Groundwater flow model of Willcox Basin completed
As a result of continuing observations of groundwater level declines in the Willcox Basin, the Arizona Department of Water Resources initiated development of a numerical groundwater flow model in late 2015.
The Willcox Basin covers an area of approximately 1,911 square miles in southeastern Arizona and is essentially a closed basin.
That modelling has been completed. Major findings of the modelling include:
- The three-year ADWR modelling project finds high rates of groundwater pumping in Willcox Basin altering the groundwater flow system “to a significant extent.”
- Evidence of the amount of groundwater removed from storage between 1940 and 2015 ranged from 4.9 million to 6.2 million acre-feet (an acre-foot equals 325,851 gallons of water, or the amount of water needed to cover an acre of land a foot deep).
- Projecting forward to simulate a period of time between 1940 and 2115, the modelling concluded a net “change in storage” – meaning, in this case, a reduction in storage – ranging from 19.8 million acre-feet to 24 million acre-feet.
- Going forward to 2115, the modelling simulated long-term “draw down” in various portions of the aquifer range from a minimum of 354 feet (in the aquifer system north of the Willcox Playa) to as much as 917 feet (in the aquifer system near Kansas Settlement).
- Both data and modelling indicate that significant declines in regional groundwater levels continue to occur.
- Based on the Willcox Model results, pre-development estimates of groundwater in storage circa 1940 ranged from 80 to 97 million acre-feet. Recent estimates of groundwater in storage (2015) range from 73 to 92 million acre-feet. Projection estimates of remaining groundwater in storage range from 57 to 77 million acre-feet. However it must be noted that a significant portion of the remaining groundwater in storage is found at considerable depth and may not practical to remove.