Flash flooding hits northern Los Angeles County

By David Jacobson, Temblor

Check your flood risk

santa clara river copy
Overflowing of the Santa Clara River in Southern California caused flash flooding in the small town of Acton. (Picture from lacreekfreak.wordpress.com)


Yesterday, (August 3) a sudden downpour north of Los Angeles caused flashed flooding in Acton, a small, unincorporated part in Los Angeles County that is home to a little over 7,000 people. The flash flooding also brought with it a substantial amount of mud which washed out roads, caused Metrolink delays, damaged homes and roadways, and forced rescue teams to evacuate at least one resident. Local officials have already sent out bulldozers to clear the mud, which could take days or weeks to clean up.

This Temblor map shows the FEMA flood zones around Acton, California. Also added to this map is an area of major flooding as interpreted from helicopter footage. What can be seen is that the FEMA maps did a relatively good job forecasting where flooding was most likely.


In the Temblor map above, we show the FEMA flood map for Acton, California. What can be seen is that much of the small town is within a 1% chance per year flood zone (more than 1 in 10 chance of it happening in a decade). This means that if someone is within this zone and has a mortgage, they must carry flood insurance. If not, flood insurance is optional. While no 0.2% chance per year flood zones (more than 1 in 50 chance in a decade) are shown in this map, it does not mean that they do not exist. It is just likely that these zones have not been mapped.

This picture, taken from a helicopter, shows a pickup truck being engulfed by flash floods in Acton, California. This truck’s occupant had to be rescued by helicopter and transported to safety. (Picture from: ABC 7 News)


From these maps one can see that the FEMA flood maps do a relatively good job highlighting where flooding is most likely, illustrating the importance of knowing whether you are in or close to a flood zone. To find out if you are in or close to a flood zone, click here. If you are in a flood zone, taking action through insurance can protect you from unnecessary losses.


LA Times
ABC News