Sedimentation in Kansas Reservoirs

Nationally, sediment is a concern for several important issues including water quality, health of aquatic organisms, and reservoir storage capacity. Sedimentation affects the useful life and aesthetic quality of reservoirs. Knowledge of the quantity and rate of sediment deposition in a reservoir is of fundamental importance for effective reservoir and watershed management. The U.S. Geological Survey (USGS), in cooperation with Federal, State, and local agencies, has completed 20 reservoir sediment studies in Kansas during the past 10 years using a combination of bathymetric surveying and sediment coring. Specific objectives of the studies were to: (1) estimate total sediment volume and mass, (2) estimate annual sediment deposition and yield, (3) assess sediment quality with respect to available guidelines, and (4) provide a baseline for future assessments.

Results of these studies indicated that decreases in the conservation-pool water-storage capacity due to sedimentation ranged from less than 10 percent for Cheney Reservoir (south-central Kansas), Hillsdale Lake (northeast Kansas), and Webster Reservoir (north-central Kansas), to about 25 to 40 percent for Perry and Tuttle Creek Lakes (northeast Kansas). If the historical rates of sedimentation continue, the design sediment pools in Perry and Tuttle Creek Lakes will be filled by 2021 and 2023, respectively. Results also indicated that mean annual net sediment yield ranged from about 0.03 acre-ft/mi2 for the Webster Reservoir watershed to about 1.59 acre-ft/mi2 for the Perry Lake watershed. A statistically significant positive correlation was determined for the relation beween sediment yield and mean annual precipitation for 11 reservoirs in Kansas.

Sediment quality is an important environmental concern because sediment may act as a sink for water-quality constituents and as a source of constituents to the overlying water column and biota. Sediment quality was assessed on the basis of nonenforceable guidelines adopted by the U.S. Environmental Protection Agency (USEPA). Results from most of the reservoirs studied indicated that arsenic, chromium, copper, and nickel typically were detected at concentrations that exceeded USEPA threshold-effects levels. Concentrations greater than the threshold-effects levels occasionally produce adverse biological effects. Cadmium, lead, and zinc were detected at concentrations that exceeded the threshold-effects levels at some of the reservoirs. DDE (a degradation product of the pesticide DDT), which was detected at several reservoirs, had a sediment-deposition profile at Perry and Tuttle Creek Lakes that reflected the history of DDT use. Also, the sediment in several small reservoirs had elevated concentrations of copper and lead that reflected the historical use of copper sulfate (to control algal blooms) and leaded gasoline.

Currently, sediment sources within the Perry Lake and Lake Wabaunsee watersheds are being investigated. The objective of this study is to determine, through a comparison of the composition of reservoir bottom sediments and sources materials, if the majority of the deposited sediment in the two reservoirs originated from the erosion of surface soils or channel banks within the watersheds. An understanding of sediment sources will help future management efforts achieve meaningful reductions in sediment loads and yields. Some reductions will improve the water quality, and extend the life, of affected reservoirs.

Juracek, K.E., 2006, Sedimentation in Kansas reservoirs [abs.], in Program of 23rd Annual Water and the Future of Kansas Conference, March 16, 2006, Topeka, Kansas: Manhattan, Kansas, Kansas State Research and Extention, unnumbered page.