High runoff produced by excessive rainfall or sudden spring thaws after periods of heavy snowfall will cause rivers or other body of water to overflow, inundating areas and threatening or causing heavy damage. The risk of damage or life loss may result when floodwaters strike cities, industries and farms located on or near river valleys. Usually the damaged area is in a floodplain, which is a strip of relatively level land bordering a stream.
Vulnerability Floodplain locations that exist near the Big Sioux River, its tributaries and Nine Mile Creek are especially vulnerable to flooding. Urban areas are specifically susceptible because of the attractiveness of the floodplain for land development. Populations at risk include those living or working in floodplains as well as the elderly, the homeless and non-English speaking persons. Property at risk includes any structures residing in the floodplain as well as crops, livestock, homes, businesses, and automobiles. The environmental exposure that is likely to occur affects vegetation, wildlife, the quality of water in surrounding water bodies.
History In 1961, the Army Corp of Engineers completed a flood control project for the City of Sioux Falls. The project consisted of: Diversion headworks, entirely automatic in operation located on the Big Sioux River flood plain just north of the Airport A diversion channel and a concrete diversion chute and stilling basin which would carry the diverted flood waters in a generally southeasterly direction to the Big Sioux River below the falls Channel improvement and levees along the Big Sioux River; channel improvement and levees along the lower one-half mile of Skunk Creek Necessary railroad and highway alterations In October 1996, the most recent Big Sioux River levy system project started. The project was intended to protect the city of Sioux Falls against a 100 year flood event.