A few years back, in a pair of bright white steel airplane hangers just off of the Old Bisbee Highway southeast of Tombstone, a study emerged that changed the way scientists and water managers alike thought about water runoff and the effects of urbanization.

Roughly five years in the making, the 2004 Goodrich et al. study probed the regional aquifer to determine what impact ephemeral, or temporary, water channels had on replenishing the area’s groundwater.

The hangers house the Southwest Watershed Research Center’s Walnut Gulch field office. for the experimental watershed’s 37,000 acres.

The watershed land, which surrounds Tombstone, was originally established as a research facility by the U.S. Department of Agriculture in the mid-1950s to look into the effects that upstream conservation efforts were having on downstream users.

Today, their mission is to develop knowledge and technology to conserve water and soil in the semi-arid lands.

Much of the surprise came about because, for years, groundwater recharge in southern Arizona was handled in the same way as on the East Coast. However, out West where roughly two-thirds of annual precipitation is generated by high intensity summer monsoons, storm water runoff was found to play a much larger role.

“If you’re out in New York or Pennsylvania and a Wal-Mart goes in with a great big paved parking lot, that would inhibit infiltration and recharge,” said Dave Goodrich, a research hydraulic engineer with the USDA Agriculture Research Service in Tucson “But actually, in our environment, by putting up more impervious area or urbanization, you’re getting more water into these channels than you would otherwise.”

Subdivisions, shopping malls and other urbanized areas seal the ground with concrete and asphalt. In New York or Pennsylvania these areas would inhibit the East Coast’s steady rains from infiltrating the groundwater. Development in southern Arizona sheds storm water and can actually concentrate it into waterways.

Once in the channels, water can soak down past the roots of plants to the aquifer because of the area’s coarse sand and gravel.

“If there’s more runoff from urbanization you can potentially try to manage some of that water to increase recharge,” he said.

The research gives planners and developers a way of choosing a location and method of building that would help to direct water into the aquifer in order to recharge, or refill it.

“We’ve looked at ground water use by pumping in the basin, by riparian vegetation, but until some of this ephemeral channel recharge (research) we didn’t know that urbanization itself has changed the way that groundwater is recharged in the basin and has probably lead to an increase of recharge,” said Russ Scott, a research hydrologist with the USDA.

“As the watershed gets urbanized, we will expect more runoff because you have more impervious surfaces. There’s going to be more runoff in a storm after things get urbanized. Therefore, we would also expect that more recharge would occur,” he said.

The Walnut Gulch Experimental Watershed is a kind of scientific playground. With a network of 88 raingauges that were recently upgraded from paper roll to digital format by Walnut Gulch Supervisor John Smith, 125 meteorological instrument installations, 11 large flumes to measure runoff, two complexes for soil moisture, temperature and energy flux measurements, and plenty of other gadgets and gizmos, researches have no shortage of tools.

In determining the impact of storm water runoff, researchers did everything from measuring changes in subsurface mass to levels of tree sap flow.

The researchers of the USDA who study data collected by the staff at Walnut Gulch are not in the business of setting agendas.

Their primary function is to generate information that can be used by organizations like the Upper San Pedro Partnership and Cochise County when informing legislators and developers.

“We take our overall understanding of conditions in the aquifer and we use science to inform the kind of decisions we’re capable of making,” said Carl Robie, Cochise County water policy director. “We’ve taken some measures that are having a positive impact.”

As a county government, Cochise does not have the authority to regulate water, or make land use decisions based solely on water issues. However, the county has created general rules that apply research conducted in Walnut Gulch and other centers.

Among those rules is a decision the county made to deny any increase in density that would result in pumping within two miles of the San Pedro River. Also, about a year ago, the county adopted a policy that required developers to prove a 100 year availability of water for their subdivisions, he said.

Furthermore, subdivisions cannot use more water than would be required at base zoning. That means that if a developer wanted to put several houses on land zoned for one home, the net water use could not be more than what would have been used if there were only one. The developer can use detention basins, rainwater harvesting, plumbing fixtures, dry wells and other methods to make that happen, he said.

“(Conservation easements) take some of the stress and strain off of the San Pedro River,” he said.