Modeling the Impact of Complex Irrigation, Agricultural Impoundments, and Mining Activities on Salinity and SAR in the Tongue River Watershed, Montana

The Tongue River watershed extends through two states and exhibits highly variable topography and climate patterns. While the Big Horn Mountains represent 9 percent of the total watershed area, they contribute roughly 63 percent of all the water in the Tongue River system through snowmelt. Other unique watershed features include high-altitude reservoirs and diversions, extensive irrigation for agriculture, coal bed methane operations, and stock ponds. Tetra Tech developed a comprehensive model of the watershed based upon locally available datasets and innovative process-based model customizations using the Loading Simulation Program in C++ (LSPC) modeling platform. The focus of the model was to simulate hydrology, salinity, and sodium adsorption ratio (SAR). This paper highlights the challenges, solutions, methods, and results associated with this complex modeling application.