Basic Principles

Stormwater runoff is the result of manmade hydrologic modifications that normally accompany urban and suburban development. Impervious surfaces, soil compaction, and tree and vegetation removal alter water's movement through the environment by reducing interception, evapotranspiration, and infiltration and converting precipitation to overland flow. These modifications impact not only the characteristics of the developed site, but also the watershed in which the development is located. Stormwater has been identified as a major source of pollution for all water body types in the United States; cited as the largest source for ocean shorelines, 2nd largest source for estuaries and Great Lakes shorelines, 3rd largest source for lakes, and 4th largest source for rivers.1 However, the impacts of stormwater pollution are not static—they generally increase with more development and urbanization

Traditional stormwater management practices focus on the collection and rapid removal of rainwater and snowmelt away from the point of impact, through a system of underground pipes and storm sewers, transferring water directly to sewer outfalls without any sort of pre-treatment. The primary focus is to reduce or control localized flooding - accomplished in most, but not all instances. The water collected by these extensive systems is treated as a waste product to be disposed of. This approach generates vast quantities of polluted runoff, disrupts the natural hydrologic cycle, and adds to the contamination and scouring of streams and rivers.

In contrast, "green" or sustainable stormwater best management practices (BMPs) treat water as a resource to be preserved and maintained, taking advantage of natural processes to clean and filter runoff and emphasizing the importance of the hydrologic cycle. This new approach seeks to manage stormwater on individual development or redevelopment sites in a decentralized manner as opposed to the traditional approach of concentrating and conveying runoff through pipes and hardened channels to large-scale, regional ponds or basins. The new approach seeks to slow runoff, mimicking a site's pre-development hydrology and protecting headwater streams and runoff conveyances from erosive stormwater flows.

A small-scale ecoroof finds a home at People's Co-Op in Portland.
Stormwater BMPs focus on retention, detention, or infiltration of rainfall and snowmelt to maintain a natural water balance. Slowing the movement of water through a system leads to fewer problems with erosion and increases the chance for on-site filtration and purification of overland flow. This is often accomplished by using vegetated areas in place of impervious surfaces. Plants serve to slow the movement of water through an area, leading to fewer problems with streambank erosion and increasing the chance fo on-site filtration and purification of overland flow.

BMPs, designed to accommodate the particular needs of a specific site or installation, can reduce the quantity of water transferred to stormwater infrastructure, improve water quality, and add aesthetic and recreational value. BMPs are also often more economical than traditional approaches. The emphasis on built structures is lessened, which reduces installation and maintenance costs.

The shift to more sustainable stormwater practices involves more than a simple change in structural components; it represents a new way of approaching the concept of stormwater management and water use. This evolution within the field of stormwater management is driven by pressure from several directions:

  • Regulatory: The current focus on reducing nonpoint source pollution and rising concerns over aging stormwater infrastructure is pushing regulators to look for new and innovative solutions.
  • Environmental: Heightened awareness of environmental degradation and the disruption of natural processes is encouraging a shift towards sustainable practices and the treatment of water as a resource, not as a waste product.
  • Community: Dissatisfaction with current development paradigms and a growing awareness of environmental issues is creating a desire for increased amenity afforded by areas promoting a green aesthetic.

Including BMPs in your stormwater management "toolbox" is a powerful way to strengthen project design and bring benefit to your organization and the community.

The resources provided below are designed to expand upon the ideas presented above and provide a solid foundation from which to launch your efforts to encourage sustainable stormwater management.

Stone weirs detain stormwater and add an attractive built feature to the lush gardens at the Portland Convention Center.
Basic Principles (PDF, 42K)
Each BMP must be designed to address the specific regulatory and environmental conditions under which it will operate. With that in mind, there are a few basic principles that help tie these practices together.

Benefits of Green Development (PDF, 153K)
Stormwater BMPs impart added benefit to individual projects, surrounding communities, and the organizations responsible for their implementation.

Myths and Misconceptions (PDF, 42K)
Even after extensive exposure to the concepts of sustainable stormwater management, you may still have lingering questions or concerns about the approach. Many of these concerns are shared by those who have come into contact with this new paradigm. With answers to these common questions and an understanding of some of the issues surrounding the shift to sustainable stormwater management, you can increase the likelihood of the success of your project.

The Language of Change (PDF, 51K)
As the ideas and drivers surrounding stormwater management change, so too do the words used to describe the concepts and practices involved.

1 U.S. EPA. 2002. National Water Quality Inventory, 2000 Report. EPA-841-R-02-001. U.S. Environmental Protection Agency, Office of Water, Washington, DC

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