Floods | Ndh-Live

Floods

Floods are easy to

understand. They occur

when more water comes

(as rain, overland flows or snowmelts) than

rivers, creeks or dams can contain.

But, there are quite a few causes and

types of floods that can destroy

property and injure people.

How do you stay safe during a flood?

Learning Objectives

To understand how floods cause natural disasters, you should be able to:

Describe five types of flooding.
Explain the difference between a flood warning and a flood watch.

Vocabulary

coastal flooding—higher than normal tides flooding low areas of coastal towns.

flash floods—local floods caused by rapidly flowing water in streams, hollows and canyons that usually give little warning.

flood—an overflowing of water into areas that are normally not covered by water.

inland flooding—flooding away from a coast, often caused by storm surges or intense rain from storms.

storm surge—an abnormal rise in seawater level during a storm caused by a storm’s winds pushing water onshore.

Flooding

Flood waters surround, cover, and destroy buildings, roads, and crops. According to the National Oceanic and Atmospheric Administration (NOAA), floods are the most common type of meteorological (weather) disaster, and cause more deaths than thunderstorms, tornadoes, hurricanes or lightning.

Local low spots, such as underground parking garages, dips in roads, and tunnels can be death traps if flood waters quickly fill them. Only 6” of flowing water can cause loss of control of a car; a foot of water will float many vehicles and two feet of water can carry away most vehicles.

Types of Flooding

1. River flooding—These floods happen when more water flows down a river than its banks can hold. Water pours over banks and levees built to contain it and floods surrounding lands and towns. Overflowing river banks happen with intense or long-lasting rain, rapidly melting ice and snow, or remnant storms from hurricanes.

2. Coastal flooding—Higher than normal tides flood coastal streets and other low areas of coastal towns. The normal number of high tide flooding days has increased 500% since the 1950s. Earth is rapidly warming, which causes sea level to rise all around the world. High tide flooding happens multiple times a year in many coastal towns.

3. Storm surge flooding- A storm surge occurs when ocean water gets pushed toward the shore by the force of a big storm, usually a hurricane. The size of the surge and the

flooding depends on the force of the storm, the angle of the approach, and the shape of the coastline.

Image: Storm surge coming ashore. Photo: USGS

Storm surge is often the greatest threat to life and property from a hurricane. And unlike high tide flooding, storm surges can flood areas tens of miles inland. Hurricane Katrina is an example of a hurricane that produced catastrophic flooding; Katrina’s storm surge was 25 to 28 feet above normal tide levels.

4. Inland flooding—Flooding away from

coasts is called inland flooding, even

though a lot of it is caused by storm

surges of ocean water and intense rain

from hurricanes that travel far from the

coasts. Image: Flooded streets in Louisiana. Photo: NOAA

A lot of inland flooding is also due to extreme rain storms. The number of extreme rainfall days is steadily increasing. In the past, more land was covered by vegetation that allowed water to seep into the ground. Now, cities and towns’ concrete pavements do not allow rain to soak into the ground, so it floods over the hard surfaces.

Another cause of inland flooding is ice jam

flooding. During winter and spring in cold

climates, pieces of floating ice in a stream

can accumulate and pile up at bends in the

stream or river.

Image: An ice jam in Eagle, Alaska. Photo: U.S. National Park

Service. Public Domain https://commons.wikimedia.org/w/index.

php?curid=6722103

The jammed pieces continue to build up

and can hold back a significant amount of water. The water floods places upstream until the jam breaks, but then places downstream are flooded. Ice jam floods cause damage to property and homes built along the stream.

5. Flash floods—Flash floods are local floods caused by rapidly flowing water in streams, hollows and canyons. Sometimes an intense rainstorm empties a lot of water into a stream miles away. People can be overwhelmed by water rushing down the stream. People often drown in flash floods because they have no warning.

Larger flash floods occur when a dam holding millions of gallons of water fails. The break causes high walls of water to rush downstream. In coal mining areas, sludge containing water, slate, clay and coal wastes from mining are contained within ponds. The dirty liquid mixture behind these dams is made of water, ash and soil. In 1972, in southern West Virginia, three coal ash ponds along Buffalo Creek failed sending 132 million gallons of sludge water down the creek; many people were killed and injured.

Flooding Hazards and Injuries

Any kind of flood can result in dangerous situations that cause damage to property and injuries. Many types of injuries, such as fractures (broken bones), cuts, and sprained muscles occur in cleaning up after flood waters have gone down.

The National Weather Service issues flood warnings and watches to warn people of the dangers of a potential flood. A flood watch means that conditions are favorable for flooding; flooding may not occur, but it is possible. A flood warning means that flood will happen soon or is already occurring in some places.

Check Your Understanding

1. Describe five conditions that cause flooding.

2. Explain the difference between a flood warning and a flood watch.