Application of Geo-Spatial Technology in Identifying Areas Vulnerable to Flooding in Ibadan Metropolis (original) (raw)

This study makes use of the integrated approach of Remote Sensing and GIS techniques in flood management with the goal of identifying areas vulnerable to flood hazard in Ibadan Metropolis. Ibadan is the largest indigenous city in the continent of Africa and had experienced a lot of various severities of flood occurrences in the last fifty years. Topographic Map and Landsat TM image of 1993 and 2000 respectively were processed, scanned, digitized, interpolated, classified and overlaid using ILWIS 3.3 academic and ARC GIS 9.2 software modules to generate classified land cover map, Digital Terrain Map (DTM), Triangulated Irregular Network (TIN) and flood vulnerability map of the study area respectively. The results obtained shows that, areas lying along the banks of River Ona and River Ogunpa are most vulnerable to flood hazards with the vulnerability decreasing towards the northern part of the city, much of the area is built up with improper planning and this gives rise to high vulnerability to flash flood hazards. The Odo Ona, Idi Isin, Eleyele, Olopometa and Molete areas are the most vulnerable to flood threat. The incessant violation of land use plan, unchecked population growth, old nature of the structures and poor materials used in the construction of the houses make the areas vulnerable to flood hazard. In reducing the vulnerability of these areas from flood there is need for improved land use planning, removal of structures from River Ona and Ogunpa flood plains around the city, intensify environmental education to the residents and enhance the active participation of government agencies in the continual generation of flood vulnerability maps of urban centres. 1. Introduction Flooding is the commonest natural hazard that can happen any time in wide variety of locations within rainy season due to high intensity of rainfall events. The projections of climate change trends indicate increase of the occurrence of the intense rainfall events both in terms of the intensity as well as their frequency (IPCC, 2007). The projected high intensity rainfall events coupled with the changes in the land use patterns are expected to have implications on the intensity of river flooding and local flash flooding in a flood plain region and can significantly alter the spatial extent of future flood risk. A flood is an overflow of expanse of water that submerges the land. Floods are among the most destructive acts of nature. Over the past thirty years, floods have been the most catastrophic natural disaster affecting, on average, about 80 million people per year or half of the total population affected by any natural disaster, causing economic damage worth over US$11 million annually around the world (IFRCRCS,1998). As human activities downstream of rivers increases, it results to increase in greater flood damage, floods are also increasing in size and frequency due to human activities in the upstream section of the river system (Dutta et al., 2006). Worldwide , flood damages to agriculture, properties and public utilities amount to billions of dollars each year in addition to the loss of precious human and animal lives. In most 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 the river bed. 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. The role of Geographic Information Systems (GIS) in disasters analysis and management is typically important in critical life saving measures and has been using in developed countries in the last two decades. Advancements in remote sensing (RS) technology and GIS the help in real time monitoring, early warning system and quick damage assessment of flood and drought disasters (Ishaya et al., 2008a. A Geographic Information System is a tool that can assist floodplain managers in identifying flood prone areas in their community. With a GIS, geographical information is stored in a database that can be queried and graphically displayed for analysis. By overlaying or intersecting different geographical layers, flood prone areas can be identified and targeted for mitigation or stricter floodplain management practices. Remote Sensing can be very effective for flood management in two ways; firstly by detailed mapping that is required for the production of hazard assessment maps, hence for input to various types of hydrological models, and secondly by developing a larger scale view of the general flood situation within a river basin with the aim of identifying areas at greatest risk and in the need of