Gila River - Dams and Diversions

Dams and Diversions

The only major dam on the Gila River is Coolidge Dam 31 miles (50 km) southeast of Globe, Arizona, which forms San Carlos Lake. The Painted Rock Dam crosses the Gila near Gila Bend, although the river is a transient one at that point. A number of minor diversion dams have been built on the river between the Painted Rock Dam and the Coolidge Dam, including the Gillespie Dam which was breached during a flood in 1993. Many dams have also been built on tributaries, including Theodore Roosevelt Dam on the Salt River, New Waddell Dam on the Agua Fria River, and Bartlett Dam on the Verde River. Many major dams in the Gila River system were built and operated by the U.S. Bureau of Reclamation which also constructed most of the large dams throughout the Colorado River basin. Others, such as Coolidge Dam, are owned by local water supply agencies, irrigation districts or Native American tribes.

The Gila River and its main tributary, the Salt River, would both be perennial streams carrying large volumes of water, but irrigation and municipal water diversions turn both into usually dry rivers. Below Phoenix to the Colorado River, the Gila is usually either a trickle or completely dry, as is also the lower Salt from Granite Reef Diversion Dam downstream to the Gila, but both rivers can carry large volumes of water following rainfall. A long time ago, the Gila River was navigable by boats from its mouth to near the Arizona – New Mexico border. The width varied from 150 to 1,200 feet (46 to 370 m) with a depth of 2 to 40 feet (0.61 to 12 m). The natural discharge of the river was roughly 1,300,000 acre feet (1.6 km3) per year, with a mean flow of about 1,800 cubic feet per second (51 m3/s) at the mouth. The river's present discharge near the mouth is less than 180,000 acre feet (0.22 km3) per year, with an average flow of just 247 cubic feet per second (7.0 m3/s). Overdraft from the Gila River system has prompted the construction of the Central Arizona Project, which delivers some 1,500,000 acre feet (1.9 km3) annually from the Colorado River to supplement water supplies in the basin.

The upper Gila River, including its entire length within New Mexico, is a free-flowing one. Recent efforts to allow for damming or otherwise diverting this stretch have met with stiff political resistance, having been named as one of the nation's most endangered rivers due to proposed dam projects such as Hooker Dam. During his time in office, former New Mexico Governor Bill Richardson had promised to block any such attempt during his term, and he had even considered pushing for a statutory prohibition against any such projects on the state's portion of the river.