Comparing Gully Length and Average Gully Width Relationships on Two Geological Sediments of Varying Vulnerability to Erosion in the North Central Nigeria: A Recent Study

Gully erosion is an environmental problem that confronts the international community. This study was
undertaken to investigate the relationships between gully length and average gully width on two
geological sediments of varying resistance to erosion. Thirty-seven and five gully samples formed
respectively on two homogenous geological sediments (the Ajalli Sandstones (AS) and the Upper
Coal Measures (UCM)) underlying the Idah-Ankpa Plateau of the North Central Nigeria were
measured and their lengths (L) and average widths (W) were subjected to correlation analyses and
the sample bivariate regression to examine and compare their relationships on the two formations.
Results show that on the highly erodible AS, L is positively, poorly, and not significantly correlated
with W (R = 0.201, R2 = 0.040), whereas the correlation is stronger, significant, but negative at the
0.05 level on the UCM (R = -0.930, R2 = 0.865). The regression equations show that L is a poor
predictor of W on the AS (W1 = 6.387 + 0.03L1, R2 = 0.040), and a very good predictor of the
parameter (W) on the UCM (W2=18.135 – 0.033L2, R2 = 0.865), which appears as a negative value.
And the valid range of gully lengths for the prediction of the average width on the AS can be ranked
as 0 = L < ∞ (infinity), whereas the ranking is of the form 0 ≤ L ≤ 549.55 m on the UCM. The study
suggests that the correlation of W with L becomes stronger, negative and significant as the resistance
to erosion of the geological sediments increases. It also suggests that the predictability of W using L
as a tool improves and transforms to a negative value as the resistance to erosion of the formation
increases.