Management of Stormwater Runoff

Why manage stormwater?

Stormwater runoff has two major negative impacts:

1. Runoff water entering sewers, lakes, rivers and streams may cause flooding and other quantity related problems.
2. Stormwater often carries pollutants that may severely impact water quality.

In urban areas, the stormwater effects are intensified because surfaces such as roads, parking lots, sidewalks, driveways and rooftops do not allow rainfall to seep into the ground, causing most of the water to run off into storm sewers or combined sanitary sewers which may discharge into nearby rivers. In general, the more impervious the surface, the greater the volume and rate of runoff as well as higher loads of pollutants.

However, runoff from some pervious areas, such as construction sites, can potentially carry high pollutant loads, too. Sediments from construction sites can clog sewers and waterways (increasing the likelihood of flooding) and degrade aquatic habitat. Heavy metals can accumulate in fish tissue. Excessive nutrient levels often associated with agricultural practices cause increased algae growth in lakes, thereby reducing oxygen levels and damaging fish populations. The range of problems caused by stormwater pollution can be vast.

How do you reduce stormwater impacts?

Traditional stormwater management objectives focus on controlling flooding and reducing erosion. Today, stormwater management includes the additional goal of improving water quality. Implementing best management practices (BMPs) can meet these multiple goals.

What are Best Management Practices (BMPs)?

BMPs are any structural, vegetative or managerial practices used to treat, prevent or reduce water pollution caused by stormwater runoff. Stormwater BMPs range from impoundments to pollution prevention activities.

Source Control

Source control, often called pollution prevention, may be the most effective means of preventing water quality degradation caused by stormwater runoff. Many pollutants come into contact with stormwater due to improper materials use and storage, waste disposal practices and accidental spills. Therefore, some prime examples of controlling pollutants at the source include proper containment measures, spill prevention and cleanup, waste reduction, public education, illegal dumping controls, and illicit connection controls. These methods, which can result in significant water quality benefits, prevent pollutants from coming into contact with stormwater runoff in a cost- effective manner.

BMPs are directed toward minimizing the runoff from new developments and siting infrastructure so as to discourage development in environmentally sensitive areas that are critical to maintaining water quality. These controls are very cost-effective if implemented in the site planning phase of new development projects and sizable redevelopment projects. Examples of these controls at the municipal planning level include zoning ordinances, subdivision regulations, and buffers and setback requirements. At the site planning level for new development and redevelopment, these controls include minimizing impervious areas that are connected directly to the storm drainage system, and providing setbacks from surface water and wetlands to protect their environmental integrity.

Extended Detention Ponds

Instead of directing stormwater directly to a river, it is transported to an impoundment. These impoundments hold the water, which allows many pollutants to settle to the bottom of the pond. The water is then released slowly into the river, reducing the chances of flooding. Impoundments can be an effective, low cost means of providing water quality improvement and reduced flooding to a watershed. Usually, the longer the stormwater is detained, the greater the removal of pollutants.

Wet Detention Pond

The principle behind the wet pond is that incoming storm runoff displaces old water, which flows out of the pond. The new runoff is stored in a permanent pool in the pond until the next storm. This creates long detention times and high pollutant removal rates and provides flood protection. The size of the pond is a direct function of the pollutant removal rate; the larger the pond, the greater the removal rate. A unique feature of wet ponds is the presence of aquatic plants and algae that can remove significant amounts of soluble nutrients from stormwater, effectively reducing downstream algal growth.

Infiltration Basins

Infiltration basins capture stormwater and retain it until some, or all, of the stormwater filters into the surrounding soil. Infiltration basins are effective for removing both soluble and fine particulate pollutants. Course grained pollutants clog infiltration basins and should be removed by another BMP or by routine maintenance to prevent premature failure. Large basins can be used to control peak runoffs during large storms. Groundwater recharge can be enhanced using this structure.

Porous Pavement

Porous pavement allows stormwater runoff to infiltrate the pavement layer and enter the underlying soil. This provides for a high degree of soluble and fine particulate pollutant removal, groundwater recharge, low flow augmentation and stream bank erosion control. Porous pavement is feasible on sites with gentle slopes, permeable soils and relatively deep water table and bedrock levels.

Water Quality Inlets

Water quality inlets, also referred to as oil/grease separators, remove sediments, oils and greases from parking lots and industrial runoff prior to discharge to the stormwater channel or infiltration basin. Moderate removal of course sediment, oil/grease and debris can be expected. Routine maintenance is required to remove trapped pollutants.

Conventional Stormwater Control

Enclosures and channel modifications are historically the most widely used methods to manage storm drainage. Open channel modifications usually consist of cleaning, widening, deepening and/or straightening existing water courses. Enclosure improvements may include the installation of storm sewers to direct stormwater to a BMP or receiving water body. Although these practices have localized flood control benefits, they may have negative water quality and quantity impacts downstream.

Cost Estimating Guidelines: Best Management Practices and Engineering Controls
This manual was designed to assist community planning and public works managers develop storm water runoff control programs in the most effective manner for their specific concerns. The intent of the manual is to provide an introduction to, and cost information for, common methods used to control storm water runoff. The manual has been organized into six categories to aid you in identifying specific BMPs.

BMPMAN.PDF (**30.4 MB**)

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Please address all comments and suggestions about the contents of this Web page to rougeweb@co.wayne.mi.us.

The Rouge River National Wet Weather Demonstration Project is funded, in part, by the United States Environmental Protection Agency (EPA) Grants #XP995743-01, -02, -03, -04, -05, -06, -08 and C-264000-01.