Maintenance & Operation of The Flood Control System

For over 100 years, the Los Angeles County Flood Control District (District) has provided flood protection and water conservation throughout much of Los Angeles County.

The Los Angeles region is unique because steep, easily erodible mountains are located close to the coast. Erosion occurs when loose soil, rocks, and debris—collectively called “sediment”—are carried downstream, typically during rainfall events. Although Los Angeles receives rain periodically, when storms do occur, they can be intense and produce significant runoff.

Wildfires, which are increasingly common in the Los Angeles region, significantly increase the amount of sediment that erodes and flows from the mountains. Following a wildfire, eroded sediment along with fire debris—such as dense ash and charred vegetation—enters the flood control drainage system during rainfall events. The volume of sediment produced depends on the intensity and duration of the rain, as well as the severity of the fire in the burned area. Intense storms in a recently burned watershed can cause catastrophic property damage. The first five years after a fire are the most critical for sediment management. By years four and five, vegetation typically recovers enough to reduce sediment flows to roughly half of the amount immediately following the fire. Complete recovery to pre-fire conditions generally takes about 10 years.

The flood control system that protects the residents of Los Angeles County is the largest municipally owned system of its kind in the world, providing the backbone of flood protection for the Los Angeles Basin as well as the San Fernando, San Gabriel, and Santa Clarita Valleys. Maintaining and operating such a vast system is no small feat. It requires hundreds of full-time employees, coordination with contractors and vendors, and compliance with numerous regulations to ensure the system continues to protect communities effectively.

The disastrous flood of 1914, which caused over $10 million in property damage, prompted the California Legislature to authorize the creation of the Los Angeles County Flood Control District in 1915. The District was established to manage flooding and conserve stormwater and other wastewater resources. In 1985, District personnel were merged with other County engineering departments to form the Los Angeles County Public Works. Today, Public Works administers the District’s responsibilities, maintaining and operating 14 dams, 491 miles of open channels, 3,400 miles of storm drains, 189 debris basins, and 37 sediment placement sites. Much of the flood control system is over 50 years old, creating a significant need for ongoing maintenance and repairs. As new developments connect to existing infrastructure, the system continues to expand, further increasing the demand for maintenance operations.

To strategically position personnel throughout the County and address flood control system concerns, three distinct service areas have been established: south, east, and west. Each area is served by a primary field office housing engineering staff and management. Additional satellite offices are located throughout the areas as needed to support infrastructure operations. The map below depicts the three service areas. In addition to these field offices, Public Works maintains a headquarters office at 900 South Fremont Avenue, Alhambra, CA.

¹ Quote taken from LA County Department of Public Works Director, Donald Wolfe, in a June 2006 Metro Investment Report Interview