Creek Tributary Mitigation

This area southeast of Sioux Falls has experienced increased flooding in recent years from intense storm events and upstream development. Lincoln County needed to improve the conveyance capacity of the system and maintain base flood levels to protect infrastructure and private property.

IMEG and the County Floodplain Manager developed a strategy for flood protection working with FEMA, the South Dakota DOT, South Dakota DENR, South Dakota State Preservation Office, and the U.S. Army Corps of Engineers. IMEG collected topographic information of the stream bed, floodplain, roads, and culvert crossings and used that information in preparing the hydrologic study of the watershed. Wetland boundaries were delineated within the tributary’s floodplain.

A plan was developed through collaboration with the U.S. Army Corps of Engineers, FEMA, state agencies, Lincoln County, the City of Sioux Falls, and the local rural homeowners’ association. As the final plan developed, it was determined that wetland impacts could be minimized while providing flood protection to transportation infrastructure and maintaining acceptable base flood elevations. The project repaired or replaced eight culverts, constructed a sheet pile detention to minimize impacts to wetlands, and raised a road. The culverts were all constructed to allow for fish passage.