Thundering water. That’s what you might expect at the Nevada Spillway. But today, it stands silent, a testament to both engineering and the raw power of nature.
The Nevada Spillway is part of the Hoover Dam. Many people ask about seeing water flowing over the dam’s top. It has never happened and likely never will. The spillways prevent that. They act like an overflow in a bathtub. If water levels rise too high, it goes into the spillway instead of over the dam. This protects the powerhouse at the dam’s base. Water and electrical generators do not mix. It also keeps the vehicles crossing the dam safe.
The Nevada Spillway sits 27 feet below the dam’s top. Water entering it flows into a 50-foot diameter tunnel. This tunnel is 600 feet long and steeply inclined. It connects to one of the original diversion tunnels. The Nevada Spillway can handle 200,000 cubic feet of water per second. That’s like having a Niagara Falls right here.
Each spillway has four steel drum gates. They are each 100 feet long and 16 feet high. These gates do not stop water from entering the spillway. However, they allow an extra 16 feet of water to be stored in the reservoir. Each gate weighs about 5 million pounds. They can be operated automatically or manually.
The Nevada Spillway has been used twice. The first time was a test in 1941. The second time was during a flood in 1983. On August 6, 1941, the Arizona spillway was used. The reservoir had reached a maximum elevation of 1220.44 feet. On August 14, the drum gates were raised for hours. An inspection found the tunnel lining intact. There were few signs of erosion. Operations continued until the reservoir lowered to 1205.60 feet on December 1, 1942. The average discharge flow was about 13,500 cfs. The maximum flow was 38,000 cfs on October 28, 1941. One of the drum gates dropped unexpectedly that day.
The fast-falling water eroded the tunnel lining. The eroded area was 115 feet long and 30 feet wide. Its maximum depth reached about 45 feet. The cavity’s original volume was 1069.6 cubic yards. Repairs began quickly. A special concrete repair process was used. After repair, the tunnel was smoothed to prevent future erosion.
Record flows into Lake Mead occurred in 1983. The water rose over the spillway gates of Nevada and Arizona. The flows eroded the concrete base again. This also required repairs.
The Hoover Dam’s spillways, including the Nevada Spillway, protect the dam. They manage water flow. They stand ready to handle immense volumes of water. They safeguard the dam’s power generation and structural integrity. They stand as a crucial part of this iconic American landmark.