Planning Water Quality Operations for San Diego County Water Authority Emergency Storage Project Reservoirs

A water quality study of the proposed Olivenhain Reservoir in San Diego County, California, was conducted to guide the design of the inlet and outlet towers and mixing facilities from a water quality operations perspective. Seasonal salinity management and taste and odor control by selective withdrawal and mixing were evaluated. The Olivenhain Reservoir is a joint project of the Olivenhain Municipal Water District (OMWD) and San Diego County Water Authority (CWA). OMWD will use the reservoir to supply water to their proposed membrane filter water treatment plant. CWA will use the reservoir as part of their Emergency Storage Project (ESP) for seasonal storage. Olivenhain Reservoir will have a storage capacity of about 24,000 acre-feet (AF). Olivenhain Reservoir will be connected to the CWA aqueduct with a pipeline. The design of the planned connection between Olivenhain Reservoir and Lake Hodges, an existing reservoir with a capacity of about 30,000 AF was also evaluated. The predicted water quality profiles for three operations scenarios were evaluated and compared with measured water quality profiles from nearby reservoir. Recommendations were developed for selective outlet design and reservoir mixing management strategies. The water quality model will be used to guide operations and maintenance decisions for salinity management, nutrient control, mixing, and outlet elevation selection.