Climate Change, Flooding, and Heterogeneity Effects on Subsurface Storage and Recovery of Water

Climate change will result in less snow in the Sierra Nevada Mountains and hence less stored surface water to sustain California through its annual April-to-October ‘drought' and through multi-annual droughts. There will likely be more winter runoff and possibly wetter conditions in northern California, but the earlier timing of this runoff precludes capturing it in existing reservoirs. Downgradient of the reservoirs, the Central Valley aquifer system contains vast unused storage space above the water table, but there is currently no feasible mechanism for depositing the excess winter runoff into that vadose zone efficiently and rapidly enough to offset the need for construction of new surface reservoirs. We propose, however, that by (1) recognizing and characterizing the three-dimensional heterogeneity of the subsurface, which is typically composed of less than 50-percent aquifer materials, (2) designing surface spreading facilities that optimize recharge by locating over the small number of good connections to the deep groundwater systems, and (3) by allowing floodplain inundation in strategic locations, a regional, coordinated subsurface storage and recovery operation could replace a substantial fraction of current surface water storage facilities. Subsurface data and modeling analyses indicate that the subsurface of the Central Valley typically consists of 20-40% aquifer materials (sands and gravels) in a matrix of aquitard materials, yet the aquifers appear to be extensively interconnected through largely unknown networks that occasionally intersect land surface. Existence and detection of these intersections will be discussed, and integrated groundwater and surface water modeling of their effects will be shown.