Drought, development drying up Ariz. river, says USGS

Posted: May 8, 2013

Written by

April Reese, Greenwire
Verde River

One of Arizona's longest free-flowing rivers could dry up within a few decades if development continues to deplete groundwater that sustains the waterway, a report released yesterday by an environmental group warns.

The report, which is based on information collected by a volunteer team of flow monitors and data from a U.S. Geological Survey stream gauge, cautions that if groundwater continues to be pumped to supply growing communities, the Upper Verde River's entire base flow -- the part of the river sustained by groundwater discharges -- will be drastically reduced.

The Verde River -- "verde" means green in Spanish -- was named for its lush riparian ecosystem, which supports a panoply of animals and plants amid the region's arid and semiarid lands, the Sierra Club report notes. The river provides habitat for desert nesting bald eagles, osprey, endangered Southwestern willow flycatchers, river otters and other species.

But the twin threats of development and drought could soon turn the river's upper 24 miles to brown, the report warns.

"We conclude that if the trends continue, we'll start seeing the river dry up in places in the summertime," said Steve Pawlowski, who oversees the Grand Canyon Chapter of the Sierra Club's "Water Sentinels" program, which trains volunteers to measure river flows. "It won't be long before we start losing reaches of the river."

According to the group's measurements, together with USGS stream gauge data, summer base flows in the Upper Verde River already have dropped considerably in the past five years. Water Sentinels measured record low flows of about 9 cubic feet per second during the summers of 2010 and 2011 at its site in Perkinsville, Ariz. If current flows continue to decrease, the upper Verde River could start running dry in the summer within a decade, the report says.

The communities of Prescott and Prescott Valley have preliminary plans to pipe in water from the Big Chino sub-basin -- the primary source of the groundwater feeding the river -- to meet future demand for water as their populations expand.

"We're hoping to get water managers up there to take into account protection of Verde River, and delay plans for withdrawal or mitigate for it so we don't dry up the river," Pawlowski said.

Supporters of the $140 million pipeline project, which would siphon 17,770 acre-feet of the Big Chino aquifer's water to the Prescott area each year, say the area cannot supply its residents, farms, ranches and industries over the long term without it (Greenwire, April 16, 2012).

Prescott is home to about 40,000 people, but by 2024 the population is expected to increase to 55,000 residents.

The project has received the necessary approvals from the Arizona Department of Water Resources but has struggled to secure funding and remains in limbo.

"There's nothing currently happening with that," said Patti Crouse, a spokeswoman for the city of Prescott.

Still, it's part of the city's water plan and could become increasingly attractive as conditions in the region become warmer and drier due to climate change, Pawlowski said.

In the Verde River area, average temperatures already have increased by between 1 and 3 degrees Fahrenheit over the past century, according to USGS. And it's going to get hotter: Temperatures will likely increase by between 3 and 10 degrees by the end of the 21st century, climatologists predict.

The warming of the region is expected to bring more frequent and longer droughts -- such as the one the area is enduring now -- and increase evaporation rates, which in turn would decrease the amount of groundwater supporting the river's base flow.

Pawlowski and his volunteers gathered flow monitoring data from December 2006 through March 2012, making monthly trips to the river to measure flows at three different sites, all along the uppermost stretch of the river: Perkinsville, Bear Siding and above Verde Springs, the river's headwaters.

Arizona Water Sentinels also analyzed flow data from the USGS stream gauge at Paulden, Ariz., near the headwaters, and from the Salt River Project's Campbell Ranch gauge.

The report recommends several actions officials can take now to minimize the threat to the river, including stepped-up water conservation efforts and securing in-stream flow rights. But state water officials have been sluggish in processing applications for in-stream water rights, Pawlowski said.

Michelle Moreno, a spokeswoman for the Arizona Department of Water Resources, said the department had not reviewed the report and could not comment on it.

While the state has designated "active management areas" within which communities must limit their groundwater use to avoid overpumping, they can still import water from elsewhere. Under state law, communities are not required to consider the effects of groundwater pumping on river flows; groundwater and surface water are managed separately.

Prescott and Prescott Valley are taking steps to reuse water and recharge the aquifer, according to the Arizona Department of Water Resources.

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