Spatial Analysis Flood Risk Exposure in Ajeokuta Using Geographic Information System (GIS)

Heavy floods in Nigeria have shown increasing trend in recent years. Ajeokuta is one of the areas affected annually by flood due to its location along the river Niger basin.  Flood risk mapping and analysis are vital elements for appropriate land use planning in flood prone areas. The aim of this paper is to demarcate flood risk potential areas and determine the spatial impact of the recent major flood event in Ajeokuta using Remote Sensing and GIS techniques. Identified flood inducing factors in the study area, such as slope, elevation, drainage density, proximity to the river and land use were reclassified and combined to delineate flood risk zones using multi-criteria approach in a GIS environment. The idea was to identify the areas with the highest number of flood inducing factors and assess its proximity to the inundated areas during the recent flood events as a criteria for determination of locations for future flood events. Moderate resolution imaging spectroradiometre (MODIS) data of NASA terra satellite, SRTM, Landsat image with resolution of 30m, geographical map of the study area and geographical information system (GIS) were used for this purpose. Each of the flood indicators was reclassified into four which included high risk, moderately risk, low risk, and no risk  through  ranking process. Flood risk map (FRM) was later generated by overlaying the reclassified maps of all the parameters using addition operator and validated with a view to assisting decision makers on the menace posed by the disaster. The flood risk map revealed that the very high risky places covered area of 376.31 square kilometers (27.63%) while high risky covered 322.88 square kilometers (23.71%), The low risky areas covered 151.76 square kilometers (11.14%)  and areas free from risk covers 511.040 square kilometers (37.52%). This analysis further revealed that 56 settlements are within the very high risk zone these  includes  Geregu, Gbokojo, Adogu, upake, Adogo, Achaga, Badogo, upaga etc Keywords: Risk, Flood Disasters, GIS, S.R.T.M, MODIS DOI: 10.7176/JEES/10-8-07 Publication date:August 31st 202

Earth Observation System-Based Impact Assessment of 2012 Flood in Delta State Nigeria

Flooding is one of the most serious natural hazards in the world. It has become a common natural disaster which has claimed many lives, displaced millions and resulted to the destruction of properties and degradation of contiguous farmland.  Though over the decades the people of Delta state have had to contend with sporadic overflows from the river but not in the scale of 2012 flood event. Flood in 2012, submerged coastal villages, displaced millions of people, submerged several square kilometers of land,  disrupt economic activities and properties worth of millions of naira was lost. This study was provoked based on the fact that since the disaster, no reliable investigation and inventory has been made as a guide for mitigation for future occurrence. Currently Earth observing system (EOS) is gaining popularity in solving many environmental problems due to its accurate and timely delivery of information required for decision making. Therefore the aim of this study was to determine the impact of 2012 flood in delta state.  Pre-flood and flood imageries captured by and Moderate Resolution Imaging Spectroradiometre (MODIS), Land sat imagery with resolution 30m, SRTM with resolution 30 arc second, questionnaire, interview, Global positioning system (GPS)  and geographic information system (GIS) was used for data collection and analysis. The map generated from the non-flood image captured on 20th October 2010 was used as a reference to determine the extent of flooding from the disaster image. Spatial impact was determined based on the extent of the submerged land territory while physical economic impact was measured based on property damages. This study revealed that a total landed area of 2185Sq.kms was covered by flood excluding the original extent of the river. Further assessment  revealed that 785000 people were affected, crops worth’s 3.1 billion naira were destroyed, 231 communities in 12 local government of the 25 local government areas were adversely affected these include 118 communities market, 743 market stalls, 220 primary schools, 84 secondary schools, 435 fish farms, 526 poultry farms, 58 piggeries and 5099 houses. Keywords: key words, MODIS, SRTM, Flood,  Hazard, Imagery DOI: 10.7176/CER/12-9-08 Publication date:September 30th 202