Sediment deposition in Lake Aquilla is occurring at much higher rates than anticipated during the planning and design of the reservoir. Based on volumetric storage capacity measurements taken by the Texas Water Development Board (TWDB) in 1995, the capacity of the lake has been reduced by approximately 6,438 acre-feet since impoundment began in 1983.
A preliminary study of the Lake Aquilla basin (USDA-NRCS-WRAT, 1998), performed with the SWAT watershed scale model, indicated that significant reductions in erosion and sedimentation could be achieved by installing conservation practices. However, simulated sediment loads from a few subbasins remained very high, and questionably low sediment reductions were attained by applying practices on cropland.
This study used more detailed GIS layers, an improved SWAT model, and the APEX farm scale model to provide additional insight to erosion and sediment sources in the watershed. The improvements to SWAT were mainly in the sheet and rill erosion subroutines for the land phase portion of the model.
The report (in three parts) on the SWAT and APEX modeling can be downloaded in portable document format (pdf) by clicking on the following links.