Wednesday, April 27, 2011

Verde River subflow

Phil Pearthree, Chief of the AZGS Environmental Geology Section, is speaking tonight to the Verde Valley Water Users Association in Camp Verde, about our recent report and maps delineating Holocene river alluvium and other geologic units along the river and its tributaries.

AZGS mapped the Verde River corridor under contract from the AZ Dept. of Water Resources for use in water adjudication hearings.

Reporter Steve Ayers explained the significance of this work very clearly in a story in the Verde Independent:
Of all the decisions made to date in the 35-year-old statewide water rights adjudication case, one of the most significant was the court's determination of what constituted subflow.

They defined the subflow as the water contained within the "saturated floodplain Holocene alluvium," the geologic formation consisting of sand, gravel and loose rock deposited in the river's floodplain over the last 10,000 years.

The definition is significant because the subflow of a stream is treated that same as water flowing above ground, as far as state law is concerned.

Which means, in order to legally use subflow, you must have a surface water right. In the Verde valley there are over 7,000 residential wells, the vast majority of which are pumping in or in close proximity to what is assumed to be the subflow zone of the Verde River and its tributaries.
[right, index of geologic maps completed by AZGS]

Ref: Mapping of Holocene River Alluvium along Oak Creek, Wet Beaver Creek, West Clear Creek, Fossil Creek, and the East Verde River, Central Arizona, 2010, J.P. Cook, P.A. Pearthree, J.A. Onken, E.R. Bigio. AZGS DM-RM-03, 43-p report and 10 map sheets, A, B, C, D, E, F, G, H, I, J (5 plates).

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