Flood Vulnerability Mapping of Lokoja Metropolis Using Geographical Information System Techniques

Abstract

Adequate geographic information on flood vulnerability is required to be able to prepare for flood disasters. This study applies Geographical information System Techniques to produce flood vulnerability map of Lokoja metropolis due to its confluence nature and its potential to cause devastating effect to the surrounding communities. This study is aimed at mapping flood vulnerable areas within Lokoja metropolis, for an effective flood disaster management and proper planning. Satellites imageries MODIS of 2011and 2012, SPOT 5 of 2011, location map of Lokoja Metropolis, SRTM DEM, rainfall data, water discharge/gauge data, and GPS coordinates; acquired during field survey were integrated to map areas vulnerable to flooding. In this study Rank Sum method alongside Principal Component Analysis (PCA) is used to calculate the weight of factors that contributed to flooding within Lokoja metropolis. The study is limited to environmental factors such as hydrology, slope, soil type, drainage density, landform and landuse/landcover. Different maps were generated; composite map of the study area, flood extent map, flood plain map, slope map, flow direction map, flow accumulation map, Triangular irregular network, flood vulnerability map and also pie chart showing percentage area impacted, histogram showing the pattern of rainfall within Lokoja metropolis was generated. The approach resulted in four classes of flood vulnerability ranging from not vulnerable, less vulnerable, more vulnerable and most vulnerable areas. The area not vulnerable accounted for 20.25%, less vulnerable area accounted for 34.57%, more vulnerable area accounted for 28.57%, and the most vulnerable area accounted for 16.61%. The study concludes by proffering a number of recommendations aimed at addressing the issue of flooding within Lokoja metropolis. The recommendations includes; construction of levee along areas that are vulnerable to flooding, widening and construction of standard drainages around Lokoja metropolis, dredging of surrounding water bodies to deepen their depth, among others.