CHAPTER ONE
1.0 INTRODUCTION
Floods are among the most devastating natural disasters and cost many lives every year (Dilley et al. 2005). Flooding seriously affects people‘s lives and property (Wang, 1999). In a time period of 6 years (1989–1994), 80% of declared disasters in US were related to flooding; flood themselves around the world average four billion dollars annually in property damage alone (Wadsworth 1999). The frequency with which they occur is on the increase in many regions of the world (Drogue et al. 2004). It is reported that flood disasters account for about a third of all natural disasters (by number and economic losses).
In Nigeria, aside from droughts, floods cause almost 90 % of damages resulting from natural hazards (Adeoye et al., 2009). Floods that occur in Nigeria are as a result of extensive rainfall, drainage blockages and dam failures (Jeb and Aggarwal, 2008). Flooding are common features in Nigeria during Urban flooding which occurs in towns, on flat or low-lying terrain especially where little or no provision has been made for surface drainage, or where existing drainage has been blocked with municipal waste, refuses and eroded soil sediments (Folorunsho and Awosika 2001). Flooding cannot be completely avoided, but damages from severe flooding can be reduced if effective flood prevention scheme is implemented. Mitigation is hence the cornerstone of emergency management. Flood risk‟ means the combination of the probability of a flood event and of the potential adverse consequences for human health, the environment, cultural heritage and economic activity associated with a flood event‖ (EC, 2007). Recent flood disasters in Nigeria have been of major concern to people, communities and institutions. Flash floods are the most common in Nigeria during the peak of the rainy season (June-October) and the 2012 flood event in Nigeria is described as the worst in recent times. Kogi State was the most affected state due to its location at the confluence of the country‘s major rivers (Niger-Benue Rivers)
Kogi state experienced a serious flood disaster in 2012 and the situation is beyond description and it has attracted humanitarian assistance from NEMA, Red Cross and many among others. It has lead most settlements inundated rendering millions of people homeless, destroyed thousands of hectares of farmlands and livestock and also loss of aquatic animals. This flooding came as a result of water release from Ladgo dam into river Benue, Shiroro and Kanji dam also released water into river Niger, as well as climate change itself which led to excess precipitation (NEMA, 2012).
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In 2008, Jeb and Aggarwal stated that reduction of risk of flooding will depend largely on the amount of information on floods that is available and knowledge of the areas that are likely to be affected during a flooding event. Therefore, it is necessary to use modern day techniques in developing measures that will help government and relief agencies in identification of flood prone areas and in planning against flooding events in the future. The knowledge of remote sensing and geographical information system (GIS) is a tool which can be used to investigate and map areas that are less or more vulnerable to flooding in conjunction with forecasting techniques to predict the precipitation intensity and duration in the nearest future. Geographic Information Systems (GIS) are widely used to analyze natural hazards such as landslides, flooding, among others. GIS is extremely useful for integrating various geographic data, and for numerical analysis of such data. In this work, the use of geospatial techniques and disaster management cycle will be employed solving this devastating flood that has render people homeless and infrastructures and farmlands destroyed in Kogi state. The stated techniques above will help in the monitoring and managing subsequent flood disasters occurrence in the future.
1.1 STATEMENT OF RESEARCH PROBLEMS
Ø In recent years, the increase in population and expansion of settlements in hazardous areas has fostered the impact of the floods worldwide.
Ø In Kogi State where a quite number of its citizens resides mostly in relatively low lying areas and river flood plains due to the huge natural resources and also agricultural potentials present, It has led to fast and exponential increase in human settlement and other subsistence activities in the area.
Ø Flooding has been one of the major natural disasters in Kogi, during the disaster lot of lives and properties were lost, inundation of institutions, farmlands, destruction of roads, bridges and especially the major road to gain entrance from southwest into the northern area.
Ø According to the Nigeria Emergency Management Agency (NEMA), five districts, namely, Adankolo/Kabawa, Sarkin Noma/Galilee, Phase 1 – Old Poly quarters, Ganaja and Gadumo were flooded in August and early September, 2012 when River Lagdo burst its banks.
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Ø Responsive, preventive and mitigation measures depend to a large extent on quality and reliability of flood data.
Ø Therefore, this research is set out to assess the vulnerability of human settlement in Lokoja metropolis and map out areas affected, examine levels of vulnerabilities, implications and suggest planning recommendations.
1.2 AIM AND OBJECTIVES
The aim of this study is to assess flood vulnerability in Lokoja metropolis with the view of making appropriate physical planning recommendations.
Objectives
1. To review the causes and effects of flooding as well as floodplain management strategies in urban areas.
2. To delineate flood prone areas within Lokoja metropolis and examine the pattern of flooding over time.
3. To carry out flood effects analysis in the study area.
4. To make physical planning recommendations.
1.3 SCOPE AND LIMITATION
The scope of the study is Lokoja metropolis, Nigeria and the study is concerned with assessing effect of coastal flooding in areas vulnerable to same.
1.4.0 RESEARCH METHODOLOGY
1.4.1 Approach to the Study
For every research study or process, certain procedures must be followed in order to achieve a better knowledge and understanding of the study. However, this study used the approaches or steps hereunder:
Satellite/Land sat image acquisition
Field survey/Interview with Officials of various
Miniseries
Creation of workspace
and importing of
satellite/Land sat image
Geo referencing
Digitizing and Mapping out flood prone areas
Time series analysis of flood prone areas
Implications of flooding over time
Flood effect assessment and analysis
Make Physical planning recommendations
based on the outcome of analysis
Figure 1.1 Approach to the study
Below are brief explanations of the various steps to be taken to achieve the objectives of this research work as shown in the above diagram (approach to the study).
I. Satellite image acquisition: The satellite image of Lokoja Metropolis will beacquired using remote sensing software package Google earth. The satellite image will be captured in parts to obtain a high resolution image. The image parts will be stitched together using Image Assembler software and saved in TIFF format. The
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purpose of this procedure is to be able to obtain an image of a very large place with high resolution.
II. Field survey/Interview with Officials of various Miniseries: This process alsohelped in determining the flood prone areas using global positioning system (GPS) for ground trekking and touring round the floodplains boundaries also interviews will be conducted with officials of Kogi State Town Planning and Development Board (KSTPDB) and Kogi State Ministry of Lands, Housing and Urban Development alongside data on last flooding events will be collected as applicable.
III. Creation of work space and importing of image: This is the basis for all the workdone on ArcGIS. The work space specifies the default location for outputs. It is a directory containing geographic data sets for use with ArcGIS. A work space is an information directory for the feature attribute table and it can be a folder that contains shape files, Geo-database and so on. On the other hand, importing the satellite image of the study area simply means adding the satellite image with spatial reference into
ArcGIS environment or work space.
IV. Geo referencing: It is the process of giving a cartographic material such as satelliteimagery, aerial photograph, map, or statistical data a real world coordinate system and map projection. In GIS environment, we have two coordinate systems: the geographic coordinate system and the projected coordinate system. The satellite image of the study area (Lokoja Metropolis) will be geo referenced using the projected coordinate system (UTM Minna 32N) for it is suitable for a small place when compared with the world. This was possible with the aid of well-established control points.
V. Digitizing and Mapping of flood prone area: The satellite imagery of the study areawill be converted into a digital format through the process known as digitizing using ArcGIS software. Urban features such as structures, roads, water body will be converted to digital format. In mapping out the flood prone area, the digitized features will be overlaid on a digital elevation model (DEM). The digital elevation model (DEM) will be downloaded from United States Geological Survey (USGS) website. The x, y coordinates of these features will be recorded and stored as spatial data, also the direction of flow will be gotten from the DEM with the ArcTool box.
VI. Time series analysis of flood prone areas: It involves creating a data base forvarious vulnerability level of human settlement. After acquiring satellite imageries from different years from GOOGLE EARTH HISTORY, the raster will be converted to digital format (digitizing). The ArcGIS will be used to delineate the flood prone
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areas using the yearly mean water level data from NIWA with the aid of raster calculator. After delineating the yearly flood prone area, the ArcGIS will be used to show the pattern of flooding on study area.
VII. Implications of flooding over time: The results from the flood effect assessment andAnalysis will be used to identify the implications and also identify vulnerabilities in the study area. For the purpose of this research, the implications will be limited to Record of property/houses lost, farmlands and number of people affected or records provided to me by Officials of Ministry. The result of the analysis will be the basis for urban planning recommendations and proposals.
VIII. Flood effects assessment and analysis: After identification of the resultant implications of flooding, flood effect assessment will be conducted in order to determine the extent of damages caused by flooding.
IX. Make Physical planning recommendations: The Physical planning recommendations will be based on the outcome of the analysis.
ASSESSMENT OF FLOOD VULNERABILITY IN LOKOJA METROPOLIS, KOGI STATE
