While oil gets most of the attention now, water will have a much more important role in future resource conservation debates.In our own part of the world, water gets very little attention unless there is too much or too little. The fact is, we normally have an abundant supply of water through generous rainfall each year. However, with the continued development of our local watersheds, greater attention needs to be paid to conserving this important and necessary resource.
Since our source of water is rainfall, the wisest strategy is to make the best use of this resource. Making the best use involves keeping as much of the rain that falls as possible. This can be done by holding water in large reservoirs. Locally we have several reservoirs on the Brandywine and Red Clay Creeks, but our largest reservoir is the underground aquifer.
The challenge is to make the most effective use of rainfall by recharging as much as possible into the underground reservoirs.
Thirty years ago, the state of the art in stormwater management was detention basins. Current technology emphasizes getting the stormwater into the ground. This has several advantages.
First, it reduces runoff that can create flooding and other problems downstream. Second, and just as important, it recharges the ground water system which, in turn, sustains streams and provides water for residential, commercial, and industrial uses.
In order to maximize stormwater recharge, both good designs and innovative approaches are required. Also helpful is the development of materials that can assist in recharging stormwater. Recharge wells and rain gardens on residential developments are beginning to become more commonplace. Even green roofs, which reduce runoff from rooftops by as much as 75 percent, are being used locally on commercial and institutional buildings.
One of the lesser-used techniques, but one that has been available for some years, is porous paving. This type of paving has its greatest application in low traffic areas. Driveways and parking lots are good candidates for porous paving. The development of this material began at least 25 years ago and several installations in Chester County date back that many years. Porous paving looks like a typical macadam road. On closer examination, however, you will begin to see that the design of the paving allows water to go through small openings.
While porous pavement using typical macadam constituents has been around for some time, a newer product, porous concrete, has recently become more available. Porous concrete works much the same way as porous macadam.
Typical concrete is a mix of cement, sand and small stone. Porous concrete is made without the sand. It is also made with less water and applied drier than typical concrete. As a result, the finished product has small voids that allow the water to pass through.
Porous concrete has similar applications to porous macadam. It can be used in driveways, parking lots and sidewalks. It is applied in much the same fashion as regular concrete, but requires a base of about ten inches of clean stone to provide for drainage.
Porous concrete as well as porous macadam do not have the icing problems that nonporous surfaces have since water drains through and does not remain to be frozen. Porous surfaces do require occasional cleaning but are otherwise low maintenance and very durable. While these applications are slightly more costly than nonporous surfaces, they do reduce the need for additional stormwater management structures such as detention basins. As the technique becomes more popular, costs will come down.
A recent demonstration of porous concrete was held at Delaware Valley Concrete Company's plant in Kennett Square. Attendees watched as a prepared area containing ten inches of clean stone was covered with six inches of porous concrete mix. After the concrete was spread out within the forms, a roller was used to level and compact the concrete. Color, texture, and shape can be added to the concrete for a custom appearance. When the surface is finished, the concrete is covered with plastic for seven days in order to cure. Once finished, the concrete is durable and will infiltrate water very effectively.
As recharge of stormwater takes on a higher priority, existing techniques will be refined and new techniques will be developed. Capturing more rain through ground water recharge will ensure that future water supplies will be able to meet increasing demand while sustaining surface and ground water systems.
o Robert G. Struble Jr. is executive director of the Brandywine and Red Clay valley associations, the oldest and second oldest watershed organizations in the country. He lives