Saturday, September 30, 2023 12:24 am

THE REPORT:  2023 Phoenix AMA Groundwater Model; Rose Law Group water lawyer and chair of water law depart, David Johnson qualms concerns

By Arizona Department of Water Resources

The Arizona Department of Water Resources has developed and calibrated a groundwater flow model of the Phoenix Active Management Area (AMA). The model area combines the Lower Hassayampa, West Salt River Valley (WSRV), and East Salt River Valley (ESRV) sub-basins; and includes portions of the Maricopa-Stanfield, Lake Pleasant, and Eloy sub-basins. The Phoenix AMA model replaces the existing Salt River Valley (SRV) and Lower Hassayampa sub-basin groundwater models.

The model is calibrated to the time period of pre-1900 through 2021. Data used in the calibration include 40,577 water level measurements collected from 4,562 wells, 325 aquifer test results, vertical head difference observations from 56 well pairs, observations of stream gains prior to widespread groundwater pumping, and gaged streamflow rates on the Salt and Gila Rivers. The calibration results indicate that the model reasonably reproduces the study area’s historical water level and streamflow conditions. Residuals are calculated as observed minus simulated values. The mean, absolute mean, and the root mean square error (RMSE) for the head residuals are 1.2 feet, 37.2 feet, and 49.7 feet, respectively. The normalized RMSE is 3.6%. These calibration statistics indicate that the regional model is well-calibrated. Furthermore, the model covers 122 years, during which the system undergoes a wide range of hydrologic conditions, making the model suitable to handle future anticipated conditions that fall within the variability that the long history has covered.

Rose Law Group water lawyer and chair of water law department, David Johnson: “There are hundreds of thousands of lots in Maricopa County that have water so this will not affect near term residential growth. Remember that it does nothing to stifle the growth of industrial, office or multifamily. The longer term issue will be worked out with ADWR and the real estate community over the next many months and years.”

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