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Remediating Stormwater Impaired Streams

Julie Foley, Master's thesis research project in Natural Resources at the University of Vermont, 2007

Stormwater impaired streams represent a particular challenge to remediate. To help address this issue, an Investigative Docket process was initiated by the Vermont Water Resources Board in 2004 to explore options for designing and implementing effective cleanup plans for stormwater-impaired waters. This Docket concluded that the primary cause of stream water quality impairment by stormwater is excessive runoff from impervious surfaces.

The Docket also concluded that the primary objective of stormwater management should be to return the hydrologic characteristics of impaired streams to a regime that closely parallels the hydrologic properties of streams not currently impaired. However, there was no agreed upon protocol or framework to identify such targets or to prioritize specific locations where stormwater reductions would provide the greatest benefits.

Julie's project was initiated to develop a framework that could be used to fill this knowledge gap. A set of 12 stormwater impaired streams and 15 unimpaired (or "attainment" ) streams was chosen. Only a few of these streams had flow gauging records and so flow was estimated by using a simple stormwater hydrologic model(P-8) and the output from this model was used to generate "synthetic" flow duration curves (FDC) for comparison.

Statistical clustering methods were used to identify groupings of storm water impaired and attainment watersheds. A hierarchical cluster analysis of inherent watershed characteristics identifed watershed groupings that included both impaired and attainment streams.

For these groupings, the mean one-day estimated flow values for the attainment waters were chosen as flow targets for the corresponding impaired watersheds. These flow values satisfied the target setting requirements for assessments of Total Maxiumum Daily Loads (TMDLs). A risk assessment methodology to address the TMDL pollutant load allocation requirement was developed. Binary logistic regression methods were used to estimate the probability that a watershed was impaired based on it characteristics.

The areas with greater impairment probabilities can be tarteted for priority management actions. This approach utilizes readily available data, employs simple models, is acceptable to a wide array of stakeholders and is amenable to adaptive management.

Julie Foley earned her BA in Geology at Colgate University and is currently employed as a Wetland Resource Manager by the Vermont Agency of Natural Resources.

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Last modified October 16 2009 12:35 PM

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