UC Santa Cruz

Groundwater resources in the San Lorenzo River Basin (SLRB) are in a state of chronic overdraft, requiring well-informed mitigation measures. Distributed Stormwater Collection-Managed Aquifer Recharge (DSC-MAR) presents a cost-effective method of aquifer replenishment by collecting runoff and infiltrating it as recharge, but its successful implementation demands thorough knowledge of the distribution and availability of hillslope runoff. We apply a surface hydrology model to analyze the dynamics of hillslope runoff at high resolution (0.1 to 1.0 km2) across the 350 km2 SLRB watershed. We used a 3 m digital elevation model to create a detailed model grid, which we parameterized with high-resolution geologic, hydrologic, and land use data. To analyze hillslope runoff under a range of conditions, we developed a catalog of dry, normal, and wet climate scenarios from the historic record. Simulation results show high spatial variability of hillslope runoff, and indicate opportunities for runoff as potential supply for MAR during all climate scenarios. Additionally, our results reveal a consistent increase in the spatial and temporal variability of runoff under a wet climate scenario. The simulation's high-resolution output enables quantification of hillslope runoff at sub-watershed scales, commensurate with DSC-MAR catchments, demonstrating this method as a viable tool for MAR decision making and site planning.