Digital Terrain Modelling for Flood Routing and Inundation Analysis in the Benue River Valley

The Benue River valley is one of Nigeria's most flood-prone corridors, experiencing near-annual catastrophic inundation events that destroy crops, displace communities, and damage critical infrastructure across Benue, Kogi, and Anambra States. This study applies digital terrain modelling for flood routing and inundation analysis in the Benue River valley, focusing on the reach between Makurdi and the Benue-Kogi state boundary. A high-resolution Digital Terrain Model is constructed from an integration of airborne LiDAR strips, GPS cross-section surveys at fifty-metre intervals, and SRTM infill for areas beyond the LiDAR coverage swath. The HEC-RAS 2D unsteady flow model is parameterised using the DTM, Manning roughness values calibrated against documented flood events, and upstream discharge boundary conditions from the Benue River hydrometric station. Design flood simulations for ten, fifty, and one hundred year return period events are conducted, and resultant inundation depth and velocity rasters are computed for each scenario. Spatial analysis intersects the inundation rasters with population, infrastructure, and agricultural land datasets to estimate potential impacts per scenario. Results are validated against the 2022 catastrophic flood extent documented by the National Emergency Management Agency. The study provides a DTM-based inundation atlas for the valley as an operational emergency planning tool. Keywords: digital terrain model, flood routing, inundation analysis, Benue River, HEC-RAS.