Whittier Narrows Dam

Residents may have read an article or heard on the news about the Whittier Narrows Dam located in Pico Rivera. This dam is a flood risk management and water conservation project and is located 11 miles east of downtown Los Angeles. The Dam was constructed in 1957 to keep the San Gabriel and Rio Hondo rivers from flooding homes in a stretch of Los Angeles County from Pico Rivera to Long Beach.

Whittier Narrows Dam Safety Modification Study

The U.S. Army Corps of Engineers (USACE) who operates the Dam is proposing plans to reduce the potential for and consequences of catastrophic flooding resulting from failure of the Whittier Narrows Dam during very rare flood events. As one of the cities downstream from the Whittier Narrows Dam, the City of La Palma could be effected if the dam, channels, or levees below the dam are unable to contain waters from an exceptionally large and rare storm, which has a 1 in 900 – or 0.1% – chance of occurring in any given year.[i]

During this 1 in 900 chance rare storm, depending on the magnitude of the storm and the size of a dam breach, La Palma could see flood waters ranging anywhere from zero to eight feet.[i] It is important to note that a storm of this size has not been seen since before the dam’s construction. For reference, the flooding associated with Hurricane Harvey, a Category 4 hurricane, in Texas in 2017 has been estimated to be an approximate 1 in 500 – or 0.2% – chance of occurring in any given year.[i]

La Palma Flood Risk Assessment

In general, La Palma is in an area where there is a moderate to low risk of flooding due to geographic location near various creeks according to the Federal Emergency Management Agency (FEMA). The risk is reduced, but not completely removed, by the levees along Coyote Creek. Below is a map showing the areas of La Palma that are most at risk for flooding. For example, the western part of La Palma with the grey stripped lines is in an area with reduced flood risk due to levees, which indicate less than a 1% chance of annual flooding. The other areas of La Palma shaded orange have a 1 in 500 – or 0.2% – chance of annual flooding.

Flood Insurance Information

Under federal law, flood insurance is mandatory for all federal or federally-related financial assistance for the acquisition and/or construction of buildings, such as homes, in high-risk flood areas. Since La Palma is not in a high-risk flood area, flood insurance is not required. However, residents may want to consider purchasing flood insurance. The National Flood Insurance Program allows property owners in La Palma to purchase affordable flood insurance to protect against flood losses. For more information about flood insurance visit: www.floodsmart.gov

 [i] 2018 Whittier Narrows Dam Safety Modification Study