Updated:
January 23, 2008 17:00  

We’ve all seen those photos in the newspaper: After heavy rain, someone in a canoe or kayak paddles down what is usually the middle of a street. It may look like fun, but it is dangerous.
Flooding can happen in Florida and any of the other 49 states. Even relatively dry states such as Nevada and Arizona have serious floods from time to time. In Florida, flooding occurs frequently, but often the floods are minor. Nonetheless, Floridians must be careful because even minor floods can take a life. Once in a while, Florida can experience major floods that can cause many deaths and loss of property. We must be prepared.

Flood ingredients

What makes a flood happen? Rain, right? Yes, but let’s break the subject down a bit. Flooding is caused by:

• the amount and rate of the rainfall (meteorology) and
• what happens to the rain after it hits the ground (hydrology).

Meteorologists try to predict accurately when, where and how much rain will fall. The total amount of rain and how fast it falls (the rainfall rate) affect how much water will run off. The more water that runs down into streams or lower areas, the worse the flooding can be.
The atmosphere above Florida is usually more moist than in most other states. Our state is nearly surrounded by the Atlantic Ocean and the Gulf of Mexico, and the state receives a lot of evaporated water from these seas. During summer, thunderstorms erupt over the state as the sun heats the ground. Our moist air rises and forms thunderstorms and heavy rainfall.

Hurricanes and flooding

Tropical cyclones often cause our state’s worst flooding. Because of Florida’s location and the fact that much of the state is a peninsula, Florida can experience more hurricanes than any other state in the country. Most hurricanes move out of the warm waters of the Atlantic Ocean and Gulf of Mexico, bringing very heavy rainfall.

In fact, the Florida record for the most rainfall during a 24-hour period occurred during Hurricane Easy in September of 1950. During that storm, 38.7 inches of rain fell at Yankeetown, along the Gulf Coast in Levy County. This heavy rainfall caused extensive flooding near Yankeetown and south of Ocala.

More recently, Hurricane Irene flooded much of south Florida in 1999, and Hurricanes Frances and Jeanne flooded many areas in 2004. Hurricanes may flood neighborhoods and towns due to poor drainage and may flood streams and rivers as all of the rainwater flows into the stream.

Meteorologists at the National Hurricane Center, the Southeast River Forecast Center and local Florida weather offices all watch hurricanes very closely to try to forecast how much rainfall a hurricane may produce and how much flooding may occur. These meteorologists use satellite pictures, Doppler radar and computer models to try to warn people well in advance of the flooding, so they can save lives and property. (See story on hurricanes, Page 10.)

Go with the flow – predicting water’s movement

When rain hits the ground, it can behave many different ways. The study of the movement of water along and under the ground is called hydrology. Hydrologists look at all the aspects of water’s behavior and make predictions, just as meteorologists predict the weather.

Why would one river or small creek flood when another does not, even with the same amount of rainfall? To answer this, hydrologists look at the size and shape of the stream’s basin. The basin is the area that captures the rainfall and funnels it into the main stream. From there on, the water depth in the stream is determined by the size and shape of the stream’s channel and shores. A flood results when water flows over the stream’s banks into normally dry areas.

Imagine a wide riverbank. The river may spill over and flood a large area, but the flood will be fairly shallow. A steeper riverbank may result in some areas experiencing deeper flooding along the shores. Either way, people along rivers and streams need to be ready for such floods.

Another factor that hydrologists look at is the condition of the soil and earth beneath. Is it sandy? If so, the water can soak in rather than flow away into a stream. Is it already wet? If so, there is less room for new water and there will be more runoff. Are there sinkholes and lakes and underground caverns that can hold the new water? If so, there will be less runoff.

Most of Florida is fairly flat and has sandy soil, lakes, swamps and prairies. This means that there can be a lot of rain and expansive areas without major stream flooding. But sometimes significant flooding does happen.

Flooding- It's not just for rivers anymore

We also see our share of urban flooding. As our state’s population increases, buildings and pavement replace the natural land. This creates more water runoff and can increase flood problems.
Urban flooding – streets and ditches and other drainage systems – occurs because of the shear amount of runoff, which can be especially dangerous and costly in these developed areas where we live and drive.

Most deaths due to flooding in the United States are due to people driving their cars into flooded areas. It may only take 12 to 16 inches of water to cause a car to float.
Once a vehicle begins to float, the situation for the driver and passengers becomes dangerous and often deadly. So, remember the advice: Turn around. Don’t drown!

River forecasts online

At the National Weather Service (NWS), hydrologists team up with meteorologists to produce the best river and flood forecasts and warnings possible. These NWS river forecasts are available on the Web in an enhanced format. The Web pages show maps with river forecast points, color coded for river levels. Specific point forecasts are linked and displayable in graphs. These hydrographs show past, current and forecast river stage levels along with flood potential information. River flood forecasts are now available on the easy-touse AHPS Web site at: www.weather.gov/ahps. If you live along or near a river, you should pay attention to the forecast, especially in times of significant rains. It takes time to prepare for river flooding, so get a head start by being alert to the forecasts.

Turn around. Don't drown!

Many people die from freshwater flooding because they try to drive through water that covers roads. Moving water only as deep as a car’s hubcaps can be enough to move the car, possibly into a river or a stream. Remember, when you approach water covering a roadway, turn around... don’t drown! Did you know that just 6 inches of fast-moving floodwater can knock you off your feet and 2 feet of water can sweep an SUV off a road? Each year, more deaths occur due to flooding than from any other thunderstorm-related hazard. The main reason is people underestimate the force and power of water. Many of the deaths occur in automobiles, as they are swept downstream. Of these drownings, many are preventable, but too many people continue to drive around the barriers that warn you the road is flooded. Floods can happen in most of the places where people live. Look in your local newspaper (don’t forget the newspaper’s Web site for archived stories) to find information about when and where the risks of flooding were high. Write a fully developed paragraph in response to the following questions. How did the weather create those conditions? How quickly did the water level rise? Did people prepare for the possibility in some way? Was there any property damage or loss of life? Who is responsible for monitoring and predicting these conditions in your area? Write a second paragraph explaining how people can avoid injuries due to flooding.

Sunshine State Standards: SS.B.1.3, SS.D.1.3, SC.H.3.3, LA.B.2.3

Moving Floodwaters In some areas the water will all flow toward a stream, creek or even a river. When it does so it is moving water and all of the water in one area will usually move toward a particular location or river. The area where the water is moving is called a “flood basin,” and meteorologists watch these areas very closely during storms. Usually a stream or creek will flood first and then several days later the water from many flooded creeks will make its way into the larger rivers causing them to flood. When flooding occurs along the rivers, people may have to leave their homes and businesses for several days until the water goes down. It is important that you do not swim or play near flooded streams, creeks or rivers as you could easily be swept into the water.

El Niño and Flooding Every few years, the waters of the Pacific Ocean near the Equator and along the west coast of South America warm up. When this happens we call it an El Niño and El Niño can have large effects on the weather in Florida . A warm and moist jet stream comes out of the Pacific Ocean and over Florida , causing our cold season to be very rainy with possible flooding. This happened in 1998 and 2003. This winter it appears that an El Niño may be forming and it is possible we may see yet another cold season with very heavy rainfall.

The 2004 Indian Ocean tsunami waves were
far reaching. Photo Credit: Vasily V. Titov,
Associate Director, Tsunami Inundation Mapping Efforts
(TIME), NOAA/PMEL - UW/JISAO, USA.

Several tsunami struck around the world during the past several years, and some had very wide impacts. After the big Indian Ocean tsunami, the question must have come up in your mind, “Can a tsunami happen here?” The answer is yes, because any large body of water, such as the Atlantic Ocean or Gulf of Mexico , is capable of producing a tsunami.

“Tsunami” is a Japanese word, which means harbor wave, and they are well named because tsunami waves easily pass beneath a ship at sea without even being noticed; however, when those waves reach land they swell to great heights in coastal areas and harbors. Tsunami also move very fast, almost as fast as a jet plane and can strike with little or no warning.

Tsunami can be generated whenever a large amount of water is rapidly moved, and there are several ways that this can happen. Some of the possible causes are volcanoes, large underwater earthquakes, underwater landslides, large landslides (when a portion of an island breaks off and slides into the water) or even an asteroid striking the ocean. Some of these events, such as island landslides and asteroids, may not occur for thousands of years, but earthquakes that generate tsunami happen every couple of years. In 2006, there were several earthquakes in the Gulf of Mexico , and while they were not strong enough to cause tsunami, they do show that there is much about the structure of the ocean floor that we simply do not know.

We can think of a tsunami like a rock thrown into a pond. When the rock enters the pond, it pushes water away from the point of impact, and several circular ripples begin to move across the water. These ripples spread out until the wave reaches the edge of the pond, and then they roll over the edge as breaking waves. This is what happens with a real tsunami, except instead of a pond, the waves can cross entire oceans and instead of a ripple the breaking waves can be very tall.

There is a fault in South Carolina that actually has generated a tsunami in Florida . On Aug. 31, 1886, a strong earthquake shook the city of Charleston , destroying a large number of the city's buildings. This earthquake also shook northern Florida , and, approximately 15 minutes later, a tsunami hit the beaches near Jacksonville . Luckily, not too many people lived in Jacksonville at that time, but if the same thing occurred today, many people could be hurt or even killed. A strong earthquake is nature's natural tsunami warning, and if you feel a strong earthquake, or if the water begins to act strangely for no apparent reason, you should get to higher ground quickly.

There are several areas near Puerto Rico and Europe where large tsunami-generating earthquakes can occur, and these tsunami can travel great distances, even crossing an entire ocean. This type of tsunami is called a tele-tsunami, and one occurred in the Pacific Ocean last November. On Nov. 15, 2006, an earthquake near the Kuril Islands of Russia sent a tsunami wave across the Pacific Ocean to Hawaii and Crescent City , Calif. While no one was killed, some people were swept into the water and docks and roads were damaged. In the United States , we have a system to watch for this threat, and if Florida were to be threatened by a tele-tsunami, we would have several hours of warning to get to higher ground.

When a tsunami strikes a coast, it can do so as a series of waves, and each new wave can be larger than the wave before it. Additionally, there may be some time between waves, so it is not safe to assume that the tsunami is over after the first wave hits. Very strong currents and rapid changes in the height of waves could be very dangerous along the Florida coast. It is very important to follow the instructions of emergency managers and public officials if a Tsunami Warning is issued. If a Tsunami Warning is issued, never go to the water to watch the waves, and remember that you may only have minutes to take action.