The interplay of snow, surface water, and groundwater reservoirs for integrated water resources management

Abstract:

Changes in climate, growth in population and economy have increased the reliance on groundwater to augment supplies of surface water across the world, and especially the Western United States. Martis Valley, a high altitude, snow dominated watershed in the Sierra Nevada, California has both surface (river/reservoir) and groundwater resources that are utilized to meet demands within the valley. The recent drought and changing precipitation type (less snow, more rain) has stressed the regional surface water supply and has increased the reliance on groundwater pumping. The objective of this paper is to quantify how changes in climate and depletion of snow storage result in decreased groundwater recharge and increased groundwater use, and to assess if increased surface water storage can mitigate impacts to groundwater under historic and future climate conditions. These objectives require knowledge on the spatiotemporal distribution of groundwater recharge, discharge, and surface and groundwater interactions. We use a high resolution, physically-based integrated surface and groundwater model, GSFLOW, to identify key mechanisms that explain recent hydrologic changes in the region. The model was calibrated using a multi-criteria approach to various historical observed hydrologic fluxes (streamflow and groundwater pumping) and states (lake stage, groundwater head, snow cover area). Observations show that while groundwater use in the basin has increased significantly since the 1980’s, it still remains a relatively minor component of annual consumptive water use. Model simulations suggest that changes from snow to rain will lead to increases in Hortonian and Dunnian runoff, and decreases in groundwater recharge and discharge to streams, which could have a greater impact on groundwater resources than increased pumping. These findings highlight the necessity of an integrated approach for evaluating natural and anthropogenic impacts on surface and groundwater resources.