Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2004
Publication Date: 8/1/2005
Citation: Bennett, S.J., Rhoton, F.E., Dunbar, J.A. 2005. Texture, spatial distribution, and rate of reservoir sedimentation within a highly erosive, cultivated watershed: Grenada Lake, Mississippi. Water Resources Research. 41:w01005.2005.
Interpretive Summary: The characterization of flood control reservoirs in terms of sediment properties and storage capacity is important relative to assessing its longevity, and estimating sediment yields in the watershed. Fifty bottom sediment cores from Grenada Lake, MS were analyzed for particle size distribution, radioactive cesium, and bulk density. Additionally, an acoustic profile of the sediment was developed. Our results showed that post-impoundment sediments in the reservoir were enriched in clay relative to watershed soils, and that only 3% of the flood storage capacity had been lost in 50 years. This is an indication that large amounts of eroded sediment remain stored in upstream tributaries and floodplains above the reservoir.
Technical Abstract: There are more than 75,000 dams nationwide that have served a multitude of purposes over the past 50 years. Currently emphasis is being placed on the removal or decommissioning of these aged infrastructures, especially those considered harmful from an environmental perspective. The objective of the present study was to evaluate one such reservoir located in the highly erodible loess uplands of north-central Mississippi. Grenada Lake is a relatively large flood control reservoir built in 1954, and the Yalobusha River, one of the streams entering the reservoir, has a long history of channel instability, bank erosion, and channelization. Through vibracoring, geochronologic, and geophysical techniques, the texture, quantity, and pattern of sedimentation since dam construction are determined. Post-impoundment sediment rich in clay-sized materials and depleted in silt-sized materials has accumulated at relatively uniform rates of 15 to 20 mm yr-1 or 7 to 13 kg m-2 yr-1. Despite large estimates of sediment yield from upstream channel environs, Grenada Lake has lost a minimal 3% of its storage capacity in 50 years of operation. Large quantities of eroded sediment, especially within the Yalobusha River basin, remain upstream of the reservoir, stored on floodplains and in tributary valleys.