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Flood protection works will depend upon the nature of the river, social and
economic impact etc. For example in certain areas there may not be any
habitation or agricultural land. Protecting such barren areas at a cost may not
be required. On the contrary, there are areas where there may be enormous
crop loss or damage to the property, roads, bridges etc. Such areas need to be
protected from the vagaries of flood.
Depending upon the river characteristics and the local problems, the following
methods are used for flood protection works :
1)
Marginal embankments or levees
2)
Pitching of banks and provision of launching aprons
3)
Groyens or spurs
1.
Marginal embankments or levees :
Marginal embankments are like earthen dams constructed along the rivers and
therefore have considerable length depending upon the vulnerability of the river
section. Embankments have side slopes on both river side and land side. The
embankment walls are constructed suitably so as to prevent flood water
spreading into the nearby land. The top of the embankment may have width
varying between 2.5m and 10m and it is kept at least 1m above High Flood
Level i.e. free board. The gradient of the slope of embankment on the river side
is about 3.1 with stone pitching over filter layers. The weight of the stone should
be such as not to be carried out by the high velocity of the river water during
flood. The slopes on the land side should take care of the hydraulic gradient or
seepage gradient which should be at least 1m below the top surface of the
embankment and should be kept within the embankment. There are more than
30,000 km of embankment in India for flood protection work.
Fig. 6.2 : Typical Section of levees or embankments
