RAPID ASSESSMENT OF GROUNDWATER RESOURCES IN ZANZIBAR

Sub-Saharan Africa is believed to host large groundwater reserves that remain unutilized. The SADC Groundwater Management Institute estimates that the 16 member states of the Southern Africa Development Community have groundwater reserves amounting to at least 2.5 million litres per year (at least 2491m3 / capital / year), which exceeds that of Europe and Asia. Despite this, the institute noted that the region utilizes only 1.5% of its potential groundwater reservoir. The SADC Water Division on the other hand reports that, only 61 per cent of the region’s population has access to clean water, mainly due to poor infrastructure. This implies that the other 40 percent is exposed to unclean and unsafe water sources.

The Tanzanian autonomous archipelago region of Zanzibar is grappled with this challenge. In order to have a better insight of the challenge, the Ministry of Water, Energy and Minerals of Zanzibar launched a study to undertake a rapid assessment of the groundwater potential in Zanzibar (Pemba and Unguja). The study was supported by SADC Ground Water Management Institute (GMI), Zanzibar Water Authority and Global Water Partnership under the technical guidance of Dr. Subira Munishi of University of Dar es Salaam.

The study highlighted that groundwater remains the major source of water in Zanzibar. This is because there are very few rivers that flow throughout the year while most of them have a short travel time after which they quickly infiltrate and disappear into the underground zone. The rapid assessment study also highlighted the continued deterioration of groundwater quality, mainly due to the nature of aquifers in the archipelago. The unconfined nature of the aquifers makes them to be highly prone to diffuse pollution from diverse anthropogenic activities. Dr. Subira showed through an elaborate mapping exercise that, settlement and urban dwellings are strategically located where the major aquifers and springs are; with the settlements being attracted by water availability but consequently threatening the sustainability of this vital resource.

The rapid assessment study revealed that most wells in Unguja, the largest island of the Zanzibar archipelago with a population of close to 900,000 people, have higher salinity values (amount of dissolved salts in water) that are two or four times above the permissible limits. In the southern part of Unguja, with the largest ground water reserves, water wells have salinity values as high as seven times above the recommended limits. The study also shows that springs and shallow wells in the Islands of Unguja and Pemba have very high levels of bacteriological pollutants mainly due to anthropogenic activities.