001 - EWP - Rabbit Mountain

The Rabbit Mountain project is located in very northern Boulder County along the Boulder County Reach of the Little Thompson River just to the north of Rabbit Mountain Open Space. The project is accessed via CR 4 in Larimer County.
In September 2013, over the span of a week, heavy rainfall fell across the Little Thompson watershed and several other areas. The heavy rainfall caused widespread flooding. This project site is at the base of the foothills where the Little Thompson River flattens in slope. The flattening slope and the concrete diversion structure (low head dam) caused a large quantity of sediment to deposit at this project site. Sediment consisting of gravel, cobble, and boulders was 2 – 3 feet deep (1,900 cubic yards).
This flooding altered the geomorphology of the site, eroded banks, and lowered the width/depth ratio. Just downstream of this project site, the landowner lost several thousand cubic yards of land. After the flooding the river was much wider, boulders were strewn about, and many trees were deposited.
The design team (NRCS – Natural Resource Conservation Service and Enginuity Engineering Solutions, LLC) has completed a 50% design, construction plans and hydraulic models for the site. The NRCS, Enginuity, and Little Thompson Watershed Coalition (LTWC) will jointly provide construction oversight for the project.
This project proposes to construct the following improvements:
1) Stabilize the left (north) streambank to protect against additional damage to existing infrastructure,
2) Establish cover on critically eroding land,
3) Reduce threats to life or property, and
4) Improve the sediment transport capacity of the river by decreasing the width/depth ratio.
The primary objective of the work proposed at the Rabbit Mountain Project, is to protect life and property. This would be accomplished by channel shaping to improve the discharge and sediment transport capacity, rounding out two sharp bends in the river to improve the flow efficiency and reduce potential for bank erosion, re-enforcing banks near structures to withstand higher flows, and re-establishing native vegetation.