Big Tujunga Dam

Big Tujunga Dam
Name	Big Tujunga Dam
Location	Angeles National Forest, Los Angeles County, California, United States
Coordinates	34°20′N 118°10′W
Type	Concrete arch dam
Height	195 ft
Length	758 ft
Reservoir	Hansen Reservoir
Owner	Los Angeles Department of Water and Power

Big Tujunga Dam is a concrete arch dam located in the San Gabriel Mountains of Los Angeles County, California, within the Angeles National Forest near the community of Sunland-Tujunga and the city of La Cañada Flintridge. The structure impounds the Big Tujunga Creek to form Hansen Reservoir, operated by the Los Angeles Department of Water and Power, and contributes to regional Los Angeles Aqueduct-era water projects and flood control systems associated with the Los Angeles River and San Fernando Valley infrastructure.

History

Initial proposals for controlling flows on Big Tujunga Creek emerged amid late 19th- and early 20th-century flood events that affected Los Angeles and the San Fernando Valley, including the catastrophic floods tied to the Great Flood of 1914 and the Los Angeles Flood of 1938. Planning linked to the expansion of Los Angeles Department of Water and Power holdings, the development of the Los Angeles Aqueduct, and regional flood mitigation involved agencies such as the U.S. Army Corps of Engineers, the County of Los Angeles, and the Civilian Conservation Corps during the New Deal. Construction of the dam responded to interwar and postwar growth pressures similar to projects at Hoover Dam, Grand Coulee Dam, and other western waterworks, reflecting policies of the Bureau of Reclamation and municipal authorities. The dam’s commissioning paralleled broader Southern California development driven by figures and institutions active in the early 20th-century Los Angeles expansion.

Design and construction

Engineers designed the structure as a concrete thin-arch dam, following principles used at dams such as Morrow Point Dam and early 20th-century arch designs influenced by European projects like Malpasset Dam and American precedents at Glen Canyon Dam and Shasta Dam. The design process involved firms and bureaus experienced in mountain hydrology and masonry, drawing on standards from the American Society of Civil Engineers and the U.S. Bureau of Reclamation engineering practices. Construction required coordination with contractors, heavy equipment suppliers, and logistical networks serving the San Gabriel Mountains, with workforce patterns similar to projects overseen by the Army Corps of Engineers and contractors who worked on regional roadways such as Angeles Crest Highway.

Specifications and structure

The dam is a concrete arch structure standing roughly 195 feet high and spanning approximately 758 feet across Big Tujunga Canyon. Its crest, spillway, and outlet works were engineered to handle flows from the San Gabriel Mountains watershed, with staging for sedimentation control and debris management comparable to installations at Hansen Dam and Sepulveda Dam. The reservoir, Hansen Reservoir, provides transient storage with a capacity designed to moderate flood peaks affecting downstream areas including Sun Valley and the San Fernando Valley. Structural components include reinforced concrete arches, buttresses, intake towers, and gated spillways influenced by standards from the American Concrete Institute and seismic criteria later updated to reflect findings from events like the 1971 San Fernando earthquake and the 1994 Northridge earthquake.

Operations and water management

Operational control rests with the Los Angeles Department of Water and Power, coordinating releases with downstream facilities such as Hansen Dam and channel systems managed by the Los Angeles County Flood Control District. The dam’s role includes flood detention, sediment trapping, and measured releases to protect downstream urban areas including Burbank, Glendale, and North Hollywood. Water management practices integrate forecasting from the National Weather Service, hydrologic modeling from institutions like the United States Geological Survey, and regional plans aligned with goals pursued by Metropolitan Water District of Southern California and state entities such as the California Department of Water Resources. Operational adjustments often respond to storm events tied to atmospheric rivers and Pacific storm systems that affect the Transverse Ranges.

Flood control and seismic safety

Flood control design addresses high-intensity rainfall and debris flows characteristic of the San Gabriel Mountains and the Mediterranean climate of Southern California, incorporating lessons from historic floods that reshaped policy across agencies including the U.S. Army Corps of Engineers and county planners. Seismic safety measures reflect updated criteria after earthquakes like the 1933 Long Beach earthquake, the 1971 San Fernando earthquake, and the 1994 Northridge earthquake, leading to retrofits and monitoring consistent with recommendations from the California Geological Survey and the United States Geological Survey. Emergency action plans coordinate with local jurisdictions including Los Angeles Fire Department, Los Angeles County Sheriff, and municipal emergency management offices to mitigate downstream hazard during extreme events.

Environmental impact and ecology

The impoundment altered fluvial dynamics on Big Tujunga Creek, affecting native riparian habitat and fish communities historically associated with the Los Angeles River watershed, including impacts noted in studies by academic institutions such as the University of California, Los Angeles and the California State University, Northridge. Sediment trapping has influenced geomorphology downstream, with implications for species reliant on alluvial processes found in regional preserves like Topanga State Park and restoration efforts similar to work on the Los Angeles River revitalization. Management responses involve coordination with regulatory bodies including the California Department of Fish and Wildlife and federal statutes like the Endangered Species Act when assessing habitat for species documented by environmental NGOs and research centers focusing on Southern California ecosystems.

Recreation and access

Hansen Reservoir and surrounding lands in the Angeles National Forest provide recreational opportunities tied to trails, fishing, birdwatching, and interpretive access coordinated by agencies such as the U.S. Forest Service, the Los Angeles Department of Recreation and Parks, and local volunteer groups associated with organizations like the Sierra Club and San Gabriel Mountains Forever. Nearby attractions and access routes include Crystal Lake Recreation Area, Angeles Crest Highway, and trailheads connected to systems used by hikers traversing to points like Mount Wilson and San Gabriel Peak. Public access and safety are managed in coordination with county and forest authorities, balancing recreation with watershed protection and infrastructure security overseen by municipal and federal partners.

Category:Dams in California Category:Buildings and structures in Los Angeles County, California