In the water cycle, water evaporates from bodies of water, condenses in the clouds, and precipitates back to the earth. The precipitation often happens in the form of rain or snow. Some of the rain that falls back to the earth is absorbed by the land. The water that the ground cannot absorb becomes runoff. Runoff feeds back into lakes, rivers, and oceans. Sometimes, though, runoff from a rainstorm is so great in volume that the normal path for the runoff is overwhelmed, and an area becomes flooded.
Flooding can be caused by a number of different events, including rainstorms. A dam failure can also cause a flood. Dams are used throughout the United States to generate hydroelectric power from flowing water. If a large amount of water enters a lake or a reservoir behind a dam in a short period of time, the lake or the reservoir may swell over the top of the dam. That water can flood the areas that lie below the dam. This kind of flooding can occur in the spring when ice and snow at higher elevations melt rapidly and release water into streams and rivers.
Hurricanes and other tropical storms may also cause flooding. As a hurricane develops, it gathers moisture and wind speed. At the end of August in 2005, Hurricane Katrina crossed over portions of the southeastern United States. Hurricane Katrina is one of the strongest hurricanes to hit the United States in the past 100 years. The storm brought high winds and heavy rainfall to many areas. But perhaps the greater damage of the storm was in the flooding that it caused. In particular, the city of New Orleans, Louisiana, on the Gulf Coast suffered a great deal of flood damage.
When Katrina hit the Gulf Coast, it dropped rain at a rate of more than one inch per hour. These heavy rains deposited so much water at such a quick rate that many of the levees around New Orleans failed, and much of the city flooded. A levee is a barrier built along the banks of a river or a lake. The barrier keeps the body of water from overflowing when the water level rises. More flooding in New Orleans was caused by storm surges of ocean water. Storm surges happen in coastal areas and are caused by strong off-shore winds and low atmospheric pressure. Within two days of Hurricane Katrina hitting the Gulf Coast, about 80% of New Orleans was under flood water.
The damage from Hurricane Katrina was severe. Yearly flooding in the United States causes about $2 billion in damage. The amount of damage caused by floods from Hurricane Katrina will likely total several times the yearly average. Buildings and streets in New Orleans were under standing water for several days. Water can weaken the structure of buildings. During floods, sewer systems can back up and stop working. Power lines can be knocked down, making waters very dangerous. Loss of power lines also leaves people without electricity. Flood water is often dirty because it picks up materials and substances from streets and buildings. It can be difficult to find clean drinking water in flooded areas. After Hurricane Katrina, New Orleans suffered from all these problems.
After an area has flooded, people wait for the water to flow back to the ocean, lakes, and rivers. If the water does not recede quickly enough, it might have to be pumped out of an area. Structures must be tested to see if they are stable or if they have been too damaged to be considered safe. Many structures will have to be torn down and rebuilt. There is a lot of cleaning to do after a flood. Dams and levees must be repaired or rebuilt. Streets must be cleaned of debris and mud. Power lines, water lines, and sewers must be fixed. People have to clean out their homes and move back in. A bad flood can disrupt normal activities for weeks or months.
- What is a flood?
[anno: Answers may vary but could include that a flood is a pooling of water in an area that is not normally covered by water.]
- What caused flooding in New Orleans after Hurricane Katrina?
[anno: Flooding in New Orleans after Hurricane Katrina was caused by heavy rainfall, broken levees, and storm surges.]
- What kinds of damage can a flood cause?
[anno: Flooding can cause structural damage to buildings and streets. Flooding can knock down power lines. It can damage water and sewer lines. Flooding makes things very dirty.]
- What might it be like to live in an area that has been damaged by a flood? What might be different after the flood? How would daily life change? Write a few sentences imagining what it would be like to live in an area that suffered from a flood.
[anno: Answers will vary.]