Why Big Chino Pumping Threatens the Verde

An often-repeated view is that the extraction of approximately 8,700 acre-feet per year (af/y) of ground water by Prescott and Prescott Valley from the Big Chino Water Ranch will have little if any effect on the springs that feed the upper Verde River. This optimistic view gained support from the report of Prescott's hydrologic consultants, who suggested that ground water from the Big Chino Valley may supply little if any of the ground water that feeds these upper Verde River springs.
In contrast, two recent reports by the U.S. Geological Survey—one by Laurie Wirt and colleagues, the other by Kyle Blasch and colleagues—show that the vast majority, if not all, of the ground water that enters the upper Verde River from these springs—an average of 17,900 af/y over the 14 years from 1990 through 2003—comes from aquifers in the Big and Little Chino watersheds, with most of it (somewhere between 14,300 af/y and 15,400 af/y) coming from the Big Chino watershed, including Williamson Valley. Further, these reports show that perennial (continuous) flow (also known as base flow) in the upper 22 miles of the river is dependent upon the ground water that issues from these springs. Should the springs go dry, the Verde River above Perkinsville will be dry or nearly so except at times of storms or snowmelt. In addition, the amount of perennial flow that enters the Verde Valley above Clarkdale will be reduced by about 30 percent. By Bill Meyer and Ed Wolfe, 2007. View Document.