Introduction to flood Types of flood Causes of flood Flood categories Flood impacts Typical adverse effects Flood management Flood Control

1. Flood

2. Presented by:
Muhammad Sohail Riaz
Presented to:
Miss Hira Fatima

3. Table of Content
• Disaster
• Introduction to
flood
• Types of flood
• Causes of flood
• Flood categories
• Flood impacts
• Typical adverse
effects
• Flood management
• Flood forecasting
• Possible Risk
Reduction Measures
• Mapping of the flood
prone areas
• Land use control
• Construction of
engineered structures
• Flood Control
• Detention facilities
• Floodproofing and its
types
• Channelization
• Flood benefits
• Conclusion

4. Disaster
 Disaster is a natural or human , caused
phenomenon, which causes serious
disruption of the functioning of a community
or a society causing widespread human,
material, economic and environmental losses
which affects community, society by using its
resources

5. Cont…..
 Floods are a common feature in the country
that occur every year in many parts including
South India

7. INTRODUCTION
 A flood occurs when the Geomorphic
Equilibrium in the river system is disturbed
because of intrinsic or extrinsic factors or
when a system crosses the geomorphic
threshold
 (a) Flooding in a river due to disturbance of
river bed (intrinsic threshold)
 (b) Flooding in a river due to heavy rainfall
(extrinsic threshold)

8. Cont……
 Floods in major cities especially during rainy
season are proving to disastrous not only to
the environment but also have serious
implications for human life and property.
 Most frequent and deadliest

9. Cont…..
 Floods can form where there is no stream, as
for example when abnormally heavy
precipitation falls on flat terrain at such a rate
that the soil cannot absorb the water or the
water cannot run off as fast as it falls.

10. TYPES OF FLOODS
 Flash floods
 River floods
 Storm surge
 Urban Flood

11. Flash floods
 Flash floods are local floods of great volume
and short duration
 A flash flood generally results from a heavily
rain or “cloudburst” on relatively small and
widely-dispersed streams
 Runoff from the intense rainfall results in high
flood waves. Discharges, quickly reach a
maximum and diminish almost as rapidly

12. Cont…..
 Flood flows frequently contain large
concentrations of sediment and debris
 Flash floods also result from the failure of a
dam
 Flash floods are particularly common in
mountainous areas and desert regions but
are a potential threat in any area where the
terrain is steep, surface runoff rates are high,
streams flow in narrow canyons, and severe
thunderstorms prevail

14. Riverine floods
 Riverine floods are caused by precipitation
over large areas or by melting of the winter’s
accumulation of snow, or by both
 These floods differ from flash floods in their
extent and duration. Whereas flash floods are
of short duration in small streams, riverine
floods take place in river systems

15. Cont……
 Floods on large river systems may continue
for periods ranging from a few hours to many
days. Flood flows in large river systems are
the distribution of precipitation
 The condition of the ground (amount of soil
moisture, seasonal variations in vegetation,
depth of snow cover, etc.) directly affects
runoff

17. Storm surge
 Storm surge or tidal surge is an offshore rise
of water associated with a low pressure
weather system, typically a tropical cyclone
 Storm surge is caused primarily by high winds
pushing on the ocean's surface
 The wind causes the water to pile up higher
than the ordinary sea level

18. Cont….
 Low pressure at the center of a weather
system also has a small secondary effect, as
can the bathymetry of the body of water
 It is this combined effect of low pressure and
persistent wind over a shallow water body
which is the most common cause of storm
surge flooding problems

19. Cont……..
 The term "storm surge" in casual (non-
scientific) use is storm tide; that is, it refers to
the rise of water associated with the storm,
plus tide, wave run-up, and freshwater
flooding

21. Causes of flood
 Natural
 Heavy rains
 Melting of ice during volcano eruption
 Earthquake
 Marine landslip

22. According to duration flood
categories:
 Slow-Onset Floods: Slow Onset Floods usually
last for a relatively longer period, it may last
for one or more weeks, or even months

23. Cont……..
 Rapid-Onset Floods: Rapid Onset Floods last
for a relatively shorter period, they usually last
for one or two days only
 Flash Floods: Flash Floods may occur within
minutes or a few hours after heavy rainfall,
tropical storm, failure of dams or levees or
releases of ice dams
 It causes the greatest damages to society

24. FLOODS IMPACTS
 Human Loss
 Property Loss
 Affects the Major Roads
 Disruption of Air / Train / Bus services
 Spread of Water-borne Communicable
Diseases

25. Cont…..
 Communication Breakdown
 Electricity Supply Cut off
 Economic and Social Disruption
 Increase in Air / Water Pollution

27. Typical adverse effects
 The most important consequence of floods is
the loss of life and property
 Structures like houses, bridges; roads etc. get
damaged by the gushing water
 Boats and fishing nets also get damaged
 There is huge loss to life and livestock caused
by drowning

28. Cont…….
 Lack of proper drinking water facilities,
contamination of water (well, ground water,
piped water supply) leads to outbreak of
epidemics, diarrhrea, viral infection, malaria
and many other infectious diseases
 Flooding also leads to a large area of
agricultural land getting inundated as a Result
there is a huge crop loss

29. Cont……
 This results in shortage of food, and animal
fodder
 Floods may also affect the soil characteristics
 The land may be rendered infertile due to
erosion of top layer or may turn saline if sea
water floods the area

30. Flood forecasting
 Anticipating floods before they occur allows
for precautions to be taken and people to be
warned so that they can be prepared in
advance for flooding conditions
 For example, – Farmers can remove animals
from low-lying areas and utility services can
put in place emergency provisions to re-route
services if needed

31. Cont…..
 Emergency services can also make provisions
to have enough resources available ahead of
time to respond to emergencies as they occur
 In order to make the most accurate flood
forecasts for waterways, it is best to have a
long time-series of historical data that relates
stream flows to measured past rainfall events

32. Cont……
 Radar estimates of rainfall and general
weather forecasting techniques are also
important components of good flood
forecasting

34. Flood management
 Cannot be absolutely controlled only
managed
 Aims of flood management
 Protection of people & property
 Reduction of flood risk
 Monitoring, research, forecasting & warning

36. Possible Risk Reduction Measures:
 Mapping of the flood prone areas
 Land use control
 Construction of engineered structures
 Flood Control Detention Flood proof
channelization
 Flood Management

37. Mapping of the flood prone
areas
 Historical records give the indication of the
flood inundation areas and the period of
occurrence and the extent of the coverage
 Warning can be issued looking into the earlier
marked heights of the water levels in case of
potential threat

38. Cont…….
 In the coastal areas the tide levels and the
land characteristics will determine the
submergence areas
 Flood hazard mapping will give the proper
indication of water flow during floods

40. Land use control
 The number of casualties is related to the
population in the area at risk
 In areas where people already have built their
settlements, measures should be taken to
relocate to better sites so as to reduce
vulnerability

41. Cont…….
 No major development should be permitted
in the areas which are subjected to high
flooding
 Important facilities like hospitals, schools
should be built in safe areas
 In urban areas, water holding areas can be
created like ponds, lakes or low-lying areas

43. Construction of engineered
structures
 Construction of engineered structures in the
flood plains and strengthening of structures
to withstand flood forces
 The buildings should be constructed on an
elevated area
 If necessary build on stilts or platform

45. Flood Control
 Flood Control aims to reduce flood damage
 This can be done by decreasing the amount
of runoff with the help of reforestation,
protection of vegetation, clearing of debris
from streams and other water holding areas,
conservation of ponds and lakes etc

46. Cont……
 Flood controls, such as dams, can be built
and maintained over time to try and reduce
the occurrence and severity of floods as well

48. Detention facilities
 Detention facilities, such as dams, store flood
waters and release them at lower rates, thus
reducing or eliminating the need for major
downstream flood control facilities, the
construction of which would disrupt the
developed areas

49. Cont…..
 Perhaps the greatest disadvantage of
detention facilities, assuming a structurally
sound facility, is the false sense of security
that such structures create among the
general public
 These facilities are almost never designed to
contain the probable maximum flood
 Thus they require a way to pass discharges in
excess of the design flood

51. Floodproofing
 Retrofit floodproofing of existing buildings is
sometimes a viable solution, depending upon
the location of the structure within the
floodplain and its structural integrity
 There are two basic types of floodproofing:
active and passive

52. Active floodproofing
 Active floodproofing is temporary, requiring
some positive action on the part of building
owners and/or occupants immediately before
a flood event
 It will not be effective if personal are not
available to perform the necessary functions
when the flood occurs

53. Cont….
 Active floodproofing requires some type of
flood detection and warning system to give
time for the personnel to install the
floodproofing devices
 In flash flood situations the personal may not
be available to respond in time

54. Passive floodproofing
 Passive floodproofing is permanent and does
not require any action at the time of the flood
 Active floodproofing is most effective in areas
with long warning lead times; it should not be
relied upon, if possible, in flash flood areas

55. Cont….
 Flood Proofing reduces the risk of damage
 Measures include use of sand bags to keep
flood water away, blocking or sealing of doors
and windows of houses etc
 Houses may be elevated by building on
raised land

57. Channelization
 The construction of open channels is a
commonly used method of reducing the size
of a floodplain or floodway
 To prevent erosion, channels can be lined
with grass, wire-enclosed, rock, concrete
layers deep
 Open channels allow water to enter them at
almost any point

59. Flood benefits
 Floods (in particular more frequent or smaller
floods) can also bring many benefits, such as
– Recharging ground water, – Making soil
more fertile and increasing nutrients in some
soils
 Flood waters provide much needed water
resources in arid and semi-arid regions where
precipitation can be very unevenly distributed
throughout the year

60. Cont…..
 Freshwater floods particularly play an
important role in maintaining ecosystems in
river corridors and are a key factor in
maintaining floodplain biodiversity
 Flooding can spread nutrients to lakes and
rivers, which can lead to increased biomass
and improved fisheries for a few years

61. Cont…..
 For some fish species, an inundated
floodplain may form a highly suitable location
for spawning with few predators and
enhanced levels of nutrients or food
 Fish, such as the weather fish, make use of
floods in order to reach new habitats
 Bird populations may also profit from the
boost in food production caused by flooding

63. Conclusion
 Although flood is the most deadliest disaster
still, but it has some benefits like:
 Recharges ground water
 Fresh water flood help in maintaining food
plain ecosystem
 Boost in food production for birds
 Facilitation of weather fish to new habitat