Documented performance

February 2006 » Feature Articles

International database helps improve selection and design of stormwater best management practices.


Have you been required to estimate phosphorus concentrations in effluent from a planned retention pond? Have you had to address assertions by a local planning commission that stormwater best management practices (BMPs) don't work and that contamination of a receiving water is inevitable? Have you wondered what the range of performance is for various BMPs for removal of total suspended solids (TSS), or searched for reliable BMP performance data for use in a Total Maximum Daily Load (TMDL)? If questions of this type are relevant to your practice, then the International Stormwater BMP Database is a valuable resource that can help you make better-informed decisions regarding BMP selection and performance.

During 2005, the International Stormwater BMP Database project team made significant progress in its now decade-long effort to promote a scientifically based understanding of the ability of stormwater BMPs to improve urban runoff quality. This effort resulted in information that can be used to improve BMP selection and design. The project team, led by principal investigators Jonathan Jones, P.E., of Wright Water Engineers, Inc., and Eric Strecker, P.E., of GeoSyntec Consultants, now benefits from the broad-based support of a coalition.

Jeff Moeller, P.E., of the Water Environment Research Foundation (WERF), is leading a coalition of funding providers and interested agencies, along with the oversight of a project subcommittee led by Ben Urbonas, P.E., of the Urban Drainage and Flood Control District in Denver.

“WERF subscribers have identified information on the design and effectiveness of various BMPs as one of their top stormwater research needs,” said Moeller.

“The BMP database is an important component to fulfilling this need because it provides a mechanism for the scientific collection and management of data to evaluate the performance of BMPs and to link performance to design. This information ultimately will lead to better designs of BMPs, improved water quality, and significant cost savings for municipalities and others.” The coalition supporting the project now includes the American Public Works Association (APWA), the Federal Highway Administration, the U.S.

Environmental Protection Agency (EPA), and the Environmental and Water Resources Institute of the American Society of Civil Engineers (ASCE).

Members of the original technical sponsor of the database, the Urban Water Resources Research Council of ASCE, continue to be involved in the project sub-committee.

Project Status

As of January 2006, the project provides design, reporting, and monitoring information on approximately 250 structural and non-structural BMP studies from throughout the United States and several other countries included in a standardized format in an online, publicly available database ( Table 1 (page 30) summarizes the BMP performance studies now available online.

Approximately 145 of these studies met criteria enabling application of the statistical analysis techniques adopted by the project team. Results of these analyses are available online for individual BMPs and groups of BMPs, such as wet ponds, dry ponds, and swales.

The database continues to grow by about 30 to 40 BMP performance studies per year, and data are added periodically to existing multi-year studies. The project team continues to solicit data sets from researchers for inclusion in the database, since continued growth in data is necessary to draw more statistically significant inferences regarding factors that lead to better BMP performance. Requirements for submittal of BMP studies can be downloaded from the project website, along with a BMP monitoring guidance manual.

Assessing performance

In addition to developing a standardized database of BMP studies, a key goal of the project is to determine appropriate methods for assessing BMP performance, and then to use the collected and analyzed performance data to improve BMP selections and designs. Through the input of a diverse technical review committee associated with the Urban Water Resources Research Council of ASCE, a set of standard statistical techniques was adopted to analyze the data contained in the database. Application of these analysis techniques has reinforced one of the original project findings - percent removal is not an appropriate measure of BMP performance for many reasons.

The statistical characterizations developed for the BMP data, which are provided in the summary analysis for individual BMPs and categories of BMPs, focus on the quality of effluent achieved, whether statistically this effluent quality is significantly different from influent quality, and the extent to which the BMP treated or bypassed flows.

More recently, the database project team also has been exploring the extent to which a runoff volume reduction was achieved by the BMP; this is a factor that can reduce pollutant loadings and is particularly relevant to achieving TMDLs, as well as meeting other stormwater goals.

A few examples of the types of analyses now available through the project website include the analyses shown in Figures 1 and 2. Figure 1 shows differences in TSS effluent concentrations by BMP type, and also shows the relatively low TSS concentrations achieved by various BMP types.

Figure 2 provides a log-normal probability plot demonstrating a statistically significant difference between the influent and effluent concentrations of TSS for biofilters (such as swales), a data set that grew significantly during 2005 partly because the California Department of Transportation provided a large data set.

Although researchers and municipal staff are increasingly recognizing that percent removal is not an appropriate technique to use in characterizing BMP performance, many continue to struggle with a reasonably understandable approach to replace the easy-tounderstand - but misleading - percent removal approach.

During 2006, the project team will be working to improve the “packaging” of its data summaries to reach a broader audience and to enable more widespread use of the data.

Using the database

The project team routinely receives inquiries from engineers and researchers regarding how they can use the database with regard to water quality issues such as TMDLs, storm drainage, and quality criteria manuals and applications to individual development projects. Examples of how the database has been used to date include the following: • GeoSyntec Consultants used the database for the Lahontan Regional Water Quality Control Board in California to estimate potential effects of BMPs on load reductions to support the development of achievable TMDLs for Lake Tahoe.

• Michael Barrett, professor at the University of Texas, and GeoSyntec Consultants used the underlying data in the database in recent WERF projects to characterize the performance of BMPs and their life-cycle costs, and for development of a unit processesbased approach for BMP selection and design.

• The Washington State Department of Transportation (WSDOT) has provided, and continues to provide, data to the project because WSDOT perceives benefits from the no-cost statistical analyses of their data sets and recognizes the benefit to the overall state of the practice.

• In Oregon, GeoSyntec Consultants used the database in the development of the Clackamas County Stormwater Master Plan, and assisted the Municipal NPDES Stormwater Permit holders in use of the database for modeling the potential effects of their BMPs in meeting benchmarks.

• In Columbia, Mo., Wright Water Engineers used the database to assess the level of protection that could be expected from use of multiple BMPs in series.

• In the course of monitoring the performance of various stormwater treatment systems in Colorado, Wright Water Engineers used the database to compare performance of local BMPs with comparable BMPs across the nation. These comparisons have been valuable, especially on those occasions when observed performance has not fulfilled expectations.

• The Mid-America Regional Council, along with the Kansas City Metro Chapter of APWA, is using the BMP database as one source of information to update its Manual of Best Management Practices for Stormwater Quality. In addition, the Johnson County, Kan., Stormwater Management Program is providing funding for implementing and monitoring local BMPs in accordance with the database requirements.

• For multiple, large development projects in Southern California, the information from the database has been used to assist in BMP selection and design, as well as modeling predictions of overall performance for compliance with the state's Environmental Policy Act.

• Also in California, both environmental groups and dischargers have used or cited the database in debates over whether effluent standards are appropriate for stormwater permits.

Further development Changes to the database project planned for 2006 include the following:

• transition of the project website to a permanent home on EPA's server (similar to STORET),

• addition of the ability to include Low Impact Development (LID) technique performance studies in the database,

• development of a spreadsheet-based data entry format, and

• major revisions to data-retrieval options to improve userfriendliness.

By mid-2006, users will be able to retrieve fact sheets on BMP performance by BMP type and pollutant category in a format comparable to that shown in Figure 1. Researchers will still be able to obtain more detailed underlying data, but now that the database has grown significantly, data summaries will be available to a broader user group in a format that is easier to use for efforts such as storm drainage criteria manuals, TMDL efforts, and other uses.

For more information about the project or to obtain information about how you can submit your study to the database, please see the project website at

Jane Clary is senior environmental scientist, and Jonathan Jones, P.E., is CEO with Wright Water Engineers, Inc. Marcus Quigley, P.E., is senior project engineer, and Eric Strecker, P.E., is principal with GeoSyntec Consultants. The authors can be contacted at,,, and, respectively.





International Stormwater BMP Database project background

In the 1990s, the U.S.Environmental Protection Agency (EPA) mandated that most municipalities in the United States with populations greater than 10,000 obtain a National Pollutant Discharge Elimination System (NPDES) stormwater runoff discharge permit.One of the requirements of this permit program is the use of non-structural and structural best management practices (BMPs) appropriate to local conditions for new development and significant re-development. The requirements also include a provision to periodically evaluate existing flood control systems for potential retrofits to improve water quality of stormwater system discharges.

In response to this program,communities need to know which types of BMPs are appropriate and how to monitor the performance of the BMPs they select to ensure they function properly.However,a scientifically sound, centralized, and straight-forward BMP performance database for assessing the appropriateness of BMPs under a variety of site conditions was lacking.

In addition, BMP studies in the literature historically had not followed standardized data collection, reporting,and performance-evaluation protocols, making a scientific and consistent evaluation of these data difficult, if not impossible.

In response to this problem, the International Stormwater BMP Database project began in 1994. The EPA initially funded the project with the Urban Water Resources Research Council of the American Society of Civil Engineers (ASCE) through multiple grants.The project's original, longterm goal,which remains the central focus of the project, is to gather scientifically valid technical design and performance information to improve BMP selection and design so that local stormwater problems can be addressed cost-effectively.

The database project's principal investigators received the society-wide 2003 State-of-the-Art in Civil Engineering Award from ASCE for their efforts on the database project.

In 2004, the project transitioned to a more broadly supported coalition of partners led by the Water Environment Research Foundation.Wright Water Engineers, Inc.,and GeoSyntec Consultants are the entities maintaining and operating the database clearinghouse and web page, answering questions, conducting analyses of newly submitted BMP data, conducting updated performance evaluations of the overall data set, disseminating project findings,and upgrading the database.

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