Geospatial Assessment of Drainage Density and Infiltration Characteristics in Coastal Catchments of Southern Nigeria

Abstract

Drainage density and infiltration capacity are fundamental morphometric indicators of catchment hydrology, influencing runoff generation, groundwater recharge, and flood susceptibility. This study provides a geospatial assessment of six coastal catchments in southern Nigeria Bomadi, Orashi, Forcados, Niger, Ekole, and Nun using 30-m SRTM DEMs, topographic maps, and GIS-based morphometric analysis. Parameters including stream order, drainage density, stream frequency, bifurcation ratio, infiltration number, and basin shape indices were extracted and statistically analyzed to compare hydrological regimes. The results reveal marked heterogeneity across basins. Forcados shows the highest drainage density (4.60 km/km²) and high infiltration number (19.50), indicating poor infiltration and elevated flood risk. Orashi also exhibits high drainage density (3.15 km/km²) and the highest infiltration number (54.02), confirming dominance of surface runoff and strong structural influence. Conversely, Niger (Dd = 2.04; If = 7.10) and Ekole (Dd = 2.06; If = 3.50) display lower values, reflecting greater infiltration capacity, groundwater recharge potential, and attenuated flood peaks. Bomadi (Dd = 2.13; If = 9.56) and Nun (Dd = 2.95; If ≈ 8.5) occupy intermediate ranges, balancing infiltration and runoff. Notably, bifurcation ratios exceed 9 in Orashi (9.93) and Ekole (9.50), suggesting tectonic or lithological controls, while other basins show more stable branching (~1.8). These findings delineate two hydrological clusters: runoff-dominant basins (Orashi, Forcados) and infiltration-prone basins (Niger, Ekole, Bomadi, Nun). The study demonstrates that drainage density and infiltration indices are robust diagnostic tools for flood mitigation, groundwater sustainability, and climate-resilient planning in Nigeria’s deltaic environments, with wider applicability to global coastal systems.