Monitoring data from a managed aquifer recharge system that collects stormwater runoff in central coastal California. Precipitation, runoff, infiltration, sediment, survey

Groundwater is increasingly important for satisfying California’s growing
fresh water demand. Strategies like managed aquifer recharge (MAR) can
improve groundwater supplies, mitigating the negative consequences of
persistent groundwater overdraft. Distributed stormwater collection (DSC)
MAR projects collect and infiltrate excess hillslope runoff before it
reaches a stream, focusing on 40–400 ha drainage areas (100–1000 ac). We
present results from six years of DSC–MAR operation—including high
resolution analyses of precipitation, runoff generation, infiltration, and
sediment transport—and discuss their implications for regional resource
management. This project generated significant water supply benefit over
six years, including an extended regional drought, collecting and
infiltrating 5.3 × 105 m3 (426 ac-ft). Runoff generation was highly
sensitive to sub-daily storm frequency, duration, and intensity, and a
single intense storm often accounted for a large fraction of annual
runoff. Observed infiltration rates varied widely in space and time. The
basin-average infiltration rate during storms was 1–3 m/d, with
point-specific rates up to 8 m/d. Despite efforts to limit sediment load,
8.2 × 105 kg of fine-grained sediment accumulated in the infiltration
basin over three years, likely reducing soil infiltration capacity.
Periodic removal of accumulated material, better source control, and/or
improved sediment detention could mitigate this effect in the future.
Regional soil analyses can maximize DSC–MAR benefits by identifying
high-infiltration-capacity features and characterizing upland sediment
sources. A regional network of DSC–MAR projects could increase groundwater
supplies, while contributing to improved groundwater quality, flood
mitigation, and stakeholder engagement.