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MODELING PLUMES IN SMALL STREAMS
Citation:
Frick, W E., D. L. Denton, AND K. P. George. MODELING PLUMES IN SMALL STREAMS. Presented at 227th American Chemical Society National Meeting, Anaheim, CA, March 28-April 1, 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:
Pesticides accumulate on land surfaces from agricultural, commercial, and domestic application, and wash into streams and rivers during dry and wet weather. Flood water retention basins or structures often collect this contaminated runoff, providing intermediate storage and limiting the effluent to one or more storm drains. When storm drains are flowing, the outfall terminals, or ports, form plumes in the receiving stream. Depending on effluent and receiving water flows, effluent and ambient pesticide concentrations, and other variables, such as chemical decomposition, the plumes can form regions of limited impact or overwhelm ambient conditions and lead to extensive downstream degradation. In some cases modifying the conditions of discharge, for example, reducing pump flow rates, will reduce downstream plume concentrations. The EPA Visual Plumes model is used to illustrate the use of models to predict in-stream plume concentrations, trajectories, and cross-sectional distributions of pesticides. A small urban creek in California, is used to simulate a storm drain site. Another example shows the model applied to a very shallow stream in Alaska. The model helps to understand the relationship between effluent and ambient flows and suggests ways to limit harmful concentrations of pesticides in small streams.