Using CODAR Data on Surface Currents to Estimate the Source Water Area for Fish Larvae Potentially Subject to Entrainment by the Diablo Canyon Power Plant Along the Coast of Central California

The standard approach for evaluating the effects of power plant and desalination plant intake systems in California is a modified Empirical Transport Model (ETM). The fundamental inputs to this model are estimates of mortality based on the ratio of the estimated number of organisms entrained to the estimated number in the portion of the source water being sampled. The estimates of mortality are then extrapolated to the larger source water along the coast using data on coastal currents and the period of time that the organisms are in the water column and exposed to entrainment. Extrapolating the actual source areas for the larvae has recently been facilitated by the availability of data on surface currents from high frequency radar installations (CODAR) sites along the California coast. This presentation describes the use of this approach in a recent study on the effects of entrainment at the Diablo Canyon Power Plant in central California. The study also incorporated two acoustic Doppler profilers (ADCP) that were used to adjust the speed and direction of the surface currents measured by the CODAR to values being measured in the water column by the ADCPs. The resulting extrapolated source water areas were consistent with general knowledge on the ocean currents in the area, including the presence of eddies north and south of the headland where the plant is located. The recent policy on once-through cooling adopted by the State of California requires that plants mitigate for impacts for the period between the date they are required to comply with the Policy and the actual date of compliance. The preferred approach for scaling mitigation in the Policy is based on the estimates of mortality and source water areas from ETM, which are greatly improved through the use of CODAR.