Hoover Dam

13. Spillways

The dam is protected against over-topping by two spillways. The spillway entrances are located behind each dam abutment, running roughly parallel to the canyon walls. The spillway entrance arrangement forms a classic side-flow weir with each spillway containing four 100 ft (30 m) long and 16 ft (4.9 m) high steel drum gates. Each gate weighs 5,000,000 pounds (2,300,000 kg) and can be operated manually or automatically. Gates are raised and lowered depending upon water levels in the reservoir and flood conditions. The gates cannot completely stop water from entering the spillways but help maintain an extra 16 ft (4.9 m) of lake level.