NBC’s “Today” show came to Arizona in late March to tape an update on Biosphere 2 and two of...
Old Tires Find New Life in Sand Dam
The old adage, one man_s trash is another man_s treasure, was never truer than in Stuart Hoenig_s love affair with worn out tires. Automobile tires, truck tires, heavy equipment tires, all sizes and shapes of tires interest Hoenig, an adjunct professor of agricultural and biosystems engineering at the University of Arizona in Tucson.
The reason is simple. "These are highly engineered structures," Hoenig says. "Cutting tires up for scrap is like buying a house and tearing it down for firewood."
While most municipalities would argue that tires are a nuisance _ currently there are more than 100 million stacked up around the country _ Hoenig sees them as a huge, largely untapped reservoir of building material that can be used to construct everything from fences to rifle ranges, or houses to dams. They can even be sliced in half and buried under golf courses to trap and conserve water.
The very durability that makes them difficult and costly to dispose of is one of their major assets. Hoenig says you can cut the tread off the tire, lay it flat on a roof next to a bunch of other treads, cover this with tar and make a surface that won_t leak for 200 years.
To further prove just how useful tires can be, Hoenig supervised construction of a sand dam made of individual automobile tires about 50 miles west of Tucson on the Brawley Wash.
Only 30 years ago, Brawley Wash was a dirt road. But storm runoff raced down its tracks year after year, transforming the road. Now it_s a 55-mile-long, 165-foot-wide, 30-foot-deep gash on the face of the desert. The arroyo slices deeper and wider with each rainstorm, eating away at grazing land on the King_s Anvil Ranch, where the tire dam was built.
Sand dams are designed to prevent erosion and build up soil by trapping the silt carried by water in the wash. This silt forms a barrier, causing the water from later storms to spread out, move more slowly and soak into the wash. This helps to minimize downstream erosion.
At the same time, the silt creates a lush riparian oasis upstream from the dam that provides excellent wildlife habitat. Hoenig_s tire dam was built three years ago and now five acres of grass-covered silt lies upstream. "Cows, deer, coyotes and javelina can be found there, while downstream it_s just a dry arroyo," Hoenig says. In addition, the sand filled a gap in a ranch road that had to be bulldozed after every rain.
A concrete dam can produce the same benefits, of course. But concrete is expensive. The tire dam cost $6,500. It_s made of automobile tires filled with one-inch gravel, tied together with plastic ties and anchored into the wash bottom with rebar. A similar concrete dam would cost about $70,000, Hoenig says.
But constructing this dam involved placing the individual tires, fastening them together and filling them with gravel, which turned out to be labor intensive and time consuming. "We feel that makes the use of individual tires too labor-intensive in industrialized countries," Hoenig says.
The alternative comes in the form of bundled tires. These are bales of passenger car tires that weigh about a ton each. Using these large blocks of tires would be much less labor intensive. They are commercially available and Hoenig would like to see the state and local governments use them to build soil conserving sand dams in Arizona_s arroyos.
So far, he hasn_t had much success. "We would like to generate some interest, but so far we haven_t gotten anywhere," Hoenig says. Part of the problem may be the low-tech, scrap-yard image of old tires. Sure, they can look bad, Hoenig admits. But if that_s a problem just cover them with a thin layer of concrete.
The sand dam in Brawley Wash was built as a geological engineering master_s thesis project by Joshua H. Minyard. Dinshaw Contractor, professor and registered civil engineer in UA_s civil engineering and engineering mechanics department, designed the dam.