Sand Hill River Rock Riffles and Fish Passage

Background

In the 1950s, the US Army Corps of Engineers (USACE) completed a flood control project which involved the construction of the Sand Hill Ditch. Due to significant slope found in portions of the USACE project area, four large concrete drop structures were installed on the Sand Hill River as part of the flood control project. During normal flows, each of these concrete drop structures create a vertical drop of approximately five feet. Since the original construction of the Sand Hill Ditch by the USACE, the channel has downcut significantly, causing bank stability issues and subsequent slope failures as the slopes became steeper and the channel bottom became lower.

The Project

Initially, six fish passage barriers existed on this stream segment. The Sand Hill River Watershed District (SHRWD), along with HEI and in cooperation with MnDNR, developed the SHRWD Fish Passage Master Plan to restore upstream fish migration in the Sand Hill River by modifying these six structures. All six structures have since been modified to allow fish passage.

Riffles were installed at two culvert crossing sites. The four drop structures were modified to transform the fish passage barriers into rock rapids with a gradual slope. This restored river connectivity to the 50 miles of the river upstream of the dams. Reconnecting this substantial spawning and rearing habitat will improve the composition and quality of the fishery in the Sand Hill River and Red River Basin. Twenty rock riffle grade control structures were designed along the 5-mile stretch of the ditch. HEI worked closely with MnDNR and the USACE on the project design on behalf of the SHRWD.

Learn more about this project in our StoryMap.