Simulation of groundwater flow in mountain watersheds

Many mountain watersheds provide a reliable source of freshwater for habitat and human use downstream. Hydrodynamics of these basins can be particularly sensitive to change, which may arise from climate change, natural/anthropogenic alteration and other forcing. The timing and intensity of runoff and the recharge of groundwater must be at least partially understood to simulate the potential effects of change. The effects of groundwater on basin drainage are often neglected in simulations due to a lack of empirical data. This study focused on the integration of remote sensing data, geomorphic principles, theoretical distributions of heterogeneity, basin discretization methods, and saturated flow computation to apply a novel technique to understand groundwater behaviour in mountain watersheds. Methods included a geomorphometric analysis to computationally simulate the distribution of geomorphic landforms, which were used to estimate heterogeneity in the shallow subsurface and provide opportunity to evaluate groundwater flow. Morphometric attributes of various landforms were studied and compared to their genetic origin to identify potential landforms. The resulting landforms were subsequently divided into equivalent porous media units (EMUs) based on the theoretical distribution of heterogeneity within landform types. EMUs were evaluated as irregular units used to discretize a saturated groundwater flow model. Groundwater flow was calculated using recharge simulated by any hydrometeorologic model and was routed using Darcian flow from EMU to EMU. Methods of simulating groundwater flow in this study were found to be well suited for the basin type of the study area used (St. Mary Watershed, Montana, USA), albeit with limitations. Results of the geomorphometric analysis compared well with published surficial geology data. The basin discretization method presented in this research would benefit from implicit groundwater flow solving, and application in a basin where abunda