History and background information

The Los Angeles Flood of 1938, which included significant flooding along the Tujunga Wash and at its confluence with the Los Angeles River, resulted in increased support to dam and channelize the city's creeks and rivers. In 1939, due to repeated floods and the damage they caused in the eastern portions of the San Fernando Valley, the U.S. Army Corps of Engineers began the project. The Corps worked in conjunction with the Los Angeles County Flood Control District (LACFCD). They had already considered planning to implement flood risk management within the area since 1915 after a previous series of floods.[5] In 1939 the Corps, by use of eminent domain, seized the horse ranch of Homer and Marie Hansen to build the dam.[1] After a year of construction and over $11 million in initial costs, the dam and its corresponding facilities were finished.[5] The 2-mile (3.2 km) long, 97-foot (30 m) high dam was built to control the runoff and floodwaters.[6]

During storms and flooding, the dam is intended to catch water within the reservoir. Provisions in the dam's standards of operations promote water conservation efforts coordinated with the Los Angeles County Department of Public Works. The provisions allow the dam to discharge water onto spreading grounds located south of the dam, which then percolates into groundwater recharge basins and is stored as part of the city's water supply.[5]

Accumulation of debris from previous floods reduced the amount of storage capacity of the reservoir. As a result, in 1981, the Corps proposed raising the height of the dam rather than starting the expensive process of removing the build up of silt, sand, gravel and other debris.[7] The proposal did not pass, and responsibility was redirected back to the Corps providing maintenance of the dam. The Corps must occasionally excavate sediment and vegetative debris to clear clogged outlet works and maintain full capacity of the dam.[5] In the mid-1940s, the Hansen Dam Basin's recreational possibilities were considered as it attracted thousands of visitors every year. Development of recreational facilities began in 1952 with the creation of Holiday Lake, which was used by swimmers, boaters, and anglers. By 1991, the lake had become completely filled with sediment and was abandoned.[5]