Project Background

The purpose of the project is to address flood risk management along the Big Sioux River in and around the vicinity of Watertown, South Dakota. Watertown is located in Codington County in the northeastern section of the state. The Big Sioux River meanders from north to south through the western side of Watertown. The river flows into Lake Kampeska northwest of the city and back out in the same inlet/outlet location which makes Lake Kampeska and the surrounding structures susceptible to severe flood damages as well during flood events.  The City of Watertown has two large glacial lakes on the west side which includes Lake Kampeska as mentioned above, and Pelican Lake. In 2009 and 2022, FEMA updated the floodplain maps for the community which expanded the area that might be inundated by a one percent flood event, which significantly increased the number of structures involved in a flood insurance program.

The Watertown area has experienced eleven major floods since 1943, averaging a major flood approximately once a decade.  Watertown’s susceptibility to flood damages has increased over time as the City has grown and development has increased around nearby Lakes Kampeska and Pelican. Major floods occurred in 1943, 1952, 1969, 1972, 1986, 1993, 1997, 2001, 2010, 2011, and 2019. The city of Watertown and Lake Kampeska area sustained flood damage to sewers, utilities, roads, rail spurs, life stations, boat docks, etc., during all flood events. The 1997 flood event was the most severe flood on record for the Big Sioux River and Lake Kampeska. Majority of floods occur in early spring during snow melt and high amounts of rainfall.  Due to the timing of the flood events, ice jams have occurred near Lake Kampeska and along the Big Sioux River by the bridges on 3rd Avenue, Kemp, and the railroad trussell which exacerbate the flood damages. The frequency of flood fights requires a lot of resources from the city of Watertown in terms of costs and manpower.

The scope of this study is to develop and review flood risk management alternatives to identify a feasible and economically justified recommended plan. Flood risk management solutions have been studied previously and resulted in a Chiefs Report in 1994, and two general re-evaluation reports in 2000 and 2012. All three studies resulted in the Mahoney Creek Dry Dam alternative as the preferred alternative. However, due to lack of support by the public, the study was stalled. An additional Value Engineering (VE) study and Economic Optimization Study were completed in 2012.  After the 2019 flood event, the city of Watertown requested USACE study flood risk management alternatives once again along the Big Sioux River.  This was authorized by Congress in 2022 and a feasibility cost sharing agreement was signed on August 19, 2022.

For more information, contact:

CENWO-CW-PlanningOutreach@usace.army.mil

 - or-

Sponsor Representative, Justin Petersen, Assistant City Engineer, with the City of Watertown at: jpetersen@watertownsd.us.