Documenting the Occurrence of Gully Erosion in Relation to Rainfall Intensity in Anambra State

Gully erosion is among the most severe forms of land degradation affecting Southeast Nigeria, causing extensive loss of agricultural land, property, and lives. This study documents the occurrence of active gully erosion sites in Anambra State and analyzes their relationship with rainfall intensity parameters using data from the 2019 to 2023 period. Rainfall intensity records, expressed as maximum 30-minute intensity (I30) values, were extracted from NiMet records at Awka and Onitsha stations. Active gully site locations were inventoried using field GPS surveys and cross-referenced with Google Earth imagery, yielding a database of 47 active gully heads. Statistical correlation between I30 values and gully head advance rates measured during field visits was examined using Spearman's rank correlation. Results reveal a significant positive correlation (rho = 0.69) between high-intensity rainfall events and gully head extension rates, particularly in areas underlain by sandy loam soils. Anthropogenic factors, including road construction, quarrying, and deforestation, are identified as critical predisposing factors that amplify the erosivity of rainfall events. The study maps high-risk gully initiation zones using a composite erosion risk index incorporating slope, soil type, land cover, and rainfall erosivity. Recommendations include soil conservation engineering interventions at identified high-risk sites and enforcement of environmental impact assessment requirements for construction projects. Keywords: gully erosion, rainfall intensity, Anambra, erosivity, land degradation.