Erosion of the Tarkio Drainage System, 1845-1976

ABSTRACT HISTORIC and geologic evidence indicated that channel and gully erosion was nearly nonexistent when the loess-mantled Tarkio Basin of southwestern Iowa and northwestern Missouri was settled about 1845. The pattern of channel development—gleaned from old land surveys, records from drainage districts, highway bridge surveys, and other documents-—is related to the intensity of agriculture and is complexly linked to the general runoff regimen and to changes in soil-water content along channel boundaries. Some channel enlargement during the post-settlement period, 1845-1976, is quantified. Channel profile changes during recent years, 1939-1976, are reconstructed. The excessive scour in a channel reach of West Tarkio Creek is tentatively explained on the basis of geomorphic principles and differences in substrata erodibility.