Reservoir Sedimentation Along the Upper Washita River in Western Oklahoma and Northern Texas

Abstract

In response to Dust Bowl flooding of the 1930's, numerous flood control dams were built in Oklahoma and Texas to slow discharge of tributaries into the main stem of the Washita River, effectively reducing peak flows and downstream flooding. The dams in this region have a projected sediment storage lifetime of 50 years, and some are approaching the end of their projected lifetime. Field measurements where made to estimate the volume of sediment impounded behind flood control structures by first determining thickness of sediment at the dam. Next, volume of sediment was estimated by calculating it as a geometric wedge shape, thickest at the dam and tapering to zero upstream. Calculated sediment volume for each site was then compared to predictions by the WEPP (Water Erosion Prediction Project) model for each reservoir. The WEPP model was found to severely underestimate sediment in each reservoir, with no statistical significance between observed and predicted values. Further investigation indicated that 77.5% of residual could be explained by considering length of section line roads in each watershed. In addition, all flood control dams measured were found to be filled to only a fraction of their sediment storage capacity, or to contain immeasurably small amounts.