SAN DIEGO RIVER – OCEAN BEACH WATER QUALITY IMPROVEMENT PROJECT
Abstract:The project design of the San Diego River-Ocean Beach Water Quality Improvement Project, Phase I included an initial focus on the San Diego River and assumed that local sources (bird and dog feces) were not the primary cause of bacterial contamination at Dog Beach. The study sought to identify any potential infrastructure (either sanitary sewer or storm drain systems), urban runoff and anthropogenic patterns that may be the primary causes of the observed water quality degradation. Based on limited historical upstream monitoring results of bacterial contamination within San Diego River, the study design assumed the River may be transporting this bacterial load downstream and causing beach closures at Dog Beach and Ocean Beach.
This project was initially designed to satisfy these assumptions and identify potential sources throughout the River. The River Segment Source Identification Surveys were conducted to identify specific segments of the River having elevated bacterial levels and follow-up with source identifications. The Near Beach Diversion System Surveys were conducted to determine the effectiveness of the diversion system. These surveys provided results suggesting that upstream reaches of the River are not a source of bacterial contamination at Dog Beach. Therefore, the project was refocused to re-examine local sources. Several focused studies were subsequently designed to identify potential local sources and mechanisms of transport.
Inspections of the storm drains and near beach diversion systems found that samples collected at the base of Outfalls 13 and 14 had significantly higher bacterial concentrations than the nearest upstream station. The exchange of water during a tidal cycle in the estuary provides the mechanism for these elevated bacterial levels to impact the shores of Dog Beach. In addition, focused studies of tidal washing effects showed that bacterial levels increase with high tides. During periods of high tides, the wrack line, consisting of decomposing marine vegetation, dog feces and likely bird feces was washed, providing a mechanism for transporting bacteria into the water column. Samples of this wrack line were analyzed and extremely high levels of all three bacterial indicators were documented. These results suggest that the mixture of kelp and sand used to build the sand berms was a source of bacteria to the water column at Ocean Beach and Dog Beach when the current flows south to north along the shoreline.
Document Type: Research Article
Publication date: January 1, 2004
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