MOUNTAIN FRONT RECHARGE IN A SEMI-ARID CLIMATE, SOUTHWEST MONTANA

Groundwater recharge to regional valley benches originates largely from adjacent Mountain Front Recharge (MFR). The Madison Valley in Southwest Montana is a semi-arid cold climate that receives 31.75cm annual valley precipitation. In this study, two drainages are characterized and compared, looking at the hydrological processes between the stream and groundwater. North Meadow Creek is a high elevation stream dominated by snowmelt and contains reaches of gaining and losing surface water to groundwater. Daylight Creek is a spring fed disconnected stream. Methods used a surface water balance, temperature as an environmental tracer and two and three component mixing models to investigate groundwater underflow, stream and groundwater fluxes, and source waters for streams. The smaller Daylight Creek watershed is a disconnected stream with a range of specific vertical discharge at 2-5m/s to 8-10m/s. The larger North Meadow Creek watershed contains three unique zones. The upper mountainous reach is a gaining stream, the middle reach is a transition from gaining to losing, and the lower zone is a losing reach. Specific vertical discharge has a range of 5.0-5m/s to 8.0-6m/s. A two and three component mixing model was utilized to fractionate soil water and groundwater. North Meadow Creek has a soil water pulse during the spring melt and a fluctuating fraction groundwater contribution of 10% to 75% throughout the study period. Daylight Creek has no seasonal trend and a constant 40%-50% groundwater contribution during the study period