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Location: Folsom, California, USA
Completion Date: 1956
Cost: $81.5 million
Reservoir Capacity: 43.9 billion cubic feet
Purpose: Hydroelectric power, irrigation, recreation
Reservoir: Folsom Lake
Engineer(s): U.S. Army Corps of Engineers
On July 17, 1995, a spillway gate on the Folsom Dam broke open as it was being raised, causing an uncontrolled five-story cascade to gush down the face of the dam. Nearly 40 percent of Folsom Lake drained out past the broken gate before it could be repaired. Normally, when a reservoir becomes too full -- like after a heavy rainstorm -- engineers open spillway gates, which allow the excess water to drain out of the reservoir at a controlled rate of speed. When these gates open suddenly and engineers lose the ability to control the flow, disaster can result.
Luckily, no major flooding occurred as a result of the failure, and the Folsom Dam was fully repaired at a cost of $20 million. After a year of thorough investigation, the United States Bureau of Reclamation blamed the disaster on a design flaw. Some spillway gates, like the ones at Folsom Dam, roll up and down on giant brass and steel pins, like a big garage door. As the gate opens and closes, the pins can become hot with friction. Friction reduced the strength of the pins in the Folsom Dam spillway gate and caused the gate to break.
Today, engineers trained in rope-climbing techniques can inspect these difficult-to-reach spillway gates and help prevent similar disasters from happening.Here's how this dam stacks up against some of the biggest dams in the world.
(reservoir capacity, in cubic feet)