Verde Valley well owners are unfairly treated by flatlanders
I'm sure some of the readers recall that this subflow zone issue sent Chip Davis and other citizens of Yavapai County into a tizzy. SRP used the ADWR methodology to claim that individually owned wells within the saturated Holocene alluvium (the subflow zone as defined by ADWR) are using SRP water. SRP claims that a few thousand wells along the Verde River are in the subflow zone and thereby withdrawing water from the saturated Holocene alluvium that is Verde River water.
Several interested parties including the Verde Valley Water Users Association responded to the ADWR report. I wish to briefly discuss why I feel the presumption of hydraulic connection of many wells in the Holocene alluvium and the river under natural conditions is a stretch of common sense.
So what is Holocene alluvium, anyhow? It is a thin layer of dirt deposited by floods that forms the banks and floodplain along much of the Verde River and tributary streams. It is special dirt because it arrived since the last ice age or during the past 10,000 years or so. It is loose material and not cemented with calcium carbonate like much older rocks such as the Verde Formation. Holocene alluvium also has gravel where the rounded gravel has been transported long distances and the angular gravel is from local streams.
How has the Verde River behaved to produce the terraces and floodplains we see along the channel of the river? The geologic evidence shows there has been down cutting all along the river for nearly the past 2 million years. This erosion has continued through the past 10,000 years. The general erosion has at times been temporarily interrupted by periodic filling of the entrenched channel and by alluvium deposited along floodplains and terraces by flood flows. Recent (Holocene) terrace deposits along the Verde River are thin (considerably less than 100 feet), and old underlying rock units are exposed at many localities in the bed of the river, clearly showing that the stream down cutting has continued to the present.
So what is the significance of the fact the river is cut into the old underlying rock units such as the Verde Formation? Because the river acts as a drain for the watershed, it means the water level in the river generally is below most of the Holocene alluvium. In other words, the Holocene alluvium that is adjacent to the Verde River typically is above the water level of the river. In most places the Holocene alluvium is only a thin veneer on top of the older underlying rocks in which the Verde River is incised.
It is a myth that the river channel has been formed in a large mass of saturated Holocene alluvium as depicted by SRP and VVWUA.
Flatlanders would have us believe their theory that there is a lot of saturated Holocene alluvium along the river and that wells in this "subflow zone" extract water from this saturated alluvium that is directly connected to the Verde River. The fact is nearly all of the wells along the river penetrate the much older Pleistocene alluvium and the Verde Formation that is below the Holocene.
SRP neglects to consider the third dimension that shows the river bed is below the Holocene alluvium in many places all along the river as described by the Arizona Geological Survey (AGS). Generally speaking, there appears to be little water extracted by wells from saturated Holocene alluvium simply because there is not much saturated thickness in the Holocene. There is a much greater likelihood that wells are developed in the underlying older Pleistocene alluvium or the Verde Formation along the river.
SRP and the VVWUA have invented a myth that many wells in the Holocene alluvium extract water from the Verde River. The hydro geologic evidence shows that any natural connection between any saturated Holocene alluvium and the river would be the exception rather than the rule.
There is natural connection between the saturated Pleistocene alluvium and the river but this older alluvium is below the Holocene alluvium.
Could it be SRP and VVWUA have confused this older Pleistocene alluvium with the Holocene? The connection between the Quaternary alluvium, that includes both the Holocene and mostly the older Pleistocene, and the Verde River is clearly shown by the USGS in Figures 4 and 5 of ADWR Bulletin No. 3. Where are any reliable publications that show the thickness of the Holocene alluvium or the saturated Holocene alluvium along the Verde River?
So what does this mean to all the mom and pop well owners along the rivers? It means that when the VVWUA assumes the Holocene alluvium is 100-feet thick, they include an unbelievable number of wells in the subflow zone for no clear reason. There is no basis to assume the Holocene alluvium is 100 feet thick for illustrative or any other purposes as the VVWUA has done. Such a silly assumption is baseless and can only weaken a legal argument against ADWR.
There are three important reasons to dispute VVWUA's notion the Holocene alluvium is thick:
• The AGS has published that the Holocene alluvium is thin and generally above the river bed.
• In most areas of the western United States, the Holocene is a period of stream incision.
• One-hundred feet of aggradation in 10,000 years (0.01 foot per year) is world-class fast and ridiculous.
I believe the claims of the VVWUA and SRP that there are more than 1,111 wells in the saturated Holocene are unfounded and silly. Based on the available evidence, I believe there are very few mom and pop wells developed in a Holocene subflow zone and this is a position local well owners should take.
Perhaps the problem I'm addressing is related to how ADWR defined the subflow zone. In this regard, what you call something is important, perhaps the problem is also related to the fact that flatlanders have treated older Pleistocene alluvium and possibly much older alluvium as Holocene alluvium.
In this regard, I challenge any of the flatlanders to produce a three- dimensional map of the Holocene alluvium along the Verde River. Happy geophysics!
I do not own a well in the Verde Valley but several of my friends and neighbors do. Local well owners are being unfairly treated by flatlanders. We have enough real water problems in Yavapai County and don't need confusing and unfounded claims by SRP and ADWR.
Interested readers can easily view old marl with a gypsum like appearance in the low-water channel of the Verde River about 200 feet below the Black Bridge in Camp Verde. This marl is much older than the surrounding Holocene alluvium.
See for yourself.
Winn Hjalmarson is a retired hydrologist of the U.S. Geological Survey and is an independent consulting hydrologist. He co-authored the USGS report on the Verde River source waters. He has taught at the University of Arizona as an adjunct professor and served on a committee for the National Research Council. He has 40 years experience with the hydrology of arid lands and fluvial processes.
Click Below to: