Ah, the soothing sound of softly falling rain. Rain brings life to our islands, keeping the forests lush, nourishing our gardens, replenishing our groundwater and feeding our lakes, streams and wetlands. 

But the rain can become stormwater, draining off of roads, parking lots, and commercial work areas carrying pollutants to the same lakes, streams wetlands and marine waters.

An array of techniques for managing stormwater runoff  is collectively called “low impact development” or LID for short. LID emphasizes conservation and use of on-site natural features to protect water quality. Examples of LID include grassy swales, rain barrels, green roofs and rain gardens.

One example, pervious paving, is a low impact development technique that helps assure that the rain is beneficial, not a transporter of  toxins. No matter which of its many forms is employed, these surfaces effectively filter and drain stormwater back into the soil. Pervious paving can be used for walkways, patios, driveways, parking areas and more.

So what is pervious paving? It’s a variety of products and techniques including:

PICP comprises a layer of solid concrete pavers separated by joints filled with small stones. Water enters the joints between the pavers and through an “open-graded” base-crushed

stone layers. The void spaces among the crushed stone store water and infiltrate it back into the soil. The stones in the joints provide permeability, and the base filters stormwater and helps reduce pollutants.

These products use forms and on-site concrete pouring to create concrete paving with voids which are planted with grass. The concrete is poured onto a  gravel subsurface that provides excellent drainage. The overall look is that of a lawn.

A concrete concoction with few fine materials captures rainwater and allows it to allows rain to seep into the ground, This pavement technology creates more efficient land use by eliminating the need for retention ponds, swales, and other stormwater management devices.

There are examples of these techniques around the islands. One of the newest is right in Friday Harbor at 470 Argyle Avenue, the new site of the historic Churchill House. Parking areas and walkways at the site have been created with a “grass block” technique using pre-formed concrete grids with open areas for soils and grass. Because the work will result in a reduction of stormwater runoff, the Town of Friday Harbor waived the bulk of the annual stormwater fees for the project owners.

Planning a project and/or like further information on pervious paving?

Local resources include:

Town of Friday Harbor

Mike Bertrand 378-2810

San Juan County

Shannon Hoffman 370-7582

Conservation District (LID Manual)

http://www.sanjuanislandscd.org

Puget Sound Action Team

www.psat.wa.go/Programs/LID.htm