Water Banking through Artificial Aquifer Recharge
Arizona Water Banking Authority, Central Arizona Project, Arizona Department of Water Resources
Industries: Water Supply, Policy
SUMMARY: Arizona is a growing, semi-arid state that established a framework to address groundwater overdraft in the most populated parts of the state by adopting the 1980 Groundwater Management Act. That statutory framework was later expanded to include aquifer storage and recovery. Relying on this framework and its deep alluvial groundwater basins, Arizona has stored millions of acre feet for future use. The largest single storer, the Arizona Water Banking Authority, was established in 1996 to assist with water management goals and to help mitigate the effects of Colorado River shortages. This model of water banking allowed Arizona to utilize its full entitlement of Colorado River water and also store water on behalf of Nevada.
- Arizona has a record of fast-growing population and significant groundwater depletion.
- The Central Arizona Project (CAP) – which supplies Colorado River water to cities, tribes, industry and agriculture – has a junior priority that is subject to significant curtailment during declared shortages on the Colorado River.
- The CAP is capable of delivering roughly 1.5 million acre-feet of water per year, but in the early 1990s agriculture used less of the CAP water supply than was anticipated.
- Underutilization of CAP water was a concern, since water unused by Arizona becomes available for use in California, which had become accustom to the extra supply.
- 1980 Groundwater Management Act (GMA) established Active Management Areas (AMAs) delineated by groundwater basins. Within the AMAs, groundwater rights were created and quantified.
- Amendments to the GMA established a regulatory framework for aquifer storage and recovery.
- Colorado River water delivered through the Central Arizona Project (CAP) has reduced reliance on groundwater, particularly by the municipal sector.
- Arizona’s permitting system for storage and recovery allows for the accrual of long-term storage credits, allowing water to be stored for future recovery.
- The Arizona Water Banking Authority (AWBA) was established in 1996 to mitigate groundwater depletion, provide water in times of Colorado River shortages, and allow interstate storage.
- Arizona law defines two primary types of artificial aquifer recharge – direct and in lieu. Direct recharge, or “underground storage”, involves adding water into aquifers through infiltration basins, injection wells, vadose zone wells, trenches/infiltration galleys, and in-channel projects. In lieu recharge, or “groundwater savings”, involves CAP water or effluent being delivered for use in place of groundwater. The party supplying the water is then credited for the amount of groundwater being substituted by the user, most commonly an agricultural user.
- Water stored in aquifers is subject to minimal evaporation losses, and can be recovered, subject to a state-issued recovery well permit, in a different area than where it was initially recharged within the AMA. That flexibility has led to reduced dependence on groundwater and more extensive use of renewable water resources like CAP water.
- A long-term storage credit is issued for water that is kept in storage beyond the calendar year in which it was recharged, subject to a one-time “cut-to-the aquifer” (typically five percent). The cut-to-the-aquifer cannot be recovered.
- The AWBA facilitated an interstate water banking arrangement with Nevada. To accomplish this, CAP water was recharged for later recovery within Arizona, which will allow Nevada to divert an equal amount of Colorado River water from Lake Mead for its use. Nevada is obligated to cover the cost of the eventual recovery of stored water in Arizona.
- Through 2013, the AWBA has stored more than 4,807 million cubic meters of CAP water, 740 million cubic meters of which are reserved for Nevada. This brings the AWBA to 90.5 percent completion of its 100-year in-state water resources reliability goal.
- Favorable hydrogeological conditions in Arizona allow for infiltration rates up to one to two meters per day. High infiltration rates make evaporation losses minimal, while facilitating a cost-effective way to store water.
- Through artificial recharge, Arizona has banked a substantial amount of water to mitigate anticipated delivery cutbacks due to shortages on the Colorado River, while also utilizing more of its Colorado River entitlement in place of groundwater supplies.
- The AWBA has access to multiple sources of funding, including a tax on all property owners in CAP’s service area, a fee on groundwater pumping, and legislative appropriations.
Submitted/Excerpted from: Sharon B. Megdal et al. "Water Banks: Using Managed Aquifer Recharge to Meet Water Policy Objectives."