Post-Flood Assessment and Damage Mapping Using Satellite Imagery in Lokoja, Kogi State

Lokoja, as the confluence city of the Niger and Benue rivers, experiences severe annual flooding that causes extensive damage to residential properties, agricultural land, commercial establishments, and urban infrastructure in the North Central zone. This study conducts a post-flood damage assessment and spatial mapping exercise for the 2022 and 2023 flooding events in Lokoja using pre- and post-flood Sentinel-1 SAR and Sentinel-2 optical satellite imagery. SAR-based flood mapping exploits the backscatter contrast between inundated and dry surfaces to delineate flood extents under both clear and cloud-obscured conditions. Change detection between pre- and post-flood optical images identifies building damage signatures, road disruptions, and agricultural loss zones. Field validation surveys and NEMA damage assessment reports are used to calibrate and verify remotely sensed damage classifications. Results produce spatial damage maps classifying affected areas into destroyed, severely damaged, moderately damaged, and affected-but-intact categories, disaggregated by land use type. Total affected cropland is estimated at 12,400 hectares, with residential building damage concentrated in the Adankolo, Ganaja, and Felele districts adjacent to the river banks. The study develops a replicable rapid flood damage assessment protocol applicable to annual flood emergency cycles in the Niger-Benue confluence zone. Keywords: flood damage assessment, Sentinel-1, Lokoja, post-disaster mapping, change detection.