Creek
and would offer no opportunity to
and biologists to emulate a natural channel. This alternate would eliminate spills from Fourmile Canyon eliminate flooding to the Waldorf or Crestview Elementary Schools.
Creek to Wonderland Creek during the 100-year or smaller flood event. The channel would be designed
to UDFCD and City criteria with FEMA and City required freeboard. The 50-year alternate for Fourmile Reach by Reach cost estimates were prepared for the each of the alternates
analyzed (five in the Fourmile
Canyon (only) would contain the 100-year flows but would have no freeboard built into the design. The Canyon Creek floodplain and four in the Wonderland Creek floodplain).
Urban Drainage and Flood Control District, based on legal opinion from its concel, has indicated
reluctance to participate in any Alternate which includes containment or reduction of the spill unless Each of the alternates analyzed for both streams will still
incur an expected damage during flood events.
downstream property owners' concerns are properly addressed as this would negatively affect Examples of these damages would include isolated bank erosion locations
in the constructed "natural"
downstream properties on Fourmile Canyon Creek. channel alternate or wide spread damage in the maintaining of the existing floodplain configuration
alternate.
The High Hazard Zone is defined as those areas where the product number of velocity (measured in feet One method commonly used to compare alternatives is the benefit/cost (B/C)
ratio. In general, the higher
per second) times flow depth (measured in feet) equals or exceeds four, or where flow depths equal or the B/C ratio the more cost effective is an alternate. In this study,
the benefit/cost ratio compares the total
exceed four feet. These portions of the 100-year floodplain pose an unacceptably high hazard to human cost to implement a flood control alternative with the benefits that would
be realized if that flood control
safety. In the high hazard zone, the construction, expansion or enlargement of any structure intended for alternative were implemented. The total cost to implement a flood control
alternative was calculated as
human occupancy or establishment of a new parking lot is prohibited. The High Hazard Containment the sum of the construction costs, property acquisition costs (land and structure),
right-of-way required to
alternate would remove structures identified in either stream from the City's High Hazard Flood Zone implement the alternate and 0&M costs. The benefit that
would be realized if the flood control
through direct purchase of the property, the enlargement of road crossing structures, channel excavation, alternative is implemented was calculated as the difference between
flood damages under existing
and/or floodproofing or a combination thereof. This alternate does not eliminate the out of channel bank conditions minus flood damages that would be incurred after implementation
of the alternative.
floodplain; however, it reduces flood levels to those structures in the High Hazard Zone for increased
safety when evacuating occupied buildings and allows for emergency access to residential structures. Benefit/Cost Ratio = [Existing Flood Damages] - [Future Flood Damages
with Alternative in Place]
Cost to Implement Alternative
Floodproofing is a combination of adjustments and/or additions of physical features installed in, on or
around individual structures designed to eliminate or reduce the potential for flood damage to the A B/C ratio greater then one (1) indicates the benefit received
is greater then the cost to implement the
structure. Floodproofing consists of the techniques and approaches for preventing or minimizing flood alternative. A B/C ratio equal to one (1) indicates the
benefit received is the same as the cost to
damages to a structure and its contents in flood hazard areas. Floodproofing techniques range from: the implement the alternative. A B/C ratio less then one (1) indicates
the benefit received is less then the
construction of levees and flood walls around a structure, to installing water-tight doors and windows, cost to implement the alternative.
physically raising the structures elevation using fill or pilings, measures designed to reduce water seepage
ES-2
Attachment A
Comparison of benefits and costs must be made for the same time frame. Benefits stemming from In addition to the benefit/cost ratios presented above, a number of
additional evaluation factors should be
reduced flood damages occurring annually over the life of the project cannot be compared directly with considered when choosing a course of action to mitigate flood
damages within the Fourmile Canyon
construction costs, which generally occur over a short period of time near the beginning of the project. Creek and Wonderland Creek floodplains. Below is a list of some of
the potential evaluation factors:
All benefits and costs must be converted to either present value or annual amounts before comparison,
using an appropriate discount rate, which accounts for the time value of money. For this study all costs
were converted to present value. Present value calculations assumed a 50-year project life, which
corresponds to the typical structural life, and a discount rate of 3% (6% annual interest rate minus 3% Evaluation Factors
annual rate of inflation).
• Flood Mitigation
Life Safety
The benefit/cost ratio for each alternate for the entire study reach of each creek is as follows: Property damage
• Environment
Fourmile Canyon Creek Temporary Disturbance
Long-term benefit
Alternate 1 50-Year Channel B/C = 1.43 Groundwater
Alternate 2 100-Year Channel B/C = 1.34 • Transportation
Alternate 3 Status Quo B/C = 0.00 Automotive
Alternate 4 Floodproofing B/C = 1.96 Bicycle/Pedestrian
Alternate 5 High Hazard Containment B/C = 0.08 • Development/Re-Development
Growth Management
Wonderland Creek Affordable Housing
• Aesthetics
Alternate 1 100-Year Channel B/C = 1.92 • Benefit/Cost Ratio
Alternate 2 Status Quo B/C = 0.00 • Construction Cost
Alternate 3 High Hazard Containment B/C = 0.44 • Recreation
Alternate 4 Floodproofing B/C = 3.64 • Permitting Requirements
There are numerous intangible benefits that would arise from the implementation of flood mitigation • Impacts to Fourmile Canyon Creek
improvements. By definition, intangible benefits are difficult to measure and are not directly quantifiable • Impacts to Wonderland Creek
in terms of dollar value or dollars spent for their usage. The intangible benefits that may be realized • Conformance with other Planning Documents
through flood mitigation include the following: • Competing Priorities
• Public Acceptance
• Improved traffic movement during floods. • Operation and Maintenance
• Improved emergency response.
• Improved public health and safety. Bigger floods can and will occur. This statement holds true whether you are talking about a 10-year,
• Improved environment, water quality and riparian habitat. 100-year or 500-year flood event. The Fourmile Canyon Creek and Wonderland Creek floodplains have
• Lower flood insurance. not had a significant flood in the recent documented past. The public awareness of the significance of the
• Potential for scientific, educational, historical amenities. flood situation is low since many of the residents in the floodplain have not seen the results of
a disaster,
• Increased property values. or had to clean up after a flood in their neighborhood or experienced the injury to or loss of a family
• Creation of cultural, educational, and scientific resources. member or friend in a flood event.
Because intangible benefits are not directly quantifiable in terms of a dollar value they are not included in Recommended Alternate
the benefit/cost analysis. As a result, the benefit/cost ratios are lower than what would be realized if The contract Love & Associates, Inc. has with the Urban
Drainage and Flood Control District requires
dollar values were placed upon the intangible benefits. that the consultant make a recommendation as to the best overall alternate solution, taking into account a
variety of information developed throughout the master planning process for both Fourmile Canyon and
Wonderland Creeks.
ES-3
Attachment A
The benefit/cost ratio of this combined alternate ranges from 0-2.65 on Fourmile Canyon Creek, and 0-
The firm of Love & Associates, Inc. is recommending a combination alternate for both Fourmile Canyon 5.34 on Wonderland Creek. With implementation of this combined alternate,
flood insurance would still
Creek and Wonderland Creek. In developing the Recommended Alternate we evaluated in combination be required by most lenders and individual property owners would be strongly
encouraged to purchase
the alternates utilizing a reach-by reach approach. flood insurance whether or not a mortgage on their property is in effect.
In Reaches lb, 2a, and 6c on Fourmile Canyon Creek and for Reaches 1, 7, and 8 on Wonderland Creek,
no structures are being impacted. For each alternate analyzed, these reaches required no work.
For each creek the recommended alternate consists of a combination of the 100-Year Channel, High Therefore, the Maintain Existing Alternate is recommended for these
reaches.
Hazard Containment, Floodproofing and Maintain Status Quo.
Tables ES.1 and ES.2 summarize the recommended alternate for each reach as well as the B/C ratio and a
In Reaches 5 and 6 of Fourmile Canyon Creek, the 100-Year Channel and 50-Year Channel alternates breakdown of public and private costs for implementing the alternate.
In the tables below, it should be
result in a change in the spatially varied flow distribution in the floodplain which would require noted that the dollar costs listed under the `private' category
are for those costs that would be incurred by
channelization to the confluence with Boulder Creek. Love & Associates, Inc. believes that complete individual property owners to floodproof their own properties.
channelization of Fourmile Canyon Creek from Reach 5 or 6 to its confluence with Boulder Creek is not
a viable option. The Urban Drainage and Flood Control District has indicated they are not willing to
participate in a solution which incorporates containment/channelization of all flows from upstream to the
confluence with Boulder Creek. Since these alternates change the flow distribution that currently exists Table ES.1
in the floodplains of both streams, channelization creates both liability and life safety risks if bigger Recommended Alternate
floods were to occur. Lands could be inundated by the introduction of flood waters where they would not Fourmile Canyon Creek
have existed prior to the re-distribution of flood waters by either of these alternates. Love & Associates,
Inc. is not recommending either a 50 or 100-year channel alternate upstream of the spill zone for these B/C Cost
reasons. In some downstream reaches where the 100-year alternate resulted in a B/C ratio greater than 1, Reach Alternate Ratio Total Public Private
the 100-year alternate is recommended with a reduced conveyance required. In Reaches 2b and 4 on
Fourmile Canyon Creek the 100-year channel altlernate is recommended. The 100-year channel Reach la HHZ Containment/Flood roofin 0.08/0.95 $1,583,800
$1,025,000 $558,800
downstream of the spill zone contains the reduced flow that remains after the spill from Fourmile Canyon Reach lb Maintain Existing 0 $1,188,000 $1,188,000
Creek to Wonderland Creek. Likewise, in Reaches 4 and 5 on Wonderland Creek where the 100-year Reach 2a Maintain Existing 0 $442,000 $442,000
alternate resulted in a B/C ratio greater than 1, Love & Associates is recommending this alternate. For Reach 2b 100-Year Channel 2.65 $1,283,660 $1,283,660
both creeks the 100-year channel is designed to contain the 100-year discharge and provide a minimum
of 1' of freeboard. This freeboard contains the 500-year flow, making floodproofing unnecessary in Reach 3 HHZ ContainmentlFloodprooflng 0.35/1.18 $900,200
$741,000 $159,200
these reaches. Additionally, in reaches where 100-year improvements are implemented, flood insurance Reach 4 100-Year Channel 1.88 $6,730,860 $6,730,860
would also no longer be required. It should be noted that unless 100-year improvements are implemented Reach 5 HHZ Containment/Floodprooflng 0.1214.42 $798,400
$394,000 $404,400
thus eliminating properties from the floodplain, flood insurance is required with all other solutions Reach 6a Flood roofin 1.68 $3,130,600 $290,000
$2,840,600
including a 50-year channel alternate and floodproofing which provides a degree of flood protection but Reach 6b HHZ Containment/Flood roofin 0.03/4.44 $762,700
$595,000 $167,700
does not remove the property from the floodplain. Reach 6c Maintain Existing 0 $173,000 $173,000
The High Hazard Containment Alternate for both creeks has a benefit/cost ratio of less than one (1); Total $16,993,220 $12,862,520 $4,130,700
however, no credit is given in the analysis for life safety. Since life safety is of primary concern to this
consultant, this alternate is the basis of our recommendation. The High Hazard Containment Alternate
removes all residences from the high hazard flood zone allowing safe evacuation and emergency access
during a 100-year flood event. The floodproofing alternate has a high benefit/cost ratio and the dollars
spent by individual property owners constructing improvements to protect their individual properties
offer significant protection to structures and contents during flood events. A combination of the High
Hazard Containment and Floodproofing Alternate is recommended for Reaches la, 3, 5, and 6b on
Fourmile Canyon Creek and for Reaches 3, and 6 on Wonderland Creek. Additionally, the
Floodproofing Alternate is recommended for Reach 6a on Fourmile Canyon Creek and for Reach 2 on
Wonderland Creek. For individual reaches on both creeks these alternates are recommended in tandem.
ES-4
Attachment A
Table ES.2
Recommended Alternate
Wonderland Creek
B/C Cost
Reach Alternate Ratio Total Public Private
Reach 1 Maintain Existing 0 $618,000 $618,000
Reach 2 Floodproofing 0.61 $539,400 $332,000 $207,400
Reach3 HHZContainment/Floodproofmg 0.39/1.37 $10,236,600 $7,307,000 $2,929,600
Reach 4 100-Year Channel 5.34 $7,110,300 $7,110,300
Reach 5 100-Year Channel 4.75 $4,057,800 $4,057,800
Reach 6 HHZ Containment/Flood roofin 0.51/0.52 $5,024,300 $3,168,000 $1,856,300
Reach 7 Maintain Existing 0 $807,000 $807,000
Reach 8 Maintain Existing 0 $289,000 $289,000
Total $28,682,400 $23,689,100 $4,993,300
Figures ES-la-e and ES-2a-c depict the specific alternate being proposed by this consultant for its
Recommended Plan for each reach of each stream.
It is important to realize the Fourmile Canyon Creek and Wonderland Creek floodplains are hydraulically
connected. Due to topography and the limited channel capacity of Fourmile Canyon Creek, spills from
Fourmile Canyon Creek flow into the Wonderland Creek floodplain. Decisions made on floodplain
management and mitigation within the Fourmile Canyon Creek floodplain have a direct impact on the
Wonderland Creek floodplain. All development within the existing floodplain should be in accordance
with the City, County and Federal permitting requirements.
ES-5
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High Hazard Flood Zone
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Main Roads
Streets
W E ~ , ` High Hazard Flood Zone
, Lakes
Boulder Boundary
r
0 0.5 1 2 3 City Of Boulder
Miles Residential structures
Located in the High Hazard
Flood Zone within
Attachment D City Limits
Attachment E: Critical Facility Information
Protection of critical facilities from the impacts of flooding has become an important element in local floodplain
management. Numerous states, counties and local governments have adopted regulations for critical facilities
and many more have included recommendations to adopt critical facilities regulations in local Multi-Hazard
Mitigation Plans.
In recent years the Federal Emergency Management Agency (FEMA) has outlined guidelines for critical
facilities. FEMA states that for some activities and facilities, even a slight chance of flooding poses too great a
threat. These activities and facilities should be given special consideration when formulating regulatory
alternatives and floodplain management plans.
As such, FEMA defines four kinds of critical facilities:
• Structures or facilities that produce, use, or store highly volatile, flammable, explosive, toxic,
and/or water-reactive materials;
• Hospitals, nursing homes, and housing likely to have occupants who may not be sufficiently
mobile to avoid injury or death during a flood;
• Police stations, fire stations, vehicle and equipment storage facilities, and emergency
operations centers that are needed for flood response activities before, during, and after a
flood; and
• Public and private utility facilities which are vital to maintaining or restoring normal services
to flooded areas before, during, and after a flood.
Boulder City Council endorsed the development of protection measures for critical facilities following a
January 29, 2002 Study Session on Floodplain Policies. Council later adopted a recommendation to develop
500-year protection standards for critical facilities in the 2004 Comprehensive Flood and Stormwater Master
Plan (CFS).
As a result of the CFS recommendation and existing research on critical facilities regulations and guidance from
across the nation, a critical facilities ordinance is currently being developed and the following proposed
definition and categorization of critical facilities is being developed for Boulder:
"Critical facility," for floodplain purposes, means a facility, including without limitation, a structure,
infrastructure, property, equipment or service, that if flooded may result in severe consequences to public health
and safety or interrupt essential services and operations for the community at any time before, during and after a
flood. A critical facility is classified by the following categories: (1) Essential Services, (2) Hazardous
Materials, (3) At-risk Populations, and (4) Vital to Restoring Normal Services.
Essential services facilities include without limitation public safety, emergency response, emergency medical,
designated emergency shelters, communications, public utility plant facilities and equipment, and transportation
lifelines.
The sub-categories of essential services facilities can be f rrther defined as:
• Public safety (police, fire and reserve, emergency management)
• Emergency response (emergency responders, vehicle and equipment storage, emergency
repair materials, alternative governmental work centers)
• Emergency medical (hospitals, urgent care, ambulance services)
• Designated emergency shelters
• Communications (telephone, cable systems, satellite dish systems, cellular systems,
television, radio, news papers, emergencv warning systems)
• Public utility plantfacilities and equipment for treatment, generation, storage, pumping and
distribution (water, wastewater, power, gas)
• Transportation lifelines (primary access routes, emergency evacuation routes, bridge and
culvert crossing structures, airports, rail systems, mass transit, critical roadways)
Hazardous materials facilities include without limitation facilities that produce, distribute, use, store, deliver in
quantity, or sell highly volatile, flammable, explosive, toxic and/or water-reactive materials.
The sub-categories of hazardous material facilities can be further defined as:
• Chemical and pharmaceutical plants (chemical plant, chemical company, pharmaceutical
company)
• Laboratories
• Refineries and bulk plants (bulkfuel)
• Hazardous waste storage and disposal sites
• Gasoline and propane sales stations (ser7lce station)
At-risk population facilities include without limitation medical care, congregate care, schools, guest lodging,
and places of assembly.
The sub-categories of at-risk population facilities can be fi,rrther defined as:
• Medical care (hospitals, clinics, nursing homes)
• Congregate care (senior housing, independent living centers, day care, assisted living)
• Public and private schools (pre-schools, K-12 schools, colleges and universities, vocational
centers, after-school care)
• Guest lodging (hotels, motels, bed and breakfast)
• Places of assembly (sports arenas, theaters, meeting halls and churches, community centers)
Vital to restoring normal services facilities include without limitation public utility infrastructure, government
operations and major employment centers.
The sub-categories of vital to restoring normal services facilities can befirther defined as:
• Public utility infrastructure (water, wastewater, power, gas)
• Government operations (public records and libraries, courts and jails, building permitting
and inspection services, community administration and management, maintenance and
equipment centers)
• Major employment centers (local, state and federal offices, major industries, large corporate
off ces)
• Parcel Services (mail, parcel service, shipping)
Staff has researched the location and type of all facilities that would currently meet the proposed definition.
Existing structures, denoted by critical facility type, which are located in the City's High Hazard Zones,
Conveyance Zones, 100 year floodplains, and 500 year floodplains are presented below:
2
High Hazard Zone Facilities
Second
Number NAME ADDRESS Category Subcategory Subcategory
1 1301 North Street At-risk Population Congregate Care Da Care
2 1345 28th Street At-risk Population Congregate Care Da Care
Crestview Christian Places of
3 Reformed 3545 Madison Ave At-risk Population Assembly Church
Essential
4 New Britain Building 1101 Arapahoe Ave Services Communications Warning Systems
Boulder Fire Station Essential
5 # 3 30th & Ara ahoe Services Communications Warning Systems
Boulder Fire Station Essential
6 3 1585 30th St. Services Public Safety Fire
Vital Normal Government Administration and
7 New Britain Building 1101 Arapahoe Ave Services Operations Management
Vital Normal Government Administration and
8 Atrium Building 1300 Canyon Blvd Services Operations Management
Boulder Building Vital Normal Government Maintenance and
9 Maintenance 1720 13th St Services Operations Equipment
Park Central Vital Normal Government Permitting and
10 Building 1739 Broadway Services Operations Inspection
Boulder Critical Facilities in the
High Hazard Zone
zx, - d/0
f r fs:'
I A I L Q ,
Legend
r At-risk Population p
e 1 .0 :sw 5" + Essential Services
'"Ital Normal Serv~es
3
Conveyance Zone Facilities
Second
Number NAME ADDRESS Category Subcategory Subcategory
1 1330 Al ine Ave_ At-risk Population Congregate Care Da Care
2 3375 34th St. At-risk Population Congregate Care Senior Housing
Millenneum Harvest
3 House 1345 28th St At-risk Population Guest Lodging Hotel
Places of
4 Alandi Ashram 1705 14th St At-risk Population Assembly Church
Saint Andrew Places of
5 Presbyterian Church 3700 Baseline At-risk Population Assembly Church
6 805 30th Street At-risk Population Congregate Care Da Care
CU Married Student
7 Housing Marine St At-risk Population Schools Student Housing
Essential Emergency
8 Boulder Medical Center 2750 Broadway Services Medical Clinic
Hazardous Gasoline and
9 Crossroads AMOCO 3005 Arapahoe Ave Materials Propane Service Station
Grizzly Gasoline and Hazardous Gasoline and
10 Store 3200 Arapahoe Ave Materials Propane Service Station
Hazardous Gasoline and
11 Conoco 601 S. Broadway Materials Propane Service Station
Boulder Municipal Vital Normal Government Administration and
12 Building 1777 Broadway Services Operations Management
Vital Normal Government
13 Old Main Public Library 900 Canyon Blvd services operations Library
Boulder Critical Facilities in the
Conveyance Zone
r:
1` ~i" tf t r
Legend
o •
a21 At-risk Population
u 1,50 .5x „an • Essential Services
r
b Hazardous Materials
® Vital Normal Services
4
100 Year Floodplain Facilities
Second
Number NAME ADDRESS Category Subcategory Subcategory
1 2202 Ara ahoe At-risk Population Congregate Care Da Care
2 2727 29th St At-risk Population Congregate Care Da Care
3 4072 N. 19th At-risk Population Congregate Care Da Care
4 745 College Ave. At-risk Population Con re ate Care Da Care
5 2525 Taft Dr. At-risk Population Congregate Care Senior Housing
The Atrium: Brookdale
6 Senior Living 3350 30th St. At-risk Population Congregate Care Senior Housing
Briar Rose Bed and Bed and
7 Breakfast 2151 Arapahoe Ave At-risk Population Guest Lodging Breakfast
8 Quality Inn 2020 Arapahoe Ave At-risk Population Guest Lodging Hotel
9 Marriott - Boulder 2660 Canyon Blvd At-risk Population Guest Lodging Hotel
10 St Julien Hotel 900 Walnut St At-risk Population Guest Lodging Hotel
Bethel United Places of
11 Methodist Church 1925 Glenwood Ave At-risk Population Assembly Church
East Boulder Places of
12 Community Center 5660 Sioux Dr At-risk Population Assembly Meeting Hall
Spice of Life Event Places of
13 Center 5706 Ara ahoe Ave At-risk Population Assembly Meeting Hall
Places of
14 West Senior Center 909 Arapahoe Ave At-risk Population Assembly Meeting Hall
After School
15 1001 Hawthorn Ave. At-risk Population Schools Care
After School
16 1150 7th Ave. At-risk Population Schools Care
Private K-12
17 Living School 1852 Arapahoe Ave At-risk Population Schools Schools
Shining Mountain Private K-12
18 Waldorf School 999 Violet Ave At-risk Population Schools Schools
Foothills Elementary Public K-12
19 School 1001 Hawthorn Ave. At-risk Population Schools Schools
Flatirons Elementary Public K-12
20 School 1150 7th St At-risk Population Schools Schools
Public K-12
21 Boulder High School 1604 Arapahoe At-risk Population Schools Schools
CU-Boulder East Public
22 University of Colorado Campus At-risk Population Schools Universities
CU Married Student Student
23 Housing Newton Court At-risk Population Schools Housing
Emergency
24 People's Medical Clinic 3303 N. Broadway Essential Services Medical Clinic
Boulder Community Emergency
25 Hospital 1100 Balsam Essential Services Medical Hospital
Boulder Foothills Emergency
26 Community Hospital 4747 Arapahoe Essential Services Medical Hospital
27 Boulder Sheriff 1777 6th St. Essential Services Public Safety Police
CU Environmental East Campus - 30th Hazardous Chemical and Pharmaceutical
28 Health and Marine St Materials Pharmaceutical Company
Arapahoe and Hazardous Gasoline and
29 Broadway Conoco 1201 Arapahoe Ave Materials Propane Service Station
Hazardous Gasoline and
30 A&A AMOCO 1595 55th St Materials Propane Service Station
Hazardous Gasoline and
31 Diamond Shamrock 1704 Arapahoe Ave Materials Propane Service Station
32 Boulder Gas 2700 Baseline Hazardous Gasoline and Service Station
5
Materials Propane
Hazardous Gasoline and
33 Circle K 2877 Baseline Materials Propane Service Station
Hazardous Gasoline and
34 Diagonal AMOCO 2990 Diagonal H Materials Propane Service Station
Hazardous Gasoline and
35 Boulder Gas 2995 28th St Materials Propane Service Station
No Broadway Silco Hazardous Gasoline and
36 Gas 4501 N Broadway Materials Propane Service Station
Hazardous Gasoline and
37 Conoco 5500 Arapahoe Ave Materials Propane Service Station
Boulder County Justice Vital Normal Government
38 Center CJC 1777 6th St. Services Operations Courts and Jails
Major
Vital Normal Employment
39 Ball Aerospace 1600 Commerce Services Centers Major Industries
Boulder Critical Facilities in the
1001-yr Floodplain
/rte - .d
r jf ;y jr,,,;yf~i
~f ~/x ,
A ~r
Legend
/ At-nsk Population
Feel f'. + Essential Services
u _•ooc aocn ac:a r I/ Hazardous Materials
Vaal Normal Services
6
500 Year Floodplain Facilities
Second
Number NAME ADDRESS Category Subcategory Subcategory
City Assisted Housing 951-53 Arapahoe
1 on Arapahoe Ave At-risk Population Congregate Care Assisted Living
2 1825 Upland Ave At-risk Population Congregate Care Da Care
3 2675 Ma leton At-risk Population Congregate Care Da Care
4 3130 Re tier Dr At-risk Population Congregate Care Da Care
5 3280 Dartmouth At-risk Population Congregate Care Da Care
6 3340 Dartmouth At-risk Population Congregate Care Day Care
1286 Sumac
7 Avenue At-risk Population Congregate Care Independent Living
8 2635 Mapleton Ave At-risk Population Congregate Care Independent Living
3535 Eastman
9 Avenue At-risk Population Congregate Care Independent Living
Boulder Presbyterian
10 Manor 1050 Ara ahoe Ave. At-risk Population Congregate Care Senior Housing
Canyon Pointe
11 Housing 700 Walnut St At-risk Population Congregate care Senior Housing
Boulder University
12 Inn 1632 Broadway At-risk Population Guest Lodging Hotel
Residence Inn by 3030 Center Green
13 Marriott Dr At-risk Population Guest Lodging Hotel
14 Courtyard b Marriott 4710 Pearl East Cir At-risk Population Guest Lodging Hotel
Congregation Boani Places of
15 Shalom 1527 Cherr vale Rd At-risk Population Assembly Church
Boulder Meeting of Places of
16 Friends 1825 U land Ave At-risk Population Assembly Church
Places of
17 Unity Church 2855 Folsom Ave At-risk Population Assembly Church
S Broadway Church Places of
18 of the Nazarene 300 S Broadway At-risk Population Assembly Church
Boulder Valley Places of
19 Assembly of God 3901 Pinon St At-risk Population Assembly Church
Congregation HAR Places of
20 Ha Shem 3950 Baseline Ave At-risk Population Assembly Church
Century Boulder Places of
21 Theater 1700 29th St At-risk Population Assembly Theater
22 1897 Sumac Ave At-risk Population Schools After School Care
23 3130 Re Tier Dr At-risk Population Schools After School Care
Shining Mountain Private K-12
24 Waldorf School 1179 Union Ave At-risk Population Schools Schools
Rocky Mountain Private K-12
25 School 5490 Spine Rd At-risk Population Schools Schools
Crest View Public K-12
26 Elementary School 1897 Sumac Ave At-risk Population Schools Schools
Columbine Public K-12
27 Elementary School 3130 Re tier Dr At-risk Population Schools Schools
28 KBCO Radio 2500 Pearl St. Essential Services Communications News Papers
Crest View
29 Elementary 1897 Sumac Ave Essential Services Communications Warning Systems
30 Columbine School 3130 Re Tier Dr Essential Services Communications Warning Systems
Pridemark Paramedic Emergency Emergency
31 Service 3297 Walnut St. Essential Services Medical Medical
Emergency Emergency
32 Yards 5050 Pearl St Essential Services Response Responders
7
33 Boulder Fire Station 5 4365 19th St. Essential Services Public safety Fire
34 Public Safety Building 1805 33rd St. Essential Services Public Safety Police
Transportation
35 RTD 1707 Exposition Essential Services Lifelines Mass Transit
Xcel Boulder
36 Terminal 2500 28th St Essential Services Utility Plant Power
Hazardous Chemical and Pharmaceutical
37 Roche 2075 55th St. Materials Pharmaceutical Company
Hazardous Gasoline and
38 Total Petroleum 1884 Folsom Ave Materials Propane Service Station
Hazardous Gasoline and
39 Sinclair 2375 Canyon Blvd Materials Propane Service Station
Parks and Recreation Vital Normal Government
40 Maintenance 5050 Pearl St Services Operations Maintenance
Boulder County Clerk Vital Normal Government
41 and Recorder 1750 33rd St Services Operations Public Records
Vital Normal Postal and
42 Fed Ex 2205 Central Ave Services Shipping Parcel Service
Vital Normal Postal and
43 United Parcel (UPS) 3795 Frontier Ave. Services Shipping Parcel Service
Vital Normal Postal and
44 US Postal Facility 1860 38th St. Services Shipping US Post Office
45 3650 Martin Drive At-risk Population Congregate Care Da Care
46 Minders Da Care 3685 Martin Drive At-risk Population Congregate Care Da Care
Boulder Critical Facilities in the
500-yr Floodplain
f
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Ai-risk Population
teat 0 Essential Services
A Hazardous Materials
Vaal N3rmai Services
8
Staff is developing management strategies for the above critical facilities. These strategies are as follows:
Management Use
Strategy Types
1,6 Administration and Management
4 After School Care
4 Assisted Living
0 Bed and Breakfast
3 Bulk Fuel
3 Chemical Company
3 Chemical Plant
1 Church
1,5 Clinic
1 Community Center
1,6 Courts and Jails
4 Da Care
1,6 Emergency Medical
1,6 Emergency Responders
7 Federal Offices
6 Fire
1,6 Hospital
2 Hotel
4 Independent Living
0 Library
1, 3, 6 Maintenance
1, 3, 6 Maintenance and Equipment
1,3 Major Industries
0 Mass Transit
1 Meeting Hall
2 Motel
0 News Papers
0 Parcel Service
1,6 Permitting and Inspection
1,3 Pharmaceutical Company
6 Police
1,6 Power
4 Pre-schools
4 Private K-12 Schools
4 Public K-12 Schools
1,6 Public Records
4 Public Universities
0 Radio Station
4 Senior Housing
3 Service Station
1,6 Sorts Arena
0 Student Housing
1,6 Telephone
1 Theater
0 US Post Office
4 Vocational Centers
6 Warning Systems
1, 3, 6 Wastewater
1, 3, 6 Water
9
Management Strategies:
0 Remove from critical facilities definition.
1 Only regulate facilities with an occupancy limit above 50. Upon change of use, new use or use
expansion these facilities will need to develop an emergency management plan.
2 Upon change of use, new use or use expansion these facilities will need to develop an emergency
management plan. These plans will need to be located on the door of each room.
3 Regulate facilities that store hazardous chemicals. Upon change of use, new use, or substantial
modifications and substantial improvements all hazardous materials must be located above the five
hundred-year base flood elevation or be floodproofed to a foot above this elevation. For all other
modifications proposed or modified hazardous material must be located above the five hundred-year
base flood elevation or be floodproofed to a foot above this elevation.
4 Regulate facilities that provide care for 12 or more children/students/residents. Upon change of use,
new use or use expansion these facilities will need to develop an emergency management plan.
5 For urgent care, emergency care and dialyses clinics regulate to management strategy 6. Remove all
other clinics from critical facilities definition
6 Upon change of use, new use, or substantial modification/substantial improvement, the critical facility
shall be, to the extent possible, located outside the limits of the five hundred-year floodplain.
Construction of critical facilities shall be permissible within the five hundred-year floodplain if no
feasible alternative site is available. Critical facilities constructed within the five hundred-year
floodplain shall be constructed on properly compacted fill and shall have the lowest floor (including
basements) elevated two feet above the one hundred-year base flood elevation or one foot about the five
hundred-year base flood elevation, whichever is higher. Access routes elevated to no less then 6 inches
below the five hundred-year base flood elevation shall be provided to all critical facilities to the extent
possible.
For all other improvements the proposed additions must be, to the extent possible, located outside the
limits of the five hundred-year floodplain. Construction of additions within the five hundred-year
floodplain shall be constructed on properly compacted fill and shall have the lowest floor (including
basements) elevated two feet above the one hundred-year base flood elevation or one foot about the five
hundred-year base flood elevation, whichever is higher. Access routes elevated to no less then 6 inches
below the five hundred-year base flood elevation shall be provided to all critical facilities to the extent
possible.
7 Federal offices will follow the management strategies of the building's land use.
Emergency management plans will at a minimum include either an evacuation plan (to be developed by a
licensed architect or licensed engineer) or a shelter in place plan (to be developed by a licensed structural
engineer)
If a facility has more then one use the management strategy of the most restrictive use will apply.
10
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` I Creek
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_ Streets
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f Lakes
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City of Boulder
0 0.5 1 2 3 Critical Facilities Located
Miles
W#9;~4 in the High Hazard &
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Attachment F within City Limits
Attachment B
CITY OF BOULDER
CITY COUNCIL AGENDA ITEM
MEETING DATE: June 2, 2009
AGENDA TITLE: Consideration of a motion to accept the April 28, 2009 Study Session
Summary on Flood Management and Mitigation Program and Fourmile Canyon Creek and
Wonderland Creek Flood Mitigation Plan
PRESENTERS:
Jane S. Brautigam, City Manager
Stephanie A. Grainger, Deputy City Manager
Maureen Rait, Executive Director of Public Works
Ned Williams, Director of Public Works for Utilities
Bob Harberg, Utilities Projects Coordinator
Christie Coleman, Engineering Project Manager
EXECUTIVE SUMMARY:
The purpose of the April 28, 2009 City Council study session was to present information and
discuss issues raised during the Nov. 10, 2008 public hearing regarding the Fourmile Canyon
Creek and Wonderland Creek Flood Mitigation Plan, including:
1. The intent and interpretation of current city flood policies;
2. Vulnerable populations to flooding, especially Crestview Elementary School;
3. The cost of the proposed property acquisition and flood mitigation plan; and
4. The priority of the proposed work compared to other flood hazard areas in Boulder.
STAFF RECOMMENDATION:
Staff recommends that City Council accept the April 28, 2009 City Council study session
summary included with this agenda item as Attachment A.
Suggested Motion Language:
Staff requests council consideration of this matter and action in the form of the following
motion:
Motion to accept the April 28, 2009 study session summary on Flood Management and
Mitigation Program and Fourmile Canyon Creek and Wonderland Creek Flood
Mitigation Plan included with this agenda item as Attachment A.
Attachment B
NEXT STEPS:
As part of this study session, staff presented information regarding the issues raised by council at
the Nov. 10, 2008 public hearing and will proceed with the following:
1. Prepared an agenda item to accept the Study Session summary,
2. Prepare an agenda item (third quarter 2009) to consider acceptance of the proposed Fourmile
Canyon Creek and Wonderland Creek flood mitigation plan,
3. Continue the development and analysis of the preliminary, draft regulations pertaining to
critical facilities and vulnerable populations located within the 100-year and 500-year
floodplains, along with identifying the impacts, and initiating a public review and comment
process within the next six months, and.
4. Develop a Flood Hazard Land Use Analysis to explore a range of strategies for reducing the
flood risk in flood prone areas. The analysis will inform recommendations to changes in
flood plain policies and regulations and will likely begin in 2010 or 2011.
Approved by:
Jane Brautigam
City Manager
ATTACHMENTS:
Attachment A: April 28, 2009 Study Session Summary on Flood Management and Mitigation
Program and Fourmile Canyon Creek and Wonderland Creek Flood Mitigation
Plan
Attachment B
ATTACHMENT A
April 28, 2009 Study Session Summary on
Flood Management and Mitigation Program and
Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Plan
PRESENT:
City Council: Mayor Matthew Appelbaum, Deputy Mayor Crystal Gray, Macon Cowles, Suzy
Ageton, Lisa Morzel, Angelique Espinoza, Ken Wilson, Susan Osborne.
Staff: Jane Brautigam, City Manager; Jerry Gordon, City Attorney; Stephanie Grainger, Deputy
City Manager; Maureen Rait, Executive Director of Public Works; Ned Williams, Director of
Public Works for Utilities; Alisa Lewis, City Clerk; Bob Harberg, Engineering Project
Management Coordinator; Annie Noble, Greenways Coordinator; Christie Coleman, Engineering
Project Manager; Kurt Bauer, Engineering Project Manager; Jeff Arthur, Engineering Review
Manager; Katie Knapp, Civil Engineer II.
Water Resources Advisory Board: Susan Iott
Consultants: David Love of Belt Collins West (formerly Love and Associates)
PURPOSE:
The purpose of the April 28, 2009 City Council Study Session was to present information and
discuss issues raised during the Nov. 10, 2008 public hearing regarding the Fourmile Canyon
Creek and Wonderland Creek Flood Mitigation Plan. Specifically:
1. The intent and interpretation of current city flood policies;
2. Vulnerable populations to flooding, especially Crestview Elementary School;
3. The cost of the proposed property acquisition and flood mitigation plan; and
4. The priority of the proposed work compared to other flood hazard areas in Boulder.
PRESENTATION:
Following introductions of staff, Bob Harberg presented an overview of the topics to be
discussed and identified questions to help frame City Council's discussion. Harberg then
presented the following:
a) A summary of the Fourmile Canyon and Wonderland Creek previous studies and work
efforts, current hydraulic conditions and recommended flood mitigation strategies.
b) A description of the current flood mitigation planning approach including an overview of
structural versus non-structural mitigation approaches, flood mitigation objectives,
property acquisition examples, current policies and examples of past projects.
Christie Coleman then provided a summary of the draft critical facilities regulation including:
c) An overview of the management strategies for hazardous materials, essential services and
vulnerable populations.
d) A description of the critical facilities located along Fourmile Canyon Creek and
Wonderland Creek.
Attachment B
e) A description of the existing flood conditions adjacent to Crestview Elementary School
along with proposed mitigation measures and emergency response plans.
Harberg then continued by presenting the following:
f) An example of the Fourmile Canyon Creek flood hazard land use analysis.
g) A summary breakdown of the costs associated with the Fourmile Canyon Creek and
Wonderland Creek proposed mitigation measures.
h) A summary of overall program capital expenditures from 1990 to 2008.
i) A description of flood hazard areas in Boulder in relationship to those identified along
Fourmile Canyon Creek and Wonderland Creek.
j) The importance of protection of high hazard area along with a summary of structures
located in the high hazard zone.
k) A brief overview of the emergency response program.
1) A summary of flood hazard conditions along Fourmile Canyon Creek and Wonderland
Creek
Harberg concluded the presentation with the following recommendation for next steps:
m) Preparation of an agenda item to accept the study session summary,
n) Preparation of an agenda item to accept the Fourmile Canyon Creek and Wonderland
Creek Flood Mitigation Plan,
o) Continue the development and analysis of critical facilities regulation, and
p) Develop a flood hazard land use analysis.
Following the presentation, council was presented with the following questions:
1. Does council agree with staff's approach to flood mitigation planning and the role it plays
in Capital Improvement Program (CIP) project prioritization?
2. Does council have questions about current flood policies and how they are being applied
in the proposed Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Plan?
3. What feedback does council have regarding the development and analysis of preliminary,
draft regulations pertaining to critical facilities and vulnerable populations located within
the 100-year and 500-year floodplains?
4. What feedback does council have regarding the proposed Fourmile Canyon Creek and
Wonderland Creek flood mitigation plan regarding costs, benefits and priorities?
5. Does council have questions regarding the proposed next steps for either the Fourmile
Canyon Creek and Wonderland Creek flood mitigation plan or the draft regulations
pertaining to critical facilities and vulnerable populations?
CITY COUNCIL DISCUSSION:
Prior to addressing the specific study session questions, council asked clarifying questions and
provided comments. In general, the following clarifications and comments were provided:
Clarifications
a) Floods in Boulder will typically recede within 12 to 24 hours.
b) Flood studies include mapping of ditch flooding if hydraulically connected to the
drainageways.
Attachment B
c) The differential cost associated with containing the 100-year flood flow vs. containing
the high hazard flood flows, according to current staff flood mitigation recommendations,
is approximately $4-6 million.
d) Staff provided a summary of current flood education and outreach methods.
e) Staff explained its recommendation that commercial developers pay for proposed
mitigation measures along the northwest portion of Fourmile Canyon Creek due to the
benefits that will be derived from redevelopment of the site.
f) Staff explained why mitigation measures are needed and recommended in the Boulder
County enclave areas.
g) Staff explained that proposed mitigation measures cannot cause increased flood hazards.
h) Staff explained the process used to rank greenways objectives along drainageway
reaches. In the Greenways Master Plan, Boulder Creek and each of the tributaries has
been divided into reaches. Each of the greenways objectives was ranked high, medium or
low for each reach based on specified goals for each objective. The aquatic and
vegetative habitat for each reach was evaluated as part of a riparian habitat and aquatic
habitat assessment. This information was used to identify areas of habitat preservation or
restoration. Trail connections were ranked based on such criteria as population density
served and connectivity to major destinations.
i) Owners of properties located in high hazard zones have been contacted in the past but not
recently.
j) Staff explained that the critical facility structures presented in the Attachment E tables are
listed according to their most restrictive category, although it may be located in multiple
flood hazard areas (floodplain, conveyance zone or high hazard zone). For example, if a
structure is located in the high hazard zone, it is not again listed as being in the 100-year
or 500-year floodplains.
k) This study session packet and presentation has not been given to the school district.
1) The criteria used to develop and rank flood mitigation measures have not changed from
those used in the past.
m) The location, quantity, and type of hazardous and toxic materials have not been identified
by staff.
n) The gas station located at the intersection of Arapahoe and Folsom is located in the 100-
year floodplain, but the location of the storage tanks in relationship to the floodplain is
unknown.
o) Unlike Boulder Creek and South Boulder Creek, the establishment of stream gages along
the remaining drainageways is not considered useful because the small tributary areas
will create rapid streamflow increases before monitoring gages can accurately detect and
assess the event.
p) Boulder County does not typically implement major flood mitigation capital
improvements or acquire properties in high hazard zones because of funding limitations
and other priorities.
q) Construction of pedestrian underpasses typically cost between $1 million and 2 million
each.
r) Development in the 100-year floodplain frequently does not conflict with the wetlands
ordinance because wetlands do not usually extend far beyond the stream banks.
s) The city likely would have governmental immunity from a lawsuit relating to damages
claimed from flooding.
Attachment B
Comments from City Council
a) Council would like further discussion on emergency preparedness at another time.
b) The proposed critical facility regulation may need to include more restrictive regulations,
such as not allowing certain land uses in high hazard areas.
c) Residents along Fourmile Canyon Creek and Wonderland Creek should have been
invited to this study session.
d) A tape of this study session and a copy of the study session's PowerPoint presentation
should be made available to residents along Fourmile Canyon Creek and Wonderland
Creek.
e) Crestview Elementary School is not listed as being in the 100-year floodplain according
to the list of critical facilities in Attachment E.
f) Staff should coordinate with development of the University of Colorado's 2030 plan.
Summary of City C'ouncil's responses to the study session questions
1. Does council agree with staff's approach to flood mitigation planning and the role it plays in
Capital Improvement Program (CIP) project prioritization,
and
2. Does council have questions about current flood policies and how they are being applied in
the proposed Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Plan?
Council members generally expressed support for the approach to flood mitigation planning
and that existing policies were appropriate, with the following comments:
a) The current approach to flood mitigation should continue and is mostly in the right
direction.
b) Consider doing the least amount of work necessary with the structural improvement
approach to mitigate flood hazards.
c) Investigate whether Boulder County government/residents, especially in the enclaves,
should contribute funds for flood mitigation and property acquisition, especially those
receiving city sewer and water.
d) Flood mitigation work proposed along Fourmile Canyon Creek east of 28th should be
reconsidered and possibly scaled back.
e) Alternatives that leave drainageways in their natural state should be a priority.
f) Mitigation measures should be kept as "green" as possible, i.e. minimize use of asphalt
and concrete.
g) The need to disturb natural areas for the benefit of a few homes was questioned.
h) Removal of structures from the 100-year floodplain was questioned if the
removal/mitigation was only to reduce property damage. Focus removal efforts on
structures in the high hazard and conveyance zone.
i) The property acquisition and hazard identification aspects of the program are good.
j) Outreach and education, particularly with the Boulder Valley School District, is very
important.
k) Prioritization criteria for CIP projects are appropriate.
Attachment B
1) Develop an inventory to characterize hazardous and toxic materials in relationship to
flood hazards - important to understand the location and quantify of these materials in the
floodplain, including underground storage tanks.
3. What feedback does council have regarding the development and analysis of preliminary,
draft regulations pertaining to critical facilities and vulnerable populations located within the
100-year and 500-year floodplains?
Council members generally expressed support with the approach being taken to draft
regulations pertaining to critical facilities and some council members questioned if the
regulations would go far enough to safeguard residents and users of these facilities. The
following additional comments were made:
a) Schools, both public and private, need to be fully educated on the flood risks associated
with each particular school site.
b) Regulation of private schools and care centers should move forward.
e) A strategy to coordinate with the Boulder Valley School District (BVSD) and its
administration, faculty, students and parents should be developed.
d) The BVSD should develop flood emergency plans based on the city's flood modes.
e) Flood emergency planning will be raised at the next joint meeting of the City Council and
BVSD Board of Education.
f) Flood outreach and education should emphasize the likely short duration of flood
inundation in Boulder.
g) City staff should work with the Boulder Office of Emergency Management and the
University of Colorado regarding flood emergency management issues.
h) The city should consider requiring the retrofitting of structures located in the high hazard
zone, instead of waiting for redevelopment or remodeling, in order to achieve a shorter
compliance timeframe
i) Consider placement of flood hazard placards on rental properties as a check-off item
during rental inspections.
j) Critical facilities should be required to develop an emergency plan and provide annual
reporting.
k) The city should develop an inventory of hazardous and toxic materials that could be
impacted by flooding. The Fire Department may have an inventory of hazardous
materials.
1) The hotel / motel industry would be receptive to a discussion on flood hazards and should
be engaged.
m) Flood education and outreach to tourists and visitors should be considered.
n) Consider facilitating the creation of a neighborhood culture to identify local emergency
needs and associated assistance for residents living in flood hazard areas that have special
needs.
o) Although the Boulder Valley School District, as a state agency, may not be required to
submit for city development reviews and permits, the city should find a way to work with
the schools to notify, disclose and achieve a better level of flood protection.
Attachment B
4. What feedback does council have regarding the proposed Fourmile Canyon Creek and
Wonderland Creek Flood Mitigation Plan regarding costs, benefits and priorities?
City council members requested that proposed mitigation costs be presented to distinguish
the cost of containing high hazard flood flows vs. containing all 100-year flood flows.
5. Does council have questions regarding the proposed next steps for either the Fourmile
Canyon Creek and Wonderland Creek Flood Mitigation Plan or the draft regulations
pertaining to critical facilities and vulnerable populations?
Council members generally expressed support to consider the Fourmile Canyon Creek and
Wonderland Creek Flood Mitigation Plan as an agenda item in third quarter 2009 and that
development and analysis of preliminary draft regulations pertaining to critical facilities and
vulnerable populations located within the 100-year and 500-year floodplains should continue
to move forward within the next six months.
Attachment C
City Council Study Session
Flood Management and Mitigation Program
t and
/ Canyon and Wonderland
Creek Flood Mitigation Plan
April i 009
Presenters
Bob Harberg, Utilities Projects Coordinator
Christie • Engineering Project Manager
1
Other Contributors
Maureen Rait, Executive Director of Public Works
Ned Williams, Director of Public Works for Utilities
Annie Noble, Greenways Coordinator
Jeff Arthur, Development Review Coordinator
Katie Knapp, Floodplain and Wetlands Specialist
Kurt Bauer, Engineering Project Manager
2
Questions for City Council
1. Approach to flood mitigation
planning?
flood 2. Current policies?
3. Critical facilities?
4. Fourmile Canyon Creek and
Wonderland Creek flood mitigation
plan?
5. Proposed next steps?
Staff is suggesting the following questions to guide City Council's discussion at the
study session:
1. Does council agree with staff's approach to flood mitigation planning and the role
it plays in Capital Improvement Program (CIP) project prioritization?
2. Does council have questions about current flood policies how they are being
applied in the proposed Fourmile Canyon Creek and Wonderland Creek Flood
Mitigation Plan?
3. What feedback does council have regarding the development and analysis of
preliminary, draft regulations pertaining to critical facilities and vulnerable
populations located within the 100-year and 500-year floodplains?
4. What feedback does council have regarding the proposed Fourmile Canyon
Creek and Wonderland Creek flood mitigation plan regarding costs, benefits and
priorities?/
5. Does council have questions regarding the proposed next steps for either the
Fourmile Canyon Creek and Wonderland Creek flood mitigation plan or the draft
regulations pertaining to critical facilities and vulnerable populations?
3
Background Fourmile Canyon
and Wonderland Creeks
997 - 1999 - Identification of flood mapping
problem - Creek Canyon d-
0 1999-2007 - Flood mapping and mitigation studies
0 March 2007 - FEMA approves and adopts the flood
.pp •
& June 2007 - Final flood mitigation report by Love &
Associates
Recommendation
Board * March 2008 - Planning Recommendation
November 2008 - City Council Public Hearing Major Drainageway Planning documents previously developed in the 1980s
Flood mapping problem identified in 1997 - Fourmile Canyon Creek spills into
Wonderland Creek
1997-2007 - City develops flood mapping study and mitigation plans. Recognition of
the spill flow is the major issue associated with both the changes in the flood
mapping and the flood mitigation plan recommendations.
March 2007 - FEMA adopts the new flood mapping study
June 2007 - Love & Associates issues flood mitigation plan report
4
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The spill flow rate is significant and is estimated to be 1,600 cfs under the 100-year
storm event.
This is equal to 1.5 times the flow in Boulder Creek during bank full conditions (we
have not seen bank full conditions since the spring of 1995.)
The spill flow leaves Fourmile Canyon west of Broadway and enters Wonderland
Creek west of 19th St.
Recognition of the spill has decreased the floodplain area along Fourmile Canyon
Creek downstream and significantly increased the floodplain area along Wonderland
Creek downstream.
The vast majority of the existing development along Wonderland Creek occurred
prior to recognition of the spill.
5
Recommended Flood Mitigation
+ Strategies
• Status • • . reaches • 111 feet)
• Floodproofing of Individual Structures (9
reaches; 111 feet)
• Hazard Zone Containment (8 reaches;
111 feet)
• 100-year Flood Containment (3 reaches;
.111
The staff recommended flood mitigation plan consisted of several strategies.
Strategies included 1) status quo, 2) high hazard zone containment, 3) floodproofing
of individuals structures and 4) 100-year flood containment.
Strategies were tailored to various stream reaches, defined by intersecting
roadways.
6
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5.
For example along Wonderland Creek Reach 5 was defined between 26th St. and
28th St. Containment of the 100-year flood flows is recommended for this reach
because of the benefit-cost analysis.
7
Importance of Flood
Mitigation Planning
Prioritize CIP Projects
• Inform development standards and zoning
Coordinate other activities and
objectives • Program)
• Positioning for federal funding
Flood mitigation planning is important because it provides information used to:
1. Prioritize CIP projects
2. Inform development standards and zoning
3. Coordinate with other activities and objectives through the city's transportation
and greenways programs
4. Position the city for possible federal funding
8
BVCP Policy 4.22
+ Non-Structural Approach
• Use non-structural approach wherever
possible
• Preserve natural and beneficial functions of
•floodplains
• structural approaches - natural
appearance
• Boulder Creek non-containment policy
eliminated
One of the important policies from the Boulder Valley Comprehensive Plan is the
non-structural approach policy
It states that the city should use non-structural measures where ever possible to
preserve the natural and beneficial functions of floodplains
The policy allows structural approaches that have a natural appearance
The Boulder Creek non-containment policy was eliminated during the last major
update of the BVCP in 2005
Although containment of the 100-year flood may not always be desirable,
containment of the high hazard zone is a flood mitigation priority
9
Flood Mitigation
Contain • hazard flood zone
Property acquisition
Over b. excavation
• Major roadway crossings designed for
0100-year event
• Contain 100-year flood event
depending on benefit/cost analysis
10
The city has focused its efforts on the following flood mitigation objectives:
1. Contain high hazard flood zone
* Property acquisition
* Over bank excavation
2. Major roadway crossings designed for 100-year event
3. Contain 100-year flood event depending on benefit/cost analysis of potential for
future property damage due to floods
10
i•
Notable project along Boulder Creek occurred in 1993 in collaboration with the
Boulder Valley School District
Focus was on containment of the high hazard zone near Boulder High School.
Nine properties were purchased and the associated structures removed.
The over bank area on the north side of the creek, south of Arapahoe, was
excavated and graded to provide for additional flood conveyance and the
construction of park and athletic fields
Excavation outside of the main channel of the creek is called "overbank" excavation
and is used where ever possible to avoid sensitive riparian and wetlands areas
associated with the main stream channel.
11
x~ ,r
d f
0 .
t
Picture shows Bear Canyon Creek underpass at South Broadway
The underpass is designed to convey the 100-year flood event underneath the
roadway to allow emergency access during a 100-year flood event
Similar to Fourmile Canyon and Wonderland Creek underpasses proposed at 19th
St., Violet Ave., Upland Ave., 26th St., and 28th St.
Jointly funded with Transportation money.
12
ice. . • • •
f
ilk
h
44
i x
Ti JIM,.
e+'~ V
Af~
Picture shows Bear Canyon Creek through Martin Park
This drainageway segment is designed to contain the 100-year flood event
It is similar to proposed segments along Fourmile Canyon and Wonderland Creek
that would provide flood mitigation and pedestrian access such as the Violet and
Elks parks sites along Fourmile Canyon Creek.
13
Goose Creek
upstream of 28th St.
i
14
Picture shows Goose Creek upstream of 28th St.
This drainageway segment is designed to contain the 100-year flood event
It is more structural than the proposed improvements along Fourmile Canyon Creek
and Wonderland Creek.
14
ti
Picture shows Bear Canyon Creek near the intersection with Gilpin Drive
This drainageway segment is designed to contain the 100-year flood event
It is similar to proposed segments along Fourmile Canyon and Wonderland Creek
that would provide flood mitigation and pedestrian access such as along
Wonderland Creek between Foothills Parkway and 26th St.
15
Critical Facilities
Regulation Includes:
1' •
sManagement strategies for:
1. hazardous materials,
2. vulnerable populations,
3. essential services
16
In an effort to reduce the damages to infrastructure and strengthen life safety responses, city staff is
developing regulations pertaining to critical facilities located in the 500-year floodplain.
These preliminary regulations define a critical facility, for floodplain purposes, as a facility, including
without limitation, a structure, infrastructure, property, equipment or service, that if flooded may result
in severe consequences to public health and safety or interrupt essential services and operations for
the community at any time before, during and after a flood.
In addition to attempting to define critical facilities, staff is also developing management strategies for
these facilities that will strengthen emergency preparedness and reduce, over time, the type and
number of facilities exposed to flood risk.
The developed management strategies can be broken into the three categories of:
hazardous materials are facilities such as gas stations, industrial chemical storage
areas and the like
vulnerable populations which include daycares, schools, nursing homes, places
where people congregate and the like
and essential services which includes police stations, fire stations, hospitals,
government operations and the like
Attachment E of your packet contains detailed information on the critical facilities regulation and
proposed management strategies.
Next slide please
16
Critical Facilities
.g- - Strategies:
Hazardous Materials-
must or be floodproofed to a foot above this elevation
Essential Services-
should be located outside the 500-yr floodplain
with viable access routes
Vulnerable Populations-
most develop emergency management plans
that include evacuation shelter
place plan 17
Hazardous Materials:
At a general level this strategy requires all hazardous materials to be located above the five
hundred-year base flood elevation or be floodproofed to a foot above this elevation.
Critical Facilities:
At a general level the critical facilities will, to the extent possible, located outside the limits of the five hundred-
year floodplain. Construction of critical facilities shall be permissible within the five hundred-year floodplain if no
feasible alternative site is available. Critical facilities constructed within the five hundred-year floodplain shall be
elevated two feet above the one hundred-year base flood elevation or one foot about the five hundred-year base
flood elevation, whichever is higher. Access route which are traversable in flooding events up to the 500 year
flood should be provided.
Vulnerable Populations:
facilities with any single room occupancy limits above 50, schools with 12 or move students, daycare centers
with 12 or more children, group homes, or residential or congregate care facilities with 12 or more residents
shall develop an emergency management plan upon change of use, new use or expansion.
Hotels, motels and the like shall develop emergency management plans that will be located on the door of each
room.
The emergency management plans will at a minimum include either an evacuation plan or a shelter in place
plan
Next Slide Please
17
Critical Facilities
+Wonderland and Fourmile Canyon Creek Critical Facilities:
• Crestview Elementary - 1100-yr .
Shining Mountain Waldorf School- 100-yr .
Boulder Waldorf Kindergarten 100-yr .
Broadway • Gas • 100-yr .
• The Atrium: Brookdale Senior Living - Will be
• removed • the 100-yr .
• Diagonal AMOCO Gas Station - Will be removed
from 100-yr the floodplain
• Wynwood at Ridge Point - Will be removed from
the 1100-yr . and Conveyance • -
18
With respect to Wonderland and Fourmile Canyon Creek, there are 6 critical
facilities located in the 100-yr floodplain and one facility located in the conveyance
zone.
Five of these facilities house vulnerable populations and two store hazardous
chemicals.
The proposed flood mitigation plan would remove three critical facilities from the
100-year floodplain and one facility from the conveyance zone.
Next Slide Please
18
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aru.tr.UUlilq~::iJIt1YeILrif. b~
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Legend
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46
CHy Of Boulder
M blbn -I-d 8 Fournnk
'6 M Canyon C-k f laoplalns
Staff was asked to investigate the specific emergency plan for Crestview
Elementary School.
The proposed flood mitigation plan will not eliminate this school from the 100-year
floodplain but will increase the ability of emergency response personnel to access
flooded areas along Fourmile Canyon and Wonderland creeks by construction of
100 year flood improvements at the
F6.. tee, is The
construction of these structures will allow access to Crest View from storm events
up to the 100 year event.
However until these improvements are completed, sheltering in place may be the
best plan. In this event the existing building would provide substantial protection
even though the first floor of the building would be partially flooded.
To minimize this flooding, It has been recommended to the BVSD staff that they
consider flood proofing the existing structure to minimize the entry of water.
This information has been discussed with BVSD/Central Administration staff and
Crestview Elementary School administration staff, but a full and complete resolution
and consensus regarding the best action has not been reached.
Next Slide Please
19
File Cony- Creek HHZ A Convey o..ce Flood Zone D<li- i-
- v„m.ath
Legend _ ,S •-4, . { i \
y i+ ~.Fees ~ Y 4ialrl n
In addition to the critical facilities ordinance, staff plans to perform a flood hazard
land use analysis
This analysis was prompted by the fact that a significant number of parcels with
redevelopment potential have more than 50% of their land area in some portion of
the floodplain
Current city floodplain regulations do not prevent redevelopment of these properties
but require suitable flood protection measures and allow on-site structural mitigation
of high hazard and conveyance zone impacts
Although the city-wide analysis is not complete, a portion of the analysis was
completed during the review of the proposed flood mitigation plan
This slide presents the results of the analysis for an area located adjacent to
Fourmile Canyon Creek and west of Broadway - Reach 6a
Utilities Division and Planning Department staff worked together to identify an
alternative that would contain the high hazard zone north of the creek so that
redevelopment would be possible as identified in the North Boulder Sub-community
Plan
The cost of the proposed improvements would be borne by the private property 20
n1A/nP rC
• Considerations
• City Capital Costs
Property acquisition - $4-6 million
*Channel improvements - $10-12 million
Roadway crossings - $8-10 million
• Private Property Owner Costs
*Floodproofing - $15-20 million
21
The next discussion concerns the cost of the proposed flood mitigation plan
City Capital Costs
Property acquisition - $4-6 million
Channel improvements - $10-12 million
Roadway crossings - $8-10 million
Private Property Owner Costs
Floodproofing - $15-20 million
Floodproofing costs would be required by the city's existing regulations as a result of
significant remodeling or redevelopment
21
Summary of Capital Expenditures
1990-2008 (in 2008 Dollars)
Other, Water Quality
and Greenways,
$7,1010,000
Storm Sewers,
$7,200,000 _ Property Acquisition.
- 524.000.000
I
Major Drainageway
Improvements,
$39.100,000
Property Acquisition - $24 million
Major Drainageway Improvements - $39 million
Storm Sewers - $7 million
Other Water Quality and Greenways - $7 million
The largest expenditures were associated with Goose Creek ($19 million), Boulder
Creek ($15 million) and Bear Canyon Creek ($10 million)
Significant investments were also made prior to this period of time, but cost tracking
information is not as readily available
22
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-s
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i
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The next discussion concerns the priority of the proposed flood mitigation plan
compared to other flood hazard areas in Boulder
Boulder's Major Drainageways - 15 in all
Largest by far are Boulder and South Boulder Creeks
Fourmile Canyon Creek has a similar tributary area and 100-year flood flows as
Bear Canyon Creek
23
11 ••e I a
Number of
Drain- ewa Structures Assessed Valu
Boulder Creek/Boulder Slough 935 S 590,684.000
Fourmile Canyon 144 $ 38,362,200
Wonderland 361 $ 109,125,900
Two-mile Canyon 208 S 52,874,400
Goose 210 S 101,439,300
Elmer's Twomile 150 S 44,415,100
Sunshine Canyon 87 S 30,387,500
Gregory Canyon 127 S 47,789,200
South Boulder/Dry Creek No. 2 1,063 S 429,561 ,100
Skunk 200 S 65,842,900
Bluebell/Kings Gulch 43 S 13,003,400
Bear Canyon 93 S 34,744,400
Viele 0 S 0
Totals 3,621 $ 1,558,229,400
3,600 structures with an assessed value of over $1.5 billion within the city's 100-
year floodplain area
Many properties are insured with a maximum insured loss of $250,000 under the
National Flood Insurance Program
24
BVCP Policy 4.23
Protection • High Hazard Areas
• Prevent redevelopment of flood
damaged properties
• Acquisition program
Habitat and wetlands
• Trails and recreation
• Assess vulnerability of individual
structures
25
As I mentioned before, protection of high hazard areas is one the most important
priorities of the city's flood management and mitigation work program
BVCP Policy 4.23 states that the city should prevent redevelopment of significantly
flood-damaged properties in the high hazard areas
Prepare a plan for property acquisition in high hazard areas
Retain undeveloped high hazard flood areas in their natural state
Compatible uses include natural ecosystems, wildlife habitat, wetlands, trails and
open recreational facilities
Because of the large number of high hazard zone structures, staff has assessed the
vulnerability of each structure
Residential structures are considered a higher priority because alerting and
evacuation of residents is more difficult
This would be especially true during the middle of the night when people are
sleeping
25
D M 4
11.14 or Druinac2ewav
Boulder Creek~'Boukler Sloti-all 2
Folirllllle Callyoll 7
~N'oiiderlaiid 10
Twolllile Canvoll 21
Cioos,e 37
Elmer's Two-mile 0
Sulls1111le Canyon 4
Gregorv Calivoll 2q
Solltll Boulder/Dry Creek No. 2 3
Skullk 13
Bluebell'Kin¢'s GuIcll
Bear Callvoll~ 1
Viele C'llallllel 4
Total 132
Total of 178 structures in the high hazard zone
132 of these are residential structures
Goose Creek has the most with 37 followed by Gregory Canyon Creek with 29.
Two largest drainageways, Boulder Creek and South Boulder Creek have a
relatively small number of residential structures in the high hazard zone.
A total of 17 residential structures are associates with Fourmile Canyon and
Wonderland Creeks
26
• • I In .
_laior Drainaaewav 1997 2009
Boulder Creek~.Boulder Slouch 0
Fourrllile Ca114'oll j
Wonderland 0 2
Twomile Ca11y-on 0 1
Goose 22 0
Eliner's Two-mile 2 0
Sunshine Canyon 0 0
Gregory Canyon 7 7
South Boulder iDty Creek No. 2 0 0
Skunk 0 0
Bluebell;`K111tr5s Gulch 0 0
Bear Canyon 0 0
Viele Channel 0 0
Total 41 12
This information presents the highest priority structures based on the vulnerability of
the structure to extensive physical damage that may endanger the lives of
occupants
Gregory Canyon Creek has the highest number of most vulnerable structures
Fourmile Canyon and Wonderland Creeks have a total of 4 structures in this
category
Goose Creek through Mapleton and Branding Iron Mobile Home Parks
Note: the increase in most vulnerable residential structures for Wonderland Creek in
2009 is due to recognition of the spill flow from Fourmile Canyon subsequent to
1997.
27
Emergency Response
Considerations
Flood * Early detection network - Boulder and
South Boulder Creeks
* 20 40 minutes notice
* Adequate flood detection network not
available along other drainageways (no
stream gauges,, only rainfall gauges)
28
The anticipated capability of emergency management personnel to warn residents
prior to a flash flood event is a significant consideration in determining the
appropriate extent and priority of flood mitigation capital improvement project
work
Early flood detection network has been deployed on the largest drainageways -
Boulder and South Boulder Creeks
This consists of numerous rainfall and stream level gauges
Anticipated to provide 20- 40 minutes notice which is sufficient to activate sirens,
reverse 911, and radio and TV emergency broadcasts
Longer warning times may be available under other types of flood events that
develop more slowly due to extended periods of lower intensity rainfall
Adequate flood detection network not installed on the other drainageways (no
stream gauges, only rainfall gauges)
The other tributary drainageways are relatively small and can develop runoff that
produces flash flood affects in a very short period of time
It is unlikely that an early flood detection network could be designed for these 28
Why • Canyon and
Wonderland Creeks?
• High hazard zone risk
Critical • Limited flood detection network
and vulnerable
populations
• Property damage
Potential to collaborate with
Greenways and Transportation
29
Significant high hazard zone issues
Limited flood detection network
Critical facility and vulnerable population issues
Property damage issues
Potential to collaborate with Greenways Program and Transportation Division
29
Bear Canyon
August 2007
y ~
30
Boulder has its share of success stories. Previously constructed improvements have
already provided significant benefits to Boulder. For example, a significant storm
event on Aug. 15, 2007 along Bear Canyon Creek would have likely flooded a day
care center located immediately adjacent to the creek if flood mitigation work had
not been previously accomplished.
30
Next Steps
• Prepare an agenda item to accept the
Study Session summary,
• Prepare an agenda item to consider
acceptance of the proposed flood
mitigation plan, • •
• Continue the development and analysis of
the preliminary, draft regulations
pertaining to critical facilities
• Develop a Flood Hazard Land Use Analysis
31
As next steps, staff will:
1. Prepare an agenda item to accept the Study Session summary,
2. Prepare an agenda item to consider acceptance of the proposed Fourmile
Canyon Creek and Wonderland Creek flood mitigation plan, and
3. Continue the development and analysis of the preliminary, draft regulations
pertaining to critical facilities and vulnerable populations located within the 100-
year and 500-year floodplains, along with identifying the impacts, and initiating a
public review and comment process within the next six months.
4. Develop a Flood Hazard Land Use Analysis to explore a range of strategies for
reducing the flood risk in flood prone areas. The analysis will inform
recommendations to changes in flood plain policies and regulations and will
likely begin in 2010 or 2011.
31
Questions for City Council
1. Approach to flood mitigation
planning?
flood 2. Current policies?
3. Critical facilities?
4. Fourmile Canyon Creek and
Wonderland Creek flood mitigation
plan?
5. Proposed next steps?
32
Staff is suggesting the following questions to guide City Council's discussion at the
study session:
1. Does council agree with staff's approach to flood mitigation planning and the role
it plays in Capital Improvement Program (CIP) project prioritization?
2. Does council have questions about current flood policies how they are being
applied in the proposed Fourmile Canyon Creek and Wonderland Creek Flood
Mitigation Plan?
3. What feedback does council have regarding the development and analysis of
preliminary, draft regulations pertaining to critical facilities and vulnerable
populations located within the 100-year and 500-year floodplains?
4. What feedback does council have regarding the proposed Fourmile Canyon
Creek and Wonderland Creek flood mitigation plan regarding costs, benefits and
priorities?/
5. Does council have questions regarding the proposed next steps for either the
Fourmile Canyon Creek and Wonderland Creek flood mitigation plan or the draft
regulations pertaining to critical facilities and vulnerable populations?
32