




































 
 
 

Asian Review of Environmental and Earth Sciences 
Vol. 4, No. 1, 46-57, 2017 

ISSN (E) 2313-8173 / ISSN (P)2518-0134 
DOI: 10.20448/journal.506.2017.41.46.57 

 
 
 
 
 

 

46 

 

Characteristics and Productivity of the Sediments and Volcanic Rocks Aquifers in 
Sunuta Sub-Basin, Northeast Ethiopia 

 
Gobeze Begashaw1    

Tafesse NT2
     

 

 
( Corresponding Author) 

 
1Amhara Design and Supervision Works Enterprise 
2Department of Geology, University of Botswana, Botswana. 

 

 
Abstract 

Sunuta sub-basin is found within the lower Awash basin, Northeast Ethiopia, having an area of 
1490.5km2. The objective of the research was to characterize the different sediments and volcanic 
rocks aquifers and evaluate their respective productivity. To achieve these objectives, primary and 
secondary data were collected. Primary data such as geological, geological structures, and 82 
water levels were collected during field investigation. 35 constant pumping test and 33 borehole 
log data were collected as secondary data from water offices in the area. With the exception of 
specific capacity, all other hydraulic properties were determined from recovery test data using 
Theis and Neuman analysis methods. Specific capacity was determined from constant discharge 
test data. The Mesozoic sandstone, Tertiary and Quaternary volcanic rocks and recent sediments 
are the main geological formations of the sub-basin. The aquifer types around the escarpments are 
unconfined whereas in the rift floor the aquifers are confined and semi-confined. In the rift floor 
the sediment thickness varies from 166-200m and also found interlayered with volcanic rock of 
rhyolite and basalt, forming multilayer confined and semi-confined aquifer. The general 
groundwater flow direction is from west to east. The different geological formations that are 
found constituting the area are categorized hydrogeologically into aquifer with intergranular 
weathered and fracture porosity and permeability, extensive aquifer with intergranular porosity 
and permeability and aquifer with fracture porosity and permeability. Analysis of pumping test 
data revealed that hydraulic conductivity ranges from 0.268 to 31.1 m/day and transmissivity 
ranges from 9.6 to 2420 m²/day with mean values of 9.55 m/day and 632.79 m²/day, respectively. 
Specific capacity ranges from 0.07 to 65.31 l/sec/m with mean values of 5.45 l/sec/m. On the 
basis of their corresponding transmissivity and specific capacity value, the different aquifers of the 
studied area were categorized into three aquifer potentiality groups: low, moderate and high 
potentiality aquifer. Any future development of groundwater should be focused on the moderate 
and high potentiality aquifers. 

 
Keywords: Afar depression, Aquifer types, Groundwater productivity, Hydraulic properties, Tertiary volcanics. 

 
Citation | Gobeze Begashaw; Nata T. Tafesse (2017). Characteristics and 
Productivity of the Sediments and Volcanic Rocks Aquifers in Sunuta Sub-
Basin, Northeast Ethiopia. Asian Review of Environmental and Earth 
Sciences, 4(1): 46-57. 
History:  
Received: 4 October 2017 
Revised: 6 December 2017 
Accepted: 11 December 2017 
Published: 14 December 2017 
Licensed: This work is licensed under a Creative Commons Attribution 3.0 

License  
Publisher: Asian Online Journal Publishing Group 
 

Contribution/Acknowledgement: Both authors contributed to the conception and 
design of the study. 
Funding: The authors duly acknowledge Amhara Design and Supervision Works 
Enterprise for sponsoring this research work and providing the necessary data. 
Competing Interests: The authors declare that they have no conflict of interests. 
Transparency: The authors confirm that the manuscript is an honest, accurate, and 
transparent account of the study was reported; that no vital features of the study have 
been omitted; and that any discrepancies from the study as planned have been explained. 
Ethical: This study follows all ethical practices during writing.   

 

 

Contents 
1. Introduction ........................................................................................................................................................................................................... 47 
2. Methodology .......................................................................................................................................................................................................... 48 
3. Results and Discussions ....................................................................................................................................................................................... 49 
4. Conclusions ............................................................................................................................................................................................................ 57 
References ................................................................................................................................................................................................................... 57 
 
 
 
 

 

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Asian Review of Environmental and Earth Sciences, 2017, 4(1): 46-57 

47 

 

 

1. Introduction 
1.1. Background  

Groundwater is the second largest available reservoir of fresh water [1]. Worldwide, more than 2 billion 
people depend on groundwater for their daily supply. A large proportion of the world’s agriculture and irrigation is 
dependent on groundwater, as are a large number of industries. Whether groundwater or surface water is exploited 
for water supply is largely dependent on the location of aquifers relative to the point of demand [2]. In Ethiopia 
also groundwater is the major fresh water resource currently used as source for water supply, irrigation and 
industries.  

The study area, Sunuta sub-basin, is well known by uneven distribution of rainfall, scarcity of rainfall, scarce 
surface water and frequent occurrence of drought. Most of the streams are intermittent. The communities’ 
economy mainly depends on livestock production and in some parts in agriculture. Water problem is the main issue 
of the peoples living in this sub basin. This problem, even though, it has been there for long time at present it gets 
worst due to increased in the number residents, livestock’s numbers and agricultural activities in the sub-basin.  

Currently the Federal Democratic Republic of Ethiopian Ministry of Agriculture is undertaking an extensive 
plan for irrigation in the Awash basin (where the study area is located) of the Afar National Regional State in 
different zones using groundwater potential and surface waters to sustain food security of the region and for 
development of the country. Among the areas selected by the ministry for groundwater-based irrigation 
development is the study area.  

The sustainability of this project is highly depending on the proper development, utilization and management 
of the groundwater of the area. Proper and sustainable development of groundwater on the other hand depends on 
proper well site locations that are normally done based on the knowledge of the characteristics of the different 
aquifers and their respective productivity. Such hydrogeological information’s are not available in the Sunuta sub-
basin. This research that makes its objectives on characterization and productivity evaluation of the different 
aquifers is proposed to generate such kind of hydrogeological information’s that can be employed for better 
development of groundwater in the sub-basin.  
 

1.2. Description of the Study Area  
1.2.1. Location  

The study area is located in Afar National Regional State in Zone 4 of EwaWoreda and Amhara National 
Regional State in north Wollo zone. It is found at about 490 km northeast of Addis Ababa. Geographically, the 
sub-basin is located between the UTM coordinates of 556695 to 650305 m E and 1292222 to 1335000 m N, having 
an area of about 1497.5 sq km and a perimeter of 245.9 km (Figure 1). Hydrologically, the sub-basin is located 
within the Awash basin, an endorheic basin drain by a perennial river called Awash that flows along the rift valley 
into the Afar triangle. 
 

 
Figure-1. Location map of the study area. 

Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 

 

1.2.2. Phsiography and Drainage Pattern  
Topographically, the sub-basin is ranging from steep slope to flat land. The elevation ranges from 3479m 

above sea level in the western side to 745m above sea level in the northeastern parts.  



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The dominate topography in the sub-basin is plain and very gently sloping (0 – 4%) areas, which has an area 
coverage of 61% of the total study area. Gently sloping (4 -8%) areas coverage is 22% of the total study area. Areas 
that have a slope ranging from 8 to 30% and greater than 30% constituted 16% and 1% of the total study area, 
respectively. The elevation is decreasing from west to northeast sides of the sub-basin.  

The climate of the area is semi-arid to arid with no or occasional rainy season. It is drained by few perennial 
rivers such as Chereti, Sirinka, and Uwa that rise from western and northwestern mountains (Figure 2). Among 
these only Uwa is the only river that crosses the study area with high discharge during wet season and low 
discharge during dry season. The discharge from this river percolates into the thick sediments of Sunuta plain in 
the eastern parts. Besides to these perennial rivers, the sub-basin is also drained by intermittent streams that rise 
from the western, northwestern, southwestern and southern mountains. With the exception of the northeastern 
parts of the area, the general flow direction of the rivers is west to east. In the northeastern parts of the sub-basin, 
the flow direction of the rivers is northwest to southeast. Generally the drainage pattern of the study area is 
dendritic (Figure 2). 

 
2. Methodology  

Different methods have been used to achieve the objectives of this research. Delineation of the study area was 
done from available topo maps using different software’s, and then finalized by taking GPS readings at different 
sites of the study area for ground checking.  

Collections of pertinent documents, previously done regional and nationwide geological and hydrogeological 
maps, different studied documents around the study area, geological logs and pumping test data of the existing 
boreholes in the study area from different organizations were done. Data for geology and hydrogeology were 
collected in the field with the help of GPS.  

Geological and structural investigations as a technique was conducted in the field paying particular attention 
to the different features of the overlying sediments and underlying volcanic rocks units for groundwater storage 
and transmission. Landsat TM satellite image 15m resolution was used to locate and delineate large-scale tectonic 
structures, specially, faults and fracture systems of the study area with conjunctive use of the field investigation. 
These discontinuity features are extracted and digitized using ARC GIS10.1 software. 
 

 
Figure-2. Drainage map of the study area. 

Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 

Inventory of groundwater structures (boreholes and hand dug wells) were conducted as part of the 
hydrogeological investigation. Except the western area, most of the study area groundwater point elevation was 
obtained by Surveyor’s level in order to have accurate well elevation. For determination of the hydraulic properties 
of the different aquifers 35 constant discharge and recovery pumping test data together with their corresponding 
geological and geophysical logs were used. The data were analyzed using AquiferTest v.3.5 software. With the 
exception of specific capacity, all other hydraulic properties were determined from recovery test data using Theis 
and Neuman analysis methods. Specific capacity was determined from constant discharge test data.  

To determine the different aquifer types and also to characterize the nature of each aquifer besides to the 

preparation of hydrogeological logs, plots of pumping test data on semi‐log scale (specialized plot) and Log‐Log 
scale (diagnostic plot) were prepared for different deep wells using Microsoft office excel 2007 and the drawdown 
behavior were compared with the various theoretical models. Theoretical models comprise the type of aquifer and 
initial and boundary conditions [3]. According to this author, specialized plots are specific to a given flow system. 
Diagnostic plot allows the dominating flow regimes to be identified.   
 
 



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3. Results and Discussions 
3.1. Geology 
3.1.1. Regional Geology 

Ethiopia can be divided in to four major physiographic regions, known as the western plateau, southeastern 
plateau, the main rift and the Afar depression. 

The Afar depression lies within the Afro-Arabian Rift System. This rift system extends from Syria in the north 
and passes through Jordan Valley, Dead Sea, Red Sea, Afar Depression, and East African Rift and terminates in 
southern Africa. The central part of the Afar depression is dominated by lowland plains corrugated by horsts and 
grabens and rare local high relief peaks representing shield volcanoes. It can be divided into northern, east-central, 
southeastern, and southwestern regions on the basis of similar structural trends [4]. Most of the Sunuta sub-basin 
is included in the southwestern part of the Afar depression in the south western region and partly it lies on the 
western escarpment (Figure 3). The geological units of the Afar depression and marginal areas can be divided into 
four broad groups: (1) Neoproterozoic basement, Mesozoic sedimentary rocks, and Eocene– Miocene basalts; (2) 
Miocene igneous rocks (3) Pliocene volcanic rocks (4) Quaternary volcanic and sedimentary rocks. 
 

 
Figure-3. Geological map of the Afar depression (after [5, 6]). 

Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 

3.1.2. Local Geology  
Sandstone  

The sandstone is exposed in the western area in a locality west of AleleSubula town 6 km at Messala ridge 
(595760 E, 1305598 N, 1246m) (Figure 5). The sandstone is existed underlying the Ashange basalts along NNW-
SSE trending normal faults and tilted along with the Ashange basalts by about 350 towards NNE. The upper part 
of the sandstone is red/pink in color, fine to coarse-grained and conglomeratic while the middle part is whitish and 
pebbly.  

Petrographic studies by Water Works Design and Supervision Enterprise [7] reported that the sandstone is 
medium to coarse grained, equigranular with clastic texture, and is composed of quartz (90%), opaque oxides (5%) 
and alkali feldspar (3%). Individual grains are angular to sub-rounded and well sorted. Quartz grains measure 0.5 
mm on average but some are up to 2 mm long. Small amounts of rock fragments are also present. The cement is 
brownish ferruginous material.  
 

Basalts  
The western margin of the study area is covered by Ashange and Aiba basalt whereas the Dahala basalt covers 

the eastern margin of the study area (Figure 5).  
The Ashange basalt is exposed in the Western escarpment at Hamaro, Humo, Sirinka, Dehawodih, and Merto 

area chains of ridges that extend north-south direction in the western parts of the study area. It is characterized by 
thinner individual lava flow thickness of about 5 meters and more alkaline affinity (Figure 4). This unit is highly 
weathered with alteration minerals filling in the vesicles forming amygdales. The individual flows of this unit are 
known to be continuous only for few kilometers along strike. 
 



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Figure-4.a) Contact between different flows of Ashange basalt: on the top part moderately weathered and fractured and the lower part is 
deeply weathered.  
b) Contact between Aiba basalt without secondary material and the lower one is Ashange basalt with secondary material filling and the red 
color line with small thickness 0.3 m indicates paliosoil. 
Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 

 
Granites  

This rock type is found in the form of dykes in the western parts of the study area (Figure 5). It is well exposed 
in Sirinka and Amaro area. The Sirinka granite, which has grey color, is the longest one extended from Sirinka to 
Alwuha away from the study area cutting the Ashange basalt with strike of 250NE. The granite has a grey and 
pink to red color, scarcely fractured in the top part whereas with depth it has a massive nature.  

Petrographic studies by Water Works Design and Supervision Enterprise [7] reported that the granite is 
holocrystalline, coarse grained and inequigranular/moderately porphyritic (20%) and partly glomeroporphyritic. 
Phenocrystminerals are dominated by quartz (70%) and include alkali feldspar (sanidine) (~30%). Quartz is 
subhedral to anhedral and measures up to 5 mm long. Alkali feldspar, which is also euhedral to subhedral, has 
tabular habit and measures up to 1.5 mm long. The remaining smaller-sized minerals are constituted of equal 
proportions of quartz, sodic plagioclase, sanidine, myrmekite and small amounts of opaque oxides.  
 

Mabla Rhyolite  
The Mabalaryolite is found in the western and northeastern parts of the study area forming isolated hills and 

ridges (Figure 5). In the western parts the unit is highly affected by NNW-SSE trending faults and also tilted 
eastward.  

Petrographic studies by Water Works Design and Supervision Enterprise (2011) reported that the rhyolite has 
vitrophyritic texture, and is composed of micrroclitic volcanic glass (~70%), rock fragment (~22%), quartz (~6%) 
and fine –anhedral opaque Fe-oxide (~2%). The groundmass is composed of volcanic glass and rock fragments that 
consist of rhyolite and pumice.   
 

Fluvio-Lacustrine Sediments  
These are found covering the plain areas in the western (Sirinka plain and Woydo plain) and eastern (Sunuta 

plain) parts of the study area (Figure 5). Recent sediments are also found having limited areal extent along the 
river courses in the different parts of the study area. 

Because of high elevation and slope variation between the eastern and western parts of the study area, erosion, 
transportation and denudation created on the western parts favors for the eastern parts of the study area to become 
depositional area. The sediments don’t have uniformity in terms of grain size and thickness throughout the area 
where they are found. They area consist of clay, silt, sand and gravel. In the eastern parts (Sunuta plain) the 
thickness of the sediments varies from 166 – 200m whereas in the western parts it varies from 18 – 50 m. The 
sediments are also found interlayering with basalt.  
 

3.1.3. Geological Structures  
Generally in the study area, there are two related structural features; the Afar depression and the western 

escarpment that formed by down-warping and subsequent faulting and rift ward tilting of fault blocks. The major 
structures are fractures, joints, lineaments and faults. The length of fractures, lineaments and faults varies from 2-6 
km with different trends. Their major trends of these structures are N-S, E-W, NW-SE and NE-SW. The 
dominant trend in the western parts (around Sirinka) of the study area is NNW-SSE direction. 
 



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Figure-5. Geological map of the study area and cross-section from A to B. 

Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 

 
3.2. Hydrogeology 
3.2.1. General 

The saturated aquifer thickness of the sub-basin depended on the existence or not of the interlayered and 
underlying weathered and fractured volcanic rocks and the nature of the sediments. The interlayered and/or 
underlying volcanic rocks have variable weathered and fractured zones thickness, which is also serving as an 
aquifer.   

In the sub-basin the water level ranges from 2.65 m to 79.54 m with a mean of 54.89 m. The deeper water level 
is found in the eastern parts (Sunuta plain) whereas in the western parts the water level is not deep. In the study 
area most of the drilled boreholes show that water table greater than 40m depth. 
 

3.2.2. Aquifer Types  
Interpreting a pumping test is primarily a matter of identifying an unknown system. System identification 

relies on models, the characteristics of which are assumed to represent the characteristics of the real aquifer system. 
Theoretical models comprise the type of aquifer (Figure 6), and initial and boundary conditions. In a pumping test, 
the type of aquifer and the inner and outer boundary conditions dominate at different times during the test. They 
affect the drawdown behavior of the system in their own individual ways. Therefore,to identify an aquifer system, 
one must compare its drawdown behavior with that of the various theoretical models. The model that compares 
best with the real system is then selected for the calculation of the hydraulic characteristics. System identification 
includes the construction of diagnostic plots and specialized plots. Diagnostic plots are log-log plots of the 



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drawdown versus the time since pumping started. Specialized plots are semi-log plots of drawdown versus time, or 
drawdown versus distance to the well; they are specific to a given flow regime. A diagnostic plot allows the 
dominating flow regimes to be identified; these yield straight lines on specialized plots. The characteristic shapes of 
the curves can help in selecting the appropriate model. The choice of theoretical model is a crucial step in the 
interpretation of pumping tests. If the wrong model is chosen, the hydraulic characteristics calculated for the real 
aquifer will not be correct [3]. Depending up on this theoretical log-log and semi-log plots models, the actual 
pumping test executed have been plotted using Microsoft excel in log-log and semi-log form to compare with the 
theoretical and also with conjunctive use of the actual field data of the geological and hydrogeological log data. The 
aquifer is categorized based on these theoretical curves as confined, unconfined and semi-confined aquifer (Figures 
7 - 9). Because of different reasons the pumping test data does not exactly fit with theoretical curves, careful 
analysis were made to distinguish the layers from the hydrogeological log data. The alluvial aquifer has thick clay, 
silt, sand and gravel on the top part and the underlain material is fractured basaltic rocks and beneath this rock 
unit is massive basalts. 
 

 
Figure-6. Log-log and Semi-Log plots of the theoretical drawdown. 

Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 

 
Figure-7. Log –log plots of Badule water supply well showing unconfined aquifer. 

                            Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 



Asian Review of Environmental and Earth Sciences, 2017, 4(1): 46-57 

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Figure-8. Semi-log plots of SW17 water supply well showing Semi-confined aquifer nature. 

                   Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 

 
Figure-9. Semi log Time-Drawdown plot of HD2 irrigation well show confined aquifer nature in Afar Sunuta plain. 

Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 

 
3.2.3. Aquifer Characterization 

The study area is characterized by highly rugged topography in the western area, which is dominantly covered 
by volcanic rocks, and the low land, which is plain area covered by unconsolidated sediments and volcanic rocks. 
Unconsolidated sediments underlying by the volcanic rocks of different types are found covering 60 percent of the 
total study area whereas volcanic rocks of different types are found exposed on the surface on the remaining 40 
percent of the total area. This lithological variation favors the study area to have multi later aquifer system which 



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is sediment-volcanic- sediment-volcanic types of aquifer system mainly observed in the low land area in the eastern 
parts. The western parts of the study area also have alluvial sediments in Sirinka, and Woydo area underlying by 
basaltic rock, which is the major water bearing formation in this part of the sub-basin. Based on such occurrences, 
hydrogeologically these geological formations are categorized into three medium: aquifer with intergranular 
weathered and fracture porosity and permeability, extensive aquifer with intergranular porosity and permeability 
and aquifer with fracture porosity and permeability. 
 
Aquifer with Intergranular Weathered and Fracture Porosity and Permeability (High productivity) 

Unconsolidated sediments and the underlying volcanic rocks constitute such aquifers that are characterized by 
the presence of both intergranular and fracture porosity and permeability (Figure 10). Aquifers of this type are 
found in northern, northeastern, eastern and central parts of the sub basin (Figure 12). The aquifers are mainly 
unconfined and confined types. 
 

 
Figure-10. Hydrogeological log of HD2 irrigation well with high productivity of Quaternary basaltic aquifer. 

           Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 

Extensive Aquifer with Intergranular Porosity and Permeability (High to Very High Productivity) 
This is a porous medium constituted mainly by unconsolidated sediments of different types. It is found in 

limited area coverage in the western parts whereas in the central, eastern, northern and southern parts it is found 
covering extensive areas. Geological logs data obtained from deep wells drilled in the different parts of the eastern 
and central parts of the sub-basin (SW14, SW19, SW20, SW21, SW23, SW26, SW32, SW33 and SW35) revealed 
that the thickness of the fluvo-lacustrine sediments ranges from 166m to 200m. The discharge of these wells 
ranges from 28l/s to 62 l/s with an average discharge of 49.5l/s. The maximum recorded drawdown with a 
pumping rate of 38l/s for 24hrs is 63.35m. The sediments are found underlined by volcanic rocks of different types. 
Moreover this area has also sediments interbedded with volcanic rocks of different types (Figure 11).  
 

Aquifer with Fracture Porosity and Permeability 
This is a fracture medium constituted mainly by fractured volcanic rocks of different types. It is found mainly 

in the western parts of the sub basin (Figure 12) that are characterized by rugged topography. Since the area is 
water contributing area to the central and eastern low land areas of the sub basin, the aquifers are low yield 
aquifers.  
 
 
 



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3.2.4. Aquifer Productivity 
The basic aquifer properties that were considered for evaluating the aquifer potentiality are transmissivity (T), 

hydraulic conductivity (K) and specific capacity. The pumping test data of 35 deep wells were analyzed and the 
results are summarized and given in Table 1. 

The computed values of hydraulic conductivity ranges from 0.268 – 31.1 m/day with mean value of 9.55 
m/day. The lowest one found in the western parts of the study area whereas the highest is found in the eastern 
parts. The average hydraulic conductivity of the aquifers of unconsolidated sediments by taking 8 irrigation wells 
is 8.2 m/day. The result of the analysis also reveal that transmissivity ranges from 9.6 to 2420 m2/day and specific 
capacity ranges from 0.07 to 65.31 l/sec/m with mean values of 632.79 m2/day and 5.45 l/sec/m, respectively. 
 

 
Figure-11. Hydrogeological log of SW14, SW33 and SW35 drilled in sediments interbedded with volcanic rocks. 

           Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 

 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 



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Table-1.Computed hydraulic properties of aquifers. 

No. Well D X Y Depth (m) Q (l/s) S Q/Sw T K 

1  GBH-2  563729  1301682  151  2.1  32.07  0.07  9.6  0.268  
2  SWTW1  566480  1299859  240  19.53  70.97  0.28  96.7  1.4  

3  Badule#2  607012  1310055  286.5  28  12.57  2.23  507  7.78  
4  Merto 627929  1308203  179  22.5  7.39  3.04  245  3.41  
5  Sunuta#2  630875  1305530  225  53  10.16  5.22  1010  14  
6  Sunuta#6  629928  1304713  216  55  6.18  8.90  1220  20.1  
7  HD2  628093  1323022  203  80  14.93  5.36  506  12.6  
8  SW 07  629196  1305200  204  64  0.98  65.31  517  7.8  
9  SW 10  628394  1306098  202  60  3.5  17.14  2420  31.1  
10  SW12  629484  1305759  202  75  25.32  2.96  644  17  
11  SW 13  628801  1306978  193  62  4.3  14.42  1970  26.6  
12  SW14  630033  1306230  228  80  12.93  5.41  519  7.21  
13  SW 15  629348  1307106  200  53  38.63  1.37  56.4  1.34  

14  SW 16  629209  1307721  168  55.5  57.34  0.97  934  19.4  
15  SW 17  628670  1307551  138  53  40.98  1.29  336  5.09  
16  SW 19  629083  1308282  218  55.5  59.86  0.93  341  4.74  
17  SW 20  628952  1308892  200  50  63.35  0.79  38.6  0.68  
18  SW 21  628276  1309272  176  55.5  25.5  2.18  224  3.74  
19  SW22  628391  1308445  124  55  64  0.86  513  12.2  
20  SW 23  628542  1308130  212  53  74.9  0.71  222  2.64  
21  SW 24  629668  1308794  200  52  73.57  0.71  151  2.29  
22 SW 25 628808 1309507 203 58 - - 241 4.01 
23  SW26  628590  1309855  214  62  14.39  4.31  771  8.56  
24  SW27  628471  1310444  202  73  8  9.13  1520  21  

25  SW 32  625457  1305814  174  48  14.34  3.35  931  12.9  
26  SW33  625468  1305024  180  28  6.14  4.56  906  18.9  
27  SW 35  625813  1304050  235  56  12.21  4.59  744  10.7  
28  SW 41  625022  1307597  238  50  23.89  2.09  538  6.4  
29  SW 43  625793  1310860  216  50  27.05  1.85  980  16.3  
30  SW 44  625744  1311458  240  46  48.24  0.95  323  3.59  
31  SW 45  625646  1312069  246  46  40.37  1.14  249  2.76  
32  SW 46  625615  1312667  248  24  40.94  0.59  300  3.34  
33  SW 49  621674  1309303  246  30  68.35  0.44  131  1.46  
34  SW 50  621759  1308681  246  50.6  4.49  11.27  1943  21.6  
35  SW 53  622123  1307034  240  40  48.72  0.82  90.3  1.25  

           Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 
 

In this research, based on the analyzed result of transmissivity and specific capacity, an attempt was made to 
classify the aquifers of the study area into different class of potentiality. This classification was made on the basis of 
Sen [8] scheme.  

Accordingly, the unconsolidated sediments and volcanic rocks of the study area are grouped into three-aquifer 
group. These are: 

1. Low potential aquifer (Tertiary volcanics and overlaying sediment);  
2. Moderate potential aquifer (Alluvial and fluvo-lacustrine sediments with underlying volcanic rocks); and,  
3. Highly potential aquifers (Fluvo-lacustrine sediments and underlying basalts and rhyolites).  

 

Low Potential Aquifer  
Low potential aquifer is mainly found in the western part of the study area (Figure 12). As it was observed during 
field survey, Tertiary Ashange basalt fractures are filled by secondary minerals such as calcite and zeolites which 
decrease the permeability and porosity. The overlying alluvium is also dominated by silt and clay. The computed 
hydraulic conductivity and transmissivity for the borehole drilled in this aquifer is 0.27 m/day and 11.7 m2/day. A 
continuous pumping test was conducted for 1440 minute with a discharge of 2.1l/s and the maximum drawdown 
recorded was 32.07 m. The SWL is 44.66m and the depth of the borehole is 151 m.  
 

Moderate Potential Aquifer (Alluvial and Fluvo- Lacustrine Sediments with Underlying Volcanic 
Rocks)  

This aquifer is located in the western parts adjacent to the rivers and also in the eastern parts occupying 
topographically low land areas (Figure 12). Transmissivity values computed from pumping test data of the deep 
wells that were drilled in this aquifer in the eastern parts of the sub-basin ranges from 50-500 m2/day, indicating 
the moderate potential aquifer. In the western parts computed transmissivity and hydraulic conductivity (Table 1) 
from pumping test data of the deep wells that is drilled in this aquifer also reveal moderate potentiality nature of 
this aquifer. 
 

High Potential Aquifers (Fluvo-Lacustrine Sediments and Underlying Basalts and Rhyolites)  
This aquifer types is found in the eastern and northeastern parts of the sub-basin (mainly in the Afar 

depression, Figure 12) forming multilayer aquifer system. Deep wells that have a depth ranging from 124 to 
286.5m were found drilled in this area for domestic and irrigation purposes. The discharges of the wells range from 
22l/s (for water supply wells) to 80l/s for (irrigation wells). The lithological logs of these wells show that the 
thickness of the sediment ranges from 166 to 200 m with the interlayered weathered-fractured basalt and rhyolite. 
Transmissivity values these multilayer aquifers computed from pumping test data of the deep wells ranging from 
500 to 2420 m2/day. 



Asian Review of Environmental and Earth Sciences, 2017, 4(1): 46-57 

57 

 

 

 
Figure-12. Hydrogeological map of the study area 

Source: Gobeze Begashaw, M.Sc. Thesis, University of Mekelle, Mekelle, Ethiopia, 2016. 

 
4. Conclusions 

The different geological formations that are found constituting the area are categorized hydrogeologically into 
aquifer with intergranular weathered and fracture porosity and permeability, extensive aquifer with intergranular 
porosity and permeability and aquifer with fracture porosity and permeability.Confined, unconfined, and semi-
confined aquifer types, which exist as multilayer aquifer system, are the major aquifer types that were identified in 
the area.  

Analysis of pumping test data revealed that hydraulic conductivity ranges from 0.268 to 31.1 m/day and 
transmissivity ranges from 9.6 to 2420 m²/day with mean values of 9.55 m/day and 632.79 m²/day, respectively. 
This variation of both hydraulic conductivity and transmissivity is a result of differences in intensity of weathering, 
degree of fracturing and interconnectivity nature of fractures in the volcanic rock units. Specific capacity ranges 
from 0.07 to 65.31 l/sec/m with mean values of 5.45 l/sec/m. 

On the basis of their corresponding transmissivity and specific capacity value, the different aquifers of the 
studied area were categorized into three aquifer potentiality groups: low, moderate and high potentiality aquifer. 
Any future development of groundwater should be focused on the moderate and high potentiality aquifers. 
 

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Reclamation and Improvement, 1990. 
[4] B. Alebachew and A. G. Mohamed, Tectonics of the Afar depression: A review and synthesis. Richardson, TX 75083-0688, USA: 

Department of Geosciences, The University of Texas at Dallas, 2005. 
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Any queries should be directed to the corresponding author of the article. 
 

https://scholar.google.com/scholar?hl=en&q=Block%20rotation%20and%20continental%20extension%20in%20Afar:%20A%20comparison%20to%20oceanic%20microplate%20systems
http://dx.doi.org/10.1029/90tc01792

