Gully length and average gully depth relationships on two geological sediments in the North Central Nigeria

Abstract

Abstract: Gully erosion is widespread in Nigeria and has been reported in all the states of the Federation.  This study was carried out to examine the relationships between gully length and average gully depth on two geological sediments of varying vulnerability to erosion. The dimensions of 37 and 5 random gully samples formed respectively on the Ajalli Sandstones (AS) and the Upper Coal Measures’ (UCM) geological sediments underlying the Idah-Ankpa Plateau of North Central Nigeria were measured.  The gully length (L) and average depth (D) variables were subjected to correlation analysis and the sample bivariate regression to examine their relationships and the predictability of D using L as a prediction tool on the two formations.  Results show that on the highly erodible AS, L has no correlation with D (R = 0.004, R² = 0.00).  On the more resistant UCM, L is strongly, significantly, but negatively correlated with D (R = –0.899, R² = 0.808, P < 0.05).  The regression analyses indicate that L is not a predictive tool for D on the erodible AS (D₁ = 6.469 + 0.00L₁), whereas on the more resistant UCM, L is a useful parameter for the prediction of D (D₂ = 13.929 – 0.022 L₂), which appears in the form of bed aggradation.  The study suggests that the correlation of gully length with average depth transmutes to a stronger, negative, and significant value with increasing resistance to erosion of the geological formation housing the gully.  It also suggests that the reliability of the gully average depth estimation using the length as a prediction tool improves with increasing resistance to erosion of the geological sediments.  However, the relationship of gully length with the average depth could also be affected by other factors, such as the vertical homogeneity of the sediments.