An Assessment of the Influences of Surface and Subsurface Water Level Dynamics in the Development of Gullies in Anambra State, Southeastern Nigeria

Abstract

ully erosion?induced problems have been challenging the people and government of Anambra State in southeastern Nigeria for a long time. In spite of the numerous geoscientific and engineering studies so far conducted in the area, the underlying causes of these problems still remain poorly understood. In an attempt to contribute to the understanding of the underlying processes responsible for the persistent gully erosion problems in Anambra State, an integrated study utilizing hydrological, geomorphological, and geophysical data was undertaken. Results of the analyses show that bulk density, pH, and organic matter content of the soil range from 1610 to 1740 kg m?3, 5.10 to 5.30, and 0.32% to 0.46%, respectively. Particle size analyses results show that the soils are dominated by coarse sand materials (50%?68%). Variations in the Atterberg limit parameters (liquid limit, plastic limit, and plasticity index) also point to the dominance of coarse materials in the shallow subsurface. Vertical electrical sounding results capture the shallow surface as being dominated by resistive sandy materials that are underlain by lowly resistive clayey materials. Thus, the area is dominated by porous, friable, and poorly cemented coarse materials that are located on a long and steeply sloping terrain of the tectonically elevated Awka?Orlu cuesta. Both overland and subsurface flow processes are responsible for the gully erosion problems confronting the area. Human activities (e.g., deforestation, uncontrolled urbanization, and absence of requisite legislation to protect the environment) and the high elevation of the Awka?Orlu cuesta have aggravated the severity of the problems. An aggressive reforestation program particularly with native trees, promulgation of necessary legislation to protect the environment, and setting up and empowering an enforcement agency should be vigorously pursued. Also, necessary enlightenment campaigns on best agricultural practices that can reduce surface runoff in soil and water conservation may also be helpful in changing the mindset of people.