An update on the progress of a tool that's helping communities meet Phase II requirements

By the Urban Water Resources Research Council of the American Society of Civil Engineers

At then end of last year, the National Stormwater Best Management Practices (BMP) Database contained approximately 160 BMPs. This represents substantial growth of the standardized BMP information contained in the database since its initial release of 71 BMPs to the stormwater management community in June 1999. The Urban Water Resources Research Council of the American Society of Civil Engineers, under a cooperative agreement with USEPA, continues to focus on compiling and entering high-quality BMP data into the national database. The significantly expanded database can now be searched on-line or downloaded through the project Web site at www.bmpdatabase.org.

The concept of developing a national database arose in the mid-1990s from the realization that, although there was a plethora of published information on BMP performance, the studies did not follow standardized data collection, reporting, and performance evaluation protocols. Lack of standardization made scientific and consistent evaluation of these data difficult. The need for BMP performance information is particularly critical now since EPA has mandated that most municipalities in the United States with populations larger than 10,000 must obtain a stormwater runoff discharge permit by 2003. One of the key requirements of this permit program is implementation of nonstructural and structural BMPs appropriate to local conditions. Communities need to know which types of BMPs are appropriate for them (e.g., which BMPs function best in cold climates or in areas of heavy rainfall) and how to monitor the performance of the BMPs they select to ensure they function properly. The National Stormwater BMP Database–and data analyses that are made possible as a result of this database–will allow, in the long term, improvement of the BMP selection and design process so that local stormwater management can be much more effective than it is today.

Thus far, key project tasks have included (1) collecting and evaluating existing BMP design and performance data, (2) designing and creating the national BMP database, (3) developing BMP performance evaluation protocols, and (4) evaluating the data collected and reporting initial findings. A companion project to develop stormwater BMP monitoring guidance was completed when it became apparent that much of the available BMP data was of limited value because of inconsistent BMP monitoring and reporting protocols used in the past, making evaluation of data and transferability of findings difficult and often impossible. The monitoring guidance manual is a practical and comprehensive aid and is available through the project Web site.

The database can be used to both track BMP performance and research performance of BMPs. Key categories of data requested in the database include (1) test-site location characteristics, (2) sponsoring and testing agencies, (3) watershed characteristics, (4) BMP design parameters and cost data, (5) monitoring locations and instrumentation, (6) monitoring costs, (7) precipitation data, (8) flow data, and (9) water-quality data. The types of structural BMPs currently accepted in the data-entry module are various types of detention basins, retention basins, infiltration basins, wetland basins, wetland channels, biofilters/grass strips, filter media, hydrodynamic devices, percolation trenches/dry wells, and porous pavement. Types of nonstructural BMPs accepted in the data-entry module include education, recycling, maintenance practices, and source controls. The requested data sets were developed with peer review and input from an international group of experts in the stormwater management field. Based on data received to date, the greatest challenge is to ensure the reporting of accurate precipitation, flow, and water-quality data. The National Stormwater BMP Database Clearinghouse reviews new BMP data sets before they are posted to the master database to ensure that required data (e.g., design parameters, flows, and water-quality data) have been provided and to ensure that the data are technically reasonable (e.g., relationships between peak flows and flow volumes relative to the tributary watershed and precipitation events are evaluated).

Several large data sets received in the last year include multiple BMPs from Shaw Yu, Ph.D., at the University of Virginia and Robert Pitt, Ph.D., at the University of Alabama—Tuscaloosa, as well as 36 BMPs from the California Department of Transportation. These data are undergoing quality assurance (QA) review and will be posted on the project Web site upon completion of the QA reviews. Table 1 summarizes the BMPs in the database according to BMP type.

Table 2 summarizes the types of BMPs currently contained in the database by geographic distribution.

The expanded data set will be analyzed in the summer of 2002 to determine whether new trends regarding BMP performance can be identified. This data analysis effort will build upon the initial findings of the data analysis conducted in 1999, which can be downloaded from the project Web site. These are some of the preliminary findings:

• BMP performance should not be based on comparisons using percent removal alone. It might be appropriate to use this measure only on carefully chosen data subsets, such as sites that have similar stormwater runoff water quality.
• The chosen performance evaluation method can affect reported pollutant removal efficiencies. For example, some BMP types might have been mischaracterized as less effective because of cleaner influent. Most BMPs and biochemical processes will exhibit lower percent removals when the concentrations are low in the influent.
• Retention ponds and wetland basins are not well represented by individual storm-by-storm comparisons because paired inflow and outflow data often are not from the same event.
• Effluent quality is useful for characterizing the effectiveness of the BMP; however, it is still important to determine whether the BMP had a statistically significant effect on water quality at each test site.
• Downstream geomorphic and biological responses and aquatic habitat assessment might be better gauges of long-term BMP effectiveness than pollutant-removal efficiencies alone, but there is insufficient information at this time to clearly suggest which BMPs might best mitigate the effects of urbanization on receiving waters.
• More BMP performance data are needed for sound statistical analysis of their effectiveness and of what design parameters most influence their performance.

For more information, please contact the National Stormwater BMP Database Clearinghouse operated by Wright Water Engineers on behalf of the project team (303/480-1700 or clary@wrightwater.com) or visit the project Web site. The clearinghouse is available to help facilitate electronic transfer of BMP data into the database and welcomes submissions of BMP data to the master database.

See the complete article on the National Stormwater BMP Database in the March/April 2001 issue of Stormwater at www.forester.net/sw_0103_national.html.

Home + About + Subscribe + News + Calendar + Glossary
Talk + Images + Advertise + Contact Us + Search + Register + Services

Erosion Control Magazine | MSW Management Magazine
Grading & Excavation Contractor | ForesterPress | Forester Communications

© 2000 - 2002 Forester Communications, Inc.