Many systematic steps are being taken for control and management of floods.
The quantity of water and rate of its flow is controlled in water flow system.
The following steps are effective in flood control:
1. Reduction in run off:
Surface run off increases due to unexpected heavy rainfall. This has been increasing with depletion of forest. Due to forest cover, rain drops do not fall on the ground intensely and ground surface absorbs them and flow of water does not gain speed suddenly. By increasing the rate of infiltration in the catchment area, run off can be reduced. It can be done by afforestation on a large scale. Dense vegetative cover forms a canopy between ground and rain water by creating interception. Their roots, leaf litter and humus hold water in them.
2. Control on deforestation:
Deforestation may be banned in catchment areas of rivers and afforestation should be resorted to. Forest cover would reduce soil erosion and reduce sedimentation of rivers due to its deposition on account of soil erosion.
3. Reduce flood level:
Level of flood in water flow route can be reduced through the following means:
(i) Canal system may be developed in nearby areas as per capacity of the stream.
(ii) Improvement in stream can be made to reduce level of flood. This improvement can be made by deepening the base of water flow and increasing the width. Many problems are also faced in these activities like increase in soil erosion capacity, effect on water creatures and living organisms, flood water immediately reaching lower streams etc.
(iii) Flood diversion:
Effect of flood can be reduced by diverting flood water towards marshy lands, depressions and lakes etc. Many types of engineering methods can also control floods. Construction of flood control storage reservoirs is the main method by which surplus water can be stored. Such types of water reservoirs were constructed in the Miami River of United States of America between 1913 and 1921.
Tennesse river of United States of America too was suffering from recurrent floods, water logging and various diseases caused on its account up to 1933. Fast soil erosion had made lands barren and unfertile. However, since 1933, Tennessee Valley Authority (TVA) controlled the above terrors by constructing many dams and water storage reservoirs.
On the pattern of TVA, efforts were made for flood control in Damodar Valley Corporation (DVC) in India. It constructed four dams (Karonar, Panchet, Tilaiya and Maithan) on Damodar and its companion rivers Barakar and Konar, as well as water reservoirs having water storage capacity of 1,603 million cubic metres at the time of floods.
(iv) Meanders and diversions in rivers cause obstruction in flow of water.
Hence, more diverted routes should be made straight. Meanders are a natural phenomenon. United States of America made meanders of Mississippi river straight near Greenville during 1933 and 1936, thereby reducing the meandered route of 530 km to 185 km.
(4) Embankment and construction of dams:
By construction of embankments on sides of rivers, excess water can be controlled at the time of flood. Such types of engineering works have been executed in north eastern India, Gangetic plains and Bangladesh. Embankments to the extent of 12,265 km were constructed on a large scale under flood management activities between 1954 and 1979. Embankments were constructed in 246 km by the sides of Kosi river banks, 249 km by the sides of Bagmati river banks, 208 km by the sides of Mahananda river banks and 317 km by the sides of Budhi Gandak river banks.
The Central Flood Control Board had demarcated flood affected areas in 1957. After identification of flood affected areas, flood water flow routes should be interconnected for land utilization and after study of flood cycles, mapping of large affected areas should be done.
5. Forecast of floods:
Devastation due to flood can be prevented by flood forecasting. Central Water Commission (CWC) has established an all-India system of warning and forecasting of floods.
CWC makes announcements regarding forecast of estimated flood situation through 157 centres located in 62 river basins and sub-river basins. Out of them 109 centres are functional m Ganga, Brahmaputra and Meghna river systems, 15 centres are working for rivers flowing in the west. Similarly, eight centres are established in river Krishna, three centres in river Mahanadi, 13 centres in river Godavari and nine centres are established for rivers flowing in the east.
Out of these centres, the following are more important:
For Brahmaputra and its companion rivers and Berar river.
Ganga and its companion rivers of Uttar Pradesh.
Ganga and its companion rivers in Bihar.
Suvarnarekha, Burhabalang, Baitarni and Brahmani rivers.
For flood of Narmada river.
Yamuna and Sahibi river up to Delhi.
Godavari and companion rivers.