A high water level that overflows the natural banks along any portion of a stream is called a flood. Thus, floods are commonly associated with a stream or river. A stream floods when its discharge is greater than the capacity of its river channel. Excess water flows over the river banks and submerges the adjacent land which is usually dry. When it happens, the channel and the flood plain together allow passage of water. Floods are natural phenomena that occur in all river systems. Some floods are seasonal, for example, those associated with monsoon rains. Sometimes flash floods also occur. There are many causes of floods.
The important causes of floods
- Heavy rainfall, cloud burst, and prolonged rainfall;
- Heavy melting of snow and ice;
- Large catchment area;
- Changes in the river courses;
- Silting of river beds;
- The collapse of dams;
- Unscientific use of land utilisation;
- Transgression of the sea at the occasion of tropical cyclones; and
Effects of Floods
The frequency, intensity, and magnitude of floods are increasing day by day. Floods cause more damage than any other single disaster in India. It creates numerous problems for society and the environment. Floods in India are taking thousands of lives every year. The crops are adversely affected, there is the loss of livestock, the lines of communication are disturbed creating great problems for the movement of people and good. Unfortunately, floods are becoming more frequent and devastating.
Flood Affected Areas in India
Floods are universal in India. Except for the hilly and mountainous regions, they occur in almost all the parts states of the country. The frequency and intensity of floods are, however, more serious in the states of Andhra Pradesh, Assam, Bihar, Gujarat, Haryana, Jammu and Kashmir, Manipur, Odisha, Punjab, Rajasthan, Tamil Nadu, Uttar Pradesh and West Bengal.
The middle and lower Ganga-Brahmaputra plains have the largest flood-affected areas. Floods are a common phenomenon in the deltas of Mahanadi, Krishna, Kaveri, Mahi, Sabarmati, and in the Sutluj plains of Punjab.
Brahmaputra, Ganga, Yamuna and their tributaries — Gandak, Kosi, Mahanadi, Godavari, Jhelum, Krishna, Kaveri, Mahi, and Satluj record frequent floods, especially during the rainy season (July to September).
Flood Control Management
Looking at the devastating floods of 1949 and 1954, the Government of India took planned steps to control the floods. In the initial phase of flood control planning, the main thrust was towards the development and construction of multi-purpose projects. The Damodar Valley, Kosi, Bhakhra, Hirakad. Rihand projects were some of the important multi-purpose projects designed to control the floods and so generate electricity. In 1976, the Rashtriya Barh Ayog (National Flood Communion) was constituted. The Commission identified the areas in different states which are more prone and vulnerable to floods. According to one estimate, about 50 million hectares of land of India is flood-prone. The Central and State Governments have taken the following steps to reduce the menace of Floods:
1. Flood Forecasting: Flood forecasting involves giving prior information regarding the occurrence of floods. It is of immense help in taking timely action to reduce the loss of human lives, livestock. and movable property. The Central Water Commission stated flood forecasting in November 1958 when the first flood forecasting station was established near the old railway bridge of Delhi. At present, there are 175 flood forecasting stations on various rivers in the country. The Flood Forecasting Network covers 15 states and two Union Territories. The flood forecasting stations issue daily-flood forecasts and warnings throughout the flood season from May to October.
2 Reduction in Run-off: Reduction of run-off is one of the very effective methods of flood control Run-off can be reduced by inducing and increasing infiltration of the surface water into the ground in the catchment area. This can be done by large scale afforestation, especially in the upper catchments of the rivers.
3. Construction of Dams: Dams and multi-purpose projects are being constructed across the rivers to store the surplus water in the reservoirs. A number of such reservoirs were constructed during the First Five Year Plan. In the subsequent plans also, many dams were constructed to reduce the run-off of the rivers.
4. Channel Improvements: The channels of the rivers more prone to flood are improved by deepening and widening. The water of such rivers is also diverted into canals.
5. Construction of Embankments: The central and state governments have constructed a number of embankments along the rivers to reduce the menace of floods. Such embankments have been constructed along the Brahmaputra, Beas, Gandak, Ganga, Ghagra, Godavari, Kaveri, Kosi, Krishna, Mahananda, Narmada, Ravi, Sabarmati, Son, Satluj. Tapi, and Tista rivers and their tributaries.
6. Flood Plain Zoning: Flood plain zoning is also an important step to control the floods. It is based on information regarding flood plains, particularly the identification of floodways in relation to land use. Detailed maps of the flood-prone areas are prepared after a detailed study of flood cycles.
7. Legal Measures: In addition to the steps given above, legislative measures are taken to restrict the construction of industrial and residential units in the flood-prone areas.