|Wilson, Christopher - UNIVERSITY OF IOWA|
|Smith Jr, Sammie|
Submitted to: Journal of Soil and Water Conservation Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 22, 2007
Publication Date: June 1, 2007
Citation: Wren, D.G., Wells, R.R., Wilson, C.G., Cooper, C.M., Smith Jr, S. 2007. Sedimentation in three small erosion control reservoirs in northern Mississippi. Journal of Soil and Water Quality. 62(3): 137-144. Interpretive Summary: Sediments trapped in reservoirs represent an opportunity to assess historic erosion patterns in watersheds. In the present study, sedimentation rates in forested watersheds of the Holly Springs National Forest were determined. These areas were recovered from gullied land by planting of pine trees in the Yazoo-Little Tallahatchie project. The observed low rates of sedimentation demonstrate the efficacy of reforestation at arresting erosion in watersheds. The study allowed for the comparison between 3 different methods of measuring sediment depth: 137Cs, 210Pb, and textural characteristics all indicated similar amounts of sediment accumulation. Current-use pesticides were detected in the cores, indicating a likely wind-born transfer of agrichemicals from the heavily farmed Mississippi Delta area.
Technical Abstract: The water storage capacity and dam integrity of thousands of flood control reservoirs built since 1950 are potentially compromised by excessive impounded sediments. The fate of these structures depends on the amount and characteristics of this accumulated material. To aid in understanding the scope of impairment of small reservoirs in the hill lands of northern Mississippi, physical sediment characteristics and reservoir storage capacity were evaluated in three small reservoirs (<8 Ha (20 acres)) built in the early 1960’s as part of the Yazoo-Little Tallahatchie erosion control project. A vibrating corer was used to collect continuous cores of deposited sediment and parent material. Particle size, bulk density, and activities of 137Cs and 210Pb were used to identify the boundary between parent material and post-impoundment sediment. Sediment accumulation rates ranged from 1 to 3 mm/year (0.04-0.12 in/year) with reductions in storage capacity of 7% to 19%. Selected cores were tested for selected older residual pesticides (pre-1972) and more recent or current-use contaminants resulted in positive findings for current use pesticides that may have been transported by prevailing winds from the heavily farmed Mississippi Delta area.