When was the Hoover Dam built?
Hoover Dam
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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-foot-long (30m) and 16-foot-wide (4.9m) steel-drum gates. Each gate weighs 5,000,000 pounds (2,300,000 kilograms) and can be operated manually or automatically. Gates are raised and lowered depending on water levels in the reservoir and flood conditions. The gates could not entirely prevent water from entering the spillways but could maintain an extra 16ft (4.9m) of lake level.[106]
Water flowing over the spillways falls dramatically into 600-foot-long (180m), 50-foot-wide (15m) spillway tunnels before connecting to the outer diversion tunnels, and reentering the main river channel below the dam. This complex spillway entrance arrangement combined with the approximate 700-foot (210m) elevation drop from the top of the reservoir to the river below was a difficult engineering problem and posed numerous design challenges. Each spillway's capacity of 200,000cuft/s (5,700m3/s) was empirically verified in post-construction tests in 1941.[106]