Aspects of the Hydrology of the Western Niger Delta Wetlands: Groundwater Conditions in the Neogene (recent) Deposits of the Ndokwa Area

Abstract

Groundwater conditions in the thin Neogene deposits of the Sombreiro-Warri Deltaic Plain and the Freshwater Swamp physiographic environments of the Ndowa area are not well understood. Physical examination indicates that the deposits are lithologically similar to those of the Benin Formation. All deposits exhibit a fining upwards cyclical sequence of fine, medium-coarse grained and pebbly quartz and feldsphatic sands and differ from each other only in the topmost superficial cover of approximately 6-10m thickness. The configuration of the water table as deduced from measurements in dug wells show that it mirrors the general topography. Ground water movement is unidirectional from the recharge mound centered on Urhonigbe towards the south and east of the area into a major ground water sink stretching from Ogume to Aboh and beyond. The sink evidently sustains the surrounding wetlands year round. Transmissivity of the multilayered aquifer is estimated at 71m² per day. Differences in the chemistry of groundwater from the three physiographic regions are reflected in elevated levels of lead and cadmium at an average concentration of 0.01mg/l and 0.13mg/l respectively in the Sombreiro-Warri Deltaic Plain terrain. Furthermore, while the order of cation abundance in Benin Formation outcrop groundwater is Ca>Mg>K>Na, it is Na>K>Ca>Mg in the Sombreiro-Warri Deltaic Plain and the Freshwater Swamps. Coliform bacteria occur in all samples tested. These findings have important implications for water and environmental management of the Ndokwa area that deserve further and closer examination.