The topography is hilly, particularly in areas in the headwaters of the subbasin. About 85 percent of the Delaware River Basin is agricultural land with about 40 percent in row crops such as sorghum, soybeans, wheat, and corn. Mean annual precipitation is about 35 inches, and mean annual runoff is about 8 inches. Most of the precipitation falls from April through September, which generally coincides with the growing season. Mean monthly runoff is largest in spring and summer and smallest in fall and winter.
Perry Lake is used for flood control, recreation, and public-water supply.
Outflows from the lake contribute about 9 percent of the streamflow in the Kansas River and can substantially affect the water quality downstream on the Kansas River. Herbicides, including, atrazine, alachlor, cyanazine, and metolachlor have been extensively applied in the Delaware River Basin. Atrazine was applied in the largest amounts and was the herbicide most frequently detected in the Delaware River. In 1989, an estimated 240,000 pounds of atrazine was applied to fields planted with corn and sorghum in the basin. A markedly different pattern in seasonal fluctuations of atrazine concentrations in streamflow is apparent between the unregulated upstream reaches of the Delaware River and the regulated reach of the river downstream from Perry Lake.