Sediment Yield from a 259-ha Flatlands Watershed

Average annual sediment yield was 5.3 t/ha from a 259-ha Mississippi Delta watershed during a 6-yr (1975-1980) period. About 234 ha of the watershed was under cultivation (cotton, soybeans and wheat) while the remaining 25 ha was primarily in wooden depressional areas. Cultivated fields had slopes that ranged from 0.2 to 1.4%, while slope lengths were generally less than 66 m. Average annual rainfall was 1404 mm, 57 mm above the 27-yr average for the area. Annual runoff averaged 394 mm for the 6-yr period. The average measured sediment yield for the combined months of March, April, and May was about 3.5 t/ha, or 67% of the average annual sediment yield. Approx. 85% of the sediment leaving the watershed was classified as clay material with about 98% of the sediments particles 0.016 mm in size.