An aerial view of an aquifer recharge facility in Southern Arizona. Oro Valley delivers its CAP water to these types of facilities throughout Southern Arizona. The CAP water percolates through the sand and gravel to be added to the aquifer. The CAP water that is not recovered and utilized remains underground and is “stored” at these facilities to be recovered and utilized in the future if needed.

Editor’s note: In the first two articles of this three-part series, Oro Valley Water Director Peter Abraham addressed the following questions: What triggers a supply shortage? How much will the Tier 1 supply shortage be and who will it affect? How did we end up in a supply shortage situation to begin with? At what point does the water surface elevation at Lake Mead stabilize? In this third and final installment, he answers the questions: What is being done to mitigate the supply shortage? What does our future use of Colorado River water look like?




ater resource professionals have been planning for a hotter and dryer future for decades. In the face of growing demands and ongoing drought, the 2007 Colorado River Lower Basin shortage guidelines laid the operational foundation for a changing river. The implementation of the 2019 Lower Basin Drought Contingency Plan (LBDCP) built upon these previous guidelines and requires the lower basin states to take larger reductions in Colorado River water deliveries and sooner compared to the original guidelines approved by the Bureau of Reclamation in 2007. 

As discussed last week, the potential declaration of a Tier 2 shortage further reduces the demand on the Colorado River by 1,288,000 acre-feet per year. It is at this point we expect to see the closing of the over-allocation gap and the water surface elevations of Lake Mead stabilize. If the Tier 2 shortage is not enough to mitigate the declining water surface elevation of Lake Mead, a Tier 3 shortage could be declared. A Tier 3 shortage would result in a reduction of CAP water deliveries for the higher priority municipal users like Oro Valley. The Bureau of Reclamation’s latest projections indicate that there is a 59% chance that a Tier 3 shortage could be triggered by the year 2025.

Fortunately, Arizona and forward-thinking water providers have been planning for a future where the possibility of reduced CAP water deliveries could become a reality. In 1996, Arizona created the Arizona Water Banking Authority (AWBA) to store the unused portion of Arizona’s annual Colorado River entitlement in Central and Southern Arizona. The AWBA stores water in underground aquifer storage facilities. This stored water can be recovered during times of shortage to provide back-up water supplies (known as “firming”) for Arizona’s municipalities.

Since 1996, Arizona has stored nearly 4 million acre-feet of groundwater with over 600,000 acre-feet stored in Southern Arizona. During a Tier 3 shortage, any reduction of CAP water deliveries to municipalities would be offset by AWBA water deliveries. Additionally, municipalities, including Oro Valley, have been storing the unused portion of their annual CAP allocation in nearby underground aquifer storage facilities. Like the water stored by the AWBA, this stored water can be recovered during times of shortage.

Oro Valley is also a member of the Central Arizona Groundwater Replenishment District (CAGRD). Being a member of the CAGRD is an important mechanism for Oro Valley to hedge against the possibility of reduced CAP water deliveries. Oro Valley currently uses about 50% of its CAP allocation to replace the groundwater we pump. Replenishing the aquifer with CAP water to offset the groundwater we pump is a requirement of Arizona’s 1980 Groundwater Management Act.

At any time Oro Valley can utilize the CAGRD to replenish the groundwater we pump, thereby preserving our CAP allocation for only delivery and storage. The decision to utilize a portion of our CAP water allocation to replace the groundwater we pump in lieu of the CAGRD is a financial one. Replacing the groundwater we pump with a portion of our CAP water allocation is less expensive than paying the CAGRD to replace the groundwater on our behalf.

Additionally, thanks to the 2017 CAP System Use Agreement that was approved by the Bureau of Reclamation and the CAP, the CAP water system can now be legally used to transport suitable water supplies other than Colorado River water. Allowing for the transportation of suitable water resource supplies other than Colorado River water in the CAP water system has resulted in the emergence of new water markets that creates expanded opportunities for the transfer of water resources between sellers and buyers. 

In closing, Oro Valley is well positioned to meet the challenges presented by the supply shortages on the Colorado River water system. Our water resource utilization plan balances the use of our available groundwater supplies with our CAP allocation, our access to stored water held by the AWBA, our own stored water supplies, membership to the CAGRD as well as our ongoing collaboration with other water service providers, the agricultural industry and the Indian Tribes to ensure the perpetuity of a safe and reliable water supply for Oro Valley. 


Peter Abraham is director of the Oro Valley Water Utility

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