Five things you may not know about the CAP system

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CAP canal on cloudy day

1. The system – or even portions of it – are rarely dewatered.

Empty CAP canal

CAP’s mission is to reliably manage and deliver Colorado River water to Maricopa, Pinal, and Pima counties. This means that only rarely is any section of the canal dewatered. In December 2019, necessary siphon work required a section be dewatered. This mesmerizing time lapse video shows the Salt Gila Pumping Plant forebay refilling.

2. Annual outages provide an opportunity to do preventive maintenance, inspections, testing and repairs.

CAP worker maintaining canal

Reliable water deliveries are a priority, but that requires well-maintained and efficient infrastructure which is achieved through annual outages. During scheduled outages, water continues to move through one half of the plant while equipment on the other half is taken out of service so CAP craftsmen can complete the work. Thanks to system redundancies and CAP’s storage reservoir, Lake Pleasant, this work does not impact deliveries.

3. The flow of water is controlled by check structures.

CAP canal check structure

The system has 39 check structures that control the flow of water into and out of a segment, or pool, of the canal. Each check structure contains two radial gates that operate independently, a feature designed to provide system redundancy. The gates are operated by electric variable speed motors that control center dispatchers can move in increments as small as 1/100 of a foot. The max capacity is 3,000 cubic feet per second.

4. The entire 336-mile system is fenced.

At Central Arizona Project (CAP), protecting our infrastructure as well as the safety of our employees, neighbors and wildlife along the CAP canal system is among our highest priorities. Because of this, the CAP canal is fenced, posted with ‘keep out’ signs and patrolled and monitored by our Protective Services agents.

5. The canal is a trapezoidal shape.

The canal is nearly always filled with water, so it’s rare to see the actual shape – which is trapezoidal. This canal shape, as well as narrowing width and shallowing depth as it tapers along the entire 336-mile system, is not a coincidence. The specific trapezoidal shape is a balance of hydraulic efficiency and constructability.