1.1 Background to the Study
The acronym GIS stands for geographic information system, it is a
system which allows a capture, updating and displaying of a number of
previously unconnected dataset bringing them into a common reference
system for spatial analysis from which relationship can be identified
and decisions made (Sowton
1991).
Floods are probably the most recurring, widespread, disastrous and
frequent natural hazards of the world. India is one of the worst
flood-affected countries, being second in the world after Bangladesh
and accounts for one fifth of global death count due to floods. Nigeria
is not an exception and indeed the study area as series of flooding
have affected inhabitants and disrupted socioeconomic activities. Flood
management and control are necessary not only because floods impose a
curse on the society, but the optimal exploitation of the land and
proper management and control of water resources are of vital importance
for bringing prosperity in the predominantly agricultural based
economy of this diversely populated country. This cannot become
technically feasible without effective flood hazard maps (Pradan, 2004)
Flood hazard mapping and flood inundation
modeling are the vital components in flood mitigation measures and land
use planning. Advances in geospatial technologies (GPS, Remote sensing
and GIS) has enabled the acquisition of data and analysis of the river
basin for flood mitigation projects (either structural or
non-structural) in a faster and more accurate manner. GIS facilitates
integration of spatial and non-spatial geographical data such as
rainfall and stream flows. Other information such as flood maps,
infrastructures and land use, social and economic information can be
inventorized for future use. Flood maps prepared using satellite images
of real flood events and information from the ground are useful for
flood damage assessment, future flood mitigation planning. Flood
vulnerability maps produced using GIS enabled effective tools for land
use planning, flood management and development control. Therefore, an
attempt has been made to apply modern techniques like Geographical
Information System (GIS) for the management of flood in Port Harcourt,
the study area, as it has been proved that the use of Geoinformatics
to manage the databases, maps, and photos improves the ease of the
analysis (Wisner et al., 2004; Noson, 2002).
1.2 Statement of Problem
Floods are among the most destructive acts of
nature. World-wide, flood damages to agriculture, houses and public
utilities amount to billions of dollars each year in addition to the
loss of precious human and cattle lives (R.K.Khanna, 1989). In majority
of cases, ‘flooding’ is caused by a river over-spilling its banks. This
can be due to excessive precipitation, combined with inadequate
channel capacity. Over-spilling can also occur due to obstruction in or
aggradation of the river bed.
Flooding can also result from inadequate water way
at rail and road crossings, or when there are encroachments in the
flood plain. Flooding can also occur at confluences of streams when the
main river is in high stage and backs up into the tributaries and
areas there about.
Flood risk is among the most severe risks on human lives and
properties, and has become more frequent and severe along with local
economic development. As the watershed becomes more developed, it also
becomes more hydrological active, changing the flood volume, runoff
components as well as the origin of stream flow. In turn, floods that
once occurred infrequently during predevelopment periods have now
become more frequent and more severe due to the transformation of the
watershed from rural to urban land uses. The forecast and simulation of
floods is therefore essential for planning and operation of civil
protection measures and for early flood warning. The effects of Global
warming has also accelerated the melting of ice, which in turn
increased the water level and resulting in the occurrence of flooding.
Flooding causes a lot of damage, which is usually, characterize by loss
of properties and even leaving families homeless.
The 2012 Nigeria floods began in early July
2012, and have killed 363 people and displaced over 2,100,000 people as
of 5th November, 2012. From May to September, Nigeria has a rainy
season and suffers from seasonal flash floods. These flash foods are
sometimes lethal, especially in the rural areas or overcrowded slums,
where drainage is poor or does not exist at all. On 2 July 2012, many
Nigerian coastal and inland cities experienced heavy rains, and
residents of Lagos were "gasping for breath" due to the flooding. In
addition, there was a gridlock on major roads, causing people to cancel
or postpone appointments they may have had. Thousands of stranded
commuters had to pay increased fares for the few bus drivers who were
willing to risk travelling on the roads, and construction of work by
the Nigerian government on the inner Oke-Afa Road took a "heavy toll."
In mid-July 2012, flooding in the Ibadan
metropolis caused some residents at Challenge, Oke-Ayo, and Eleyele to
flee from their residences and save their lives. The flooding also
prevented some Christians from attending churches in the morning, while
a few bridges caved in. In late July 2012, at least 39 people were
killed due to flooding in the central Nigerian Plateau state. Heavy
rainfall caused the Lamingo dam to overflow near Jos, sweeping across a
number of neighborhoods in Jos, and approximately 200 homes were
submerged or destroyed. In addition, at least 35 people were missing,
while Manasie Phampe, the head of the Red Cross in the state, announced
that relief efforts were ongoing. The floods left 3,000 people
homeless, many of whom are taking refugee in government buildings in
Jos. In mid-August, flooding killed at least 33 people in central
Nigeria's Plateau state. Over 12,000 people were affected by the
flooding in six districts of the state, while hundreds were rendered
homeless (Wikipedia).
Port Harcourt was not an exception, as a heavy rainfall weekend
wreaked havoc in Port Harcourt, Rivers State, destroying property and
rendering families homeless (The Vanguard Nigeria). The perennial
flooding has caused a lot of damage and untold hardship to the
inhabitants of the study area. The study therefore seeks to assess the
vulnerability of the study area to flooding using Geoinformatics
techniques.
1.3 Aim and Objectives
The aim of this research is to employ Geoinformatics (Geographical
Information System (GIS), remote sensing and cartographic) techniques
to generate flood vulnerability map showing buildings and roads that
are susceptible to flooding in the study area of Port Harcourt at
different buffer distances.
The following specific objectives were pursued in order to achieve the above aim:
- Conversion of existing analogue map to digital format by digitizing (creating spatial database).
- Creating a suitable attribute database for the study area.
- Link both spatial and attribute database.
- To generate buildings in the study area to ascertain those that are vulnerable to flooding.
- To produce vulnerability maps of the study area.
- To identify the impact which floods will have on the socio-economic livelihoods of the people.
- Make recommendations based on the findings.
1.4 Significance of the Study
The recent flooding that occurred in various part of Nigeria makes
this research expedient, to allow for action to prevent such disaster
from occurring. The significance of this research work cannot be
overemphasized as it has tremendous importance and positve impact on
almost all sectors of the economy, government departments and the
society at large. These significance include;
- The research work provides information on the flood vulnerability of infrastructures in the study area.
- The work provides satellite derived data of the study area for further studies and research.
- The research work increases and add to the knowledge of the study area.
- It further exposes and prove the potentiality, accuracy and
efficiecy of Geoinformatics as a technology for the study of flood
hazard management.
1.5 Scope of the Study
The scope of the study is limited to Port Harcourt which is the
study area and its immediate environment. The study only took into
consideration buildings that are vulnerable to flooding at selected
buffer distances of 20 meters, 30 meters and 50 meters; and roads that
are susceptible to flooding at selected buffer distances of 60 meters,
80 meters and 100 meters.
1.6 Study Area
1.6.1 Location
Port Harcourt (Igbo: Diobu, Iguocha or Ugwuocha;
Pidgin: "Po-ta-kot") is the capital of Rivers State, Nigeria. It is
situated in ObioAkp, Rivers, Nigeria, its geographical coordinates are
Latitude 4° 47' 21" North, and Longitude 6° 59' 55" East and its
original name (with diacritics) is Port Harcourt. It lies along the
Bonny River and is located in the Niger Delta. According to the 2006
Nigerian census Port Harcourt has a population of 1,382,592.
1.6.2 Climate
Port Harcourt features a tropical monsoon climate with lengthy and
heavy rainy seasons and very short dry seasons. Only the months of
December and January truly qualifies as dry season months in the city.
The harmattan, which climatically influences many cities in West
Africa, is less pronounced in Port Harcourt. Port Harcourt's heaviest
precipitation occurs during September with an average of 370 mm of rain.
December on average is the driest month of the year, with an average
rainfall of 20 mm. Temperatures throughout the year in the city are
relatively constant, showing little variation throughout the course of
the year. Average temperatures are typically between 25°C-28°C in the
city.
1.6.3 Geology/ Soil
Port Harcourt lies on the recent coastal plain of the eastern
Niger Delta. Its surface geology consists of fluvial sediments. This
includes the recent sediments transported by Niger River distributaries
and other rivers, such as Andoni, Bonny and New Calabar. These
materials deposited as regolith overburden of 30m thickness are clays,
peat, silts, sands and gravels. The depositional sequence exhibits
massive continental sand stones overlying an alternation of sandstones
and clays of marginally marine origin, but eventually grading downwards
into marine clays. Sands, by far, form the largest group of rock types
in Rivers State, while mud constitutes all the polluted brackish
waters of the riverine areas. However, peat constitutes the various
vegetal and animal remains that lie in bogs and shallow pits. The
gravel and pebbles form the last unit of the subsurface rock type, and
are usually found at the base of the river channels. There are three
major soil groups in Rivers State, namely: the marine and fluvial
marine sediments; the mangrove swamp alluvial soils; and freshwater
brown loams and sandy loams. The marine and fluvial marine sediments
are found in the wet coastal region. The soils are organic in nature
and essentially sandy in texture. Some consist of mud mixed with
decayed organic matter. The mangrove swamp alluvial soils are found in
the northern part of the coastal sediments zone. They are brownish on
the surface, sometimes with an unpleasant and offensive odour. The
soils of the swamps are rich in organic matter in the top layer, but
contain too much salt especially in the dry season. The third soil
group, the brown loams and sandy loams are found in the fresh water
zone of the delta. The levees which form the common land forms of this
zone are made up of rich loams at their crests, changing to more acidic
and more clayed soils along their slopes.
1.6.4 Vegetation
The "upland" area was originally occupied by rainforest which has
been drastically modified by human activities. In most places, economic
trees, particularly oil palm, have been preserved and thus the
sobriquet for this vegetation as "oil palm bush." The riverine area is
divisible into three main hydro-vegetation zones namely, the beach
ridge zone, the saltwater zone and the freshwater zone. The beach
ridge zone is vegetated mainly by fresh water swamp trees, palms and
shrubs on the sandy ridges and mangroves in the intervening valleys or
tidal flats. The saltwater zone is the tidal flat or swamps vegetated
by the red stilts rooted mangrove (Flhizophora racemosa) and two other
species of mangrove. The outliers of raised alluvial ground or coastal
plain terrace within the swamps are vegetated by tall forest tree
species and oil palm. The freshwater zone is mainly the Upper and Lower
Delta floodplains of the Niger, having fresh water forest trees which
are the edaphic variants of the rainforest. The Abura tree, oil palm,
raffia palm, shrubs, lianas, ferns and floating grasses and reeds are
the typical vegetation.
1.6.5 Hydrology
Rainfall in Port Harcourt is seasonal, variable, and heavy. Port
Harcourt is a city of physical difficulties, such as low lying terrain
riddled with an intricate system of natural water channels; too much
surface water and a high rainfall; uninhabitable mangrove swamps and
some parts of the state suffer from inaccessibility due to seasonal
flooding.
1.6.6 Socio-economics activities
Port Harcourt is the heart of Nigeria’s Oil industry with
virtually all major multi-national oil companies being represented
there until recently owing to security threats from Niger Delta
militants and Cultists. The economic activities of Port Harcourt
include manufacturing such as food processing, car assembly,
manufacture of paper products, paints, petroleum products refinery and
road construction, metal works and cement making, enamelware, bicycles,
furniture, and soap making. Services include legal services,
hospitality, medical, Educational and engineering services. Extractive
industries also exist such as mining of coal, tin and petroleum, oil
and gas liquefaction. Also agricultural and agro based businesses exist
in the city some of which are logging and timber processing, tobacco
processing and cigarette making, plastic moulding and the manufacture
of rubber based products like tyres, bands and tube and glass making.
Imports are mainly automobiles, electronics, textiles and processed
food. Sometimes rice, millet and meat and other agricultural produce are
imported as well. Then numerous small scale enterprises like consumer
retailing, artisanship and transportation businesses also thrive in the
city. Various government organs such as the Nigerian Ports Authority,
NNPC and the customs play various regulatory roles in the local
economy. The main industrial area of the city is Trans Amadi.
Residential areas include Port Harcourt Township known locally as
"Town", G.R.A phases 1-5, Abuloma, Amadi-ama, Amadi Flats, and
Borokiri.
Crime rate in Port Harcourt Nigeria is one of the highest. The
worst cases so far have been crimes committed by criminal gangs
disguising their illegality as freedom struggles for the marginalized
locals of the oil rich Niger Delta Region. Other than these and
congestion, Port Harcourt Nigeria is largely a peaceful and sociable
city. With many recreational and fun spots, Port Harcourt can boast of a
number of 5 star hotels such as the Meridien Hotel, Presidential Hotel
among others. Also newly open entertainment centres with cinemas,
night clubs, bars and restaurants can be found in the city.
1.7 Limitations of the Study
This research work was not without some limitations. The major
limitations of this study was that the study area was very wide and so
difficult to get all the attributes for roads and buildings with
available map not providing all the names of the roads and rivers;
and the usage of buildings.
These limitations however were overcame by
proper digitization of the satellite imagery, giving code names to
roads and rivers were the names were not known and generalizing
buildings.