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Churdan was 1.01 times larger than the 100-year recurrence-interval discharge. Highway Division, Iowa Department of Transportation. Various Federal, State, and local agencies cooperated in the collection of streamflow data used in this report, acknowledgment of which is contained in the annual water-data reports of the U.S. Geological Survey (USGS). STUDY AREA The Raccoon River basin is located in west-central Iowa, and the Raccoon River flows into the Des Moines River within the city of Des Moines (figs. 1 and 2). The basin is located entirely within Iowa, drains 3,629 mi2, and includes parts of 17 counties. Three major rivers in the basin, the North, Middle, and the South Raccoon Rivers, flow generally northwest to southeast and converge west of the city of Van Meter to form the Raccoon River. The Middle Raccoon River marks the southernmost advance of the Wisconsin glacier during the last period of glaciation in Iowa, which ended about 14,000 years ago (Ruhe, 1969). North of the Middle Raccoon River, the larger part of the Raccoon River basin has an immature topography with an ill-defined STUDY AREA 1