Sediment Yield Dynamics during the 1950s Multi-Year Droughts from Two Ungauged Basins in the Edwards Plateau, Texas

Abstract

Sediment yield dynamics on the Edwards Plateau region of Texas was dramatically influenced by a multi-year drought that occurred there during the 1950s. To assess the effect of this drought on sediment yield, we used the Soil and Water Assessment Tool (SWAT) to identify the factors that contributed erosion and to propose potential mitigation measures in case of future drought recurrence. The basins of interest to this study were Brady Creek One (BC 1) and Deep Creek Three (DC 3), located in McCulloch County, Texas. Although the streams in these basins are not gauged, the land cover and reservoir sediment budgets have been assessed in a past study. Calibration of SWAT flow simulation was accomplished using parameter transfer from a gauging station located in San Saba River. The results showed that sediment yield from storms above 60 mm was five times more during and immediately after drought period than during continuous wet seasons. Approximately half of the total drought period sediment yield was from five major rainstorms. The multi-year drought coupled with historical high grazing intensity resulted in significant loss of plant cover, which was considered critical in determining erosion and sedimentation rates. To test this hypothesis, the model was run for the periods of high land cover (1990s) using the 1950s multi-year drought data which showed that sediment yield was 24% of that simulated for 1950s land cover. It was concluded that maintenance of surface cover could play a critical role associated with multi-year drought extreme events.