Iowa has six major river basins. River basins are comprised of smaller watersheds- expanse of land drained by smaller streams, rivers, lakes or wetlands. The majority of land within these watersheds is used fir agricultural purposes. In general, land devoted to row crop agriculture sheds runoff after 1.25 inches or rain. Urban areas located downstream of large watersheds in Iowa are heavily affected by this agricultural runoff.

In 2008, more that 90% of the 3.6 million acres in the Cedar River Watershed above Cedar Rapids was comprised of rural land, primarily used for planting of corn and soybeans. Consequently, the runoff from these agricultural fields was the primary contributor to the record flood flows that devastated Waverly, Cedar Falls, and Cedar Rapids. It is in the best interested of cities to partner with agriculture to restore the landscape’s ability to absorb more rainfall and shed less runoff.

In smaller watersheds, stormwater runoff has a significant impact on the flash flooding of local streams in areas of urban development. Fourmile Creek Watershed in central Iowa measures almost 77,000 acres, and 36 percent of this watershed is urban land. Urban runoff in this area contributes to downstream flooding.