The document explains floods as natural events caused by excessive water overflow, affecting urban and rural areas, with types categorized into fluvial, pluvial, and coastal floods. It outlines the causes, effects, and potential management strategies for flood risks, emphasizing both natural phenomena and human-induced factors. Additionally, it highlights the immediate and long-term impacts of floods, including loss of life and property, but also points out some positive effects like nutrient replenishment for agriculture.

1. Ms Asma Akbar Ali
October 2020
River Floods
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2. What are Floods ?
Flood is overflow of excess water that submerges
land or an inflow of tide onto land. The most
destructive are those that happen when the
river system is over filled and water runs onto
the settlements causing the breaking up of
structures and drowning of people and animals
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3. Urban Floods & Rural Floods
1. These are a natural event or occurrence where a
piece of land (or area) , that is usually dry land,
suddenly gets submerged under water.
2. Some floods can occur suddenly and recede
quickly. Others take days or even months to
build and discharge.
3. When floods happen in an area that people live,
the water carries along objects like houses,
bridges, cars, furniture and even people. It can
wipe away farms, trees and many more heavy
items.
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5. Pluvial floods (flash floods and surface water)
Fluvial floods (riverfloods)
NORMAL RIVER
LEVEL
OVERFLOWING WATER
SNOWFALL
HIGH WINDS
STORM SURGE
Coastal flood (stormsurge)
STRAIN O N
URBAN DRAINAGE
SYSTEM
WATER IS
FORCED ASHORE
1. Fluvial floods are river floods
2. Pluvial floods are flash
floods & surface water
3. Coastal flood are storm surge
Types of floods
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6. Fluvial are River Floods
A fluvial, or river flood, occurs when the water level in a river, lake or stream rises
and overflows onto the surrounding banks, shores and neighboring land.
The water level rise could be due to excessive rain or snowmelt.
The damage from a river flood can be widespread as the overflow affects smaller rivers
downstream, which can cause dams and dikes to break and swamp nearby areas.
The severity of a river flood is determined by the duration and intensity (volume)
of rainfall
SNOWFALL
NORMAL RIVER
LEVEL
OVERFLOWING WATER
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7. Pluvial floods are flash floods & surface water
A common misconception about flood is that you must be located near a body of
water to be at risk. Yet pluvial flooding can happen in any location, even in areas
with no water bodies in the vicinity. There are two common types of pluvial flooding:
• Surface water floods occur when an urban drainage system is overwhelmed and
water flows out into streets and nearby structures.
• Flash floods are characterized by an intense, high velocity of water. They can also
occur via sudden release of water from an upstream levee or a dam.
STRAIN ON
URBAN DRAINAGE
SYSTEM
W
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8. Coastal flood are storm surge
Coastal flooding is the inundation of land areas along the coast by seawater.
Common causes of coastal flooding are intense windstorm events occurring at the
same time as high tide.
The severity of a coastal flood is determined by several other factors, including the
strength, size, speed, and direction of the windstorm.
HIGH WINDS
STORM SURGE
WATER IS FORCED ASHORE
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10. Causes of floods
Natural Causes
1. Melting of snow in summer
2. Monsoon Rain
Human Made INCREASES THE RISK
1. Deforestation
2. No construction of Dams to store water
3. No embankments alongside the rivers
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11. Effects of floods
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1. Primary – Physical damage due to the direct
force of water
2. Secondary – disruption of services due to the
primary damage
3. Tertiary – Long term social, emotional
economical damage

12. Effects of floods
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Loss of lives and property: Immediate impacts of flooding include
loss of human life, damage to property, destruction of crops, loss of
livestock, non-functioning of infrastructure facilities and
deterioration of health condition owing to waterborne diseases.

13. Flood Reduction & Management
1. Planting trees
2. Enlarging the water Channel
3. Building embankments
4. Building extra channels to spread out the
water
5. Build reservoirs e.g. dams
6. Reduce settlements and building structures
at high risk areas
7. Evacuation & Rehabilitation
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14. Preventing increasing risk of Floods
Natural phenomenon so Natural floods cannot always be
prevented but human behaviours predisposing to High risk of
floods can be controlled
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15. Mitigation: What can be done to reduce
the flood risk
1. Flood warning
2. Evacuation plan
3. Training
4. Preparedness for First response (first Aid)
5. CPR
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16. Positive Impact of floods
1. Return nutrients by washing out the top
layers and spreading a newer layer of
alluvium
2. Flooded field is use able for rice cultivation
3. Fish production is increased by fresh and
newer fishes brought into the delta
4. Inland fish reproduction and breading is
enhanced (AQUA LIFE)
5. Ground water is filled up
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