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Engineering
WELL CHARACTERISTICS AND HYDRAULIC PROPERTIES OF AQUIFERS IN THE COASTAL PLAIN SANDS, LAGOS, NIGERIA
E. O. Longe
average depth of 100 metres in Shomolu area of Lagos metropolis, Nigeria. A review of both the theoretical and practical applications of pumping tests in groundwater resource evaluation for coastal plain sands aquifer was carried out. The main activities involved collation of information related to well logs, step-drawdown and constant rate pumping test from existing database on borehole drilling in six wells comprising 10 controlled pumping tests in Shomolu area of Lagos metropolis. Graphical methods based on Rorabaugh’s Hantush–Bierschenk’s analyses were used to determine the components of drawdown due to well loss and aquifer loss from the step-drawdown pumping tests. Conventional analytical methods based on non-equilibrium equation were used to assess the local hydraulic regime of the groundwater system using constant rate pumping test data. The transmissivity values of the multi-layered aquifer system ranged between 345.6m2/day and 2, 332m2/day while the storage coefficient values ranged between 2.8 × 10–4 and 4.5 × 10–4. Both results indicate confined aquifers of artesian conditions. The results from the step-drawdown pumping tests indicate well losses to have constituted a significant component of drawdown in the tested wells mainly due to poor well design, well development; and non-Darcian flow in the multi-layered aquifer. The pumping tests allowed for theoretical and practical prediction of aquifer and well yields in the study area.
13 Pages
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