Dec 16 2019Share

Protecting CAP Infrastructure Through Collaboration and Investment

By Warren Tenney

It’s not often that we get an inside view to a portion of the impressive infrastructure that makes up the Central Arizona Project (CAP). This rare occurrence took place at the Salt River Siphon last week, as attendees at a reception were given the opportunity to safely descend into the bottom of the aqueduct for a rare look at this vast structure.

At the end of October, CAP partially emptied water from the Salt River Siphon which allowed for a small portion of the canal to dry. This enabled staff to make planned repairs to the siphon that takes the CAP canal under the Salt River. These protective measures ultimately help deter corrosion and erosion to ensure continued reliability of the delivery of Colorado River water to Central and Southern Arizona. The last time this type of planned maintenance took place was back in 2001.

Undertaking a maintenance project of this magnitude does not come easily or quickly. It required extensive planning and elaborate collaboration with stakeholders, partners, and customers for the past several years to ensure water could still be supplied as needed. However, through an elaborate coordinated operation, affected CAP water users  - Mesa, Chandler, Gilbert, and Tucson - temporarily received their CAP water from the Salt River Project (SRP) delivery system.

The Salt River Siphon, which is located at about the halfway point in the CAP’s 336 miles of infrastructure, is in North Mesa. The Salt River Siphon is a 21-foot diameter pipe that runs under the Salt River before the canal carries water into Pinal and Pima counties. Approximately 75 percent of all CAP water deliveries travel through the siphon. CAP has a total of ten siphons that carry Colorado River water under natural drainage ways that include the Agua Fria, New River, Salt, Gila, and Santa Cruz Rivers. The siphons allow for natural floodwaters to travel unimpeded and protect the CAP system from damage that may have occurred if constructed at ground level.   

This planned maintenance project also highlights the cost investment needed to maintain and protect water infrastructure as the cost of this project added up to be approximately six million dollars. However, maintenance of this sort will not be required to take place again at the Salt River Siphon for another ten years or so.

Salt Water Siphon 3With the project complete, the reception was held at the Salt River Pumping Plant to celebrate the success of the maintenance and repair project. This event enabled attendees the opportunity to not only walk the emptied portion of the canal to marvel at the infrastructure and its impressive design, but to celebrate the regional cooperation this project required. To physically be able to visit this site reiterated how important collaboration is when it comes to safe, reliable and sustainable water infrastructure and water delivery in Arizona.

Now water once again flows where we stood just last week, restoring full service of Colorado River water to customers who were also a vital part of this critical maintenance project led by CAP.

For 50 years, Arizona Municipal Water Users Association has worked to protect our member cities’ ability to provide assured, safe and sustainable water supplies to their communities. For more water information visit

Stay up to date & sign up for the AMWUA Blog:

Sign Up Now

To stay informed, sign up for the AMWUA blog

Sign Up Now