Surface Water Management Division

Healthy Lakes: Reducing the Impacts of Runoff   

In a natural setting, runoff from rainrall is typically slowed and filtered by vegetation or absorbed into the ground before entering lakes or streams.  However, as land is developed hard surfaces such as driveways, houses, patios, and walkways (also known as impervious surface) prevent rain water from infiltrating into the ground.  Instead the rain runs off these materials and picks up pollution that is washed directly into the lake.  The most common sources of polluation are lawn fertilizers, pathogens from pet waste, gasoline, motor oil, and heavy metals from vehicles.  Intercepting or slowing rain water can reduce runoff and be a key to protecting your lake.  

Runoff from driveways and roofs picks up harmful pollutants that wash into lakes

By intercepting runoff with vegetation or allowing it to infiltrate into the ground polluted runoff does not reach the lake

Strategies for Reducing Runoff Impacts

You can help reduce the amount of pollution entering lakes with a few modifications to your property.  Listed below are some of the methods for either increasing the interception of water before in enters the lake or increasing the infiltration of water into the ground.  Many of the strategies listed below are also considered Low Impact Development or Natural Drainage techniques.  

Avoid piping water into lakes

Piping runoff directly into the lake from either your roof or driveway is the worst method for handling runoff.  All of the harmful nutrients and pollutants are injected directly into the lake at the end of the pipe.  Instead, water should be directed away from the lake.  Instead of ditching or piping water into the lake, allow the water to run across a yard or garden.  You can also use a rain barrel to catch the rain from your roof and use it later to water your garden or lawn.

Runoff from roofs and driveways is polluted and should not be piped into lakes

Create a buffer of native vegetation 

The lake shoreline is the last line of defense for lakes. A naturally vegetated shoreline filters stormwater runoff preventing excessive nutrients and pollutants from entering the lake.  Shoreline buffers can also add to the beauty of your property without compromising lake views.  Find out more about creating a lake shoreline buffer.

 

Start a rain garden

A rain garden is just what is sounds like - a garden planted with the intention of capturing rain water from rooftops, driveways, and patios.  Rain gardens are planted in small depressions and act like a native forest that would collect, absorb, and filter runoff.  They are typically small in size but are extremely effective.  Gardens can either be placed strategically to capture rainwater or water can be piped to them from roofs or driveways.  Find out more information about how to plant a rain garden in the resources listed below. 

 

Use pervious pavement for driveways and walkways

Most driveways, patios, and walkways are considered impervious surface, which means water cannot percolate through them into the soil.  Even dirt or gravel surfaces can become compacted and prevent infiltration.  There are now many alternatives available that allow the water to infiltrate into the soil below.  The options include perviuos concrete, asphault, and gravel or grids of paving bricks that can be used for  These options provide the structure you need for driving and parking while reducing polluted runoff.

Berry & Shanaz Bettinger demonstrate water flowing through pervious pavement installed at the Snoqualmie Gourmet Ice Cream Facility

 

Resources for Reducing Stormwater Runoff

Rain barrel Information and Sources (external)  Information from King County on local rain barrel sources. 

Tools for Stormwater Management (external):  An excellent source of information on reducing runoff including rain barrels, rain gardens, pervious pavement, and green roofs - developed by the Lake Superior Duluth Streams Organization. 

Rain Garden - Handbook for Western Washington Homeowners (external): A simple but comprehensive guide to designing, creating, and maintaining rain gardens in Western Washington

Low Impact Development:  Technical Guidance Manual for Puget Sound  (external):  An extensive technical manual to implementing low impact development to reduce the impact of stormwater on water quality developed by the Puget Sound Action Team and the Washington State University Pierce County Extension.   

 

Related Topics

Lakes Main Page

Lake Shoreline Buffers

Lake Friendly Lawn Care

Low Impact Development

Natural Drainage

 

Contact:

 

Gene Williams, Senior Planner, 425-388-3464 extension 4563

Marisa Burghdoff, Water Quality Specialist, 425-388-3464 extension 4639

Jen Oden, Water Quality Specialist, 425-388-3464 extension 4352