The construction of Chatfield Dam in the Denver Metropolitan area had a significant impact on the health of the South Platte River. Flow regulation altered the natural hydrograph of the stream and the dam’s trapping of sediment created a stream system that was sediment starved. As a result significant channel downcutting occurred and the stream geometry, which was established based on higher natural flows, was overly wide for the regulated flow regime. ERC was contracted by Urban Drainage and Flood Control District to develop a master plan to enhance the natural characteristics of the stream and riparian corridor for this 2.4 mile reach of the South Platte. Stream improvements were intended to resize the active channel to be in balance with current reservoir releases and create improved aquatic and riparian habitat all while ensuring that the stream retains the hydraulic conveyance needed to minimize flooding. ERC’s initial geomorphologic assessments evaluated past and current flow hydrographs and development of hydraulic and sediment transport models to help define a stable channel configuration. Based on results of these analyses, ERC developed an overall enhancement plan which included creation of a meandering channel sized to convey current flows within the confines of the overly wide existing channel. Low gradient riffles were designed to increase habitat variety and deeper pools were included to provide habitat critical for low flow conditions. This master plan also incorporated bank stabilization, protection of the local trail system, riparian corridor restoration, upland improvements and wetland creation. Bank stabilization was completed using a variety of structural approaches where needed to interrupt areas with active lateral migration and softer vegetated measures where possible. Improvements were prioritized based on relative benefits of individual stream reaches and shareholder/community input. Construction costs were developed as part of the master plan.
ERC’s restoration master plan was then used as an instrument to gather community support and project funding. The plan was endorsed by local jurisdictions, which contributed funds for the project and aided in additional fundraising for the proposed work. Phase I was completed in 2013 with Phases II and III completed in 2015.