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Potential Future Declines in Base Flow to the Upper Verde River Due to Groundwater Extraction

This report builds on earlier work by the USGS in cooperation with the Arizona Department of Water Resources and Yavapai County to develop a regional flow model for northern Arizona. The USGS, in conjunction with the Verde River Basin Partnership (VRBP) and the Town of Clarkdale, subsequently applied the model in a series of simulations to gain a greater understanding of the past and potential future human impacts on the Middle Verde River's streamflow.


The work discussed in this paper was carried out to: (A) test the accuracy and predictive capability of the model within the Big Chino and Little Chino sub-basins; (B) illustrate the historical change in base flow at the USGS Paulden and Clarkdale streamgages; and (C) perform forward-looking simulations for the period 2005-2110 that evaluate potential effects on base flow in the upper Verde River resulting from; (1) unchanged water demand from 2005 through 2110, (2) continuing drought, (3) increased water demand, (4) extraction of the ADWR allocated 12,000 acre-feet per year (ac-ft/yr) of groundwater from the central part of the Big Chino sub- basin beginning in 2020, and (5) the cumulative effect of cases (1) through (4).


My testing of NARGFM showed that excellent agreement was found between historically observed and simulated groundwater elevations within the area of concern. In addition, simulated trends in both groundwater elevation and discharge to the Verde River are accurate to within industry-standard ranges.


My forward-looking simulations using the NARGFM show that the cumulative effect of continuing drought, increased water demand, and extraction of 12,000 ac-ft/yr (16.6 cfs) of groundwater from the Big Chino, will decrease the base flow to the Verde River by 12.8 cfs at the Paulden streamgage by the year 2110. Since the base flow at the Paulden streamgage in 2005 was approximately 19 cfs, this would leave only 6.2 cfs in the river. View Document.

Author: Peter Kroopnick, PhD. Revised April, 2015

 

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Studies and Experts Agree: Withdrawing Groundwater from the Big Chino Valley Will Reduce Flow in the Verde River!

Independent experts have made the title statement “Withdrawing Groundwater from the Big Chino Valley Will Reduce Flow in the Verde River” on numerous occasions over many years. However, public officials with an interest in withdrawing groundwater from the Big Chino Valley and piping it to the Prescott region for new subdivisions have frequently rejected these expert determinations. Their rejections have not been accompanied by rigorous analysis and evaluation of the data. Given the prominent voices of public officials, it is easy to see why the public can be confused.

In this paper, we bring forth the words of the independent studies and experts in the hope that the public can better decide whom and what to believe.

View the document.

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Vegetation Management

CWAG's view of the watershed improvement project under consideration by the UVRWPC. View Document.

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Well Hydrographs for the Prescott AMA

Annotated hydrographs throughout the Prescott AMA showing the change in water levels, by Doug McMillan. View Document.

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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.

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