Gully Erosion Study in Bida Town, North-Central Nigeria using Integrated Geoscience Techniques

Abstract

The present study used different geoscience techniques to determine soil characteristics and subsurface conditions that lead to the gully erosion in Bida area, north central Nigeria. Geological, hydrogeological, geotechnical and geophysical investigations were employed in this study. The geological mapping revealed Bida Sandstone as the principal lithology in the area and it agrees with the stratigraphic configuration of the study area. The well inventory showed a shallow water level (1.4 m to 6.9 m), with groundwater flowing towards the central portion of the area, which coincides with the areas been ravaged by gully erosion. A total of 24 soil samples were collected from four different Gully sites in Bida and subjected to geotechnical analyses. The value of Moisture Content (MC) ranged from 2.95% to 18.08% with an average value of 10.66% The Maximum Dry Density (MDD) varied from 1.89g/cm³ to 2.04g/cm with a mean value of 1.94g/cm while the Optimum Moisture Content (OMC) is in the order of 10.30% to 11.40% with average value of 10.85% The low values of MDD and OMC indicates loose formation with little or no binding materials and soils with these characteristics are prone to gully erosion. The results of the sieve analysis indicate that the area is dominated with fine to medium grained sand. The plasticity test showed that the soil samples from the study area are non-plastic except for sample locations L1C and L4C with very low plasticity (plastic limit between 4,40% and 29.60%, liquid limit from 10.78% to 14.40% and plasticity index of 10.00% to 18.82 %). This implies that the soil in the study area is non-cohesive soils. The 2D resistivity carried out at gully erosion sites indicate intermediate to high resistivity values of 110 Ωm to 190 Ωm in the profile distance interval of 5m to 60m, this is characteristics of non-plastic soils like sandstone. Underlying the intermediate to high resistivities is the layer flanked by zones of significantly lower resistivities indicating zones of water saturation with resistivity of about 67 Ωm. The study established the dominance of gully erosion in Bida area can be attributed to the presence of non-plastic and friable sandstone formation, increased rainfall, shallow water table, intensity of groundwater flow, saturation of the subsoil, poor drainage system, sand mining along river course and deforestation. Remediation techniques such as construction of concrete terracing and planting of trees, cover crops and wind resistant grasses as well as proper drainage system for the entire Bida town are highly recommended