Simulating Runoff Quality with the Highway Runoff Database and the Stochastic Empirical Loading and Dilution Model

Abstract

Stormwater practitioners need quantitative information about the quality and volume of highway runoff to assess and mitigate potential adverse effects of runoff on the Nation's receiving waters. The U.S. Geological Survey developed the Highway Runoff Database (HRDB) in cooperation with the FHWA to provide practice-ready information to meet these information needs on the local or national scale. This paper describes the datasets that are available in version 1.1 of the HRDB and demonstrates how data and statistics from the HRDB can be used with the Stochastic Empirical Loading and Dilution Model (SELDM) to simulate highway runoff. The HRDB includes 249 sites, 6,849 runoff events, and 106,869 event mean concentrations (EMCs) collected during the 1975-2017 period. It includes data from 16 States in the conterminous United States and from Hawaii. The EMCs in the HRDB include measurements for 415 different water-quality constituents. These water-quality measurements include 32,944 trace-metal; 27,496 organic; 15,684 nutrient; 13,016 physical property; 10,307 major inorganic; 6,773 sediment; and 649 other constituent values. There are large variations in the data. For example, EMCs for total suspended solids and total phosphorus range from 0.4 to 5,440 mg/L and 0.004 to 22 mg/L, respectively; geometric means range from 1.58 to 1,379 mg/L and 0.017 to 2.82 mg/L for these constituents, respectively. The example simulations indicate that risks for adverse effects of runoff can vary by orders of magnitude; the HRDB and SELDM facilitate selection of representative statistics from available datasets. State departments of transportation (DOTs) need quantitative information about the properties of highway runoff, including event mean concentrations (EMCs) of water-quality constituents, runoff flows, and runoff loads to assess and mitigate potential adverse effects of highway runoff on the Nation's receiving waters. Organization and centralization of highway-runoff data from various sources has consistently been identified as a high-priority environmental research need by the Federal Highway Administration (FHWA), the Transportation Research Board (TRB), and the National Cooperative Highway Research Program (NCHRP) (1-5). To meet this need, the U.S. Geological Survey developed and published the Highway Runoff Database (HRDB) in cooperation with the FHWA (6-8). The HRDB is a data warehouse and a preprocessor for the Stochastic Empirical Loading and Dilution Model (SELDM) (6, 9). Since the initial publication in 2009, the HRDB has been used in research efforts to evaluate potential effects of runoff on receiving waters (10-12), evaluate the performance of post-construction stormwater best management practices (11, 13-15), and estimate total maximum daily loads (TMDLs) (16-18) for national and state research efforts.

Approaches for assessing flows, concentrations, and loads of highway and urban runoff and receiving-stream stormwater in southern New England with the Stochastic Empirical Loading and Dilution Model (SELDM)

“…The annual average daily traffic (AADT) volume, which is a count of the number of vehicles using the roadway per day, is commonly viewed as a basin characteristic of roadway sites that is indicative of runoff quality. AADT data is primarily collected to measure and plan roadway capacity needs, but it has been used, with mixed success, as an explanatory variable for estimating highway-runoff quality (Driscoll and others, 1990;Granato and Cazenas, 2009;Smith, and Granato, 2010;Wagner and others, 2011;Granato and Friesz, 2021a). In the National highway-runoff monitoring study by the FHWA (Driscoll and others, 1990) water-quality monitoring sites were categorized as being "rural" if they had an AADT value of less than 30,000 vehicles per day (VPD), and were categorized as "urban," if they had an AADT greater than or equal to 30,000 VPD based on statistical differences in runoff quality.…”

“…About 9.2 percent of all bridge crossings and 20.3 percent of State-maintained bridge crossings in southern New England have AADT values over 30,000 vehicles per day, which is the traditional rural to urban water-quality threshold known as the Strecker number (Driscoll and others, 1990). In comparison, the population of Highway-Runoff Database monitoring sites (Granato and Cazenas, 2009;Granato, 2019a;Granato and Friesz, 2021b) in southern New England has a median of 61,534 VPD, with 69 percent of sites having AADT values greater than 30,000 VPD (fig. 5).…”

“…[Regression equations were developed for use in the Stochastic Empirical Loading and Dilution Model (SELDM) and other applications by using rainfall and runoff data from 58 highway and 167 nonhighway sites (Granato and Cazenas, 2009;Granato, 2010Granato, , 2013. The highway equations were developed by using sites with impervious fractions from 0.27 to 1.00; the nonhighway equations were developed by using sites with impervious fractions from 0.0001 to 0.994.…”

“…All concentrations were simulated by using statistics for the logarithms of data. The logarithms of concentration and stormflow commonly are analyzed and simulated by using the logarithms of the data because these variables vary by orders of magnitude and are bounded by zero (Driscoll and others, 1979;Athayde and others, 1983;Di Toro, 1984;Van Buren and others, 1997;Novotny, 2004;Granato and Cazenas, 2009;National Research Council, 2009b;Smith and Granato, 2010;Granato, 2013;Smith and others, 2018;Stonewall and others, 2019;Weaver and others, 2019;Jeznach and Granato, 2020;Granato and Friesz, 2021a). The logarithms of concentration were used to develop the random statistics and dependent-relation statistics.…”

Assessing Roadway Contributions to Stormwater Flows, Concentrations, and Loads with the StreamStats Application

“…Currently (2017), the U.S. Environmental Protection Agency (EPA) reports that there are 42,527 impaired water bodies nationwide and 71,193 TMDLs have been approved since 1995 ( 5 ). Many of the constituents of concern for these water-quality impairments, including pathogens, nutrients, trace metals, organic carbon, and sediment, have also been identified as highway and urban runoff quality constituents ( 3,4,6–8 ). Research indicates that DOTs need information, tools, and techniques to address increasing concerns about their roles and responsibilities in the TMDL processes ( 1,3,4,6,9,10 ).…”