Wednesday, June 8, 2011

French Sponge

A ghost creek haunts our backyard. The neighbor remembers the fold of earth that once cut across our properties, down to the end of the block, and on through the neighborhood to connect with Boggy Creek. Now there's a buried culvert for street runoff, and when it pours, a ghost flows between our houses and through our backyard.

The water poured into the next yard until I built a French drain. The idea came from Vince at the Cathedral of Junk, who engineered the way water flows through his yard. He'd talked about the possibilities of geological A/Cs by digging a long underground tunnel that opens up a hundred or so feet from the house. If you had an attic vent, it would suck air through the cooling underground and into your house. French drains usually route water out of the yard (and into your neighbors, or wherever). Henry French, not the French, suggested the design in his 1859 book, Farm drainage: The principles, processes, and effects of draining land with stones, wood, plows, and open ditches, and especially with tiles. How the south was drained. He laid curved roofing tiles along the bottom of trenches, then filled in different sized gravel as filters. These days, instead of roofing tiles, landscape architects use various perforated tubes and geotextiles to do the job.

Wanting to save as much rainwater as possible, not shunt it off the land, I used the principles of the French drain to build a sponge. I shoveled out trenches two feet deep in an L shape at the yard's heart, drilled a hundred holes in PVC scavenged from a backyard pile, laid them in the trenches, and filled in a half ton of gravel. While excavating I found an old path of paving stones a half foot underground. I moved dirt displaced from the trenches to form a swale that routes the ghost creek to our fig trees. Wrapping the PVC in geotextiles would have helped absorb water and reduce clogging from roots and migrating soil. If I were doing it all over, I'd encase my PVC in used baby diapers, an undervalued and underestimated geotextile that lines landfills everywhere. Maybe diapers would have leached bad things into the soil. Now the ghost creek soaks into the French sponge, the fig and pecan trees, and the Boggy Creek watershed.

Just upstream at the old airport, backhoes and bulldozers dug out a stormwater retention basin surrounded by restored Blacklands prairie as part of the Mueller Development. Street runoff from the New Urbanist housing/retail development floods into the basin, filling it up to slowly soak in. A sprinkler system beneath the Blacklands prairie keeps the wildflowers blooming even in drought years like this one. The pond/prairie patch is a machinic landscape or living machine designed to save rainwater that, through its deployment on the land, engineered that water's flow out of the Boggy Creek watershed to the neighboring Tannehill Branch Creek watershed. The pond, stocked with native fish, bubbles at the center to prevent eutrophication. You can jog or walk your dog around the pond on a hilltop path overlooking the water, riparian plants, waterfalls, and a wild old tree on a peninsula. Many benches to sit and contemplate nature.

No comments:

Post a Comment