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10:57 AM Sun, Sept. 23rd

Talk of the Town: 1960s water report on aquifer was accurate

In both a written and then an oral presentation of its review of a recently published United States Geological Survey (USGS) report to the Upper Verde River Watershed Protection Coalition, Montgomery and Associates representative, Ed McGavock, was critical of a "Geologic Framework of Aquifer Units and Ground-Water Flowpaths, Verde River Headwaters, North-Central Arizona" (by Wirt and others, 2005).

McGavock was particularly critical of a referenced report "Sources of springs supplying base flow to the Verde River headwaters, Yavapai County, Arizona: U.S. Geological Survey Open-File Report 99-0378" by Wirt and Hjalmarson, 2000).

Wirt and Hjalmarson concluded that the lowest mean daily flow of record at the USGS streamflow gauge near Paulden of 15 cfs during May 13-23, 1964, coincided with pumping to fill artificial lakes for real estate promotion near Wineglass Ranch in Big Chino Valley. Wirt and Hjalmarson also suggested a hydraulic connection between the Big Chino aquifer and the Verde River base flow.

In his presentation, McGavock not only said this story never happened based on his incorrect understanding of artificial-lake pumping and changes in base flow in the Verde River, but he also incorrectly assumed what I was thinking while collecting and reviewing hydrologic data during the 1960s as a USGS employee.

In particular McGavock was not correct when he said that I had made no connection between the short-term 25 percent decrease in base flow and lake-supply pumpage at that time because I knew there was none.

I'd like to discuss this story that "never happened." As a young engineer in the early 1960s I worked in the Upper Verde River area. Among other tasks, I helped choose the site for the Verde-Paulden gauge (that USGS installed in 1963), collected groundwater data such as water levels at index wells (wells in which the USGS measured water levels regularly over the long term) and groundwater pumping for farming. I also collected and reviewed surface-water data.

While documenting groundwater information I had collected during 1964-65, I included information about the artificial-lake filling at the Holiday Lake subdivision located at the lower end of Big Chino Valley next to Highway 89.

I also summarized information about past lake filling that I learned while inspecting the area with the owner of the Holiday Lakes subdivision who reported that they also filled the artificial lakes during 1960, 1961 and 1962. This first period (1960-65) corresponds to the lowest water levels recorded in a nearby USGS index well, the same index well used in the USGS report "Hydrogeology of the Upper and Middle Verde River Watersheds, Central Arizona, by Blasch and others (2006), "for the lower end of Big Chino Valley.

During this period (1960-65) base flow at the Verde-Paulden gauge also dropped from about 20 cfs to 15 cfs, the lowest base flow recorded at the site to this time. Lake-filling pumping at Holiday Lakes also occurred in 1970-72, and the base flow at the Verde-Paulden gauge dropped to 16 cfs during this same time period. No one recognized the significance of these low discharges and low groundwater at the time because of the short operational history of the gauge.

Clearly McGavock's conclusion that the lowest mean daily flow of record at the USGS streamflow gauge near Paulden gauge of 15 cfs during May 13-23, 1964 and 16 cfs during March 15, 1972, did not coincide with pumping to fill artificial lakes constructed for real estate promotion near Wineglass Ranch in Big Chino Valley is incorrect.

His inappropriate and incorrect assumption that I knew no connection existed between the two as a young engineer collecting this data during the 1960s is also wrong.

It's not possible to establish at this time whether a one-to-one relationship exists between the pumpage and the two lowest recorded periods of baseflow, but in his criticism of me, McGavock offers no alternative reason for these two periods.

Certainly, officials now fully recognize that groundwater in the Big Chino Valley discharges to the upper Verde River and that withdrawal of this water by wells reduces the amount of ground-water discharging to the river by an amount equal to or nearly equal to the withdrawal.

Wirt and Hjalmarson also suggested on a hydraulic connection between the Big Chino aquifer and the Verde River base flow. This is now widely recognized fact.