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Home My WebLink AboutNon-Agenda Item - Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Planning Update CITY OF BOULDER WATER RESOURCE ADVISORY BOARD INFORMATION ITEM SUBJECT: Fourmile Canyon Creek and Wonderland Creek Flood Mitigation Planning Update FROM: Ned Williams, Director of Public Works for Utilities Bob Harberg, Utilities Project Coordinator Nancy Steinberger, Utilities Project Manager DATE: April 10, 2002 Background: In October 2000, City Council provided direction regarding the Fourmile Canyon Creek Flood Mitigation Plan based on city staff and Independent Review Panel (IRP) recommendations. The city and the Urban Drainage and Flood Control District (UDFCD), working with Love & Associates, have completed a draft Phase B (preliminary design) of the flood mitigation plan. The preliminary design has been developed consistent with the alternative recommended by city staff and selected by City Council. This includes provisions to contain flows (up to the 100-year storm level) that currently spill from Fourmile Canyon Creek into Wonderland Creek within the Fourmile drainageway (see Attachment A - Fourmile Canyon Creek Flood Mitigation Selected Plan.) A draft Phase B plan is now available for public review. It has been delivered to various city staff, the IRP and various neighborhood groups. It is also available in the Municipal Government Reference Center of the main Boulder Public Library (see Attachment B - Draft Phase B Executive Summary.) The city and UDFCD are also studying Fourmile Canyon Creek downstream of Highway 119 to its confluence with Boulder Creek. These studies were initiated based on the desire to contain spill flows within the Fourmile drainageway as mentioned above. This would create the potential for additional flood damages in the downstream area of Fourmile, and this factor needs to be considered. The entire study reach is located within unincorporated Boulder County. Two reports are available for public review: 1) Technical Memorandum Hydrology - Floodplain and Damage Analysis and 2) Technical Memorandum - Alternative Analysis (see Attachment C - Status of Fourmile Canyon Creek Downstream Study Efforts.) Concurrent with the Fourmile process, a flood mitigation plan for Wonderland Creek upstream of Foothills Parkway has been developed based on the assumption that spill flows will be contained in the Fourmile drainageway as mentioned above. Because the two streams are linked, this plan needs to be considered together with the plan for Fourmile. This plan is also available in the Municipal Government Reference Center of the main Boulder Public Library and an executive summary is being developed for distribution. Public Process to Date: A public meeting was held on Wednesday March 13, at 6:30 p.m. at the Boulder Meadows Community Room during which the Phase B preliminary design was presented and discussed (see Attachment D - Meeting Notes from March 13, 2002 Public Meeting.) Staff also met with MaryFran Myers of the IRP on March 21, 2002 (see Attachment E -Notes from Meeting with MaryFran Myers.) The IRP is currently considering the preliminary design and other flood mitigation related issues. A meeting with property owners in the downstream area is being scheduled for the week of April 22. A website has been developed and is available at: http://www.ci.boulder.co.us/publicworks/depts/utilities/proi ects/fourmile/index.htm Next Steps: Utilities Division staff will request a recommendation from the Water Resource Advisory Board after a public hearing (June.) The Greenways Advisory Committee will also be provided information concerning the flood mitigation plans. Public hearings with the Planning Board (July) and City Council (August) are also anticipated. Please contact Bob Harberg at (303) 441-3124 or e-mail at HarbergB@ci.boulder.co.us if you have any questions. Attachment A: Fourmile Canyon Creek Flood Mitigation Selected Plan Attachment B - Draft Phase B Executive Summary Attachment C - Status of Fourmile Canyon Creek Downstream Study Efforts Attachment D - Meeting Notes from March 13, 2002 Public Meeting Attachment E - Notes from Meeting with Mary Fran Myers of the IRP DRAFT November 27, 2000 Attachment A Selected Plan for the Fourmile Canyon Creek Major Drainageway Planning Study March 7, 2001 The plan selected by the City of Boulder (City), Boulder County (County) and the Urban Drainage and Flood Control District (District) (hereinafter all listed entities as a group may be referred hereinafter as "Sponsors") to be shown by Love & Associates, Inc. (Love) in the final Fourmile Canyon Creek (hereinafter referred as "Fourmile") Major Drainageway Planning Project Report (hereinafter called "Final Plan") is described in two parts that follow. The first part discusses the selected plan and the direction needed to complete the remainder of this project. The second part provides additional direction for the Final Plan. SELECTED PLAN AND DIRECTLY RELATED ISSUES General Direction The Selected Plan includes the following principle elements, goals and objectives: 1) Eliminate spill flows to Wonderland Creek in excess of those currently anticipated in the existing hydrology adopted by the Federal Emergency Management Agency. Provide a larger conveyance zone along Fourmile such that the residual 100-year floodplain is no large (i.e., covers areas) than are currently depicted on the FIRMS for City and County or have been found to be the 100-year floodplain limits and elevations delineated by Love under an agreement with City to update the FIRM for Fourmile, whichever is smaller. City owned property may be utilized for additional residual flood plains whenever feasible and causes no additional damages to structures owned by City. Use of City owned property is subject to further review by the respective City Department and Advisory Board. This should be close to, but not necessarily identical to the 50-year conveyance alternative presented in the Fourmile Canyon Creek Major Drainageway Planning, Phase A, dated June 2000 (hereinafter referred to as Phase A Report). In response to comments from the County and in accordance to the City's desires to incorporate these comments into the Final Plan, drainageway improvements along Four-mile, downstream of the current study limits, will need to occur before the upstream spill flows are contained. This may require the purchase and removal of structures and the enlargement of the drainageway system's capacity. The major elements of this plan include: a) Overall, an expanded drainageway capacity and, possibly, corridor b) Where consistent with project goals, maintain existing channel configuration c) Redirection of overflows from the northwest to Fourmile Selected Plan: Fourmile Canyon Creek 1 04/11/02 DRAFT November 27, 2000 d) Enlarged Fourmile's capacity e) Enlarged roadway crossings f) Modifications to irrigation ditch crossings g) Replacement and/or modification to pedestrian trails and crossings h) New and modified drop structures i) Sediment capture facilities and wetland mitigation j) Bank stabilization 2) The enlargement of the conveyance for Fourmile described under Item 1 above will require the purchase and removal of several structures identified in the Phase A Report and the reconstruction of several roadway crossings. Assume that the enlarged drainageway will remove any other structures from Boulder's high hazard zone. 3) Containing the 100-year flood along Fourmile within a larger drainageway is promising if the incremental project cost and environmental/social impact are minimal and the benefits associated with reduced property damage outweigh these incremental costs. Love has developed estimates to help guide the Sponsors in the decision if a larger channel in some of the reaches is justified in relation to the relative flood risks that may be associated with properties identified to be in the floodplain. 4) Show the redefined residual 100-year floodplain and floodway assuming the project is implemented. Recommend that in the interim, City and County regulate the floodplain defined by Love under separate agreement with City. 5) Recommend in the Final Plan that City and County continue to implement their current floodplain management regulations, including regulation of the high hazard and conveyance zone, and the regulation of the 100-year floodplain with flood proofing and elevation certificate requirements 6) Recommend in the Final Plan that City's drainage and flood control utility programs prioritize the acquisition of properties in the high hazard zone and of damaged properties in post flood situations. 7) Recommend in the Final Plan that the City and County continue to participate in FEMA's flood insurance Community Rating System and public education. 8) Recommend in the Final Plan that City and County reexamine and enhance as necessary their emergency preparedness and response programs, including flood forecasting, early warning and disaster coordination and assistance. Review these regulations and programs in light of recommendations provided by the Independent Review Panel in their September 28, 2000 report as part of the impending update to the Comprehensive Drainage Utility Master Plan. 9) Implementation of the recommended flood mitigation may increase flows in the Fourmile floodplain downstream of the limits of this study (approximately Highway 119) to Boulder Creek. Additional studies, which are beyond the current scope of the Selected Plan: Fourmile Canyon Creek 2 04/ 11 /02 DRAFT November 27, 2000 consultant's agreement, are needed to determine if properties located downstream of the study limits are adversely affected by implementation of upstream flood mitigation measures. Consultant is to propose on said additional studies to District, City and County. 9) Consider the various functions of the creek channels and their floodplains including flood conveyance, riparian habitat, open space, aesthetics, recreation, urban development, water quality and transportation. 10) Acknowledge that changes to the contributing watershed upstream can and will affect the flood hazard nature (i.e., runoff and in transport of sediment) of Founnile through City and County. The Final Plan should suggest that such changes be monitored and aggressively dealt with by the City and Count whenever they may increase flooding and sediment loads arriving at the upper reaches of the City. 11) The independent Review panel suggested that this study consider a variety of floodplain management tools, including channelization, improved crossing structures like bridges and culverts, acquisition and/or relocation of flood prone buildings to make more of the overbank floodplain accessible to flood flows, flood proofing of buildings that remain in flood prone areas, flood warning and emergency evacuation programs, and flood insurance. This involves assessment of individual structures, best dealt with detailed assessment of individual buildings and properties that typically occur at the time of development or redevelopment. Current city regulations require flood proofing and elevation certificates for these properties. Suggest in the Final Plan that the City and County include the examination of individual structures on a "time permits" basis to determine the effectiveness of such a program and that the city consider some type of incentive program for flood proofing existing structures throughout the city as part of the update to the drainage utility master plan. 12) The valley bottom of Fourmile Canyon Creek where it emerges from the mountain front west of Broadway is in many respects an alluvial fan. The channel, flow, and adjacent areas are therefore susceptible to rapid, drastic changes when intense upstream precipitation brings large loads of sediment and debris. As is now known, large flows, such as would occur during the 100- to 500-year floods are likely to spill out of the Fourmile channel and flow downhill across the fan south to Wonderland Creek. Recommend that the City consider the occurrence of the 500-year flood event in flood mitigation and emergency planning for Fourmile. Existing regulatory maps depicting the 100 and 500-year floodplain limits and flood damages were estimated for flood events up to the 500-year event as part of the Phase A Report. In so doing it should be recognized that any regulatory flood of level of protection can be exceeded by the vagaries of mother nature and that economics; affordability and some level of residual risk have to come into play when deciding what level of protection is desired. Suggest in the Final Plan that the City and County consider these eventualities in updating its drainage utility master plan. 13) Consider the probable depth of flooding for 50, 100, and 500- year frequencies and the high hazard zone. Selected Plana Fourmile Carryon Creek 3 04/11/02 DRAFT November 27, 2000 14) Consider and identify all critical hydraulic structures, such as bridges and culverts, where flood elevations would be increased due to insufficient flow capacity. Potential improvements to hydraulic capacity should be considered and determined for each of these structures. The most serious needs, in terms of risk to citizens and to adjacent buildings and infrastructure, should be considered and addressed as quickly as possible. 15) Consider the minimum level of protection being the flood 100-year event for all residential and commercial buildings near the creeks. The term "level of protection" should not be limited to channelization of the creeks. Instead, recommend in the Final Plan that the effects of a wide range of public and private action should be considered. 16) Buildings within the 100-year floodplain that are facing the greatest degree of risk should be considered for removal. This could be accompanied by reshaping the overbank floodplain to protect remaining buildings. Recommend that buildings facing a lesser degree of risk be elevated or otherwise flood proofed to suitable levels of risk. In addition, recommend that the owners of all buildings remaining in the floodplain should purchase flood insurance annually and should be informed of the costs of not doing so. 17) Critical buildings and infrastructure (schools, medical facilities, electric utilities, etc.) should be considered for treatment to reduce their vulnerability to the 500-year flood level. However, the cost of securing this level of protection may be high and must be prioritized with other flood risks in the Boulder community. Recommend the City consider a higher level of protection for critical buildings and infrastructure (schools, medical facilities, electric utilities, etc.) as part of its update of the drainage utility master plan. 18) Recommend the City develop and implement a specific flood warning and evacuation plan for Fourmile, the spill area, and Wonderland Creek. An early warning system triggered by storm forecasts and rain gauges located in the upper Fourmile watershed currently exist. Rapid rise stream gauges (high water alerts) are deployed along the Boulder Creek drainageway to supplement storm forecast and rain gauge information. Similar devices could be installed along the Fourmile Canyon Creek drainage basin. Because the distance along the Fourmile Canyon Creek drainageway is relatively short in comparison to Boulder Creek, similar rapid rise stream gauges would provide much less timely notice. Recommend the city consider supplementing the early warning system as part of its update to the drainage utility master plan, recognizing that when the rise in stage is detected on this upper reaches of the creek, it may be too late to evacuate residents. Severe flood forecasting, confirmed by rain gages in the upper watershed, are most likely features of an early warning system to provide warning in possibly sufficient time to take action, an unfortunate reality. 19) Recommend the City and County, in cooperation with the US Forest Service and other appropriate land management agencies, consider monitoring the condition of the upstream watershed on a regular basis and implement improvement programs as needed. An example would be to canvass, and mitigate, the vulnerability to wildfire west of Broadway in order to lessen the increase in flood risk that a wildfire could Selected Plan: Fourmile Canyon Creek 4 04/11/02 DRAFT November 27, 2000 pose for downstream residents. Recommend that when such a wildfire occurs, appropriate jurisdictions be called upon to re-analyze the flood hydrology and prepare a set of floodplain maps to reflect the new watershed conditions and flood risk; or implement measures after such a fire that would help mitigate its effects should a large rainstorm occur in the watershed. Suggest that a temporary rough estimate of enlarged flood zones would help bring awareness of what may happen in a large rainstorm and that physical action in the field, such as aggressive revegetate, mulching and sediment checks would help mitigate them until such time revegetation takes hold. The County currently requires best management practices for soil erosion and wildfire mitigation in the upstream Foothills basin through land use regulations and the site plan review process. The County also provides tax incentives to property owners who establish forest management plans encompassing wildfire mitigation and control of soil erosion through the United States Department of Agriculture Forest Service. Recommend the City consider additional monitoring and programs aimed at wildfire mitigation and prevention and other potential changes in the upstream watershed as part of the update to the drainage utility master plan. Reach-by-Reach Direction On a reach-by-reach basis, the Final Plan will include: Reach 6C and 6B - West Edge of Urban Development to Mouth of Fourmile Canyon 1) Channel work: a) Show no changes to the existing channel configuration. b) At the east end of the reach, show facilities needed to interceptor the 100-year flood flows and direct them towards the main channel downstream fo this reach. Reach 6A - Broadway to West Edge of Urban Development 1) Channel work: a) Channel conveyance capacity 3,300 cfs. Allow discharges in excess of 3,300 cfs to overtop the south bank and spill to the south. Basically follow the typical channel cross section Figure 8-3 the Phase A Report. b) Excavation of north overbank to increase channel capacity. This will require the removal of Rosewood Avenue located on the north bank of the creek between Broadway and the Self-Storage facility. c) Unless needed to achieve conveyance capacity, do not modify the channel invert or south overbank. d) Modified existing drops to match the proposed channel geometry. e) Revegetate, landscape and mitigate all wetlands damaged by the project. f) Modify the Silver Lake Ditch crossing as needed to achieve conveyance capacity. Selected Plana Fourmile Canyon Creek 5 04/1 1/02 DRAFT November 27, 2000 2) Pedestrian Trail a) No modifications to the pedestrian trail on the south overbank. b) Modified existing pedestrian crossing to match the proposed channel geometry. 3) Road Crossing Structures a) Enlarged Broadway box culvert. 4) ROW and Property Acquisition a) Acquisition in fee or easement of the needed right-of-way for the enlarged conveyance capacity channel, plus adequate maintenance access. b) Include and show the drainage right-of-way width of approximate 50 feet currently owned by the City. c) Use the existing Rosewood Avenue right-of-way on the north bank of the creek between Broadway and the Self-Storage units for channel expansion. 5) Miscellaneous a) Recommend the acquisition of off-site right-of way in fee or easements and the construction of the off-site transportation improvements and related utility relocations necessitated by the removal of Rosewood Ave. As an option look at securing flood easement south of Fourmile. b) Recommend that the development of the channel improvements be coordinated with the development of the Housing Authority's site located along the south bank. Reach 5B - West Edge of Violet Park Site to Broadway 1) Channel work: a) Channel conveyance capacity 3,300 cfs. Allow discharges in excess of 3,300 cfs to overtop the south bank and spill to the south. Basically follow the typical channel cross section Figure 8-3 the Phase A Report. b) Excavation of north and south overbanks to increase channel capacity. This will require the removal of Rosewood Avenue located on the north bank of the creek between Broadway and the Self-Storage facility. c) Unless needed to achieve conveyance capacity, do not modify the channel invert or south overbank. d) Construct new grade control structures as needed to stabilize existing head cutting. e) Remove and dispose debris and concrete slabs found along the north bank. f) Revegetate, landscape and mitigate all wetlands damaged by the project. Selected Plan: Fourmile Canyon Creek 6 04/1 1 /02 DRAFT November 27, 2000 2) Pedestrian Trail - a) Replace the existing pedestrian crossing immediately downstream of Broadway with one that does not impede the 100-year flood adversely. b) Show a pedestrian/maintenance trail along north overbank.. 3) Road Crossing Structures a) Enlarged Broadway box culvert. 4) ROW and Property Acquisition a) Acquisition in fee or easement of the needed right-of-way for the enlarged conveyance capacity channel, plus adequate maintenance access. The Phase A Report shows a 135-foot channel top width and an additional 75-feet of fee simple or drainage easement right-of-way. b) Include ands how the 60-foot drainage easement along the north bank that will be dedicated to City as a part of the development of the library site. 5) Miscellaneous a) Coordinate development of the channel improvements with the development of the City's Library site along the north bank. b) Coordinate the development of channel improvements with the proposed development/redevelopment of the property along the south bank. Reach 5A - Violet Avenue to West Edge of Violet Park Site 1) Channel work: a) Channel conveyance capacity 3,300 cfs. Allow discharges in excess of 3,300 cfs to overtop the south bank and spill to the south. Basically follow the typical channel cross section Figure 8-3 the Phase A Report. b) Excavation of south overbank to increase channel capacity. c) Unless needed to achieve conveyance capacity, do not modify the channel invert or north overbank, d) Repair of failed drop structure and stabilize erosion at east end of this reach. e) Removal and disposal of debris and concrete slabs found along the north bank. f) Revegetate, landscape and mitigate all wetlands damaged by the project. g) A sediment capture and wetland mitigation facility at the east end of this reach. 2) Pedestrian Trail a) A new pedestrian/maintenance trail near the south edge of the park outside the reparian area. b) A new pedestrian/maintenance access crossing structure c) A new multi-use underpass at Violet Avenue. Selected Plan: Fourmile Carryon Creek 7 04/1 1 /02 DRAFT November 27, 2000 3) Road Crossings a) Replace the Violet Avenue bridge with a structure that incorporates a multi-use underpass. 4) ROW and Property Acquisition a) Show that the needed right-of-way for the enlarged conveyance capacity channel, plus adequate maintenance access is located on City property. The Phase A Report shows a 170-foot channel top width and an additional 75-feet of fee simple or drainage easement right-of-way. 5) Miscellaneous a) Coordinate development of the channel improvements with the development of the City's Violet Park along the south bank. b) Provide for a plan that preserves and restores to a maximum extent possible, but still meet the conveyance goals, the existing creek riparian habitat and continue to allow the developed of a relatively level park surface of this site. Reach 4 - 26th Street to Violet 1) Channel work: a) Channel conveyance capacity 2,750 cfs with no in-channel freeboard. b) Excavation of north and south overbanks to increase channel capacity. c) In Phase B of this project, optimize the use of an array of flood mitigation techniques including channel alignment, cross section geometry, acquisition of floodprone structures; to provide the needed flood conveyance capacity to accommodate redirected spill flows, reduce flooding depths of flooded residences to a maximum practicable level, minimize disturbance to adjoining properties and maximize the long-term benefit to the riparian habitat. d) Unless needed to achieve conveyance capacity, do not modify the channel invert or north overbank. e) Provide for all needed grade control structures to stabilize existing head cutting. f) Daylight the piped section of creek between Upland Avenue and Violet Avenue. g) Revegetate, landscape and mitigate all wetlands damaged by the project. 2) Pedestrian Trail a) A newXedestrian/maintenance trail along south overbank between Violet Avenue and 19 Street. b) A new multi-use underpass at Upland Avenue, 19ffi Street and 26° Street Avenue. c) A modified pedestrian crossing at Riverside Avenue to match the proposed channel geometry. d) Show the removal of a pedestrian bridge between 19'h Street and Upland Avenue and at 26 h Street. Selected Plan: Fourmile Canyon Creek 8 04/11/02 DRAFT November 27, 2000 e) Provide for maintenance access to the channel between 19'h Street and 26'h Street. 3) Road Crossings a) Replace the existing bridge structures and incorporate a multi-use underpass at Upland Avenue, 19 ' Street and 26 h Street b) Remove the driveway culvert and install a cul-de-sac, on the north overbank, at the west end of Sumac Drive. c) Replace the Topaz Drive culvert. 4) ROW and Property Acquisition a) Show the needed right-of-way acquisition in fee simple or easement for the enlarged conveyance capacity channel, plus adequate maintenance access is located on City property. The Phase A Report shows a 85-foot channel top width. This reach is located on private property and is also located in Boulder County. b) A 25-foot drainage easement currently exists through this reach. c) Phase A Report identifies the acquisition of 2 residential properties. The City currently owns the Sumac residential property. Acquisition of it is not required, but a reservation of a drainage easement for construction of channel improvements and maintenance access across it has to be identified. In addition, the City currently owns the property at 1800 Violet, which is also required for construction of the channel improvements. Reach 3 - 28'h Street to 26`' Street 1) Channel work: a) Channel conveyance capacity 2,750 cfs with no in-channel freeboard. b) Excavation of north verbanks to increase channel capacity. c) In Phase B of this project, optimize the use of an array of flood mitigation techniques including channel alignment, cross section geometry, acquisition of flood prone structures and floodproofing of individual structures;to provide the needed flood conveyance capacity to accommodate the redirected spill flows, reduce flooding depths of flooded residences to a maximum practicable level, minimize disturbance to adjoining properties and maximize the long-term benefit to the riparian habitat. d) Unless needed to achieve conveyance capacity, do not modify the channel invert or south overbank. e) Provide for all needed grade control structures to stabilize existing head cutting. f) Daylight the piped section of creek between Upland Avenue and Violet Avenue. g) Revegetate, landscape and mitigate all wetlands damaged by the project. 2) Pedestrian Trail a) New pedestrian/maintenance trail along north bank between 26 h and 28 h Streets outside of riparian area. Selected Plan: Fourmlle Carryon Creek 9 04/ 1 1 /02 DRAFT November 27, 2000 b) Remove two pedestrian crossings and replace with one pedestrian crossing. 3) ROW and Property Acquisition a) Show the needed right-of-way acquisition in fee simple or easement for the enlarged conveyance capacity channel, plus adequate maintenance access is located on City property. The Phase A Report shows a 115-foot channel top width. This reach is located on private property and is also located in Boulder County. b) With the exception of an existing 25-foot drainage easement, the improvements for this reach, located west of the Farmers Ditch, are located on private property. c) The improvements located east of the Farmers Ditch are located on City property. 4) Miscellaneous a) Show needed modifications to the Farmers Ditch crossing. b) Coordinate development of the channel improvements with the development of the City's Elks Park site located along the north bank. Reach 213 - 30'' Street to 28 s Street 1) Channel work: a) Channel conveyance capacity 2,750 cfs with no in-channel freeboard. b) Excavation of north and south overbanks to increase channel capacity. c) In Phase B of this project, optimize the use of an array of flood mitigation techniques including channel alignment, cross section geometry, acquisition of flood prone structures and floodproofing of individual structures; to provide the needed flood conveyance capacity to accommodate the redirected spill flows, reduce flooding depths of flooded residences to a maximum practicable level, minimize disturbance to adjoining properties and maximize the long-term benefit to the riparian habitat. d) Unless needed to achieve conveyance capacity, do not modify the channel invert or south overbank. Existing berm along the north bank to remain. e) Provide for all needed grade control structures to stabilize existing head cutting. f) Daylight the piped section of creek between Upland Avenue and Violet Avenue. g) Revegetate, landscape and mitigate all wetlands damaged by the project. h) A new sediment capture and wetland mitigation facility at the west end of this reach. 2) Pedestrian Trail a) Lower the pedestrian/maintenance trail along the north overbank. b) Replace the existing pedestrian crossing. Selected Plan: Fonrn ile Canyon Creek 10 04/11/02 DRAFT November 27, 2000 3) ROW and Property Acquisition c) Show the needed right-of-way acquisition in fee simple or easement for the enlarged conveyance capacity channel, plus adequate maintenance access is located on City property. The Phase A Report shows a 160-foot channel top width. d) This reach is located on private property and is also located in Boulder County. a) The work on this reach is located within an existing drainage easement. Reach 2A - Downstream Limits of Palo Park Channelization to 30th Street 1) Channel work: a) Maintain the existing channel configuration. b) Recommend the monitoring of sediment deposition and the loss of flood conveyance capacity in this reach to determine when the restorative maintenance to reestablish channel capacity will need to be performed. Recommend the level of sediment accumulation at which sufficient freeboard is lost to mandate the convayance capacity restoration. c) When the monitoring so indicates, remove sediment and reestablish low flow channel. d) Revegetate, landscape and mitigate all wetlands damaged by the maintenance work. Reach 1 - State Highway 119 to Palo Park Channelization 1) Channel work: a) Maintain existing channel configuration e) Recommend the monitoring of sediment deposition and the loss of flood conveyance capacity in this reach to determine when the restorative maintenance to reestablish channel capacity will need to be performed. Recommend the level of sediment accumulation at which sufficient freeboard is lost to mandate the convayance capacity restoration. f) When the monitoring so indicates, remove sediment and reestablish low flow channel. g) Stabilize and restore eroding banks. b) Provide for needed grade control structure(s) to stabilize existing head cutting. c) Selectively remove woody debris to reduce downstream culvert/bridge clogging. d) Remove and replace 47th Street culvert. e) Revegetate, landscape and mitigate all wetlands damaged by the project. Selected Plan: Fourmile Canyon Creek 11 04/11/02 DRAFT November 27, 2000 EXECUTIVE SUMMARY Include an Executive Summary in the Final Report. Direct this summary at the general public and elected officials. This summary should, at the minimum, contain: 1. A brief summary of the planning process including the numbers of progress and public meetings. 2. A brief description of the decisions made by project sponsors during the development of this plan. 3. A brief summary of all design criteria specifically developed for this plan. 4. A brief summary of the following sections of the final report: Purpose, Study Area, Alternatives Analysis, and Preliminary Design. 5. A map showing the area and all major improvements. 6. A brief summary of hydrology to compare results of this plan to existing and historic conditions. 7. A tabular and narrative summary of costs showing costs for capital improvements, engineering/administrative/contingencies, land values, all sorted by drainageway reach, tributary, and outfall system. The reach length (miles), tributary catchment area (square miles), and their totals should also be included in the table. Incorporate the following note on each drawing: "This drawing is for master planning purposes and represents preliminary and conceptual engineering. Alternatives to this outfall system will be considered by local agencies and the Urban Drainage and Flood Control District provided the alternative offers an equivalent hydraulic capacity and stream stability. The alternative must comply with all requirements of the local jurisdiction and the Urban Drainage and Flood Control District. This drawing shall not be used for construction purposes. In addition, there may be State and Federal requirements that will need to be considered and met. This drawing is not a final design and shall not be used for construction purposes. " ADDITIONAL DIRECTION 1. Unit costs should be updated to reflect the most current costs available. 2. Include an Acknowledgements section listing all participants in the planning study (i.e., stakeholders). Include in the list their name, organization and function in the planning process (e.g., City of Boulder Utilities Department; Provided Review and Input. Or xxxx attended two progress meetings and provided the following input:. 3. All maintenance-access routes should be shown along all improved reaches. To the extent feasible, the alignment of these routes should be coordinated with existing and planned recreational trails identified using input provided by City, County and and Selected Plan: Fonrmile Canyon Creek 12 04/11/02 DRAFT November 27, 2000 local stakeholders. 4. - Report cost estimates of improvements based on jurisdiction where those improvements are located as well as in which reach. 5. Report cost estimates for maintenance of detention basins, channels, and storm sewer systems in the preliminary design. 6. Show a note on each sheet of the drawings: "Boulder County and the City of Boulder manage and regulate all land use change, development and redevelopment activities within the 100 year floodplains in order to prevent future flood damages to buildings and structures from the 100 year flood to a maximum extent possible, and to minimize damages from larger floods. The recommendations of this plan provide a set of options subscribed to by Boulder County and the City of Boulder in carrying out their flood plain management and regulatory responsibilities and obligations. " Selected Plan: Fourmile Canyon Creek 13 04/11/02 FOURMILE CANYON CREEK MAJOR DRAINAGEWAY PLANNING DRAFT PHASE B REPORT PRELIMINARY DESIGN EXECUTIVE SUMMARY Purpose and Objectives The purpose of the study is to analyze the existing and future drainage conditions with the Fourmile Canyon Creek floodplain, develop alternate drainageway planning concepts to mitigate existing flood damages, and prepare a preliminary design of the alternative selected by the Project Sponsors. The study is divided into two phases. The first phase (Phase A) covers the hydrologic, hydraulic, and alternate evaluation aspects of the project. The second phase (Phase B) covers the preliminary design of the selected alternate. This effort was undertaken under the Urban Drainage and Flood Control District Agreement No. 98-11.09 and was jointly sponsored by the Urban Drainage and Flood Control District (UDFCD) and the City of Boulder (City), also known as the Project Sponsors. Love & Associates, Inc. is the lead consultant for this project that, in cooperation with the Project Sponsors and Anderson & Company, has prepared this preliminary design report. Planning Process The planning effort began in June of 1999. Since that time, a series of progress meetings have taken place to exchange information and discuss ideas and findings of the study. The progress meetings were regularly attended by representatives of the sponsoring agencies as well as Boulder County. Concurrent with the progress meetings, a series of public meetings were conducted to discuss the planning effort and solicit public input. An Independent Review Committee (IRP) was convened to review the data, methodologies, assumptions, and recommendations of the planning effort. A discussion of the various alternatives investigated to mitigate flood damages and a recommendation of a preferred alternative were presented in a Draft Phase A Report, dated March 10, 2000. Many of the review comments on the Draft report received from the Project Sponsors, Boulder County and concerned citizens were incorporated into this Final Phase A Report, dated June 9, 2000. The Project Sponsors reviewed the Phase A report and made a decision on the alternative that is to be studied in greater detail in Phase B of this planning effort. The type, size, location of various improvements have been developed in greater detail. In the process, cost estimates will be refined and the relative priorities and phasing of these facilities will be identified. The Phase ES-1 _B report will serve as planning tool for the Project Sponsors and private development within the Fourmile Canyon Creek floodplain. Background Information The study area, shown in Figure 1-1, includes approximately four (4) miles of the Fourmile Canyon Creek floodplain from the mouth of the canyon to just downstream of the Boulder- Longmont diagonal (SH 119). An ongoing study has been undertaken by this consultant to extend this study downstream to the confluence with Boulder Creek. At this time it is envisioned that this expanded study reach will be included in the final Phase B report for Fourmile Canyon Creek. Major drainageway planning documents were previously developed for Fourmile Canyon Creek by Greenhome & O'Mara, Inc in 1984 and 1987 and were based on floodplain studies prepared for the Federal Emergency Management Agency (FEMA) by Greiner, Inc. Due to recent development that has occurred in the floodplain and inaccuracies found in the original studies the City of Boulder commissioned a re-study of the Fourmile Canyon Creek Floodplain in 1997. Love & Associates was retained by the City to complete a re-study and draft results were presented in Fourmile Canyon Creek Floodplain Study and Letter of Map Revision, dated May 18, 1999. The Draft Restudy indicated significant problems with the original study, resulting in additional properties located within the Fourmile Canyon Creek Floodplain. Of particular importance, the re-study identified reaches of Fourmile Canyon Creek west of 19a' 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 19a' Street but also result in an increase in the flows in Wonderland Creek. During the 100-year flood, approximately 3,300 cubic feet per second (cfs) is in Fourmile Canyon Creek near the mouth of the Canyon, of this amount approximately 1,600 cfs will overtop the south bank, spill and flow to Wonderland Creek. The remaining 1,700 cfs will remain in the Fourmile Canyon Creek Channel. Damage Analysis All property, structures and infrastructure within the 500-year floodplain were included in the damage analysis. The damage analysis was calculated using the UDFCD Methodology for Evaluation of Feasibility: Multi-Jurisdictional Urban Drainage and Flood Control Projects. Flood damages were calculated for the 2-, 5-, 10-, 50-, 100-, and 500-year flood events. For the economic analysis, a 50-year project life was chosen, which corresponds to a typical structure life. A 6% annual interest rate was selected, which corresponds to the cost of borrowed capital for the entities involved and a 3% annual rate of inflation was assumed. The resultant net discount rate used in present value calculations was 3%. The total present value of damages in the entire Fourmile Canyon Creek 500-year floodplain was estimated to be approximately $ 26 million dollars. ES-2 Identification of Potential Flood Mitigation Alternates Early in the study, a broad range of alternates were identified. These alternates were screened following an analysis and detailed discussions held during progress meetings on a reach by reach basis. An environmental assessment and opportunities analysis was undertaken by P. Kaia Anderson of Anderson & Company, Inc. This analysis utilized an extensive biological database, which had been collected on the City of Boulder stream tributaries, including Fourmile Canyon Creek. Habitat assessment matrices were developed to display the relative ranking of each reach of stream utilizing the previous studies. Wetlands and notable natural features were recognized. Environmental hazards and geomorphology was discussed. Environmental goals and objectives were developed and channel treatment concepts discussed. Flood engineering and environmental concerns were then molded into an alternate evaluation analysis for long term and short term benefits for the three final alternates: Alternate 1, 50-year channel improvements; Alternate 2, 100-year channel improvements; and Alternate 3, maintain existing channel configuration. Alternates 1 and 2 have many similarities, since both would construct a natural type of waterway following the general historic channel alignment. The purist definition of a "natural channel" would be impossible to re-construct since road crossings have been constructed, the channel has been straightened, the banks of the creek have been filled, and development has encroached on the natural floodplain. Therefore the term "natural channel" in this report is defined as a channel designed by an inter-disciplinary team of engineers, geomorphologists, and biologists to emulate a "natural" channel. Alternate 3, maintain existing floodplain configuration would adopt the new floodplain mapping without proposing mitigation improvements at this time. Non-structural methods including flash flood forecasting and warning systems and evacuation plans would be implemented. Flood insurance and floodproofing of structures would also be recommended (at the private property owner's expense). Floodplain regulations would be strictly enforced. This 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 mitigate spills and flooding to the south of Fourmile Canyon Creek and would offer no opportunity to eliminate flooding to the Waldorf or Crestview Elementary Schools. Reach by Reach cost estimates were prepared for the three final alternates. Each of the alternates will still incur an expected damage during flood events. Examples of these damages would include isolated bank erosion spots in the constructed "natural" channel alternate or wide spread damage in the maintaining of the existing floodplain configuration alternate. 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% ES-3 (6% annual interest rate minus 3% annual rate of inflation). Flood damages, benefits, alternate implementation costs and benefit/cost ratios for each alternate are summarize in the table ES-1. Table ES-1 Flood Damages, Benefits, Alternate Im lementation and Benefit/Cost Summa Damages Damages w/ Cost to Benefit Existing Implementation Implement Cost Alternate Conditions of Alternate Benefit Alternate and O&M Ratio Alt. 1 50-Year Channel 25,986,000 3,266,000 22,720,000 13,824,000 1.64 Alt. 2 100- Year Channel 25,986,000 1,021,000 24,965,000 19,149,000 1.30 Alt.3 Maint. Existing Channel 25,986,000 25,986,000 0 3,297,000 0 Because intangible benefits are not directly quantifiable in terms of a dollar value they are not 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. Bigger floods can and will occur. This statement holds true whether you are talking about a 10- year, 100-year or 500-year floods. The Fourmile Canyon Creek floodplain has not had a significant flood in the recent past. 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, or had to clean up after a flood in their neighborhood. Selected Alternate After review of the Phase A report, the Project Sponsors selected an alternate for each reach of Fourmile Canyon Creek to be developed further, and to be depicted in the final preliminary design report. See Appendix D for details. The Selected Plan includes the following principle elements, goals and objectives: Eliminate spill flows to Wonderland Creek in excess of those currently anticipated in the existing hydrology adopted by the Federal Emergency Management Agency. Provide a larger conveyance zone along Fourmile such that the residual 100-year floodplain is no larger than currently depicted on the FIRMs for City and County or larger than the 100-year floodPlain delineated by Love & Associates Inc. in the re-study to update the FIRM. This ES-4 should be close to, but not necessarily identical to the 50-year conveyance alternative presented in the Phase A Report. In response to comments from the County and in accordance to the City's desires to incorporate these comments into the Final Plan, Drainageway improvements along Fourmile, downstream of the current study limits, will need to occur before the upstream spill flows are contained. This may require the purchase and removal of structures and the enlargement of the Drainageway system's capacity. The major elements of this plan include: a) Overall, an expanded Drainageway capacity and, possibly corridor. b) Where consistent with project goals, maintain existing channel configuration. c) Redirection of overflows from the northwest to Fourmile. d) Enlarged Fourmile's capacity. e) Enlarged roadway crossings. f) Modifications to irrigation ditch crossings. g) Replacement and/or modification to pedestrian trails and crossings. h) New and modified drop structures. i) Sediment capture facilities and wetland mitigation. j) Bank stabilization. Reach by reach cost estimates were prepared for the selected alternate. These costs are presented in Table ES-2 below. Construction costs include a contingency factor of 40 percent for mobilization, engineering, administration, and construction contingency. Right-of-way costs include a markup of 5% for administrative costs. The overall estimated probable construction cost for the selected design is $13,906,000. I ES-5 Implementation Costs - Summary Reach Drainage Crossing Utilities Non-Flood Right-of-Way Sub-Total Facilities Structures Control Improvements $ $ $ $ $ $ Reach 1 $ 110,000 $ 395,000 $ 14,000 $ $ $ 519,000 Reach 2A $ - $ - $ - $ $ $ - each 2B $ 632,000 $ - $ - $ $ $ 632,000 Reach 3A $ 271,000 $ 331,000 $ - $ 58,000 $ $ 660,000 Reach 3B $ 258,000 $ 72,000 $ - $ 24,000 $ 138,000 $ 492,000 Reach 4 $1,151,000 $1,498,000 $362,000 $ 121,000 $ 1,629,000 $ 4,761,000 Reach 5A - East End $ 126,000 $ 467,000 $ 55,000 $ 26,000 $ - $ 674,000 Reach 5A - West End $ 228,000 $ - $ - $ 72,000 $ - $ 300,000 Reach 5B $ 369,000 $ 36,000 $ - $ 30,000 $ 143,000 $ 578,000 Reach 6A $2,332,000 $ 431,000 $280,000 $ 1,370,000 $ 877,000 $ 5,290,000 Reach 6B $ - $ - $ - $ - $ - $ - Reach 6C $ - $ - $ - $ - $ - $ Sub-Tots $5,477,000 $3,230,000 $711,000 $ 1,701,000 $ 2,787,000 Total $13,906,000 Phasin¢ As mentioned in the Project Sponsors selected alternate above, drainage improvements to reaches downstream (not yet defined) will have to be defined and implemented before the spills to Wonderland Creek, shown in this report, are contained. However, particular sites can be improved on a case by case basis without adversely impacting other properties. For example, a portion of Reach 4 can be constructed within the Park lands north of the Elks Club independent of other improvements without causing additional flood flows being conveyed to downstream reaches. These improvements should be designed assuming that the spill flows are contained for the 100-year onset. Additional Considerations It is important to realize that 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. Results of the Wonderland Creek study are discussed in a separate publication being prepared by City staff ES-6 Regardless of the flood mitigation alternative selected, this Phase B study recommends the City of Boulder and Boulder County adopt the current floodplain mapping as the regulatory floodplain. The regulatory Wonderland Creek floodplain is also in the process of being updated to reflect the spill flows from Fourmile Canyon Creek. All development within the existing floodplain should be in accordance with the City, County and Federal permitting requirements. ES-7 SHEET E-2: EOURMILE CANYON CREEK - STATION 307+00 TO 238+36 • Flatten channel slope to 1.3%. Reach 6A, 6B and 6C • Construct 2 drop structures. • 12 Structures recommended for acquisition. Channel Work • Remove debris and concrete slabs from the north bank. • 100-Year channel design capacity 3,590 cfs with no freeboard and no spills to Wonderland Creek. • Revegetation, landscaping and wetland mitigation of disturbed areas. • Construct interceptor channels at the east end of the reach to collect overbank flows and direct them towards the main channel. Pedestrian Trail • Excavate north and south overbanks and lower the channel invert approximately 2.5 feet to increase channel e Remove & replace the existing pedestrian crossing immediately downstream of Broadway. capacity. This will require the removal of Rosewood Avenue located on the north bank of the creek between . Construct pedestrian/maintenance trail along north overbank. Broadway and the Self-Storage facility. Exercise precautions when excavating in volatile organic • Construct pedestrian crossing to serve proposed library. containment plume area. • Rock walls along both sides of the channel are required to achieve the additional flow capacity. ROW/Property Acquisition • Flatten channel slope to 0.62%. . 145-foot minimum channel top width is required for the proposed channel improvements • Remove existing drop structures and replace with 12 drop structures. • The City of Boulder has identified a 60-foot drainage easement along the north bank that will be dedicated as • Revegetate, landscape and mitigate wetland damage of all disturbed areas. a part of the development of the library site. Channel improvements will require the acquisition of an additional 85-foot minimum ROW or drainage easements along the south bank. Pedestrian Trail • Lowering the existing pedestrian/maintenance trail on the south overbank. Miscellaneous • Remove and replace the existing pedestrian crossing. • Coordinate development of the channel improvements with the development of the City of Boulder Library site on the north bank and redevelopment of the property on the south bank. Road Crossing Structures • Enlarge the Broadway Box culvert by adding third 9'Hxl6'Wx60'L cell. No over topping of roadway Reach 5A - West End during 100-year event assuming 20% debris blockage. • 9'Hx43'Wx50'L RCB or equivalent clear span bridge at the proposed 9a' Street crossing. No over topping of Channel Work roadway during 100-year event assuming 20% debris blockage. . 100-Year channel design capacity 3,590 cfs with no freeboard and no spills to Wonderland Creek. • Excavate south overbank to increase channel capacity. ROW/Property Acquisition • No modifications to the channel invert or north overbank. • 100-foot minimum channel top width is required for the proposed channel improvements. • Revegetate, landscape and mitigate wetland damage of all disturbed areas. • City of Boulder currently has a drainage right-of-way width of approximate 50 feet. • Construct a sediment capture and wetland mitigation facility at the west end of this reach, • Expand the channel into the existing Rosewood Avenue right-of-way located on the north bank of the creek between Broadway and the Self Storage units. Pedestrian Trail • ROW and property acquisitions, associated with the roadway improvements, are discussed below. • Construct pedestrian/maintenance trail along south overbank. • Construct pedestrian crossing structure at west end of reach. Miscellaneous • Modify the Silver Lake Ditch elevated crossing to match proposed channel geometry. ROW/ProppAy Acquisition • Obtain off site right-of way and construct offsite transportation improvements consistent with the North . 250-foot minimum channel top width is required for the proposed channel improvements. Boulder Subcommunity Plan with related utility relocations necessitated by the removal of Rosewood • This reach is located on City of Boulder property. Avenue. Offsite roadway improvements, include an extension of 9t' Street from Cherry Street north to 10th Street, a westerly extension of Yarmouth Avenue from Broadway to the new 9'h Street extension, relocation Miscellaneous of Rosewood Avenue and the creation of 11t' Street between the relocated Rosewood Avenue and the • Coordinate development of the channel improvements with the development of the City of Boulder Violet Yarmouth Avenue extension. Park site located on the south bank. a • This mitigation approach will preserve the existing creek riparian habitat and will allow for the development Reach 5B of this park site. Channel Work • 100-Year channel design capacity 3,590 cfs with no freeboard and no spills to Wonderland Creek. • Excavate north and south overbanks and lower the channel invert approximately 2.5 feet to increase channel capacity. REA0H,6C REACH 6B 6A ' - REACH REACH 5A TEST 690 ds Oo aat_)>Qo~3 o c a Ooesic o` oo~35AO cie ~i j* . , GO oo N r fUdURE ANSP14YA \ - LEET,EANK - `'YARMOUTH AVE - CEPTgR kTEN$ AN EL E DETAIL ON T _ ` , h1Is SHEET - 'l ~ A EXISTING g PROPOSE fYllc LxsnNC loo YEAR, 00-YEAR FLOOgPLAIN ON T1#h' F FLOODPLAIN Mi ICAL)' a~ car S c RFiOCATED 'co"STRTRU { DROP STRUCTURE - \ ' .,.,CONSTRUCT R>~SEWOOD AVE. r (TYP:OF 2) DROP.i SPLITFLOW LINE ("VP of tz) " TRAIL RIGHT; BANK - FUTURE CHANNEL ROW/' J 1. INTERCEPTOR 1Y- - LIBRARY EASEMENT ' -SEE DETAIL REM,OVE CE - SRE - i(T1T+ICAL) THIS SHEETiA~ NOTES n 1. THIS DRAWING IS FOR MASTER PLANNING PURPOSES AND 2. TYPICAL CROSS SECTIONS LOOKING DOWNSTREAM ~US~1TN REPRESENTS PRELIMINARY AND CONCEPTUAL ENGINEERING. MULTI 9'Hz431Wx501 RCB►,r i 4L E , ~ ~ ALTERNATIVES TO THIS MAJOR DRAINAGEWAY SYSTEM WILL BE 3. MA=MAINTENANCE ACCESS CONSIDERED BY LOCAL AGENCIES AND THE URBAN DRAINAGE OR EWIYALENTCIF IU 0 G / y, AND FL000 CONTROL DISTRICT PROVIDED THE ALTERNATIVE SPAN BRIDGE', J 9t1'>'S EFCJPy~ACNJ/Hi 'TG~YEAk OFFERS AN EQUIVALENT HYDRAULIC CAPACITY AND STREAM f f A 400gYI STABILITY. 1HE ALTERNATIVE MUST COMPLY WITH ALL ON ON NE EXCf~'i~ATING IN' OLA,ALE TR.OODPLAIN YA1H REQUIREMENTS OF 'THE LOCAL JURISDICTION AND THE URBAN G 0 ANI4'CO AMIN / IMPROVEMENTS ` 6UJ,'fIWA R PJ:~1MNT (TEMPI I, 9M T 3U DRAINAGE AND FLOOD CONTROL DISTRICT. THIS DRAWING WILL ANT NOT BE USED FOR CONSTRUCTION PURPOSES. IN ADDITION, BOULDER TY D, THERE MAY BE STATE AND FEDERAL REQUIREMENTS THAT WILL BOULDDER HOUSING AND pLy._. MI AA NEED TO BE CONSIDERED AND MET. THIS DRAWING IS NOT A = 1 REPS TRAIL FINAL DESIGN AND SHALL NOT BE USED FOR CONSTRUCTION PURPOSES 100' ROW/EASEMENT -145' ROW/EASEMENT /~fO - C N IN REMOVE ROSEWOOD VENUE ROADWAY 10G-YEAR t00-YEAR WATER ,21 ! ,'E ACP, AF j IA Q~ WATER SURFACE ERRRACE SURFACE 0 6.9' ®8.5 AD YX /p~~~p~ V=8.ift/se EXISTING 3 6'W I LL CHANNEL ® V=8.Oft/sec BOTH SIDES) EXISTING U x O 9 9 10.5 CHANNEL 10 15 5.5 6.5 - Q l 8.5 - _ - 5 2.5 SPLL$ TO ~ - ( -WONDERLAND CREEi(//// f - . 2 1.5 0 1.5 2 2 1.5 1 LS 2.5 STING LOWER 10''RAIL PROPOSED 1OO-YEAR i PROPOSFDI 11NG CHANNELS FLCODPLAIN a CHANN0. I 'o' 1R UL 25' (TYPICAL) 18' 25' 46' 7 a 32' 18' 25' MA MA o x~ -TYPICAL CHANNEL SECTION REACH 56 -TYPICAL CHANNEL SECTION REACH 6A kt P SCALE: 1"=20' zso' Row/EASENtwT SCALE: 1"=20' G4~~~ P ► R~" ` a 100-YEAR WATER RPACE 0 4.9' WS,Sft/sec i 12' ACCESS _ -zod m' 84' ROW /EASEMENT ROAD 7' ROW/EASEMENT MON. 16 *t i 7T TOP WIDTH f' 0 7 2% i \ 2 2 2.5 4 I a k;or v~r > 0 5, 1 ltlph - 200 tt EXISTING PROPOSED t 5 PEE 4 FREEBOARD a G CHANNEL CHANNEL 10' TRAIL do MA EAST BANK 12' 03-sw CFS 12 s 24' 65. 0. 1100 CFS S-0.32% 185' S-0.277 L=400' I.. n REACH 5A-'NEST END. TYPICAL CHANNEL SECTION v-Soft/eec ELEFT BANK NLARGE EX STING W1FALL CHANNEL Y-S.oft/sec 2 a SCALE: 1"=20' SCALE: 1•=20' SCALE: 1•=20' so g Designed ByS!_ Date 9 5 , MAJOR DRAINAGEWAY PLANNING E E URBAN DRAINAGE AND ROOD CONTROL DISTRICT PLAN E2 m M aiar+~ csa'a~oa. soon-~~ Drawn By.DM - Date: FOURMILE CANYON CREED SHEEP J CITY OF BOULDER STA 307+00 TO STA 238+36 wa Date Revision A 30 ae Checked By D L Dote. PHASE 'B' PRELIMINARY DESK I VIE& RF1gi 5A EA$f ~A°fACH 4' MACH 313 REACH 3A as; aye hl ooeaw~o, , ei r ~ODMP4-0 ~ cfi ~ a ds ti CI~jNq 0 \CNwAY N ~ - rP ~j ✓ . 6y;pAss' G • r i s f t ~ Y " no m +aa ~ t ~ ` ' T~' PEE 1 1 -S - 1 •Y~~` - A7Qi., - - I men- 200 tL 7 . 0. R R G$ 6 S :SAN Y r N , ro . f1 w N 1 wv' gyp DROP' TRA4• C ? SiRU TURE_ - - ~''P _ . Ail M1f),QAy1JGNT.,. REPLACE U" -4-) Lf1UE 4 .REMOW,`T0PA2'DWE W,LYERMT - LARGE' DROtS - \ -.1 REPLACE -MIN; 4.3~hIz30'11hF401 - d y -SIRUCTU V(~ER,eR 'w/auLTI USE 'ON-S - R VAIMT Y el A DERP ,9111tA31fCSO~ JtCB fQIA a TRbI,cONNECTJox 'SPaN BRNGE 3 f F r EdUIVAffNT'-CLEAR SPAN BRIDGE CIA -SAE , AIL 1 E 1 y r 2§8, aEMOVe.A` 13 CE TRAIL " Gn i0•:MX - TIMEli& BRIDGE71t ~RJL'R~U5E INRQERPAS5. %--REPLACE TGfi;; d. GEOMETRY . zi3 W*dAl -4tCB QR EQUFIIIIT AN-1'1PJD(E . •ES00$IINO 100-YEAR ' sx SPAAI BRIDCft ~ / + ~ •~1.OODPLAIAY-(A~EN.Y may/ _ ,r ENT - 1. - SIRIAM 5N~AdWz r ♦ L fJ9UIYFl t CLEAR g I' - o - STABIJZE ~ Tfl U y' f. - y ~•-e>~~ , ~ pr~ ~ ~ BANKS - , , : • . ~ / _ wrf`~p t FUTURE • ,i, I IX A - 4' _ y - f _ PARK _ 11 .1 _ t -41 INiCP STRUCTURES To- G _ t 1 THIS DRAWING IS FOR MASTER PLANNING PURPOSES AND a - - •,REMOVE SUMAC Ater t' STABLIZE;1XK71N 2~ ~ ORNEWAY CULVERT W.AOCUPS (TYP bF.15 LARGEIlDkk - 4 REPRESENTS PRELIMINARY AND CONCEPTUAL ENGINEERING. ALTERNATIVES TO THIS MAJOR DRAJNAGEWAY SYSTEM WILL BE CONSIDERED BY LOCAL AGENCIES AND THE URBAN DRAINAGE •,i 1 }'!i • STRtiC1URE5 3 AND FLOOD CONTROL DISTRICT PROVIDED THE ALTERNATIVE FEF]:OCATE IX RECONSTRUG.T - w SANITARY SENT]t OFFERS AN EQUIVALENT HYDRAULIC CAPACITY AND STREAM "P~ - - TARAERS DITCH REMOVE 450STI GG_ STABILITY. THE ALTERNATIVE MUST COMPLY WITH ALL ' D• SHOE r \ VE _CROSSZNC SEE DETAIL', - ~ AN~CROSSINGS - REQUIREMENTS OF THE LOCAL JURISDICTION AND THE URBAN - - REMO DRAINAGE AND FI-000 CONTROL DISTRICT. THIS DRAWING WILL SOP IRUC T ONE-TRAIL CROSSING NOT BE USED FOR CONSTRUCTION! PURPOSES. IN ADDITION. 0 MATE.TOO-YEAR.. 1 STABIIRE STIAN. THERE MAY BE STATE AND FEDERAL REQUIREMENTS THAT WILL _ FLOQBF'LAN-VM11L CHANNEL 1 :SPLITS 11HAI RETURN NEED TO BE CONSIDERED AND MET. THIS DRAWING IS NOT A POTS,' ;-TO .Fi~I1RMkE~fXiEEK - • `#eEADCU75 (iVP Bk FINAL DESIGN AND SHALL NOT BE USED FOR CONSTRUCTION T PURPOSES - - x 2. TYPICAL CROSS SECTIONS LOOKING DOWNSTREAM { `~E X44 - G G~ O~tm qIA YFNF APL / 0 ON, 3. MA=MAINTENANCE ACCESS STREEfi t o E TR ROM, 4A ~ ~ ^ _ 94' ROW/EASEMENT 230' ROW/EASEMENT i VARIES 250' TO 160' TO MATCH AVAILABLE R.O.W. 135' # RESIDUAL 1DO-YEAR FLOODPLAINON °100-YEAR RESIDUAL WATER SURFACE 100-YEAR PARK CHEXISTING ANNEL ~dk a; WATER SURFACE FLOODPLAIN 0 7.2' WATER SURFACE PROPERTY 100-YEAR WATER TYPICAL BOTH V=7.9ft/sec ®6.5 SURFACE 0 4.8' E ° - 0 5.6' EXISTING w SIDES V=7.9ft/sec V=5.2ft sec V=6.2ft/sec GROUND EXISTING / ® ' 4 CHANNEL TRAIL GR(~.1ND rn0 7 6.9 6 6.5 I 3.5 5 4 8 _ 2 4 2.5 5.5 6 6.9 2 \ 2 / I 1.5 rn~ 2 2 I 2 1.5 1.5 °i D PROPOSED 10' TRAIL 10' TRAIL 0PROPOSED 1 0 0 2 PROPO 10' TRAIL 0 CHANNEL AMA OR MAINTENANCE PROPOSED CHANNEL CHAN EL AND MAINTENANCE 65' 95' ACCESS CHANNEL 25' 68"42' ACCESS 40' 14' q0' MA 201' 29 REACH 5A-EAST END. TYPICAL CHANNEL SECTION REACH 36-TYPICAL CHANNEL SECTION REACH 4-TYPICAL CHANNEL SECTION WIDEN TO 230' WIDER TO 163' REACH 3A-TYPICAL CHANNEL SECTION SCALE: 1"=20' SCALE: 1"=20' AT FUTURE PARK AT FUTURE PARK SCALE: 120' SCALE: 1"=20' IDgL ACCESS BRlQQF o D"i9ned By. SOL Dote: 9 5 01 URBAN DRAINAGE AND ROOD CONTROL DISTRICT MAJOR DRAINAGEWAY PLANNING 2 Lw,-»» Dro.n BY DM oulc 9/5/01 FOURMIL E CANYON CREEK crA Ae1017CPLAN T/'1% ClrA 1711108 SHEETS E3 SHEET E-3; FOURMILE CANYON CREEK - STATION 238+36 TO 173+86 Reach 5A - East End • Channel improvements will require the acquisition of an additional 69 feet of right-of-way or drainage easement through this reach and require acquisition of 2 residential structures. The City currently owns the property at 1800 Channel Work Violet and 2446 Sumac, which are required for construction of the channel improvements. • 100-Year channel design capacity 3,590 cfs with no freeboard and no spills to Wonderland Creek. Miscellaneous • Excavate south overbank to increase channel capacity. • During final design optimize channel alignment and cross section geometry to convey the required flood flows, • No modifications to the channel invert or north overbank. minimize disturbance to adjoining property and maximize the long-term benefit to the riparian habitat. • Revegetate, landscape and mitigate wetland damage of all disturbed areas. • Construct large multi-crest drop upstream of Violet Avenue and relocate existing 10-inch sanitary sewer. Reach 3B Pedestrian Trail Channel Work • Construct pedestrian/maintenance trail along south overbank. • 100-year channel design capacity 3,581 cfs with 0.4 feet of freeboard. • Construct a multi-use underpass at Violet Avenue. • Excavate north overbank to increase channel capacity. • No modifications to the channel invert or south overbank. Road Crossing Structures • Construct 3 grade control structures to stabilize existing head cuts. • Remove Violet Avenue bridge and replace with 9'Hx43'W'50'L RCB with multi-use underpass or equivalent clear span bridge. No over topping of roadway during 100-year event assuming 20% debris blockage. Revegetate, landscape and mitigate wetland damage of all disturbed areas. ROW/Propegy A urcq 'sition Pedestrian Trail • 160- to 250-foot channel top width is required for the proposed channel improvements. • Construct pedestrian trail along north overbank. • This reach is located on City of Boulder property. Miscellaneous ROW/Propegy Acquisition • Coordinate development of the channel improvements with the development of the City park site. • 135-foot minimum channel top width is required for the proposed channel improvements. • This mitigation approach will preserve the existing creek riparian habitat. • A 25-foot drainage easement exists through this reach. • Channel improvements will require the acquisition of an additional 110 feet of right-of-way or drainage easement Reach 4 through this reach. Miscellaneous Channel Work • Modify the Farmers Ditch crossing to match proposed channel geometry. • 100-Year design capacity 3,581 cfs with residual floodplain on both north and south overbanks. • Excavate north and south overbanks increase channel capacity. Reach 3A • Construct 15 drop/grade control structures to stabilize existing headcuts. • Daylight the piped section of the creek between Upland Avenue and Violet Avenue. Channel Work • Revegetate, landscape and mitigate wetland damage of all disturbed areas. • 100-Year channel design capacity 3,581 cfs with residual floodplain on City property located along the north bank. • Provide maintenance access along the channel between 19th Street and 26th Street. • Excavate north overbank to increase channel capacity. • No modifications to the channel invert or south overbank. Pedestrian Trail • Construct 8 grade control structures to stabilize existing head cuts. • Construct pedestrian/maintenance trail along south overbank between Violet Avenue and 19th Street. • Revegetate, landscape and mitigate wetland damage of all disturbed areas. • Construct a multi-use underpass at Upland Avenue, 19th Street and 26th Street. • Modify pedestrian crossing between 19th Street and Upland Avenue and at Riverside Avenue to match the proposed Pedestrian Trail channel geometry. • Construct pedestrian trail along north overbank. • Remove pedestrian bridge at 26`h Street. • Remove two pedestrian crossings and replace with one pedestrian crossing. Road Crossing Structures Road Crossing Structures • Remove existing bridge structures at 19th Avenue, Upland Street and 26th Street and replace with 9'Hx43'Wx50'L • Remove existing timber bridge structure and replace with 5'Hx40'Wx40'L RCB or equivalent clear span bridge. No RCB with multi-use underpass or equivalent clear span bridge. No roadway over topping. multi-use underpass and 18" maximum roadway over topping. • Remove the driveway culvert and install a cul-de-sac, on the north overbank, at the west end of Sumac Drive. • Remove existing culvert at Topaz Drive and replace with 4.5"hx30'Wx40'L RCB or equivalent clear span bridge. No ROW/Propegy Acquisition multi-use underpass and 18" maximum roadway over topping. • 230-foot minimum channel top width is required for the proposed channel improvements. • Channel improvements are located on City of Boulder property. ROW/Property Acquisition • 94-foot minimum channel top width is required for the proposed channel improvements. Miscellaneous • This reach is located on private property and in Boulder County. • Coordinate, development of the channel improvements with the development of the future City of Boulder Park site A 25-foot drainage easement exists through some of this reach. located on the north bank. SHEET E-4: FOURMILE CANYON CREEK - STATION 307+00 TO 238+36 Reach 2B Channel Work • 100-Year channel design capacity 3,468 efs with a minimum of 3-feet of freeboard. • Reconstruct the existing levee located along the north bank to contain 100-year flow. • No change of channel invert or right and left overbanks. • Construct 4 grade control structures to stabilize existing headcuts. • Revegetate, landscape and mitigate wetland damage of all disturbed areas. • Construct a sediment capture and wetland mitigation facility at the west end of this reach. Pedestrian Trail • Existing trail on north overbank and pedestrian crossing to remain. ROW/Property Acquisition • 170-foot minimum channel top width is required for the proposed channel improvements. • This reach is located within an existing drainage easement, Reach 2A Channel Work • Maintain existing channel configuration. Miscellaneous • Monitor sediment deposition and flood conveyance capacity. Remove sediment and reestablish low flow channel when the channel capacity is less than the 100-year discharge. Reach 1 Channel Work • Maintain existing channel configuration. • Construct 1 grade control structure to stabilize existing head cut. • Stabilize bank to minimize erosion. • Perform select removal of woody debris. • Remove and replace 47t' Street culvert. Pedestrian Trail • Existing trail on north overbank and pedestrian crossing to remain. Miscellaneous • Monitor sediment deposition and flood conveyance capacity. Remove sediment and reestablish low flow channel when the channel capacity is less then the 100-year discharge. s REACH 26 REACH 1 - Rte, ~A A ds ~ do ~ ds 0Oo-3A66 ds \ rO .~O ''A1RAL NSIQN - STABILIZE BANKS p ~ 9 y f I 1 f w ~ I N /j''. - ~ 1 1u61•,~'zoa~ ft. , . ~ ~ ~tn~ O~ - rj'j'. ` y _ - - ~s pp , ~ 0 ,>1 , , ~ ~ uG ~ ORS STRUCTURE .A . U~J Z ~Y q CONSTRUCT STRUCTURE - t3,:~ v~ R N I ?0 STABNZE STING QG7 ~~-MEADCUL - p STABILIZE EROSl6N UN ER - - 1 _ AIL PEDESTRIAN ~ Q EXISTING PEDES1RIAtJ, CROSSING TO .REMAIN p REPLACE th STR - 1 EET CULVERT ~ _ - ~ V 'GC` p W/ 5 X43'Wx50'LRCB OR , P~ - - . EQUIVA R SPAN BRIDGE ,1 ,3 p \ = f O ; FL000PLAINO-TSAR L} \ a Ca OTE _ _ - FLOWPLAIN BETWEEN TiIGHWAY 114 AND, . YZED /NS CREEK TO BE AN ,MOA FROM MPLEMENTATION F' J ' ' PRELIMINARY DESIGN MENTA EMEN . n RY O p~60~ CHAN)FAW/ V ' FLDODPL4N MITIGATION STRt7EGf5 TO . ON slTCtAM SEDIMENT BE IMPLEMENTED OR CONSTRUCTER CAPTURE fACIUTY AND , Y , :DOWN'STREAM OF HIGHWAY 119 PRIOR WETLAND 1$7TD'ATTON TRVC lE Z UPSTREAM 'OFnHIGHWAYM1190VE TS u ~u p P~Q : 1 I J EOUR4 G a Yu ~o aau bROP- SiRUCTURES'TR Q STAD¢IZE EXISIJNG - - 9' 1 HFAOC 1TS `-OF- i) ~j EMSTING -PEDESTRIAN {yj Z„ :._CRQS9NG i0 Rr7AAIN APPRO%IMA ' 00-YEAR FLQODPLAIN ,,110 <~A J~ WNH CHANNEL PROVEMENIS f J 'a _ IW Z Z - \ c 170 ROW/EASEMENT c Q ~~1 Q P~~ _ - EXISTING CP REMOVE AND 100-YEAR / V Nam BOULDER CHANNEL $ \ TERRACE REPLACE LEVEE WATER SURFACE SLOPE 6.6 t 1. THIS DRAWING IS FOR MASTER PLANNING PURPOSES AND V-8.ift/sec of NORm~ _ , REPRESENTS PRELIMINARY AND CONCEPTUAL ENGINEERING. 9.6 _ W Rpak, ALTERNATIVES TO THIS MAJOR DRAINACEWAY SYSTEM WILL BE 'i OF? n' CONSIDERED BY LOCAL AGENCIES AND THE URBAN DRAINAGE A-- a O ' - AND FLOOD CONTROL DISTRICT PROVIDED THE ALTERNATIVE - - OFFERS AN EQUIVALENT HYDRAULIC CAPACITY AND STREAM 10 rc 2 STABILITY. THE ALTERNATIVE MUST COMPLY WITH ALL - ja REQUIREMENTS OF THE LOCAL )URlSDICTION AND THE Uf~AN 6 8 6 0 o.m DRAINAGE AND FLOOD CONTROL DISTRICT. THIS DRAWING WILL F p" - ` ~Q NOT BE USED FOR CONSTRUCTION PURPOSES. IN ADDITION, TRAIL EXISTNG THERE MAY BE STATE AND FEDERAL REQUIREMENTS THAT WILL 100' TRAIL o p <flQ - r~ 'a Z NEED TO BE CONSIDERED AND MET. THIS DRAWING IS NOT A ' d rc u FINAL DESIGN AND SHALL NOT BE USED FOR CONSTRUCTION ' a PURPOSES. 5 80' - 65' - i~ 2. TYPICAL CROSS SECTIONS LOOKING DOWNSTREAM REACH 2B-TYPICAL CHANNEL SECTION 3. MA=MAINTENANCE ACCESS SCALE:1 "=20' - Ix ~ I LJAJOR DRAINAGEWAY PLANNING PLAN m „ Designed By.. SOL Date: 9/5/Ot URBAN DRAINAGE AND FLOOD CONTROL DISTRICT t Drawn By DIM Dater` Q]_ FOURMILE CANYON CREEKA 173 F86 TO STA 112+36 SHEEP E4 a ^""'6~fi10 Checked ey °JL Date: CITY OF BOULDER PHA 'B' PRELIMINARY DESK3N No Dote Redsion r ra .meTrc»I lr~l CITY DEPARTMENT OF PUBLIC WORKS ~r OF P.O.Box 791 1739 Broadway BOULDER Boulder, Colorado 80306-0701 i Attachment C Status of Fourmile Canyon Creek Downstream Study Efforts State Highway 119 to Boulder Creek Confluence March 13, 2002 As part of the Fourmile Canyon Creek Master Planning effort, an evaluation is currently being performed to determine if properties located downstream of State Highway 119 are adversely affected by implementation of the proposed upstream flood mitigation measures. The results of two draft reports, "Technical Memorandum: Hydrology, Floodplain and Damage Analysis - Draft, January 18, 2002" and, "Technical Memorandum: Alternative Analysis - Draft, January 18, 2002" prepared by Love and Associates, Inc. under contract with the City of Boulder and the UDFCD are summarized below. This summary is provided as an update on the status of the downstream study, and provides information for discussion purposes. The data provided is draft and is subject to change. A major goal of the Selected Plan is to eliminate spill flows to Wonderland Creek in excess of those currently anticipated in the existing hydrology adopted by FEMA. In order to achieve this goal, structural changes will be made in the Fourmile Canyon Creek drainage basin to contain spill flows up to the 100-year event. Another goal of the Selected Plan is to maintain the residual 100-year floodplain for Fourmile Canyon Creek to be no larger than is currently depicted on the FIRMS for the City and County or the 100-year floodplain limits and elevations under the current (non-containment) conditions. In most of the upstream segments of Four-mile Canyon Creek, this will require enlarging the conveyance zone or other structural flood improvements to accommodate the additional flow. A cost-benefit analysis of the upstream study area has shown that structural improvements combined with other floodplain management techniques are cost effective, therefore City Council has recommended that the spill-containment approach be implemented. In the downstream reach of Fourmile Canyon Creek (between State Highway 119 and the confluence with Boulder Creek) there are 17 properties with structures and 3 properties without structures that are damaged by the current (non-containment) 100-year flood. The 100-year flood under the proposed, containment conditions will not inundate any additional residential structures or properties. However, depths will increase over the current (non-containment) conditions, therefore an incremental increase in damages and in the risk to life and safety may result from the upstream project. The incremental change between current (non-containment) conditions and proposed (spill-contained) conditions is small, with an average depth increase of 10 inches compared to the current conditions (the average depth for the 100-year event is 4.38 ft under current conditions, compared to the average spill-contained depth of 5.22 ft for the 100-year event). Because the regulatory model assumed that floodwaters were contained within the Fourmile Canyon Creek basin, the proposed upstream containment project has limited effects on the depths and boundaries of the 100-year flood shown on the regulatory flood map. Compared to the regulatory model, there is actually a 1-inch decrease in average flood depths under the proposed, containment conditions. Due to the small depth increase and the broad extent of the floodplain area in the downstream reach, the incremental increase in damages between current (non- containment) and proposed (spill-contained) conditions for the downstream reach is correspondingly small. Currently, damages from the 100-year flood on properties downstream of State Highway 119 are estimated at $2,676,000 (present value), whereas damages from the 100-year flood plus the contained-spill floodwaters are estimated at $2,805,000 (present value). The incremental increase in damages is therefore estimated at $129,000 which is an order of magnitude less than the cost of structural flood mitigation measures such as channel capacity increases or flood storage facilities. Various options are being discussed to address the potential adverse impacts from additional flows on the downstream properties. The low cost-benefit return on structural mitigation measures has prompted the City to begin discussing innovative ideas such as providing funds for supplemental flood insurance or flood proofing measures in exchange for a signed liability waiver from each property owner. The City's legal staff and the UDFCD legal counsel are currently evaluating the legality and feasibility of compensating property owners for incremental increases in flood damage and risk. A public meeting to discuss the approaches for mitigating the impacts from the incremental increase in flows downstream of State Highway 119 will be held in April 2002. It is anticipated that a legal opinion regarding the purchase of liability waivers will be available at that time. Attachment D Meeting Notes from March 13, 2002 Public Meeting Fourmile Canyon Creek Phase B Preliminary Plan Community Review March 13, 2002 Meeting Notes Dick Wilson and Jack Lacy asked for an update. They could not stay for the meeting. Comment made: "This will never get to our property in our lifetime>" "How do we plan to pay for this?" Will <the City> adopt a new floodplain map in the interim? How does this link to the CDUMP process? When properties are acquired post-flood, are these purchased at fair market value? What are "critical hydraulic structures?" Is there an evacuation plan for Crest View Elementary School? Do you have maps to show quantities of water/drainage? Will the new channel be concrete? Have you considered the loss of flows due to the wells in the mountains? There was no water in Fourmile Canton Creek last year. Have you explored the existing utilities impact on the flows? Why do <people/the City> want to build bike paths on all of the creeks? Has there ever been a historic flood that spilled to Wonderland Creek? Is Bob's timeline real? If you remap this corridor, you will raise people's flood insurance rates, and require people need to go get flood insurance. Why would the City want to do that to citizens? Ben Urbonas: City is required by FEMt1 to regulate to the "best known flood. " Given the priorities of working on different creeks across the city, could Fourmile move ahead of South Boulder in prioritization because we have more agreement on the plans... No conflicts like with CU? Concern for the whole acquisition thing. Know this is an important way to clear flood zone, but don't want to see my neighbor get screwed. What about the projects in process around town to rip off the tops of bridges? To what flood standard are these bridges being reconstructed? Should make these fit/span flood needs. What about span at Fourmile and Broadway? FROM PINK COMMENT FORMS: Timothy Alm: Presentation gave me fairly good - to - great info. Learned of meeting from sign on Broadway bridge. Marjorie Maagoe: Great information! Learned of meeting via a League of Womens Voters email Want a copy of the preliminary map 3545 Arthur Court #1 Boulder, CO 80304 303-444-8277 William and Penelope Sharp: Fairly good information. Would like to learn more about progress with berm and re-channeling along Reach 2B Greatest concern... 28`h and 30`h Street bridges clogging with vegetation The preliminary design has some good elements. Contact me at: 303-444-2893 Charles Ogsbury: Meeting provided fairly good information. Would like to learn more about work to be done on section 6A, west of Broadway along Rosewood. My greatest concern is that Rosewood will be removed, as it is the frontage road and primary access to my property and parking. The preliminary design work has some good elements. Learned of the meeting from the postcard mailing. Please contact me: (303) 449-0041 or (303) 440-6392 John Christenson and Marilyn LeMoine: Tonight's meeting gave me great information! I would like to learn more about cooperation between the City and County. We are in the County east of 28`h. My greatest concern is that the bridges at 28`h and 30`h look like they need widening. Especially 28`h. Looks like it would turn into a dam. The preliminary design work looks pretty good! Learned of the meeting from the postcard mailing. "Thank you for all your effort and willingness to include us." Attending: Dave Nelson 4535 Broadway Boulder, CO 80304 Jack Lacy 4587 Broadway Boulder, CO 80304 Jack Aragon 418 Lee Hill Road Boulder, CO 80304 Marjorie Maagoe 3545 Arthur Crt. 41 Boulder, CO 80304 Elizabeth Black 4340 No. 13`h Boulder, CO 80304 Dick Wilson Ray Horton 3738 6151 Street Boulder, CO 80301 Dorothy Horton Timothy Alm 1375 Violet 97 Boulder, CO 80304 303-808-0605 Charles Deane 625 Pleasant Street Boulder, CO 80302 303-444-9234 Deb Keammerer 5858 Woodboume St. Boulder, CO 80301 303-530-1783 Allen Goldstone 2495 Agate Rd. Boulder, CO 80304 303-447-2167 Gerald Straty 3614 No. 61" St. Boulder, CO 80301 Odus Sharp 4244 Corriente Pl. Boulder, CO 80301 Marilyn LeMoine 4220 Corriente Pl. Boulder, CO 80301 John Christenson Anne Stetina 1953 Poplar Lane Boulder, CO 80304 Ed Byrne 4324 Snowberry Ct. Boulder, CO 80304 Richard Adramane 2475 Lee Hill Road Boulder, CO 80302 Charles Ogsbury 698 Dixon Boulder, CO 80302 303-440-6392 Bill Mitzelfeld 1530 55`h Street Boulder, CO 80302 Leslie Lomas 2290 Emerald Rd. Boulder, CO 80304 Attachment E Notes from Meeting with Mary Fran Myers and Bob Harberg March 21, 2002 Dolans Restaurant RE: IRP Review of Fourmile Canyon Creek: Phase B Preliminary Plans, Eastern reach add-on Phase A, Wonderland Discovered in intro discussion *Document error: discovered that there are two white bound books for distribution - one is hydrology and one is technical analysis and damages. Need to check with IRP to see who has which and deliver other copy. PHASE B DISCUSSION: Take selected plan and determine what this (could/should) look like in the drainageway. In the Selected Plan the City Council elected to contain the spill flow, consistent with staff recommendations. Still looking at the 50-year flood, in most cases; not 100-year- except where necessary to contain spill flow. In containing the spill flow, we will need to make certain improvements to protect the downstream properties Between 19`h Street and 26`h Street (Githens/County areas) will build to protect to 50 year and the High Hazard Zone (HHZ). Preliminary to the final design Implementation Plan All reach-specific improvements have been addressed in the Implementation Plan Section 9-2: Identify properties to be acquired. There are 6 - 12 properties to be acquired; some of this is easement on developable land: NOT structures. City/County continue to recommend (their) coordinated floodplain management effort. 1 Mary Fran's Questions: Has there been any effort to perform analysis to determine what impact of doing flood proofing may be - to reduce damage potential in affected zones? We could break new ground by flood proofing individual structures to meet flood protection needs for properties already there, versus redesigning the creek. Might be able to consider different level of channel work. Bob concern: this does not address other City multiple objectives for the corridors. E.g., Greenways. Yet, Bob is looking at a legal treatment for the properties located in Eastern County reaches: Woodboume Hollow, and there will be alternative treatments explored for Githens Acres. They have lots of tree and old vegetation. City needs to better understand and determine viability of flood waivers in legal evaluation. Question: When and where does the City "multiple objective" need come into play? Reminder: the multiple objectives are: Greenways, Cultural, Transporation Environment and Recreation. ? How do we determine between action needed to provide flood protection (citizen's willingness to pay for this) and the added investment toward these other goals? Bob: we know that there are 2000 cfs. To be added if the spill is contained, thus we are guided to consider impacts of this added flow, or impacts if this spills. ? Can we incentivize the individual property owners to flood proof, provide low- interest loans? Have you explored ways to incentivize self-help? (identified in the proposed flood policies at 1-28 study Session) BOB: Some of these interests are being addressed in the CDUMP. We are looking at the benefits to the community of the increased CRS rating.; continuation of our flood insurance program, added and improved emergency response and warning, rain gauges and sirens. ? Where is this in the budget process? (Budget info identifies City priorities) BOB: proposed bonding at the end of this year, funds for 2003 budget process. Looking at bond at $6 million. MFM: When you push items 6 - 8 form your list off onto CDUMP (from the IRP's recommendations for Fourmile), any new bond funding is then directed toward structural responses, activity moves forward on the traditional, structural approaches. That is not what City Council directed. This does not achieve other flood management goals. BOB: $6 million will probably go to acquisition, and some structural improvement from the Diagonal to 26`h (through the Elks site.) The $6 million will also address revisions to the floodplain maps and flood warning and response improvements. Some of the acquisition will probably be easement on developable land. Brief discussion of Items 10 and 11: Downstream Issues and Multiple Objectives: * Funding for the work comes from Transportation, Greenways and Parks * Habitat assessment is used to identify areas for improvements * Bob said that they had Environment people review the proposal and they found some things missing. The staff review is still in process. * City participating in cost of firefighting - helicopter for JeffCo airport this summer. Prep for fire protection... Item 13: IRP comments: MFM: Skimmed the analysis, has notes from Gilbert. CONCERN.• there is no City advocate for the non-structural and self-help type endeavors. The flood management program is managed by people who have managed and implemented "traditional approach" only. Maybe City needs to invest in someone to advocate for non-structural approaches? BOB: recommendations? Flood Self-Help expertise? Clancy Phillipborn - local legend Bob Kissner Wally Wilson French Wetmore - wrote book for CRS Kevin Stewart - UDFCD Eve Grunfest - "risk perception" work on fish floods John Hens - HDR *Bob has a report from John Hens for CDUMP. Would be good for Alan to use for HAP work. Inundation mapping 3 How to build a response to Phase B from IRP? DUE: April 19`h • Could we task members with questions to answer, pieces of report on which to comment? Timing: concern that we put cart before the horse if the things we have recommended are pushed off to CDUMP. Put this on hold until CDUMP "made real?" MFM: A crack at IRP thoughts... • Make clear to members that the numeric information is slated and prioritized • Address structural design: criteria about containing spill- 100 yr/50 yr... differences • Timing? Concern for this being pushed ahead of the CDUMP recommendations. Could it be coincident with CDUMP? Wait until CDUMP completed? Budget? • Should put questions to IRP. Get Brian's comments. • What about the citizen's review? MF would like a copy of draft CDUMP document. Would like to know how this differs from the old CDUMP? End. 4