Abstract
This research is aimed at appraising the root causes of gully erosion at Inyishi in Ikeduru Local Government Area of Imo State, Nigeria, and the possible geotechnical control and management techniques that could be applied in curbing the menace. In pursuance to these objectives, field and laboratory investigations were undertaken. The field works involved reconnaissance and chain surveys, and contouring of the gully catchments. It was observed that gullies were initiated in the research area by flow concentrations induced by environmental factors related to roads and aligned buildings constructed with inadequate drainage facilities upstream of the gully locations. Laboratory investigations carried out involved engineering analyses of soil samples collected at the gully sites and beds for the determination of the soils grain sizes, Atterberg limits, moisture content, specific gravity, permeability, shear strength and bulk density relations. A summary of the engineering properties of the soil revealed its poorly graded and sandy nature, its inadequate fine materials content, low liquid and plastic limits, which ranged between 35.80 to 42.20 % and 28.35 to 35.00 % respectively, as well as its low permeability index of 1 × 10-2cm/sec. These findings, coupled with the fact that the gully area was underlain with friable and cohesionless soil, with small time of concentration, which renders it easily disaggregated by runoff are pointers to the relative ease of water infiltration and seepage at the gully locations. The erosive power of the slope within the gully area was estimated by chain surveying of the entire catchment. The efficacy of natural local materials such as vetiver grass, wood shavings, palm kernel shells, coconut husk, bread fruit husk, dead plant mulch, etc. for the geotechnical works on gully erosion control and management was explored. General specifications on the geotechnics of managing the installed control works for their sustainable services were proffered.
Highlights
Speaking, three factors – heavy surface runoff, ground slope of the research area and its soil type combine in the determination of its soil erodibility
This research is aimed at appraising the root causes of gully erosion at Inyishi in Ikeduru Local Government Area of Imo State, Nigeria, and the possible geotechnical control and management techniques that could be applied in curbing the menace
In this research the study area was visited to identify the location of the gullies, the topographic survey was initiated for possible reclamation works, the geotechnical data were analyzed, the hydraulic design parameters such as rainfall intensity and quantity of runoff were evaluated and the appropriate geotechnical measures, including soil conservation techniques for gully erosion control in the research area were recommended. 2.3
Summary
Three factors – heavy surface runoff, ground slope of the research area and its soil type combine in the determination of its soil erodibility This underscores the fact that different soils are detached and eroded at different rates under specific conditions such as organic matter content of the soil, its clay content, porosity, hydraulic conductivity, and the vegetal covering in the area. All these affect the shearing resistance of the soil to runoff and other erosion causing agents. For a given rainfall rate, Chukwueze (1986) showed that soil detachment (erosion) is directly proportional to the shear strengths of soils, which Ogbukagu (1986) observed was high in the soil types of the South-
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