Sunday, June 19, 2011

Numerical ground water model released for Verde River basin

The highly anticipated USGS report on the regional groundwater flow model for northern Arizona was released publicly last week after a storm of controversy. Steve Ayers, with the Verde Independent newspaper reports that
"Prior to the release, politicians and staff from the City of Prescott and Town of Prescott Valley did some arm-twisting through Rep. Paul Gosar's office, which gave them access to the report and the ability to make changes.

Although some changes were made, Leenhouts has since stated that the changes were for clarification and did not affect the substance of the report or the model's ability to do the work it was designed to do.

Nevertheless, the incident has been disappointing to several area leaders given the fact the USGS investigations are not typically subject to political review before being made public."

The abstract for the USGS report concludes:

Major results from the simulations include the importance of variations in recharge rates throughout the study area and recharge along ephemeral and losing stream reaches in alluvial basins. Insights about the groundwater-flow systems in individual basins include the hydrologic influence of geologic structures in some areas and that stream-aquifer interactions along the lower part of the Little Colorado River are an effective control on water level distributions throughout the Little Colorado River Plateau basin.

Better information on several aspects of the groundwater flow system are needed to reduce uncertainty of the simulated system. Many areas lack documentation of the response of the groundwater system to changes in withdrawals and recharge. Data needed to define groundwater flow between vertically adjacent water-bearing units is lacking in many areas. Distributions of recharge along losing stream reaches are poorly defined. Extents of aquifers and alluvial lithologies are poorly defined in parts of the Big Chino and Verde Valley sub-basins. Aquifer storage properties are poorly defined throughout most of the study area. Little data exist to define the hydrologic importance of geologic structures such as faults and fractures. Discharge of regional groundwater flow to the Verde River is difficult to identify in the Verde Valley sub-basin because of unknown contributions from deep percolation of excess surface water irrigation.

Pool, D.R., Blasch, K.W., Callegary, J.B., Leake, S.A., and Graser, L.F., 2011, Regional groundwater-flow model of the Redwall-Muav, Coconino, and alluvial basin aquifer systems of northern and central Arizona: U.S. Geological Survey Scientific Investigations Report 2010-5180, v. 1.1, 101 p.

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