Floods and obsolete warning system
A flood is defined as a body of water that rises to overflow into land settlements which are not normally under water. When there is heavy rainfall in the catchment areas it is natural that flood situation will arise. Floods invariably create problems of a serious nature. Hence it is considered a natural disaster.
Riverine floods develop slowly when there is rainfall for a continuous period, especially during monsoons. It may come in the form of a flash floods with excessive rainfall falling within a period of time duration. This happens when a tropical cyclone or a depression strikes. Flooding can also occur from a dam breach episode producing effects similar to a flash flood. The flood effect can be of a local impact in the neighbourhood or community or it can be very large or it could be floods affecting a large area of the river basin.
Riverine floods
Sri Lanka is blessed with 103 rivers. Of these 17 rivers are associated with flood problems. These 17 rivers have a catchments area of about 1,600 square kilometres. It is a known fact that with the population explosion since independence, land area has become scarce and as a result low income families were forced to occupy flood plains of rivers which have been demarcated as reservations. A case in point is the unprotected areas between the bunds in the Kelani basin where people are now living. When the water level reaches, 5 feet mean sea level (msl) some of these areas within the unprotected area in the Kelani basin get submerged, when flood water rises up to 7 feet msl. all unprotected areas go under water. Flood situations would arise due to unscrupulous actions of man. Putting up structures and land use without considering flood risks have often invited flood situations. "Uncontrolled/unplanned" land use in the Kelani Ganga catchment area is an example. It has posed problems in carrying out dynamic flood control plans.
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