ISE 2016* Application of adaptive hydraulics for estimation of river bed evolution after dam removal on the habitat quantity and quality of aquatic resources and river recreation (#90)
High resolution river topography and sediment characteristics within the San Marcos River, Texas were used to model channel changes and aquatic resource habitat under existing conditions and two dam removal alternatives. An unstructured finite element model (Adaptive Hydraulics - ADH) was used to solve the hydraulic and sediment transport equations while dynamically adapting the mesh properties. Initial water surface elevations were obtained from calibrated two-dimensional hydrodynamic models. Sediment characteristics and depth were derived from penetrometer readings behind Capes Dam. Bed evolution was assessed for existing, half height, and full dam removal at 8.5 m3/s over a 30 day period. Results at 8.5 m3/s showed the system would experience minor amounts of scour under existing conditions, which is what would be expected during bank full conditions in a stream that is in dynamic equilibrium. The bed was then evolved under half-height and full removal using the 8.5 m3/s discharge for 30 days. The resulting topography was then modeled at the long term average flow (4 m3/s), observed drought low flow (2.3 m3/s) and the lowest observed flow from the period of record (1.3 m3/s). The hydraulic solutions were then used to estimate habitat quantity for the endangered aquatic macrophyte Zizana texana and endangered fish Etheostoma fonticola. In addition, the evolved channel conditions under the three lower flow rates were evaluated for recreation use by canoes, kayaks, and tubing. Complete dam removal showed increased habitat for the two endangered species while retaining recreational opportunities similar to existing conditions within the river.
