Overflow situation Unusually high stage

in a river River overflow its

banks and inundates the adjoining area.

Significance: damage in terms of life, property and economic loss.

Thousands of crores of rupees are spent every year in flood control and forecasting.

Death 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)500,000– 700,000

1938 Yellow River (Huang He) floodChina 1938

4)231,000Banqiao Dam failure, result of Typhoon 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 100,000

St. Felix's Flood, storm surge Netherlands 1530

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

8)100,000Yangtze river flood China 1911

Heavy rainfall Huge snow melting Failures of dams,

barrages etc.,(koshi)

Landslides causing blockage of river

Riverine floods• Slow kinds: Runoff from sustained rainfall or rapid

snow melt exceeding the capacity of a river's channel. Causes include heavy rains from monsoons, Unexpected drainage obstructions such as landslides, ice, or debris can cause slow flooding upstream of the obstruction.

• Fast kinds: include Flash floods which are much more dangerous and flow much faster than regular floods. Result from tropical storms, dam failures or excessive rain and snow.

Estuarine floods• Commonly caused by a combination of sea tidal

surges caused by storm-force winds.

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.

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 other type of structure.

• Casualties - People and livestock die due to drowning. It can also lead to epidemics and diseases.

Secondary effects• Water supplies - Contamination of water. Clean

drinking water becomes scarce. • Diseases - Unhygienic conditions. Spread of water-

borne diseases

• Crops and food supplies - Shortage of food crops can be caused due to loss of entire harvest.

• Trees - Non-tolerant species can die from suffocation

Tertiary/long-term effects• Economic -, rebuilding costs, food

shortage leading to price increase, temporary decline in tourism etc.

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-structural

measures

Storage Reservoir Detentio Reservoir Levees Floodways Channel Improvement Watershed Management

Flood Plain zoning Flood forecasting and Warning Evacuation and relocation

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

for complete flood control. Graph Kheichera rakhnu hai………

DETENTION RESERVIORS -Consist of an obstruction to a river

with uncontrolled outlet. -For small structures and temporary

storageLEVEES -Also called dikes or flood

embankments -Earthen structures parallel to the

course of river.

Height higher than the design flood level.

One of the oldest and common methods of flood protection

Considerable care and maintenance required since earthen

FLOODWAYS -Channels into which part of the flood

will be diverted during high stages. -Natural or man-madeCHANNEL IMPROVEMENT -Widening or deepening of channel -Reduction of channel roughness

(clearance of vegetation)

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

FLOOD PLAIN ZONING Identifies the flood prone areas of a river

and regulates the land use to restrict the damage due to flood.

Development plans are prepared FLOOD FORECASTING AND WARNING Enables civil authority to take appropriate

control measures. Orbiting satellites—Pictures—Cloud

growth—rainfall prediction—flood prediction

-historical records of flooding with study on the parameters: season, river channel topography, soil conditions, rainfall intensity and weather.

Study of FLOOD HYDROGRAPH

Hydrograph: Study of the hydrological characteristics of a catchment.

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 on rainfall 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 factorsLimitations Precipitation must be from rainfall only Non uniform ppt—doesn’t give good results (unit hydrograph)

EVACUATION AND RELOCATION Evacuation of communities along with

their live stocks and other valuables. Temporarily—Nonstructural measure,

Permanent resettlement—Structural measure

Decrease loss burden

-Flood is on of deadliest natural disaster.

-Preventive measures to be taken in time.

-Better engineering structures to prevent flood control

-Stringent government steps.

-Awareness on flood disaster is required.

Any question?????