A method to evaluate duration of the storm effects on in-stream water quality
Wet weather impacts arising from urban catchments are widely recognized as a major cause of unsatisfactory receiving water quality and violation of the water quality standards. If the water body has been classified as partially supporting or not supporting the designated use, the states or designated agencies perform an Use Attainability Analysis (UAA) to determine the proper use of the water body and the water quality conditions needed to achieve this use. This study contributes to future UAA studies aiding the accurate identification of water quality problems and the effectiveness of management alternatives to achieve designated uses by developing a methodology to determine the duration of storm effects on water quality. The methodology to determine the duration of storm effects on water quality involves mainly two steps. First, calibration of an appropriate water quality model that is capable of simulation of unsteady-state conditions. Second, execution of the calibrated model with a number of storm loadings randomly sampled from a specific probability distribution that represents realistic ranges of pollutant concentrations. The purpose is to observe the variations in the simulated water quality constituents to determine the duration of the wet weather condition for a given storm. It is proposed that when the variations in the simulated water quality parameters become negligible, the river system goes back to pre-storm, dry-weather conditions. Latin Hypercube Sampling method was used to determine the duration of the storm effects on in-stream water quality constituent concentrations in the Chicago Waterway System (CWS). Particularly, dissolved oxygen (DO), carbonaceous biochemical oxygen demand and ammonium concentrations were taken into consideration. It was found out that duration of storm effect on DO varies between 2 days to 2 weeks depending on the location and the magnitude of the storm. The relation between the precipitation and the duration of the storm effect was investigated a strong relation between the precipitation recorded in the CWS area and the duration of the storm effects on in-stream water quality constituents was found. Hence, regression equations can be used to predict the duration of the storm effects for the future.
"A method to evaluate duration of the storm effects on in-stream water quality"
(January 1, 2006).
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