The Green Power of Pervious Paving

by Owner on March 30, 2009

I bet you’ve probably not thought much about where rainwater goes, but it happens to be one of the biggest green challenges facing local communities.

The problem is stormwater management. In the natural state of things rain falls on the ground and gets absorbed, eventually dripping down to the aquifer that slowly replenishes local rivers and streams. It’s a system that is beautiful in its simplicity, as only nature can make it–it takes water away from places that don’t need it to places that do.

Urban development badly gums up this process. Buildings, parking lots, streets, highways and the rest of a city’s infrastructure serve as a permanent, impermeable cover over the ground through which stormwater cannot pass. In a dense urban enclave like my home city of Arlington, VA, 40 percent of the county’s land area is a solid mass of impermeable construction. Even 10 percent impervious cover can measurably impact stream hydrology and ecology, and 25 percent cover will cause serious stream degradation–so the typical urban landscape causes an enormous impact on the ability of local streams and rivers to replenish themselves.

Cities deal with this problem through a network of storm sewers, but it’s a terrible solution. Stormwater running down the street into a sewer grate picks up every last candy wrapper, cigarette butt, discarded plastic bottle, lawn chemical, and oily asphalt chunk in its path. This toxic brew is then blasted at high speed into local streams and rivers, killing anything in the vicinity or downstream as the sludge is carried to larger rivers and bays. Since streams come to depend on sewers instead of groundwater for replenishment, they also dry out a lot faster during times of drought as the primary water source disappears and the depleted aquifer is unable to compensate.

What can you do about this? It’s too late to do much about existing construction, but we can make sure we don’t make a bad situation worse. When it comes to your land, consider the use of pervious paving instead of impermeable materials like asphalt, brick, or ordinary concrete.

There are many pervious options available for paving our driveways, patios and garden walking paths. Gravel, crushed stone, open paving blocks, grass pavers, mulch, turf, and porous concrete are all possibilities that allow water to drain as nature intended. They are sometimes a bit more expensive to install, but the cost may be offset by the elimination of any need to manage running water since it simply drains away into the ground. You also have to be sure to keep the porous surface free of debris that blocks rainwater seeping through it, which may require sweeping or vacuuming a few times a year.

Not only will these materials let rainwater pass through, they will also allow the soil underneath to breathe naturally and harbor normal bacteria and insect life. That’s a good thing for your trees and bushes surrounding the paving.

Please consider replacing any impervious paving materials on your property, or plan for using pervious ones if you’re designing your landscape. You’ll do a lot of good for your neighborhood’s stormwater management and nearby streams.

Check out these ladies talking about the many benefits of using porous concrete:

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