Clark County gets more than 41 inches of rainfall a year. That's an astounding 25,400 gallons of water for every 1,000 square feet of developed area. In other words, the parking lots and shopping areas of Westfield Vancouver Mall alone will generate 68.4 million gallons of runoff this year.
With about 400,000 residents and growing, continued urban development for Clark County is inevitable. Southwest Washington has to find creative methods to handle stormwater runoff without over-burdening stormwater systems, or degrading the quality of streams and rivers.
Recent regulatory proposals by the Washington state Department of Ecology have government officials and developers concerned that guidelines for larger or more numerous bioswales and detention ponds will negatively impact buildable land and drive up the cost of economic growth. But what if developers could reduce or eliminate the need for ponds by using pervious pavers?
Developers may shy away from the thought of pervious pavers because they can be up to four times the cost of traditional pavers. But best management practices from the Environmental Protection Agency note that while "pervious pavement can range up to $8 per square foot depending on the design, pervious pavements, when used in combination with other techniques such as bio-retention cells, vegetated swales or vegetated filter strips, may eliminate or reduce the need for land-intensive best management practices, such as dry extended detention or wet retention ponds. In areas where land prices are high, the savings associated with decreased land consumption should be considered."
Developers should also note that runoff for an entire asphaltic concrete or asphalt driveway or parking lot can be managed with just a strip of high performance pervious pavers down one side or around the perimeter. The cost does not have to be prohibitive when the area is designed efficiently, and often, the benefits for using high performance pervious pavers go far beyond cost efficiencies.
One local solution is a pervious paver, which is a mix of natural rock and inert binder that provides a flow-through rate of more than a gallon of water per second, per square foot. That means the pavers are effective even during an excessive 5-inch-per-hour storm event.
Vancouver is home to the first pervious paver production facility on the West Coast – Permapave Northwest.
The company is looking at a number of white aggregates to produce a rooftop paver able to be certified for LEED points in Washington and Oregon, while being acceptable for cool roof standards in California.
Deen Gill is chief estimator at Permapave Northwest in Vancouver. He can be reached at 360-694-0141 or
estimating@permapavenw.com.
