Increasing Storm Water Capture for Water Supply using Forecast Informed Reservoir Operations (FIRO) in Orange County, California

Stormwater represents a significant source of water used by the Orange County Water District (OCWD) to recharge the Orange County groundwater basin. Over the last 20 years, OCWD has captured and recharged an average of 50,000 acre-feet per year (afy) of stormwater. Much of this recharge is made possible by the capture of stormwater in the Prado Dam Conservation Pool. OCWD has and continues to work closely with the US Army Corps of Engineers (USACE) to manage the conservation pool and to increase the amount of water that can be temporarily impounded in the conservation pool. Currently, the Conservation Pool is allowed to rise to elevation 498 ft msl (approx. 10,000 af of storage) during the storm season and to 505 ft msl (approx. 20,000 af of storage) during the non-storm season. OCWD has been working with the USACE on a Feasibility Study to permanently allow for storage of stormwater up to elevation 505 msl year-round. Even though increasing the Conservation Pool will increase the amount of stormwater captured, the weather forecasting used to manage the conservation pool can be improved in order to minimize lost opportunities to capture water or unnecessary releases of water to the ocean. To increase the efficiency of stormwater capture, OCWD is partnering with the Center for Western Weather and Water Extremes (http://cw3e.ucsd.edu/) to study the viability of using Forecast-Informed Reservoir Operations (FIRO) at Prado Dam. FIRO represents the next generation of operating water reservoirs using the best available technology. Moreover, given the importance of atmospheric river (AR) storms on water supplies in California, FIRO represents a methodology to take advantage of our increasing understanding of AR storms which are infrequent but provide a large percentage of total precipitation.