Groundwater Hydrology of the Henry's Fork Springs

Abstract

The Henry's Fork springs supply water important to agriculture, recreation, and fish and wildlife, but no information exists about the recharge processes for these springs. In the absence of regional well data, a methodology combining physical data and environmental isotope investigations was developed to assess spring recharge areas, flow paths, and residence times. The stable isotopes of oxygen and hydrogen were used to constrain recharge elevation and location, and chlorofluorocarbons 11 and 12 were used to estimate residence times. Recharge area siu was calculated from regional water budgets, and depth of water drculation was estimated from aquifermass-llalance considerations. Statistical analysis of temporal variability in spring discharge indicated that winter baseflows from the springs were a function of annual precipitation during the three previous years. Recharge for the larger springs occurs at elevations of 2,200 to 2,400 m, maximum depth of circulation is about 500 m, and recharge areas for the springs range from 15 to 300 km2. Ratios of oxygen and hydrogen isotopes indicated negligible water-rock isotopic exchange under geothermal conditions nor evaporation during the recharge process. However, both high heat-flux values and evidence of mantle helium in spring waters point to connection via upward diffusion between spring flow paths and the underlying mantle. Chlorofluorocarbon (CFC) concentrations in Big Springs, Lucky Dog, Warm River, and Snow Creek indicated recharge years that ranged from pre-1900 to 1994.