Abstract
The evaluation of geotechnical properties of rock materials is used to ascertain the environmental factor that necessitated gully erosion in Orlu and its environs, Imo State, Nigeria. The study is aimed at geotechnically defining the characteristics, causes and formation of the gully erosion with particular emphasis on the current land degradation in the study area. Data used in the study were derived from field measurements, and laboratory analysis. Gully variables such as length, depth and widths were also determined. The result of the geological mapping revealed that there are three geologic formations encountered in the study area namely; Ameki, Ogwashi Asaba, and Benin Formations. The result of the field studies shows that 27% of the gullies observed occur in Ameki Formation while no gully was discovered in Ogwashi Asaba formation. The grain size distribution curves interpretation revealed that 80% (by weight) of the soils are medium to coarse grained sand and fine gravels, while the remaining 18% and 2% are for fine grained sand and coarse grained silt. The Atterberg Limit Test interpretation shows that the plasticity index of the formations ranges from 24.83% to 48.42%. Based on the results of the geotechnical properties of rock materials in the study area, the factors responsible for gullies occurrence in the study area were identified as topography, rainfall, geology, and anthropogenic factors. The devastating effects of gully erosion in the study area were observed to include loss of about 22km2 of arable lands; 2 major and 6 minor road failures; loss of many houses and other infrastructures; pollution of surface and underground water. Finally, it is recommended that the appropriate authorities, individuals and all stakeholders in the environmental protection agency should develop ideas in environment watch towards gully erosion control.
Highlights
Geologic environment of Orlu and environs has undergone destruction due to natural phenomena and man-made activities
The result shows that the kurtosis of the samples ranges from very platykurtic to extreme leptokurtic and the coefficient of uniformity obtained from the samples indicates that the soil samples are uniformly graded within the study area except Afor-nta Isiekenesi that has well graded soil (Table 4)
The conditions that favour gully erosion in the Ameki and the Benin Formations are complete within the study area
Summary
Geologic environment of Orlu and environs has undergone destruction due to natural phenomena and man-made activities. Most common natural disasters of different magnitudes affecting the area include landslides and gully erosion (Okagbue and Uma 1987). The formation of gullies has become one of the greatest environmental disasters facing many towns and villages in Southeastern Nigeria (Adekalu et al, 2007). This region is fast becoming hazardous for human habitation with resultant problems of destruction of roads, economic trees, houses, and loss of arable land. The objective of this study is to investigate the occurrence, source and possible solutions to the gully erosion in Orlu and environs
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