Summary of BMP information
1. Waterways and receiving waters near urban and suburban areas are often adversely affected byurban storm water runoff. Impacts may be manifested in terms of:
• alterations in hydraulic characteristics of streams receiving runoff such as higher peak
flow rates, increased frequency and duration of bankfull and sub-bankfull flows,
increased occurrences of downstream flooding, and reduced baseflow levels
• changes in receiving stream morphology such as increased rates of sediment transport
and deposition, increased shoreline erosion, stream channel widening, and increased
stream bed scouring
• aquatic habitat impacts leading to changes in fish and macroinvertebrate populations
and loss of sensitive species
• public health and recreation impacts such as increased risk of illness due to contact
with contaminated water bodies, contamination of drinking water supplies, beach
closures, restrictions on fishing, and shellfish bed closures.
2. A wide variety of BMPs, both structural and non-structural, are available to address urban
storm water runoff and discharges.
• For various reasons (such as cost, suitability to site, etc.) some of these BMP types are
widely used, some infrequently; some are relatively new designs that are not widely in
• Many BMPs are used primarily for water quantity control (i.e. to prevent flooding),
although they may provide ancillary water quality benefits.
• Some BMP types have been analyzed for performance in terms of site-specific
pollutant removal, although not extensively enough to allow for generalizations.
• The pollutant removal performance of some BMP types is essentially undocumented.
• Some BMP types, particularly non-structural and those that do not have discrete inflow
or outflow points, are difficult to monitor.
• There is no widely-accepted definition of "efficiency" or "pollutant removal" for storm
• The role of chemical pollutant monitoring vs. receiving stream biological monitoring in
evaluating BMP performance is not well documented.
3. Only a few cost studies have been conducted for storm water BMPs.
• Due to the limited cost data, a lack of clear definitions of performance, and limited
"performance" data, it is difficult at this time to develop cost-effectiveness comparisons
for various BMP types.
4. The benefits of individual BMPs are site-specific and depend on a number of factors including: • the number, intensity and duration of wet weather events;
• the pollutant removal efficiency of the BMP;
• the water quality and physical conditions of the receiving waters;
• the current and potential use of the receiving waters; and
• the existence of nearby “substitute” sites of unimpaired waters.
Because these factors will vary substantially from site to site, data are not available with which to develop estimates of benefits for individual BMP types.
5. A number of researchers are continuing to work on BMP performance monitoring, and there
are several attempts underway to develop comparison frameworks through the construction of
comprehensive databases on BMP design characteristics and performance.