A Geospatial Analysis of Stormwater Runoff and Capture for Enhanced Groundwater Recharge

We developed and demonstrate use of data tools for identification of sites where managed aquifer recharge (MAR) might be accomplished through capture of stormwater runoff. This study was completed in the Pajaro Valley, central costal California, which relies heavily on groundwater to meet agricultural, municipal, and domestic demand. An earlier study evaluated regional suitability for MAR in the Pajaro Valley based on surface and subsurface conditions, but did not explore the availability of water sources. In the present study, we combine a digital elevation model of basin topography, soil type, land use information, and historical precipitation records to assess where in the Pajaro Valley there may be enough runoff generated by storms to justify establishment of local MAR projects on this basis.

Attribute screening was used to position 600 hypothetical capture-recharge sites in the study region: 200 one-acre infiltration basins with 50–100-acre drainage areas, 200 two-acre infiltration basins with 100–200-acre drainage areas, and 200 three-acre infiltration basins with 200–300-acre drainage areas. Precipitation scenarios were applied for a period of 20 years, simulating the influence of the number of storms, storm duration, and storm intensity in each year. Results suggest that the large majority of drainage areas 50–100 acres in size would not produce adequate runoff to meet a project goal of ≥100 ac-ft/year/field site. Evaluation of long term (20 year) potentials for 100–200 acre drainage areas show that approximately 10% of hypothetical MAR projects have the potential to produce 100+ ac-ft/year of recharge under normal (median historical) precipitation conditions. Approximately 50% of hypothetical 200–300 acre drainage areas have the potential to meet this goal given the same conditions. This approach advances traditional methods of recharge mapping by incorporating precipitation and runoff analyses for specific sites, and has the potential to aid in the establishment of a distributed system of MAR projects to improve groundwater conditions in this and other basins.