FLOODING

DEFINTIONS
• A flood occurs when water is unable to
permeate the soil or rises above its surface,
resulting in overflowing river valleys with
blocked roads and flooded buildings.
• A drought is a period when there is insufficient
rainfall to sustain plant growth.
• A flood is defined as an occurrence of an
unusually high level or flow of water covering a
land surface that is usually dry. Flooding is
typically a consequence of persistent rainfall.
• These land surfaces usually include low-lying
areas where human settlement is dense and
flooding can give rise to overflowing river
valleys, blocked roads, damaged
infrastructure and so on.

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 TYPES OF FLOODING
1. Riverine Floods
• This type of flooding occurs when water overflows the channel of a river, i.e., the water has exceeded
the channel capacity of the river and has overflowed its banks.
• Riverine flooding can also occur when the velocity of water is too high to the point where it flows out
of the channel at sharp bends. However, the water in these cases may be still well contained in
straight sections within the channel.
• This type of flooding occurs when there is excessive rainfall like that during the rainy season or
during storm events.
(A flood plain is the area where the river water spills over when flooding occurs)
e.g.: Caribbean – Essequibo River in Guyana
Local – Caroni River
- Arouca River

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 Examples of Riverine Flooding
ESSEQUIBO RIVER IN GUYANA CARONI RIVER AROUCA RIVER

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 2. Coastal Flooding
• This type of flooding occurs when low-lying land along a coast becomes
covered with water. This flooding does not intrude far inland and is usually a
mixture of fresh and salt water which is called brackish water.
•Coastal flooding occurs during hurricanes and storms or when storms surges
force sea water high up onto land. These are caused by factors such as unusually
low atmospheric pressure or high winds.
•e.g., International – Hurricane Katrina caused coastal flooding in New Orleans
(2005)
•Regional – Hurricane Irma without water along the coast of Long Island in the
Bahamas for more than a day which was followed by the water surging back and
flooding the coast.
•Coastal flooding can also be a result of rising sea levels due to global warming
which can be seen in the Maldives.
•Tectonic activity causing the down-faulting or slumping along a coastal area and
tsunamis caused by underground earthquakes can also lead to coastal flooding.

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 Examples of Coastal Flooding
• Hurricane Katrina in New • Hurricane Irma in the Bahamas
Orleans

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3. Estuarine Flooding
•Coastal flooding can also occur in association with river
estuaries. Estuaries are areas where the mouth of a river is
widened and drowned by sea water. During periods of high tide,
when river discharge is very high, the river water is unable to
flow quickly enough into the sea. This causes the river’s water
to back up and the water overtops the riverbanks which results
in flooding.
•Additionally, under normal circumstances, the flow of water in
many rivers is reversed during high tide as the water forces its
way upstream.
•e.g.: The Bay of Fundy in Canada.

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4. Urban and Riverine Flash Floods
•Flash floods are those which occur very suddenly and are usually
localized. There is little time between the start of rainfall and the onset of
flood conditions. These floods can occur within an hour or even minutes of
the start of intense rainfall. They are very common during severe
thunderstorms. They can occur in river valleys, flood plains and urban
areas.
•Urban Flooding occurs as a result of the ground surface being
impermeable by concrete or asphalt making the permeability of the soil
severely diminished. Therefore, with intense rainfall, the water will exceed
the infiltration capacity of the land and overland flow with flooding occurs.
•This type of flooding can also occur when watercourses are blocked by
waste material and heavy rainfall quicky overflows channels.

•Riverine Floods may also be flash floods where intense downpour can
suddenly cause water moving large volumes of sediment downstream in
rivers with highly variable discharges. This is common is steep valleys and
mountainous areas.

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 CAUSES OF FLOODS
METEOROGIAL FACTORS HYDROGICAL FACTORS CHANGES IN SEA-LEVEL

oThese factors include oThese factors are oLong term changes of

rainfall events usually linked to where the sea-levels may intensify
during periods when it rainfall accumulates flood conditions. Once
is prolonged and intense when flows off the land the se level rises it is
in association with surface and back into more difficult for rivers
storms and hurricanes. water bodies or rivers. to deposit large volumes
  The size of the river as of water into the sea.
well as the speed at
which the water is
moving influence the
onset if flooding.

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 CAUSES OF FLOOD

oDue to human activities such as urbanization which

causing changes in the Earth’s natural landscape
increases the risk of flooding. Other activities such as
deforestation, mining and infrastructural development
results in reduced infiltration and increased runoff. The
straightening, diverting or covering of natural
waterways also contribute to flooding.

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 IMPACTS OF FLOODING
SOCIAL

oRivers after been through the regular occurrence of flooding, creates flood plains which are
enormous areas of flat land which have always been attractive to human populations for
settlement and access to fresh water. The river can also be used as a means for transport.
oIntense flooding may cause injuries and some cases death. People may experience loss or
damage of valuables, their homes, documents which lead to disrupt of their lifestyle and in severe
cases lead to homelessness and poverty.
oWater-borne diseases may become widespread such as cholera and leptospirosis and those as a
result from the breeding of mosquitoes like dengue, malaria, chikungunya.
oTraffic congestion may increase due to limited roadways.

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 ECONOMIC
Flood plains are also very fertile land areas which are suitable
for farming which guarantees successful production in the
agricultural industry. This provides livelihood and food security
for people.
Due to the regular occurrence of water, flood plains are home to
unique flora and fauna which attracts tourism.
Damage caused by flooding can be extended to homes,
buildings, roadways, infrastructure which are costly for the
community and government to clean, repair or replace.
Land prices for areas prone to flood will decrease.
There may be disruptions in productions of goods and services.
Food supply may be scarce leading to the increase in food
prices.
 

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 POLITICAL
•Citizens may become distressed to the negative impacts of flooding
and dissatisfied the government’s lack of aid or resources in such a
difficult time which may lead to political uproar.
 

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 WHY ARE MOST CARIBBEAN
COUNTRIES VULNERABLE TO
FLOODING?

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 • In the Caribbean, most countries are
vulnerable to flooding because of our
wet climate.

They are most vulnerable during the

rainy season which runs from June to
December.

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 CONTINUATION
• Another major reason is due to the Intertropical
Convergence Zone (ITCZ).
• This is a band of low pressure around the Earth which
generally lies near to the Equator. The trade winds of the
Northern and Southern hemispheres come together here,
which leads to the development of frequent thunderstorms
and heavy rain.
• The ITCZ moves throughout the year and follows the
migration of the Sun’s overhead position typically with a delay
of 1-2 months. As the ocean heats up more than the land the
ITCZ moves North and South over land areas.

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 CASE STUDY

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 • Trinidad is the most southerly island of the Caribbean located within a
tropical humid zone. Due to such a location and lying within the
Intertropical Conference Zone (ITCZ). High-intensity rainfall and flash
flooding are common. Flooding in Trinidad is mostly due to both natural
and human factors. Most flooding is experienced during the rainy season
(June to November). The ITCZ brings about heavy downpours, easterly
waves and conventional showers. Human Factors include the increase in
urban development that reduces infiltration by soils, slash and burn
agriculture, deforestation, forest fires which disrupts the natural layout of
land. These is in company with the improper disposal of waste which
blocks the flow of water.
• Major flooding occurs in many regions in Trinidad, specifically in the
Caroni, Caparo, Santa Cruz and Penal-Debe.
• The most damages from flooding are endured in the Agricultural Sector.
For the past three decades an estimate of over US$300 million of
agricultural produce has been destroyed by flooding. 
• Given that Trinidad does not actively make use of mitigating practices on a
wide scale to reduce or prevent flooding, it is recommended that land-use
planning and land zoning is exercised as well as land restrictions on the
use of land resources of both rural and urban areas. It is also
recommended that this is supported by legal regulations, management
plans and institutional arrangements.

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MITIGATION AND
PREVENTION
STRATEGIES
 PREDICTING FLOODS
• This includes the study of weather data to estimate and forecast
flood discharge. Rainfall intensity, duration, volume and location, the
rate of the change of water levels in rivers are relevant weather data
that should be studied.

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 MODIFYING THE EVENT

This includes environmental control to

decrease the impacts of flooding. This can be
done by building damns, spillways, storage
reservoirs, concrete-lined water channels
and straightening the courses of rivers.

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 LAND USE ZONING AND HAZARD RISK MAPS

• This entails educating the public on which areas are prone to

flooding and encouraging them live in low-risk areas and
reserve those of high-risk to for pasture, leisure or wildlife.

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 FLOOD RESISTANT DESIGN
•This is any measure either structural or behavioural that is intended
to prevent damage to a building from flooding, Modifications can be
made to buildings or homes to block water from protruding in such as
string, resistant windows. Sandbags may be stockpiled beforehand as a
temporary water-proofing method to protect low floor and basements.

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Thank You!