This document discusses floods, including their characteristics, causes, impacts, and mitigation measures. It defines a flood as an overflow of water onto dry land. Flooding can be triggered by heavy rainfall, snowmelt, or dam/levee breaks. Impacts include property damage, loss of life, and environmental contamination. Mitigation approaches include both structural methods like levees and non-structural methods like floodplain zoning and education. Overall, the document provides a broad overview of floods and strategies for reducing their harmful effects.

2.  What is Flood?
 Characteristics of flood
 Causes of flood
 Flood forecasting
 Flood plain zonation
 Impacts of flood
 Mitigation measures of flood
 Reference

3.  Flood can be defined as an overflow of large
quantities of water onto a normally dry land.
 Flooding happens in many ways due to
overflow of streams, rivers, lakes or oceans or
as a result of excessive rain.
 Whenever flooding takes place, there is the
possibility of loss of life, hardship to people,
and extensive damage to property.
 Flooding also destroys crops and can wipe
away trees and other important structures on
land.

4.  Flood can be characterized by the following
attributes:
 Triggering factors
 Spatial occurrence
 Duration of the event
 Time of onset
 Frequency
 Magnitude
 Secondary events

5.  Triggering Factors of Flooding
 Floods can be triggered by different natural and anthropogenic phenomena.
 Sometime it is prolonged rainfall that causes floods, sometime torrential rains or
storms cause flooding situation.
 In summer season, high average temperature can result in increased melting of the
snow hence, high discharge downstream.
 Spatial Occurrence
 Spatial occurrence refers to the area and the extent of the area affected by the flood.
Floods don’t occur randomly.
 They occur in areas that are in geographical proximity to water bodies, where
prolonged rainfall occur or in areas with poor drainage system.
 Duration of the Flooding
 Duration of the event means the time span between the start and end of the flooding
or the event that caused the flood.
 Usually this is difficult to be defined for floods as the recede very slowly and does
not vanish completely, rather the flood water moves from one area to another.
 It can also be defined as the time duration through which the flood lasted.

6.  Time of Onset of the Flood
 It is the time span between the start of the event causing the flooding and the time
when the flood has actually occurred. For instance, the delay between the rainfall
and the peak discharge.
 Frequency of Flooding
 Frequency of flood events mean how often the flooding occur in a given time
period for example, a year.
 Flood recurrence intervals can range from multiple times a year to once in 10 years
or even 30 years.
 Seasonality of Flood
 Seasonality refers to the season that has the most probability for flood.
 By knowing the season for the flood hazard we can take steps to prevent, mitigate
or in the worst case prepare for the hazard.
 Magnitude of Flood
 Magnitude refers to the energy released during the hazardous event.

7.  Intensity of Flood
 Intensity of floods is the damage caused by it.
 It can be characterized by depth of inundation, volume of inundation,
velocity of flow and rate of rise of water.
 The more the depth of water, more will be its volume, velocity and its
damaging capacity.
 Derived Events (Secondary Events)
 Disasters can also trigger secondary disasters causing damages and
destruction.
 Floods can hit down electric poles and cause widespread electrocution or
even fires.

8.  Rain
 Rain is the leading contributor to most of the flooding
cases witnessed across the world.
 Too much rain causes water to flow overland
contributing to flooding.
 River Overflows
 This happens when the river or stream holds more
water upstream than usual, and it flows downstream
to the neighboring low-lying areas, typically referred to
as the floodplains.

9.  Lakes and Coastal Flooding
 Lake and Coastal flooding occurs when large storms or tsunamis causes
the water body to surge inland.
 he situation is even worsened when the winds blowing from the ocean
carry rains in them
 Dam Breakage
 Flooding occurs when the embankments built along the sides of the
river to stop high water from flowing onto the land breaks.
 Sometimes, the excess water from the dam is deliberately released from
the dam to prevent it from breaking thereby causing floods.
 Melting of the Glaciers and Mountain Tops
 When the temperature rises in summer, the accumulated snows and ice
are subjected to melting resulting in vast movements of water into
lands that are normally dry.

10.  Flood forecasting is the use of forecasted precipitation and
stream flow data in rainfall-runoff and stream flow routing
models to forecast flow rates and water levels for periods
ranging from a few hours to days ahead, depending on the size
of the watershed or river basin.
 Flood forecasting can also make use of forecasts of precipitation
in an attempt to extend the lead-time available.
 Flood forecasting is an important component of flood warning.

11.  Flood-plain zoning means demarcating such zones and
preventing indiscriminate development and human
settlement in such areas.
 In 1957, the Central Flood Control Board had mooted the idea
of demarcating flood zones and the measures to prevent
indiscriminate development and settlement in such areas.
 It also provided for setting up of flood zoning authorities in
all the states to take up surveys and demarcation of flood
zones or plains.
 It recommended legislative support to prohibit the use of
flood plains and removal of unauthorised constructions.

13. Floods can have devastating consequences and can have effects on the
economy, environment and people.
 Economic
 During floods (especially flash floods), roads, bridges, farms, houses and
automobiles are destroyed. People become homeless. Additionally, the
government deploys firemen, police and other emergency apparatuses to
help the affected.
 All these come at a heavy cost to people and the government.
 Environment
 The environment also suffers when floods happen. Chemicals and other
hazardous substances end up in the water and eventually contaminate the
water bodies that floods end up in.
 In 2011, a huge tsunami hit Japan, and sea water flooded a part of the
coastline. The flooding caused massive leakage in nuclear plants and has
since caused high radiation in that area.

14.  People and animals
 Flooding causes kills animals, and others insects are
introduced to affected areas, distorting the natural balance of
the ecosystem.
 Many people and animals have died in flash floods.
 Many more are injured and others made homeless. Water
supply and electricity are disrupted and people struggle and
suffer as a result.
o Some Positive Impact of Flood
 Floodwaters carry lots of nutrients that are deposited in the
plains. Farmers love such soils, as they are perfect for
cultivating some kinds of crops.

15. The flood mitigation can be done by following ways:
 Structural
 Non-structural
 Structural Mitigation Measures
 Levees : A levee is an embankment constructed by engineers
out of organic materials such as earth and stone, in order to
prevent the flooding from a free flowing body of water in a
specific location such as a residential community.
 Flood walls: Flood walls are constructed out of materials such
as concrete or steel in order to control the flow of flood waters
and prevent the flooding of specific areas.


16.  Fills: A fill is an area of land dug out usually behind a levee in order to
capture excess flood waters and prevent flood damage to human
structures.
 Dams: The primary purpose of this structure unlike a levee is to retain
water, not to manage flood water.
 Reservoirs: The man-made lakes produced as a result of the creation of a
dam which can slow the flow of the river downstream.
 Reducing bed roughness: This method of mitigation smooths the bed of
the river, which allows for the river to flow faster and reduces the
likelihood of a flood.
 Non-Structural Mitigation Measures
 Land use planning and zoning tools: Local municipalities can institute
zoning laws in their comprehensive plans in order to prevent
development of residential and commercial properties in high risk flood
prone areas.
 Education: Homeowners and renters need to educate themselves before
moving into a new home to determine if their home is in a floodplain area.
 Environmentally sensitive area protection: Areas such as wetlands can be
protected by local municipalities by preventing development in those
areas.

17.  Flood forecasting and warning methods: By using methods,
such as a stream gauge, local officials can determine whether
or not a river or creek will flood based on the level of the
water and how quickly it is rising.
 Planning: By a local municipality creating a comprehensive
and all hazard mitigation plan, communities can reduce the
risk of flood damages to property and life.

18.  Eartheclipse.com
 Nationalgeographic.com
 Mnestudies.com