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Big Tujunga Dam
Big Tujunga Dam is a concrete arch dam in Los Angeles County, California, spanning Big Tujunga Creek northeast of Sunland. Completed in 1931 by the Los Angeles Department of Water and Power, it serves mainly for flood control. The dam was originally planned as one of several similar flood-control dams inside Big Tujunga Canyon and was thus referred to as Big Tujunga Dam No. 1 until the large Hansen Dam was completed in 1940, eliminating the need for the other components of the original project.
Its reservoir is called Big Tujunga Reservoir, and has a capacity of . Although it is located inside the Angeles National Forest, public access to the lake is forbidden. The water is kept at a low level except during the rainy season. Because of the small storage capacity of the reservoir, it has filled completely with sediment on several occasions, including 1969 and 2011; as a result frequent dredging is required to keep the dam operational.
==Seismic retrofit project==
In 1976, the dam was recognized as in danger of failure from earthquakes (the San Andreas Fault runs nearby) and the reservoir's level was temporarily restricted to about 25% of capacity. Approximately of concrete was added to the dam, transforming it from a thin-arch to a thick-arch design. A new spillway was built and the original one was expanded, increasing the release capacity from to more than .〔 The seismic retrofit project was completed in July 2011 at a cost of $100 million.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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