How to Prepare For a Flash Flood

When you know there’s a storm coming like Hurricane Harvey, you know to expect that there will likely be dangerous levels of rain and at least the potential for flooding. What I’m talking about here is a “flash flood,” which by its very definition is unpredictable. Combine that unpredictability with the force of rushing water and it’s easy to see why flash floods are deadly. So what can you do?

Floods can happen anywhere, anywhere it rains, not just in places where it rains alot. And surprisingly, according to NSSL, the National Severe Storms Laboratory, in the U.S. floods kill more people each year than tornadoes, hurricanes or lightning.

What are the risks of flash floods?

Places where there are a lot of roads, buildings or sidewalks (you average city in other words) are at risk for flash floods, because water can’t be absorbed through those surfaces. If there’s a lot of water all at once, it has nowhere to go. City storm drains can’t handle a lot of water all at once.

Riverside environments
It’s nice to live by a river, but these are the areas that are at highest danger of flooding in general. Embankments or levees are built to withstand what is considered a reasonable amount of water, but they might not be build high enough to handle an abnormal amount of water.

It’s not likely that dam would fail, but not impossible. Again, according to NSSL, in 1889 a dam break upstream from Johnstown, Pennsylvania, released a 30- to 40 foot wall of water that killed 2,200 people within minutes.

Rocky, clay soil
These soils don’t absorb water. The water keeps flowing along because it can’t absorb into the ground.

Very intense rainfall
Try water a plant that hasn’t been watered in dry weather in several days. You might expect the water to soak right in to the soil, but the opposite happens. It runs off. If the soil is already saturated, likewise, the water will have nowhere to go.

Steep mountains or canyons
Flash floods frequently occur after rainfall in canyons areas, where the soil, geography and steep terrain funnel water into one small area.

Can a flash flood be predicted?

A few inches, like 6 inches or even less of fast-moving water, can knock a person off their feet. A foot of moving water can carry you away. And more than that could carry away something as large as a car.

The reason they’re called “flash floods” is because they really CAN’T be predicted with any certainty. The best you can do is keep yourself aware of the factors that can contribute to a flash flood.

  • Keep an eye on your local weather. If there is a significant rain event, stay aware of it.
  • Keep yourself informed about local emergencies if you live near a dam.
  • If you live near a river or near a place where there is a low water crossing, make it your business to stay informed about weather and water conditions.
  • Is the ground filling up with pools of water? If so, and it continues to rain, that means the soil is getting saturated and there is nowhere for the water to go.
  • Know the higher ground in your area where you can move to if necessary.
  • Do not try to walk through moving water. Even if it looks shallow.
  • Do not try to drive through a flooded road.
  • Have stored water. If there’s a flood the community’s water supply may not be safe to drink.
  • Stay out of buildings that have flooded. Water can cause structural damage.
  • Avoid the mud left over from a flood. It can contain sewage and chemicals.

Be Prepared for Flash Floods

  • Avoid parking your car near water (rivers/streams) when there is a significant rain event.
  • Take a page from Hurricane Harvey lessons and get yourself a rowboat, kayak or inflatable raft that you keep under your bed or in your car.
  • Be aware of the flood warnings:
    -a Flood Watch means flash flooding or flooding is possible within the designated watch area – be alert. This is the lowest warning level.
    -a Flood Warning means flash flooding or flooding has been reported or is imminent – take necessary precautions at once! Get to higher ground! This is serious!
    -An Urban and Small Stream Advisory means that flooding of small streams, streets and low-lying areas, such as railroad underpasses and urban storm drains is occurring. This could be serious!