Aquifer Recharge

collect much of the debris that could clog the culvert and cause water to back up and potentially flood the street.

With the current emphasis on creating sustainable landscapes, the application of and reliance on traditional storm water removal infrastructure—such as municipal storm water systems—are being subsumed by on-site water reuse and water conservation strategies. Grading solutions that allow water to be absorbed in the soil to recharge the underground aquifer or stored in a retention pond for later uses, such as for onsite irrigation, are becoming increasingly common. Methods for conserving surface water on-site include the creation of water gardens and detention ponds, the creation of minimal slopes to allow surface water to percolate into the soil, and use of porous paving surfaces such as crushed rock, modular units, or even porous concrete and asphalt. The photograph in Figure 14.22 provides an example of surfacing an expansive level or slightly sloping area with compacted crushed rock, a design approach with definite aesthetic appeal which at the same time contributes to water recharge of the area’s aquifer. Figures 14.23-A and 14.23-B show examples of the use of modular paving set in sand to provide a smooth surface comfortable for walkers, bikers, or parents pushing strollers. Rainwater can penetrate to the subsoil below the paving or be directed to the adjacent landscape areas. Puddles, which commonly occur with nonporous paving, are minimal where porous or modular paving surfaces are used. Figure 14.23-A shows a walkway and street surfaced with modular concrete pavers, and the surface in 14.23-B is a walkway surfaced with modular granite rock. Figure 14.23-C shows a dense, highly urbanized shopping setting where the designer selected a combination of concrete pavers and compacted crushed rock for the paving surfaces. Water Figure 14.22 Surfacing an expansive can penetrate into the soil below both paving surfaces to area with compacted crushed rock, The Hague, the Netherlands provide moisture for the trees.

Figure 14.23-a Use of modular concrete units set in sand for a Delft, the Netherlands, neighborhood walkway and road Figure 14.23-B Use of modular granite units set in sand for a Delft, the Netherlands urban walkway

Porous concrete is seeing increased use as a means to return surface runoff to the ground, rather than directing it for disposal via a municipal storm water system. In the example of porous concrete use shown in Figure 14.24, a new walk that crossed near the base of an older Live Oak resulted in minimal impact on the surface root system and, at the same time, provided moisture where encroachment of paved surfaces were threatening the health of the tree.

Figure 14.23-C Mixed use of modular concrete paving units and compacted gravel surface in the new central shopping district in Almere, the Netherlands

A

B

Figure 14.24 Porous concrete walk (A) and conventional concrete pavement (B) on the Louisiana State University