dam project funded by Goodyear and Phelps Dodge Copper Co. may hold the
key to preventing soil erosion in the 80-mile-long Brawley Wash in the
Altar Valley southwest of Tucson, Ariz.
More than 1,000 discarded passenger
tires have been used to construct the dam, which is believed to be the
first of its kind in the United States. It was built on one of the numerous
dry arroyos that feed into the wash on the 50,000-acre King’s Anvil Ranch,
located about an hour’s drive from Tucson. Nearly nine miles of the Brawley
cross the property.
The wash began as a wagon trail in
the 1840s and '50s, carved by prospectors traveling south into Mexico to
seek their fortune in gold and silver. Time, Arizona’s annual summer rains
and erosion combined to make the wash 200 feet wide and 25 feet deep in
most sections. The Brawley stretches north from the Mexican border and
feeds into the Santa Cruz river near Marana, Ariz., northwest of Tucson.
The 45-foot-long, 35-foot-wide, 6-foot-high
tire dam is the brainchild of Joshua Minyard, who holds a bachelor of science
degree in geological engineering from the University of Arizona, and Dr.
Stuart Hoenig, professor emeritus, electrical and computer engineering,
University of Arizona. The tires are bound together with industrial-grade
plastic strapping, filled with gravel and anchored in the arroyo.
Minyard began thinking about tire dams
after discussing soil erosion problems with John King, the owner of the
ranch. Success of the project, which was approved by Pima County and the
Arizona Department of Environmental Quality, will open the door for additional
dams on the Brawley itself using large off-road tires such as those from
Hoenig and Minyard seized upon the
idea of using tires because it was less costly than building a concrete
dam — and they felt the tires would aid in entrapping sediment carried
north by rushing water, while allowing water to pass through. Hoenig notes
that a lush fertile landscape is visible where concrete barriers were built
on a similar wash in southeastern Arizona.
In sudden Arizona summer downpours,
water run-off can become violent — sweeping away anything in its path.
"Typical streams here can drop 50 to 80 feet per mile, so when they are
running they can really move," Hoenig said. The men hope to see some visible
signs of soil retention toward the end of the rainy season.
The Anvil Ranch has been in John King’s
family since 1908. He credits his family’s ranching longevity to fortune
and struggle. His grandfather, Manuel Joseph King, began ranching in the
vicinity in 1898. King said that in 1919 his grandfather was able to jump
across the Brawley, the main portion of which is about a mile from the
family’s adobe home. The state has had two very dry summers that were somewhat
alleviated by a wet winter season. Arizona needs to receive about 8 inches
of rainfall in July and August, according to King. Those two months of
rain will fill tanks and help him grow cattle feed until the next year.
"The arroyos run deep and wild. You
need to slow the water down and allow it to spread out. We’ve tried all
sorts of barriers and nothing we could construct would hold," King said.
"A soil retention structure would slow erosion, giving the plants a chance
to regenerate and heal the land."
Minyard and Hoenig began building the
dam in June. Work was done on weekends with a crew of 15 or more Pima County
residents working on community projects as part of their probation. "They
have really been an asset to this project. We would not have been able
to make the progress that we have without them," Minyard said.
Hoenig said several neighboring ranch
owners have made inquiries about building tire dams on their property.
He and Minyard believe tire dams could be utilized to stop soil erosion
across the entire state of Arizona.