Seasonal Distributions of Peak Flows from Small Agricultural Watersheds

Knowledge of seasonal distributions of peak runoff rates is needed for use with watershed models, and for the development of new techniques of estimating peak flow rates and their frequencies of occurrence from small agricultural watersheds. The peak flows in 312 station years of data from seven small agricultural watersheds in Ohio were analyzed to determine the seasonal and land‐use distributions of peak flows and their return periods. The assumptions often made when using design storms that peak flows occur during the seasons of highest rainfall intensities was largely confirmed, but there were exceptions. Between 92 and 94% of the peak flows, regardless of land‐use and soil type, with return periods greater than two years, occurred during the seasons of highest rainfall intensities. A similar seasonal distribution of peak flows was found from an analysis of specific agricultural land uses. More peak flows occurred during the winter season for flows with return periods smaller than about five years for some land uses. Seasonal distributions of peak flows greater than five years are largely independent of soil type and land use, allowing extrapolation of results beyond the study area in Ohio.