Erodibility Characteristics of Three Geological Sediments in the Idah-Ankpa Plateau of the Anambra Basin, Nigeria

Three geological sediments, namely, the Upper Coal Measures (UCM), the Ajalli Sandstones (AS), and the Lower Coal Measures (LCM), underlie 100% of the landscape of the Idah-Ankpa Plateau (IAP) of the Anambra Basin, Nigeria. The total number of gullies in occurrence on the IAP formation has been estimated at 740, 100, and 1 for AS, UCM and LCM respectively. A total of 34 samples were randomly collected from gully side walls at a depth range of 0 – 15 cm. At sites where gullies did not exist, sampling pits were dug up to a depth of 15 cm within which samples were collected. Fifteen samples were collect from the AS, 14 from the UCM, and 5 from the LCM. Particle size distribution was determined by the hydrometer method, and the dry bulk density was computed from undisturbed cores after weighing, drying at 105oC, and reweighing. The two sets of data were analyzed using descriptive statistics. Results show that the AS had a mean % sand plus %silt = 95, %clay = 5, and a mean dry bulk density = 1.31 g/cm3; the UCM had values of 80, 20, and 1.57 g/cm3; and the LCM 61, 39, and 1.71 g/m3 respectively. The data indicate that the AS sediments are the most prone to detachment and transport, followed by the UCM. Therefore, the vulnerability of the sediments to erosion can be ranked as AS>UCM>LCM, and this can be attributed to their wide variations in particle size distribution and dry bulk density. The findings also agree with the order of proliferation of gullies on the IAP. Activities that trigger accelerated erosion on the AS should be controlled.