Groundwater quality degradation due to salt water intrusion in Zanzibar Municipality

Abstract

Saltwater intrusion problems are widespread where there are over pumping of groundwater from coastal aquifers. Water samples were collected from production boreholes in Zanzibar municipality and analyzed for salinity indication parameters comprising of chloride, electrical conductivity, total dissolved salts and percentage salinity levels. Historical water quality data of boreholes were also collected and used to establish trends. The water quality results indicated that the groundwater from the boreholes is progressively becoming more saline against the pumping age. The increase in salinity indicates progressive saltwater ingress in the aquifers. These trends show that saltwater intrusion is still limited around the shoreline areas especially Beit-el-Ras and Mbweni. The aquifer under the historic Stone Town area is also showing high potential for saltwater intrusion for which increased pumping of groundwater may render it saline. To curb this problem, controlled groundwater pumping and establishment of a long-term monitoring programme have been recommended.

Keywords: Zanzibar, groundwater, saltwater intrusion, water quality, Tanzania, stalinization