Keep it flowing: Hundreds gather to hear scientists talk about Verde River study
CAMP VERDE - U.S. Geological Survey scientists aren't accustomed to attracting large crowds to hear about the results of their water studies, but approximately 400 people packed into a Camp Verde school auditorium Thursday to hear them talk.
"It's fantastic to see so many people here...to hear the results of a science project," said Jim Leenhouts, associate director of the USGS Arizona Water Science Center.
The Verde River Basin Partnership (VRBP) commissioned the USGS computer model runs and report to show how fundamental groundwater is to the Verde River and its rare desert riparian corridor. The model runs and report were made public Tuesday.
"We can't continue to point fingers," VRBP Chair Tom O'Halleran said. "It's all of us. And we're in this together, whether we like it or not."
Yavapai County supervisors Tom Thurman, Chip Davis and Craig Brown attended, as well as elected officials from Coconino County, the Verde Valley and Chino Valley.
Prescott and Prescott Valley officials, who have refused to join the VRBP, did not attend despite personal invitations. They have prevented the Yavapai County Water Advisory Committee from using the model.
The relation between groundwater pumping and surface water loss isn't new to scientists, noted Brad Garner, lead USGS author of the report. He quoted noted hydrogeologist C.V. Theis from 1940: "All water discharged by wells is balanced by a loss somewhere."
Groundwater withdrawal from wells has reduced the flow of the Verde River, said Bill Meyer, a retired hydrologist and VRBP Coordinating Committee member.
"That has been the subject of much controversy and debate" in the Verde Basin, he said.
And human population growth is the ultimate driving behind the river depletion, he added.
Yavapai County went from a population of about 16,000 in 1910 to 211,000 in 2010, he said. Verde Valley well numbers rose from 228 in 1950 to 6,436 in 2011. And most are close to the river.
Because the Verde Valley's wells are so much closer to the river than the wells in the Upper Verde Basin population center of Prescott, the model shows the baseflow at the lower end of the Verde Valley dropping faster by 2005 than it does at the top of the Verde Valley, even though the Upper Verde groundwater use is about 50 percent greater.
Model creator Don Pool later said that was one of the more interesting results of the model runs.
The packed crowd reminded VRBP Technical Advisory Group Chair Ed Wolfe of another gathering there a decade ago, when Sen. John McCain talked about water issues related to Yavapai Ranch land exchange legislation. That meeting led to the 2006 creation of the VRBP to help study Verde water needs, and Thursday was hailed as a milestone in its work.
The VRBP never got the federal money envisioned in McCain's legislation, but the USGS and Walton Family Foundation came through with $77,000 and $335,000 respectively to pay for the model runs, report and related products to help Verde Valley officials plan ahead on water issues.
"These decisions will be passed on to future generations," O'Halleran said after noting that students from throughout the basin met with the USGS scientists directly before the VRBP meeting. "We need to find a way to work together."
The USGS is policy-neutral, but its work is relevant to policy, Garner said.
Garner asked the audience how the Verde River flows in Midsummer after two months without rain.
"Baseflow comes from the ground, and humans can change it," he said. Baseflow is what keeps the river alive when it's not snowing, raining or receiving snowmelt.
The model demonstrated how quickly baseflow can drop once people dig wells in the basin.
It looks back to 1910 when few wells existed. By 1941 the model runs show that well withdrawals in the upper basin dropped the river at Clarkdale by 215 af/year, Garner said outside the meeting.
Over a century, the river in the Verde Valley has dropped about 11 percent from well pumping, Garner said.
The USGS model estimates the river's annual baseflow dropped by about 4,900 acre-feet between 1910 and 2005 at the upper end of the Verde Valley (Clarkdale gage), mainly because of groundwater pumping in the Prescott region. The annual flow dropped about 10,000 af at the lower end of the valley (Camp Verde gage) because of groundwater uses in both the Upper and Middle Verde.
The model also shows that the river's flow will continue to drop through 2110 as human water demands increase, even using highly conservative demand estimates.
The conservative future hypothetical scenario shows a decrease of 2,700 af to 3,800 af at the upper end of the Verde Valley, and a decrease of 5,400 af to 8,600 af at the lower end of the Verde Valley between 2005 and 2110. It uses just a three percent increase in human water use every decade for 50 years, and then zero growth for the next half-century.
The Verde Valley's human population actually grew 13 percent between 2000 and 2010, the USGS noted.
The past 10,000 acre-foot loss at Camp Verde equates to 14 cubic feet per second, or 6,200 gallons per minute, or filling an Olympic pool every two hours, or 12 percent of the entire baseflow of the river at that point, Garner said.
The model runs assumed that population growth would continue in the same locations as today. It did not include the 8,000 af of annual pumping that Prescott and PV officials plan to do in the Big Chino Aquifer someday.