United States Department of Transportation
i
Methods for Development of Planning-Level Estimates of Water Quality at Unmonitored Stream Sites in the Conterminous United States
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2009-06-01
[PDF-1.40 MB]
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Edition:October 2003–September 2009
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Abstract:This report documents methods for data compilation and analysis of water-quality-transport curves that meet data-quality-objectives for order-of-magnitude planning-level estimates of stream-water quality at unmonitored sites in the 84 U.S. Environmental Protection Agency Level III nutrient ecoregions in the conterminous United States. The water-quality- transport curves developed in this analysis are intended for use with a stochastic data-generation algorithm, for use with a highway-runoff model designed to better quantify the risk of exceeding water-quality criteria as precipitation, discharge, ambient water quality, and highway-runoff quality vary from storm to storm. Transport curves are regression relations used to estimate constituent concentrations from measured or estimated water-discharge values. Three constituents, total phosphorus, total hardness, and suspended sediment, were selected for regression analysis to develop transport curves for each ecoregion. However, the data compilation and interpretation methods described herein may be used with other water-quality constituents. A total of 24,581 USGS surface-water-quality monitoring stations with drainage areas ranging from 0.002 to 1,140 square miles were identified in the conterminous United States and cataloged for retrieval of water-quality data. The number of paired water-discharge and water-quality samples for total phosphorus, total hardness, and suspended sediment concentrations was 246,403; 107,289; and 275,950, respectively. Examination of transport curves developed with these data indicate that these curves are appropriate models describing the underlying processes of washoff or dilution expected for each constituent, and that predictions made using these transport curves are comparable with published estimates for each water-quality constituent. All of the geographic information system files, computer programs, data files, and regression results developed for this study are included on the CD-ROM accompanying this report. The CD-ROM also contains a data directory with more than 1,876,000 paired discharge and water-quality measurements that include 21 other constituents commonly studied in highway- and urban-runoff studies.
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Content Notes:Supplemental file includes example of a Water-Quality Transport Curve Developed with the Kendall-Theil Robust Line Software (Version 1.0.0)—PLATE.
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