Engineering geological mapping of Dar es Salaam city, Tanzania

Abstract

Engineering geological mapping of Dar es Salaam city in Tanzania has been carried out using desk studies supplemented by field reconnaissance as well as limited laboratory tests. Desk studies involved interpretation of medium to large-scale topographical maps, Landsat imagery and sequential aerial photographs from 1953-1990. These studies also evaluated small to medium scale geological, pedological maps together with ground water data from 50 boreholes. Two basic maps were prepared, namely, geomorphological and geological map depicts the spatial extent of the Neogene geological formations. Three distinct sandstone terraces could be distinguished in Dar es Salaam region at 0-15 m and 30 – 40 m above sea level. The terraces comprised sandstones fringed by coral reefs and were backed on their west by uplifted weathered clayey sandstones. Three synoptic construction maps were also prepared:- hazard, resources and land use maps. The hazard map classifies the terrain according to slope steepness, delineates areas susceptible to soil erosion, beach erosion, landslides, flooding, as well as expansive, karstic and saline grounds. The resources map delineates areas with respect to soil fertility as well as the occurrence of sand and gravel, limestone, kaolin, brick clays, heavy minerals and ground water deposits. With respect to light construction of foundations, the middle terrace appeared to be the most suitable in comparison to other terrains.


Tanz. J. Sci. Vol. 28(2) 2002: 83-96