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San Pedro River drying up
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Rio Salado College PA's/Online Instructors Education Assessment Technology, Inc Social Studies Content Writer General CORT WAREHOUSE/DRIVER Construction Komatsu Equipment Co Mechanic General CORT Warehouse Supervisor Tucson RegionRiver's flow again dwindling at gauge San Pedro could be on verge of vanishing, scientists warn
Arizona Daily Star
Tucson, Arizona | Published: 07.04.2007
For the third year in a row, the San Pedro River is in danger of running dry at a key monitoring station northeast of Sierra Vista.
Federal hydrologists say the river could dry up at the Charleston gauge by the end of this week if monsoon rains don't start falling. The San Pedro, the Southwest's last free-flowing desert river, has lost 80 percent of its summertime flow over 70 years. Many scientists have warned that it could dry up permanently if something isn't done to arrest overpumping of groundwater by farms and surrounding cities and suburban areas, particularly with the drought continuing.
Talk of solutions to the river's ills is intensifying. Last month, the U.S. Bureau of Reclamation released a report analyzing a dozen ideas for bringing in more water to keep the river flowing. It recommended further study of three, including extending the Central Arizona Project from Tucson.
Also in June, Gov. Janet Napolitano signed into law a bill that could lead to creation of a new water district in Cochise County. If voters approved it, the district would have the power to find ways to increase the river's supply and to require that all new developments demonstrate an assured 100-year water supply without drying up the river. Dr. Robin Silver, a Phoenix environmentalist, may launch a voter initiative effort seeking stricter controls over pumping near the river.
On Monday and Tuesday evenings this week, the river at the Charleston gauge ran at 0.057 cubic feet per second. In July 2005, the river dried up at that gauge off and on for 13 days. On June 29, 2006, it dropped to 0.012 cfs before monsoon rains.
Monday evening, the stream was running at a trickle, although large pools of water remained both north and south of the Charleston Road bridge.
The river's fate depends on whether rains start falling quickly enough — there's a 20 percent chance Thursday and 30 percent chance over the weekend in the Sierra Vista and Bisbee areas — to counteract this week's triple-digit temperatures in Sierra Vista.
"It's going to depend on how hot it is during the day and whether or not it rains," said Emmet McGuire, a hydrologic technician for the U.S. Geological Survey who was taking measurements at the gauge Tuesday night.
The USGS and other agencies blamed the 2005 river-drying on a late monsoon, drought and pumping for agriculture and homes near the border. It said well-pumping in Sierra Vista had reduced groundwater's flow to the river only 5 percent since 1995. Environmentalists and scientists disputed that.
This year's low flows are more significant because it's the third straight year for them, said Thomas Maddock, a University of Arizona scientist who has been warning about dangers to the river for 15 years. "It's not just the drought," said Maddock, head of UA's Hydrology Department.
Jim Leenhouts, a USGS hydrologist, said he tends to agree with Maddock. A review of June "low-flow" periods lasting seven days at a time shows that in recent years they have been unusually low compared with those in earlier decades, he said.
"To make a distinction between a very low flow and a zero flow is artificial," even if the river doesn't run dry, he said.
The Charleston gauge is an important measure of the flow because the impermeable bedrock underlying the underground aquifer rises close to the ground surface. That gives the river a more reliable groundwater supply than in other places.
The 2005 drying was the first at the gauge since records started being kept in 1904. In contrast, the river's Tombstone gauge virtually never measures water this time of year.
The Palominas gauge ran at 0.02 cfs Tuesday and was at 0.063 cfs when Geological Survey technicians last measured it in person June 25. The agency's gauge on the Babocomari River, a San Pedro tributary, has shown zero flow since June 16.
Rep. Gabrielle Giffords, D-Ariz., has announced that Congress has appropriated $400,000 for the Upper San Pedro Partnership, a 21-agency consortium overseeing the San Pedro's fate but still needs $300,000 to give the partnership what it needs for work on solutions.
It's doubtful that the CAP could be extended to Sierra Vista because of the high cost and competition for the water from Tucson and Phoenix, but it is worth a formal study, she said. Various CAP options would cost $162 million to $277 million for construction, with $27 million to $64 million in annual operating costs, according to the new Bureau of Reclamation report.
Other ideas recommended for more study are pumping water to the river from the long-shuttered Copper Queen mine in Bisbee and capturing stormwater for recharge into the aquifer.
For construction, the first would cost up to $51 million. The second would cost up to $61 million. Both would have annual operating costs of about $5 million.
She said that before CAP comes to Sierra Vista, assurances would be needed that the extra water would be used to ensure that well pumping is controlled. But she said the region is already doing a lot to control pumping and cited recent 50 percent water-use reductions by Fort Huachuca.
Silver said it looks as if the Center for Biological Diversity, of which he is board chairman, is moving toward launching a San Pedro initiative to make sure the well-pumping is controlled.
"We can't control drought or a late monsoon," he said. "The only thing we can control is excessive groundwater pumping."
● Contact reporter Tony Davis at 806-7746 or tdavis@azstarnet.com.
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