Floods are among Earth's most common–and most destructive–natural hazards.
LATEST NEWSWest Japan is experiencing widespread flooding after Typhoon Lan touched down in late October 2017. The powerful storm resulted in landslides, torrential rain, and massive waves that injured over ninety people and left three dead. HOW FLOODS DEVELOP A flood occurs when water overflows or inundates land that's normally dry. This can happen in a multitude of ways. Most common is when rivers or streams overflow their banks. Excessive rain, a ruptured dam or levee, rapid ice melting in the mountains, or even an unfortunately placed beaver dam can overwhelm a river and send it spreading over the adjacent land, called a floodplain. Coastal flooding occurs when a large storm or tsunami causes the sea to surge inland. Most floods take hours or even days to develop, giving residents ample time to prepare or evacuate. Others generate quickly and with little warning. These flash floods can be extremely dangerous, instantly turning a babbling brook into a thundering wall of water and sweeping everything in its path downstream. Disaster experts classify floods according to their likelihood of occurring in a given time period. A hundred-year flood, for example, is an extremely large, destructive event that would theoretically be expected to happen only once every century. But this is a theoretical number. In reality, this classification means there is a one-percent chance that such a flood could happen in any given year. Over recent decades, possibly due to global climate change, hundred-year floods have been occurring worldwide with frightening regularity. Moving water has awesome destructive power. When a river overflows its banks or the sea drives inland, structures poorly equipped to withstand the water's strength are no match. Bridges, houses, trees, and cars can be picked up and carried off. The erosive force of moving water can drag dirt from under a building's foundation, causing it to crack and tumble. In the United States, where flood mitigation and prediction is advanced, floods do about $6 billion worth of damage and kill about 140 people every year. A 2007 report by the Organization for Economic Cooperation and Development found that coastal flooding alone does some $3 trillion in damage worldwide. In China's Yellow River valley, where some of the world's worst floods have occurred, millions of people have perished in floods during the last century. When floodwaters recede, affected areas are often blanketed in silt and mud. The water and landscape can be contaminated with hazardous materials, such as sharp debris, pesticides, fuel, and untreated sewage. Potentially dangerous mold blooms can quickly overwhelm water-soaked structures. Residents of flooded areas can be left without power and clean drinking water, leading to outbreaks of deadly waterborne diseases like typhoid, hepatitis A, and cholera. But flooding, particularly in river floodplains, is as natural as rain and has been occurring for millions of years. Famously fertile floodplains like the Mississippi Valley in the American Midwest, the Nile River valley in Egypt, and the Tigris-Euphrates in the Middle East have supported agriculture for millennia because annual flooding has left millions of tons of nutrient-rich silt deposits behind.
Here are some safety tips to prepare for rising water—and what to do once a flood has begun.
BEFORE A FLOOD • Avoid building in a floodplain. • Construct barriers (levees, beams, floodwalls) to stop floodwater from entering your home. • Seal walls in basements with waterproofing compounds to avoid seepage. • If a flood is likely in your area, listen to the radio or television for information. • Know the difference between a flood watch and a flood warning. A watch means flooding is possible. A warning means flooding is occurring or will occur soon. WHEN A FLOOD IS IMMINENT• Be prepared! Pack a bag with important items in case you need to evacuate. Don't forget to include needed medications. • If advised to evacuate your home, do so immediately. • If there is any possibility of a flash flood, move immediately to higher ground. • If possible, bring in outdoor furniture and move essential items to an upper floor. • Turn off utilities at the main switches or valves if instructed to do so. Disconnect electrical appliances. DURING A FLOOD • Do not walk through moving water. As little as 6 inches (15 centimeters) of moving water can make you fall. • If you have to walk in water, wherever possible, walk where the water is not moving. Use a stick to check the firmness of the ground in front of you. • Do not drive into flooded areas. If floodwaters rise around your car, abandon the car and move to higher ground if you can do so safely. • Do not touch electrical equipment if you are wet or standing in water. AFTER A FLOOD • Listen for news reports to learn whether the community's water supply is safe to drink. • Avoid floodwaters; water may be contaminated by oil, gasoline, or raw sewage. Water may also be electrically charged from underground or downed power lines. • Avoid moving water. • Be aware of areas where floodwaters have receded. Roads may have weakened and could collapse under the weight of a car. • Stay away from downed power lines, and report them to the power company. • Return home only when authorities indicate it is safe. • Stay out of any building if it is surrounded by floodwaters. • Service damaged septic tanks, cesspools, pits, and leaching systems as soon as possible. Damaged sewage systems are serious health hazards. • Clean and disinfect everything that got wet. Mud left from floodwater can contain sewage and chemicals. Comments are closed.
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Erik E. Mason
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