The Impact of Sedimentation on Water Quality in Kansas Reservoirs

Reservoirs are a vital source of water supply, provide flood protection, support diverse aquatic habitat, and provide recreational opportunities throughout Kansas. Understanding agricultural, industrial, and urban effects on reservoirs is important not only for maintaining acceptable water quality in reservoirs but also for preventing adverse environmental effects. Excessive sediment can affect the water quality and useful life of reservoirs and can alter their aesthetic qualities.

The U.S. Geological Survey compared sediment transport and concentrations of chemical compounds adsorbed to bed sediment among six reservoirs located throughout Kansas. The reservoirs were chosen on the basis of differing topography, underlying geology, land use, and climate. Bottom-sediment cores were collected from Cheney Reservoir in south-central Kansas, Lake Olathe, Hillsdale, Cedar, and Tuttle Creek lakes in northeast Kansas, and Webster Reservoir in northwest Kansas. The sediment cores were analyzed for total phosphorus, bulk density, and other selected chemical compounds. The chemical data were combined with reservoir bathymetry to estimate annual sediment and phosphorus yields for each of the reservoir watersheds.

Sediment and phosphorus yields varied considerably amony the six reservoirs. Mean annual sediment yields ranged from 107 pounds per acre per year for the Webster Reservoir watershed to 2,890 pounds per acre per year for the Hillsdale Lake watershed. Mean annual phosphorus yields ranged from 0.04 pound per acre per year for the Webster watershed to 3.74 pounds per acre per year for the Cedar Lake Watershed. Northeast Kansas recieves substantially more precipitation than western Kansas, has more topographic relief, and a significant percentage of cropland in the watershed. Therefore, northeast Kansas may be more prone to erosion loss that results in greater transport of phosphorus through the watersheds to the reservoirs in this part of the state.

Reservoir-sediment studies in Kansas have been useful in reconstructing historical trends in water-quality inflow from the watershed that can be used to measure the effectiveness of land-management practices implemented in upstream basins. These studies also may be used by resource-management agencies to evaluate the historical effects of nonpoint-source pollutants on total maximum daily loads (TMDLs) in the watershed. With the addition of bathymetric syrveys and the inclusion of additional reservoirs, sediment studies also can be used to establish baselines for historical yields of phosphorus and other constituents in future water-quality assessments throughout Kansas. Additional information on U.S. Geological Survey reservoir-sediment studies can be found at: http://ks.water.usgs.gov/studies/ressed/.

Additional information on Reservoir Sediment in Kansas can be found at: http://ks.water.usgs.gov/studies/ressed/

Mau, D.P., 2002, The impact of sedimentation on water quality in Kansas reservoirs [abst.], in Program of 19th Annual Water and the Future of Kansas Conference, March 5, 2002, Lawrence, Kansas: Manhattan, Kansas State University, p. 21.