Model Inputs and Outputs for Simulating and Predicting the Effects of Climate and Land-Use Changes on Thermal Springs Recharge: A System-Based Coupled Surface-water and Groundwater Model for Hot Springs National Park, Arkansas

This data release contains model input and output files for simulating and predicting thermal spring flows at Hot Springs National Park (HOSP), Hot Springs, Arkansas. A three-dimensional hydrogeologic framework of the Hot Springs anticlinorium beneath Hot Springs National Park was constructed to represent the complex hydrogeology of HOSP and surrounding areas to depths exceeding 9,000 feet below ground surface. The framework, composed of 6 rock formations and 1 vertical fault emplaced beneath the thermal springs, was discretized into 19 layers, 429 rows, and 576 columns and incorporated into a 3-dimensional steady-state groundwater-flow model constructed in MODFLOW-2005. Historical daily mean thermal spring flows were simulated for one stress period of approximately 34 years (1980-2014), chosen to represent the period of record for historical climate data used in the quantification of the boundary conditions. The groundwater-flow model was manually calibrated to historical daily mean thermal spring flows of 88,000 cubic feet per day observed over a 12-year period of record (1990-1995 and 1998-2005) at the thermal springs collection system. Calibration was achieved by calculating starting heads and general head boundary conditions from the Bernoulli equation and then adjusting the horizontal and vertical hydraulic conductivities of the rock formations and vertical fault and the hydraulic conductance of head-dependent flux boundaries. The groundwater-flow model was coupled to a surface-water model developed in the Precipitation-Runoff Modeling System (PRMS) by using PRMS-simulated gravity drainage as a specified flux recharge boundary condition in the groundwater-flow model. Together, the MODFLOW and PRMS models were used to (1) locate the areas of groundwater recharge to the thermal springs by using forward and reverse particle-tracking capabilities of MODPATH, (2) simulate the effects of variable recharge rates on the spring flows at the thermal springs, and (3) assess possible effects of climate and land-use change on the long-term variability of spring flows at the thermal springs.