New ADWR report shows continued water mining
PRESCOTT – Prescott Active Management Area residents continued depleting their groundwater supply last year, building on a mining situation that has been going on for at least eight years.
"This report continues to reflect over-reliance on mined groundwater," Prescott Active Management Area (AMA) Director Jim Holt said. "That's the report's most important message."
Frank Corkhill, the Arizona Department of Water Resources (ADWR) hydrologist who wrote the report, agrees.
The Active Management Area, which the state designated in 1980, covers 485 square miles and generally includes the Prescott tri-city area.
The ADWR released its annual report this past week that quantifies the amount of aquifer overdraft or "mining." It bases its estimate on statistics from wells that it monitors, as well as precipitation and stream gauges.
The agency estimates that the AMA reduced the groundwater storage in its aquifer by 12,440 acre-feet or 4.1 billion gallons in 2003. One acre-foot generally fulfills the needs of three households.
That's the second-largestoverdraft that the agency has ever recorded since 1994 when it started its well-monitoring program. The highest overdraft occurred in 2002, when residents drained 15,450 acre-feet. The agency has recorded overdrafts every year.
The year 2002 was the driest on record here. Holt said it's likely that 2002 produced the highest overdraft because people were watering vegetation in their yards more often because of the dry weather, and to save their trees from the peak of the bark beetle epidemic.
The state estimates that the amount of groundwater stored in the aquifer declined by about 110,000 acre-feet from 1994 to 2003, leaving 2.9 million acre-feet. The agency is quick to note, however, that users could never extract that much water and the idea of continually draining the aquifer is contrary to the AMA's state-mandated goal of "safe yield" that would balance aquifer inflow with outflow.
The City of Prescott remains the largest single user of groundwater in the AMA at 8,152 acre-feet, followed by Prescott Valley at 4,860 acre-feet, agricultural users at 4,037 acre-feet and residential wells (including Chino Valley) at 3,255 acre-feet.
The report includes measurements from a record number of wells in the AMA. It calculates that groundwater levels in 95 of the 105 wells, or 90 percent of the wells, dropped in 2003. That's the highest percentage of wells dropping since the agency started measuring wells in 1995. At that time, it was measuring only 16 wells and water levels dropped in 15, or 93 percent, of the wells that year.
Each year since, water levels in at least 72 percent of the measured wells dropped except in 1996, a relatively wetter year partly because of the El Niño weather effect. That year also was the only break in below-normal precipitation during the continuing long-term drought.
Well water-level declines in 2003 ranged from one-tenth of a foot to 31.9 feet, with an average decline of 2.7 feet.
The water-level declines occurred in most parts of the AMA. A detailed map in the report shows the declines or increases of each well.
The public can download the entire 28-page report via the ADWR Web site at www.water.az.gov. Click on the word "publications."
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