Integrated Hydrologic Modeling of Lake Tahoe and Martis Valley Mountain Block and Alluvial Systems, Nevada and California

The U.S. Department of Interior has identified the Truckee River basin as highly likely for potential water supply conflict in the future. A critical water supply to the Truckee River is outflow from Lake Tahoe, and surface and groundwater contributions from the Martis Valley hydrographic area. This paper highlights the development of an integrated surface water and groundwater model, GSFLOW, in the Lake Tahoe and Martis Valley hydrographic areas to ultimately assess the effects of changing climate on surface and groundwater resources, and to identify the hydrologic mechanisms responsible for observed and simulated effects. Maintaining a balance between accurate representation of spatial features (e.g., geology, streams, and topography) and computational efficiency is a key objective for developing a realistic and computationally efficient model that can adequately simulate important hydrologic processes, including groundwater, stream, lake, and wetland flows and storages. Computational efficiency is required in order to calibrate to a diverse set of observation data, including surface water flows, lake levels, and groundwater head observations. Our work highlights how maintaining continuity between mountain block, stream zones, and basin fill units through data driven and conceptual layering is efficient, and results in accurate calibration to both surface water and groundwater observations. Additionally, we treat spring and wetland areas as groundwater head observations equal to land surface elevation, which provides constraints on groundwater heads over a much broader part of the model domain relative to well head observations alone.