Over the years the overflow parking lot at Elachee Nature Science Center has been paved with all types of surface treatments. And all of them caused erosion as rainwater ran off during hard rains.

So this time when it was time to replace the parking lot surface, Elachee trustee board member Jock Horner said he knew there had to be a better way.

"Over the years there has been a metamorphosis of different surfaces and none of which are optimum," Horner said. "When you get torrential rain, we were getting bad runoff. ... The water was running off the lot into the woods and creating erosion.

"So the thought process was it would be a nice idea to take that parking lot and put a pervious surface and make it an example and an educational tool."

The new parking lot surface is a product called Geoweb, a recycled plastic product produced by Presto Geosystems. And, as a bonus, it was about 50 percent cheaper than paving the 25,000 square-foot lot.

"I want to say that the very first (surface) that I looked at was $8 a square foot, so that'll get your attention, and then you have to install it," said Horner, who served as interim director during part of the project while current director Andrea Timpone was away.

Horner added that Geoweb seemed perfect for Elachee's purpose because there was not much grading of the land and the runoff and erosion would not be an issue.

"It looks like a giant web and it's above ground," he said. "This material comes in big rolls, and they spread it out. And they use pieces of rebar and it holds it apart, then they lay the gravel in it."

Alan Whitehurst, president of Vecco Inc. in Alpharetta, is the Georgia distributor of the Geoweb system and said the system has been on the market since the mid-1980s.

"You can drive on it without the gravel marbeling out underneath your tires," Whitehurst said. "Actually you can use it for grass parking. It allows water to go back into the ground so you don't have to use asphalt or concrete surfaces for parking lots, fire lane access."

The overflow parking lot project design was an effort by Horner, Timpone, other Elachee staff and many volunteers. The project was complete around October, after signs, fences and other accessories were installed.

Along with the new parking lot, which is located at the hiking and biking trailhead, there also is a rain garden.

Timpone said the rain garden was designed and planted by the Hall County Master Gardeners.

"They came in as volunteers and planted it," he said. "Our staff was involved a little. The plants are drought tolerant, but they can also stay wet."

To fill the rain garden, the turnaround of the parking lot is sloped toward the garden to water the plant area. This is possible because the Geoweb system is perforated and flexible.

"Basically what happens is the water settles on the surface, and because it's very porous it percolates down and it hits the layer that you graded to and it starts filling up," Horner explained. "It also can run laterally because of all this perforation. Once it's full it doesn't just overflow ... it moves through it. So however it's graded the water will tend to run in the direction you've graded it to."

According to the Geoweb Web site, the Geoweb Cellular Confinement System provides solutions to soil stabilization and protection. The product is used as a cost-effective way to slope, channel or retain areas such as parking lots.

Horner and Timpone have been very happy with the Geoweb product but said they are happier about what it will do for the environment.

"From the perspective of something coming from it into the environment, there would be nothing," said Horner, who is considering installing the product at his home. "It's basically retaining the gravel, is what its purpose is. You don't end up with the problem of anything washing off of the initial surface."