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 data set 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 geo spatial 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 pre-development 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:
1. Conversion of existing analogue map to digital format by digitizing (creating spatial database).
2. Creating a suitable attribute database for the study area.
3. Link both spatial and attribute database.
4. To generate buildings in the study area to ascertain those that are vulnerable to flooding.
5. To produce vulnerability maps of the study area.
6. To identify the impact which floods will have on the socio-economic livelihoods of the people.
7. 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.