Umudike Journal of Engineering and Technology

Small watersheds generate the flash floods and localized inundation that account for a disproportionate share of global flood damage, yet most remain ungauged and structurally uncharacterized, particularly across the developing world. Digital Elevation Models (DEMs) coupled with Geographic Information System (GIS) tools have become the standard means of delineating such watersheds and quantifying their morphometric properties without recourse to extensive field survey. This review systematically synthesizes sixteen primary peer-reviewed studies — twelve regional case studies of small, flood-prone watersheds spanning Asia, Africa, the Middle East, Europe and the Americas, and four methodological, DEM-comparison and review studies — that combine DEM and GIS techniques to delineate small watersheds and compute their linear, areal and relief morphometric parameters. The generalized DEM-to-parameter workflow is traced from data acquisition through stream ordering to flood-susceptibility prioritization, and the vertical accuracy and resolution trade-offs of commonly used open-access DEMs (SRTM, ASTER, Cartosat, ALOS PALSAR, and the Copernicus Global Land Operations DEM, GLO-30) are compared. The review further synthesizes how bifurcation ratio, drainage density, form factor, circularity ratio, relief ratio, and compound-factor or analytic-hierarchy-process-based prioritization schemes are applied worldwide to flag flood-prone sub-watersheds. Persistent gaps include inconsistent DEM-resolution selection for small basins, limited field validation, and the absence of a universally agreed classification of parameter values. It is accordingly recommended that small, headwater-dominated basins be characterized using sub-15 m DEMs (e.g., ALOS PALSAR/AW3D, Cartosat, LiDAR or IfSAR) where feasible, and that DEM-derived boundaries and susceptibility rankings be validated against field- or community-reported flood data.