Delineation of saltwater zones around the coastal area of Ogidigben in the western Niger Delta from 2d electrical resistivity tomography

Abstract

For freshwater aquifers to be intruded by saltwater, the aquifers must be adjacent and hydraulically connected to the sea. Saltwater zones must also exist below or above freshwater zones in aquifers. Groundwater aquifers in the coastal region of the study area are vulnerable to saltwater intrusion and under severe threat. The paper addresses the use of 2D electrical resistivity tomography (ERT) to map saltwater zones in order to assess the potential of saltwater intrusion into freshwater aquifers. Interpretation of acquired 2D ERT data revealed that profiles nearer the coast depicted significant thin lenses of freshwater zones and thick saltwater zones. Thickness of freshwater lenses varied from 4m- through- 8m to 16m. These lenses have thickness that increases with distance from the shoreline towards the land. The low resistivity images which characterized the uppermost layers of some of the profiles at seashore area (911 Nigh Club) suggest the inundation and infiltration of saltwater into the groundwater aquifers caused by tide. The potentiality of saltwater intrusion into groundwater aquifer is more pronounced around the vicinity of the Ocean than inland areas. The interface between saltwater and freshwater is situated at 60m depth below the surface. Consequent upon the identification of saltwater and freshwater zones, the paper suggests pumping optimization of freshwater lenses and management approach centered on continuous monitoring of groundwater quality and water level decline.

Keyword: Saltwater intrusion, coastal aquifer, Ogidigben, Western Niger delta, 2D electrical resistivity tomography