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

Abstract

Gully 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 23 , 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.

Geohydrodynamic properties of hydrogeological units in parts of Niger Delta, southern Nigeria

“…10 shows that groundwater flow in the study area trends the northeast-southwest direction. The estimation of groundwater flow through elevation (Okoyeh et al, 2014) indicates that water in the pore spaces flows into the Bight of Bonny. The flow direction is believed to be influenced by geologic formation controlled by geohydrodynamic properties and geogravitational pull.…”

Geophysical investigation of Obot Ekpo Landslide site, Cross River State, Nigeria

“…Surface resistivity methods such as VES and two dimensional (2-D) ERT are usually used to investigate various forms of environmental, geotechnical, geological, seismotectonic and hydrogeological problems due to the dependence of resistivity of subsurface materials on various geological parameters Drahor et al, 2006;Grandjean et al, 2006;Hamzah et al, 2006;Akpan et al, 2009Akpan et al, , 2013Heincke et al, 2010;Arango-Galván et al, 2011;Chambers et al, 2011;Okoyeh et al, 2013). These geological parameters include lithology, porosity, degree of saturation and nature of the saturating fluid.…”

“…Rather, isolated communities in the country are usually challenged annually by recurring flood, erosion and storminduced hazards (George et al, 2008a,b;Akpan et al, 2009;Ezezika and Adetona, 2011;Okoyeh et al, 2013), in addition to the occasional outbreaks of epidemics such as yellow fever (Ezezika and Adetona, 2011), cholera (Adagbada et al, 2012; http://dx.doi.org/10.1016/j.jafrearsci.2015.05.015 1464-343X/Ó 2015 Elsevier Ltd. All rights reserved. Ogunniyi, 2014) and meningitis (Collard et al, 2013).…”

“…These widespread processes and activities have made landslides to be a common natural disaster in locations such as riverbanks, hilly and mountainous areas and other inclined terrain. Although documentation of severe and damaging landslide activities do not exist in Nigeria, records are replete with environmental problems resulting from recurrent small-scale mass-movements, particularly in the gully erosion-prone Nanka Formation in Anambra Basin (Egboka and Nwankwo, 1985;Okoro et al, 2011;Okoyeh et al, 2013) and along the banks of Cross and Calabar Rivers.…”

Geoelectrohydrogeological indices of evidence of ingress of saline water into freshwater in parts of coastal aquifers of Ikot Abasi, southern Nigeria

“…This fact can be confirmed from the values of WEC and the TDS which are respectively far > 700 mS/cm and 500 mg/L considered as condonable values for none saline water. This distribution affects the water divides and the groundwater flow directions which are determined by geogravitational pull and geohydrodynamic properties(Okoyeh et al, 2014;George et al, 2015). The distribution of resistivities within the penetrated layers shows electrical boundaries separating layers of different conductivities with either localised or continuous saturations…”