With sustained El Nino rains approaching, concerns are mounting in regards to flooding (flash floods & risk of flooding after wildfires) in the Southern California region and with good reason. Concerns have been validated after seeing floods occur after scattered showers in various parts of Southern California. Now keep in mind that the scattered showers we have witnessed have produced an incredible amount of rain in the span of 1 to 2 hours with some areas getting as much as an 1 1/2 of rain.
The most notable floods were seen on interstate 5 and on highway 58 which were hit with flooding and mudslides trapping motorists. Just this last week it was reported that a man was killed when his car was swept by flash floods in the Palmdale, CA area. This is indeed tragic!
One of the biggest concerns for many agencies are the recent burn areas throughout Southern California. Normally, vegetation absorbs rainfall, reducing runoff. However, wildfires leave the ground charred, barren, and unable to absorb water, creating conditions ripe for flash flooding and mudflow. Flood risk remains significantly higher until vegetation is restored—up to 5 years after a wildfire. We are also seeing that the ground is so dry after many years of drought that absorption is impossible further adding to flooding risks in the foothills and mountains.
Anyone living in or near one of the burn areas should take heed and start planning their evacuation routes in case flooding or mudslides should occur. We suggest that residents in these areas monitor weather forecasts and understand the threats that face them. In some areas where flooding and mudslides are frequent, K-Rails are being installed in an effort to divert any water or mud flow away from homes or critical structures. Keep in mind that properties directly affected by fires and those located below or downstream of burn areas are most at risk for flooding.
We are encouraging many residents in those areas to start planning on placing sandbags around the perimeter of their homes in an effort to minimize flooding damage. Sandbags can be obtained at many fire stations in the area for free. Take the time to get what may be needed to protect your home.
There is also a high probability of urban flooding as seen recently in the city of Boyal Heights when storm drains were blocked by a mattress. Many storm drains are compromised and this could lead to significant flooding in many areas. It is important that residents check their storm drains and if there is a lot of debris that needs to be cleaned, to report this potential hazard to street services. The key is minimizing flood risks.
- Flash Floods
A flash flood is a rapid flooding of low-lying areas in less than 6 hours, which can be caused by intense rainfall. Flash floods are known to roll boulders, tear out trees, and destroy buildings and bridges.
Mudflows are rivers of liquid and flowing mud on the surface of normally dry land, often caused by a combination of brush loss and subsequent heavy rains. Mudflows can develop when water saturates the ground, such as from rapid snowmelt or heavy or long periods of rainfall, causing a thick, liquid, downhill flow of earth. Mudflows are covered by flood insurance but are different from other non-covered earth movements where there is not a flowing characteristic—such as landslides or slope failures.
As with any potential urban flooding, flash floods or mudslides, there is a risk of drowning and death. By taking the necessary steps to preparedness, many can reduce the incidents of drowning or death. However, some have been caught by surprise such as those caught in flash floods.
Flash Flood Preparedness Tips:
- Since many leisure activities occur in and around streams and rivers, be aware of potential risks.
- Don’t play in flood waters. This is especially applicable to children and pets.
- Whenever thunderstorms are occurring in the area, pay attention to rapidly changing conditions.
- If you notice a stream start to rise and become muddy, or hear a roaring sound upstream, a flood wave could be rushing toward you. Head to higher ground immediately.
- Never drive into a flooded roadway or through flowing water. Turn around. Don’t drown.
- Don’t walk through moving water. Six or more inches of moving water could cause you to fall and could carry you away.
- Monitor NOAA Weather Radio, or your favorite news source for vital weather-related information.
- Be especially cautious at night when it is harder to recognize flood dangers.
- If caught in a flood, abandon your car. If flood waters rise around your car, abandon the car and move to higher ground if you can do so safely. You and the vehicle can be quickly swept away.
- If you are at home when a flash flood hits, if you have time, secure your home and turn off utilities at the main switches or valves if instructed to do so. Disconnect electrical appliances. Do not touch electrical equipment if you are wet or standing in water.
The following are 8 key facts about flash flooding:
- The national 30-year average for flood deaths is 127.
- Almost half of all flash flood fatalities occur in vehicles.
- Rapidly rising water can reach heights of 30 feet or more.
- Two feet of water on a bridge or highway could float most vehicles.
- Flash flood damage and most fatalities tend to occur in areas immediately adjacent to a stream or arroyo.
- Highly populated areas have a high risk for flash floods.
- During a flash flood, low spots, such as underpasses, underground parking garages and basements can quickly become death traps.
- Embankments, known as levees, are built along the sides of river banks to prevent high water from flooding bordering land. In 1993, many levees failed along the Mississippi River, resulting in devastating flash floods.