Geospatial Assessment of Erosion-Induced Land Degradation and Gully Morphodynamics in Imo and Abia States

Severe soil erosion in Imo and Abia States of South East Nigeria has been documented as one of the most economically damaging land degradation processes in the country, yet spatially comprehensive assessment of gully morphodynamics and land loss rates underpinned by rigorous measurement methodologies remains limited. This study conducts a geospatial assessment of erosion-induced land degradation and gully morphological change across a 2,400-square-kilometre study area in Imo and Abia States, combining multi-temporal UAV photogrammetric surveys, Sentinel-2 change detection, and DEM differencing analysis. UAV campaigns at six-month intervals over a two-year period provide high-resolution volume change estimates for twenty actively monitored gully systems. Sentinel-2 change detection over the full study area maps the spatial distribution and annual expansion rates of degraded land patches. Morphodynamic variables including headcut retreat rate, sidewall expansion velocity, and volume loss per unit contributing area are extracted and analysed in relation to substrate lithology, slope gradient, and antecedent rainfall derived from the GPM IMERG archive. Results demonstrate that gully retreat rates are highest in the Okigwe and Orlu zones, averaging 3.4 metres per year at headcuts, with the highest volume loss rates linked to deep laterite substrates exposed by road construction. Regression analysis identifies slope, contributing area, and road density as the strongest predictors of gully activity. Findings are submitted to the Ecological Fund Office and the South East Regional Development Commission. Keywords: gully morphodynamics, erosion, UAV, Imo State, Abia State.