Landscape Architect Articles

2009 April LCN - Hardscapes: Capturing Rainwater Via Pavement04-09-09 | News

Capturing Rainwater Via Pavement

Compiled by Matthew Doyle, assistant editor, and Kimberly S. Whitman, Pavestone Company

As water use for ornamental water features and landscaping in general becomes ever more controversial, hardscapes can actually provide a solution. When permeable pavers are teamed with an in-ground rainwater harvesting system as depicted, the result can be independence from water regulations and restrictions. Furthermore, the argument that water supplies are being unwisely diverted for aesthetics is rendered largely moot. All Images Courtesy Pavestone

Diverting what is increasingly perceived as a scarce resource for ?EUR??,,????'?????<

Independence from Municipal Supplies- According to Jennifer Zuri of Aquascape, Inc. ?EUR??,,????'?????<

Ecological Benefits- Whisenand noted ?EUR??,,????'?????<

LEED Credits- Up to 12 LEED credits can be gained from the system making it an ideal application for LEED building projects. Combine this point with the aforementioned independence from possible irrigation restrictions, the ecological benefits and the ever-growing popularity of green products, and you have the potential for some powerful sales tools.

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At this stage, the tank inner liner is in place to create a waterproof sandwich consisting of an outer geotextile, 45-millimeter EPDM liner ?EUR??,,????'?????<

Installing the Water Storage Tank

Note: the following is only meant as a general overview, not a complete guide to a successful installation.

Excavation- The first step was excavating to the depth required by the rainwater storage basin and following a contour that would fit the same, as well as the downspout filter box, overflow detention area and pump vault. Note a depression was created for the pump vault to ensure adequate flow. Clay-free backfill (minimum 4?EUR??,,????'?????<
Waterproofing- An outer non-woven geotextile layer was emplaced next, overlapping the material in a ?EUR??,,????'?????<
Tank Module Installation- The cylindrical pump vault and its associated plumbing were then placed in a convenient position to be connected via the downspout filter box to the nearest downspout. The actual structural support for the tank comes from 85% recycled polypropylene framework modules (termed tank modules by the manufacturer) capable of supporting 38 psi.

They ship in side, bottom, top and interior panels, so each module was assembled before placing it in the excavated area. Stacked blocks share a common panel for the top of the lower unit and bottom of the upper unit. The basin was filled with the specified number of modules needed for the tank size required.

The Eco-Venetian pavers sit atop a bedding layer of coarse, hard and angular material conforming to the grading requirements of ASTM No. 8 or No. 9 in a 2?EUR??,,????'?????<

Cover- Next came the pavement subgrade. A woven geotextile layer was placed on top of the now filled basin, completely covering the framework. The gaps between the liner and tank modules were then backfilled with open-graded aggregate.

The overflow came next. A flexible pvc line was ran from the highest point possible on the side of the pump vault to the overflow release point. This can either be the stormwater system or an infiltration area constructed from several tank modules wrapped in geotextile. Individual site conditions should guide your decision on a release point. The basin top was then backfilled with open-graded aggregate.

Final Steps- The feed lines for the water feature were put in place next, running from their connection in the pump vault plumbing to the ornamental unit?EUR??,,????'?????<
The booster pump that?EUR??,,????'?????<
The downspout filter went in place next, which was a matter of simply dropping the unit into the already excavated area. The flexible feed line was then connected to the point provided on the pump vault. The excavated area was then backfilled before dropping in the filter basket to complete this step.

At this point, all the tank modules are in place and are being covered to create what is effectively the pavement subgrade. A geotextile has been laid atop the structural support modules before open graded aggregate was poured in to backfill the sides. The overflow (similar in design and function to a dry well) has also been installed, and aggregate backfill is being spread in preparation for the bedding course.

Installing Permeable Pavers

Bedding Course- With the water storage basin in place and open graded aggregate covering the top supported by a geotextile, it was time to put in the bedding course. Hard, angular material meeting the grading requirements of ASTM No. 8 or No. 9 was used in a uniform layer screeded to grade with a depth of two inches.

Pavers- Pavers could now start going in while insuring a 1/4?EUR??,,????'?????<