FLOOD INUNDATION MAPPING AROUND LOKOJA CONFLUENCE AREA, KOGI STATE, NIGERIA

Abstract

Flood is characterized as a batch of water spreading over an extent that was mostly dry. Flooding results into a lot of damages and the extent of damage varies from place to place. Lokoja and environs witness flood almost every year with tremendous loss of lives, properties and degradation of the environment. The aim of this research is to evaluate flood in Lokoja and the environs using less complex geo-spatial flood inundation mapping tool. The assessment was carried out using HAND (Height Above Nearest Drainage) tool to identify the probable extent of flood and vulnerable communities at different levels of flood. Datasets used in the study were SRTM based DEM, settlement map and topographic map. Stream was digitized using topographic sheet in polyline format and later converted into raster format in GIS environment using ArcGIS toolbox. HAND is a hydrological terrain analysis approach which uses DEM and stream network as the only input for producing flood inundation maps. HAND value is defined as difference between elevation of a given cell and elevation of nearest cell along stream where it drains. Thus, all cells on the landscape that have a HAND value smaller than the specified stage (water level) were treated as inundated. Different flood inundation scenarios were generated based on varying thresholds and corresponding vulnerable communities were identified. It was concluded that the HAND has a reasonably good prediction skills, and is a low-complexity flood models that can be considered as a suitable alternative for fast predictions in large-scale hyper-resolution operational frameworks, without completely overriding hydrodynamic models' efficacy.