How Large is the Overdraft?

Very Large and Accumulating

Beginning in 1985, each year ADWR has calculated the overdraft in the Prescott AMA.  ADWR’s results are in the graph below.

In five of the first 11 years in the period from 1985 through 1995, productive winter storms provided more new groundwater than was extracted. Those were relatively positive years for our PrAMA aquifer when the overdraft averaged a relatively low annual average of approximately 2,600 acre-feet.

A substantial change began in 1996.  From 1996 through 2018  there were only two years, 2005 and 2010, with winters wet enough to provide a surplus in aquifer storage.  The average annual overdraft during those 23 years is more than 13,000 acre-feet per year—more than 5 times the average annual overdraft for 1985 through 1995.  The 2018 overdraft is estimated at 18,000 acre-feet, equivalent to a football field flooded 3.5 miles deep!

As the graph below shows, the estimated cumulative overdraft from 1985 through 2018, is a staggering 333,650 acre-feet — roughly 1/3 million acre-feet or about 110 billion gallons that are almost certainly gone forever. Rather than making progress toward the achievement of safe yield, we are moving further and further away from stabilizing our aquifer.

 

Updated October 14, 2020