Red Rock Hydroelectric Project – New hydro development at an existing flood control dam

Abstract

The Red Rock Hydroelectric Project converted the existing Red Rock Dam near Pella, Iowa, from a non-powered dam into a multi-purpose dam. The existing flood control dam was constructed by the U.S. Army Corps of Engineers (USACE) in the 1960s on the Des Moines River near Pella, Iowa. The hydroelectric project was developed by Western Minnesota Municipal Power Agency and generates up to 55 MW with an average annual energy output of 178 gigawatt-hours. The new intake, penstock and powerhouse are located immediately adjacent to the spillway. Construction required large excavations into the upstream and downstream sides of the existing embankment dam and two penetrations through the existing gravity dam monoliths. Extensive water and earth-retention systems, prescriptive construction staging, and a robust dam safety surveillance program were designed to maintain and monitor the integrity of the existing dam throughout construction and avoid impacts to active USACE flood control operations. Construction was completed in 2020. This paper provides an overview of the unique challenges involved with the design and construction of a new hydroelectric project at an existing and active flood control dam.