Book Description

The study of rainfall and drainage discharge was undertaken (1)to determine the rates of runoff for which drainage districts in northern Iowa, should be designed and (2) to study the changes which extensions of farm-lateral systems produce in the discharge characteristics of such districts. The field data include rainfall and drainage records for each season, April to October inclusive, in the 13-yr. period, 1920 to 1932, for: Three districts with drainage areas of 12, 25, and 35 sq. miles, including two tile-lateral areas of 4 1/2 and 1 1/4 sq. miles; the dredged channel for the West Fork of the Des Moines River with a drainage area of 2,100 sq. miles; and a district with no surface inlets of 3 1/2 square miles. Following the completion of the field study, frequency studies of rainfalls and of peak rates of runoff were made by the station-year method, and the results used as a basis for evaluating the discharge data. The extensions of farm-lateral systems were not sufficient to permit conclusions concerning their effects upon the discharges from the various districts. While the first objective was not realized fully the data contribute to the information upon the probable magnitudes and frequencies of maximum rainfalls and discharges from drainage districts and the frequencies, amounts, and durations of excesses in discharge above selected design rates of runoff.