To improve groundwater recharge, the Piru Stormwater Capture for Groundwater Recharge Project is planned to capture stormwater from over a hundred acres and then transport it to the Piru Spreading Grounds, a currently inactive 23-acre capture site. As the runoff is collected, transported, and seeps into the soil, the process is intended to filter out sediments and pollutants and reduce bacteria concentration, thereby recovering impaired watershed process by recharging groundwater and improving water quality.
A potential unintended consequence of stormwater capture is a reduction of instream flows, with the potential to affect the frequency or duration of successful fish passage conditions up (by adults) or down (by juveniles) Piru Creek. Salmonids require specific minimum conditions in order to safely pass through a watershed, including sufficient wetted depth and width in the creeks and rivers through which they pass. Stillwater Sciences was contracted to conduct the necessary hydrology, fisheries, and water resources studies to support this project and to evaluate potential project effects on Piru Creek’s fish passage for protected species, specifically California steelhead. Additional support was also provided by GSI Water Solutions Inc., to integrate an understanding of groundwater with surface-water flows as they may be affected by the capture project.
The fish passage study determined hydraulic conditions needed for steelhead migration; determined minimum discharges and the duration, frequency, and seasonality that those minimum discharges have historically occurred; and predict the project effects on the flow regime in Piru Creek and groundwater behavior based on the proposed project activities.