Beach sediments were collected from four selected beaches along the barrier bar lagoon coastal system Lagos Nigeria namely Badagry, Takwa, Alpha and Eleko beaches. The sediments were texturally analyzed in order to determine the statistical parameters of their grain size distribution. The result shows that Badagry and Alpha beach sands are medium grained with average mean values of (1.10 Ф and 1.14Ф respectively). Eleko beach sediment is coarsely grained with an average mean value of (0.56 Ф) while Takwa Bay beach sediment is fine grained and very well sorted with an average mean value of (2.25 Ф.). This suggest that Eleko beach sediment being coarse grained is deposited in a high energy condition hence less vulnerable to erosion compared to Takwa bay beach sediment which is fine grained and deposited in low energy condition hence more vulnerable to erosion. Alpha and Badagry beach sediment are medium grain and deposited in a moderate energy condition hence more stable to erosional forces than Takwa bay beach sediment. The grain size and amount of sand on a beach depends on wave energy and geological sensitivity of the sediments to the forces of erosion
The impact of solid waste disposal on the groundwater within the vadose and saturated zone of two dumpsites namely Aba-Eku and Ajakannga in Ibadan Metropolis was investigated using Vertical Electrical Sounding (VES) to determine the depth and thickness of subsurface layers. Aba-Eku Landfill site is located at the extreme south-western area of Ibadan, along Ijebu road covering an area of approximately 3.5 acres, while that of Ajakannga landfill site is located at the south-eastern area of Ibadan, Both qualitative and quantitative interpretations of the field data were carried out from Vertical Electrical Sounding (VES). The qualitative interpretation reveals points of anomalous resistivity along the traverses of 10m station separation. Partial curve matching and computer assisted iteration techniques were used for the interpretation of the VES data. The approximated topography of the dumpsite was plotted using GPS readings. The pictorial pattern produced gives an elevation model of the two dumpsites. An integrated analysis of qualitative and quantitative interpretations reveals the lithologies of the subsurface for VES with topsoil (0.5m-1.0m) with resistivity ranges from (9.2-68.3)Ohm-m, clayey soil (2.0-11.3m) with resistivity ranges from (2.2-12.30)Ohm-m, overlying the fresh basement of unknown thickness of the respective dumpsites. The result from the VES data gives a qualitative lithology of topsoil and clayey soil (aquitard) which has a low resistivity zone < 100 Ohm-m, underlain by higher resistive basement. The combination of both interpretations obtained from geophysical survey and the digital elevation map was used for the establishment of the environmental and health hazards associated with groundwater movement within the subsurface (vadose and saturated zones) along the two dumpsites.
A geophysical technique was employed to investigate seawater intrusion into freshwater aquifers in the coastal environment of the Lagos, Badagry, and South-Western Nigeria. Electrical resistivity method employing the Schlumberger technique was used to acquire data for eighteen vertical electrical soundings, and five 2-D electrical resistivity imaging using the Wenner array to investigate the vertical extent of seawater intrusion. The Wenner electrode array, which utilizes current electrode half spacing from 1m to 600m, was used to acquire resistivity data in the proximity of the lagoon. Curve types such as the KQ, KQQ, and HKQ were generated for the investigated area also; 4-5 geoelectric layers were generated to a maximum depth of 68m. The subsurface lithology comprise of fine through medium grained sand to coarse sand intercalated in most cases with sandy clay and clayey sand. The resistivity of the intruded saline water was found to range between 7-32Ωm at a depth interval of 9.2 -54.5m and the thickness of saline layers was found to be greater in areas close to the coast. This study shows that both the 2D electrical resistivity imaging and wenner sounding resistivity methods are efficient tools for investigating the saltwater-freshwater interface in coastal areas. Detailed survey should be carried out before citing boreholes due to variation in depth to deeper fresh aquifers. It is recommended that down-the-hole geophysical loggings should be carried out after drilling so that the screen can be installed at appropriate non-saline zone.
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