Risk Based Critical Condition Analysis for the Red River Fecal Coliform TMDL
Abstract:Identification of critical conditions has been a challenging task in total maximum daily load (TMDL) development for nonpoint source (NPS) pollution. Traditional approaches to establish critical conditions based on minimum river flow conditions, such as 7Q10, alone may not be appropriate for time varying NPS dicsharge such as rainfall generated agricultural or urban runoffs. While determining load capacity of the river to assimilate pollutants and still meet water quality standards, river flow as well as rainfall conditions should be considered for NPS pollution. Rainfall, intensity and duration, have a significant impact on runoff flowrate and pollutant concentration and should be considered while determining critical rainfall conditions. In this study, an analysis of rainfall's impact on river water quality was conducted for Red River of the North fecal coliform TMDL as a function of rainfall intensity and duration. The analysis results were used to identify the combinations of rainfall intensity and duration that caused the greatest impact on river water quality and estimate the risks associated with combinations of river flow and rainfall conditions. For watersheds such as the reaches of upper Red River Basin in the present study that have great seasonal variations and very low river flow rates during certain periods of a year, minimum river flow conditions may not be appropriate for critical river flow conditions. A risk based statistical analysis was developed to determine critical river flow conditions. Results from the risk based analysis for critical river flow and rainfall conditions were used in determining the river loading capacity and load reduction requirements.
Document Type: Research Article
Publication date: October 1, 2007
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