1. Flooding in India is primarily caused by heavy rainfall during the monsoon season from June to October, which exceeds the capacity of rivers to contain the flows. 2. Structural flood mitigation measures include embankments, levees, flood walls, channel improvements, and diversion works to contain flood waters. Non-structural measures include flood plain zoning, forecasting, and proofing. 3. Flood damage analysis considers both tangible losses that can be estimated monetarily, such as property and crops, as well as intangible losses which are more difficult to value, like loss of life, health impacts, and social effects.

1. MODULE- IV
Flood management
Prepared by
Bibhabasu Mohanty
Dept. of Civil Engineering
SALITER, Ahmedabad

2. Content
Indian rivers and floods, Causes of flooding,
Alleviation, Leeves and floodwalls, Flood ways,
Channel improvement, Flood damage analysis

3. Introduction
 cause of misery for the country since ages
 because, major habitation clusters like towns
and cities been located near rivers since the
beginning of civilization
 India National Commission on Irrigation and
Drainage (INCID), ‘Flood’ as a relatively high
flow or stage in a river, marked by higher than
the usual, causing inundation of low land .

4.  The flood problem in the country is mainly due
to southwest monsoon during the months from
June to October.
 The average annual rainfall of India is about
1170 mm, of precipitation takes place in about
15 days and less than 100 hours altogether in a
year.
 The average annual flow of the rivers of India
has been estimated to be about 1869 BCM.

5. The Brahmaputra and the Ganga rivers
contribute the major part of these flows.
The rivers carry major portion of their flows
during the southwest monsoon period when
heavy and widespread rainfall occurs.
Flooding is caused by the inadequate capacity
within the banks of the rivers to contain the
high flows brought down from the upper
catchment due to heavy rainfall.

6. Areas having poor drainage characteristics get
flooded by accumulation of water from heavy
rainfall.
Some parts of the country mainly coastal areas
of Andhra Pradesh, Orissa, Tamil Nadu and
West Bengal experiences cyclones which often
are accompanied by heavy rainfall leading to
flooding.

7. Indian rivers and floods
• The rivers in India can be broadly divided into
the following four regions for a study of flood
problems:
1. Brahmaputra River Region
2. Ganga River Region
3. Northwest River Region
4. Central India and Deccan Region

8. Brahmaputra River Region
 Covers the States of Assam, Arunachal Pradesh,
Meghalaya, Mizoram, Northern parts of West
Bengal, Manipur, Tripura and Nagaland.
 Catchments of these rivers receive very heavy
rainfall ranging from 110 cm to 635 cm a year
which occurs mostly during the months of
May/June to September.
 Main problems are overspills, drainage
congestion, bank erosion, landslides, change in
river courses.

9. Ganga River Region
 Covers the States of Uttar Pradesh, Bihar, South and
central parts of West Bengal, parts of Haryana,
Himachal Pradesh, Rajasthan, Madhya Pradesh and
Delhi.
 Normal annual rainfall of this region varies from about
60 cm to 190 cm of which more than 80% occurs
during the southwest monsoons.
 Damage is caused by the northern tributaries of Ganga
by spilling over their banks and changing their courses,
inundation and erosion problems are confined to a
relatively few places.

10. Northwest River Region
 Main rivers in this region are the Sutlej, Beas, Ravi,
Chenab and Jhelum, tributaries of Indus, all flowing
from the Himalayas.
 Region covers the States of Jammu and Kashmir,
Punjab, parts of Himachal Pradesh, Haryana and
Rajasthan.
 Compared to Ganga and Brahmaputra River regions,
flood problem is relatively less in this region. Major
problem is that of inadequate surface which causes
inundation and water logging over vast areas.

11. Central India and Deccan Region
Important rivers in this region are Narmada, Tapti,
Mahanadi, Godavari, Krishna and Cauvery.
Andhra Pradesh, Karnataka, Tamil Nadu, Kerala,
Orissa, Maharashtra, Gujarat and parts of Madhya
Pradesh.
Annual rainfall in Western Ghats around 500cm,
remaining 75 to 125 cm.
Stable and sufficient capacity to carry flood water,
except the delta region of Orissa.
Problems like congestion, bank erosion, landslides,
change in river courses

13. Causes of flooding
Intensity of rainfall in catchment area
Topography of catchment
Sedimentation of rivers and reservoirs
Obstruction in river flow
Contraction of river section
Inadequate cross drainage works

14. Other causes
Heavy melting of snow and ice
Failure of dam
Because of earthquake

15. Alleviation (Flood mitigation)
Flood control aims to attempt:
Modify the flood
Modify the susceptibility to flood damage
Modify the loss burden
Bearing the loss or living with floods

16. Flood control measures
Construction of protective works
Reduction of flood flows by storage
Modifying the susceptibility to flood damage
Soil conservation in catchment area

17. Structural mitigation measures
Storage reservoir
detention reservoir
retarding reservoir
Confining river flow by embankments:
Embankments constructed parallel to river bank
to continue the river water within a specified
section.
Surrounded area protected from flood.

19. Channel improvement works:
Increase the discharge or velocity of stream or
to decrease the stage and duration of flood.
Increase in size of cross section by widening and
excavating stream bed.
Increasing velocity by smoothing river bed.
Diversion works

21. Flood wall:
Concrete walls constructed just on the river
bank.
Act as retaining wall.

22. Flood ways:
Low lying areas along river known as floodways.
These are vast depression into which portion of
flood water diverted from river through natural
or artificial channel.
Floodways ordinarily used during major floods
and land in floodway used for agricultural
purpose.

24. Construction of cut-off:
During heavy rainfall when large flood discharge
approaches the sharp bend of the river, it
overflows its bank and submerges the
surrounding area.
 so cut-off constructed to reduce travel time and
water flow with high velocity along a straight
path.

25. Runoff reduction by watershed management.
Aforestation
Contour farming
Check dams
Gullying
Bank protection
Diversion drains

26. Non- structural mitigation measures
Flood plain zoning
Flood forecasting
Flood proofing
Mathematical modeling

27. Levees
An earth dyke or embankment.
Used for flood control.
Constructed along the river.
Material placed in layers and compacted with
least pervious material placed along the river
side of levee.
Height and top width of levee depends on
H.F.L of river.

28. Levee cross section must be adjusted to fit the
site and available materials.
Minimum top width 3 m usually recommended.
River side protected by stone pitching and
country side protected by turfing.
Generally, levees run along river bank with a
margin of 2 m between toe of levee and top of
river bank.
Sometimes, it may run some distance away from
river bank.

31. NATURAL LEVEES FORMATION

32. Location of levees
Located on both the banks such that sufficient
area of flow is provided between them.
If flood plain between levees is shallow and flat,
channel width is large, therefore height of levee
is low.
A deep and narrow flood plain will necessitate
high levees.
When a city or agricultural districts is to protect
a ring levee may be provided.

33. Flood walls
Flood wall is usually of masonry or concrete.
Usually constructed in which enough land is not
available for levees.
If land is costly or limited, it is more economical
to construct flood wall.
Constructed on river bank.
Proper foundation should be provided and
precaution should be taken against scouring.

35. Flood ways
Low lying areas along the course of the river are
known as floodways.
Depression into which a portion of the flood
water diverted from a river through natural or
artificial channel for temporarily storing.
 After flood recedes, the store water is permitted
to flow back to river.

37. Two functions in flood control:
Create large shallow reservoirs which store a
portion of flood water, decrease flow in main
channel.
Provide additional outlet for water, increase
velocity.

38. Construction is limited by topography of the
valley.
Availability of low value land.
Floodways used during periods of major floods,
land can be used for agricultural purpose.
Diversion channel carrying water may be natural
or artificial.

39. Channel improvement
Channel improvement as flood control measures.
River can be made to carry higher discharges at
lower levels by improving its hydraulic
conditions.
Increase in size of cross section of channel
Realignment of channel along a shorter route
Increasing velocity of flow in channel
Increasing waterways at crossing

40. Flood damage analysis
Direct damage: damage to crops, houses, human
lives, live stock, roadways, rail tracks etc.
Indirect damage: due to transport loss factories,
shops and business in flood affected centre may
be closed. Temporary unemployment.

41. Two types of losses due to flood disaster,
Tangible loss
Intangible loss
Tangible loss: loss can be estimated in terms of
money value.
Personal properties like building, materials etc.
Loss of crops
Loss due to disruption of business
Loss due to disruption of road and railways

42. Intangible losses: can't be estimated in money
values.
Loss of human life and cattle
Loss of health due to disease
Loss caused by social distress