Flood are natural phenomena characteristic of all rivers. As is known, the rainfall in India is largely dependant on the monsoons and cyclonic depressions. Most of the rainfall is received during the southwest monsoon season (June to September) during which heavy spells of rain are often experienced in the catchments of rivers over periods of a few days at a time. It could therefore be said that high rainfall coupled with inadequate channel capacity leads to flooding. Choking of river beds by natural causes or artificial obstructions aggravate the problem.

Flood damages are the combined result of the natural phenomenon of floods coupled with the human activity in the flood plains. The fertile river silt has promoted large-scale settlements and cultivation of lands near the riverbanks and adjacent areas or even in the riverbed region. While these activities are increasing on one hand, on the other the river continue to experience varying magnitudes and intensities of floods, which cause damages, sometimes in disastrous proportions. In a way flood damage is the price paid for the human occupation and exploitation of the flood plain of the river. Even single events could result in a heavy toll of death as also property loss.

As mentioned, the basic cause of flooding is the high rainfall. Apart from that, the size of the catchment also usually governs the character of the flooding. On large rivers with big catchments basins, such as the Ganga or the Brahmaputra, the river flow in the lower reaches is relatively slow to change; in contrast to this, flash floods, most commonly associated with small catchments lead to very high build up very quickly. They leave very little time between the start of the flood and the peak discharge. Coastal floods are associated with tropical cyclones, storms surges and tidal conditions.

The general characteristics of floods are as discussed so far but it must be noted that flooding are the complex results of interaction of a number of connected phenomena and that the flooding characteristic of each river is different from the other. They cannot be easily classified even in types or groups. However, in every case; the people and the activities in the flood plains are adversely affected.

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If there would have been no occupation of the riverfront or economic activities nearby, high floods might come as also subside without humankind being affected or bothered much. We, however, are concerned with flood losses. Flood losses may be defined as the destruction or impairment, partial or complete, of the value of goods and services or of health, resulting from the action of floodwaters and the silt and debris they carry.

India is one of the highly flood prone countries of the world. Flood damage statistics, compiled from reports from the State Governments indicate that on an average (based on data for 1953-1990) about eight million hectares of land are affected by floods in India, involving about thirty three million people. In a high flood year, the figures will be many times more. Our neighbor Bangladesh also suffers seriously from floods. The floods of 1988, which caused high losses in India, also caused serious flood problems there, affecting 45 million people and crop damage on two million hectares of land.