|Abstract/Description or Keywords
||This research investigates the nature and controls of surface water–groundwater interaction at the watershed scale, and investigates how mechanisms which control this interaction during baseflow conditions might best be represented within an integrated surface-subsurface numerical model. The study site is the 46 km² Bertrand Creek Watershed, which is situated in a glaciated landscape in southern western British Columbia. A conceptual model of surface water–groundwater interaction along Bertrand Creek is developed based on a field data collection program conducted during the dry seasons of 2006 and 2007. The investigation relies on a suite of field techniques to characterize the nature of the interaction, including hydrologic measurements, stream water chemistry, and point-based measurements of streambed flux. These measurements are complemented by an assessment of topographic slope over the alluvial aquifer to infer the groundwater flow direction. Results indicate that topography adjacent to the stream is a principal control on water exchange between Bertrand Creek and the underlying aquifer. Topography influences the direction of groundwater flow adjacent to the stream and determines the persistence and magnitude of groundwater discharge along the channel. The conceptual model is used to develop an integrated numerical model of Bertrand Creek Watershed using HydroGeoSphere. HydroGeoSphere is a three-dimensional physics-based model that simulates overland flow, unsaturated flow, and groundwater flow in a fully integrated manner. The watershed model is calibrated using field data collected in 2007, including measured streamflows, groundwater contributions to streamflow, hydraulic heads, soil moisture contents, and change in surface water height in a pond. The calibrated watershed model is then evaluated against, and suitably represents, hydrologic data collected in 2006. Simulating baseflows and the seasonal hydrologic response requires that features controlling the spatial distribution of recharge, such as surficial soils and topography, are adequately characterized and represented within the model. Model results further demonstrate that evapotranspiration, particularly transpiration within the riparian zone, is a significant control of baseflows in Bertrand Creek. Finally, the calibrated model is used as a predictive tool to assess the impact of groundwater withdrawals on streamflow depletion.