Hydrology for Disaster Management

Special Publication of the Nigerian Association of Hydrological Sciences, 2012

http://www.unaab.edu.ng

Flood Management in an Urban Setting: A Case Study of Ibadan Metropolis

1*
Ajayi O., 2Agbola S. B, 3Olokesusi B. F., 4Wahab B., 5Taiwo O. J., 6Gbadegesin M., 7Taiwo D.
O., 8Kolawole O., 9Muili A., 10Adeola M. A., 11Olutade O. G., 12Shiji F. and 13 Abiola N. A.
1
Department of Geology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.
2
Department of Urban and Regional Planning, University of Ibadan, P. O. Box 22182,U. I. Post Office, Ibadan,
Oyo State, Nigeria.
3
Director Policy Engagement and ICT, Nigerian Institute of Social and Economic Research
U. I. P. O. Box 5, Ibadan, Oyo State, Nigeria.
4
Department of Urban and Regional Planning, University of Ibadan, P. O. Box 22182, U. I. Post Office, Ibadan,
Oyo State, Nigeria.
5
Department of Geography, University of Ibadan, P. O. Box 22182, U. I. Post Office, Ibadan, Oyo State, Nigeria,
6
Honourable Commissioner for Health, Ministry of Health, Oyo State Secretariat, Agodi, Ibadan, Oyo State,
Nigeria.
7
c/o Ministry of Physical and Urban Planning, Oyo State Secretariat, Agodi, Ibadan, Oyo State, Nigeria.
8
Ministry of Works and Transport, Highways Department, Oyo State Secretariat, Agodi, Ibadan, Oyo State,
Nigeria.
9
Director of Works, Works Department, Olorunsogo Local Government Council, Igbeti, Oyo State, Nigeria.
10
Ministry of Environment and Habitat, Oyo State Secretariat, Agodi, Ibadan, Oyo State, Nigeria.
11 12
Ministry of Physical Planning, Oyo State Secretariat, Agodi, Ibadan, Oyo State, Nigeria. Divisional Police
Headquarters, Iresa-Adu, Oyo State, Nigeria.
13
Ministry of Justice, Oyo State Secretariat, Agodi, Ibadan, Oyo State, Nigeria.
*
Corresponding author: E-mail - owolabi_ajayi@yahoo.com

Abstract
This paper revisits flooding problems in Ibadan Metropolis, in the past fifty years, especially the most recent
flood of August 2011. Flood disasters can be attributed to the unnecessary risks people take when they
encroach on flood plains. There will be no flood disasters if human beings stayed away from the flood plains.
The methodology adopted for the flood investigations includes site visits, interviews of affected inhabitants,
and analyses of flood data collected during the field investigations. These investigations were complemented
with review of past records of flooding, and interpretation of satellite imagery of flood affected areas,
especially for inaccessible areas, to produce flood hazard maps.
Results of the spatial analysis of flooding in the 11 local government areas of Ibadan indicate that 26,553
buildings were constructed within the statutory set back to the rivers and streams while 2,105 were flooded.
Large scale encroachment into the river floodplains was observed throughout the area. The major cause of
flooding in Ibadan Metropolis is due to uncontrolled urbanization of the area.
The Nigerian Meteorological Agency (NIMET) predicted that there will be very heavy rains and flooding in a
number of states in Nigeria in 2012. In Oyo State, Ibadan is specifically mentioned as a city to experience
flooding. This emphasises the urgent need to put in place measures to facilitate effective management of the
anticipated floods to prevent the re-occurrence of the damage and losses of the 2011 disaster.

Key words: Hydrology, Urban Floods, Flood Mapping, Flood Insurance, Flood Management, Emergency
Response, Waste Management

Introduction
Hydrology and Floods
Water covers over seventy percent of the surface of the earth. Hydrology is the study of the
occurrence, distribution, movement, and properties of water on the earth and their

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interrelationships with the environment, as well as investigations for water on other

planets. Water is fundamentally one of the most important natural resources on earth.
Certainly, without water, life as we know it will not exist. The search for extra-terrestrial life
is essentially the search for water on other planets. The science of hydrology enables us to
understand the complex water systems of the earth and to solve problems associated with
water. Hydrologists are scientists who play a crucial role in finding solutions to water
problems.
The framework for the study of water on earth is the hydrologic cycle. The hydrologic cycle
(Figure 1) is the continuous process by which water is transported from the surface of the
earth (including the oceans, lakes, rivers and wetlands) to the atmosphere and back to the
land in an endless cycle. The hydrologist studies the fundamental transport processes to
describe the quantity and quality of water as it moves through the hydrologic cycle.
Converting the natural forests of rural land to urban land in cities or their periphery usually
increases the runoff from rivers and streams and creates erosion problems. Urbanization
changes the response of a hydrological basin or watershed to precipitation. Urbanization
decreases the natural vegetative cover which promotes infiltration at the expense of
sediment loss and surface runoff. It also increases impervious surfaces, such as roads,
paved surfaces (parking lots) and buildings. The natural flow paths of the stream may be
altered or replaced by artificial storm drains as a result of urban development.
Other problems associated with urbanization, apart from flooding, include negative impacts
on surface water and groundwater quality, as well as increased rate of sedimentation in
impoundments and surface storage reservoirs, such as dams. The delicate balance of the
hydrologic cycle could be so affected to the point of climate change, either locally or on a
regional scale.
The science of hydrology permits the understanding and management of floods to prevent
avoidable disasters, assuming that underlying principles of hydrology are properly
understood and the requisite mitigating measures are implemented in urban planning,
design and construction. Unfortunately, the fate of most urban settings all over the world,
especially those located in flood prone areas; indicate that the lessons from urban hydrology
are not taken too seriously. Hence, flooding of catastrophic proportions is reported on a
regular basis. The metropolis of Ibadan is not an exception as it has witnessed several
devastating floods, occurring almost on an annual basis, in its recent history, especially since
1951, due to rapid and uncontrolled urbanization of the metropolis.
This paper revisits the flooding problems in Ibadan Metropolis, in the past fifty years,
especially the most recent flood of August 2011. The authors investigated the remote and
immediate causes of the recurrent floods in Ibadan Metropolis, as members of a Special
Task Force set up by the Government of Oyo State, for the purpose of, among other things,
assessing causes and effects and recommending measures necessary for effective flood
management in Oyo State.

Vulnerability of Urban Settlements to Flooding

Flooding is caused by several factors and is invariably preceded by heavy rainfall. The other
causes of flooding are moderate to severe winds over water, unusual high tides, tsunamis
due to undersea earthquakes, breaks or failures of dams, levees, retention ponds or lakes,
or other infrastructure that retains surface water. Flooding can be aggravated by impervious

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surfaces or by other natural and man-made hazards which destroy soil and vegetation that
can absorb rainfall.
After any rainfall, some of the water is retained on the soil and may form ponds. Some of
the water infiltrates into the soil, some evaporates, and any excess water moves along the
land surface as surface runoff. Flooding occurs when the soil, stream channels and man-
made reservoirs cannot absorb or contain all the water. A flood that occurs suddenly, with
little or no prior signs, is called a flash flood and is due to intense rainfall over a relatively
small area.
Flooding is inevitable, resulting from the natural rainfall-runoff process. Flooding is a natural
phenomenon and the magnitude of floods is periodic. The periodicity of floods implies that
every year some area surrounding the river (on both sides) is flooded. Every other period,
(two, five, ten, fifty, one hundred and even a thousand years) is associated with increasing
areas around the river which gets inundated. Areas inundated by floods adjacent to the river
or stream are known as flood plains. Flood occurrences may be due to natural or
anthropogenic (man-made) factors.
In a study of the flooding problems in Lagos State, Adeloye and Rustum (2011) indicated
that climate change is not the culprit but anthropogenic factors The investigation revealed
that, contrary to popular wisdom, climate change or unusually high rainfall is not the
primary cause of the flooding problems in Lagos. Rather, increased urbanisation, lax
planning laws in relation to the erection of buildings in flood plains and the inadequacy of
storm drainage facilities in the city are to blame .
Man does not have much control over the natural causes of floods, such as the magnitude
and frequency of rainfall (and associated floods), except perhaps to avoid encroachment
into the natural flood plains to prevent flood disaster. However man has total control over
the anthropogenic causes of floods, such as limiting construction or development on
natural flood plains, eliminating blockages from the natural flood plains to allow free
passage of flood water and increasing the capacity of hydraulic conveyance structures to
conveniently carry flood flows. Conventional wisdom dictates that man should stay away
from flood plains or appreciate the RISKS associated with encroaching on the flood plain.
Flood disasters are associated with the unnecessary risks people take when they encroach
on the flood plains. There will be no flood disasters if human beings stay away from the
flood plain.

Physical Setting
Location
Ibadan is located in south-western Nigeria and is the capital of Oyo State. Ibadan is centred
about latitude 7o 25’ North and longitude 3o 5’ East (Figure 2) and is located approximately
145 km north of Lagos. It is situated close to the boundary between forest and grassland,
which makes it a melting point for people and products of both the forests and grassland
areas. Ibadan is regarded as the largest indigenous city in tropical Africa.
Since its founding in the 1800s, Ibadan has played a prominent role for people living in the
south-west of Nigeria. It was the capital of the old Western Region, when Nigeria had only
three regions. The territory of the old Western Region has since been divided into seven
states and a sizeable part of the present Lagos State belonged to the old Western Region.
Ibadan hosts the premier university in Nigeria (The University of Ibadan) which was

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established as a College of the University of London in 1948. As a result of these historical

antecedents, Ibadan has continuously witnessed influx of people which has contributed to
its rapid growth both in population and physical expansion to cover a very large land mass.
In terms of demographic growth, Ibadan experienced geometrical increase in population
between 1851 and 1921. By 1856 the population was estimated at 60,000 (Hinderer, 1856)
which rose to over 200,000 in 1890 (Millson, 1891), 238,094 in 1921, and 386,359 in 1931
(Mabogunje, 1962). The 1991 census in Nigeria put the population at 1,222,570 (Ayeni,
1994) with a density of 475.11 persons per square kilometre. Its population is estimated to
be about 2,550,593 according to 2006 estimates by the National Population Commission. Its
projected population by 2010, using 3.2% growth rate, is about 2,893,137 (Table 1).
In terms of physical expansion and land coverage, this pre-colonial urban centre has
expanded very fast sprawling daily into the hinterland. Fabiyi (2006) noted that developed
land in Ibadan increased from only 100 ha in 1830 to 12 km2 in 1931, 30 km2 in 1963,
112 km2 in 1973, 136 km2 in 1981 and 214 km2 in 1988 (Table 2). An aerial photograph in
1964 showed that the city had spread beyond the drainage basins of Ogunpa and Kudeti and
to the catchment area of Ogbere stream in the east (Figure 2). Today the city spread has
extended to Odo-Ona Kekere village in the south to Iroko/Motunde villages in the north,
Asejire in the east and Bakatari in the West (Central Council of Ibadan Indigenes, 2011).

Relief and Drainage

Ibadan lies mostly on lowlands which are punctuated by rocky outcrops and series of hills.
These outcrops are mainly granitic. Three major landforms of hills, plains and river valleys
dominate the whole landscape of the region. The average elevation is 230 m above mean
sea level. The metropolis is drained by three important rivers, R. Ogunpa, R. Ona and R.
Ogbere (Figure 3) and their several tributaries including Omi, Kudeti, Alaro and Alapata.
This combination of hills and river valleys provide a good drainage for the city but it has
suffered a lot of abuse due to blockages of the water courses by solid wastes coupled with
the construction of structures along the river courses and sometimes right within the river
course itself. These practices constitute the major reasons for the incessant flooding as
occasioned by the recent flood disaster on the night of 26th August 2011.
The metropolis is drained by three important rivers, R. Ogunpa, R. Ona and R. Ogbere. There
are several tributaries of these rivers. The major tributary of R. Ogunpa is the R. Kudeti, both
of them drain the eastern part of Ibadan. The western part of the city, which consists of
more recent residential and other developments, is drained by the R. Ona and its numerous
tributaries, including the Alalubosa, Oshun and Yemoja streams.

Climate and Vegetation

Oyo State exhibits the typical West African Monsoon climate marked by distinct seasonal
shifts in wind patterns. Between March and October, the city is under the influence of moist
maritime south-west monsoon winds which blow inland from the Atlantic Ocean, marking
the rainy season. The dry season occurs from November to February when the dry dust-
laden winds blow from the Sahara desert. The area experiences high relative humidity and
generally two rainfall maxima regimes during the rainfall period of March to October. The
mean temperatures are highest at the end of the Harmattan (averaging 28°C), that is from
the middle of January to the onset of the rains in the middle of March. Even during the

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rainfall months, average temperatures are relatively high, between 24°C and 25°C, while
annual fluctuation of temperature is about 6°C.
Most areas of Ibadan are covered by the rain forest and derived savannah. Growth and
development have, however, led to significant loss of vegetation. The wetlands are
threatened by urban expansion into the wetlands and rural areas. The thick, low-lying
forests are prone to flooding as observed in areas like Ajibode, National Institute for
Horticultural Research (NIHORT) and Oke Ayo along the course of River Ona.

Geology and Soils

Ibadan is underlain by basement complex rocks which are mainly metamorphic rocks of
Precambrian age with granite, quartzite and migmatite as the major rock types. The minor
rock types include pegmatite, aplite and diorite.
The soils of Ibadan region were formed from the underlying rocks especially granite gneisse,
quartz-schist, biotite gneisse and schist. They were formed under moist semi-deciduous
forest cover and belong to the major soil group called ferruginous soils (Hopkins, 1965;
D’Hoore, 1964). Aweto (1994) identified four main soil associations in Ibadan region on the
basis of soil parent materials as the Iwo, Okemesi, Egbeda and Mamu soil associations. The
soils of the Iwo association were formed from coarse grained granites and gneisses and
those of Okemesi from gneisses, schist and quartzites. Those of Egbeda and Mamu were
formed from fine grained biotite and schist, and from sericite schists respectively.

Methodology
The methodology adopted for the flood investigations includes site visits for physical
inspection of the affected areas; interviews of affected inhabitants, review of past reports
and records of flooding in the area; and analyses of flood data collected during the
investigations.
During the fieldwork component of the investigation, apart from the physical inspection of
damaged structures and infrastructures, the team demarcated flooded areas and
determined depths of flooding. This flood plain mapping in the field was complemented
with analysis and interpretation of satellite imagery of the flood affected areas, especially
for inaccessible areas, to produce a flood hazard map.
The records and reports of past floods in the metropolis were reviewed as part of the
present exercise. Data were collected on climate, drainage infrastructures, physical
planning, and applicable laws and regulations for flood control in Ibadan metropolis.

Discussion of Results
History of Flooding in Ibadan Metropolis
Ibadan has recorded varying degrees of flooding. For instance, there were flooding in the
watersheds of Ogunpa and Kudeti streams (one of the two major streams in Ibadan) in
1955, 1960, 1961, 1963, 1969, 1978 and 1980. The flooding of 1969 is unique because it
resulted from a mere 25.4 mm rainfall (Akintola, 1981). An accurate assessment of the
havoc caused by floods in Ibadan over the years is difficult to obtain (CBN, 1999). However,
a number of official estimations have been made at different points. For instance, the losses
arising from the flood disaster of August 1980 in Ibadan were estimated at N300.0 million
while the number of lives lost was put at 500 people (Akintola, 1994). Between 1995 and

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1998, over 12 million Naira, were estimated to have been lost to floods in Ibadan (NEMA,
undated). Table 3 shows the history of the most recent thirteen flood events in Ibadan.
The rain gauge at the IITA recorded an all time high of 187.5mm rainfall on August 26, 2011
which started at 16.40 hr until 20.00 hr with intermittent drizzling until 23.00 hr
accompanied by wind speed as high as 65 km/hr. IITA reported that the rainfall was most
intense between 18.10 hr and 19.20 hr when 75% or 140.63 mm of the rain fell. This is an
average rainfall intensity of 127.84/hr (National Water Resources Institute, 2011).

Natural and Anthropogenic Causes of Floods in Ibadan

The causes of flooding in Ibadan have been well documented by past studies. Flood
problems in Ibadan have been attributed to land use factors. Notable among these land use
factors is the relentless construction of buildings along flood plains. By the early 1960s, the
floodplain settlement along the Ogunpa and Kudeti river channels was almost completed,
such that the mean distance of buildings along Ogunpa river valley is a mere eleven metres
to the river bank, whereas the mean distance of floodable land is to the rivers is over ninety
metres (Akintola 1994). Plates 1 - 4 illustrate such development within the flood plain in
proximity to the river. This practice aids flooding in Ibadan metropolis and has continued up
to the recent time.
Deforestation has been identified as another contributing factor to the flooding problem in
Ibadan. Some areas, such as Agala (Agala forests), were deliberately preserved in Ibadan
under teak and cassia forests during the colonial period. These were mainly the hills in and
around Ibadan. The preserved areas, referred to as catchment areas, were supposed to
catch and store some water temporarily during rainfall (Akintola, 1994). The destruction of
these forests has aided flooding in Ibadan Metropolis due to the reduction in the infiltration
and retention capacity of these areas. This was confirmed by Akintola (1994) in a study on
infiltration process in Ibadan city which indicated varying rates or capacities for different
types of urban land-use surfaces. The changes in imperviousness of the metropolis from
1965 to 1994 are shown in Table 4.
In general, open surfaces heavily trampled upon by vehicles, human beings and animals
have lower infiltration rates than vegetated surfaces, and thus generate higher excess water
(runoff) during rainfall. By implication, the large network of paved/tarred roads and several
paved surfaces in Ibadan have contributed to the loss of infiltration capacity. The corollary
of this finding is that almost all the rain water is released into river channels at the same
time, thus leading to floods.

Conclusion
The study found out that the major cause of flooding in Ibadan Metropolis is uncontrolled
urbanization of the area, such that some of the houses are built during the dry season on
what constitutes the river bed itself. Large scale encroachment into the river floodplains was
observed throughout the area. Most of the culverts, bridges and other hydraulic structures
which were designed and constructed several years ago are no longer adequate to convey
the present runoff arising from increased urbanization of Ibadan Metropolis. The excessive
siltation of the rivers and stream beds has tended to reduce the carrying capacity of these
hydraulic conveyance structures.

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Indiscriminate dumping of refuse and solid wastes is a major problem constituting blockage
of river courses, stream channels and artificial drainage channels. The problem of improper
waste management must be solved to eliminate this cause of flooding.
It was discovered that the upper part of Ogunpa River had been heavily silted from Ashi area
through to the Agodi Gardens Reservoir/Lake which was reportedly dredged last in 2008.
The silting of the river had led to blockage of the concrete culverts built across the river all
along its course. Channelization of the rivers within the city has not been completed and the
completed portions are not well maintained to be free of obstructions.
Ibadan Metropolis has, for a long time, suffered varying degrees of flood disasters with
extremely high externalities due to an array of factors, the most prominent of which could
be attributed to human behaviour. The rainfall of the 26 th August 2011 and associated flood
disaster was very devastating based on the level of social, economic and ecological
destruction, therefore requiring concerted and decisive actions to prevent future re-
occurrence. Conventional wisdom dictates that humans should stay away from flood plains
or appreciate the RISKS associated with encroaching on the flood plain. Flood disasters are
associated with the unnecessary risks people take when they encroach on the flood plains.
There will be no flood disasters if human beings stay away from the flood plain and stop
dumping solid wastes in stream and river channels. Furthermore, the floods will not go away
and their impacts and severity will increase in the future if corrective steps are not taken.

Recommendations
The Nigerian Meteorological Agency (NIMET) has predicted that there will be very heavy
rains and flooding in a number of states in Nigeria in 2012. In Oyo State, Ibadan is
specifically mentioned as a city to experience flooding. This emphasises the urgent need to
put in place measures to facilitate effective management of the anticipated floods to
prevent the re-occurrence of the damage and losses of the 2011 disaster.
Arising from this study, based on the findings in the field, as well as the need to protect the
environment, the human population and livelihoods from unmitigated flood disasters in
future, the following recommendations are hereby suggested:
1. Create public awareness and sensitization on the real dangers of flirting with
floodplains.
2. Government must enforce compliance with physical planning and development
regulations within Ibadan Metropolis. There should be immediate stoppage of all
kinds of development in all flood prone areas in the 11 LGAs in Ibadan region.
3. Strictly enforce the provisions of the relevant sections of the Oyo State Solid Waste
Management Authority Law, (Oyo State of Nigeria, 2008), especially Schedule B (xiv)
as it affects construction or placement of structures on roadside and public drainage
channels or pedestrian walkways by shop operators.
4. Review existing laws and regulations on delimitation of set-backs to conform to the
natural flood plain of the rivers.
5. Government should ensure that drains, gutters and surface water bodies are de-
silted throughout Ibadan metropolis to allow for the free flow of urban storm water
and runoff. This should be an on-going programme.
6. Government should embark on immediate reconstruction of damaged culverts,
bridges and other hydraulic structures, especially in flood ravaged areas.

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7. All the major rivers and their tributaries must be de-silted and dredged prior to the
onset of the rainy season. This should be an on-going programme.
8. Review existing laws on streams and river set-backs to accommodate the natural
extent of river flood plains of the streams and rivers for flood control, in view of
urbanization.
9. Government should embark on the preparation of a Master (Development Plan) for
Ibadan Metropolis taking into consideration the use of flood prone areas within
stream/river setbacks for:
a. Urban and peri-urban agriculture;
b. Recreation;
c. Wildlife and Ecosystem Conservation; and
d. Intra-city water transportation (boating on Rivers Ona and Ogunpa).
10. Study the road network in Ibadan and provide alternative routes to communities
prone to flooding, especially for those with only one access road linking them with
nearby communities.
11. Government should adopt Public-Private-Partnership strategy in waste management
and assist the Private Refuse Contractors to improve waste collection and disposal
throughout Ibadan Metropolis.
12. One of the most potent preventive measures against flooding is vegetation.
Government should adopt a policy of “Greening” the Ibadan Metropolis through
planting of trees, shrubs and ornamental plants. This will reduce runoff hence
flooding, preserve soil moisture and reduce the rate of atmospheric warming.
13. Government should establish an Environmental Monitoring System within the
context of an Environmental Management Information System (EMIS) pioneered by
the Sustainable Ibadan Project (SIP), to provide real-time data for environmental
planning and flood forecasting.
14. In order to minimize losses arising from flood disasters, government should
collaborate with stakeholders such as the Nigerian Insurance Association (NIA) and
National Insurance Commission (NAICOM) amongst others, to design and promote a
State-wide Flood Insurance Programme. This is the practice and requirements for
development in flood prone areas in Canada, France and the United States. In
Nigeria, there is also an extant legislation on compulsory acquisition of Property
Insurance. Implementation of this programme would reduce the compensation
payable by government when disasters occur in future.
15. Complete the River Ogunpa Channelization Project and also channelize the major
streams and rivers, and construct embankments along the main river channels to
reduce flooding. This should be an on-going programme or initiative.
16. Government should establish sustainable integrated flood management and
emergency response system.
17. Identify and relocate all permanent structures, within the natural flood plain (50 and
100 years) of the streams and rivers, outside the natural flood plain of the streams
and rivers, in line with international best practices for flood prone areas.
18. Prepare a Flood Emergency Management Plan for Ibadan Metropolis as a matter of
urgency.

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19. Government should equip appropriate agencies with human and material resources
for Emergency Response to flooding and other natural disasters.
20. The preceding recommendations will require an appropriate institutional framework
for effective implementation. At present, the agencies that will implement the
recommendations contained in this study are scattered throughout the government
structure. It may be necessary to establish an Inter-Ministerial Implementation
Committee or create a Public-Private Partnership Framework for implementation
and sustainability of the flood management ideals presented here.

Acknowledgement
The authors of this paper, who were appointed into the Oyo State Task Force on Flood
Prevention and Management, by His Excellency, the Executive Governor of Oyo State,
Senator Ishaq Abiola Ajimobi, wish to acknowledge persons and organisations that funded
or facilitated the collection of data presented in this paper.
First and foremost, we thank the Executive Governor of Oyo State, His Excellency, Senator
Ishaq Abiola Ajimobi, for appointing us into the Task Force and for providing funds, as well
as the political and logistic support in carrying out the assessment on Flood Prevention and
Management arising from the flooding which ravaged Ibadan City on 26 th August 2011. We
thank the Deputy Governor, His Excellency, Chief Moses Adeyemo, the Secretary to the
State Government, Alhaji Waheed Olajide and other members of the State Executive
Council, especially the Commissioner for Physical Planning and Urban Development, Ms
Kafayat Adeojo, the Commissioner for Works and Transport, Alhaji Yunus Akintunde, the
Commissioner for Justice, Barrister Adebayo Ojo, and the Commissioner for Finance, Mr.
Zacheaus Adelabu Adedeji, for their various support and commitment to the task of Flood
Prevention and Management in Ibadan Metropolis.
We also wish to thank Professor Ademola Ariyo of the Department of Economics, University
of Ibadan, who is the Vice Chairman of the Oyo State Economic Management Team, for
initiating the ideas that led to the flood assessment project, the composition of Task Force
members and for sharing his expertise with the Team throughout the two-and-a-half
months that the assignment lasted. We appreciate the Commissioner of Police of Oyo State
for releasing his officers and men to provide security for members of the Task Force during
the field work to the various sites affected by the flooding. We appreciate the support given
by the Directors of the eleven (11) Local Planning Authorities namely: Tpls. Opasina,
Akinlabi, Ogunjimi, Olutade, Kareem, Sangodoyin, Amodeni, Adisa, Apampa and Olofa, as
well as their Technical staff, who participated actively in the laborious field survey to
demarcate the extent of the flooded areas, within a short period of three weeks. We thank
Tpl. Adeyemi, Tpl. S. B. Taiwo, Tpl. Dayo Ayorinde, Messrs Oyeniyi, Adeleke, Akande and
Ilori, all of the Ministry of Physical Planning and Urban Development for supervising the field
assistants.
We sincerely appreciate the efforts of the 20 Postgraduate Students of GIS and the 13
Undergraduate Students from the Department of Urban and Regional Planning, University
of Ibadan, in data collection, analysis and the subsequent production of maps of the 11 LGAs
showing the flooded buildings based on the coordinates recorded in the field using
Geographical Positioning System (GPS) equipment. We thank Mr. S. K. Ojolowo of the
Department of Urban and Regional Planning, University of Ibadan, for his participation in

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the field work and preparation of maps and production of report. We are also very grateful
to the Departments of Geology, Geography, and Urban and Regional Planning, University of
Ibadan, for hiring out some of the GPS used for the field work.

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M.O. et al. (eds.) Ibadan Region Chapter 7, pp. 72-84. Rex Charles Publishers,
Nigeria.
CBN, (1999). Urbanization and related socio-economic problems in Ibadan Area, Research
Department Occasional Paper No. 25, 80 pp.
Central Council of Ibadan Indigenes (CCII) (2011). Blue print on the physical development for
Ibadan Metropolitan area. Paper submitted to the Oyo State Government, July.
D’Hoore, L.J. (1964). Soil Map of Africa. CTA, Lagos.
Fabiyi , O. O. (2006). Urban Land Use Change Analysis of a Traditional City from Remote
Sensing Data: The Case of Ibadan Metropolitan Area, Nigeria. Humanity & Social
Sciences Journal, 1 (1): 42-64.
Fourchard, 2003. The Case of Ibadan, Nigeria, Institut Francais de Recherche en Afrique
(IFRA), University of Ibadan, 27 pp.
Government of Oyo State (2011). Government of Oyo State report on the Assessment of the
26th August 2011 Flood Disaster in Ibadan Metropolis. 78 pp. Report prepared for the
Government by the Oyo State Task Force on Flood Prevention and Management.
Members: B. Wahab, T. Agbola, O. Ajayi, F. Olokesusi, M. Gbadegesin, S. Taiwo, O.
Kolawole, A. Muili, M. Adeola, G. Olutade, F. Shiji and N. Abiola.
Hinderer, A. (1872). Seventeen years in the Yoruba Country, London.
Hopkins, B. (1965). Forest and Savanna. Heinemann, Ibadan.
Mabogunje, A.L. 1962. Yoruba Towns. University of Ibadan Press, Ibadan, Nigeria.
Millson, A. W. (1891). The Yoruba Country, West Africa. Proceedings of the Royal
Geographical Society, 13: 577-91.
National Water Resources Institute (2011). Report of Assessment of the 26th August 2011
Ibadan Flood Disaster, Oyo State, Nigeria. NWRI, Mando Road, Kaduna, 16 pp.
NEH (2007). National Engineering Handbook, National Engineering Handbook Hydrology
Chapters, Natural Resources Conservation Service, United States Department of
Agriculture (cover).

NEMA (2007). Mainstreaming Disaster Risk Reduction into Sustainable Development in Nigeria,
Vols. 1 & 2. National Emergency Management Agency, Abuja.
NEST (1991). Nigeria’s threatened environment: A national profile. Nigeria: (Nigeria
Environmental Study Action /Team).

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Oyo State of Nigeria (2008). Oyo State Solid Waste Management Authority Law, 2004.
Supplement to Oyo State of Nigeri a Gazette, No. 9, Vol. 33, of 5 th June, 2008- Part A.
Ibadan: Government Press.
Wahab, B. (2011). Ibadan: A rapidly growing city in need of a Master Plan. Paper read at the
Architects’ Congress/Annual General Meeting organized by the Nigerian Institute of
Architects, Oyo State Chapter, held at Penrose Event Centre, Obafemi Awolowo
Avenue, Old Bodija Estate, Ibadan, July 7.

Table 1: The Population Growth of Ibadan 1856-2010

Year Population
1856 60,000
1890 200,000
1921 238,094
1931 386,359
1991 1,222,570
2006 2,550,593
2010 2,893,137
Source: Wahab (2011)

Table 2: Physical Expansion of Ibadan (1830-1988)

Year Land Size
1830 100 ha
1931 12 km2
1963 30 km2
1973 112 km2
1981 136 km2
1988 214 km2
Source: Wahab (2011)

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Table 3: Flooding Rainfall Data in Ibadan

Date Depth of Rainfall Causing Flood
(mm)
9-10 July, 1951 161
16-17 June, 1955 173
16-17 August, 1960 178
27-28 August, 1963 258
14 May, 1969 137
20 April, 1978 126
31 August, 1980 274
1982 -
1984 -
April, 1986 -
June/July, 1987 -
April, 1997 151
26 August, 2011 187.5
Sources: NEST (1991:107), Nigerian Meteorological Services (2011), Ibadan Station, National
Water Resources Institute (2011).

Table 4: Percentage of Ibadan City Surface Impervious to Water Infiltration

Sections of Ibadan City % in % in 1994 % increase Rate of increase
1965
Traditional core 15.4 42.5 27.1 1.80
Modern low density 4.3 17.3 13.0 0.98
Modern high density 11.2 30.2 19.0 1.20
Utilities and reservations 3.6 17.5 13.9 1.93
Mean values 9.5 28.4 18.9 1.31
Source: Akintola (1994)

Table 5: Analysis of Flooded Buildings and those within River/Stream Set-backs in the Eleven
LGAs of Ibadan
S/No. Local Government No. of Buildings No. of Buildings River/Stream
within Statutory Flooded on August Length (km)
Setback 26, 2011*
1. Akinyele 2,527 382 435.57
2. Egbeda 2,703 332 229.30
3. Ibadan North East 4,621 228 41.17
4. Ibadan North 3,290 260 33.23
5. Ibadan North west 4,543 162 60.09
6. Ibadan South East 2,435 55 47.69
7. Ibadan South West 3,931 369 75.35
8. Ido 368 78 888.65
9. Lagelu 913 68 274.15
10. Oluyole 366 63 663.01
11. Ona-Ara 856 108 420.43
TOTAL 26,553 2,105 3,168.64
Source: Field Survey Conducted by Task Force in October 2011
*The number of flooded buildings within the most affected areas of the city covered
during the survey was a little below 10% sample of the number of buildings within
the statutory set-back from the surface water bodies.

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Figure 1: The hydrologic Cycle (NEH, 2007)

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Figure 2: Map of Ibadan (Fourchard, 2003)

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Figure 3: Drainage Map of Ibadan

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Plate 1: Buildings Constructed on Flood Plain in Apete Area

Source: Government of Oyo State (2011)

Plate 2: Buildings Constructed on River bed in Apata area

Source: Government of Oyo State (2011)

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Plate 3: Buildings Constructed on River bed in Oluyole area

Source: Government of Oyo State (2011)

Plate 4: Buildings Constructed on River bed in Apete area

Source: Government of Oyo State (2011)

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