Wednesday, November 15, 2006 - 11:30 AM

Investigation of Watershed Sediment Sources for Perry Lake, Kansas.

Kyle E. Juracek and Andrew C. Ziegler. U.S. Geological Survey, 4821 Quail Crest Place, Lawrence, KS 66049-3839


Nationally, sediment in reservoirs is a concern as related to several important issues including water quality and reservoir water-storage capacity. The ability to achieve meaningful decreases in sediment loads to reservoirs requires an understanding of the relative contribution from sediment sources within the contributing watersheds. To estimate sources of sediment within the 2,900-km2 Perry Lake watershed of northeast Kansas, representative samples of channel-bank sources, surface-soil sources (cropland and grassland), and reservoir bottom sediments were collected, analyzed, and compared. Within the watershed, a nested approach was used in which five representative subwatersheds were selected for sampling. The subwatersheds ranged in size from 20 to 50 km2. Samples were sieved to isolate the <63-micron-size fraction and analyzed for particle-size distribution, nutrients (total nitrogen and total phosphorus), carbon, 25 trace elements, and cesium-137 (137Cs).

Total nitrogen (TN), total phosphorus (TP), total organic carbon (TOC), and 137Cs were selected as the constituents that provided the best ability to discriminate between channel-bank and surface-soil sources of sediment in the Perry Lake watershed. To adjust for differences in particle-size composition, constituent ratios and clay normalization were used. Computed ratios included the ratio of TOC to TN, TOC to TP, and TN to TP. Constituent concentrations (TN, TP, TOC) and activities (137Cs) were normalized by dividing by the clay (<4-micron) content. Thus, the estimation of sediment sources involved the use of seven indicators (three constituent ratios and the clay-normalized values for four constituents).

Within the Perry Lake watershed, sediment contributions from channel-bank and surface-soil sources varied among the subwatersheds. However, for Perry Lake, channel-bank sources were predominant indicating that these sources increased in importance with increasing distance downstream in the watershed. In this presentation, methods, problems, results, and possible implications are discussed in the context of previous studies.