Models for Assessing the Cumulative Impacts on Larval Fishes Due to Entrainment From Multiple Power Plant Intakes in the Southern California Bight

The cumulative impacts of multiple power plant intakes have been a concern of resource agencies and other stakeholder groups in California and in other locations in the United States. Cumulative impacts are also required to be addressed under permitting done in compliance with the California Environmental Quality Act (CEQA). As a result, the California Energy Commission required that cumulative impacts were addressed in the documentation submitted as part of the permitting process for the repowering of the Huntington Beach Generating Station in southern California. A 2004 workshop on the issue resulted in the development of a first-order model that could be expanded as additional data became available. This model evaluated the potential effects of entrainment by the twelve power plants in the Southern California Bight, the area from point Conception to just south of the U.S.-Mexico border, that withdraw a total average of 24.0x109 l of seawater daily. Since data on larval fish entrainment were not available from all twelve plants at that time, a volumetric approach was used to estimate entrainment mortality. This approach assumed that, on average, the larvae were uniformly distributed in the nearshore areas where the intakes are located. This was shown to be a reasonable assumption for locations such as Huntington Beach, where the offshore intake is located along fairly homogeneous stretch of sandy beach. This simple model showed that power plant intakes accounted for additional mortality of 0.11 to 0.84 percent which varied depending on the period of time that the larvae were exposed to entrainment. The model was expanded to account for different rates of water movement once data on nearshore currents were available from a number of locations. These simple models of cumulative impacts can be expanded to include more detailed current patterns using high resolution CODAR surface current data that are now available for nearshore areas in California.