Stormwater is water that originates during precipitation. It may also be runoff water from overwatering that enters the stormwater system.

If it can’t soak into the ground stormwater becomes surface runoff, which either flows directly into surface waterways or is channeled into storm sewers, which eventually discharge to surface waters.

Stormwater is of concern for two main issues:

• volume and timing of runoff water (flood control and water supplies)
• potential contaminants that the water is carrying (water pollution)

Green Infrastructure (GI)

Large areas of impermeable surface created by roads, roofs, and parking lots cause stormwater to run off these surfaces instead of soaking into the ground.

Green infrastructure can reduce these environmental impacts of development by keeping more stormwater on site and filtering the pollutants stormwater contains.

Green infrastructure (GI) refers to stormwater management practices that reduce runoff and flooding. GI preserves, restores, or mimics natural hydrological processes.

GI can be a more economical and aesthetic alternative to gutters, curbs, and sewers. GI options include:

• aquatic habitat,
• soil,
• vegetation,
• rain absorbing materials

GI may be used for new development, redevelopment, and maintenance or repair projects. Many examples of green infrastructure, such as wetlands and riparian buffers, may already be present on an undeveloped site and could be preserved during construction to utilize their stormwater control benefits.

Stormwater Wetlands

Description
Stormwater wetlands are constructed wetlands designed to hold and treat stormwater runoff. These engineered systems are simpler than natural wetlands and strategically located to capture stormwater with little or no pretreatment.

Placement
Stormwater wetlands can be constructed on shallow slopes of almost all soil types. There should be sufficient drainage into the wetland to ensure the maintenance of hydrology. Avoid areas with shallow water tables if the wetland will receive highly polluted water that could contaminate groundwater.

Maintenance
Periodically inspect inflows and outflows for blockage and erosion. Sediment may need to be removed occasionally from the forebay or main pool.

Stormwater, Impervious Surface, and Stream Health

Urban development is associated with an increase in impervious surfaces, that is, surfaces such as rooftops, sidewalks, and streets that prevent precipitation from infiltrating into the groundwater.

Impervious surfaces increase the volume and energy of stormwater that reaches streams and can lead to adverse physical and water quality impacts, including erosions and increased nutrient runoff.

In this video USGS scientist Tom Cuffney and Tom Schueler, director of the Chesapeake Stormwater Network, discuss the effects of impervious surfaces on stream health.

USGS Video

Stormwater Management (PDF)
– A Guide to Managing Stormwater with Green Infrastructure