APPLICATION OF ELECTRICAL RESISTIVITY TOMOGRAPHY AND MODELING TO MAP SALTWATER INTRUSION IN OGHEYE AREA OF WESTERN NIGER DELTA, NIGERIA

Abstract

Saltwater intrusion into coastal aquifer of Western Niger Delta has been a major challenge due to strategic position to Atlantic. This study investigates the depth and distance of intrusion from the ocean using Vertical Electrical Sounding (VES), 2D Electrical
Resistivity Tomography (ERT) and intrusion modelling. Three zones of intrusion were delineated; saltwater at 3.6-36.6m (1.1-4.7Ωm), saltwater-freshwater zone at 36.6-55m (18.7-29.2 Ωm) and freshwater zone >55m (56.3-115 Ωm). Longitudinal conductance, transverse resistance and longitudinal resistance delineated saline water to range from 33- 15S 200-2400Ωm2
, 1–5.6Ωm respectively. The Dar-zarrouk parameters described the intrusion as a gradual lateral encroachment. 2D ERT delineated saltwater intrusion at various distance from the ocean within a depth of 10m, saltwater zone (2.23-3.20Ωm) and interface (3.83-5.94Ωm). The model result revealed that groundwater tends to flow towards the ocean and river with hydraulic head ranging from 0-1.5m. The model revealed that intrusion was caused by lateral intrusion which increases with time, depth and distance. The
model divides the intrusion into three zones; saltwater zone (13.0-35Mg/L), transition zone (2.0-13.0mg/l)and freshwater zone (<2.0mg/l). The model also revealed that the lateral intrusion is greater at deeper layers >150m than at top layers. Relict saltwater and lateral intrusions are two forms of salt water occurrence delineated within the study area.