The impact of charcoal production on soil hydraulic properties, runoff response and erosion susceptibility were studied in both field and simulation experiments. Core and composite samples, from 12 randomly selected sites within the catchment of Kotokosu were taken from the 0-10 cm layer of a charcoal site soil (CSS) and adjacent field soils (AFS). These samples were used to determine saturated hydraulic conductivity (Ksat), bulk density, total porosity, soil texture and color. Infiltration, surface albedo and soil surface temperature were also measured in both CSS and AFS. Measured properties were used as entries in a rainfall runoff simulation experiment on a smooth (5 % slope) plot of 25 x 25 m grids with 10 cm resolutions. Typical rainfall intensities of the study watershed (high, moderate and low) were applied to five different combinations of Ks distributions that could be expected in this landscape. The results showed significantly (p < 0.01) higher flow characteristics of the soil under charcoal kilns (increase of 88 %). Infiltration was enhanced and runoff volume reduced significantly. The results showed runoff reduction of about 37 and 18 %, and runoff coefficient ranging from 0.47-0.75 and 0.04-0.39 or simulation based on high (200 mm h -1 ) and moderate (100 mm h -1 ) rainfall events over the CSS and AFS areas, respectively. Other potential impacts of charcoal production on watershed hydrology were described. The results presented, together with watershed measurements, when available, are expected to enhance understanding of the hydrological responses of ecosystems to indiscriminate charcoal production and related activities in this region.Index terms: hydro-physical properties, infiltration, simulated runoff, watershed hydrology.(
In this study, effort has been made to achieve a comprehensive geophysical investigation on immediate and remote causes of structural/foundation failures, specifically highway(s) within the southwestern basement complex region of Nigeria. Geophysical survey involves the use of Very Low Frequency Electromagnetic method (VLF-EM) which was complemented with electrical resistivity method using two techniques; 2D Electrical Resistivity Tomography (ERT) and Vertical Electrical Sounding (VES) along Akure/Oba-Ile Airport Road, which covers a pilot test of 600 m. The VLF-EM survey produced EM anomalies and identified possible linear features along the study area. The results obtained from the VES were used to determine the second order parameters for determination of subsurface integrity/competence. The geoelectric sections identified three to five geoelectric/geologic subsurface layers along the traverse. The ERT gave information on the subsurface characteristics whose section delineated five major geologic layers comprising of the topsoil, weathered basement, fractured zone, partly fractured basement and the fresh basement. This shows that fracture and weathering are responsible for the structural failures along the study area which are products of probability functions of geodynamics. The methodology can be adopted as a model to proficiently and quickly detect changes in subsurface resistivity, integrity and identify anomalous zones which can serve as useful tool in the understanding of the probability functions of geodynamics that can bring structural and foundation failures within the basement complex region.
Geophysical investigations were carried out around the ministry of Justice building, Ekiti State Secretariat, Ado-Ekiti, with the aim of investigating the possible cause(s) of failures from the foundation of the building in the government Secretariat. The Electromagnetic and Electrical Resistivity methods were used for the investigation. The Electrical Resistivity method involves Vertical Electrical Sounding (VES) and 2D Electrical Resistivity Tomography using Schlumberger and dipole-dipole configuration. Three (3) VES points were conducted along the traverse within the investigated area with half current electrode separation (AB/2) varying from 2 m to a maximum of 65 m. The electromagnetic measurements were taken at distance separation of 10 m along the traverse line in the SE-NW direction. The VES curve types obtained in the area are H and HKH. Four geoelectric layers were delineated within the investigated area which includes the topsoil, lateritic clay, clay, and partly weathered basement which is a quartzite rock with resistivity values ranging from 47-280 ohm-m, 383-435 ohm-m, 47-78 ohm-m, and 239-4999 ohm-m and the thickness ranges from 1-1.6 m, 2.8-4.2 m, and 9.1-27.9 m respectively. The dipole-dipole results also delineate four geologic formations that revealed the differential settlement within the clayey zone of the building foundations. The electromagnetic method also delineated seven subsurface geologic formations which revealed that most of the materials characterizing the subsurface are of clayey composition. The integration of the results showed that the possible cause(s) of failures in part of the building is due to the presence of clayey formations and geologic fractures within the foundation of the studied area.
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