Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/1996
Publication Date: N/A
Interpretive Summary: Accurately predicting the effect agricultural land use changes have on the movement of sediment in a watershed is critical information for making informed management decisions on agricultural watersheds. Previous studies have shown that for small areas land use is a critical factor in the rate at which sediment is eroded. In larger areas, however, many complex factors make the relation between land use and amount of soil and sediment erosion difficult to predict. The effect of changing agricultural practices on the rate of sediment loss for a relatively large area (21.3 square kilometers) was calculated for the Goodwin Creek Watershed. Land use surveys of Goodwin Creek have been conducted annually since 1982. The percentage of land under cultivation on Goodwin Creek decreased from 26% in 1982 to 12% in 1990. Rates of sediment movement, measured as a concentration of sediment in the runoff, decreased by 62%, 66%, and 39% for the fine, sand, and gravel fractions, respectively, over the period from 1982 to 1990. The decrease in the percentage of cultivated land affects the movement of sediment through the watershed in two ways. A source of readily eroded sediment is removed and the energy of the flowing water available to move sediment is reduced. Thus, to reduce erosion in a large watershed it is important to not only control the supply of sediment to the channel, but also to control the amount of water to the channels.
Technical Abstract: The Goodwin Creek Research Watershed (21.3 sq. km) is located in the north central part of the state of Mississippi in the bluff hills just east of the Mississippi River flood plain. The watershed has been divided into 14 subwatersheds where data on rainfall, runoff, and sediment transport have been collected. Three different techniques were used to sample fine sediment (< 0.062 mm), sand (0.062-2.0 mm) and gravel (> 2.0 mm). Land use on the watershed has been surveyed annually and the percentage of cultivated land has decreased from 26% in 1982 to 12% in 1990. During this nine year period the concentration of fines on the watershed has decreased by 62%, concentrations of sand have decreased by 66%, and concentrations of gravel have decreased by 39%. The decrease in the percentage of cultivated land affects the sediment budget of the watershed in two ways. A source of readily eroded sediment is removed, and the energy of the flowing water available to erode and transport sediment is reduced. The reduced flow from the decrease in cultivated land in the watershed was probably the main cause for the lower transport rates of sand and gravel.