UC Davis

Abstract. Increasing reliance on groundwater resources has been observed worldwide during the past 50–70 years and has led to unsustainable groundwater abstraction in many regions, especially in semi-arid and arid alluvial groundwater basins. Managed aquifer recharge (MAR) has been promoted to replenish overdrafted groundwater basins and augment surface water supply. However, MAR feasibility in alluvial groundwater basins is complicated by complex geologic architecture that typically includes laterally-continuous, fine-texture confining units that can impede both recharge rates and regional propagation of increases in hydraulic head. Greater feasibility of MAR hinges on identifying locations where rapid, high-volume recharge that provides regional increases in pressure head are possible, but relatively little research has evaluated the factors that control MAR feasibility in alluvial groundwater basins. Here, we combine a transition probability Markov-chain geostatistical model of the subsurface geologic heterogeneity of the east side of the northern Central Valley, California, with the 3D, variably-saturated water flow code, ParFlow, to explore the variability of MAR feasibility in this region. We use a combination of computationally-efficient local and global sensitivity analyses to evaluate the relative importance of factors that contribute to MAR feasibility. A novel proxy parameter approach was used to describe the configuration and proportions of subsurface hydrofacies and water table depth for sensitivity analyses, and results suggest that recharge potential is relatively more sensitive to the variability of this proxy parameter than to the variablity of individual hydrofacies hydraulic properties. Results demonstrate that large variability of MAR feasibility is typical for alluvial aquifer systems and that outsize recharge rates are possible in select locations where interconnected, coarse-texture hydrofacies occur.