This article originally ran in the August 15, 2019 Wimberley View.
More Than Meets the Eye
Have you noticed the pretty pavers recently installed on the back side of the parking area by the Quarter Shops? Or the pavers installed at Blue Hole Park - two pathways last year, handicapped parking spaces earlier this summer?
Attractive as they are, there is more to these installations than meets the eye. Below those aesthetically pleasing surfaces are engineered infrastructures designed to capture run-off and filter pollutants/suspended solids before they reach Cypress Creek.
At the Quarter Shops that means 75,000 gallons of rainwater per year is now being treated. At Blue Hole, the total treated water for all three sections is 52,000 gallons per year. That's a total of 127,000 gallons per year that could have flowed across asphalt, concrete, or other impermeable surfaces conveying untreated water into Cypress Creek and the Blanco River.
The new parking lot at The Quarter Shops has a large section of permeable pavers.
To fully appreciate permeable pavers, look at how such installations are constructed. On the surface are interlocking concrete pavers that don't quite touch. The gaps are filled with small stones enabling water to drain into a reservoir specifically designed to reduce the concentration of pollutants picked up as the stormwater makes its way to and across the paver surface. The reservoir, usually about six inches or more deep, consists of clean crushed stone aggregate. Water is stored in the voids between the rocks until it infiltrates the ground or otherwise slowly drains away. Some installations include underdrain systems that route infiltrated storm water to either storage for irrigation or an existing stormwater drainage system. If soil infiltration at a particular site is sufficient, an underdrain system may not be necessary.
The design of each individual site takes into consideration both the amount of water that can be captured and structural requirements for the anticipated traffic load. Use of permeable pavers in high traffic areas is in its infancy. But such solutions are currently environmentally preferable for on- and off-street parking, driveways, and sidewalks. The physical topology of the site as well as existing soil conditions must be carefully studied in order to maximize the amount of water that can be captured and processed. Careful excavation is also required to ensure soil compaction during construction does not interfere with infiltration. The initial construction cost for permeable pavers is still higher than conventional methods. However, when savings in stormwater infrastructure and maintenance costs as well as other benefits associated with healthy waterways are considered, the lifetime costs are often lower.
Permeable pavers are just one part of a larger concept for handling stormwater often referred to as Low Impact Development (LID). Other techniques include rainwater harvesting, rain gardens, infiltration/flow through planters, swales, curb cuts and more.
Underlying these techniques is a change in philosophy for handling stormwater. Previous methods were often based on getting water off of the land as quickly as possible by funneling the often polluted run-off into ditches or pipes that drained into the nearest stream. By contrast, LID uses various solutions often spread across the site to capture as much water as possible. Subsequently, the captured water is treated using natural processes - thereby keeping many pollutants out of nearby waterways. These techniques can also reduce long-term water use as rain gardens and other landscape features can be designed to minimize future landscape irrigation by giving plants a good drink of water with every rain.
CARD encourages everyone responsible for development within the Wimberley Valley to incorporate permeable pavers and other LID practices into their projects. We believe such techniques are crucial now and in the future for keeping not just Cypress Creek, but all of Wimberley's waterways "clean, clear, and flowing."
- CARD Steering Committee
Note: CARD publications are written and approved by CARD Steering Committee members. We are listed on our About page. Archives and more information are available on this website (hayscard.org)