Definition of flood Objectives Types of floods Causes of floods Floods Impacts

1. Members:
{L} Tawhidul Islam[633549]
Md Tarek Aziz [289768]
Tauhidul Islam[872409]
Shanjida Afrin[206692]
Md Irfan[286727]
5th CMT/2

2. Over view:
• Definition of flood
• Objectives
• Types of floods
• Causes of floods
• Floods Impacts

3. • Flood is a natural disaster. an
overflow of a large amount of
water beyond its normal limits,
especially over what is normally
dry land.
• Flood is a common feature in
the country that occur every
year.

4. Objective of study:
• To identify the causes of floods
• To describe the overall impact of flooding.
• Gather knowledge about flood forecasting.
• How to control flood.
• To find out the benefits of flood.

5. 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 aggradation of
river bed (intrinsic threshold);
(b) Flooding in a river due to heavy rainfall
(extrinsic threshold)
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.

6. TYPES OF FLOODS:
• Flash floods: a sudden local flood, typically due to heavy rain.
• River floods: It occurs when a river fills with water beyond its capacity.
The surplus water overflows the banks and runs into adjoining low-lying
lands.
• Coastal floods: Coastal flooding occurs when normally dry, low-lying land
is flooded by seawater. The extent of coastal flooding is a function of the
elevation inland flood waters penetrate which is controlled by the
topography of the coastal land exposed to flooding.
• Urban floods: Urban flooding is the inundation of land or property in a
built environment, particularly in more densely populated areas, caused by
rainfall overwhelming the capacity of drainage systems, such as storm
sewers.

7. The time from peak rainfall to peak
discharge is the LAG TIME.
The soil becomes
saturated and
overland flow and
through flow reach
the river and
discharge increases.
Overland flow arrives
first.
Start of the storm there is a
slow rise in discharge, as
only a
small amount of water falls
into the channel
Rainfall is intercepted
or infiltrated into the
soil moisture store
The discharge starts to
fall slowly as water is
added from through
flow and groundwater
flows which are much
slower.
The base flow supplies
the river with water
between storms and
keeps it flowing in summer.

8. Floods
Natural
Man made
Storm Surge,
Tsunami, Glacial Melt,
Landslide, Riverine,
Estuarine & Marine Flood
Breach of
Dam/ Barrage/
Embankment
Release from Reservoir,
Urban Flood

9. Causes of floods

10. Flood Control:
• In many countries around the world, waterways prone to floods are often
carefully
managed. Defenses such as levees, bunds, reservoirs, and weirs are used to
prevent
waterways from overflowing their banks.
• In the riparian zone near rivers and streams, erosion control measures can be
taken
to try and slow down or reverse the natural forces that cause many waterways
to meander over long periods of time.
• Flood controls, such as dams, can be built and maintained over time to try and
reduce the occurrence and severity of floods as well.

11. 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.
• 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.
• 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.

12. Thank you…
Group: F
5th CMT/2