Using a Geographic Information System to Assess Site Suitability for Managed Aquifer Recharge using Stormwater Capture

Abstract:

We are completing a regional analysis of Santa Cruz and northern Monterey Counties, CA, to assess the conditions amenable to managed aquifer recharge using stormwater runoff. Communities and water supply agencies across CA are struggling to mitigate the ongoing drought and to develop secure and sustainable water supplies to support long-term municipal, agricultural, environmental and other needs. Enhanced storage of groundwater is an important part of this effort in many basins. This work is especially timely because of the recently enacted "Sustainable Groundwater Management Act" (SGMA), which requires the development of groundwater sustainability agencies and implementation of basin management plans in coming decades. Our analysis focuses specifically on the distributed collection of stormwater runoff, a water source that has typically been treated as a nuisance or waste, from drainages having an area on the order of 40-160 hectares. The first part of this project is a geographic information system (GIS) analysis using surface and subsurface data sets. Developing complete and accurate datasets across the study region required considerable effort to locate, assemble, co-register, patch, and reconcile information from many sources and scales. We have complete spatial coverage for surface data, but subsurface data is more limited in lateral extent. Sites that are most suitable for distributed stormwater capture supporting MAR have high soil infiltration capacity, are well-connected to an underlying aquifer with good transmissive and storage properties, and have space to receive MAR. Additional considerations include method of infiltration, slope, and land use and access. Based on initial consideration of surface data and slope, 7% of the complete study region appears to be "suitable or highly suitable" for MAR (in the top third of the rating system), but there is considerable spatial heterogeneity based on the distribution of shallow soils and bedrock geology.