PRESCOTT - A federal study of the Verde River headwaters used the wrong information to conclude that the Big Chino Sub-basin supplies 80 percent to 86 percent of the headwaters' baseflow, a consultant said Wednesday.
However, it's "widely accepted" for three decades that about three-fourths of the headwaters' source is from that sub-basin, added consultant Ed McGavock of Montgomery and Associates.
The municipalities of Prescott, Prescott Valley and Chino Valley paid Montgomery and Associates about $30,000 to review two recent U.S. Geological Survey reports, one about the Verde headwaters by Wirt et al. and one about the entire watershed by Blasch et al.
"We don't have a dog in the fight. We do have a reputation for telling it like it is," McGavock said during his presentation about the company's review Wednesday at the Upper Verde River Watershed Protection Coalition's monthly meeting. The Prescott-area municipalities and Yavapai County are coalition members.
The Wirt report estimates that the Big Chino supplies 80 percent to 86 percent of the baseflow for the headwaters and the first 25 miles of the river.
Montgomery said Wirt used the wrong information for her computer model that produced the 80-86 estimate, so the USGS needs to gather more information and rerun the model. His PowerPoint presentation listed five suggestions for the rerun, including the gathering of more water samples.
At the same time, McGavock said that he has believed for a long time that the Big Chino is the major source of water for the river's headwaters. He personally estimated an 80-percent contribution.
It's an important issue because decision-makers need to know the source of the Verde to protect it. Several large housing developments are on the horizon in the now-rural Big Chino area, and Prescott-area municipalities plan to supplement their depleted Little Chino Sub-basin supplies with Big Chino water by building pipelines.
Some citizens and downstream Verde Valley government officials have expressed concerns that all the pumping will hurt the river, which is an important resource for wildlife as well as people.
The USGS reports do not say whether the municipalities' plans will hurt the river, and the authors did not intend them to, McGavock noted.
"I guess that is the crux of the issue, because we have a number of people...attributing conclusions to the report," Yavapai County Supervisor Carol Springer said after viewing the PowerPoint presentation.
The USGS is working on more advanced computer models that will help forecast such effects.
NEW TEST WELL NECESSARY?
McGavock believes that the lower Big Chino aquifer could be the major source for the headwaters, and that would be a good thing because all the wells are in the upper aquifer where people do not have to drill so deep.
If the deep aquifer is the major source, pumping from the more shallow aquifer above it would have a "small impact, if any" on the river, McGavock said.
But if the upper and lower aquifers are connected and act as one aquifer, it is "almost inescapable that you will eventually impact the (headwater) springs," McGavock said.
The best way to find out is to drill a well about 1,500 feet into the Big Chino, McGavock said. Such a well would cost at least $1 million, he said.
The City of Prescott as well as the U.S. Bureau of Reclamation both drilled wells that deep more than a decade ago, but they did not help answer the question because they looked only at geology and did not measure the water levels and chemistry, he said.
Clarkdale Mayor Doug Von Gausig voiced support for the test well. He and several other Verde Valley government officials attended the coalition meeting.
Von Gausig said he appreciated the review and he hopes regional officials gather the extra data that the review recommends.
The middle Verde River at Camp Verde is flowing at its lowest level in decades, Von Gausig said, and without the Big Chino source it would be flowing at half its current rate of about 30 cubic feet per second.
McGavock said the Blasch report found a decline in the flow of the Oak Creek tributary at Sedona that is the worst in northern Arizona, and he criticized the report for not discussing that issue.
He also criticized it for stating that an aquifer discharges into the Verde River in the Verde Valley, while a chart shows nearly all the river's flow coming from tributaries.
McGavock pointed out several examples of errors he found in the reports, which he noted that the USGS is updating and correcting anyway.
Contact the reporter at jdodder@prescottaz.com
Reader Comments
Posted: Wednesday, July 11, 2007
Article comment by:
jwlheart
We all live here because we love living in a rural area Some of us want more growth but have failed to plan for it. We will eventually live out our worst nightmare: we will all be forced to live in Phoenix if we do not take matters into our own hands and manage our own water resource where we live. "Only after the last tree has been cut down, only after the last river has been poisoned, only after the last fish has ben caught, only then will you find that money cannot be eaten." -Cree prophecy.
Posted: Wednesday, July 11, 2007
Article comment by:
jwlheart
We all live here because we love living in a rural area Some of us want more growth but have failed to plan for it. We will eventually live out our worst nightmare: we will all be forced to live in Phoenix if we do not take matters into our own hands and manage our own water resource where we live. "Only after the last tree has been cut down, only after the last river has been poisoned, only after the last fich has ben caught, only then will you find that money cannot be eaten." -Cree prophecy.
Posted: Saturday, June 30, 2007
Article comment by:
Harry M Hollack
PLEASE PLEASE CAP POPULATION TO SLOW DEVELOPMENT DUE TO WATER SUPPLY FOR OUR GRANDCHILDRENS GRANDCHILDRENS!
Posted: Saturday, June 30, 2007
Article comment by:
Doug Von Gausig
Thanks for an excellent appraisal of the report and Mr. McGavock's presentation. The bottom line in the Montgomery report is clearly, "We don't yet have sufficient data to make an informed decision." The question then becomes: Will we gather the data and analysis necessary to our understanding of how pumping in the Big Chino will impact the Verde River, or will we proceed to pump and hope for the best. My vote is for being safe, not sorry.
