Hydrogeological mapping and estimation of potential evapotranspiration and recharge rate of Quaternary sand aquifers in Dar-es-Salaam, Tanzania
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Date
2015-11
Journal Title
Journal ISSN
Volume Title
Publisher
International Journal of Geomatics and Geosciences
Abstract
Dar-es-Salaam City is the largest urban centre in Tanzania, with a population of over 4
million. It gets water for domestic use from surface water (Ruvu and Kizinga rivers) and
groundwater. The groundwater was used to supplement surface water supply and has by now
become the major source of water supply in the city. However, despite the importance of
groundwater in the city, limited researches on water quantity and quality have been
conducted and generally the groundwater database is inadequate. The main objective of this
research is to investigate the availability of groundwater by developing a hydrogeological
map of the area and estimate the groundwater recharge rate of the Quaternary sand aquifer in
the plain. The deposits in the study area cover two major periods, Quaternary and Neogene.
They are made up of sedimentary rocks, which were proposed to be deposited in a
fluviatile/deltaic environment with marine intercalations along the seaward margin. The
Uluguru Mountains were probably the source of much of the materials deposited in the area.
Nearly 150 m of Quaternary deposits consist of basically three geological layers: alluvial,
coastal plain and coral reef limestone deposits. These deposits are mostly of Pleistocene to
recent age and are found mainly moving from the coast towards the mainland within the river
valleys. The Neogene deposits are of Miocene and Pliocene period. Two types of formations
characterize these deposits: undifferentiated deposits (Mio-Pliocene clay-bound sands and
gravels) and the fluviatile kaolinitic Pugu Sandstone (Lower Miocene). Hydrogeologically,
the study area has two types of aquifers in the Quaternary deposits: an upper unconfined sand
aquifer (5-50 m thick) and the lower semi-confined sand aquifer (the most productive zone
10-100 m thick). The groundwater recharge is estimated by using monthly precipitation data
for 36 years, runoff and potential evapotranspiration. The average groundwater recharge rate
in the area is 121.7 mm per year. This delivers substantial amounts of groundwater stored in
the sand aquifers of the area.
Description
Journal Article
Keywords
Quaternary aquifers, Hydrogeological mapping, potential evapotranspiration, Groundwater recharge, Tanzania