Subsurface hydrological connectivity between Laramie Range and mountain front aquifers in southeastern Wyoming

Securing sustainable water supply is critical to the arid and semiarid region of the western U.S. As "Water Towers of the West", mountain watersheds are headwater regions where groundwater is recharged from precipitation at high elevations and subsequently supplies rivers and aquifers in adjacent basin fills. In the Laramie Range and its mountain front areas in southeastern Wyoming, a semi-arid region with a snowmelt-driven hydrology, three research well fields have been established. Of the three, Blair Wallis Fractured Rock Well Field, which is located near the crest of the Range, is dedicated to investigating bedrock flow in fractured granite. A dynamic groundwater regime is observed here to respond annually to snowmelt, while the magnitude of this response is tempered by timing of snowmelt and antecedent soil moisture. At Belvoir Ranch and Government Gulch well fields, both lie in mountain front aquifers in the surrounding basin fills, a more complex snowmelt signature, modulated by fluid transport through the riparian zone and bedrock, is observed. Using data from all three well fields, subsurface recharge at the mountain front is estimated to account for up to 19% of the total precipitation over the Range. This estimation is supported by both hydraulic and strontium isotope analyses. Our finding has implications for basin water resources management, as mountain block recharge is often unknown or unquantified.