There’s a lot of information on the risks associated with storms, hurricanes, and tornadoes, but not as much about their consequences. Just about any storm can cause flooding, and many communities are not prepared to deal with it. As a result, water supplies are contaminated, emergency services are crippled, and important infrastructure can fail.
In Texas and Oklahoma, heavy rains caused major damage and a number of deaths, with more precipitation expected. Floods are not a rare occurrence, with a number of major disasters over the past few years: In 2013, Boulder, Colorado experienced 6 months of rainfall over the span of a week. Flooding in the wake of hurricane Katrina (2005) was severe enough to cause a humanitarian crisis.
To respond appropriately to a flood, we should understand the various types of flooding and the steps we can take to stay safe.
What is a Flood?
A flood is defined as an overflow of water that submerges land which is normally dry. Flooding may occur from water bodies, such as a seacoast, river, or lake. The water overcomes levees, resulting in the inundation of populated areas. It may also occur due to an accumulation of rainwater on saturated ground.
Some floods develop slowly, while others (called flash floods), can develop in a very short time and rush into areas where it wasn’t even raining. As a result, flash floods often catch the population downriver by surprise, causing severe damage and loss of life.
Types of Floods
There are several types of floods:
Floods can happen on flat or low-lying areas when the ground is saturated and water cannot run off quickly enough to prevent accumulation. Floods related to rainfall can also occur if water falls on an impenetrable surface, such as concrete, asphalt paving or frozen ground, and cannot rapidly be absorbed. In urban areas, it usually takes at least 1 inch (25 mm) of rainfall per hour to create significant ponding of water on hard surfaces.
Floods happen in rivers when the flow rate exceeds the capacity of the river channel. This happens particularly at bends in the waterway. The faster the flow rate, the more dangerous it is; people traditionally live and work by rivers due to access to fertile soil and trade routes.
Flooding on the coast is commonly caused by a combination of tidal surges caused by winds and low barometric pressure. Coastal areas may be flooded by storm events, such as hurricanes, resulting in waves over-topping seawalls and levees.
Failures of vital infrastructure, such as the collapse of a dam, may cause catastrophic flooding,. This exact event occurred in Johnstown, Pennsylvania in 1889, costing 2,200 lives. Major flooding may also be caused by the effects of an earthquake or volcanic eruption. These events often occur at sea hundreds of miles from the area affected, but result in tidal wave floods called Tsunamis.
Most people have heard of hurricane or tornado watches and warnings, but the U.S. weather service also tries to warn the populace of flooding. In order of imminent danger, they are:
• Flood Advisory: Flood advisories are issued when an expected weather event may cause some flooding, but not enough to be a major issue. Significant inconvenience may be possible and lead to dangerous situations if caution isn’t exercised.
• Flood Watch: Flood watches are issued when weather conditions become favorable to cause significant flooding. Although flood conditions are not imminent, steps should be taken to prepare for such an event..
• Flood or Flash Flood Warning: Flash flood or flood warnings are issued when the hazardous flooding is imminent or has already begun. Action should be taken to avoid life-threatening situations.
Many people ignore these warnings at their own peril. If you live in a low-lying area, especially near a dam or river, then you should closely monitor and heed warnings when they are given and be prepared to evacuate quickly. Rising flood waters could easily trap you in your home.
Preparing for Floods
If you live in a floodplain, you should:
• Build an emergency kit with food, water (yes, water), and medical supplies.
• Have a way to communicate with family members.
• Elevate the furnace, water heater and electric panel
• Install special “check valves” to prevent water from backing up into the drains of your home.
• Consider having materials to make waterproof barriers to stop floodwater from coming into the building
• Seal walls in basements
When It Happens
You can’t stop the rain from falling and you can’t stop the tide from coming in, but you can weather the effects of flooding with some sound strategy and a little preparation. Here are some flood safety tips:
Get Out Early
Make the decision to leave for higher ground before extensive flooding occurs. Closely monitor public service announcements for warnings and advice from experts.
Be Careful Walking Through Flowing Water
Drowning is the most common cause of death during a flood, especially a flash flood. Rapidly-moving water can knock you off your feet even if less than a foot deep.
Don’t Drive Through a Flooded Area
As many people drown in their cars as anywhere else. Cars stall and roads/bridges could easily be washed out. Try to figure out now if there is a “high road” to safety before a flood occurs.
Beware Of Downed Power Lines
Electrical current is easily conducted through water. Watch for downed power lines; you don’t have to touch them to be electrocuted; just stepping in the water they’re in could kill you.
Turn Off The Power
If you have reason to believe that water will get into your home, turn off the electricity. Don’t use appliances or motors that have gotten wet unless they have completely dried. You might have to take some apart to clean debris out of them.
Watch Out For Intruders
Critters that have been flooded out of their homes may seek shelter in yours. Snakes, raccoons, and other unfriendly creatures may decide your home is now their territory. Human intruders may be interested in your property, as well.
Look Before You Step
After a flood, watch where you step; there is debris everywhere. The floors of your home may be covered in mud, causing a slip-and-fall hazard. There may be damage to foundations of flooded buildings, even if the water has subsided.
Check for Gas Leaks
Don’t use candles, lanterns, stoves, or lighters unless you are sure that the gas has been turned off and the area has been well-ventilated.
Exhaust Fumes Can Kill
Only use generators, camping stoves or charcoal grills outside. You can easily be overcome by the fumes they emit.
Clean Out Saturated Items Completely
Floodwaters are not clean! Don’t use floodwater as drinking water or to cook food unless you have thoroughly sterilized and filtered it. Make sure you have food storage in waterproof containers.
Joe Alton, MD
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