Modeling and mapping groundwater protection priorities using GIS: The case of Dar es Salaam City, Tanzania

Abstract

The problems of population explosion and low level of water supply service provision are prevalent in almost all African cities, including Dar es Salaam. The Dar es Salaam city has a population of about 2.5 million, growing at about 4.3% per annum. Water supplies come from three surface water treatment plants that obtain water from Kizinga River and Ruvu River. The water system is severely under-capacitated, supplying only about 50% of the demand, a situation that makes groundwater an obvious alternative for augmenting the supply. The water authority has drilled bout 40 boreholes, which are directly connected to the main water system. In addition, there is an increasing numbers of private and community's boreholes and shallow and dug (unimproved) wells. However, the potential of groundwater as a long -term source of water supplies in the city is being undermined by urban activities, like crude waste disposal practices and sprawling of unplanned settlements, which threaten its quality. Such practices expose the public, especially the urban poor, to serious health risks. It is thus appropriate to consider sustainable means of groundwater resource utilization in the city before the problems go beyond our reach. An empirical model has been developed and used as a tool to delineate groundwater protection priorities in the city. It includes five factors: water quality, yield, vulnerability, use value of groundwater and land-use. It uses a system of weighting and rating of the factors and aggregates them in a single number, the protection index that shows relative protection priority. The model was used in a GIS environment that enabled mapping of the groundwater protection priorities for Dar es Salaam. The results showed that Charambe and Mbagala wards have high priority for protecting groundwater, while Manzese and Tandale have low. The prioritization enables rational resource mobilization and long-term groundwater management planning. Planners in allocation of land for various uses can easily adopt the model. Moreover, the model has become a first practical step towards sustainable management of groundwater in the city of Dar es Salaam.

Journal of Building and Land Development Vol. 13 (1) 2006: pp. 22-31