Be Prepared for Flooding and Mudslides


With wet weather forecasted in the coming days, heavy rain is expected in Del Norte County in the far northwestern part of the state, the California Governor’s Office of Emergency Services (Cal OES) reminds all Californians to be prepared.  

In particular, flooding is possible after heavy, consistent rainstorms; even moderate amounts of rain can cause flash floods and general flooding. A mere six inches of fast-moving water can knock an adult over and 12 inches of rushing water can carry away most cars. It’s recommended that when you see flooding, turn around.   

Flash floods can occur anywhere at any time during stormy weather. Flash flooding can also catch people off-guard and can take property off their foundations. With flash floods comes the dangers of mudslides and debris flows. 


Before a Storm/Flood  

  • Keep storm pipes and drains clear  
  • Move valuable items to higher floors of your home  
  • Use plastic tarps and sandbags to keep out water  
  • Know the best escape routes  
  • Create a go-bag with important documents and items to take during an evacuation  

During a Storm/Flood  

It may look just like muddy rainwater but beware! Floodwaters could be harmful.  

  • Don’t wait and see, leave immediately  
  • Never walk or drive through flood waters  
  • Watch for mudslides and debris flows  
  • 2 feet of rushing water can carry away any vehicle; cars, SUVs and trucks  


Flash flooding occurs so quickly that it can catch people off guard.   

What to do during a flash flood watch  

A flash flood watch is issued when the conditions are right for flooding. It doesn’t necessarily mean that a flood will happen, only that it could. Nonetheless, it should be taken seriously. Remember, flash floods can happen quickly.  

  • Listen to your TV or radio/weather radio and monitor trusted social media sites for weather updates and emergency instructions  
  • Have a plan for where you will go if you need to reach higher ground  
  • Make sure your route avoids low-lying areas  
  • Never walk or drive through flood waters  
  • Make sure your emergency flood kit is stocked  

What to do during a flash flood warning  

A flash flood warning is issued when a flash flood is imminent or is already occurring.  

  • Move to higher ground immediately or stay on higher ground  
  • Keep your radio/weather radio on, monitor updates on trusted social media sites if possible  
  • Evacuate if necessary  

If you’re driving:  

  • Move to higher ground immediately and avoid stopping near streams, rivers or creeks  
  • Never drive through flood water, even if it looks shallow. It may be deeper than it looks and just 2 feet of water can sweep your car away  

What to do if you’re camping or hiking  

  • If the thunderheads are already forming by noon, it’s a sign of potential bad weather  
  • If you cannot see through the rain falling from a thunderstorm, it is strong enough to create a flash flood  
  • Once the rain begins, flash flood conditions can develop in less than five minutes  
  • If your inner gut says ‘no,’ listen to it.  
  • However high you think you need to be to be safe from the flood, go at least twice as high  
  • If getting caught, do not try to outrun the flood unless you are very close to the end. Instead, find a place where you can climb out of the canyon or try to a secure place high on the canyon wall  
  • When camping in a narrow canyon, look for signs of previous flooding in the area and set up as high up as possible. Camp somewhere with safe pathways to go higher if needed  
  • Stay safe. Stay out of floodwater.  


Mudslide vs. Debris Flow 

  • Mudslides: a type of landslide that result from the failure of a slope, and often occurs due to the accumulation of water from prolonged rainfall and/or saturated subsurface conditions. 
  • Debris Flows: described as a “sediment-dominated slurry,” debris flows are mostly made up of soil, resulting from short-duration, high-intensity rainfall events. 
  • A mudslide is a localized slope failure, while a debris flow is a runoff event, such as a flash flood, that entrains sediment from a broad area. 
  • Debris flows and mudslides can occur many years after wildfires. Both happen fast, so heed evacuation warnings immediately 

Burn Scars 

In the years after a wildfire, areas that are often left charred by flames and devoid of vegetation can render the soil non-permeable to rainwater. Where intense fires occur, soils can develop a layer that repels water, like rain on pavement, due to the charred remnants of organic material. Rainfall that would normally be absorbed by the soil will instead quickly run off. 

Consequently, much less precipitation is required to produce a flash flood, and the potential for mudslides and debris flows increases with the loss of organic material that holds the soil in place. Because of this, locations that are downhill and downstream from burned areas are highly vulnerable to rain that can cause mudslides and debris flows, especially in and around steep terrain. 

Debris Flow 

Californians who live on or below hillsides, especially in areas impacted by recent wildfires, should be aware that precipitation increases the probability of potentially dangerous debris flows. 

A debris flow is a fast-moving mass of material — slurries of water, rock, soil, vegetation, and even boulders and trees – that moves downhill by sliding, flowing and/or falling. 

Debris flows range from a few square yards to hundreds of acres in size, and from a few inches to many dozen feet deep. Even smaller ones can be dangerous. Imagine trying to walk through a 3-inch deep mass of wet concrete moving at 30 mph. 

  • Prepare for Mudslides and Debris Flows  
  • Pay attention to local emergency response messaging and heed evacuation notifications immediately 
  • Sign-up for local emergency alerts 
  • Monitor incoming storms, especially if you live in burned areas or downstream/downslope of a burned area 
  • Have an evacuation plan in place for you and your pets 

During Mudslides and Debris Flows   

  • Remember – local authorities may indicate it is safer for you and your family to shelter in place if flash flooding is not impacting your neighborhood 
  • Do not walk through moving water – just six inches of water can sweep an adult off his/her feet 
  • Do not attempt to drive through a flood, debris flow or into flooded areas. It takes only a foot of water to float or sweep away most vehicles. 
  • If you live on a hill, do not sleep in bedrooms that are on the ground floor which face the hazardous slopes.  

Additional information on how Cal OES helps communities plan and prepare for disasters including flooding, mudslides and debris flows can be found here.