Improve Customer Experience Optimize Use of Resources Enhance Quality of Life BoCC Consent Agenda, June 19, 2018 Agenda Item Page 2 of 6 Discussion Cherry Creek is experiencing severe degradation leaving a 10 to 20-foot deep eroded/incised channel with vertical banks that are not connected to the floodplain. Cherry Creek also contains the Denver metro area s most heavily used regional trail that connects Douglas, Arapahoe, and Denver Counties along Cherry Creek up to the South Platte River. As such, the degradation imposes a significant safety and passage barrier for trail users. The degradation has resulted in the following impairments to the stream corridor:
County, and Douglas County enhance instream water quality and water quality for existing tributary areas enhance water quality for proposed roadway project at Iliff restore the stream ecology create an open space for passive recreation Floodplain benches will be created adjacent to the active channel to expand the riparian corridor and improve flood capacity. Other improvements will include approximately 10,000 feet of bank protection, 150,000 cubic yards of grading, planting of trees, shrubs, willow stakes, wetland plugs, and 30 acres of native seeding. With healthier stands of vegetation resulting from the raised water table, the project will provide a much stronger flood corridor with improved conveyance that will increase safety for the surrounding public and infrastructure, while keeping 100-year flood flows within the open space corridor. The stabilized channel will also improve water quality by reducing the heavy sediment loads being transported by the existing channel. Early Cherry Creek watershed plans recognized stream stabilization and reclamation as a watershed-wide method to control sediment, phosphorus, and other nutrients being transported to downstream waters. Rich riparian ecosystem vegetation will be achieved. BoCC Consent Agenda, June 19, 2018 Agenda Item Page 3 of 6 Technical Feasibility of the Project Riffle structures will be constructed with only one-foot drop heights and only 2.5 downstream drop faces. In addition, the riffles will be constructed with loose rock (void-filled riprap) to simulate natural river bed material, all of which is very conducive to fish passage. Similarly, sculpted concrete grade control structures will be designed with a series of step/pool sequences to allow for fish passage and provide a home for aquatic organisms. The upper banks of the creek are currently dominated by non-native and invasive species including: Smooth brome, Cheatgrass, Canada thistle, Marestail, Russian olive, and Siberian Elm. Due to the project reach s eroded condition, little to no riparian or wetland vegetation is present along the creek banks. The project includes creating more floodplain benches to provide riparian habitat and re- stabilize the banks with native riparian and upland seed. The areas with 10 to 20-foot eroded banks will be regraded and restored as native uplands. Creating wetland/riparian benches and burying exposed concrete will enhance the wildlife habitat along this reach of the creek. Mile High Youth Corps will be utilized to install trees, shrubs, willow stakes, and grass plugs to help supplement the planting contractor s overall effort. The Cherry Creek Regional Trail runs along the south bank of the creek through the project reach. This trail is a heavily used pedestrian and cycling trail within an urban corridor. Due to the steep banks and active erosion, the trail has been undermined in areas and recently repaired. Many other areas of the trail could experience failure if the creek channel is not stabilized and restored. Several recreational components will be improved throughout the project area. By re-grading the banks to a gentler slope, the regional trail will be reconstructed to the updated Denver Parks standard with a 12-ft concrete trail with 4-ft recovery zones on each side. Access points to the creek will concentrate access without compromising the success of the surrounding wetland and riparian areas. Land Ownership All of the land that the project will occur on is either owned by the City and County of Denver or Denver Water. Denver Water and the City and County of Denver each own a parcel of land in Arapahoe County, and both entities have agreed to transfer their respective properties to Arapahoe County Open Spaces to further this project. Arapahoe County s ownership will allow the County to better manage the Cherry Creek Trail and stormwater/permanent water quality from the Iliff widening project. Arapahoe County will gain approximately 10 additional acres of open space. Some buried asbestos exists on the properties that will be transferred to Arapahoe County, but it will be removed or properly buried pursuant to a Materials Management Plan as part of the overall project. Project Budget Note: Reaches 5A 5B are in the City and County of Denver. Reach 5C is the Arapahoe County portion of the project. All SEMSWA ( 700K) and proposed Arapahoe County Open Spaces funds ( 2M) will go towards Reach 5C. (see next page for complete budget information) BoCC Consent Agenda, June 19, 2018 Agenda Item Page 4 of 6
Figure 1 in Appendix A is a vicinity map for the project area. Project Description The Cherry Creek Restoration Project has been initiated to restore a one-mile reach of the Cherry Creek Corridor located approximately 2.5 miles downstream of Cherry Creek Reservoir between Quebec Street and Iliff Avenue. The project spans between City and County of Denver on the downstream side and Arapahoe County on the upstream side. Within the project reach, the Cherry Creek channel consists of a 30-foot wide active sand bed channel with a perennial base flow. The channel invert drops 30 feet and runs at approximately a 0.6 slope. Currently, the active channel is experiencing severe downcutting, leaving a 10 to 20-foot deep eroded/incised channel with vertical banks. The stream channel improvements will raise the channel bed and associated water table. An extensive planting effort is included with the project to encourage the return of native vegetation and wildlife habitat. CWCB funding is integral to the success of this project. Without CWCB s support, the project partners will have to value engineer out critical restoration components. Watershed/Stream Restoration Grant Request Total Project Cost 15,321,000 Grant Request 500,000 Funding Sources: Project Sponsors Trust/Project Account 4,041,000 City and County of Denver 2018/2019 Budget 2,500,000
Floodplain benches will be created adjacent to the active channel to expand the riparian corridor and improve flood capacity. Other improvements will include approximately 10,000 feet of bank protection,
corridor. The stabilized channel will also improve water quality by reducing the heavy sediment loads being transported by the existing channel. Early Cherry Creek watershed plans recognized stream stabilization and reclamation as a watershed-wide control method to control sediment, phosphorus and other nutrients being transported to downstream waters. Rich riparian ecosystem vegetation will be achieved as illustrated in Figure 2 in Appendix A. Technical Feasibility of the Project Aquatic Resources
Monitoring Plan The UDFCD will be responsible for monitoring the project. The UDFCD is financially supported by a property tax mill levy specifically collected for Denver and Arapahoe County. UDFCD annually inspects and performs river management services five times a year that consist of a crew walking the reach to provide vegetation management, removing debris and trash, and identifying any potential problem areas. In addition to the above maintenance, the Section 404 permit for the Cherry Creek Restoration
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