Sign up today for RiverUpdate
 
 
 
 
 
Map thumbnail
"It makes me feel good to help the environment and other people. It's important to me that I impart similar values in my children because there has to be some component of giving back and sustaining. And that's exactly what Growing Native is all about."
Pamela
 
Low Impact Development

LID Low Impact Development

STORMWATER/LOW IMPACT DEVELOPMENT TECHNIQUES

 

Background

What is Stormwater?
Stormwater is water from rainfall or snowmelt that doesn't evaporate or infiltrate into the ground, but instead runs off, either into the storm drain system or directly into our rivers and streams. Increased amounts of impervious surfaces, such as rooftops, driveways and parking lots, increase the amount of stormwater runoff. In many cases, stormwater is funneled directly from the stormdrain system into rivers, streams and lakes without being treated.

LID techniques such as raingardens are an important way to lessen the effects of stormwater pollution.

Why is stormwater a growing problem?
The increasing and rapid rate of urbanization. Trees and vegetation are replaced by extensive areas of impervious surface, such as roofs and pavement. Soils are compacted by construction equipment and grading. Compacted soils cannot infiltrate water as effectively, impervious surfaces prevent water from being absorbed into the ground, and there is less vegetation to soak up, store, and evaporate water. The result is that less water is absorbed into the ground and more runs off as stormwater.

Stormwater contains heavy metals, nutrients and sediment that degrade the natural quality of the river and surrounding streams threatening the health of humans, land and wildlife, groundwater supplies, and river recreational opportunities.

Stormwater Threatens:

  • Human Health - Stormwater picks up bacteria, chemicals and pathogens that can cause illness. In areas with combined sewer systems, heavy precipitation can also create stormwater volumes and velocities that overwhelm water treatment systems, causing raw sewage overflows.
  • Aquatic Wildlife Health - High temperatures, nutrient-fueled algae growth, and erosion threaten the health and habitats of sensitive fish, aquatic birds and other marine animals.
  • Recreation - In Washington, DC, swimming in all rivers and streams is illegal due to stormwater pollution, but fishing and boating can also be dangerous and unpleasant. 
  • Property - Erosion damages property, stream beds, and wildlife habitats.

Stormwater Solutions

Low impact development (LID), also called Environmental Site Design (ESD), is an approach to site design and stormwater management that seeks to mimic the pre-development runoff characteristics on a development site. It aims to prevent stormwater pollution by reducing or eliminating environmental pollutants picked up by stormwater, and to reduce the overall amount of stormwater entering the stormwater system.

Traditional stormwater management practices focus almost entirely on capturing and piping stormwater off-site as quickly as possible. Few efforts are made to prevent stormwater, or to retain the natural hydrology of the development site.

Site planning with low impact development (LID) practices begins with developing strategies to conserve the natural hydrologic assets and functions of a site. LID site conservation techniques include directing development away from sensitive environmental areas, preserving native vegetation and soils, maintaining existing drainage courses, and minimizing the extent of impervious areas. Stormwater that cannot be prevented is treated on-site, using natural filtration systems that capture, treat, and slow the release of stormwater.

Current Recent and Ongoing Projects:

Montgomery County Road Code: In 2007, the Potomac Conservancy, along with several other partner groups, worked with the Montgomery County Council to pass a new "road code" bill that addresses roadways as one of the largest sources of polluted runoff in the county. This bill requires management and treatment of stormwater using LID practices within the road right-of-way, instead of simply piping runoff untreated into our neighborhood streams. Thanks to this bill, familiar landscaping features like grassy medians, street trees, and sidewalk planters will do double duty, helping collect and filter polluted stormwater as they beautify our neighborhoods and provide pedestrian havens. This is the first instance in the nation that we know of where a jurisdiction has built stormwater pollution prevention requirements into its roadway design standards.

Potomac Conservancy and its partner groups worked with the County Executive to create technical regulations implementing this groundbreaking bill. Click here to Take Action on these regulations.

Additional Resources: