Visit to undertake groundwater development studies in Tabora region Tanzania (July-September 2000)

Water supply is a major problem in the Tabora Region of Tanzania. During the June to October dry season surface water supplies are scarce and often contaminated. Locating sustainable groundwater sources to supply the region’s growing population is therefore vital. However, groundwater development is constrained by uncertainty over the geological controls on groundwater availability. Limited quantities of groundwater occur in the nearsurface weathered zone and in younger unconsolidated sedimentary aquifers, as well as along fractures within the Precambrian crystalline basement rocks that underlie the region. These resources can be developed using properly constructed boreholes and hand-dug wells. (ii) The complex nature of the geology of the Tabora Region was apparent from detailed desk studies of maps, reports and digital remotely sensed data carried out prior to fieldwork. The results of these studies enabled the selection of appropriate methods for field investigations to provide the necessary data for preliminary evaluation of the hydrogeological resources of the region. The Tabora region is underlain by three main rock types: (i) High grade Precambrian age gneisses, schists and granites of the Tanzanian craton; (ii) Lower grade Cambrian age amphibolites, phyllites, meta-sediments and metavolcanics of the Nyanzian series; (iii) Late Tertiary age lacustrine sediments and associated ash deposits preserved within small scale graben structures associated with the southern extension of the major rift systems to the north. Groundwater occurs in specific aquifer types within each of these main lithological groups and appropriate techniques need to be used to evaluate each. (ii) The BGS team spent three weeks in the Kabale area of Nzega District where seven boreholes were sited and drilled; and a week at three sites in Tabora District where dry borehole sites were resurveyed and previously constructed boreholes tested. Tanzanian counterparts included a senior geologist (DDCA), a geophysicist (Ministry of Water), engineers from WaterAid and the Anglican Church, a consultant hydrogeologist and village water committee members, all of whom fully participated in field work activities. During these studies the BGS team carried out 25 km of EM34 surveys. Detailed geological data, including penetration logs and rock chip sample logs, were collected during the drilling of each of 7 boreholes to assess the lithological characteristics of the main geological formations penetrated. Twenty simple bail and Whale pump tests were carried out to evaluate the hydraulic characteristics of these formations. Twenty-eight water samples for hydrochemical analysis were collected from boreholes and hand-dug wells. All data collected were digitised and managed using spreadsheets and ArcView, a desktop geographical information system (GIS). A preliminary digital base-map of the region was compiled using digital satellite images and topographic maps.