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USING PUBLIC-DOMAIN MODELS TO ESTIMATE BEACH BACTERIA CONCENTRATIONS
Citation:
Frick, W E., D. J. Baumgartner, M Molina, T. Khangaonkar, AND G. L. Robertson. USING PUBLIC-DOMAIN MODELS TO ESTIMATE BEACH BACTERIA CONCENTRATIONS. Presented at 2004 Ocean Research Conference, Honolulu, HI, February 15-20, 2004.
Impact/Purpose:
A main objective of this task is to combine empirical and physical mechanisms in a model, known as Visual Beach, that
â— is user-friendly
â— includes point and non-point sources of contamination
â— includes the latest bacterial decay mechanisms
â— incorporates real-time and web-based ambient and atmospheric and aquatic conditions
â— and has a predictive capability of up to three days to help avert potential beach closures.
The suite of predictive capabilities for this software application can enhance the utility of new methodology for analysis of indicator pathogens by identifying times that represent the highest probability of bacterial contamination. Successful use of this model will provide a means to direct timely collection of monitoring samples, strengthening the value of the short turnaround time for sampling. Additionally, in some cases of known point sources of bacteria, such as waste water treatment plant discharges, the model can be applied to help guide operational controls to help prevent resulting beach closures.
Description:
Stretches of beach along popular Huntington Beach, California are occassionally closed to swimming due to high levels of bacteria. One hypothesized source is the treated wastewater plume from the Orange County Sanitation District's (OCSD) ocean outfall. While three independent science review panels found no strong or consistent links between the ocean discharge four miles offshore and bacteria concentrations in the surf zone, the empirical data provided only intermittent evidence of the offshore plume, making it impossible to disprove the hypothesis. Computer models could have filled the data gaps with simulated concentrations, using monitoring data to verify the models. A public-domain model to address the problem is under development. Called Visual Beach, in concept it is patterned after the USEPA Visual Plumes program, using its initial dilution models to estimate plume rise and dilution and its built-in bacteria decay models to estimate concentrations. However, it is being modified to use the Environmental Fluid Dynamics Code (EFDC) to estimate long-term waste-field movement. Using time-series records of effluent flow and characteristics, ocean currents, and density stratification, continuous estimates of waste-field location are achieved.