Saltwater intrusion in the quaternary aquifer of the Dar es Salaam region, Tanzania

Abstract

A description of the occurrence of the salt water intrusion from seawater close to the coastline of Dar es Salaam Region is presented. The present status of intrusion in two pilot areas located between Mlalakuwa and Msimbazi Rivers (locality I) and Msimbazi and Kizinga Rivers (locality II) is evaluated. The causes, effects, remedial measures and future possibility of intrusion are discussed. An investigation on the hydrodynamics of the phenomenon and analysis of the formations as well as the interfacial transition zone is currently being performed. Water samples from Mikocheni, Oysterbay, Msasani, Masaki and City Centre areas show elevated chloride, sulphate and sodium concentrations. Using Stuyfzand (1986) water classification method, about 60 percent of the samples are classified as fresh-brackish to salt and 30 percent as extremely hard. Groundwater was classified into several categories by subtype, i.e., Sodium-Chloride, Sodium-Bicarbonate, Calcium-Bicarbonate, Magnesium-Bicarbonate, Sodium-Mix and Calcium-Mix. The growing human population in and around the investigated areas has had an adverse impact on the water in the shallow aquifer through, among other factors, indiscriminate abstraction of water without knowledge of the aquifer’s capacity.