The dam is high from the riverbed, high from the foundations, and long. It has a width of at the base, tapering to at the crest. The storage capacity is at the spillway, with a minimum pool of to prevent sediment and debris from entering the dam's outlets. After the completion of Hansen Dam downstream, the importance of Big Tujunga Dam for flood control has decreased; however, it is still directly responsible for protecting about 4,600 residents living in the floodplain of Big Tujunga Canyon. In addition, the dam conserves about of runoff per year for drinking water and groundwater recharge purposes. This saves the city of Los Angeles about $2,250,000 annually due to the cost difference between local and imported water. Because of the small storage capacity of the reservoir relative to the size of its watershed, frequent dredging is required to remove sediment from behind the dam. Most of the sediment is compacted and stored at the Maple Canyon Sediment Placement Site located less than west of the dam. The 2009 Station Fire, which burned some 87 percent of the Big Tujunga watershed, caused more than 2 million cubic yards of sediment to flow into the reservoir, all of which had to be subsequently removed.
History
Aside from the village of Tujunga or Tuxunga, the former Fernandeño village in the area of the dam and Big Tujunga Canyon was called Muxúnga, which means "place of shooting" in the Fernandeño dialect of the Tongva language. The name comes from the verb muxú, which means "shoot him." The dam was completed in 1931 by the Los Angeles Department of Water and Power, at a cost of $1.2 million. It was originally planned as one of several flood control dams inside Big Tujunga Canyon and was thus referred to as Big Tujunga Dam No. 1 until the larger Hansen Dam was completed in 1940 at the mouth of the canyon, eliminating the need for the other dams. During the Los Angeles flood of 1938, the dam was able to stop a huge debris flow of boulders and uprooted trees, sparing much of Sunland, Tujunga and Glendale from destruction. In 1976, the dam was recognized as in danger of failure from earthquakes and the reservoir's level was temporarily restricted to about 25% of capacity. In 2008 the Los Angeles County Flood Control District began a project to rehabilitate the aging structure. 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 floodwater capacity from to more than. In addition, a valve was installed at the dam base to pass low flows for habitat conservation. The seismic retrofit project was completed in July 2011 at a cost of $100 million.
