Flood Mitigation Strategies

1. Mitigating the Impact of Flood on
Road Infrastructures in Nigeria
Prof. Adelere E. Adeniran, FNSE
Delivered at the
2nd Memorial Lecture
In honour of
Engr. (Chief) S. O. Fadahunsi, FNSE, CON
August 12, 2020

2. Protocol
• President, NSE
• The Honouree – Late Engr. (Chief) S. O. Fadahunsi, FNSE, CON
• Past Presidents, NSE
• National Executive Members, NSE
• Chairman, Board of Trustees NIEE, Engr. Bola Olowe, FNSE, FNIEE
• Chairman, Board of Fellows NIEE, Engr. Osodi, FNSE, FNIEE
• National Chairman, NIEE
• Past Chairmen, NIEE
• Chairmen of other Divisions of NSE
• Fellows of NSE
• Fellows of NIEE
• Members of NSE
• Members of NIEE
• Gentlemen of the Press
• Distinguished Ladies and Gentlemen

3. Preamble
• I am highly honoured to the invited by NIEE to join one of
the foremost Engineers in Nigeria, my very good friend
Engr. Kasim Ali, FNSE, mni in delivering the second in the
series of annual lectures in the memory of our late father
and mentor, Engr. (Chief) Samuel Olatunde Fadahunsi,
FNSE, CON
• Pairing me with Engr. Kasim Ali, FNSE, FNAEng, mni who was
President of NSE and later President of COREN is like
putting the 6’’ Lilliputian with the 72’ Gargantuan in
Jonathan Swift's “Gulliver’s Travel”!
• Engr. Bola Olowe, FNSE delivered the first in this lecture
series last year (Physically), I want to thank the NIEE for
the opportunity to follow after these giants of
Environmental Engineering.

4. Theme
The Impact of Flooding on the Sustainability of
roads in Nigeria
I will briefly address
Mitigating the Impact of Flood on Road Infrastructures
in Nigeria

5. Introduction
• Flood events are a part of nature.
• They have existed and will continue to exist.
• There is flooding anytime a body of water
rises to cover what is usually dry land
• Flood is one of most common hazards
– 75% of the Global declared disasters (5th in World
Bank Disaster Rating)
• It may be local or widespread
• It may develop slowly or fast

6. WORLD BANK DISASTER RISKS RATING
FIRES
HURRICANES
VOLCANOES
FLOODS
ENVIRONMENTAL IMPACTS
GLOBAL CLIMATE CHANGE
DEVELOP POLICIES FOR
ACTIONS HAVING HIGH
BENEFIT/COST FOR THE
CARIBBEAN REGION
GOAL: REDUCE DISASTER
RISK
LANDSLIDES
EARTHQUAKES
MEDICAL EMERGENCIES
Source: Primer Series by the Global Alliance for Disaster Reduction

7. Introduction Cont’d
• Flooding and its effects usually result in colossal
loses to lives and properties
• It has very huge traumatic and negative:
– physical,
– Social,
– Psychological and
– economic impacts.
• This lecture will, therefore, focus on mitigating
the impact of flooding in general and on road
infrastructures in particular.

8. Flood: The Good
• Floods are natural phenomena, which have
helped to shape natural landscapes, habitats and
ecosystems in floodplains, wetlands and other
lowlands.
• They are the reason for the rich deposit of
nutrients on flood plains (Paddy farming – Akuro)
• The Flood Plain of River Niger at the Niger Delta is
the source of wealth of Nigeria
• Floods are impossible to prevent altogether,
although measures may be taken to reduce their
frequency and the damage they cause.

9. Flood: The Bad
• Floods can turn into disasters causing widespread
damage, health problems and casualties.
• This is especially the case :
– where rivers have been cut off from their natural
floodplains
– where rivers are confined to man-made channels
– where houses and industrial sites have been
constructed in areas that are naturally liable to
flooding (the flood plain). As in the case of Ibadan
and many Nigerian cities

10. Causes of Floods and Flood Damage
• Heavy rain
• Dam and levee failure
• Low absorption or no soil percolation
• Deforestation
• Unplanned Urban Growth
• Development in flood areas
• Non-Development/Improvement to Inland
waterways

11. Urbanization and Flooding

12. Case Study: Ibadan

13. Types of flooding in road networks
• If there is insufficient capacity or no provision
for drainage system, water collects on the
surface of the road with damaging effect.
• Roads may be flooded because there is
insufficient downstream capacity of the
draining system (solid waste blockage) and
the roads are submerged.
• Low sea level causes flooding of low-lying
areas.

14. Importance of Road
• Road is an index of development
• Roads are the major medium of
transportation
• Roads are used to bring good from the
location of production to the location of
consumption
• Provision of roads leads to economic and
social development
• Etc, etc.

15. Map of Federal Road Network of Nigeria
Source: Highways Department, FMW Nigeria (2015)

16. Some Facts on Nigerian Roads
Category Length (Km) % of Total
Paved Express Road 1,194 0.61
Paved Highways 58,874 30.29
Unpaved Roads 134,326 69.10
Estimated Total (1998) 194,394 100.00
NOTE
• Many paved roads have lost their asphalt surface and are in very
poor condition or have reverted to being gravel roads.
• Many of the roads are barely usable, especially in high rainfall
areas of the south.
Source: Highways Department, FMW Nigeria (2015)

17. Huge Investment in Road Infrastructures
• Development of road
infrastructure is
expensive
• Huge Annual
Budgetary Allocations
and
• Ever increasing
expenditure on road
infrastructures in
geometrical jumps
2020 Approved Budget Allocation
Source: Fed. Min. of Finance – 2020 Budget Analysis

18. Contracts Sum for Nigerian Road Development from 2009-2017

19. Flood can wash away all these investments!

20. Impact of Flooding on Roads
• The impacts can be divided into direct and
indirect ones.
Direct impacts include the costs of reconstruction of
damaged roads and the reconstruction of landslide
areas or adjustment of erosion banks.
Indirect impacts entail the costs of interruption and
logistics disruptions. Waste of Man hours in going
through the detours and diversions.
 The inaccessibility of inundated roads during emergency
management activities could cause indirect damage to the
operability of strategic structures, such as hospitals, schools and
fire stations .

21. Effects of Floods on Roads
• Flooding in a road network can have the following
effects
Water that collects on the road because of the failure of
flood defenses leads to traffic stagnation or, if the water
reaches a certain depth, traffic stoppage.
 High water levels on the road or on the sides of the road
construction can lead to loss of bearing capacity for the
short and long term after flooding.
Intense rainfall can increase flooding and instability of the
road foundation.
Extreme rainfall and flooding are known to have damaged
bridges and culverts
The appearance of water on roads during heavy rain can
lead to road closures and safety problems for vehicles.

22. Effects of Floods on Roads
Floods:
• Damage and destroy buildings, bridges, dams,
embankments, drains, roads, railways etc Destroy farms,
food and cash crops
• Make the individual, communities and nations poor
through disruption of services and the degradation of
agriculture land
• Destroy human life, animal’s life and properties,
• Degrade the environment,
• Spread infestations; soil and water are polluted by
chemicals.
• Cause soil infertility through leaching and erosion of rich
top soil.

23. 23
Flood Damages
• Injuries and loss of life
• Social disruption
• Income loss and Emergency
costs
• Physical damage
– Structures, utilities, autos,
crops, etc.
• Lost value of public services
– Police & power poles, water
mains, hospitals, etc
Damaged PHCN and Water at Apete, Ibadan
Bridge Washed away: Emergency Foot Bridge improvised

24. Effects of Floods

25. Effects of Floods

26. 26
Homelessness and Losses

27. 27
Colossal Lost of Properties

28. 28
Discomfort and Fear

29. Effects of Floods

30. Effects of Floods

31. Effects of Floods

32. Road Sustainability Mitigating Strategies
• Nigeria has a comprehensive set of road
construction standards, but these standards are
not strictly adhere to by some states and the Local
Government Areas. This should not be so.
• Road planning and design in Nigeria should is
based on international best practices and
guidelines.
• Road planning and design should take into account
the local flood flow patterns. It should focuses on
the Nation’s floodplain hydraulics and related
ecology.

33. Road Sustainability Mitigating Strategies cont’d
• Hydraulic structures including well designed drains should
not only form part of the design but must be provided for
during construction.
• Nigeria has an Environmental Impact Assessment system in
place, although experience in its application is limited.
• The enforcement of EIA for road infrastructure is sacrosanct
for sustainability.
• The huge financial commitment of the Federal Government
on road development support the need for better guidance
on integrated planning and design of roads.

34. Road Sustainability Mitigating Strategies cont’d
• For Example, if road embankments and flow structures are properly
designed, there will be limited impact on the flood levels (water
height) and the corresponding damage mechanisms (macro-
instability, waves, overtopping).
• For example embankments should not be too steep and measures
to intercept waves should be incorporated into designs.
• Hydraulic structure should be designed to reduce flow velocities to
an acceptable level by increasing the number of flow through
structures.
• Properly designed protection, together with streamlined
abutments, is a cheaper option and very often the best way to
provide protection or at least to minimize the damage

35. Conclusion

36. Adoption of Conceptual Framework for Road Design and
Planning for Flood Prone Zones
• The integration of road planning and
design and flood risk management
plays a crucial role in developing
efficient and sustainable road
networks for the mitigation of the
effect of floods
• The Figure here presents a
framework for integrated analysis of
road planning and design.
• The figure shows the relation
between road development design
and planning (A) and the various
effects (B), which are linked to the
use of standards and guidelines (C).
• In road development and planning, all
effects should be taken into account
through the use of economically
sound and environmentally friendly
guidelines for the planning and
construction of roads in the country.
Source: World Bank – Flood Risks on Road Network