Municipal Water Leader: Tell us about SRP and its history.
Dave Roberts: SRP was formed in 1903 as one of the first Reclamation projects authorized under the National Reclamation Act. Over the years, SRP has evolved to become the largest supplier of water in the greater Phoenix metropolitan area, delivering more than 800,000 acre-feet annually to agricultural, municipal, and urban water users. It is also a community-based, not-for-profit public power utility serving more than 1 million customers in greater Phoenix.
More than 100 years ago, the federal government and local leaders and landowners in central Arizona realized that federal investment in infrastructure through partnerships with local landowners was critical to ensuring that the community in the Salt River Valley would be able to manage the waters of the Salt and Verde Rivers to allow the region to grow and prosper. Ranchers and farmers pledged their own land as collateral to obtain a loan through the National Reclamation Act to build Roosevelt Dam—the first of the seven dams and reservoirs that today provide a reliable supply of water for the greater Phoenix metropolitan area. Through the middle of the 20th century, SRP, the federal government, and local water users continued to use this model to expand the SRP dam and reservoir system, improve the resiliency of the Phoenix metropolitan area’s water supplies, and help industry grow in rural parts of the state. These investments have paid off many times over. In addition to the seven dams and reservoirs that serve Phoenix with water and hydropower, SRP’s system contains more than 1,300 miles of canals and laterals that deliver water to our customers.
Today, we are looking at the next generation of infrastructure and operational partnerships needed to maintain central Arizona’s water resiliency in light of growing water needs and a changing climate. One example is our partnership with the Central Arizona Project (CAP). From 1973 to 1993, the federal government constructed the CAP canal, a 336-mile system that brings Colorado River water to central and southern Arizona. Through the years, the leaders of SRP and CAP have understood the value of working together to ensure a reliable source of water for this region. In the 1990s, the two agencies constructed the CAP-SRP Interconnect Facility (CSIF)—a one-way interconnection that, for the first time, allowed Colorado River water to flow into SRP’s water service territory, increasing the operational flexibility of the two systems.
Municipal Water Leader: How has SRP prepared for drought conditions in the Salt and Verde watersheds and on the Colorado River?
Dave Roberts: Research that we have done with Reclamation concerning the effects of climate change shows that the reduction in water supplies produced by the Salt and Verde River watersheds is expected to relatively minor compared to the reductions that other western river basins may see. The research finds that SRP’s water supplies are produced during the winter, when sun angles, temperatures, and evaporation rates are lower than they are during late spring and early summer, when other western river basins produce their water. Additionally, the multiyear carryover storage capacity of SRP’s reservoir system and its defined water service area will help to manage a future with higher temperatures and increased temperature variability. This gives us confidence that, through continued conservation and the proactive management of our surface water and groundwater supplies, SRP can continue to deliver reliable water supplies to the Salt River Valley even in the face of climate change.
The location of SRP’s water system along the CAP canal also presents opportunities for managing the challenges to central Arizona brought on by climate change and continued drought.
One of the key projects to improve drought resiliency is the planned SRP-CAP Interconnect Facility (SCIF), which would allow water supplies from SRP’s system to move into the CAP system—in other words, the opposite of what is allowed by the CSIF. The new interconnection would further improve the flexibility of central Arizona’s water infrastructure—something that will become more important as climate change and climate variability affect the region. SRP continues to plan for the future of our water system, considering any necessary upgrades or modifications to our facilities and operations that can be used to improve our management of Arizona’s water supplies.
Municipal Water Leader: Would you tell us about your planning for the future?
Dave Roberts: Climate change research shows that we will have longer and more severe dry periods in the future, but it also shows that there will be wetter periods and larger runoff events. Right now, our system works by capturing water during the wet periods and storing it to get us through the dry periods. If the climate develops as research predicts, our reservoirs will play an even more critical role in providing a resilient water supply to the Phoenix metropolitan area.
One of SRP’s current challenges is that Horseshoe Reservoir on the Verde River is losing capacity at a rate of about 1,000 acre-feet each year due to natural sedimentation. To date, the reservoir has lost about one-third of its original capacity. The amount of sediment that has accumulated in Horseshoe could fill a football field nearly 9 miles tall. SRP has partnered with Reclamation to conduct an appraisal study and to bring together stakeholders to evaluate different options for addressing the sediment issue, including sediment removal, building new structures, and modifying existing dams. We think that, through this appraisal process, we will find a solution that meets the needs of central Arizona for the next century, ensures the resiliency of SRP’s system, and reduces central Arizona’s dependency on fossil groundwater.
Another example is a project at Roosevelt Dam, where we are working with Reclamation and the U.S. Army Corps of Engineers to improve our operational flexibility in the reservoir’s flood control space. Roosevelt Dam contains around 70 feet of additional storage capacity above the conservation pool behind the dam. SRP is only allowed to hold water in that area for 20 days; it then must release it. We are partnering with the federal agencies to evaluate options to extend the release period so that we have more time within the runoff season to put the water to beneficial use or to store it underground for later use.
Additional water created through improved operational flexibility could be used to provide a backup supply for the low-priority Colorado River supplies that are most at risk of shortage and to replace or supplement the use of fossil groundwater.
Lastly, SRP continues to operate and maintain a robust groundwater well system and underground storage projects. SRP is planning several enhancements to its well system, including piping less-active wells into our canal system to add additional active capacity and to further balance operational well capacity throughout our system. SRP is also assessing further underground water storage opportunities in its service area.
SRP continues to proactively plan for the future to ensure that the water infrastructure that has served the valley for more than a century will reliably do so for another 100 years and that our operations most effectively use the infrastructure that we have invested in.
Municipal Water Leader: Tell us about the DCP process. What does the plan mean for Arizonans?
Dave Roberts: The DCP was a tremendously successful collaborative process bringing together water interests throughout the entire Colorado River basin to ensure the sustainability of the Colorado River’s water supplies. In Arizona, the DCP aims to sustain the state’s CAP water supplies through additional measures to conserve water and improve water storage levels at Lake Mead. This is of particular importance to the Phoenix metro area. After the first 2 years of operations, the DCP is working exactly as anticipated. Water levels at Lake Mead have improved because of the additional conservation measures, and all parties within Arizona and the basin as a whole are meeting DCP objectives. So far, it is a great success story for the Colorado River basin. We should all be proud.
Municipal Water Leader: What role did SRP play in the process?
Dave Roberts: In general, the Phoenix area’s water supply is only as resilient as our least-prepared city. While SRP does have a focus on its water service area, it also takes measures to make sure all Salt River Valley cities have a resilient water supply so that businesses and families are confident they can move to the Phoenix metropolitan area without worrying about their water supply. Under the DCP, SRP agreed to provide 50,000 acre-feet of water to CAP under the two entities’ existing water exchange arrangement to help sustain municipal water supplies when CAP’s supplies are reduced due to cuts in deliveries from Lake Mead.
Additionally, SRP joined with the Gila River Indian Community to create Gila River Water Storage LLC, which provided 445,000 acre-feet of long-term storage credits to the Central Arizona Groundwater Replenishment District (CAGRD). The CAGRD is one of the lower-priority CAP water customers, but it serves customers that provide water to homes and businesses. Because the CAGRD would likely not receive any water during a Colorado River shortage, Gila Water River Storage provided these credits to help the CAGRD sustain its water replenishment obligations for the residential and municipal customers it serves. This was a key factor in helping Arizona fulfil its DCP mitigation plan.
In the future, SRP and CAP are planning to collaborate even more to help each other sustain water supplies for our respective and joint customers. Integrating our water delivery systems through the SCIF and potentially creating additional conservation storage capacity are key steps we can take to make sure that we can meet any future Colorado River shortage guidelines that are established after the expiration of the DCP in 2026.