Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
Dam located northeast of Phoenix, Arizona, United States
The Granite Reef Diversion Dam is a concrete diversion dam located 22 miles (35 km) Northeast of Phoenix, Arizona. It impounds the Salt River for irrigation purposes. If it were to overflow, more than half of the Yavapai Reservation would be flooded.
The dam diverts nearly all water from the Salt River into the Arizona and South Canals, which serve metropolitan Phoenix with irrigation and drinking water. The Salt River below Granite Reef is usually dry except following consistent and heavy upstream precipitation. When upstream lakes are full, minor and moderate releases are accomplished via floodgates at either end of the dam. The dam is designed to be overtopped by major releases, which can occur every 10 to 40 years.
The dam is 1,128 feet (344 m) long, 29 feet (8.8 m) high. Its volume is 35,000 cubic yards (27,000 m).