Presentations 2016

Stormwater Runoff Analysis for Placement of Managed Aquifer Recharge Projects in Santa Cruz and Northern Monterey Counties, California

UC Santa Cruz

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We apply a USGS surface hydrology model, Precipitation-Runoff Modeling System (PRMS), to analyze stormwater runoff in Santa Cruz and northern Monterey Counties, CA with the goal of identifying catchments (generally 100-1000 acres) from which hillslope runoff can be collected and infiltrated for managed aquifer recharge (MAR). Under the combined threats of multi-year drought and excess withdrawals, this region's aquifers face numerous sustainability challenges, including seawater intrusion and degradation of water quality. Four of the region's eight groundwater basins are classified as medium or high priority by the CA Department of Water Resources, and two of these are critically overdrafted. We address the supply side of this resource challenge by investigating the spatial and temporal dynamics of stormwater runoff, which could be used to replenish aquifers via MAR projects that use infiltration basins, drywells, and flooding of agricultural fields or flood plains.Ensuring the effectiveness of MAR using stormwater requires a thorough understanding of runoff distribution at the subwatershed scale, as well as site-specific surface and subsurface aquifer conditions. In this study we use a geographic information system (GIS) and a high-resolution digital elevation model (DEM) to divide the region's four primary watersheds into Hydrologic Response Units (HRUs), or topographic sub-basins, that serve as discretized input cells for PRMS. To facilitate evaluation of hillslope runoff at a fine scale, we create a high-resolution HRU grid (using 0.1-1.0 km2 cells) and spatial and density-weighted averaging schemes to assign topographic, vegetation, and soil characteristics. Additionally, we couple high-temporal-resolution with high-spatial-resolution climate data to generate input precipitation catalogs that drive the model, allowing analyses of a variety of climate regimes. To gain an understanding of how surface hydrology has responded to agricultural and urban development, we develop input datasets to represent both pre- and post-development conditions. Combined with a concurrent surface and subsurface analysis, our model results help screen for suitable locations of future MAR projects. Additionally, our results improve our understanding of how changes in climate and land use impact runoff and recharge.