Elkhorn Riverbank Stabilization

Background

FYRA Engineering, now Houston Engineering, Inc. (HEI), was contracted to address bank stabilization needs on a segment of the Elkhorn River near 240th Street. During the June 2010 flooding in the Elkhorn River watershed, approximately 325 feet of land was washed away, and the riverbank migrated east towards 240th Street.

The Project

The client was interested in providing immediate protection to the local infrastructure, so an interim solution was implemented while the final, long-term solution was designed and permitted. The interim solution included a combination of buried rock windrow and rock riprap placed directly on the bankline.

This construction qualified for a 404 Nationwide Permit, which was obtained. HEI performed the final design, permitting, and construction observation of the long-term solution. The design of the long-term solution included the excavation of a pilot channel with a gentler curvature that developed into a parallel river channel over time with flood flows. The rate of channel development was dependent upon the frequency and severity of flows in the river, which eventually conveyed a significant portion of the flow away from the existing bankline of concern. This reduced the stresses incurred during high flows and reduced the risk of restoring a channel of the Elkhorn River and provided aquatic habitat improvements for the endangered pallid sturgeon and other native species of fish.

Bathymetric surveying and 2D hydraulic modeling of the river segment were performed to assess the stability and flow regimes of the preferred alternative, and plan for habitat location and orientation. Permitting coordination with the
US Army Corps of Engineers was performed, construction documents were developed, and construction observation services were provided.