GIS-Based Watershed Delineation and Hydrological Characterisation of Akwa Ibom State, Nigeria
Abstract
This study assessed the hydrological characteristics of the Akwa Ibom State watershed using Geographic Information Systems (GIS)-based watershed delineation. The study was necessitated by the increasing incidence of flooding, erosion and environmental degradation in Akwa Ibom State, coupled with inadequate hydrological information for watershed management and environmental planning. The objectives were to delineate the watershed boundary and drainage network, analyse flow direction characteristics, examine flow accumulation patterns and runoff concentration zones, and identify hydrologically sensitive areas requiring management intervention. A quantitative, raster-based GIS design was adopted. A Shuttle Radar Topography Mission (SRTM) 1 arc-second Digital Elevation Model (about 30 m, acquired February 2000) was mosaicked, projected to WGS 1984 UTM Zone 32N and processed with the ArcGIS Spatial Analyst Hydrology tools through sink filling, D8 flow direction, flow accumulation, threshold-based stream extraction, Strahler ordering and watershed delineation. A Hydrological Sensitivity Index, together with a validation protocol for the DEM and the drainage network and a non-parametric statistical protocol, was specified for the analysis. The stream raster contained 1,404 uniquely numbered stream links, indicating a well-developed and connected drainage network. All eight D8 flow direction classes were present. Flow accumulation values ranged from 0 to 3,965 cells (about 3.57 km² at 30 m), with high values concentrated along major channels and near the watershed outlet. Flow length values ranged from 45 to 7,079 and watershed (basin) identifiers from 1 to 161, and areas combining high accumulation with long flow paths were identified as hydrologically sensitive. These indicators describe runoff-concentration potential, not confirmed flood extent. The study concluded that GIS-based watershed delineation provides a reproducible framework for understanding drainage behaviour and runoff dynamics in Akwa Ibom State, and recommended integrating GIS-generated watershed information into environmental planning, flood management, drainage monitoring and watershed conservation programmes.