Floods are the most common natural disaster in Nigeria. They can devastate communities and cause massive economic losses. Vulnerability to floods is influenced by location, population density, infrastructure, and land use planning. Building flood resilience requires prevention through measures like flood barriers and drainage systems. It also requires early warning systems, disaster risk reduction, and community preparedness. Success stories demonstrate how measures like raised housing, pumps, and green infrastructure can effectively manage flood risks.

1. Flood Disaster, Vulnerability and
Flood Resilience: Prevention and
Disaster Risk Reduction.
Lasisi Adedoyin K. S
Office of Environmental Services,
Ministry of the Environment and Water Resources.

2. OUTLINE
● Introduction: The Devastating Impact of Flood Disasters
● Understanding Vulnerability to Flood Disasters
● Building Flood Resilience through Prevention
● Disaster Risk Reduction: Mitigating the Effects of Flood Disasters
● The Importance of Flood Resilience
● Flood Resilience in Action: Success Stories

3. Learning Outcome
• To understand the factors that contribute to flood vulnerability;
• To understand the causes, consequences, and methods for mitigating vulnerability;
• To analyze the meteorological, geographical, and climatic factors that contribute to
flood occurrences, as well as their duration and intensity;
• To understand the causes and impacts of floods, and contributions to the
development of effective flood risk reduction strategies.

4. INTRODUCTION
● Flood disasters have the power to devastate entire communities, leaving
behind a trail of destruction and despair. From flooded homes to
destroyed infrastructure, the impact of floods can be catastrophic.
● In fact, did you know that floods are the most common natural disaster
in Nigeria? In 2022, floods in various parts of Nigeria led to an estimated
economic loss of $9.12bn i.e. =N=4.2tn (punchng). The effects of these
disasters are far-reaching and long-lasting.

5. INTRODUCTION

6. INTRODUCTION

7. INTRODUCTION

8. A flood is a large amount of
water covering an area of
land that is usually dry.
Floods can happen anywhere
in the world.

9. River Stream Canal Reservoir
Ocean

10. Flooding is caused by rain
which is a part of the
water cycle.
Can you name the
different steps of the
water cycle?
Evaporation
Sun
Condensation
Precipitation
Runoff
Sea

11. https://www.youtube.com/watch?v=Qe350nm_odA

12. Steep hills Hard dry ground
Storms & heavy rain
Very wet ground
Buildings & hard surfaces
Deforestation
Water cannot soak into
the ground
Less water is soaked up
through tree roots and leaves
More rain means more
water entering rivers
Water runs off steep hills
quickly into rivers
This can’t soak up
any more water
This can’t let any
water soak in

13. DEFINITION
● Flood is overflow of excess water that submerges land and
inflow of tide onto land;
● Most frequent and deadliest flood occurs when the
geomorphic equilibrium in the river system is disturbed
because of : Intrinsic threshold & Extrinsic threshold.

14. DEFINITION
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)

15. CAUSES OF FLOODING
Natural
• Heavy rains
• Melting of ice during volcano eruption
• Undersea earthquake
• Marine landslip
Man-made
• Bank erosion
• Breach of dam/barrage/embankment

16. Causes of floods
 River floods
 Rainfall
 Snowmelt
 Landslides
 Ice jam: ice that’s flown downstream, blocking the river further down
 Dam failures
 Coastal floods
 Storm surge
 Tsunamis
 Impact of urbanization
 Reduced infiltration
 Reduced evapotranspiration
 reduced green areas with houses
 increased run-off

17. Types of flood
•Flash floods
•River floods
•Coastal Floods
•Urban Flood

18. Flood types
Two extremes. Most floods are a combination of the two, although one type may be dominant.
Upstream (upland) - affects a small drainage basin along a tributary stream.
Often caused by local intense rainfall or dam failure. Usually they are brief in duration (hours to
days) but severe in intensity. Often referred to as a flash flood.
Downstream (lowland) - affects large drainage basins along a main or trunk stream.
Prolonged in duration (weeks or months) and regional in extent.
Usually caused by prolonged precipitation and/or snowmelt.

19. Categories of Flood
According to their duration, floods can be divided into different categories:
• Slow-Onset Floods: Slow Onset Floods usually last for a relatively longer period, it
may last for one or more peeks or even months.
• Rapid-Onset Floods: Rapid Onset Floods last relatively shorter periods, usually lasting
for one or two days only.
• Flash Floods: Flash Floods may occur within minutes or a few hours after heavy
rainfall, tropical storms, failure of dams or levees or releases of ice dams. And it
causes the greatest damage to society

20. Effects of flooding
● Primary
● Secondary
● Tertiary

21. Impact of Flooding
• Human Loss;
• Property Loss;
• Affects food production;
• Disruption of Air / Train / Bus services;
• Spread of Water-borne Communicable Diseases;
• Communication Breakdown;
• Electricity Supply Cut-off ;
• Economic and Social Disruption;
• Increase in Air / Water Pollution;

22. Benefits of Flooding
• 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.

23. Benefits of Flooding
• 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.

24. Flood Management
Cannot be absolutely controlled only managed!
Aims of flood management
• Protection of people & property
• Reduction of flood risk
• Monitoring, research, forecasting & warning

25. Soft Engineering ( non-structural)
● Flood plain zoning;
● Flood preparedness;
● Flood forecasting;
● Afforestation;
● Public relief;

26. Hard engineering (structural)
● Embankments
● Dams & reservoirs
● Channel improvement
● Drainage improvement
● Diversion of flood rivers

27. What areas are at risk from floods
• Densely populated areas are at a high risk for flash floods. The construction of buildings,
highways, driveways, and parking lots increases runoff by reducing the amount of rain
absorbed by the ground. This runoff increases the flash flood potential
• Areas near rivers are at risk from floods. Embankments, known as levees, are often built
along rivers and are used to prevent high water from flooding bordering land
• Dam failures can send a sudden destructive surge of water downstream. In 1889 a dam break
upstream from Johnstown, Pennsylvania, released a 30-40 foot wall of water that killed 2200
people within minutes.
• Coastal areas: areas close to seas.

28. Understanding Vulnerability to Flood Disasters
● Vulnerability to flood disasters is influenced by a complex interplay of factors,
including geographical location, population density, and infrastructure. For
example, communities located in low-lying areas or near bodies of water are at
higher risk of flooding. Similarly, areas with high population density may
experience greater damage and loss of life in the event of a flood.

29. Understanding Vulnerability to Flood Disasters
● Infrastructure also plays a critical role in determining vulnerability to floods.
Poorly designed or maintained drainage systems, for instance, can exacerbate
the effects of flooding. Additionally, inadequate land-use planning can result in
buildings and other structures being constructed in areas that are prone to
flooding.

30. Building Flood Resilience through Prevention
● Prevention is a key component of building flood resilience. By implementing
measures such as flood barriers, drainage systems, and land-use planning,
communities can significantly reduce their vulnerability to flood disasters.
● For example, the Netherlands has been successful in preventing flooding by
implementing an extensive system of dikes and floodgates that protect its low-
lying areas.

31. Building Flood Resilience through Prevention
● Early warning systems are also crucial in building flood resilience. These
systems allow communities to prepare for floods before they occur,
reducing the impact of the disaster. In Japan, a sophisticated network of
sensors and warning systems has been implemented to alert residents of
impending floods. This has helped to save countless lives and minimize
property damage.

32. Building Flood Resilience through Prevention
 Mitigation
 Insurance (more developed)
 Disaster aid (less developed)
 Protection
 Flood abatement
 Flood control (levees, flood control dams)
 Adaptation
 Land use planning
 Preparedness
 Forecasting and warning

33. Disaster Risk Reduction: Mitigating the Effects of
Flood Disasters
Disaster risk reduction is a critical component of building flood resilience. By
identifying and addressing potential risks before a disaster strikes, communities
can minimize the impact of flood disasters on their infrastructure and residents.
One key strategy for disaster risk reduction is Community-based Disaster Risk
Reduction, which involves working with local communities to identify and address
their unique vulnerabilities to flood disasters. This can include measures such as
improving drainage systems, reinforcing buildings, and developing evacuation
plans.

34. Disaster Risk Reduction: Mitigating the Effects of
Flood Disasters
Another important strategy for disaster risk reduction is early warning systems.
These systems use advanced technology to detect potential flooding and issue
warnings to residents in affected areas. By providing early warning, residents
have more time to prepare and evacuate if necessary, reducing the risk of injury
or loss of life. Emergency preparedness is also crucial for disaster risk
reduction, as it allows communities to respond quickly and effectively to flood
disasters. This can include training emergency responders, stockpiling
supplies, and developing response plans.

35. Flood Resilience in Action: Success Stories
● In Bangladesh, the community of Char Montola has implemented a successful
flood prevention strategy by creating raised platforms for their homes and
livestock. This has allowed them to avoid flooding during monsoon season and
protect their livelihoods. The community also participates in early warning
systems and evacuation drills to ensure their safety.

36. Flood Resilience in Action: Success Stories
The city of Miami Beach, Florida has taken a proactive approach to flood resilience by
implementing a comprehensive stormwater management plan. This includes installing
pumps and raising roads to prevent flooding during high tides and heavy rain. The city
also encourages green infrastructure, such as rain gardens and bioswales, to absorb
excess water and reduce runoff

37. Flood and Coastal Resilience Innovation Programme
25 local projects demonstrating how practical innovative actions can improve
resilience to flooding and coastal erosion in a changing climate
Action for Silk Stream Project Intro.mp4

38. Nature Based Solutions

39. The Importance of Flood Resilience
● In conclusion, we have seen the devastating impact of flood disasters on
communities and infrastructure. We have discussed the factors that contribute to
vulnerability and the importance of prevention and early warning systems in
building flood resilience. We have also explored disaster risk reduction strategies
and showcased success stories of flood resilience in action.

40. The Importance of Flood Resilience
● It is clear that building flood resilience is crucial for the safety and well-being of our
communities. We must take action to implement effective prevention measures,
employ disaster risk reduction strategies, and build strong, resilient communities.
By doing so, we can ensure that our communities are better prepared to withstand
the destructive forces of flood disasters.