ppt on floods

7/30/2019 Ppt on Floods

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A flood is an overflow of an expanse of water thatsubmerges land


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FLOODS LEAD TO .

Overflow situation

damage in terms of

life, property and

economic loss.

Thousands of

crores of rupees

are spent everyyear in flood control

and forecasting.


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Reasons for flood

Heavy rainfall(

26.7.2005)

Huge snow melting

Failures of dams,

barrages etc.,(koshi)

Landslides causing

blockage of river Tsunami


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Types of flood(cont..)

Coastal floods

Caused by severe sea storms, or as a result of

another hazard (e.g. tsunami or hurricane).

Catastrophic floods

Caused by a significant and unexpected event

e.g. dam breakage, or as a result of another

hazard (e.g. earthquake or volcanic eruption).

Muddy floods

A muddy flood is generated by run off on crop

land.


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Why flood matters??

EFFECTS The damage due to flood may vary with respect to the

magnitude of the flood.

Thus we can classify the effects as:

Primary effects

Physical damage- Can range anywhere from bridges,cars,buildings, sewer systems, roadways, canals and any othertype of structure.

Casualties- People and livestock die due to drowning. It canalso lead to epidemics and diseases.

Secondary effects

Water supplies- Contamination of water. Clean drinking waterbecomes scarce.

Diseases- Unhygienic conditions. Spread of water-bornediseases


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Effects (cont..)

Crops and food supplies- Shortage of foodcrops can be caused due to loss of entire

harvest.

Trees- Non-tolerant species can die fromsuffocation

Tertiary/long-term effects

Economic-, rebuilding costs, food shortageleading to price increase, temporary decline in

tourism etc.


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Floods In Mumbai

The Maharashtra floods of 2005 refers to the flooding of

many parts of the Indian state of Maharashtra including

large areas of the metropolis Mumbai, a city located on

the coast of the Arabian Sea, on the western coast of

India, in which at least 5,000 people died.

The term 26 July, now is, in context always used for theday when the city of Mumbai came to a standstill.


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Overview The floods were caused by the eighth heaviest ever recorded 24-hour

rainfall figure of 994 mm (39.1 inches) which lashed the metropolis on 26

July 2005, and intermittently continued for the next day. 644 mm

(25.4 inches) was received within the 12-hr period between 8am and 8pm.

The previous record high rainfall in a 24-hour period for Mumbai was 575

mm (22.6 inches) in 1974.

People were returning home from work. Many people halted in theiroffices.

Thousands of people were affected badly. Infact every family or person

must be having a story for 26th July.

Even animals died. Animals were drowned in sheds and streets affected

by floods. Plants and agriculture was destroyed to an greater extent.

Thousands of animal carcasses floated in the flood waters, raising

concerns about the possibility of disease.


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Causes of Floods in Mumbai

The expansion of Mumbai city inthe past couple of decades hasbeen beyond limits

Unplanned infrastructure atBandra-Kurla, Kalina etc, wasthe main reason for the chest

high water clogging in thoseplaces

Officials in the environmentministry claimed that it was notpractical to impose newguidelines with retrospectiveeffect "as there are millions of

buildings". Improper maintenance of

drainage systems all overMumbai

Both government and people areresponsible


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FLOOD CONTROL

Greater losses due to flood

Need for control, Measures to be taken

No complete control of flood to zero level

So Flood Management rather than Flood

Control

Classification of control measures

Structural measures and 2. Non-structuralmeasures


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Flood Control

Storage Reservoir

Detentio Reservoir Levees

Floodways

ChannelImprovement

WatershedManagement

Flood Plain zoning

Flood forecastingand Warning

Evacuation and

relocation

Structural Measure Non-Structural Measure


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Stuctural Measures

STORAGE RESERVOIR:

Most reliable and effective flood control

method

Storage reservoir to absorb incoming flood

Release in controlled way so that downstream

channels do not get flooded.

Several reservoirs to be placed in a river forcomplete flood control.

Graph Kheichera rakhnu hai


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Structural Measures (cont..)

DETENTION RESERVIORS

-Consist of an obstruction to a river with

uncontrolled outlet.

-For small structures and temporary storage

LEVEES

-Also called dikes or flood embankments

-Earthen structures parallel to the course ofriver.


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Structural Measures

Height higher than

the design flood

level.

One of the oldestand common

methods of flood

protection

Considerable care

and maintenance

required since

earthen


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Structural Measures

FLOODWAYS

-Channels into which part of the flood will be

diverted during high stages.

-Natural or man-made

CHANNEL IMPROVEMENT

-Widening or deepening of channel

-Reduction of channel roughness (clearance ofvegetation)


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Structural Measures

WATERSHED MANAGEMENT

-Aims at cutting down and delaying the runoff

before it gets into the river.

-Check dams, contour bonding, terraces etc.

-Improve soil infiltration capacity hence reduce

soil erosion


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NON-STRUCTURAL METHODS

FLOOD PLAIN ZONING

Identifies the flood prone areas of a river andregulates the land use to restrict the damage dueto flood.

Development plans are prepared

FLOOD FORECASTING AND WARNING

Enables civil authority to take appropriate controlmeasures.

Orbiting satellitesPicturesCloud growthrainfall predictionflood prediction


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Non-structural methods

-historical recordsof flooding withstudy on theparameters: season,river channeltopography, soilconditions, rainfallintensity andweather.

Study of FLOODHYDROGRAPH


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Flood hydrograph

Hydrograph: Study of the hydrological characteristics of acatchment.

Responses of a given catchment to a rainfall input.

USES

Use in the design of hydraulic structures

Development of flood forecasting and warming systems based onrainfall

Extension of flood flow records based on rainfall records

(components of hydrograph: \

1.Rising limb 2. Crest segment 3. Recession limb)

Factors affecting flood hydrograph: Physiographic and climatic factors

Limitations

Precipitation must be from rainfall only

Non uniform pptdoesnt give good results (unit hydrograph)


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Flood hydrograph


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Non-structural measure

EVACUATION AND RELOCATION

Evacuation of communities along with their live

stocks and other valuables.

TemporarilyNonstructural measure,Permanent resettlementStructural measure

Decrease loss burden


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Conclusion

-Flood is one ofdeadliest naturaldisaster.

-Preventive measuresto be taken in time.

-Better engineeringstructures to preventflood control

-Stringent governmentsteps.

-Awareness on flooddisaster is required.


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Deadliest floodsDeath Toll Event Location Date

1)2,500,000-3,700,000 China floods China 1931

2)900,000

2,000,000 Yellow River (Huang He) floodChina 1887

3)500,000700,000 1938 Yellow River (Huang He) flood

China 1938

4)231,000 Banqiao Dam failure, result ofTyphoon Nina.Approximately 86,000 people died from flooding

and another 145,000 died during subsequent disease.China 1975

5)145,000 Yangtze river floodChina 1935

6)More than

100,000St. Felix's Flood, storm surge Netherlands 1530

7)100,000 Hanoi and Red River Delta flood North Vietnam 1971

8)100,000 Yangtze river flood China 1911

Th k f ki d
http://f/Documents%20and%20Settings/Administrator/Desktop/flood/Flood%20-%20Wikipedia,%20the%20free%20encyclopedia.mht


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Thankyou for your kind

attention!!

Any question?????