Climate Change and Subsurface Storage; OR: gw age mixing and what it means to gw quality
University of California, Davis
Adaptation to climate change, groundwater quantity, and groundwater quality sustainability are interlinked in the Central Valley of California. The adaptation can be partly accomplished with strategically located subsurface storage and recovery operations designed to capitalize on the complex but heretofore largely uncharacterized subsurface geologic architecture, wherein only 20 to 50 percent of system volume can be considered aquifer yet the available volume for water storage easily exceeds the combined capacity of California?s four largest reservoirs. The source of water for this recharge could come from excess winter flows as the runoff timing continues to shift toward winter months and away from the spring and summer months. The mechanisms for recharging this water sufficiently and rapidly need to be part of a growing area of research that includes new methods of managing both the floodplains and the vadose zone. The recharge could strongly affect sustainability of both groundwater quantity and quality. Currently groundwater quantity suffers from overdraft in many areas of the Valley and the recharge would obviously help. Further, groundwater quality is likely nonsustainable as long as the dominant source of recharge remains irrigation water, which includes salinity and other contaminants. Groundwater quality could benefit or not, depending on whether the enhanced winter recharge water is less contaminated than the current irrigation sources. Determination of the subsurface geologic architecture, methods for strategic recharge and its role in solving California?s water storage problem as well as groundwater sustainability should be part of a priority research agenda for the future. Integrated hydrologic modeling of groundwater recharge and recovery schemes in the Cosumnes River watershed beneath the Central Valley floor provides insight into how subsurface storage can mitigate loss of snow storage in the Sierra Nevada Mountains.