Green Stormwater Infrastructure (GSI)

Residential Rain Garden

 What is Green Stormwater Infrastructure (GSI)?

GSI, also know as Low-Impact Development or LID, makes our homes and neighborhoods more green and slows, captures, and cleans polluted runoff from roads, roofs, and parking lots at its source, before it harms our waterways. We can put green stormwater infrastructure on private property to add attractive landscaping and help slow and clean polluted runoff from roofs, patios, and driveways.

 LID is required for new development and redevelopment projects. For LID information and pre-approved plans for new development and redevelopment projects, visit Development Services.

GSI For Your Property

Downspout Disconnection

What? Many downspouts connect our roof gutters to underground pipes that carry water to our local creeks and Lake Washington. Disconnecting your downspout from existing standpipes can be accomplished fairly easily with an elbow, pipe extension, and splash block.

Considerations: 

  • Disconnect no more than 700 square feet of roof area to a single downspout or splash-block. 
  • Downspouts should not be disconnected within 50 feet of steep slopes or landslide hazard areas. 
  • Downspouts should discharge at least 5 feet from your house foundation. 

Resources:

Native Landscaping

What? Native landscaping is the removal some of your less permeable surfaces – such as patios or lawns - and replacing them with native plants and cultivars that have deeper root systems and amended soils. Native landscaping requires less water and maintenance, and is more capable of absorbing rainwater runoff. 

Considerations:

  • New and young plants need water to grow strong roots. Watering is essential during the first two to three summers after native landscaping installation. 

Resources:

Learn more about Natural Yard Care on your property.

Native Landscaping BeforeNative Landscaping After

 

Permeable Pavement

What? Permeable Pavement can be used for walkways, parking areas, driveways, and patios. The pervious pavement reduces the amount of rainwater runoff by allowing rain to infiltrate through the surface and into the ground. Examples are pervious concrete, pervious asphalt, permeable pavers, and grass pavers.

 

Considerations:

  • Permeable pavement is best on gentle slopes less than 12%
  • Provide an overflow path for runoff from big storms to flow to street drains, landscaping, or a rain garden.

Resources:

Rain Gardens

What? Rain gardens are shallow, bowl-shaped gardens designed to collect and filter water from your roof, driveway, or other impervious surfaces. Rain gardens can be shaped and sized to fit your yard, are filled with a rich layer of mulch and compost to help water soak in, and are landscaped with a variety of plants that fit your yard, sun, and soil. 

Considerations:

  • Your property needs a fairly level yard with a slope less than 5%. Rain gardens should also be located at least 50 feet away from steep slopes to reduce landslide hazard. 
  • Rain gardens should be at least 10 feet from your house foundation. 
  • Rain gardens need well-draining soil to function properly. This can sometimes require removing your existing soil and replacing it with a specialized rain garden soil mixture.

Resources:

 Residential Rain Garden

Rain-capture Cisterns

What? A cistern is a large rain barrel that collects hundreds to thousands of gallons of water. Made of durable materials like metal, heavy plastic, or fiberglass, cisterns fill with water from your roof, gutters, and downspouts. Water can be stored until you need it for irrigation, or can be slowly released by hose to your landscape. 

Considerations: 

  • Cistern overflow should be directed at least 5 feet from your house foundation. 
  • Full cisterns can weigh thousands of pounds. Careful placement and a sturdy foundation will keep your cistern safe and secure. 
  • A dark colored tank and shaded location will limit algae growth, reduce maintenance needs, and extend the lifespan of your cistern. 

Resources:

 Cistern-Oval.jpg

Tree Planting

What? Planting trees creates a canopy, or "umbrella," of leaves that helps provide shade and reduces the intensity of rainfall before it hits the ground. Planting trees is an easy, affordable way to help the environment. 

 

Considerations:

  • Trees should be planted 10 feet from underground utilities and permanent buildings, 20 feet from street lights or other trees, and 30 feet from street corners. Trees near power lines should grow to less than 25 feet tall.  

Resources:

 planting Western Red Cedar_Green Kirkland Partnership.jpg