A patch hierarchy approach to modeling surface and subsurface hydrology in complex flood-plain environments

Geomorphology interacts with surface- and ground-water hydrology across multiple spatial scales. Nonetheless, hydrologic and hydrogeologic models are most commonly implemented at a single spatial scale. Using an existing hydrogeologic computer model, we implemented a simple hierarchical approach to modeling surface- and ground-water hydrology in a complex geomorphic setting. We parameterized the model to simulate ground- and surface-water flow patterns through a hierarchical, three-dimensional, quantitative representation of an anabranched montane alluvial flood plain (the Nyack Flood Plain, Middle Fork Flathead River, Montana, USA). Comparison of model results to field data showed that the model provided reasonable representations of spatial patterns of aquifer recharge and discharge, temporal patterns of flood-water storage on the flood plain, and rates of ground-water movement from the main river channel into a large lateral spring channel on the flood plain, and water table elevation in the alluvial aquifer. These results suggest that a hierarchical approach to modeling ground- and surface-water hydrology can reproduce realistic patterns of surface- and ground-water flux on alluvial flood plains, and therefore should provide an excellent 'quantitative laboratory' for studying complex interactions between geomorphology and hydrology at and across multiple spatial scales.