FLOODS

Heavy storms may sometimes cause huge volumes of water to depart from a river's natural course and spread over previously dry land. Unstoppable and all-pervasive, the resulting floods can be devastating to human life."
(Natural Disasters, Readers Digest, 1996)

What causes Floods?
Flooded areas of land usually start off as very dry land. Floods are caused by heavy rains that pour to much water into rivers and other waterways. Making these natural channels unable to carry all the water. Rising water flows over or breaks the banks to the waterways causing the surrounding land to be flooded. Different causes of floods can come from masses of snow melting of tidal waves.

Where do Floods occur?
The type of land that is prone to flooding are broad and flat usually situated on the banks of a river or main waterway. Rivers that flood are regarded in three different stages. They are:-

ONE:- Water comes off the mountains, eroding the beds and banks of the river as it flows.

TWO:- This type river travels through broad valleys which slows the current of the river down. If the current is slow it will transport less material down the river.

THREE:- Flood-plain stage. Little if not any erosion takes place most of the material tha tis carried in the current is suspended and deposited to the form a flood plain.

Control of floods
Some methods of flood control have been practiced since ancient times. These methods include planting vegetation to retain extra water, terracing hillsides to slow flow downhill, and the construction of floodways (man-made channels to divert floodwater). Other techniques include the construction of levees, dikes, dams, reservoirs or retention ponds to hold extra water during times of flooding.

In many countries, rivers prone to floods are often carefully managed. Defences such as levees, bunds, reservoirs, and weirs are used to prevent rivers from bursting their banks. When these defences fail, emergency measures such as sandbags or portable inflatable tubes are used. Coastal flooding has been addressed in Europe and the Americas with coastal defences, such as sea walls, beach nourishment, and barrier islands.

A dike is another method of flood protection. A dike lowers the risk of having floods compared to other methods.[citation needed] It can help prevent damage; however it is better to combine dikes with other flood control methods to reduce the risk of a collapsed dike.

Tide gates are used in conjunction with dikes and culverts. They can be placed at the mouth of streams or small rivers, where an estuary begins or where tributary streams, or drainage ditches connect to sloughs. Tide gates close during incoming tides to prevent tidal waters from moving upland, and open during outgoing tides to allow waters to drain out via the culvert and into the estuary side of the dike. The opening and closing of the gates is driven by a difference in water level on either side of the gate.

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Faseeh