- 1 FLOOD DAMAGE
- 2 Introduction to Flooding
- 3 What is a flood?
- 4 What causes flooding?
- 5 Types of floods
- 6 Which areas are more likely to flood?
- 7 Effects of flooding
- 8 Methods of flood prevention
Introduction to Flooding
Many of us have this idea that floods (or flooding) is simply, too much water around your house. People think that can be fun. Wrong. Flooding is a lot more than that.
Flooding is extremely dangerous and has the potential to wipe away an entire city, coastline or area, and cause extensive damage to life and property. It also has great erosive power and can be extremely destructive, even if it is a foot high.
What is a flood?
It is a natural event or occurrence where a piece of land (or area) that is usually dry land, suddenly gets submerged under water. Some floods can occur suddenly and recede quickly. Others take days or even months to build and discharge.
When floods happen in an area that people live, the water carries along objects like houses, bridges, cars, furniture and even people. It can wipe away farms, trees and many more heavy items.
Floods occur at irregular intervals and vary in size, duration and the affected area.
It is important to note that water naturally flows from high areas to low lying areas. This means low-lying areas may flood quickly before it begins to get to higher ground.
In this lesson, we shall see more about what causes flooding, the types of flooding, some effects of floods and what we can do before, during and after floods occur.
What causes flooding?
Here are a few events that can cause flooding:
Each time there are more rains than the drainage system can take, there can be floods. Sometimes, there is heavy rain for a very short period that result in floods. In other times, there may be light rain for many days and weeks and can also result in floods.
Rivers can overflow their banks to cause flooding. This happens when there is more water upstream than usual, and as it flows downstream to the adjacent low-lying areas (also called a floodplain), there is a burst and water gets into the land.
Hurricanes, Strong winds in coastal areas
Sea water can be carried by massive winds and hurricanes onto dry coastal lands and cause flooding. Sometimes this is made worse if the winds carry rains themselves. Sometimes water from the sea resulting from a tsunami can flow inland to cause damage.
Wrightsville Beach in North Carolina USA, September 14, 2018
A massive North Atlantic Hurricane that covered a distance of about 6,500km made landfall. The hurricane was an unusually slow-moving one, and stayed over that location for a long time, with non-stop rains. This led to catastrophic flooding, as the land was already saturated from the wet summer. Communities such as Wilmington were cut off. More than 40 people died from the hurricane and massive destruction of homes and infrastructure occurred.
Dam breaking (raptured dam or levee) (Embankments, known as levees, are built along the side of a river and are used to prevent high water from flooding bordering land)
Dams are man-made blocks mounted to hold water flowing down from a highland. The power in the water is used to turn propellers to generate electricity. Sometimes, too much water held up in the dam can cause it to break and overflow the area. Excess water can also be intentionally released from the dam to prevent it from breaking and that can also cause floods.
February 26, 1972 – Buffalo Creek Valley, West Virginia
The failure of a coal-waste impoundment at the valley’s head took 125 lives, and caused more than $400 million in damages, including destruction of over 500 homes. http://www.damsafety.org/news/?p=412f29c8-3fd8-4529-b5c9-8d47364c1f3e
Ice and snow-melts
In many cold regions, heavy snow over the winter usually stays un-melted for sometime. There are also mountains that have ice on top of them. Sometimes the ice suddenly melts when the temperature rises, resulting in massive movement of water into places that are usually dry. This is usually called a snowmelt flood
Types of floods
Some would like to see the causes of floods as types of floods, but on this page we shall look at three major flood types: Flash floods, Rapid on-set floods and Slow on-set floods.
This kind occurs within a very short time (2-6 hours, and sometimes within minutes) and is usually as a result of heavy rain, dam break or snow melt. Sometimes, intense rainfall from slow moving thunderstorms can cause it. Flash floods are the most destructive and can be fatal, as people are usually taken by surprise. There is usually no warning, no preparation and the impact can be very swift and devastating.
Rapid on-set floods
Similar to flash floods, this type takes slightly longer to develop and the flood can last for a day or two only. It is also very destructive, but does not usually surprise people like Flash floods. With rapid on-set floods, people can quickly put a few things right and escape before it gets very bad.
Slow on-set floods
This kind is usually as a result of water bodies over flooding their banks. They tend to develop slowly and can last for days and weeks. They usually spread over many kilometers and occur more in flood plains (fields prone to floods in low-lying areas). The effect of this kind of floods on people is more likely to be due to disease, malnutrition or snakebites.
Which areas are more likely to flood?
From the causes of floods and the types that we just read about, you can tell that floods are more likely to occur in some areas than others.
Generally, the natural behavior of water (and flowing water) is that it moves from higher ground to lower ground. This means if there is a higher ground adjacent a lower ground, the lower ground is a lot more likely to experience floods.
Additionally, anywhere that rains fall, floods can develop. This is so because anytime there are more rains bringing more water than it can be drained or absorbed by the soil, there is a flood potential.
In many cities, there are buildings springing up in many places where they have not been authorized. Some of these building are placed in waterways. Other places also have very bad and chocked drainage systems. The danger is that, with the rains, water will find its own level if it cannot find its way. The result is flooding and your home could be under water.
Any plain low-lying area adjacent a river, lagoon or lake is also more likely to have floods anytime the water level rises. This includes coastal areas and shorelines, as seawater can easily be swept inland by strong winds, tides and tsunamis.
Effects of flooding
Floods can have devastating consequences and can have effects on the economy, environment and people.
During floods (especially flash floods), roads, bridges, farms, houses and automobiles are destroyed. People become homeless. Additionally, the government deploys firemen, police and other emergency apparatuses to help the affected. All these come at a heavy cost to people and the government. It usually takes years for affected communities to be re-built and business to come back to normalcy.
Did you know that the cost of all floodings in the USA in 2011 was $8,640,031,956 (approx 8.5B USD) — http://www.nws.noaa.gov/hic/
The environment also suffers when floods happen. Chemicals and other hazardous substances end up in the water and eventually contaminate the water bodies that floods end up in. In 2011, a huge tsunami hit Japan, and sea water flooded a part of the coastline. The flooding caused massive leakage in nuclear plants and has since caused high radiation in that area. Authorities in Japan fear that Fukushima radiation levels are 18 times higher than even thought.
Additionally, flooding causes kills animals, and others insects are introduced to affected areas, distorting the natural balance of the ecosystem.
People and animals
Many people and animals have died in flash floods. Many more are injured and others made homeless. Water supply and electricity are disrupted and people struggle and suffer as a result. In addition to this, flooding brings a lot of diseases and infections including military fever, pneumonic plague, dermatopathia and dysentery. Sometimes insects and snakes make their ways to the area and cause a lot of havoc.
There is also something good about floods, especially those that occur in floodplains and farm fields. Floodwaters carry lots of nutrients that are deposited in the plains. Farmers love such soils, as they are perfect for cultivating some kinds of crops.
What you can do before during and after floods.
Sometimes there is no warning of flash floods, and that is why it is important to think of them and prepare for them before they happen. Here are a few things you can do.
Before the floods…
1. Know about your local relief centers and evacuation routes.
2. Keep emergency numbers and important information handy, as well as emergency supplies, kits, first aid items. These may include water, canned food, can opener, battery-operated radio, flashlight and protective clothing.
3. Fold and roll up anything onto higher ground (or upper floors of your home), including chemicals and medicines.
4. Make sure everything that is of importance is secured (jewelry, documents, pets, and other valuables).
5. Plant trees and shrubs and keep a lot of vegetation in your compound if you are in a low-lying area as that can control erosion and help soften the speed of the flowing water.
During the floods…
1. Flash floods occur in a short spate of time. As soon as they start, be quick, keep safe and ensure that children and elderly are safe by leaving the house to a higher ground.
2. Turn off all electrical appliance, gas, heating and the like if there is a bit of time.
3. Leave the area before it gets too late. Do not drive through the water as moving water can sweep you away.
4. Stay away from power lines or broken power transmission cables.
5. Try to keep away from flood water as it may contain chemicals or other hazardous materials.
After the floods…
1. Make sure you have permission from emergency officers to get back inside your house.
2. Keep all power and electrical appliance off until the house is cleaned up properly and an electrical personnel has confirmed that it is OK to put them on.
3. Make sure you have photographs, or a record of all the damage, as it may be needed for insurance claims.
4. Clean the entire home, together with all the objects in it very well before you use them again. They may be contaminated.
5. Wear appropriate gear (mask and gloves) before cleaning begins.
Methods of flood prevention
Humans cannot stop the rains from falling or stop flowing surface water from bursting its banks. These are natural events, but we can do something to prevent them from having great impact. Here are a few.
Sea / Coastal Defence Walls
Sea walls and tide gates have been built in some places to prevent tidal waves from pushing the waters up ashore. In some areas too, sand bags are made and placed in strategic areas to retain floodwaters.
In some places, retaining walls levees, lakes, dams, reservoirs or retention ponds have been constructed to hold extra water during times of flooding.
It is important that builders acquire permission before buildings are erected. This will ensure that waterways are not blocked. Also, drainage systems must be covered and kept free from objects that chock them. This way, water can quickly run through if it rains and minimize any chance of town flooding. Drainage systems should also be covered to prevent litter from getting into them.
Trees, shrubs and grass help protect the land from erosion by moving water. People in low-lying areas must be encouraged to use a lot of vegetation to help break the power of moving flood water and also help reduce erosion.
In many developing countries, drainage systems are chocked with litter and people have little knowledge of the effects that can have during a rain. When it rains, waterways and culverts are blocked by massive chunks of litter and debris, and water finds its way into the streets and into people’s homes. Education is therefore very important, to inform and caution people about the dangers of floods, what causes floods, and what can be done to minimise its impact.
These are small reservoirs built and connected to waterways. They provide a temporary storage for floodwaters. This means in an event of flooding, water is drained into the basin first, giving people more time to evacuate. It can also reduce the magnitude of downstream flooding.
Did you know?
Here are a few interesting things you can share with your friends about floods.
In Australia, floods are the most expensive type of natural disaster with direct costs estimated over the period 1967-2005 averaging at $377 million per year (calculated in 2008 Australian dollars). http://www.chiefscientist.qld.gov.au/publications/understanding-floods/consequences.aspx
Flood losses in the United States averaged $2.4 billion per year for the last decade. Floods are the number one natural disaster in the United States. http://www.floodsmart.gov/toolkits/spanish/downloads/english/facts-and-figures.pdf
A physically defined route (path) where water or run-off passes into an outlet or terminus. (Terminus can be the ocean or bigger water body) This includes rivers, creeks, tributaries, stream or estuary. A waterway may be dry, but will soon be full of moving water when there are rains.
Peak water level / flood peak – The highest level that water in a waterway reaches during a flood. This is a measure of the size (or magnitude) of a flood.
Runoff – Each time there is more water on a piece of land than it can infiltrate the soil, the excess water will flow to find its own level. The excess water flow is what we call ‘Runoff” Sometimes the rains come down heavily and the soil (or earth) cannot absorb the water quick enough. This causes the rain water to flow as a runoff.
Never swim or play around in flood water. It may contain chemicals, bacteria and disease causing organisms. If your skin comes in contact with floodwater, make sure to wash it with soap and disinfected water because the contents are unknown.
Communities particularly at risk are those located in low-lying areas, near water, or downstream from a dam.
Based on Floodsmart, a 2,000 square foot home undergoing 12inches of water damage could cost more than $50,000.
Never drive into a flooded roadway or drive through flowing water because just 2 feet of water can float a large vehicle and sway it away.
Sometimes, local emergency officers are able to tell if there is a possibility of flood during a rain or high tide at the shore. When this happens, they keep a close eye on events and inform the public about it. This is called a Flood Watch.
A flood warning is when an official announcement is given (by TV, Radio, Text Message or Phone, Email or other means) of an impending flood or an already flood that has already occurred. A flood warning instructs people to move to higher ground or take immediate precautions to avoid drowning or to minimize damage to property.
Levee: A manmade structure to contain or prevent water from moving past a certain point.
For those in higher-risk areas (Zones V and A), the cost of coverage depends on your home’s size, construction, location, and your deductible. According to FEMA, the average flood insurance policy costsabout $700 per year, but can vary wildly, depending on your home’s elevation.
The Average Cost of Water Damage Restoration. The national average price of water damage restoration is $2700, but the cost may vary depending on a number of factors.
• The cost of water damage restoration is based on several factors. These include the size of the affected area, the extent of the damage, the materials and water type. There are three categories — the least expensive to clean up is category 1, which is clean water from a faucet or supply pipe. Category 2 is gray wastewater with minor contaminants, such as overflow from a dishwasher or washing machine. Category 3 is black water, containing sewage or other toxic debris.
• Fixing a small area of water damage in a ceiling due to a leaky roof can be $100-$300 to patch the sheet rock, or $30-$50 for do-it-yourself materials — not including the cost of fixing the roof and repainting the ceiling.
• Drying a flooded basement can cost $500-$10,000 or more, depending on the size of the basement, the depth of the flooding and the water type (clean, gray wastewater or black/toxic). See How Much Does a Flooded Basement Cost. Depending on where the appliance is located in the house, cleaning up after a faulty water heater, washing machine, dishwasher or air conditioner averages about $5,000, according to HomeOwnerNet.com .
• Damage from a burst water pipe can cost $5,000-$70,000 or more with an average insurance claim costing $15,000. See How Much Does a Burst Pipe Cost.
• If an entire house is flooded with storm water, the National Flood Insurance Program provides a flood damage simulator to predict the total cost based on the height of the water. For 1-4 inches of water, the estimated cost is $7,800. For 9-12 inches, the estimate is $18,930. At 18 inches, the estimated cost is $26,285..
• Water damage might be covered by insurance. Flood insurance typically covers damage from a natural disaster, when outside water or mud overflows an otherwise dry house. Homeowners insurance does not cover floods, but may cover water damage caused by minor individualized disasters, such as a hailstorm smashing a window or a broken water pipe spewing water — as long as the problem wasn’t caused by a lack of standard maintenance. The Insurance Information Network of California discusses the difference between flood insurance and homeowners insurance .
What should be included:
• A restoration company should follow the standards of care of either the Institute of Inspection, Cleaning and Restoration Certification or the Restoration Industry Association . A company representative will inspect and evaluate the affected area, often using water-sensing equipment such as probes and infrared tools to determine the source of the problem and the extent of the damage.
• Restoration includes pumping and drying the affected areas, and sanitizing and deodorizing as needed. The Blackmon Mooring company in Texas describes the basic steps of its water damage restoration process .
• Before entering a house filled with standing water, turn off the power — but never turn the power off while standing in water. The Centers for Disease Control and Prevention provides guidelines for entering a flooded house . FloodSafety.com describes how to clean up after a flood .
• Wood, plaster and other materials absorb and retain water. They must be either dried and sanitized, or removed. DIYNetwork.com explains how to repair a water-damaged wall . Do-It-Yourself-Help.com describes how to repair water-damaged plaster , drywall and lath plaster .
• If the house and furnishings are not quickly dried and restored, there can be additional problems with mold or dry rot. See How Much Does Mold Remediation Cost and How Much Does Dry Rot Repair Cost.
• Installing a simple water alarm or a whole-house shut-off system can help prevent problems. Battery-operated units that sound an alarm when a sensor detects moisture can cost $10-$115. A system that shuts off the water to a single appliance if a leak is detected is $50-$150. Whole-house systems with a shot-off valve on the main water supply are about $500-$3,000.