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Addis Ababa University Libraries Electronic Thesis and Dissertations: AAU-ETD! >
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http://hdl.handle.net/123456789/2082
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| Title: | ASSESSMENT ON HYDRAULIC PROPERTIES OF THE ETHIOPIA TARMABER FORMATIONS |
| Authors: | ABREHA, G/SLASSIE |
| Advisors: | Seifu Kebede (Ph.D)
Engida Zemedagegnehu (Ms.C) |
| Keywords: | hydrologr |
| Copyright: | Jul-2010 |
| Date Added: | 2-May-2012 |
| Publisher: | aau |
| Abstract: | The Ethiopian Tarmaber formation represents, Oligocene – Miocene basaltic shield volcanism on the
northwestern and southeastern plateaus covering an area of about 47,194Km2 (which is 8% of the total
flood basalts aerial coverage in the country). Two types of Tarmaber formations have been mapped. The
Tarmaber Megezez formation (Ntb) with an absolute age of (16 – 13 Ma, Kazmine, 1979) is transitional
to alkali basalt which covers an area of about 22,058Km2 (which is 3.4% of the flood basalts (or traps)
aerial coverage in the country). This formation commonly outcrops in the central highland plateau, the
escarpments and the rift floor and at some localities in the south western highland plateau part of the
country (sees Fig.-2.1 & 2.3). The Tarmaber Guessa formation (PNtb), with an absolute age of (26 –
16Ma, Kazmine, 1979) is alkaline to transitional basalt, often ridge and cliff forming shield volcanoes
with minor trachytic and phonolite flows. It covers a total area of about 25,136Km2 (which is 4.5% of the
flood basalts aerial coverage in the country). This formation dominantly outcrops in northwestern
highland plateau part of the country (see fig.-2.1). The Tarmaber shield volcanoes become progressively
younger to southeastern and south western part of the northwestern Ethiopian plateaus. Well-log data
and pump test data’s analyses show that, the Tarmaber formations aquifer system can be categorized as
consolidated fractured aquifer category where the dominant aquifer types are, confined, double
porosity fractured aquifer system and single plane vertical aquifer systems. The double porosity aquifers
are related to deeply drilled wells reflecting presence of large and narrow fracture systems with high
permeability but lower storage capacity. It also shows that, Tarmaber Megezez formation (Ntb) has
better aquifer productivity than the Tarmaber Guessa formation (PNtb) and yet, both formations show
decrease aquifer productivity with respect to increased drilled boreholes depth and increased age of the
formation. Besides, boreholes drilled within the Tarmaber formations shows that, the wells have high
well loss coefficient values, indicating improper well site location, improper well design and construction
factors and well yield deteriorations with time due to clogging, corrosion and incrustation activities of
the well screens. Spatially, the Ethiopian Tarmaber formations show an increasing aquifer productivity
trend from the highland plateau areas towards the escarpment and the rift floor areas, and yet, from
the north, south, northwest, southwest, northeast, southeast and east- west directions of the highland
plateau areas toward the Lake Tana basin areas. Generally, the Tarmaber basalts aquifer productivity is
highly controlled by the location and geomorphologic setup of the formation outcrop, nature and
degree of weathering, hydrothermal processes and nature, extent, frequency and orientation of the
associated structural features and yet, weathering, hydrothermal processes and other volcanic activities
tend to decrease aquifer permeability while, fracturing, faulting and other tectonic activities tend to
increase aquifer productivity of the Tarmaber formations. |
| URI: | http://hdl.handle.net/123456789/2082 |
| Appears in: | Hydrogeology
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| 10 | | 8.31 MB | Adobe PDF | View/Open |
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