Hydrogeology of Lagos metropolis

Abstract

A study of the groundwater resources and aquifers underlying Lagos metropolis has been made. This is based on well-logs, pumping tests, well-production and water quality data. The data were obtained during construction and use of recent boreholes of the Lagos State mini water works programme.

The sub-surface geology indicates a complex lithology of alternating sequence of sand and clay deposits. Three aquifer horizons were delineated. The first, a water table aquifer (average thickness of 8 m) is mostly exploited through dug wells. The other two, confined aquifers (thickness of 10–25 and 10–35 m respectively), are harnessed through boreholes and are the basis of the mini water works.

Average values of transmissivity (T) and storage coefficients (S) are 3.53 × 10⁻³ m² s⁻¹ and 2.95 × 10⁻⁴ respectively for the second and 17.44 × 10⁻³ m² s⁻¹ and 3.29 × 10⁻⁴ for the third. The range of transmissitivity, the storage coefficient and also permeability indicate considerable inhomogeneity in the aquifers.

Chemical quality determinations show that the harnessed aquifers waters are generally soft. They are suitable for use in domestic, agricultural and industrial processes, if the excessive iron occurring is removed.