A dam problem: Characterizing the upstream hydrologic and geomorphologic impacts of dams

Dams are ubiquitous features of most river systems whose construction and/or removal can cause profound changes to the coupled hydrologic and geomorphologic watershed system. Upstream dam impacts are caused by a rise in hydrologic base level and include (i) altering surface water-groundwater interactions, (ii) changing water table depths and soilwater content distributions, and (iii) a transition in the sediment regime from transport to deposition. This dissertation employs numerical simulation to examine the hydrologic and geomorphologic impacts of dam construction and removal. The model used in this effort is the Integrated Hydrology Model (InHM), a fully-coupled, physics-based algorithm for 3D variably-saturated flow in the subsurface and 2D depth-integrated flow over the surface.; In the first phase of this study a process-based hydrologically-driven sediment-transport algorithm was added to InHM and tested against two plot-scale datasets of artificial rainfall, runoff, and erosion. The rainsplash and hydraulic erosion components of the new algorithm were able to reproduce observed sediment discharge data. The interplay between simulated hydraulic forces and erosion/deposition processes was examined.; The second phase of this study focuses on R-5, a small experimental rangeland catchment in Oklahoma. First, the datasets of climate, infiltration, soil-water content, and catchment-integrated runoff and sediment discharge were analyzed to better understand how R-5 functions hydrologically. Then, InHM was used to simulate continuous hydrologic response and event-based sediment transport at R-5 for a six-year period, setting the stage for the third phase of the study.; The third phase of the study examines, in a concept-development mode, the impacts of dam construction and removal at the Searsville Lake watershed. Both existing and new data were used to excite the model. The results from the InHM simulations indicate that (i) dam impacts are largely confined to the area immediately beneath and surrounding the reservoir, (ii) impacts on peak discharge and sediment discharge are substantial, (iii) impacts on water balance components are relatively minor and (iv) impacts caused by climatic variability generally supersede impacts caused by the dam itself.; This study demonstrates that an integrated, physics-based simulation approach can provide insight into the complex hydro-geomorphologic processes impacted by dams.