Virtual Tour of Stormwater BMPs

When it rains, water soaks into the ground, or flows over land. In developed areas, such as Montgomery County, a large proportion of the earth's surface is covered with impervious surfaces that rainwater can not permeate through. The water that flows over land is called "stormwater runoff". In natural environments, there is much less stormwater runoff because vegetation absorbs and evapotranspirates rainwater, while the roots promote infiltration into the groundwater (Figure 1).

This excess of water runoff causes problems for the citizens and natural resources of Montgomery County. One danger is that the increase in water quantity causes flooding to downstream neighbors. Flooding causes water damage and increases erosion. Some property owners lose valuable streamside property to erosion each year when flooding occurs.

In addition to causing destruction, stormwater picks up sediments and other pollutants that lessen the water quality of our streams and rivers. When rainwater flows over lawns, roofs, and parking lots, it picks up any pollutants from these areas, including dirt, fertilizers, oils, and other chemicals. The contaminated runoff is usually collected in storm sewers inlets, and conveyed through piping directly to our streams. Water pollution transported by stormwater is called nonpoint source pollution, because it does not come from a single point, pipe, or property.

As the water flows downstream, the amount of pollution in the water increases. Therefore, all the nonpoint source pollution that is picked up by stormwater in Montgomery County flows through other communities, including the city of Philadelphia. Pollution such as sediments and toxic chemicals are expensive remove from dinking water supplies. It also harmful to the wildlife and fish that live in the Schuylkill and Delaware Rivers.

The Delaware Estuary is where all of our stormwater flows into the Atlantic Ocean. According to the Partnership for the Delaware Estuary, nonpoint source pollution is the biggest water quality problem for the Estuary. In fact, it is so serious, they dedicated the entire Fall 2005 Newsletter to discuss nonpoint pollution and the ways it is being locally addressed.

Activities or structural improvements that help reduce nonpoint source pollution and limit the volume of stormwater runoff are called Best Management Practices (BMPs). BMPs are divided into two categories: structural BMPs and non-structural BMPs (Table 1). This website will help you find examples of structural BMPs in Montgomery County so you can learn how you can also help protect our water resources.

Table 1: Example of Structural and Non-Structural BMPs

Structural BMPs	Non-Structural BMPs
Pervious pavement	Reducing impervious surfaces
Infiltration basins	Protecting sensitive natural resources
Subsurface infiltration beds	Minimizing disturbance
Bioinfiltration trenches	Source control/ Street sweeping
Rain gardens/bioretention areas	Smart growth practices
Dry wells and Seepage pits	Conserving riparian areas
Vegetated swales	Protect/utilize natural flow pathways
Green roof	Re-vegetate disturbed areas with native species
Wetponds
Water quality filters on inlets	Source: PA DEP Stormwater BMP Manual

Non-structural BMPs limit the impact of development by good planning. Structural BMPs reduce volume and peak rates of stormwater flow, and some improve water quality. Most BMPs use vegetation to slow stormwater runoff, infiltrate the water into the soil, and absorb excess nutrients and other pollutants, cleaning the water leaving the BMP.

For more technical information on Stormwater BMPs, please refer the PA Department of Environmental Protection (DEP) Stormwater BMP Manual. This document is currently in draft form, but the final version is to be published in early 2008.

For a quick-reference definition of stormwater terms, you can use the online glossary provided by The Stormwater Center.

Table 1: Example of Structural and Non-Structural BMPs

page last updated 1/17/2007