Review of Gully Erosion in Anambra State: Geology, Causes, Effects, Control Measures and Challenges Associated with Its Mitigation

Abstract

In South-Eastern Nigeria, particularly in Anambra State, gully erosion presents a serious environmental challenge. With over 100 gully sites in the state, only about 30 have received measures of control but are still not fully under control. Observations have shown clearly that the underlying geology exerts major control over the development of gully erosion in the study area. Progressive gullies in certain areas of Anambra State are caused by various factors, including topography, soil and water pH, lithology type, deforestation, hydrogeology, and geotechnical rock properties. This erosion activity has resulted in the loss of productive lands, water pollution, sedimentation of waterways, and the loss of lives and properties almost every year. However, several government agencies have attempted to manage it using concrete structures, stabilization work such as planting bamboo and cashew trees to increase water intake, and pipe structures to channel the water directly to nearby surface waters through the construction of check dams, embankments, and retention ponds to control the flow of water and sediments. Despite these control efforts, several challenges persist in effectively managing gully erosion in Anambra State. Majority of the concrete structures used to control these gullies have collapsed, leading to the incessant spreading of the site. Inadequate funding, failure of engineering structures, flooding, the geologic setting of the area, limited technical expertise, population growth, urbanisation, a lack of public awareness, and a lack of proper coordination among stakeholders hinder the implementation of comprehensive erosion control measures. It is recommended that concrete drainage channels should not only be used in controlling these gullies but also be integrated with other measures to yield a positive result.