Communications in Information Science and Management Engineering
Sept. 2013, Vol. 3 Iss. 9, PP. 439-447
Combating Flood Crisis Using GIS: Empirical
Evidences from Ala River Floodplain, Isikan Area,
Akure, Ondo State, Nigeria
Michael Ajide Oyinloye1, Oluwadare Isaac Olamiju2, Babalola Sunday Oyetayo3
1, 2
Department of Urban and Regional Planning, School of Environmental Technology Federal University of Technology,
Akure, Ondo State, Nigeria
3
Department of Surveying and Geoinformatics, School of Environmental Technology, Federal University of Technology,
Akure, Ondo State, Nigeria
1
[email protected]; [email protected]; [email protected]
Abstract- Natural hazards have become an issue of growing concern throughout the world. The magnitude of the related disasters,
threatening large population living in diverse environments show a dramatic rise everywhere in recent years. Due to structural
growth and the booming economics activities within the flood plain of River Ala in Akure, Nigeria has induced flooding in this city,
with subsequent loss of properties, life and human settlement. The objectives of the paper were to determine the causes of flooding in
the area; identify areas where activities and development need to be monitored and to devise a workable framework for managing
flood problems in the study area. For this study, a SPOT imagery of the area was acquired. ArcGIS 9.0 software was employed to
obtain information by the process of digitizing the SPOT imagery for the purpose of delineating River Ala flood plain. The results
obtained implicated dumpsites within the river channel as well as structural development within the River Ala flood plain as the
major causes of environmental hazards in this section of the city, especially during rain period. The study recommends structural
and non-structural strategies for mitigating the effects of flooding on the residents and infrastructures. Structural measures in terms
of construction of levee and flood walls along river channel to protect the buildings are most vulnerable. Non-structural measures
include landuse planning and legislation against encroachment on flood plains.
Keywords- Environmental Hazards; Geographical Information Systems (GIS); Flood crisis; Nigeria
I. INTRODUCTION
Record shows that more than 200 people have lost their lives to flooding while hundreds of thousands have been rendered
homeless and properties worth of millions of Naira have been destroyed by devastating floods across the country (Oluduro,
1988; Sunday Times, 1988; Oyo Ministry of Information and Culture, 1989). Askew (1999) as cited by Etuenovbe (2011),
opines that floods cause about one-third of all deaths; one-third of all injuries and one-third of all damage from natural
disasters. In Nigeria, the pattern is similar with the rest of the world. Flooding in various parts of Nigeria has forced millions of
people from their homes, destroyed businesses, polluted water resources and increased the risk of diseases (Baiye, 1988;
Akinyemi, 1990; Nwabani, 1991; Edward-Adebiyi, 1997). Flood is a natural environmental disaster which could be aggravated
by man’s unguided development. Floods cause damage to houses, industries, public utilities, agricultural land and crops
resulting in huge economic loses, apart from loss of lives. Since flood is one of the natural disasters which endanger both life
and property, it becomes vital to know its extents and evolution. Though it is not possible to control flood disaster totally, by
adopting suitable structural measures, flood damages can be minimized (Awosika et al, 2000).
Preventing river floods is important to prevent probable loss of life and to reduce damage to sites of high economic
importance. Floods occur when soil becomes saturated and its infiltration capacity is zero; runoffs cannot be contained in
stream channels, natural ponds and constructed reservoirs, and the land surface become submerged, sweeping away its content.
Periodic floods, resulting from heavy rains, occur naturally on many rivers, forming an area known as the flood plain. The
river floods often cause the rivers to overflow their banks, sometimes with a velocity and enormously destructive surge
(Adetunberu, 2009). In Nigeria, we experience floods every year during the rainy season with farmlands getting inundated and
destroyed, properties and buildings destroyed by standing water, coastlands washed and ravaged by floods emanating from
storm surges, highways and roads in the cities and villages taken over by flood water and in several cases, loss of human lives.
Flooding occurs as a result of intense rainfall along river banks, cities and from ocean storm surges which result in massive
flooding of the low lying coastal areas (IPCC, 2007). The flood events in most southern cities of Nigeria are so prominent that
some inhabitants in many of these settlements have often described it as “an act of God”. However, apart from the Yobe’s case
in the Northern Nigeria, which was cause by breakdown of a dam, flood events in may southern capital cities in Nigeria are
mostly due to the poor consciousness of the inhabitants on environmental information, inadequate (or sometimes absolute lack)
spatial information on the flood prone areas, waste dump and construction of building (both commercial and residential, even
public offices) on river channel without adequate measure of water flow (Etim, 2008). Many attempts have been made to
control the annual flooding disaster in Akure. Part of this includes channelization of river as well as making available succor
for victims of the perennial disaster. The attempts seem unsuccessful as the situation keeps occurring and the inhabitants are
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rather helpless. It is thus as a result of this that the study has undertaken a survey of a planning methodology of the geographic
information system for development control in the city, such that the flooding menace would be curbed once and for all.
Several studies have been conducted with integration of remote sensing and geographic information system to map and
monitor flooding disaster. Ihemadu (1985) examined the suitability of satellite remote sensing as a mapping tool derived from
its characteristics of comprehensiveness, timeless, repetitiveness, regularity, reduced dependence on weather and improved
cost-effectiveness. Environmental management was effectively conducted by interpreting remote sensing data into
geographical information systems. Salahu (2001) points out that floods cause life and property loss and that the flood process
can be shown clearly by the satellite imagery and the region of most serious flooding can be determined. In other words, the
use of geo-information such as the satellite imagery is crucial to limit the damage caused by flooding and other natural
disasters to the extent possible.
The aim of this paper therefore is to assess flooding and its ecological implication on Akure using the digital mapping
capabilities of GIS with a view to determine areas that are susceptible to flooding in the study area. The objectives of this study
are to: determine the causes of flooding in Akure, identify elements in the flood plain that are vulnerable to disaster using GIS
techniques, identify existing landuses within the floodplain, and devise a workable framework for managing flooding problems
in the study area.
II. THE STUDY AREA
The study area is Akure which was made the capital of Ondo State in 1976. Akure is situated on latitude 7 015’ and
longitude 50 15’ E. It is about 370 m above the mean sea level. Akure is situated within a 48 kilometer radius to major towns in
Ondo State, viz Ondo to the South, Owo to the East and Iju/ItaOgbolu to the North. The easy access and geographical
centrality of Akure to these towns have enhanced the growth prospects of the city. Figure 1 is a map of Nigeria showing Ondo
State while Figure 2 shows map of Akure in Ondo State. Figure 3 shows the location of Ala River in the study area.
The population of Akure in 1963 was put at 71,006 and by 1999; the total population has risen to 239,124 according to the
1991 census. By the year 2006, the total population has increased to 340,021 inhabitants (NPC, 2006). The increase in annual
growth of the population has been tied to the administrative role of the town and its long standing role as a centre of economic
activities attracting a large spectrum of immigrants into it.
Fig. 1 Map of Nigeria showing Ondo State
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Fig. 2 Map of Ondo State showing Akure south local government area
Fig. 3 Map of Akure showing Ala River in the study area
III. DATA ACQUISITION AND METHOD
The study was interested in the analysis of the causes of flooding in the study area. It also seeks to use the capabilities of
GIS and remote sensing (RS) to determine the risk levels of flooding hazard in the study area. To achieve these, a SPOT
imagery of the study area as posted online on this website was imported into GIS environment where further processing was
carried out in order to make the Figure 3 useful for analysis. This image was able to show clearly the buildings and the main
river (Ala river) draining the study area. In addition, the global positioning systems (GPS) technology was used to collect
coordinates of specific points and other relevant geographic data that were missing on the image for the purpose of georeferencing and digitizing.
The questionnaire method was used to generate attribute data to further enhance our information on the study area.
However, table 2 shows the residential areas from which samples were taken. Based on the above division of the town into
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Residential Areas (RAs), samples were taken from those areas drained by the river as shown in Figure 2. The DRAs are shown
in Table 1.
TABLE 1 DELINEATED RESIDENTIAL AREAS (DRA) FROM WHICH SAMPLES WERE TAKEN
S/NO
DRA NO
DRA NAME
1
1
Ilesa Road Residential Area
2
2
Okuta Elerinla Residential Area
3
3
Akure High School/Kajola Residential Area
4
4
Ijapo Residential Area
5
5
Alagbaka Residential Area
6
12
Ayedun Residential Area
7
16
Ijoka Sijuwade Residential Area
8
17
Oke-Ijebu Residential Area
9
20
Ijomu Ilisa Residential Area
Source: Field Survey, 2012
Systematic random sampling procedure was adopted in the choice of households to be interviewed in such delineated
residential area (DRA). In this wise, every 5th house along a street was selected to be interviewed starting from the first house
until the maximum number of respondents for the DRAs covered. The choice of respondents was limited to head of household
since only such persons were able to give detailed information about any particular building and the general environment of the
study area. For the purpose of this study, only 25 questionnaires were administered in the nine DRAs, an additional 25
questionnaires was administered on the purported vacant lands the author mandated the field assistants to carry out in-situ
interpretation of questions from the English Language-the language of research to Yoruba which is the local dialect, so as to
enable respondents to answer the questions as well as retrieve immediately treated questionnaires. The instrument is about the
most effective to collect data from preponderantly semi-illiterate audience to which the research is addressed. Table 2 shows
the DRAs and the number of questionnaires administered per DRA.
TABLE 2 NUMBER OF QUESTIONNAIRES ADMINISTERED PER DRA
DRA NAME
Questionnaire
Administered
Questionnaire
retrieved
Percentages of
Questionnaire retrieved
1
Ilesa Road
25
20
80.0
2
Okuta Elerinla
25
20
80.0
3
3
Akure High School/Kajola
25
20
80.0
4
4
Ijapo
25
20
80.0
5
5
Alagbaka
25
20
80.0
6
12
Ayedun
25
20
80.0
7
16
Ijoka Sijuwade
25
20
80.0
8
17
Oke-Ijebu
25
20
80.0
9
20
Ijomu Ilisa
25
20
80.0
Vacant land
25
20
80.0
Total
250
Source: Field Survey, 2012
200
80.0
S/NO
DRA NO
1
2
The data collected using this medium was processed using the Statistical Package for Social Scientists software. Results
obtained were presented in the form of charts, tables and graphs among others.
The questionnaire was designed to elicit information about possible causes of flooding and implication of annual flooding
in the study area. The area covered by the questionnaire include major causes of flooding such as lack of drainage facilities,
block drains, building too close to the river banks and loss of properties and house collapse. The demographic and socioeconomic question specifically focused on the age, marital status of the respondents. Those variables variously affect
respondents’ choice of accommodation, housing affordability, nature of refuse generated and the occupancy ratio.
In addition, the questions on building condition focused on the type of building, type of access to building, age of building,
distance (setback) of building to river/stream, ownership status of respondents and building plan approval before construction.
All these questions were carefully analyzed and considered in addition to spatial information from GIS analysis to arrive at our
conclusions.
IV. RESULTS AND DISCUSSION
The major disaster in the study area is flooding as shown by the GIS outputs and the results of questionnaires administered.
The results are discussed as below.
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A. Delineated Map of the Study Area
Figure 4 shows the delineated map of river Ala using ArcGIS 9.0 software. The image shows the network and direction of
flow of river Ala.
Fig. 4 Map showing the river network of the study area
Figure 5 shows that the river Ala has been buffered by 30 m. The river was buffered by 30 m because that is the statutory
standard for the setback by the government. This also implies that on no condition should any buildings characteristics be
found within the buffered zone of 30 m as shown in Figure 5, it was actually discovered that there were a number of buildings
found within this range.
Fig. 5 Map showing the buffered river of the study area
B. Map Showing the Existing Landuse Within the Buffered Zone of 30 m of the Study Area
Figure 6 shows the existing landuse of the study area where the encroachment of buildings on river Ala was closely shown.
These encroaching buildings are the buildings that fall within the range of 30 m buffer zone and they are shown in colour
yellow. It was also discovered that part of the newly constructed market by the government is also falling within the buffer
zone. Figure 6 also shows the risk analysis map defining the areas at risk in the study area. This risk map shows that most of
the buildings that are even outside the 30 m buffer zone and streets are at high risk. This is because they have already been
sitting on wetlands which get flooded when there is heavy rainfall.
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Fig. 6 Map showing the existing landuse of the study area
Figure 7 shows a proposed map for the study area. The proposed map indicated that all the buildings that are within the
buffer zone must be relocated. In fact, part of the newly constructed ultra-modern market by the government will have to make
way.
Fig. 7 Map showing the proposed landuse of the Study Area
V. PLANNING IMPLICATIONS OF URBAN FLOODING
Flooding as an environmental hazard is however not entirely a physical phenomenon. In the real sense, floods only become
a hazard when they impinge unfavorably upon human activity, as they frequently do because of the affinity which human
beings tend to have for floodplains and coastal locations in this respect. A flood hazard is also a socio-economic phenomenon.
Moreover, one major cause of flooding is man’s interaction with his environment in the form of urbanization, agricultural
activity, and deforestation and construction works leading to excavation, overgrazing, blockage of drainage channels and
building near water channels without adequate set-backs. Human activities are undoubtedly assumed greater importance as a
cause of flooding (Adetunberu, 2003).
As urbanization intensifies, natural surfaces are replaced by buildings, paved roads and concrete surfaces which do not
allow water to percolate readily into the ground. The consequence is that a large proportion of the rainfall which should
normally infiltrate into the soil or be intercepted by the vegetation and thus delayed for some time before running off is
immediately available for surface runoff into streams and rivers which makes them to be flooded. Attempts by man to harness
available water resources have resulted in the construction of dams and other water control structures. The failures of these
structures, as frequent as they may be, have resulted in floods, a typical example being the collapse of the Bagauda Dam near
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Kano in August, which had disastrous environmental consequences. The encroachment of buildings on the floodplains of
streams and rivers flowing through towns and cities and the disposition of waste materials in their courses do facilitate flooding
(Adetunberu, 2003). It is therefore pertinent that the activities of man on land need to be subjected to constant control and
management with the instrument of development control using the capabilities of GIS and RS as background tools for data
collection and analysis (Olamiju, 2008).
In the study area buildings are erected on flood plains and wetlands in the town with the tacit concordance and
acquiescence of the Local Planning Authority and the community-dwellers who are ignorant of the evil of such activities. This
has ineluctably aggravated the flood situation in the town. The high rate of urbanization in the town is manifested in high
population concentration, high room densities, the emergence of new and mostly unplanned neighbourhoods and the erection
of informal settlements and slums. A common feature in most of the informal settlements and slums in the town is the
complete lack or absence of waste disposal facilities, lack of development control machineries and poor drainage facilities. In
the case of all these, the municipal authority lacks the wherewithal to respond promptly and effectively to the problem of
flooding in Akure.
The causes of flooding in the study area include erection of buildings along the flood plain without the requisite setbacks
from the stream, improper drainage and waste disposal mechanisms, the low-lying topography of the area which obstructs the
free flow of run-off by gravity (see Tables 3-4). Other variables that are responsible for flooding include: number of persons
per building, the use of building, age of building and building plan approval before construction among others (see Tables 5-8)
Table 3 shows that about forty-three (43) respondents which represent 21.5% of the total respondents admitted that the
major cause of flooding in that area is lack of drainage facilities. This has been identified as a crucial issue as it serves as
catalyst for flooding in this study area. Also, 8.5% of the total respondents concurred that blocked drains in the study area is
highly responsible for flooding. This is said to be the direct implication of indiscriminate refuse dumping in the entire study
area. This is due to the fact that it is a very old area in Akure metropolis and houses a lot of illiterates consequently destroying
the environment. Seventy-one (71) respondents which is about 35.5% of the total population strongly believed that the major
cause of flooding in that area is attributed to the fact that a lot of buildings/dwellings are too close to the river bank. These
buildings in question did not conform to the planning standard that stipulates a set-back of 30 m for rivers. Consequently, they
are all in disaster zone because whatever, water will always find its way and inevitably leads to flooding of the buildings in
question. Some buildings are really close that we do not even have up to 10 m set-back which is very ridiculous and babaric.
Sixty-nine (69) of the respondents (34.5%) equally believed that the major cause of flooding in the study area is as a result of
indiscriminate dumping of refuse.
TABLE 3 MAJOR CAUSES OF FLOODING
Causes of flooding
Freq.
%age
Lack of drainage facilities
43
21.5
Blocked drains
17
8.5
Buildings too close to river bank
71
35.5
Indiscriminate refuse dumping
69
34.5
Total
200
100
Isikan River flooding is an environmental hazard that occurs regularly every year. Each time it occurs, there is always a
structural damage which includes house collapse and loss of properties. In this study, there is high rate of property loss more
than building collapse. As a matter of fact, it is just about 34.0% of the respondents that have cases of building collapse and
this is because they are virtually living on the river. Meanwhile, about 61.0% of the respondents confirmed that they lose
properties to this menace on yearly basis. Also, as pointed out earlier, most buildings in this study area are very old as this will
hasten its collapse if the flood is very massive. Table 4 below shows the detail of what it really is.
TABLE 4 INCIDENCE OF LOSS OF PROPERTIES AND HOUSE COLLAPSE
Damages
Freq.
%age
Loss of properties
122
61.0
Building collapse
68
34.0
None of the above
10
5.0
Total
200
100
Source: Field Survey, 2012
Table 5 shows that the predominant building use in the study area is residential. Over 62% of the buildings are used for
residential purposes, while industrial, commercial and commercial/residential uses take 3.0%, 16.0% and 21.9% respectively.
The planning implication of this is that more household refuses are generated and such are deposited into nearby rivers,
streams and drainages which obstructs free flow of rivers, streams runoffs, and this phenomenon often results in flash floods
wherever rain falls.
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TABLE 5 TYPE OF BUILDING USE
Response
Freq.
%
Residential
124
62.0
Industrial
6
3.0
Commercial
32
16.0
Commercial/residential
38
19.0
Total
200
Source: Field Survey, 2012
100.0
The number of person per building also determines to a large extent the volume of refuse generated. In the study area, over
40.0% of the buildings house between 10 to 25 persons. The implication of this is enormous as more refuses are generated and
such are improperly disposed to aggravate flooding in the study area.
TABLE 6 NUMBER OF PERSON/BUILDING
Response
Frequency
Percent
1-5
28
14.0
5-10
80
40.0
10-15
92
46.0
Total
200
Source: Field Survey, 2012
100.0
From Table 7, it is obvious that 68.0% of buildings have below 15 m setback required from the stream, 24.5% have an
average of 15 m setback whilst about 7.5% of the buildings have setback above 15 m. Inadequacy of building setback from
streams in the study area could be attributed to ineffective development control mechanism and the level of ignorance of the
dwellers.
TABLE 7 BUILDING SETBACK FROM STREAM
Response
Freq.
%
30m
15
7.5
15m
49
24.5
Below 15
136
Total
200
Source: Field Survey, 2012
68.0
100.0
Table 8 shows over 45.0% of buildings in the study area did not secure building approval before construction. Up till time
of this study, there are no plans for most of the buildings in the study area.
This situation reveals that property owners in the study area develop their properties without due regard to physical
planning rules and regulations.
TABLE 8 BUILDING PLAN APPROVAL BEFORE CONSTRUCTION
Approval
Frequency
Percent
Yes
110
55.0
No
90
45.0
Total
200
Source: Field Survey, 2012
100
Facilities examined in the study area inlude toilets, bathrooms, kichen, water supply and waste disposal. In Table 9 30.0%
disposed their waste indiscriminately along roads and drainage where nobody cares for them. Those wastes that are dumps in
roads and drainages hinder the free flow of runoffs, thereby causing incessant flooding on roads and premises of buildings
nearby.
TABLE 9 CONDITION OF INFRASTRUCTURAL FACILITIES
Facilities
Freq.
%age
Toilets
28
14.0
Bathrooms
25
12.5
Kitchen
41
20.5
Water supply
46
23.0
Waste disposal
60
30.0
Total
200
Source: Field Survey, 2012
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VI. CONCLUSION AND RECOMMENDATIONS
The study has highlighted the problems of flooding in Akure and its implication on the residents of the town. It has also
identified some of the issues that have contributed to the higher incidence of flooding in the town. The major causes of these
were as a result of building too close to river banks, lack of drainage facilities and block drains. Another prominent issue is the
high rate of urbanization in Akure manifested in form of high population and overcrowding. The population is greater than
what the existing facilities can cope with.
Consequently, municipal services like waste disposal machineries are lacking, forcing urban residents to dump their wastes
in drainage channels. Most of the respondents have lived in this study area for a considerable length of time and have
witnessed many flooding incidents. Over the years, they have also suffered from various afflictions and diseases arising from a
flooded environment. For GIS output, the following results could be deduced. The map reveals that those buildings that fall
within the buffer zone of up to 30 m should be relocated. This will reduce the loss of properties and lives.
In view of these findings, this study advances some recommendations as a way of preventing the menace of flooding in the
study area. The recommendations are both behavioural and structural.
On the behavioural aspect, proper drainage channels should be put in place by the government to manage solid wastes as
one potent factor responsible for flooding due to the blockage of drainage channels; buildings that do not maintain adequate
setback to streams and rivers should be demolished and buffer strips should be maintained as open spaces; the relevant
authorities should regulate and enforce planning standards in the study area, the statutory minimum setback from stream (30 m)
on both sides should be enforced; impact of flooding through mobilization programmes, the activities of State Environmental
Protection Agency (SEPA) and Federal Environmental Protection Agency (FEPA) should be widened in the study area.
On the structural aspect, this study advocates a proper drainage plan for the study area. The drainage plan must take
cognizance of the congested nature of development in the study area and ensure that every street is endowed with drainage
channels on both sides. The road construction engineers must ensure that there is a proper coordination of the drainage
channels to guarantee that storm water from the streets is directed to a truck channel.
The capability of the truck channel has to be commensurable with the volume of storm water generated in the
neighbourhood. There is a need to study the characteristics of the storm water so as to know its intrinsic attributes, such as its
prefunding frequency of occurrence and the length of time it takes to seep into the ground (infiltration) or flow by gravity out
of the neighbourhood. It is therefore necessary and imperative for the residents to open up blocked drainage channels.
Government at state and local levels should collaborate on adequate and proper channelization of the study area.
This study, if well planned and executed in a large and policy-oriented scale would go a long way in solving flooding crisis
and generate informed programmes for policy makers.
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