Groundwater Resources Potential in the Coastal Plain Sands Aquifers, Lagos, Nigeria

摘要

The hydraulic properties of the aquifers located in the coastal plain sands, Lagos, Nigeria had been investigated. 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 tests from existing database on borehole drilling in seven wells to an average depth of 100 m. Graphical methods based on Rorabaugh's Hantush-Bierschenk's analyses were used to determine the components of drawdown due to well and aquifer losses 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 tests data. Data from 11 controlled pumping tests in Shomolu area of Lagos metropolis were analyzed. The transmissivity values of the multi-layered aquifer system range between 345.6 and 2,332 m2/day while the storage coefficient values range between 2.8x10-4 and 4.5x10-4. Both results indicate confined aquifers of artesian conditions. The step-drawdown pumping tests results indicate that well losses constituted a significant component of drawdown in the pumped wells, a phenomenon due to poor well design, well development; and non-Darcian flow in the multi-layered aquifer. The pumping test results allowed for theoretical and practical prediction of aquifer and well yields in the study area.