You are here:
GENERAL DESIGN CONSIDERATIONS IN BMP DESIGN
Citation:
O'Connor*, T P., M. Clar, AND B. Barfield. GENERAL DESIGN CONSIDERATIONS IN BMP DESIGN. Presented at World Water & Environmental Resources BMP Technology Symposium of the Congress 2004, Salt Lake City, UT, June 27 - July 01, 2004.
Impact/Purpose:
To infom the public
Description:
Today, many municipalities are implementing best management practices (BMPs). The most commonly used structural treatment BMPs that will be discussed in the presentation are ponds (detention/retention) and vegetated biofilters (swales and filter/buffer strips).
Historically, structural BMPs were employed to capture peak flows, assist in local drainage, and manage the quantity of runoff produced during wet-weather flow (WWF), i.e., flood control. Current design typically still focuses on rainfall events that range from 2 to 10 inches of daily rainfall and occur at much longer return periods ranging from 2 to 100-year. These storms may contain significant pollutant loads, but their contribution to the annual average pollutant load is really quite small due to the infrequency of their occurrence. In addition, longer periods of recovery are available to receiving waters between larger storm events allowing receiving water systems to flush themselves and the aquatic environment to recover.
Water quality control of urban runoff is still a relatively new and developing technology. The addition of water quality considerations in the design of BMPs has introduced a new dimension to the traditional hydrologic considerations for BMP design. Water quality considerations have created a shift from flood events to a continuous long-term rainfall-runoff BMP design volume approach and the pollutant loads associated with these volumes.
To treat the bulk of the pollutant loads from stormwater runoff, many states and municipalities specify a treatment volume that is designed to capture the initial component of the stormwater runoff. In practice this is achieved by specifying a rainfall amount (e.g., the first ?-inch or 1-inch) or the capture of a stormwater runoff volume that correlates to a design storm (e.g., 6-month, 1-year, or 2-year frequency storm). BMPs that encompass both peak discharge hydrology and small storm hydrology would optimally use a system that incorporates on-site treatment and storage of stormwater for the smaller storms while protecting downstream from floods. By including supplemental measures using either distributed and/or centralized controls, the peak discharge control strategies can be upgraded to perform water quality control.
Depending on the stormwater management goals and objectives identified for a specific site or area, a combination of one or more treatment BMPs may need to be used to meet the design objectives, in what is often referred to as a treatment train approach. No single BMP is as effective as a "train" (that is series) of practices and controls.
This presentation, based on an evolving U.S. Environmental Protection Agency BMP de design guide, presents general design considerations that should be considered in the sign of treatment BMPs to improve water quality.