Sediment flow behaviour from small agricultural watersheds

Runoff, soil loss, sediment concentration, and particle size distribution of sediment eroded by runoff events were measured between 1976 and 2000 from 5 small agricultural watersheds on Vertisols at ICRISAT Center, Patancheru, India. The effects of storm size and land management system on total soil loss and size distribution of sediment during runoff are discussed. At the beginning of runoff events, the clay content of the eroded material was greater than that of the top soil but as the process of runoff continued, the clay content of the sediment tended to decrease. Generally smaller storms produced eroded material with higher clay content than did the bigger storms. Large differences in particle size distribution between the land management treatments were observed for small and medium runoff events, however, these differences were small during big runoff events. The particle size distributions of sediments eroded by big storms were comparable to the size distribution of cultivated top soil of the watersheds. The peak sediment concentration for most of the storms, generally preceded or occurred simultaneously with peak runoff rates. At about the peak runoff rate of most runoff events, the texture of the eroded soil was similar to the cultivated top soil of the watershed. Land management systems not only had significant effect on runoff and soil loss but also on the particle size distribution of eroded materials. (C) 2004 Elsevier B.V. All rights reserved.