Hydrogeological Investigation: A Case Study on the Groundwater

Hydrogeological Investigation: A Case Study on the Groundwater
Potential Assessment in the Hantebet Catchment, Tigray, Northern
Nata Tadesse*, Berhane A. and K. Bheemalingeswara
Department of Applied Geology, Faculty of Science and Technology, Mekelle
University, Mekelle, Ethiopia [P.O. Box 1604, E-mail: [email protected]]
The Hantebet catchment, which is consists of a vast depressed area bounded by adjacent
Highlands, is located in the Northern Ethiopia in the Tigray Regional State having an
area of 24.4 km2. The major objective of this research work was to conduct a systematic
hydrogeological study of the area which help for better understanding, and then proper
and full exploitation of groundwater resources of the area. Extensive work was carried
out by collecting pertinent primary data of the area in the field and secondary data from
different offices. Different lithological boundaries, drainage patterns, morphological
features and geological structures were traced from aerial photographs. The major
lithological units in the basin are dolerite sills/dykes (45.2 %), shale (13.4 %), limestone
(12 %), siltstone (0.5 %) and alluvial deposits (28.9 %). Stratigraphically, limestone is
found at the base overlain by shale and followed by siltstone. The younger igneous
intrusions of dolerite as a sill and dyke are exposed on the top part of the hills and
plateaus. Alluvium with varying thickness is found overlying all these successions in the
lowlands. The major structures observed in the area are extensional fractures such as
joints, dykes, listric faults, karsts and primary beddings. These structures strongly control
the groundwater movement of the area. The different rocks and unconsolidated sediments
of the area which behave as aquifers have been classified on the basis of the type of
permeability which they exhibit and the extent of the aquifer into localized aquifer with
intergranular permeability, less extensive aquifer with fracture and karstic permeability
and localized aquifers with fractured and intergranular permeability. Even though
limestone and dolerites have a characteristics of being an aquifer due to the place where
they are found they facilitate downward flow rather than being acting as a water bearing
formation. Alluvial sediments, weathered and fractured shale, weathered and fractured
marl, weathered and fractured sandstone, and weathered and fractured dolerite dykes that
are found in the depressed area are important aquifers where groundwater can be
developed. Any future development of groundwater should be concentrated on these
types of formations in the middle of the downstream side of the basin. Later extent and
vertical thickness of the different aquifers; the productivity of the respective aquifers;
and, the presence of additional multilayer aquifers, their respective thickness and
productivity are recommended to be investigated for a better understanding of the
aquifers of the area and then for a better development of the groundwater in the area.
Keywords: Aquifer, fault, fractures, groundwater, permeability.