Spatial Statistical Mapping of Geomorphometry and Drivers of Gully Erosion of the Sedimentary Basin of South-eastern Nigeria

The south-eastern Nigeria as other parts of the tropics have been experiencing diverse levels of soil erosion for decades. An enquiry of the physical and anthropogenic drivers of soil erosion can provide a better insight into the proximate and underlying processes of occurrence of soil erosion. In this study, we employed the basin approach to investigate the nexus between geomorphometry and the socio-physical drivers of gully erosion development in the sedimentary Anambra basin. Multi-sourced remotely sensed and geospatial data were fit to multinomial regression to simulate probability maps of gully development. The laws of basin geomorphometry were also tested on linearity, shape, topographic and dimensionless metrics using digital surface model (DSM) data. Proximity to existing gully, soil, stream order, vegetation index, rainfall, flow direction, curvature and slope were found to be statistically significant to gully development across all models. The result of the study also showed that Anambra is a 7th-order basin: bifurcating averagely at 1.55; with elongation index, circularity ratio, relative relief, sinuosity index, drainage density, and mean peak flow of 3.42, 0.05, 0.21, 0.96, 0.54 km/km2 and 2,916 respectively. This suggests a synergised gully formation process such that the fluvio-dynamics and surficial factors of the basin contribute to gully development. This study thus provides decision-support mechanism for basin management such that the progressive occurrence of sheet erosion can be identified and managed prior to advancing to a fully blown gully. It also provides database for environmental engineering-oriented basin management such that disaster risk can be curtailed while ensuring safe and secured environment for the populace.