What is flood?

                        Floods are the most frequent type of disaster worldwide. It can strike anywhere and anytime. Although floods can be predicted, they often cause massive damage and destruction of property as most urban communities are located near water sources such as coasts and rivers. Flood effects can be local, impacting a neighborhood or community, or very large, affecting entire river basins and multiple states.
However, not all floods are alike. While some floods develop slowly, sometimes over a period of days, flash floods develop quickly, sometimes in just a few minutes and without any visible signs of rain. 

source;  .http://golearngeo.files.wordpress.com/2010/04/floodplain2.jpg

   How does a flood form?

A flood forms when a large amount of rain falls over a long period of time. Constant hard rain for shorter amounts of time can also cause floods. The most common floods occur when there is more water volume than can be carried by the normal system of streams and rivers, and water escapes into the surrounding regions called flood plains. There are also Flash Floods, where a normally dry channel is suddenly and without warning filled with water from heavy rainfall miles away, an event that usually ends in a relatively brief time.

This is a natural phenomenon, the way that nature deals with the wide variations in rainfall that can occur in a given area. It is quite arguable that floods are not a natural disaster; the disaster is that people have been ignorant enough to build in natural flood plains, where there is near certainty that flooding will occur at some point in the future.

Types of floods.

There are different types of floods.

1. Flash Floods:

Flash floods are the result of heavy rainfall or cloudburst over a relatively small drainage area. Flash floods carry highly destructive flood waves and are most common in mountainous areas or in steep places that have streams flowing though narrow canyons.

2. Riverine Floods:

These occur when a large amount of rain falls in river systems with tributaries that drain large areas containing many independent river basins. They may last a few hours or many days depending on the intensity, amount and the distribution of the rainfall.

3. Tidal Flood:

This results when large bodies of water, like the sea or lakes, overflow onto bordering lands. They are mainly caused by high tides, the heavy rains that accompany hurricanes, waves created by high wind surges created by storms, and long waves produced by earthquakes out at sea.

4. Ponding:

This is a slow build up of water in depressions, sinks, areas with clay base soil, and slow percolation rate.

Causes for the occurrence of floods.

Floods are caused by many factors: heavy precipitation, severe winds over water, unusual high tides, tsunamis, or failure of dams, levels, retention ponds, or other structures that contained the water.

Periodic floods occur on many rivers, forming a surrounding region known as the flood plain.

During times of rain or snow, some of the water is retained in ponds or soil, some is absorbed by grass and vegetation, some evaporates, and the rest travels over the land as surface runoff. Floods occur when ponds, lakes, riverbeds, soil, and vegetation cannot absorb all the water. Water then runs off the land in quantities that cannot be carried within stream channels or retained in natural ponds, lakes, and man-made reservoirs. About 30 percent of all precipitation is in the form of runoff small and that amount might be increased by water from melting snow. River flooding is often caused by heavy rain, sometimes increased by melting snow. A flood that rises rapidly, with little or no advance warning, is called a flash flood. Flash floods usually result from intense rainfall over a relatively small area, or if the area was already saturated from previous precipitation.

* Resulting excessive rain and climatic changers.

                  Due to climatic changers and excessive heavy rain over a prolonged period of time can have many adverse effects are occurred. Mainly,

It can cause denudation of any low lying area and areas nearby water bodies. It can bring flood thus inhibiting the life supporting activities of the people of the affected area, many have to loose their lives also
Accumulation of water for a prolonged period leads to origin of many water-borne diseases which in a meantime
becomes an issue of national concern
The affected area also suffers a loss in its various infrastructure, natural landscape of the affected area is destroyed.

* Clearance of vast areas of forest.

Deforestation is clearing Earth's forests on a massive scale, often resulting in damage to the quality of the land. Forests still cover about 30 percent of the world’s land area, so it causes for the occurrence of floods.

*illegal construction and blocking of floods

       Due to unlawful buildings near river mouth and river banks it causes flood in the area and many epidemic diseases may spread in these areas. 

*Reclamation of lowlands.

*Effects of high tides and storms.

Although storm surge and high tides are dangerous and destructive effects of flood, its winds and heavy rains can be felt well inland  from a storm's landfall.

*Reduction of wetlands (marshes).

       Many wetlands are threatened by natural factors. Human induced wetland 

Destruction is also rampant and is expected to rise in the coming decades as more 

Countries develop.

                 Most common natural landscape in urban areas, connected to each other either on surface or underground.  With the increasing urbanization over the past few decades, wetlands have been rapidly disappearing.

*Global warming and its effect

Effects warming on our planet are already visible - in the last century the average temperature has risen around 1 degree Fahrenheit (0.6 Celsius) - but the greatest single danger is that global warming will cause a dramatic rise in sea levels, flooding the world's most powerful cities under a catastrophic deluge. 

*Due to urbanization.

With the removal of trees and vegetations. Begin to building houses, roads and industrialized buildings. So more waste water is discharged into local streams, and more storms run-off and landslide occurred due to less trees and vegetations in hill areas. More sediment is washed into streams and flooding can occur because water drainage patterns are changed.   

*Solid waste disposal 

Solid wastes, when improperly disposed off can be an environmental hazard in that the surrounding environments as well as the animals are affected. When solid wastes are dumped in drainage, channels and gutters are blocked. This may cause flooding.

*High rainfall

     Heavy rainfall raises the water level. When the water level is higher than the river bank or the dams, the water comes out from the river, there will have a flooding.

Effects of flood

There are short term and long term effect caused by floods.

*A large number displaced and damage to structure and houses

The major effects of floods are destruction of life and property. Each year thousands of peoples are dying. Due to floods millions peoples are homeless. So these are devastating immediate effects of a serious flood.

*Obstruction and destruction of electricity transmission line, water pipes, communication networks and

inundation of roads and compounds.

       Plantations, roads and highways are blocked or destroyed. Airports are closed to commercial flights .The destruction of homes and buildings means the loss of almost all business revenue. Although this small economic crisis may last for a short period of time, it can end up costing a flood-devastated community millions of dollars.

              

*Creating scarcities of foodstuff.

 Floods are damage the farm land of agriculture areas. Destroy much acreage of crops, farms;   Vegetables are totally wasted. It may be occurred foodstuff.

*Spread of epidemic diseases. 

There is a threat of disease from broken sewers and contaminated water. Many diseases are spread by contaminated water and food. Sudden outbreaks follow a disaster, usually caused by a contaminated water supply.

*Inundation of river mouths.

Inundation along the River mainly course for the whole stretch from the river mouth due to the limited flow capacity attributable to the rising of riverbeds caused by sedimentation.

*Soil erosion

        Heavy rainfall and floods washes away nutrients from soil, leading to erosion. When soil loses its essential nutrients, it becomes infertile and acidic, leaving it prone to cracking under the heat of the sun. When trees are damaged by flooding, soil erosion occurs, leading to permanent damage of the land area.

STEPS TO MITIGATE FLOODS

Mitigation of floods refers to all methods used to reduce or prevent the detrimental effects of floods waters. Some methods of flood controlling have been practiced since ancient time. In many countries, rivers prone to floods are often carefully managed. Defenses such as levees, bunds, reservoirs, and weirs are used to prevent rivers from bursting their banks.

*Avoid clearing of forests in highland

One strategy for reducing floods invokes protecting or regenerating forests that lie upstream of a threatened region. Support for this approach comes from a global-scale analysis of flood risk. Increasingly, forests are being valued for goods and services beyond wood fiber; one of these is protection of forests. Functions provided by natural and managed forests have been associated with reduced hazards from floods, debris floods, debris flows, snow avalanches and rock falls.

Maintaining a high level of protection may require active management, as forests are dynamic

And the protection capabilities are strongly determined by forest condition.

*Avoid disturbing water ways

Flooding can happen when extremely heavy rainfalls occur and the runoff exceeds the capacity of the drainage system.

Here are some steps you can take to avoid flooding around your home.

*Clean your foundation drains and Sumps. These drains collect water from your house and property and direct it to the City storm sewer.  The pipes can become blocked by leaves, dirt, roots or debris and should be flushed out periodically, or in some cases replaced.

*Clear Gutters and Catch Basins. Keep catch basins and gutters clear of leaves and debris.  Rake up leaves in the fall to prevent overland flooding caused by plugged drains.  Find the catch basin nearest your home or business and check periodically that it is clean so the water can drain properly.

*Clear Ditches and Culverts. If you have an open ditch along your property, check to see that it is clear.  Common items such as toys, balls, and milk jugs can often get lodged in the culverts and cause water to back up.

*Repair Broken or Damaged Pipe. Broken or damaged pipe can cause blockages and flooding of your home.  Check that your home drainage system is working properly.

*Prevent sand mining from rivers.

Sand mining is the removal of sand from their natural configuration. Sand is used for all kinds of projects like land reclamations. Sand mining can have environmental problems. Environmental problems occur when the rate of extraction of sand, gravel and other materials exceeds the rate at which natural processes generate these materials. This may be a reason of the occurrence of floods. 

But sand mining is regulated by law in many places, but is still often done illegally.     

*Construction of dams to collect water and divert to other places or regions and levees and flood walls to control the floods. 

•Dams and reservoirs built on mainstreams or tributaries that store excessive water and release it gradually after the threat has passed.

•Levees or flood walls confine flood waters to a floodway, thereby reducing flood damage.

*Should improve channels.

1. Straightening to remove undesirable bend ways

2. Deepening and widening to increase size of waterways 

3. Clearing to remove brush, trees and other obstructions lining with concrete to increase   efficiency.

   *Establish hazard management centers and make the people aware.

Comprehensive flood hazard management is the most effective way to address flood control issues. It incorporates a variety of engineering, environmental protection and planning measures. It includes flood plain management, flood control maintenance activities, storm water management and shoreline management, protection of frequently flooded areas under Growth Management, watershed management, other flood hazard mitigation activities, and preparation for flood disasters where mitigation activities cannot prevent flooding

*Water proofing compound.

Apply waterproofing compound to basement walls. This only works if walls are free of paint and clean of debris. Waterproofing compounds protect against water seepage from the sides of the walls.

* Ordaining new laws against filling, grading, dredging and other development which may increase flood damage.