Dallol Area Groundwater Potential Assessment Summary

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FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA
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\ r *_ v MINISTRY OF WATER, IRRIGATION AND ENERGY DALLOL AREA GROUNDWATER POTENTIAL ASSESSMENT PROJECT
MUSLEY AND ADJACENT FAN AREAS GROUNDWATER POTENTIAL EVALUATION
Main Report (Final)
March 2014
GE
WATER WORKS DESIGN AND SUPERVISION ENTERPRISE
P.O.Box 2561, Addis Ababa Ethiopia
Tel: (251) 011 6614501/6631890Fax: (251) 011 6615371 email:w.w.d.s.e@ethionct.et
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report (Final), March. 2014
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EVALUATION OF DALLOL AREA '<> '
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DETAIL RECONNAISSANCE REPORT STRUCTURE OF THE REPORT
PHASE - 1 :            EVALUATION OF GROUND WATER POTENTIAL FOR MUSLEY AND ADJACENT FAN AREAS
SnNEX-I^MAIN REPORT
ANNEX-11: TEST WELLS ACCOMPLISHMENT REPORT
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report) Final), March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwatei assessment and Evaluation Project
TABLE OF CONTENT
acronyms............................................................................................................................................................................................................ IX
executive summary........................................................................................................................................................................................x
1- INTRODUCTION.......................................................................................................................................................................................................1
1.1   GENERAL...................................................................................................................................................................................................... 1
1.2  Location and Topographic situation of the area....................................................................................................................................... 2
1.3   Constraints of the Project........................................................................................................................................................................4
2. OBJECTIVE OF THE STUDY.................................................................................................................................................................................. 4
3- REVIEW OF PREVIOUS STUDIES......................................................................................................................................................................... 5
3.1  Review of previous geological investigation carried out in the area.....................................................................................................5
3.2 Review of previous Hydrogeological investigation carried out in the area...........................................................................................6
4    HYDRO METROLOGY......................................................................................................................................................................................... 9
4.1  Introduction.................................................................................................................................................................................................. 9
4.1.1     Background....................................................................................................................................................................................... 9
4.1.2    Climate.................................................................................................................................................................................................9
4.1.3     Objective and Scope of the      Study..............................................................................................................................................9
4.2           Methodology..................................................................................................................................................................................... 10
4.2.1     Data collection................................................................................................................................................................................ 10
4.2.2             Method of recharge estimation............................................................................................................................................. 10
4.3  Land.use/i_and cover and Soil Characteristics of the Project Area................................................................................................. 11
4.4           Data Availability................................................................................................................................................................................ 15
4.5   Meteorological Data................................................................................................................................................................................16
4.6  Climatic data...............................................................................................................................................................................................17
4.6.1   Precipitation.......................................................................................................................................................................................17
4.6.2   Hydrology Data..................................................................................................................................................................................19
4.6.3  Spatial Distribution of Stations........................................................................................................................................................ 19
4.7  Trend Analysis............................................................................................................................................................................................21
4.8  Ground water recharge estimation.........................................................................................................................................................22
4.8.1   Major activities....................................................................................................................................................................................22
4.8.2   Water balance model......................................................................................................................................................................... 22
4.9   Data Analysis.............................................................................................................................................................................................25
4.9.1    Introduction....................................................................................................................................................................................  25
4.9.2   Rainfall data Analysis........................................................................................................................................................................77
4.9.3   Transfer of Rainfall Data................................................................................................................................................................... 27
4.10    Other Climatic data............................................................................................................................................................................... 32
4.11  EVAPORTRANSPIRATION...................................................................................................................................................................... 35
4.12  Runoff Estimation For Dallol Ground Water Assessment Project.................................................................................................36
4.13  Ground Water Recharge Estimation of Dallol Ground Water Assessment Project Area........................................................... 41
4.14  Recharge Assessment............................................................................................................................................................................. 41
4.15  Conclusion and recommendations......................................................................................................................................................... 43
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Reportf Final), March 2014
iiiWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
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5- GEOLOGY
5.1  Introduction45
5.1.1    General45
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5.1.2   Physiographic-......................................................................................................................................................................................................... 45
5.1.2.1 Western Highlands and Rift Escarpment (A)~-.....................................................................................................................................................45
5.1.2.2   Graben Area (B)45
5.1.2.3   Alluvial Fans (C)..................................................................................................................................................................... 46
5.1.2.4   Salt Plain (D)~46
5.2  Previous Works-48
5.3    Objective of the Study49
5.4  Methodology49
5.5  Geomorphology50
5.5.1   General50
5.5.2   Land Forms50
5.5.2.1 Structural land form-............................................................................................................................................................................................ 50
5.5.2.2 Alluvial landform.......................................................................................................................... --51
5.5.23 Evaporite landform..51
5.6     Geology54
5.6.1   Regional Geology54
5.6.2   Geological Setting of the Study Area55
5.6.2.1        Precambrian Rocks ....................................................................................................................................... -........................................... 56
S.6.2.2 Granitic Intrusion 5.6.23 Limestone Unit
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5.6.2.4    Metasediments (Slates and Phyllites)-........................................................................................................................................................... 58
5.6.2.5  Meta-Conglomerate......................................................................................................................................................................................... 59
5.6.2.6   Meta-Greywacke-.............................................................................................................................................................................. -.............. 59
5.6.2.7  Meta-Volcanic Rocks60
5.6.2.8      Paleozoic Sediments 
61
5.6.2.9   Mesozoic Sedimentary Rocks.......................................................................................................................................................................  61
5.6.2.10   Tertiary Rocks62
5.6.2.11   Quaternary Deposits_................................................................................................................................................................................... 63
5.6.2.12   Sedimentary Deposits—63
5.6.2.13    Volcanic Rocks..........................................................................................................................................................................................................-65
5.6.2.14    Evaporite Deposits................................................................................................................................................................. ..................... 65
5.6.3      Tectonic Structures69
5.63.1       Regional Tectonic Setting69
5.6.3     2 Tectonic Structure of the Study Area70
6     . GEOPHYSICAL INVESTIGATION76
6.1            General76
6.2  Methodology and Instrumentation76
6.3   Volume of Work............................................................................................................................................................................................... 77
6.4  Results of VES and Transient Electromagnetic Survey78
7   - HYDROGEOLOGICAL SURVEY AND INVESTIGATION ANALYSIS108
7.1     Water Point inventory108
7.1.1   Introduction and Field Work108
7.1.2   Characteristics of Water points109
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final). March 2014
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7.2    Groundwater Quality Analysis and Evaluation.................................................................................................................................................. 114
7.2.2
Objective and Methodology............................................................................................................................................................................ 114
7.2.2
Fieldwork Sampling and Analysis.................................................................................................................................................................115
7.2.3
Major element geochemistry of the groundwater in Dallol groundwater basin........................................................................................115
7.3      Drilling of Test wells.............................................................................................................................................................................................130
8     AQUIFER CHARACTERIZATION OF DIFFERENT GEOLOGICAL FORMATIONS........................................................................................................... 137
8.1  Alluvial fan aquifers of high productivity (Shallow Aquifer System) - Qpf................................................................................................ 137
8.2  Alluvium Aquifers of Graben Areas and intermountain plains of Moderate productivity - (Qp).............................................................141
8.3    Sedimentary Rock Aquifers of moderate productivity (Deep Fractured Aquifer System near the Escarpments) - Ja + Jt
+ NRS + PZT........................................................................................................................................................................................................................... 141
8.4  Basement Aquifers of low productivity ( Mtasedimentary and Metavolcanic rocks)- PR21 + PR2t)..................................................... 141
8.5   Aquicludes ano Aqutards - ( Qh + Q + Cppt + grt )...................................................................................................................................... 142
9  GROUNDWATER FLOW, RECHARGE AND DISCHARGE..................................................................................................................................................143
9.1  Regional Groundwater flow system...................................................................................................................................................................... 143
9.2    Groundwater flow in the Alluvial Fan Aquifers...............................................................................................................................................145
. 9.3 Groundwater Recharge.................................................................................................................................................................................................. 147
9.4              Groundwater Discharge............................................................................................................................................................................... 148
10. EVALUATION OF GROUNDWATER POTENTIAL............................................................................................................................................................... 149
10.1   Evaluation of fresh Groundwater Potential....................................................................................................................................................149
10.2  Evaluation of Brackish Groundwater Potential..............................................................................................................................................150
11    ESTIMAION    OF    THE    EXPLOITABLE    GROUNDWATER    POTENTIAL    IN    PROSPECTIVE    SITES    OF    MUSLEY    AND    GEHERTU FAN AREAS................................................................................................................................................................................................................................. 151
11.1  Analytical methods of estimation of exploitable groundwater potential in the prospective site of Gehertu fan area
............................................................................................ :................................................................................................................................................ 151
11.2   Estimation of exploitable groundwater potential in the prospective Area of Musley fan................................................................. 154
REFERENCES............................................................................................................................................................................................................................159
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VWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
LIST OF FIGURES
Figure 1.1: location Map of the Project Area........................................................................................................................................................ 3
Figure 4.1: Son map of Dallol Project area......................................................................................................................................................... 13
Figure 4.2: Land use and land cover map of Dallol Project area............................................................................................... -............ 14
Figure 4.3: Mean monthly rainfall pattern of the project area..................................................................................................................19
Figure 4.4: Hydrometeorological station maps of Dallol ground water assessment project................................................................20
Figure 4.5: Long-term annual rainfall series at Dallol Project area........................................................................................................... 21
Figure 4.6: Conceptualization of the water balance of the WATBAL model................................................................................................. 22
Figure 4.7: Mean Annual Monthly Rainfal at Berhale Meteorological Station.......................................................................................... 27
Figure 4.8: Altitude and rainfall relation for the Dallol Ground water Assement Project Area........................................................28
Figure 4.9: Mean monthly distribution of Temperature, Relative Humidty,Wind Speed and Sunshine duration...................................35
Figure 5.1: Physiographic Map of the Study Area............................................................................................................................................... 47
Figure 5.2: Structural Land Form........................................................................................................................................................................... 30
Figure 5.3: Alluvial land form...................................................................................................................................................................................51
Figure 5.4: Evaporite land form............................................................................................................................................................................... 52
Figure 5.5: Land Forms in the Study Area.............................................................................................................................................................. 53
Figure 5.6: Land Sat Image of the Project Area................................................................................................................................................... 56
Figure 5.7: Granitic intrusion in the Project Area.............................................................................................................................................. 57
Figure 5.8: Folded limestone unit..............................................................................................................................................................................58
Figure 5.9: Fouated and tilted slaty cleavage exposed on the escarpment.................................................................................................. 58
Figure 5.10: Meta-Conglomerate.............................................................................................................................................................................. 59
Figure 5.11: Meta-Greywacke.................................................................................................................................................................................... 60
Figure 5.12: Meta-volcanics underlain by acidic materials................................................................................................................................ 60
Figure 5.13: Sandstone unit, exposed at the eastern part of the graben area............................................................................................ 61
Figure 5.14: Thick limestone successions.............................................................................................................................................................. 62
Figure 5.15: The Denakil red series exposure.......................................................................................................................................................63
Figure 5.16: Tthe alluvial fan and boreholes drilled for test........................................................................................................................ 64
Figure 5.17: Travertine exposure............................................................................................................................................................................ 64
Figure 5.18: Central chain of active Quaternary volcanoes........................................................................................................................... 65
Figure 5.19: The salt plain and colorful evaporite deposits, Dallul.............................................................................................................66
Figure 5.20; Geological map of the study area and Cross Section along West to East Direction..................................................... . .68
Figure 5.21: Geological cross section A- A...........................................................................................................................................................68
Figure 5.22. Tectonic framework of the western Afar margin (Zanettin and Justin-Visentin, 1975).......................................................69
Figure 5.23: limestone unit displaced by normal Faults.....................................................................................................................................71
Figure 5.24: Drag fold exposed in meta-volcanic rocks.................................................................................................................................... 71
Figures. 25: Strongly tilted fault block exposing basement rocks........................................................................... -.................................. 72
Figure 5.26: Strongly deformed and foliated basement rocks at the foot of the horst block............................................................. 74
Figure 5.27: Collumnary jointed basalts and quartz vein exposed in grano-doiorite intrusion............................................................. 75
Figure 5.28: Structural map of the study area....................................................................................................................................................75
Figure 6.1: location map for geophysical survey points and section lines.................................................................................................. 79
Figure 6.2: TEM model Curves, and interpretations for Gehrtu and Musley fan area............................................................................. 80
Figure 6.3: Vertical Salinity Distribution at depth interpreted from TEM geophysical survey........................................................... 101
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014
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Figure 6.4: interpreted TEM section on Gehertu fan area................................................................................................................................102
Figure 6.5: VES Model curves interpreted on Musley and South Musley fan areas..................................................................................104
Figure 6.6: Photos taken during geophysical investigation on site................................................................................................................ 107
Figure 7.1: Water points inventory Map................................................................................................................................................................ 110
Figure 7.2: Water point distributions in the river catchments of Dallol..................................................................................................... 112
Figure 7.3: Variations to groundwater level elevation with topography.....................................................................................................113
Figure 7.4: Relationship of Electrical conductivity with Total hard. Chloride, Sulphate and Calcium............................................... 116
Figure 7.5: TDS versus well bottom elevation..................................................................................................................................................... 117
Figure 7.6: Electrical Conductivity Map............................................................................................................................................................... 118
Figure 7.7: Topographic Control on Sodium and Chloride concentration................................................................................................... 120
Figure 7.8: Chloride distribution map of Dallol Catchment related to Topographic effect.................................................................. 121
Figure 7.9: Chloride and Sodium relationships............................................................................................................. -..................................... 122
Figure 7.10: Water Quality (TDS) Map of Musley fan and Adjacent area...................................................................................................... 12S
Figure 7.11: TDS versus well depth........................................................................................................................................................................ 126
Figure 7.12: Piper plot for water samples in the water shade areas.............................................................................................................127
Figure 7.13: Piper plot for water samples in the fan areas............................................................................................................................. 128
Figure 7.14: Test wells distribution Map............................................................................................................................................................... 134
Figure 7.15: Photos taken from driuing and pump testing.................................................................................................................................136
Figure 8.1: Hydrogeological Map of Dallol and its Water shade areas...................................................................................................... 138
Figure 8.2: Hydrogeological section across Gehertu fan area..................................................................................................................... 139
Figure 8.3: Hydro geological Section across Musley fan area...................................................................................................................... 140
Figure 9.1: Groundwater flow Map of Dallol Catchment................................................................................................................................ 144
Figure 9.2: Groundwater flow Map of Musley and Adjacent fan Areas.......................................................................................... -........... 146
Figure 11.1: Locations of proposed Production wells in Prospective (Potential ) Areas............................................... -.......................156
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Report! Final), March 2014
viiEnterprise ■ Dal>o, Area Grounds assessment and Evaluat
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LIST OF TABLES
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ABLE 4.1. SOIL  TYPE AND INFERRED HYDROLOGIC CONDUCTIVITY GROUP FOR RECHARGE WATERSHED IN DALLOL  STUDY AREA
Table 4.2. land use and land cover group for recharge watershed in Dallol Study area
Table 4.3: List of Meteorological Stations in and around Dallol Ground water study
Table 4.4: Inventory of Meteorological Datatypes
Table 4. 5: Mean Monthly Rainfall (mm) for near around Dallol project area Table 4.6. rainfall for the Dalol ground water Assessment project generated from Mekele Station Table 4.7: Mean Monthly rainfall from generated Satellite Gride data
Table 4.8: Mean Climatic Elements at key stations............................................................................................................................................
Table 4.9: Mean monthly Evaportranspiration over the Dallol ground water assessment area........................................................ ....
Table 4.10: Mean Monthly generated discharge...............................................................................................................................................
Table 4.11: Mean annual Run Off generated for each sub basins....................................................................................~
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.15
.16
.17
.26 ...28 ...29 ...33 ....36 ...38
..... 40
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Table 4.12: Ground water recharge for by WATBAL Model methods model
...41
Table 4.13: Average Parameters for calculation of Recharge
43
Table 4.14: Summary of Recharge amount from different sources on Musley fan area
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Table 7.1: Ranges of Hydrualic parameters for different geologic formations
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Table 7.2: Statistical value of physic-chemical analysis of the groundwater for water shade areas
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Table 7.3: Statistical value of the Physico-chemical analysis of the groundwater for Dallol water shade areas
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Table 7.4: Comparison of Dallol Area ground water qualities with Ethiopian Guideunes for drinking water ....
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Table 7.5: Summary of test wells drilling results
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Table 7.6: Summary of Water Quality Analysis Results
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list of annexs
annex-i water point inventory data
ANNEX- 2 WATER QUALITY ANALYSIS DATA ANNEX- 3 FIELD PHOTOS DURING GEOLOGICAL SURVEY
ANNEX-4 HYDRO-CLIMATE DATA
ANNEX- 5 WATER BALANCE OF MODEL RESULT FOR THREE WATERSHEDS ....
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Groundwater Potential Assessment ano Evaluation
oWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluate Project
Acronyms
ANRS - Afar National Regional State
DEM -     Degital Elevation Model
DTW-      Dallol Test Wells
EI-            Electrical Imaging
EC-          Electrical Conductivity
GSE-       Geological Survey of Ethiopia
MO WE - Ministry of Water and Energy
SWL     - Static Water Level
TEM        Transient Electromagnetic
TDS-        Total Dissolved Solids
VES-        Vertical Electrical Sounding
AN?     - Arabian-Nubian Shield
EAO     - East African Orogen
EARS    - East African Rift System
GSE      - Geological Survey of Ethiopia
MB               Mozambique Belt
MER      - Main Ethiopian Rift
WWDSE - Water Works Design and Supervision
NMA       - National Metrology Agency scs     - Soil Conservation Service
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Reportf Final), March 2014
ixWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Executive Summary
Groundwater exploration  and  evaluation  from integrated  studies of test well drilling,  Geophysical and  hydrogeological survey  in  Musley  and  adjacent fan  areas have revealed  the occurrence cf fresh groundwater potential in  shallow and  deep  aquifer systems within  coarse alluvial formations (coarser sand  and  gravel) with  confined  and  unconfined  system.  The test boreholes DTW-10  with 130m depth  in  Musley  fan  area and  DTW-1  with  190m depth  in  Gehertu  fan  area has yielded  more than  50  1/s fresh  water ( TDS<1000MG/L) from pump  testing.  The drawdown  is very  small which not more than  one meter for DTW-1  and  less than  five meters for DTW-10  with  48  hrs pumping duration.  Further deep  test well drilling  works along  the foot of the escarpments where the fan emerges reveals the occurrence of deep  brackish  water in  Meta -sedimentary  rock  aquifers beneath the fan  sediments.  Test wells DTW-2  with  depth  220m and  DTW-4  with  depth  250m yielded  more than  10  1/s of brackish  water with  few drawdowns.  These wells are expected  to  give more yields since there is limitation  in  the pump  heads due to  deep  water level of more than  120m beneath ground surface in these wells.
According  to  this investigation,  two  aquifer systems for the groundwater have been  identified  in Musley  and  Gehertu  fans from test drilling  results combined  with  geophysical survey  results.  From transmissivity  data analyzed  from pump  testing  of test boreholes DTW-1  and  DTW-10  on  the major fans of Musley  and  Gehertu  areas respectively  shows high  aquifer trasmissivity  value of 3000-4000 
m /day.  Based  on  this
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result,  the  fan  areas  in  Musley  and  Gehertu  have  been  proposed  as  potential
well fields with  fresh  groundwater up  to  a depth  of 120-150m in  the middle of the fans that covers 10-12kms width  of the fan  north  to  south.  From the above transmissivity  data obtained  from drilling and  by  assuming  12kms width  of the fan,  the annual groundwater recharge is estimated  from Darcian  approach  in  this fan  areas to  be around  56  M m3  .  Similarly  groundwater recharge to  the alluvial fan  aquifers is also  computed  from hydrological parameters from WATBAL on  the upper catchment and  infilitration  coefficients assumed  for the alluvial fans.  Accordingly  a total annual groundwater recharge of 40  Mm3  is calculated  for the Aquifers.  Considering  50-60m saturated aquifer thickness for fresh  groundwater in  the fans,  a static groundwater potential reserve of around 225 Mm3 is estimated in Musley , Gehertu and South Musley ( Bekerti fan) areas.
Similarly  brackish  groundwater potential which  exists below the fresh  groundwater waler zone having  relatively  more thickness than  the fresh  water is also  estimated  taking  100m average saturated  thickness of brackish  aquifer.  Accordingly  a static groundwater potential reserve of more
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than 400 Mm  is also estimated in these major fan areas.
Groundwater below the fan  sediment in  deep  boreholes and  for part of the fan  close to  the salt plain is highly  saline (TDS more than  40,  000  mg/1  sampled  from DTW-3) from water bearing  sediments of very fine sand and Clay sediments with gypsum layers.
The main  groundwater recharge for the fresh  groundwater aquifer in  the fan  sediments is possibly from infiltration  of runoff from the escarpments where as the deeper aquifers in  the meta-
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final), March 2014
xWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
sedimentary  rocks get recharged  by  the ground  water flow from upper water shade*  areas of Dallol to the west.  Transmissibility  of aquifers observed  from pumping  test in  these rocks is relatively  low (less than 1000m2 /day) and the water sampled is brackish with TDS around 10,000 -13,000 mg/1.
From hydrological analysis of hydro  climatic data on  the water shade areas of Musley  and  adjacent areas,  annual groundwater recharge of round  10  MM3 occurs from direct rainfall along  weathered and  fractured  rocks as computed  from water balance on  the sub  catchments.  And  similarly  more amount of deep  groundwater recharge is also  expected  from western  highland  sub  catchment that drains into Bada to the north east.
From groundwater contour maps generated  from measured  water level elevation  in  the water wells, the groundwater is flowing  from the escarpment across the fans and  discharged  in  the salt plain. Groundwater level in  the fan  areas ranges from 25m-78m in  Musley  fan  and  95m-140m in  Gehertu fan  or north  Musley.  The groundwater level is shallower towards east around  the toe of the fan  and deeper to the west around the neck of the fan and in areas closer to the foot of escarpment.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
INTRODUCTION
1.1 GENERAL
The   groundwater   potential   assessment   and   evaluation   work   in   Dallol   area   was   initiated   from Apr.2012  as  per  the  request  from  the  ministry  of  Water  and  Energy.  The  target  study  areas  for  this investigation  are  the  alluvial  fans  formed  along  the  foot  of  Blakiya  ridge  which  bounds  the  Dallol salt  plain  to  the  west  and  the  main  purpose  of  this  investigation  was  to  assesses  and  evaluate  the availability of fresh to brackish groundwater resource potential in the fan aquifers which can be used for potash solution mining in the area. The investigation also covers the upper river sub - catchments of  Dallol  (Saba  Ayshet  and  Musley  river  catchments  that  covers  more  than  3000  km  which  are considered  as  potential  areas  for  contributes  run  off  which  recharges  the  shallow  aquifer  in  the Alluvial  fans  and  also  as  a  source  of  recharge  to  the  deep  groundwater  system  in  Dallol  catchment. These   three   river   catchments   are   proposed   and   selected   as   study   area   with   their   water   shade boundary  delineated  based  of  the  flow  of  river  systems  of  all  tributaries  contributing  run  off  to  the Alluvial   fans   which   are   target   of   the   investigation.   The   smaller   adjacent   river   catchments   are included  also  in  the  main  sub  basin  of  Saba  river  catchment  together  with  the  existing  tributaries which  contribute  Run  off  to  the  Saba  and  adjacent  fan  areas.  The  salt  plain  to  the  east  where  the Alluvial  fans  dies  are  the  eastern  boundary  of  the  investigation.  The  final  inception  report  for  this investigation  had  been  submitted  to  the  Client  on  Nov.  2012  and  the  investigation  work  as  a  whole was  planned  to  be  conducted  in  three  phases  with  related  technical  reports  to  be  submitted  to  the clients  accordingly.  The  first  and  second  phase  of  investigation  targets  the  major  Alluvial  fan  areas of  Musley  and  Saba  areas,  and  the  third  phase  of  investigation  targeted  the  Graben  area  of  Ayshet sub  catchment  which  covers  around  1000  km2  in  the  upper  water  shade  area  of  Dallol  to  the  west. This  report  (Annex-1  Main  Report)  covers  the  investigation  and  potential  evaluation  work  of  the  first phase  which  is  the  Musley  and  adjacent  fan  areas.  The  test  wells  drilling  completion  report  of Musley  and  adjacent  fans  are  also  presented  separately  as  Annex-2  Well  Accomplishment  Report  as part of this investigation work.
According  to  the technical proposal agreed  so  far ,  the main  activities carried  out in  this first phase of investigation  in  Musley  and  adjacent fan  areas includes Waler point inventory  ,  Hydrological study, Hydrogeological and Hydrochemical survey Geological investigation and Mapping,
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final), March 2014
1Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
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Geophysical investigation  which  includes Vertical electrical sounding  ( VES) and  Transient electromagnetic survey  (TEM) on  the proposed survey lines across and along the major fan areas which finally calibrated with the test borehole drilling data, Drilling of ten test bore holes on the fan areas ,  Analysis and  interpretation  of the hydrogeological and  hydro  - geophysical data obtained from the survey and test drilling works.
Based  on  the integrated  data obtained  from the proposed  investigation  techniques,  results of the analysis and  interpretation  of hydrogeological and  hydrochemical data have been  discussed,  the groundwater system on  the fan  areas is explained  and  mapped  ,  Hydrogeological maps explaining the extension of potential zones for fresh groundwater potential on the fan areas has been prepared and  hydrogeological sections produced  to  conceptualize the hydrogeologic system on  the fan  areas of Musley and Gehertu major fan areas.
1.2 Location and Topographic situation of the area
The  area  is  found in Zone two Dallol woreda of Afar National Regional State. Dallol is located in the north eastern part of the Ethiopia around 250 kms NE of Mekele town riding on asphalt road of 50 kms up to Agula town and driving to eastwards from the main road for 200 kms through Berehale woreda  town  on  gravel  road  up  to  the  area.  The  target  study  area  for  the  alluvial  fan  deposit  is geographically  located  between  UTM  520000  -  540000  East  and  UTM  1545000  -  1590000  North (Figl.l).  The  Upper  Dallol  water  shade  areas  to  the  west  of  Dallol  Salt  plain  including  three  sub catchment  areas  of  Saba,  Ayshet  and  Musley  covers  more  than  3000  km2.  Two  major  topographic zones  in  general  describe  Dallol  area.  The  first  is  the  rugged  dissected  escarpment  west  of  Danakil depression  namely  known  Belakiya  or  Dogue  mountain  range  extending  north  to  south  that  rises from  the  depression  floor  to  elevation  above  1200m  and  this  escarpment  is  the  locus  of  a  major  rift system.  At  the  foot  of  the  escarpment,  large  step  Alluvial  fans  spread  eastwards  from  Canyon  mouth over the  flat floor of the depression where they cover the salt surface for a distance of three kms or more. The second topographic zone is the extensive low laying salt plain of the depression to the east with  elevation  more  than  120  -130m  below  sea  level  which  is  covered  with  evaporate  or  lake deposit.
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2Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment ano Evaluation Project
1.3  Constraints of the Project
It was planned to complete the whole investigation work of the three phases in the proposed study areas within 14 months time where the evaluation and reporting of Musley fan area was to be completed within six months time after the commencement of the study. But the whole project activities and  reporting  of the groundwater evaluation  for Musley  and  adjacent fans have been delayed more than a year due to various problems related to the drilling activity. The major reasons for this are:-
•    The tendering and contracting for the drilling activity which is the critical path of
the investigation has been delayed for more than six months due to limitation in 
drilling companies related to the remoteness and hardship nature of the area.
•    The climatic condition with the extremely high temperature which is more than 
42°c is one major constraint to carry out the drilling activity day time therefore the drilling was done efficiently on the night time mostly.
•     The  access  road  condition  to  collect  water  point  data  and  related  geological  and hydrogeological  data  in  the  catchment  area  of  Dallol  and  Adjacent  parts  was another constraint even if the main road to Dallol is under construction.
•    Since the geological formation on the fan areas was dominated by coarse materials
with big boulders and inter bedded clays at shallow depth, casing stacking during installation was mostly faced and installation was made after continuous riming of
the borehole.
2. Objective of the Study
The main objective of the study is to assess and evaluate the groundwater potential in Dallol area from Quantity and Quality point of view targeting the Alluvial fan deposit and accordingly potential well fields for fresh  groundwater development will be identified.  This is based  on detail geophysical investigation  in  conjunction  with  test wells drilling.  The major objectives related to this are:
■       Determining the recharge and discharge condition of the alluvial fans
■       Estimate the mean annual groundwater recharge of the alluvial fans
■      Determining the depth and lateral extent of Fresh and Brackish groundwater in the Alluvial fan Aquifers
■       Determine aquifer parameters of the alluvial fans
■     Quantitative estimation of fresh and brackish groundwater potential of the alluvial fans
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4Water Works Design and Supervision Enterprise • Dallol Area Groundwater assessment and Evaluation Project
Recommend appropriate groundwater management of the alluvial fans.
3- Review of previous studies
3.1  Review of previous geological investigation carried out in the area
different Geological studies had been carried out in the area in the past time for the purpose of investigating potash and related minerals in the area where are small scale or regional Geologic maps are prepared.  In  the explanation,  more emphasis is given  for the geomorphologic, structural evolution  and  stratigraphy  of the basin  with  respect to  the availability  of potash deposit in the area.
Geological Map of Ethiopia (Kazmin.1972; Tefera et al. 1996)
The geological map of Ethiopia (scale 1:2,000,000), first compiled by Kazmin( 1972) and then revised by Tefera et al ( 1996) constitutes an excellent reference material to have general
lithologic distributions and structural set up of the country. According to the geological map of Ethiopia, the western margin and adjacent areas of Dallol are constituted by the Precambrian basement rocks of late protrozoic with low grade metamorphism. Among these, the
Metasedement and Metavolcanic complex of Tsaliet group, Tambien group and Didikama formations constitutes the western margin of Dallol depression. The low laying plain of Dallol
is dominated by the quaternary deposit of Alluvial sediments consists of number of sheet flood terraces mainly composed of sand, gravel and fossiliferous and gypsiferous limestone of lacustrine origin. The Extensive Dallol plain to the east is covered by evaporit ( Salt formation)
of quaternary age.
Potash Mining in Ethiopia, Y.Arkin, 1969
This report deals with the evaluation of the potash reserve in the Dallol area and under this report, the geological, geomorphological and geographical descriptions of the area is explained and the general stratigraphy of the area is prepared by M. Beyth (1969). The report explains that the Danakil depression  in  which  Dallol is situated  is as a whole a down faulted block within the rift valley bounded by the Belakiya mountain range in the west and the uplifted block of the Denakii Alps in the east. The older geological formations are exposed in this area. The salt plain which occupies a large part of the depression is surrounded by a belt of marine sediments mainly salt and gypsum which were formed during invasion by the Red Sea. Gravel terraces and large alluvial fans occur al higher levels and recent lava flows and unconsolidated Alluvial over part of the salt plain.  The structural configuration  of the depression  was determined by pre existing lines of weakness which underwent rejuvenation several times.
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Preliminary Survey of Saline deposit in the Denakil depression, Ethiopia, PARSONS COMPANY, PEE -396, Survey 606-689,1958.
The report briefs the geologic studies of the saline deposits related to marketing, and process of potash  in  the Danakil depression.  The physiographic,  geologic history,  general and  detail geology of the area is described in the report. The rock types from the oldest to the youngest are complex metamorphic rocks estimated to be of Paleozoic age, Jurassic sediments and eruptive rocks of Pliocene to recent ages. Major faults with a north 30° W and transverse faults with NW to SE trend were the inherited structures in Dallol.
Potash bearing Evaporite in the Denakil Area, Ethiopia by J.G HOLWERDA and R.W HUTCHISON, Vol-63,1968, pp-124-150
This report is prepared from the exploration of evaporite sequence in the dallol depression by the Ralph M. Parsons Company of Los Angeles, California for several years. The report in general explains the regional geological and structural features. In this report, the regional geomorphologic setting of the area is described into two zones, the western highlands and the low laying eastern lowlands. The western highland is characterized by the rugged and dissected escarpment west of the Dallol depression. Here occur rocks of Precambrian to Tertiary age with surrounding fringe of quaternary deposit, the eastern low land of the Dallol depression, the plain  is constituted  by  evaporate formation  with  layers of Gypsum inter bedded  with Anhydrite and Halite and potash salts more eastwards. This salt plain end westwards along a dissected escarpment with poorly consolidated recent alluvium at its base
3. 2 Review of previous Hydrogeological investigation carried out in the area
Hydrogeological  and  Geophysical  investigation  in  Dallol  Area,  BELES  Engineering (2010)
There are few geophysical investigations done on  Dallol area with  the objectives of groundwater investigation  for water supply  of potash  mining  companies in  the area.  Bcles Engineering P.L.C (2010) had conducted few Vertical electrical soundings (VES) on the area between  Saba and  Musley  and  recommended  test drilling  on  few points.  The quality  ot acquired data for some VES in this study is observed to be poor due to ground surface problem to transmit electrical current.
The study in general shows that
• Mostly groundwater recharge occurs in the upstream part of the alluvial funs in the
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Dalol depression and along the major regional faults and river courses in fractured quaternary volcanics and quaternary alluvial deposits and the groundwater discharge water discharge occurs commonly as springs and river base flows.
• Four major hydrogeologic units have been mentioned in the area which is Precambrian rocks,  carbonate  and  clastic  rocks,  Tertiary  Volcanics  and  Quaternary  sediments. Highly productive quaternary sediment aquifer is expected along perennial Saba and other dry wades and the upstream side of alluvial fans.
Groundwater investigation, TEM imaging on Musley fan area of Dalloi, FUGRO (2011) A geophysical investigation for Transient electromagnetic survey (TEM) had been conducted for  around  7-10kms  width  of  Alluvial  fan  on  Mosley  area  by  FUGRO  GROUND GEOPHYSICS P.I.c in July-August, 2011 for SIANIC POTASH MINING PVT with the objective of water supply for potash mining companies. Here TEM survey was conducted with transect lines with parallel orientation across the Mosley Alluvial fan. For this study, it was only the interpreted data or report that the consultant could review and the row data is not available. In the report, the depth for Fresh, brackish and salt water interface was mapped and the thickness of fresh water zone is delineated. But this needs to be calibrated with test well drilling on the site. The review of this investigation shows that
•    Fresh and slightly brackish groundwater occurs in the Alluvial fan sediments
up to a depth 200-300m.
•    Additionally highly saline brines may be present at the bottom of Alluvial fan sediments and away towards east on the plain.
•    Fresh groundwater environments are associated with alluvial fans caused by 
large drainage pathways
Groundwater Condition in Dallol area, PARSONS R.M (1967)
It was reported  that in  the spring  of 1967,  the pilot mine was flooded  by  an  inflow of groundwater that issued from a series of fractures and solutions openings in the evaporate beds and it was believed that the waler which flooded the mine was derived chiefly from the water bearing beds in the Musley fan.
An investigation of groundwater condition in Musley fan was beginning in May 1967. The purpose of these studies was to determine if it would be feasible to lower the water level in the water bearing beds beneath the toe of the fan to such a degree that the eastward movement of the groundwater through  the fan  would  be cut off.  Accordingly  more than  20  shallow boreholes both production and observation wells were drilled for the groundwater investigation and some to locale a potable water supply for the mining camp at that time.
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The review from this report shows that-
• Well depth ranges from 21m to 108m and Groundwater in the wells level ranges from 7.3m to 63.1m. The Pumping test with observation wells showed that by pumping with 26 1/s on the central well the drawdown on the observation wells ranged from 0.03 to 17.98m
■   The alluvial fan deposits are thickest along the escarpment, and thinnest at the toe of the fan.
■    The Alluvial fan deposits consist of inter-fingering layers and lenses of sand, gravel and clay.
■    The beds of sand and gravel are porous and highly permeable which can store and transmit large quantities of groundwater.
■    The fan sediments area underlain by beds of crystalline salt.
■   The groundwater in most of the shallow -laying water bearing beds exists under water table conditions and the groundwater in the deeper beds exists under artesian condition.
■   Aquifer parameter- transmissivity value is 880 m2/day from pump testing
■   Mean annual Groundwater Recharge - Musley alluvial fan is estimated to be around 17,557 m3/day
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4 Hydro metrology
4.1 Introduction
4.1.1   Background
The area is located in the north eastern part of Ethiopia in the Danakil depression, an extensive interior basin with below sea level elevation as low as 120m. The basin constitutes the northern part of a much larger topographic region of the Afar depression.
The Danakil Basin is bordered to the west by the Tekeze River Basin, to the north - west by the Mereb River Basin, and to the south by Awash River Basin, and to the east by a Dallol Red sea.
Proper estimation of Ground water recharge magnitude is required for efficient study of ground water resource that deals with utilization of water for various purposes.
4.1.2  Climate
It is seen that the Dankil basin is characterized by monomodal type rainfall pattern and arid climate in the project area.
The north eastern part of the Danakil basin (around Dalol) receive most of their rainfall during July, August and September associated with the north ward passage of the ITCZ. The main influences on weather circulation in Ethiopia are the Inter Tropical Convergence Zone (ITCZ), the northeastern trade winds and the southwestern monsoons. In particular the catchments under study Dallol have characteristics of getting rain from the movement of ITCZ towards northern part of the country,  during  wet season.  Besides the influence of warm moist air mass and continental dry  mass contributes for the formation  of rain in these areas and in general the climate pattern has large variations in altitude variation.
4.1.3   Objective and Scope of the Study
The major objective of the hydrological study  is to  establish  water balance models which estimates recharge of the Dalol area groundwater basins aquifers and  estimation  of evaportranspiration of the project area. The specific objectives are:
•    Collection of climatic and hydrological data, analysis of data quality and sufficiency required for the hydrological study will be under taken.
•    Analysis and interpretation of hydrometric data, and carry out hydrological frequency analysis.
•    Analysis and interpretation of meteorological data, data consistency, and trend detection for climatic change will be performed.
•    Analysis of the interaction of surface water with ground water in the study area.
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9Water Works Design ana Supervision Enterprise - Dallol Area Groundwater assessment ana Evaluation Project
•    Formulation and calibration of water balance models to estimate groundwater recharge amounts will be performed.
•    Collected land use, soil type, land cover, permeability of recharge areas data will be assessed, analyzed and prepared for the water balance model
•    Identified Estimate the ground water recharge for each sub catchments
•    Formulation and calibration of water balance model for each stream catchments of the study area.
•    Mode of aquifer river interactions will be assessed and estimate of base flows will be made.
4.2       Methodology
4.2.1 Data collection
The Hydro-meteorological data collected for the hydrological study of the Dallol Ground water assessment are the following:
I. Meteorological data
•    Rainfall
•    Minimum and Maximum Temperature
•    Relative Humidity
•    Sunshine Hours
•    Wind Speed
•    Evaporation
II.  Hydrological data
•    Monthly discharge data
III.  Topographic, land use, land cover maps
IV Soil types and permeability maps
Monthly meteorological data including rainfall, maximum and minimum temperatures, relative humidity,  wind  speed  and  sunshine duration  are provided  by  the National Meteorological Agency (NMA).
Hydrological data no discharge data is available or provided by the Department of Hydrology in the MEW and the Run off data will generate by rainfall run off relation.
4.2.2       Method of recharge estimation
Methodology adopted is as follows:
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10Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
J Collect primary data Meteorological, hydrological, top maps, land use, soil type, and land cover.
Make analysis and interpretation of hydro-meteorological data, data consistency. Make maps and delineate project boundaries, catchments map, Locate hydro-meteorological stations with GIS.
J Formulation of rainfall runoff correlation and estimate the runoff stream the project area.
J Formulation and calibration of water balance models to estimate groundwater recharge amounts will be performed.
J Estimate the ground water recharge for each sub catchments
J Make of aquifer river interactions and estimate of base flows and calibrate WATBAL model
43 Land use/land cover and Soil Characteristics of the Project Area
Watersheds in Dallol Ground water assessment project Soil type and degree of permeability over watersheds are given in Table. 1 the soil type was extracted from ETHIO-GIS.
Table 4.1: Soil type and inferred hydrologic conductivity group for recharge watershed
in Dallol Study area
No
Area (km2)
Area
(km2)%
Soil Type
Hydrologic
soil group
Musley and Adjacent Catchment
46.3
10.3
calcaric flubisols
B
119.1
26.4
dystric nitisols
B
7.0
1.6
eutric cambisols
B
70.5
15.6
eutric fluvisols
B
34.3
7.6
eutric nitisols
B
5.4
1.2
leptosols
D
2.2
0.5
no data
~8.1
1.8
orthic acrisols
B
126.6
28.1
orthic luvisois
B
31.8
7.0
orthic solonchaks
B
Ayshet / Lelcgchcdi Cachmcnt
11.2484
l.l
chromic 
cambisols
B
15.2709
1.5
chromic luvisois
B
360.923
36.0
dystric nitisols
B
80.0679
8.6
eutric cambisols
B
40.6192
4.1
eutric fluvisols
B
0.7904
0.1
eutric gleysols
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5.5074
0.5
eutric nitisols
B
4.4325
0.4
eutric regosols
A
213.993
21.4
leptosols
D
57.7912
5.8
no data
41.3346
4.1
orthic acrisols
B
8.8145
0.9
orthic luvisols
B
155.193
15.5
orthic solonchaks
B
Saba Catchment
Sum Area km2
SOIL_TYPE
303.356
17.0
calcaric flubisols
B
28.7523
1.6
chromic 
cambisols
B
750.481
42.0
dystric nitisols
B
99.0822
5.5
eutric cambisols
B
147.116
8.2
eutric fluvisols
B
13.8194
0.8
eutric nitisols
B
3.0075
0.2
eutric regosols
A
147.779
8.3
leptosols
D
12.5333
0.7
no data
37.3844
2.1
orthic acrisols
B
3.0627
0.2
orthic luvisols
Al
240.316
13.5
orthic solonchaks
B
Group A: Sand, loamy sand or sandy loam. Soils having a low runoff potential due to high infiltration rates.
Group B ;Silt loam, or loam. Soils having a moderately low runoff potential due to moderate infiltration rates.
Group D: Clay loam, silty clay loam, sandy clay, silty clay or clay. Soils having a high low runoff potential due to slow infiltration rates.
Table 4.2 shows that the Dallol sub basin catchments areas cover more than 39.6% soils is Nitrososis , 9.9% is Eutric, 11.3% is leptosols and 20.1% is Orothics which soils having a moderately low runoff potential due to moderate infiltration rates, (Figure 4.1).
The land cover of the catchments of the study area shows at (Figure 4.2). More than 44% of the study area is covered by Shrub land, more than 31% is bareland,2l% grasse,2% cultivated land and more than 1% is covered by natural Forest area.
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12Water Works Design and Supervision Enterprise Dallol Area Groundwater assessment and Evaluation Project
The following data have been compiled to date:
>   Mean Monthly Rainfall from 10 Stations.
>   Monthly Temperature data from 7 Stations.
>   Relative humidity from 3 Stations.
>   Sunshine Duration from 3 stations.
>   Wind Speed from 2 Stations.
Compiled stations data, include some basic stations details, and are given in Table (4.4 and 4.5)
4.5   Meteorological Data
Rainfall data have been collected from 10 pluviometric stations 7 of the stations are located outside Dallol Project area And  rainfall grid  data have been  collected  from satellites data (1995-2011) years.
The following table summarizes the main characteristics of the stations and the data collected
Table 4. 3: List of Meteorological Stations in and around Dallol Ground water study
project area.
Location
No
Name of Stations
alt
Northing
Easting
Data Length
1
Adigrat
2449.8
549638
1577303
1997-2010
2
Wukro
1991.2
564854
1523197
1959-2010
3
Mekele
2248
551107
1491062
1959-2010
4
Kwiha
2248.3
558952
1488452
6
Shehet
1469.4
581569
1476611
1972-2010
7
Rebti
2008
8
Berhale
667
610220
1532659
1975-2009
9
Kuneba
1202.3
593603
1545016
2009-2010
10
Atsbi
1997-2010
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Table 4. 4: Inventory of Meteorological Data Types
Station
Latitude Deg.
Min
Longitude
Deg. Min
Temperature From To
Evaporation From To
Rel.humdity From to
Sunshine From to
Wind
Speed
From
Adigrat
549638
1577303
1997-2010
1997-2004
1998-
2007
Wukro
564854
1523197
1992-210
Mekele
551107
1491062
1959-2010
1957-2004
1997-
2007
1995-
2005
Shehet
581569
1476611
1972-2010
Rebti
2008-2009
Berhale
610220
1532659
2007-2010
Kuneba
593603
15450016
2009-2010
Atsbi
2006-2010
4.6  Climatic data
Monthly  rainfall data was collected  from NMSA for 8  rain  gauge stations as listed  on  Table 4.4  As shown  on  table 4.6  some of the stations have data gaps.  Other climatic parameters such  as temperature,  humidity,  sunshine duration  and  wind  speed  has been  collected  (table 4.5) and processed.  The climatic parameters obtained  at station  with  complete data were extracted  to  use for further estimation of evapo- transpiration of the project area.
4.6.1  Precipitation
The rainfall pattern  of the project area is mono-modal type (Figure 4.3) with  most of the rainfall occurring  in  wet season  (i.e.  July  and  Augest).  The minimum rainfall occurs during  driest months from October to  March.  Summary  of monthly  rainfall amounts falling  on  the stations taken  into consideration is given on the annex.
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Kuneba Mean Monthly Rainfall(mm)
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4.6.2   Hydrology Data
Since no  stream gauged  is in  the project area the data compilations activities involved  in  discharge data was not collected  from the study  area and  the run  off data is calculated  with  rain  fall- runoff correlation method by SCS method.
4.6.3   Spatial Distribution of Stations
The spatial distribution  of Meteorological and  Hydrological Stations with  in  the project area can  be viewed  on  the hydro-meteorological map  (figure 4.4).  Clearly  meteorological stations are distributed  outside of the project area and  the stations in  the project area were installed  for a short period of time. And there is no stream gauged in the project area.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final) March 2014660000
560000
600000
•20000
•*0000
Location of Meteorological Stations forf Dallol Ground Water Project Assesment Area
Edega
I
.egend
k)*ns
Met Slalion
VAikro
------- Roads
Water shedc Boundaiy
SJudyaiea separated
Watershed Boundar,
Figure 4. 4: Hydrometeorological station maps of Dallol ground water assessment project
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20Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
4.7   Trend Analysis
Linear and  5  years moving  average trend  analysis of rainfall data are carried  out for two representative meteorological stations for the ground  water assessment area which  are located  in  & out side of the study  area shows in  (Figure 4  5).  The trend  analysis of all the three trends shows that slightly decreases at both stations Mekele and Berhale stations with measured periods
Mean annual rainfall Trained in 1959-2010 ears to Mekele Stations
inoo
900
800
700
600
3
500
w
400
3
300
C
200
5
100
0
—•— Mean annual
rainfall(mm)
5 per Mov Avr
(Mp.in annual
raintall(mm))
- — -•Linear (Mean
annual
rainfall(miii))
1950        1960        1970         1980         1990         2000         2010         2020
Mean annual rainfall Trained in 1959-2010
ears to Berhale Stations              Mean annual
Figure 4. 5: Long-term annual rainfall series at Dallol Project area
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4.8  Ground water recharge estimation
4.8.1  Major activities
The hydrology  study  will be study  is to  establish  water balance models which  estimates recharge of the Dallol area groundwater basins aquifers under take the following  hydrological studies of analysis and  interpretation  of hydro-metrological data,  and  carry  out hydrological frequency  analyses, formulation  and  calibration  of water balance model for Dallol project area,  analyse the interaction  of surface water with groundwater in the study area and estimates groundwater recharge.
4.8.2  Water balance model
The Hydrology  study  will use Conceptualization  of the Integrated  Water Balance Model of (WATBAL  model David  Yates in  USA (Yates,  1996)).  It is a model that simulates changes in  soil moisture and  runoff.  It is essentially  an  accounting  scheme based  on  a conceptualized,  one dimensional bucket that lumps both the root and upper soil layer. The model comprises
Evapotranspiration
Effective Precipitation
-------- ►
D irect ru noff
-------------------- ►
B ascflo w
Figure 4. 6: Conceptualization of the water balance of the WATBAL model two elements. WATBAL model calibration requires simultaneous monthly data of both rainfall and runoff. Fitting with minimum of 10-year data set is required to have reliable estimate of parameters. 
The first is a water balance component that describes water movement into and out of a conceptualized basin.
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A brief description  of the WATBAL  model is given  below.  David  Yates in  USA (Yates,  1996) develops the WATBAL (an  Integrated  Water Balance Model).  It is a model that simulates changes in  soil moisture and  runoff.  It is essentially  an  accounting  scheme based  on  a conceptualized,  one dimensional bucket that lumps both  the root and  upper soil layer.  The model comprises two elements.  The first is a water balance component that describes water movement into  and  out of a conceptualized  basin.  The second  is the calculation  of potential evapotranspiration,  for which  there are three possible alternatives,  depending  on  data availability  and  the module is escamtized  at (Figure 4.6.)
The uniqueness of the lumped  water balance model is in  its use of continuous functions of relative storage to  represent hydrological processes in  the form of a differential equation.  Water enters the soil moisture store through  precipitation  and  is removed  either by  evapotranspiration  or direct runoff, surface runoff,  subsurface runoff or baseflow.  The water balance component of the model comprises six parameters related to i) direct runoff (0), ii) surface runoff (c), iii) sub-surface runoff (a and y), iv) maximum catchment water-holding  capacity  (Smax) and  v) baseflow (Rb).  The monthly  soil moisture balance is written as:
where: Peff - effective precipitation (length/time)
Rs Rss = Ev
surface runoff (length/time) sub-surface runoff (length/time) evapotranspiration (length/time)
potential evapotranspiration (length/time) Rb        =           baseflow (length/time) Smax =              maximum storage capacity (length)
relative storage (-) (0 < z > 1)
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Smax,  the maximum water holding  capacity  of a catchment reflects the relative importance of water storage on  the hydrological regime of a catchment.  It is dependent primarily  on  the nature of catchment geology  and  soils.  The storage variable,  z,  is given  as the relative storage state and  is a value between  0  and  1.  Consequently,  when  Smax  is multiplied  by  z,  it gives the volume of water stored in the catchment at any given time.
In  the model,  potential evapotranspiration  is computed  using  one of three methods: i) Penman- Monteith; Priestley  Taylor or iii) Thomwaite.  A non-linear relationship  is used  to  compute actual evapotranspiration from potential evapotranspiration.
E (z,Pet,t) = Pet
v
Surface runoff Rs,  is described  in  terms of the storage state,  z,  and  the effective precipitation, Peff.  e,  a calibration  parameter,  allows for surface runoff to  vary  both  linearly  and  non- linearly with storage.
for > Rb
(*,P,0 =     0
for P
eff
£ Rb
Sub-Surface  runoff  Rss,  is  a  function  of  the  relative  storage  state,  multiplied  by  a  coefficient a. In most cases, the value of y is 2, but for some basins may be different.
/?„ =a z7
Direct  runoff  (Rd)  is  a  function  of  the  effective  precipitation.  0  is  the  proportion  of  effective precipitation that becomes direct runoff.
The  baseflow  (Rb)  must  be  entered  into  the  model  as  a  constant  value,  determined  by  the user.
Total runoff for each time step is the sum of the four runoff components:
Rtotal = Rs + Rss + Rb + Rd
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24Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
In  WATBAL,  hydrological processes are simulated,  as described  above,  on  the basis of a conceptual approximation.  Consequently  it is necessary  to  adjust or optimize parameters until the model output is an  acceptable estimate of the observed  runoff regime.  In  order to  do  this it is necessary  to  have observed  runoff data against which  to  calibrate parameter values.  Ideally  a split sample test should  be performed.  In  this test the observed runoff record is split into two segments: one is used  for calibration  and  the other for validation.  If the statistical values derived  from the calibration  and  validation  procedure are similar,  then  the fitted  model parameters are deemed acceptable.
Thus model parameters are found  through  empirical analysis of monthly  and  annual runoff.  Key model parameters are a,  e and  Smax.  Within  the model an  automatic optimizing  routine can  be utilized  to  calibrate the parameters.  This uses a statistical relationship  to  reduce the error between the observed  and  simulated  runoff.  Optimal model parameters are rarely  found  on  the first attempt of automatic calibration.  Consequently,  even  when  using  such  a method  it is best to  combine it, with  an  element of manual adjustment of parameters.  The other model parameters can  be calibrated, but this has to be done manually.
4.9  Data Analysis
4.9.1 Introduction
There is not enough  long  direct rainfall observation  at the command  area of Dallol Ground  water assessment project.  However,  there are reasonably  sufficient stations for estimating  rainfall over the catchment and  the project area.  The mean  monthly  rainfall for stations that are located  nearby  and relevant for the study of the project area is given in Table 4.6. Observed data for these 10 stations are given  in  the Annex  4  .  The observations from Mekele meteorological station  which  is out of the project area is more or less comparable quality  and  the others meteorological stations are located  in the project area were short length  data 2- 8  years and  the mean  monthly  rainfall are generated  from this meteorological stations data is given Table 4.6
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25Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Table 4. 5: Mean Monthly Rainfall (mm) for near around Dallol project area.
Description
Jan
Feb
March
April
May
June
July
Aug
Sep
Oct
Nov
Dec
Total
Adigrat
5.2
31.5
53.1
24.4
45.3
152.2
135.9
63.5
35.2
11.7
557.9
Atsbi
0.8
6.5
11.8
25.8
159.7
252.1
15.3
2.3
474.2
Berhaie
1.6
3.4
13.0
20.0
15.9
16.6
105.0
120.9
16.9
2.9
2.9
0.5
319.5
mekeie
3.0
6.4
24.5
37.7
29.9
31.2
197.5
227.4
31.8
5.4
5.4
0.9
601.1
Sheket
4.8
3.3
7.0
35.1
34.2
27.6
125.1
128.3
15.8
15.4
2.3
8.0
406.9
Wukro
1.0
3.5
14.8
28.1
24.2
38.3
207.5
209.7
37.7
4.1
3.3
1.9
574.1
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4.9.2   Rainfall data Analysis
Rainfall in  the project area varies from over 152mm to  578  mm per annum.  Moreover,  the rainfall regime is Monomodal (Fig  4.7) and  the first season  is from March  to  May,  and  the second  season  is from august to October.
The mean annual temperature in the project area varies from 260c to over 350 c .
Berhale Mean Monthly Rainfall(mm)
Month
Figure 4. 7: Mean Annual Monthly Rainfal at Berhale Meteorological Station
4.9.3   Transfer of Rainfall Data
Altitude plays a very  important role in  the transfer of rainfall information  from gauges site to  unpaged sites.  The altitude is highly  correlated  with  rainfall data for Dallol ground  water Assesment project area and  carried  out the relation  between  the rainfall data to  the altitude with  nine meteorological stations which shows in figure 4.8
Attempts  were  made  to  formulate  a  relation  between  rainfall  and  altitude  based  on  observations  from 350 rainfall stations (Admasu, 1988). The relationship obtained has the following form:
R(u) = [Alt(u)/Alt(g)]0.52 R(g)
Where,
R(u) = mean annual rainfall at un gauged location of interest (in mm) R(g) = mean annual rainfall at nearby gauged station location (in mm) Alt(u) = elevation of ungauged site (in m above sea level) Alt (g) — elevation of nearby gauged station (in m above sea level)
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27Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Table 4. 7: Mean Monthly rainfall from generated Satellite Gride data
Station Name Ayshct Catchment
Element :Mcan monthly Rainfall
yaear
jan
feb
mar
apr
may
jun
jul
aug
sep
oct
nov
dec
Total
1995
0.0
1.0
61.0
64.0
54.0
0.0
70.0
74.0
88.0
8.0
8.0
0.0
428.0
1996
0.0
1.0
54.0
103.0
28.0
5.0
68.0
127.0
41.0
28.0
3.0
4.0
462.0
1997
0.0
0.0
0.0
0.0
0.0
11.0
68.0
70.0
5.0
6.0
2.0
0.0
162.0
1998
0.0
0.0
1.0
0.0
0.0
li.O
29.0
75.0
51.0
10.0
8.0
8.0
193.0
1999
2.0
8.0
0.0
0.0
2.0
7.0
94.0
83.0
23.0
0.0
0.0
0.0
219.0
2000
0.0
0.0
0.0
3.0
31.0
0.0
41.0
8.0
9.0
0.0
0.0
15.0
107.0
2001
0.0
0.0
64.0
75.0
17.0
0.0
63.0
104.0
54.0
6.0
0.0
0.0
383.0
2002
2.0
0.0
65.0
2.0
1.0
6.0
16.0
80.0
73.0
9.0
0.0
36.0
290.0
2003
3.0
16.0
26.0
32.0
0.0
15.0
27.0
136.0
31.0
0.0
0.0
7.0
293.0
2004
22.0
2.0
10.0
52.0
5.0
4.0
17.0
47.0
18.0
17.0
0.0
0.0
194.0
2005
0.0
1.0
50.0
64.0
54.0
0.0
75.0
74.0
88.0
8.0
8.0
0.0
422.0
2006
0.0
1.0
54.0
103.0
28.0
4.0
68.0
132.0
41.0
21.0
2.0
4.0
458.0
2007
7.0
5.0
5.0
121.0
1.0
29.0
29.0
115.0
58.0
0.0
6.0
0.0
376.0
2008
12.0
0.0
0.0
21.0
19.0
0.0
49.0
24.0
52.0
5.0
6.0
2.0
190.0
2009
1.0
1.0
22.0
10.0
1.0
0.0
80.0
72.0
6.0
90.0
7.0
6.0
296.0
2010
2.0
3.0
33.0
105.0
83.0
4.0
152.0
172.0
51.0
1.0
0.0
0.0
606.0
2011
4.0
2.0
1.0
2.0
44.0
0.0
27.0
39.0
28.0
0.0
0.0
6.0
153.0
Mean
3.9
2.8
23.6
42.1
20.4
5.7
54.8
82.9
41.6
11.9
2.6
6.0
307.8
Max
22.0
16.0
65.0
121.0
83.0
29.0
152.0
172.0
88.0
90.0
8.0
36.0
606.0
Min
0.0
0.0
0.0
0.0
0.0
0.0
16.0
8.0
6.0
0.0
0.0
0.0
107.0
STDv
6.2
44
25.2
44.2
25.3
8.1
37.5
45.7
23.8
234
3.5
9.7
1377
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29Waterworks Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation ProjeH
Station Name : Saba Catchment
Element :Mean monthly Rainfall
yaear
jan
feb
mar
apr
may
jun
jul
aug
sep
oct
nov
dec
Total
1995
0.0
1.0
40.0
38.0
61.0
0.0
81.0
64.0
58.0
7.0
15.0
0.0
305 0
1996
0.0
1.0
34.0
130.0
18.0
4.0
44.0
108.0
68.0
23.0
3.0
2.0
435.0
1997
0.0
0.0
0.0
0.0
0.0
21.0
99.0
93.0
11.0
2.0
3.0
0.0
229.0
1998
0.0
0.0
2.0
0.0
0.0
7.0
45.0
91.0
55.0
13.0
7.0
6.0
226.0
1999
2.0
7.0
0.0
1.0
3.0
6.0
85.0
58.0
21.0
0.0
0.0
0.0
183.0
2000
0.0
0.0
0.0
2.0
28.0
4.0
35.0
0.0
7.0
9.0
9.0
17.0
111.0
2001
0.0
0.0
40.0
91.0
10.0
0.0
38.0
111.0
51.0
10.0
0.0
0.0
351.0
2002
1.0
0.0
65.0
11.0
0.0
4.0
16.0
80.0
70.0
6.0
0.0
8.0
261.0
2003
1.0
12.0
27.0
22.0
0.0
4.0
33.0
108.0
28.0
0.0
0.0
5.0
240.0
2004
3.0
0.0
2.0
34.0
4.0
1.0
17.0
40.0
20.0
10.0
1.0
0.0
132.0
2005
0.0
1.0
41.0
38.0
61.0
0.0
81.0
64.0
58.0
5.0
15.0
0.0
364.0
2006
0.0
0.0
34.0
130.0
18.0
4.0
44.0
113.0
68.0
21.0
0.0
2.0
434.0
2007
0.0
8.0
7.0
29.0
4.0
5.0
5.0
109.0
44.0
0.0
0.0
0.0
211.0
2008
14.0
0.0
0.0
23.0
8.0
1.0
14.0
19.0
40.0
8.0
5.0
0.0
132.0
2009
0.0
1.0
17.0
11.0
0.0
1.0
71.0
95.0
4.0
124.0
0.0
0.0
324.0
2010
1.0
3.0
2.0
40.0
48.0
7.0
112.0
211.0
48.0
1.0
0.0
0.0
473.0
2011
1.0
1.0
0.0
0.0
24.0
2.0
29.0
56.0
26.0
0.0
0.0
3.0
142.0
Mean
1.4
2.1
18.3
35.3
16.9
4.2
49.9
83.5
39.8
14.1
3.4
2.5
271.4
Max
14.0
12.0
65.0
130.0
61 0
21.0
112.0
211.0
70.0
124.0
15.0
17.0
473.0
Min
0.0
0.0
0.0
0.0
0.0
0.0
5.0
0.0
4.0
0.0
0.0
0.0
111.0
STDv
3.4
3.5
20.6
42.3
21.1
4.9
32.2
46.9
22.2
-
29.2
5.2
4.5
116.7
30Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Station Name : Muslcy Catchment
Element :Mcan monthly Rainfall
yaear
jan
feb
mar
apr
may
jun
jul
aug
sep
oct
nov
dec
Total
1995
0.0
1.0
16.0
52.0
45.0
0.0
40.0
54.0
65.0
5.0
11.0
0.0
289.0
1996
0.0
1.0
25.0
128.0
17.0
6.0
49.0
108.0
33.0
32.0
3.0
5.0
407.0
1997
0.0
0.0
0.0
0.0
0.0
14.0
68.0
69.0
4.0
3.0
4.0
0.0
162.0
1998
0.0
0.0
1.0
0.0
0.0
7.0
30.0
72.0
56.0
7.0
9.0
8.0
190.0
1999
2.0
8.0
0.0
0.0
0.0
8.0
82.0
70.0
23.0
0.0
0.0
0.0
193.0
2000
0.0
0.0
0.0
3.0
34.0
0.0
40.0
6.0
7.0
0.0
0.0
14.0
104.0
2001
0.0
0.0
43.0
41.0
11.0
1.0
41.0
91.0
51.0
13.0
0.0
0.0
292.0
2002
1.0
0.0
43.0
4.0
2.0
3.0
14.0
43.0
66.0
1.0
0.0
14.0
191.0
2003
6.0
8.0
47.0
45.0
0.0
2.0
18.0
77.0
27.0
1.0
0.0
17.0
248.0
2004
15.0
1.0
11.0
45.0
7.0
1.0
15.0
43.0
23.0
11.0
0.0
0.0
172.0
2005
27.0
1.0
16.0
48.0
45.0
0.0
40.0
54.0
65.0
5.0
11.0
0.0
312.0
2006
0.0
0.0
26.0
128.0
17.0
3.0
51.0
108.0
33.0
32.0
0.0
5.0
403.0
2007
0.0
7.0
1.0
63.0
0.0
3.0
3.0
98.0
34.0
0.0
0.0
0.0
2090
2008
7.0
0.0
0.0
27.0
14.0
1.0
11.0
22.0
49.0
11.0
7.0
0.0
1490
2009
0.0
1.0
10.0
10.0
0.0
0.0
81.0
72.0
6.0
89.0
0.0
7.0
276.0
2010
1.0
2.0
14.0
70.0
62.0
5.0
114.0
162.0
43.0
1.0
0.0
0.0
474.0
2011
0.0
1.0
1.0
4.0
39.0
4.0
35.0
34.0
35.0
0.0
0.0
6.0
159.0
3.5
1.8
14.9
39.3
17.2
3.4
43.1
69.6
36.5
124
2.6
4.5
248 8
Mean
3.5
1.8
149
39.3
17.2
3.4
43.1
69.6
36.5
12.4
2.6
4.5
248.8
Max
27.0
8.0
47.0
128.0
62.0
8.0
114.0
162.0
66.0
89.0
11.0
17.0
474.0
Min
0.0
0.0
0.0
0.0
0.0
0.0
3.0
6.0
6.0
0.0
0.0
0.0
104.0
STDv
7.8
3.1
17.6
36.3
20.4
2.6
31.8
39.8
19 I
23.8
3.9
6.2
102.5
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31Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
4.10   Other Climatic data
The data available in  the time horizon  from 1952to  2010  were collected,  as observed  raw data,  with certain  gaps data for Most meteorological stations.  The other climatic data like the temperature at various resolution  levels,  mean  wind  speed,  mean  relative humidity  and  mean  sun  shine hours were available at some of the neighbouring stations.
Data like relative humidity, wind speed, sunshine hours, maximum temperature, minimum
temperature and the mean temperature, were processed for project area is obtained as follows below. 
Since there is no complete measured climatic data in the Dallol Ground water assessment project, the
study adopted the measured climatic data with neighbouring meteorological stations data within the
similar climate area.
Temperature
The variability  of mean  monthly  temperature recorded  from the stations is between  25.6-35.1  0C.  The maximum temperature is in the range of 38-44 0C, while the minimum is between 1.4-10.7 0C. The monthly variation of temperature is high in May/June and low in January.
Sunshine duration
Mean  monthly  sunshine duration  varies from 9.5  hrs (November) to  6.9  & 6.8  hrs (July  and September).  The maximum sunshine duration  recorded  was 11.0  hrs.  (February).  Both  stations recorded minimum sunshine duration in September i.e. 3.0 hrs.
Relative Humidity
Record  of humidity  was taken  from Mekele Adigrat and  Elidar Meteorological,  which  are located outside the study  areas.  Accordingly,  the mean  monthly  relative humidity  varies from 57.1  % (February) to 36.6 % (Jul). The maximum humidity recorded in the month of January i .e. 87%.
Wind speed
The  mean  monthly  wind  speed  is  varying  from  4.1  m/s  to  2.9  m/s  .  The  highest  wind  speed  recorded in April i.e. 4.9 m/s.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final) March 2014
32Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Table 4. 8: Mean Climatic Elements at key stations
Mean Temprature(°c)
Climatic Station
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Mean
Adigrat
15.2
16.7
17.0
18.2
18.4
18.2
16.8
15.9
15.7
15.4
15.2
14.7
16.4
Atsbi
13.1
13.8
14.9
15.4
16.5
12.8
15.6
15.5
15.0
13.2
12.1
12.2
14.2
Erebti
22.8
15.2
24.3
23.0
23.9
25.9
26.6
27.0
26.4
25.4
25.1
21.5
23.9
Mekele
9.0
9.8
11.3
12.8
13.4
13.2
12.5
12.3
11.4
10.8
9.7
8.7
11.2
Sheket
13.5
14.1
15.2
16.5
17.5
18.0
17.0
17.0
17.1
16.1
14.3
13.8
15.8
Wukro
7.9
9.2
11.5
13.5
13.4
12.6
12.7
12.7
11.0
10.3
9.0
7.9
11.0
Relative Humidty(%)
Climatic Station
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Mean
Adigrat
54.7
48.3
54.3
62.3
53.0
52.4
73.8
78.0
63.1
65.8
66.1
60.5
61.0
Mekele
57.8
53.1
53.2
47.5
38.4
39.9
69.7
75.6
53.3
47.5
50.0
55.3
53.5
Wind speed (m/s)
Climatic Station
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Mean
Elidar
3.6
4.1
4.1
4.1
3.0
2.9
3.2
3.0
2.5
3.3
4.3
4.0
3.5
Mekeie
3.3
4.0
4.0
3.7
3.0
2.1
2.0
1.6
1.9
3.0
3.5
3 7
3.0
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final) March 2014
33Waterworks Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Sunshine duration (hr)
Climatic Station
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Mean
Adigrat
9.5
9.3
8.2
8.8
8.9
7.7
5.5
5.8
7.6
8.5
8.4
9 1
8 1
Mekele
94
9.6
8.6
9 1
9.7
7.1
5.1
5.4
7.3
9.2
9.8
9.7
8.5
■ Adigrat
■ Elidar
■ Mekele
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final), March 2014
34Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Figure 4. 9: Mean monthly distribuition or Temperature, Relative Humidty,Wind Speed and
Sunshine duration.
4.11   EVAPORTRANSPIRATION
Monthly   evapotranspiration   (PET)   values   were   calculated   using   FAO   Cropwat   software   from   each meteorological station to the project sites for Dallol Ground Water assessment project shows in table
49
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Table 4. 9: Mean monthly Evaportranspiration over the Dallol ground water assessment area.
Month
Min
Temp
°C
Max
Temp
°C
Humidity
%
Wind km/day
Sun
hours
Mean
Monthly
Eto(mm)
January
19.2
32.8
54
346
9
196.5
February
21
34.3
57
346
9
186.8
March
22
36.3
55
346
8.5
227.2
April
23.7
38.2
53
346
9.1
240.9
May
26.5
41.1
44
259
9.3
254.5
June
28.3
41.9
44
259
7.9
241.5
July
28
41.3
37
259
6.9
253.0
August
26.6
40.6
44
259
7.7
244.9
September
26.1
40.3
40
259
6.8
234.0
October
23.9
38
40
259
8.4
233.1
November
21.5
36.3
49
346
9.5
223.2
December
20.3
33.7
56
346
8.9
195.6
Average
23.9
37.9
48
302
8.4
2731.2
4.12  Runoff Estimation For Dallol Ground Water Assessment Project
Since the hydrology  study  of Dallol ground  water assessment project area was not studied  before and highly  data absent problem and  the study  decided  to  estimate the runoff stream with  the catchment characters of the project area.  The study  adopted  the SCS methods of the drainage manuals which estimated  the runoff-rainfall relation  for the mean  monthly  rainfall data of the project area has been used.  A relationship  between  accumulated  rainfall and  accumulated  runoff was derived  by  SCS from experimental plots for numerous hydrologic and  vegetative cover conditions.  Data for land-treatment measures,  such  as contouring  and  terracing,  from experimental catchment areas were included.  The equation  was developed  mainly  for small catchment areas for which  daily  rainfall and  catchment area data are ordinarily available.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014
36Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
This method  of runoff assessment is based  on  physical considerations of rainfall runoff and  takes into  account specific catchment parameters such  as slopes,  area,  infiltration  rates and  catchment shape factors.  These physical characteristics are combined  with  rainfall intensity-duration-frequency to yield estimates of mean monthly runoff.
The  SCS  runoff  equation  is  therefore  a  method  of  estimating  direct  runoff  from  monthly  mean rainfall. The equation is:
Q = (P- Ia)2 / (P - la) + S
Where: Q = mean monthly runoff, mm
P = mean meanthly rainfall, mm
la = initial abstraction including surface storage, interception, and infiltration prior to 
runoff, mm
S = potential maximum retention, mm
The relationship  between  la and  S was developed  from experimental catchment area data.  It removes the necessity  for estimating  la for common  usage.  The empirical relationship  used  in  the SCS runoff equation is:
la = 0.2S
Substituting 0.2S for la in equation above, the SCS rainfall-runoff equation becomes:
Q = (P-0.2S)2/(P + 0.8S)
S  is  related  to  the  soil  and  cover  conditions  of  the  catchment  area  through  the  CN.  CN  has  a range of 0 to 100, and S is related to CN by:
S = 1000/CN-10
From  the  SCS  method  with  the  total  rainfall  obtained  283mm  and  a  Curve  Number  of  72 
would result in direct runoff of would result in 193mm of runoff.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Reportf Final), March 2014
37~ ' ■». Design a.d S,Wn,.„„n
„„ e,o„na.„„
i>>||j|t|j,|
Accordingly, the mean mon.hly generated discharge or run of for rhe three sub basins of Dallol is shown tn the following table 4.13. Based on this, the mean annual Run off for Musley sub basin is around 7441 Mm3, for Ayshet/Lelegehedi sub basin is 174.6 Mm3 and for Saba Sub Basin is around311.3 Mm3.
Table 4. 10: Mean Monthly generated discharge
Element: Mean monthly runoff (mm)
Year/Mnth
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Total
1995
0.00
0.05
36.12
38.19
31.32
0.00
42.32
45.09
54.78
1996
1 RQ
n nn
0.00
1 83
0.05
31.32
65.19
13.79
0.62
40.94
81.88
1997
22.47
0.00
.
13 79
0.00
0 11
u.uu
n rr
0.00
0.00
0.00
3.34
40.94
42.32
1998
0.62
0.00
.
0 98
0.00
0 01
0.05
let r
ZDl.D
ZT/iUn.c3 OO.Z
0.00
0.00
3.34
14.45
45.78
1999
29.27
0.01
.
2 81
1.83
1 83
n nn
u.uu
1 RQ
0.00
QQ /I
33.Q
0.00
0.01
1.39
58.94
51.31
2000
10.55
0.00
.
0 00
0 00
n nn
0.00
0.00
0.11
15.77
0.00
22.47
1.83
2001
0.00
2.31
.
0 00
.
o on
a An
1ZQ.U
3Q *1
0.00
38.19
45.78
6.79
0.00
37.50
65.88
2002
31.32
0.01
.
0.98
0.00
0 00
0 00
40.1
77A A
38.88
0.01
0.05
0.98
6.19
49.24
2003
0.11
44.40
6.19
2 31
12.48
.
0 00
.
0 00
iq in
1A1 1
101.1
16.43
0.00
5.60
13.13
2004
88.15
9.91
15.77
0.01
2.81
29.95
0.62
0.33
6.79
26.54
2005
0.00
28.58
.
54 78
7 40
0.05
.
1 R7
.
6 79
,
0 00
0 00
.5 n nn
113QQ
38.19
u.uu
1 co n
133.Z
31.Z
31.32
0.00
45.78
2006
45 09
0.00
0.05
31.32
65.19
13.79
0.33
40.94
2007
.
85.36
1.39
22 47
0.62
9 27
1.03
nm
0.62
0.00
Un q3q3
77.70
0.05
14.45
14.45
2008
2009
3.88
73.53
.
34.06
0.00
.
0 00
.
Q52
0 98
-
n nn
247.4
icn ■»
0.00
9.27
zoy.i
□ 1i7 Q
z r.o
8.02
0.00
27.90
11 19
29 95
n qq
n ni
0.05
0.05
9.91
2.81
0.05
0.00
49.24
.
43.71
2010
0.01
0.11
17.10
66.58
51.31
0.33
99.29
113.24
2011
0.33
0.01
.
29.27
.
0 98
56 16
1 RQ
U.Ul
nUQJOQ
91.8
l 1CbC33
0.05
0.01
24.50
0.00
13.13
Mean
21.12
0.9
13 79
0.5
. 23 8
.
0 00
0 05
0 00
.
0 00
.
0 00
14.6
UnqOq
26.8
11.6
1.8
33.8
Max
52.4
9.9
6.2
57
. 05
.j 1R
38.9
77.7
51.3
14.4
99.3
113 2
. 54 8
. 56 2
1R
Min
0.0
0.0
0.0
110311
0.0
0.0
0.0
6.2
.
1.8
o. Q77 3
J / /.J T3 O
/3.3
173 3
1 /^.3
3/7.3
STDv
2.5
06
4Q 1
1.5
15.8
.
nUn
28.6
15.1
3.6
23.5
29.4
.
17.2
00
00
13.6
0.8
v. 4.7
*10.1
90.5
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014
38Wat r Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Element: Mean monthly runoff (mm)
Year/Mnth
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Total
1995
0.0
0.0
25.4
23.9
41.1
0.0
56.2
43.4
38.8
2.2
7.3
00
238 2
1996
0.0
0.0
20.9
93.2
9.3
0.7
28.4
76.5
46.4
12.9
0.3
.
01
. 288 8
1997
0.0
0.0
0.0
0.0
0.0
11.5
69.7
65.2
4.6
0.1
0.3
.
00
151 5
1998
0.0
0.0
0.1
0.0
0.0
2.2
29.1
63.7
36.6
5.9
22
.
16
141 4
1999
0.1
2.2
0.0
0.0
0.3
1.6
59.2
38.8
11.5
0.0
.
0.0
.
00
113 7
2000
0.0
0.0
0.0
0.1
16.5
0.7
21.7
0.0
2.2
3.3
33
.
86
56 5
2001
0.0
0.0
25.4
63.7
4.0
0.0
23.9
78.8
33.6
4.0
.
00
.
00
2002
2^3 3
0.0
0.0
44.1
4.6
0.0
0.7
7.9
55.4
47.9
16
.
00
27
iGn n
2003
0.0
5.2
15.8
12.2
0.0
0.7
20.2
76.5
16.5
.
0.0
00
1i
148 4
2004
0.3
0.0
0.1
20.9
0.7
0.0
8.6
25.4
10.8
4.0
.
00
.
73
00
2005
70 8
0.0
0.0
26.1
23.9
41.1
0.0
56.2
43.4
38.8'
1.1
2006
00
237 9
0.0
0.0
20.9
93.2
9.3
0.7
28.4
80.3
46.4
11.5
.
00
.
01
290 8
2007
0.0
2.7
2.2
17.3
0.7
1.1
1.1
77.3
28.4
0.0
.
0.0
2008
00
6.6
. 130 8
0.0
0.0
12.9
2.7
0.0
6.6
10.0
25.4
27
UL
.
nn
CO 1
2009
0.0
o.ol
8.6
4.6
0.0
0.0
48.6
66.7
0.7
88.7
2010
00
00
00.1 717 Q
0.0
0.3
0.1
25.4
31.4
2.2
79.6
154.5
314
2011
0.0
.
00
00
37/1 R
0.0
0.0
0.0
0.0
13.6
0.1
17.3
37.3
Mean
15.1
00
.
00
n3
H3 7
0.4
0.6
11.2
23.3
10.0
1.3
33.1
58.4
Max
25.6
.
81
13
nq
03.1 1 7A7
6.6
5.2
44.1
93.2
41.1
11.5
79.6
Min
154.5
47.9
0.0
. 88 7
73
ra
0.0
0.0
0.0
0.0
0.0
1.1
0.0
STDv
0.7
1.6
1.4
.
00
00
13.7
00
j/H.O
JU J
30.7
14.4
2.7
23.9
34.8
16.1
.
21.1
2.4
2.1
.
84.7
39Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment ano Evaluation Project
Staiton: Musley 
Element: Mean monthly run off (mm )
Year/Mnth
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Total
1995
0.0
0.0
9.1
36.0
30.7
0.0
27.0
37.5
45.8
1.6
5.6
0.0
193.4
1996
0.0
0.0
15.7
93.5
9.9
2.2
33.8
78.4
21.7
21.0
0.6
1.6
278.4
1997
0.0
0.0
0.0
0.0
0.0
7.7
48.1
48.9
1.1
0.6
1.1
0.0
107.4
1998
0.0
0.0
0.0
0.0
0.0
2.9
19.5
51.1
39.0
2.9
4.2
3.5
123.1
1999
0.2
3.5
0.0
0.0
0.0
3.5
58.7
49.6
14.3
0.0
0.0
0.0
129.8
2000
0.0
0.0
0.0
0.6
22.5
0.0
27.0
2.2
2.9
0.0
0.0
7.7
62.8
2001
0.0
0.0
29.2
27.7
5.6
0.0
27.7
65.5
35.3
7.0
0.0
0.0
198.0
2002
0.0
0.0
29.2
1.1
0.2
0.6
7.7
29.2
46.6
0.0
0.0
7.7
122.3
2003
2.2
3.5
32.2
30.7
0.0
0.2
10.6
54.9
17.2
0.0
0.0
9.9
161.5
2004
8.4
0.0
5.6
30.7
2.9
0.0
8.4
29.2
14.3
5.6
0.0
0.0
105.0
2005
17.2
0.0
9.1
33.0
30.7
0.0
27.0
37.5
45.8
1.6
5.6
0.0
207.6
2006
0.0
0.0
16.5
93.5
9.9
0.6
35.3
78.4
21.7
21.0
0.0
1.6
278.4
2007
0.0
2.9
0.0
44.3
0.0
0.6
0.6
70.8
22.5
0.0
0.0
0.0
141.6
2008
2.9
0.0
0.0
17.2
7.7
0.0
5.6
13.5
33.8
5.6
2.9
0.0
89.0
2009
0.0
0.0
4.9
4.9
0.0
0.0
57.9
51.1
2.2
64.0
0.0
2.9
187.9
2010
0.0
0.2
7.7
49.6
43.6
1.6
82.9
119.3
29.2
0.0
0.0
0.0
334.2
2011
0.0
0.0
0.0
1.1
26.2
1.1
23.2
22.5
23.2
0.0
0.0
2.2
99.5
Mean
1.8
0.6
9.4
27.3
11.2
1.2
29.5
49.4
24.5
7.7
1.2
2.2
165.9
Max
17.2
3.5
32.2
93.5
43.6
7.7
82.9
119.3
46.6
64.0
5.6
9.9
334.2
Min
0.0
0.0
0.0
0.0
0.0
0.0
0.6
2.2
1.1
0.0
0.0
0.0
62.8
STDv
4.5
1.3
11.3
30.2
14.0
2.0
22.0
28.1
15.1
16.0
2.0
3.2
75.6
The mean annual run off obtained for the three sub basins of Dallol area is proportional to the area of catchment of the sub basins where the Saba sub basin contribute relatively high amount of Run off as shown in table 4.11
Sub Basin
Catchment Area in Km'
Mean Annual Run off generated
3
( Mm )
Musley and Adjacent
451
74.8
Ayshet/ Lelegehedi
1000
174.6
Saba
1786
311.3
Total
3237
560.7 Mm1
Table 4.10: Mean annual Run Off generated for each sub basins
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final), March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
4.13 Ground Water Recharge Estimation of Dallol Ground Water Assessment Project Area
For groundwater resources assessment of Dallol river ground water assesment project Basin it is very important to determine ground water recharge of the main aquifers. Although, there are a number of methods available for quantitative estimation of recharge, but only few can be applied due to non availability of primary data for calculation.
Lack  of proper estimation  of groundwater is the main  reason  why  groundwater exploitation  and management have serious problems compared to surface water in the country. For proper estimation of recharge time series data of rainfall, runoff, evaporation are required.
For the estimation  of groundwater recharges of the Dallol river ground water assesment project, the following  methods of estimation  is applied  i.e.  Recharge Assessment based  on  Rainfall Infiltration and  WATBAL  model.  Analiysis of ground  water reacharge used  with  WATBAL model is not so good due to lack of proper flow data and arid area of the project area.
4.14 Recharge Assessment
1- Based on WATBAL Model
Ground  water recharge for water shade areas is done with  WATBAL  Model and  this method  is not such  a good  method  in  this area due to  lake of hydrological flow data and  arid  climate area of the project area obtained with bad correlation results of modeled and observed flows shown in the Annex 4 . The ground water recharge calculation is done for the sub basins of Dallol catchments i.e Saba , Ayshet and  Musley  Catchment.  For Musele Watershade,  it is obtained  10  Mm3  for Musley  ,  67.0 Mm3 for Ayshet and 50 Mm3 for Saba sub catchments.
Ground Water Recharge for water shade areas of sub basins (Mm3)
Month
Sub basin
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Annual
Musley
0.51
0.35
0.67
1.10
0.76
0.44
1.00
1.63
1.38
0.94
0.60
0.48
10
Ayshet/lele gehedi
0.6
0.3
10.2
14.6
2.1
0.5
11.2
18.1
6.5
1.4
0.6
1.0
67.0
Saba
0.03
0.02
0.03
16
0.03
0.1
16.7
16.7
0.11
0.23
0.08
0.06
50.0
Table 4. 11: Ground water recharge for by WATBAL Model methods model.
Groundwater Potential    Assessment and
Evaluation of Musley fan area (Dallol) - Main Report(
41*
I
I
I
I
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1■Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
2- Recharge Estimation for Musley and Adjacent fan areas based on average parameters and
coefficients adopted from similar Hydrogeological environments
The main recharge to the groundwater of Musley fan area can be contributed from two major sources Groundwater runoff from Infiltration of rainfall that falls on the western meta-volcanic and meta-sedimentary rocks of the water shade areas and drains as sub surface flow through the escarpment rocks to the Alluvial fan aquifers.
- Infiltration of the runoff that is generated on the upper catchment areas and draining to the
Alluvial fan which is the more plausible recharge.
Therefore, the total groundwater recharge of the basin could be estimated by the following relation:
GWR = 5m Pm Am + 5s Rm
Where, GWR: Groundwater recharge in MCM/year
5m= Coefficient of groundwater recharge on the western water shade areas that drains as sub surface flow to the Alluvial fan aquifers
6s=  Infiltration  Coefficient  (proportion  of  runoff  from  the  upper  catchment  or  mountain  areas  and infiltrates in to the Alluvial fan aquifer)
Pm= Average precipitation on the upper catchment areas of Musley sub basin (m)
Rm= Annual runoff from the western water shade! mountainous areas that drain to the Alluvial fans
Am: Area of western water shade of Musley sub basin (m2)
The runoff generated on the upper water shade areas and which is draining into the Alluvial fans is estimated to be about 165.8 mm (74.8 Mm ).
The coefficient of infiltration  of runoff that enters into  the Alluvial aquifer is assumed  by  adopting from Areas with  similar hydrogeologic environments which  ranges from 0.23(Alluvial plain  areas ) up to 0.7 (on Alluvial fans of high porosity and permeability. Joan B Blainey 2008). Accordingly by averaging, the Infiltration coefficient for Dallol is assumed to be 0.4
The  data  used  for  the  calculation  of recharge by  the  above formula are summarized in the following table.
3
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42A'ate Vvorns Design ana Supervision Entc pnse - Dallol Area Groundwater assessment and evaluation Project
I able 4. 12: Average Parameters for calculation of Recharge
n/n j    Parameters
Value
Remark
1
8m
0.09
Obtained from WATBAL on the upper water shade area of the sub basin
2
5s
0.4
Assumed by averaging from similar hydro geologic environs
3
Pm
248mm
Generated from Satellite grid data
4
Rm
74.8 MCM
Generated on Water shade area
5
Am
451 km2
Accordingly,  the total Annual Groundwater recharges to  the Alluvial fan aquifers in Musley and 
adjacent fan areas is calculated to be around 40 Mm3
GWR = 0.09 x 0.248m x 451x 106 m2 + 0.4 x 74.8 x 106m3
GWR = 40.0 Mm3
* Hence, the sources and amount of recharge for the Alluvial fan aquifers in Musley sub basin is summarized in the following table
Source of Recharge to the Alluvial fan Aquifers of Musley and Adjacent areas
Annual Groundwater Recharge Mm3
1- Recharge from groundwater flow from upper the water shade areas draining as sub surface flow to the fan aquifer
10.0 Mm'
2- Infiltration from Run Off coming from
uplands
30.0 Mm-’
Total
40.0 Mm3-
Table 4. 13: Summary of Recharge amount from different sources on Musley fan area
4.15  Conclusion and recommendations
The hydrological study has accomplished the following tasks:
Analysis and  interpretation  of hydro-meteorological data over the recharge area,  Analysis and interpretation  of meteorological data,  data consistency,  and  trend  detection  for climatic change was carried  out.  Formulation  and  calibration  of water balance model for each  stream catchments of the study  area.  Assessed  and  analyzed  soil type,  land  cover,  permeability  of recharge areas and  prepared for the water balance model.  Identified  and  estimated  the ground  water recharge for each  sub catchments.  In  order to  account spatial variation  of input variables such  as rainfall,  runoff and  model characteristics the sub-basins under study  were divided  into  three sub-catchments.  The monthly  flows at each sub-catchment have been adopted the generated flow of The Musle,Ayshet and Saba sub
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3
For the estimation of ground water recharge in the study area two water balance methods have been 
tested viz. WATBAL model method on the watershade areas and recharge computation by 
integearteing and assuming some coeeficient parametrs for possible sources of recharge in the area. Groundawter recharge for Musley sub basin by WATBAL method is underestmated i.e 10 Mm  for
Musley water shade areas and the application of this method is not reliable due to lack of hydrologic
data and intensive evapotranspiration in the area. Therefore the second method with assumed 
coefficent parameters to compute the rechrge in the sub basin is relatively more appropriete.
For the simulation  purpose the Watbal model was calibrated  against 5  years (1996-2000) monthly runoff data by  minimizing  the sum of the square of difference between  observed  and  simulated values,  and  then  verified  (validated) by  using  data from an  independent period  of 1996-2005. According  to  the model simulation  the ground  water of the sub-basins is the product of relative depth (z) with  Smax  gives the current ground  waler storage volume.  But the methods used  mean  monthly rainfall for the estimation  of mean  monthly  recharge for the study  area).  To  satisfy  the inadequacy  of the metrological stations network  and  for further water resources investigation  a meteorological station on the Dallol sub basin should be properly managed.
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5- Geology
5.1 Introduction
5.1.1 General
The project area lies within  the Danakil depression.  This depression  is a closed  drainage basin  lying within  the East African  Rift System.  East African  Rift System is an  intercontinental extensional system composed  of different rift segment.  The Afar triple junction  is the main  feature in  the East African  Rift System (EARS).It joins with  Gulf of Aden,  Red  Sea and  Main  Ethiopian  Rift (MER) forming  rift-rift-rift triple junction  between  the Nubian,  Somalian  and  Arabian  Plates.  The Danakil depression  in  turn  lies within  the afar triple junction.  It is bounded  by  escarpment of Ethiopian plateau  (Bakalai mountain  range) in  the west and  uplifted  block  of the Danakil Alps in  the east. Dallol is situated within the center of a salt plain at the northern end of the Danakil depression.
The present study  implemented  in  areas surrounding  Dallol in  2012/2013  budget year with  the aim of identifying  different outcropping  lithological units and  geological structures and  at the same time providing  baseline data regarding  the groundwater potential of the area.  The total area of the project is 3248 km2.
5.1.2 Physiographic
The physiographic landscape of the area is the result of magmatism, volcanism, tectonic activities, 
erosion and depositional events. From field observation and DEM analysis, three major
physiographic regions were identified in the project area and namely:
5.1.2.1  Western Highlands and Rift Escarpment (A)
This physiographic region  is part of the northwestern  Ethiopian  plateau  and  separated  from the Dallul depression  by  western  rift escarpment which  extends from Belakiya mountain  range area towards west in  the mapped  area.  It is characterized  by  elevated  ridges dissected  by  deep  gorges,  rift escarpments and rugged terrain having the highest peak at an altitude of 2964m.
5.1.2.2  Graben Area (B)
This region  occupies the central part of the project area.  It is characterized  by  low lying  area within the mountain  ranges and  characterized  by  boulders of different rocks from the surrounding  highland area fill the Graben floor.
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5.1.2.3   Alluvial Fans (C)
This region  occupies the Eastern  portion  of the project area and  to  some extent in  southern  part.  The region  is characterized  by  low-lying  and  undulating  plains composed  of boulders of different rocks and  gravel terrace transported  by  rivers from the nearest highlands and  forms these depositional features.  These include Saba River,  other major and  small rivers which  emanate from the western highlands flows towards the rift salt plains with an average elevation of 110 m below sea level.
S.l.2.4   Salt Plain (D)
This landscape is found  in  the eastern  tip  of the mapped  area.  It is characterized  by  large salt plain where most of the potash  mining  activities based.  The rift floor gets thin  towards east with  an  average altitude of 120 meters below sea level. Dallol depression is a prominent feature in the area.
Groundwater Potential Assessment and Evaluation of Musley ran area (Dallol) - Mam Report! Final). March 2014
46Figure 5. 1: Physiographic Map of the Study Area.
Groundwafer
Potential Assessment and Evaluation of Musley fan area
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5.2 Previous Works
There have been  a few studies of geology  for potash  mining  in  and  around  the study  area; although no  detail assessment of geological mapping  to  characterize the various out cropping  geological formations has yet been  made,  some works are used  in  this study  to  interpret the geological set up and tectonics structures of the area.
Arkin  Y.,  1969,  Potash  in  Ethiopia.  The paper describes history  and  development of potash exploration  and  provides overall picture of the area.  Ministry  of Mines,  Geological Survey  of Ethiopia, Report 1969/2.
f
Ayele et al., 2006, The volcano-seismic crisis in Afar, Ethiopia, starting September 2005. The paper
describes the Seismo-volcanic crisis that occurred in northern Afar in late 2005, which involved 15 earthquakes greater than M5and a small explosive silicic eruption from a vent called Da’Ure (at
12.651°N., 40.519°N) close to Dabbahu volcano.
Barberi   et   al.,   1972,   Volcanism   in   the   afar   depression.   The   paper   describes   the   tectonic   and magmatic significance of the Afar depression.
Beyene   A.and   Abdulselam   Mohamed   G.,   2005,   Tectonics   of   afar   depression.   The   paper   outlines geomorphological and tectonic elements of the Afar depression and discuses its evolution.
Chorowicz  (2005),  the  East  African  rift  system,  the  paper  describes  EARS  as  an  intra-continental ridge system and volcanism in its relationship with tectonics.
Geological  map  of  Ethiopia  1:2,000,000  compiled  by  Mengesha  et  al.,  1996,  Regional  scale  map, showing the broad outline of geological units.
Geological  map  of  Ethiopia  and  Somalia  1:2,000,000  compiled  by  Meria  et  al.,  1973,  Regional  scale map, describes geological units in the region.
The Ralph  M.  Parson  Company  1958,  Preliminary  Survey  of Saline Deposits in  the Danakil Depression,  Ethiopia.  The paper describes the general and  detailed  geology  of saline deposits related to marketing, mining and process of potash in the Danakil depression in Ethiopia Proposal No. 606-
689-1
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5.3 Objective of the Study
In  order to  assess and  evaluate the groundwater system and  identify  potential well sites for groundwater exploitation,  knowledge of the nature and  distribution  of different outcropping lithologic units and  related  tectonic structures is very  important.  Hence,  the main  objective of the present study is mapping geological and structural features of the area.
Specific objectives are:
•    To identify and classify the lithological units exposed in the area
•    To construct the lithostratigraphy of the area
•    To identify major tectonic structures.
•    To map major geomorphologic features/elements in the project area
•    To construct the geological history of the area
5.4   Methodology
In  order  to  achieve  the  above  mentioned  objectives  of the  present study,  the  following  methods have been applied:
1)
Secondary data collection and interpretation (pre-field work)
>
acquisition and reviewing of previous reports
>
acquisition and reviewing of topographic maps
x acquisition and interpretation of geological maps
acquisition and interpretation of satellite imagery
2) Primary data collection (field work)
Primary data collection methods involve:
x identification and description of lithological units
y identification and description of geological structures
> identification and description of geomorphological features
3) Analysis, interpretation and report writing
The analysis and  interpretation  of all field  data and  final report writing  were carried  out using different software.  The maps and  sections were prepared  using  Arc G1S 9.3,  Global Mapper 12, Surfur 10,  and  Autocad  7  Data plotting,  analysis and  report writing  were done using  Microsoft office (word and excel).
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5.5  Geomorphology
5.5.1 General
The regional geomorphologic features which are manifestation of complex  interactions of the lithology,  structures,  hydrology,  climatic condition and time help to  understand the recharge condition and characterize the aquifer system in the area
The geomorphology  of the present landscape of the study  area  is built up through uplift and volcanism, faulting, denudation by erosion which produces sediment that is transported and deposited in low energy  area  within the landscape.  To  determine the types of landform in the study  area geology and geologic structures, drainage, and geologic process were considered
5.5.2  Land Forms
5.5.2.1 Structural land form
This landform type covers the western and central part of the study area It is the result of subsequent faulting, rifting and erosion and it has high drainage density It is characterized by highly dissected mountainous ranges and hills with steep slope and rugged topography This geomorphologic unit is comprises hilly terrain of faulted blocks, ridges, and rift escarpment. High relief mountains having an altitude of more than 3000m (western rift escarpment) also comprise this landform Generally this landform evolves from tectonic activities of NW-SE, NE-SW, N-S and rarely E-W trending normal faults and comprises rocks of metavolcanics and metasediment origin. Volcanic rocks of Tertiary and Mesozoic sedimentary rocks also comprise this land form.
Figure 5. 2: Structural Land Form
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5.5.2.2  ADuvial landform
This type of landform occupies low lying region and formed by stream’s erosional, transport and depositional action.  The highly  weathered and fractured material,  creep,  toppled,  eroded and transported by rivers and streams in to depositional area Sediments in this area are mainly composed of boulders, gravel, sand, silt and clay material derived from the escarpment area and has low drainage density This geomorphologic unit occupies Saba fan, and Musley fan area of eastern part of the study area
Figure 5.3: Alluvial land form
5.5.2J Evaporite landform
This type of landform is found in the eastern part of the mapped area.  It is characterized by extremely flat and large evaporate salt beds devoid of topographic features except some volcanoes and hot springs which are parallel to the depression trend. The depression gets lowest towards east with an average altitude of 130 meters below sea level. Spectacular flowered red, yellow and brown moulds of salts, iron oxides and sulfur deposits are a prominent feature of the area.
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Figure 5. 4: Evaporite land form
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014Legend
LtncHonni
Aluvtal
Evaporite
Structural
River
Study area separated
Figure 5. 5: Land Forms in the Study Area
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5.6 Geology
5.6.1  Regional Geology
The Danakil depression lies within the Afro-Arabian Rift System (AARS). This rift system extends
from Syria in the north and passes through Afar depression and East African Rift System. 
The Afar depression has triangular shape, bounded by marginal rift escarpments. It is flanked by the
Ethiopian plateau in the west, Somalian plateau in the south east, Ali-Sabieh blocks in the east and 
Denakil blocks in the north east side. The central part of the afar depression is dominated by lowland 
plains with horst and graben and rare high relief shield volcanoes.
The Danakil depression  is adown  faulted  block  within  the Afar triple junction  bounded  by  the escarpment of Ethiopian  plateau  (Balakai mountain  range) in  the west and  the uplifted  block  of the Danakil horst in the east.
The  geological  units  exposed  in  the  Danakil  depression  and  marginal  areas  can  be  grouped  in  to  five divisions (Y. Arkin, 19769):
>   Basement complex, older geological formation
>   Marine sediments (Salt and gypsum),which formed during invasion by the Red sea and
surround the salt plain
>   Gravel terrace and large alluvial fans, occur at foot of mountain ranges
>    Salt plain, covers a large part of the depression
>   Quaternary lava flows and unconsolidated sediments, over part of the salt plain
Precambrian basement rocks represent the oldest rocks in the region. They area composed of green 
schist, and slates intruded by granite, diorite intrusion and basalt, andesite sills. Volcanic rocks of
altered tuffs, lava flows and agglomerate origin are also present in this formation.
Post Cambrian  to  pre-Triassic massive,  sheared  and  folded  limestone overlain  by  Triassic sandstone exposed  in  the southern  part of the Balakai mountain  range.  Thick  sequence of sandstone units (lower,  middle,  and  upper) equivalent to  Adigrat sandstone which  are believed  to  be Triassic to lower Jurassic in  age uncomformably  underlain  by  Pre-Triassic limestone unit.  Dykes and  intrusions of basalts and  gabbro  mainly  occur in  the lower unit of this formation  and  at the contact of these intrusions some mineralization took place. Calcareous shales, marls and thinly bedded fossliferous
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limestone   interbedded   with   lenticular   gypsum   unit   believed   to   be   Triassic-   cretaceous   in   age recognized in the area and underlain by Jurassic sandstone units.
Tertiary  rocks  in  the  Danakil  depression  includes:  conglomerates,  fine  to  coarse  grained  sandstone, Shales, thin clay beds, tuffs and lava flows showing pillow structure.
Quaternary  rocks in  the region  have volcanic and  sedimentary  origin.  The sedimentary  deposits are of salt,  gypsum and  clay  deposits of the evaporite deposits; coralliferous limestone appear as raised platforms in  the area; alluvial deposits of unconsolidated  gravels,  sands and  silts which  form terraces and  alluvial fans.  The volcanic rocks include basaltic lava flows,  well preserved  cones with  craters and associated flows and thermal mineral springs.
S.6.2  Geological Setting of the Study Area
The geology  of the study  area is very  complex.  Since all known  geological formations of northern Ethiopia exposed  in  the area and  their petrogenesis is not well known,  construction  the litho stratigraphy  of the area became difficult.  The lithological description  in  this report is mainly  based on  field  observation  and  in  order to  map  the main  geologic features and  tectonic structures of the area,  an  inventory  of lithilogical units and  fault patterns has been  made from the interpretation  of Landsat satellite imagery  and  rock  sample analysis.  Interpretation  made on  satellite imageries were transferred  to  topographic maps of the same scale and  digitized.  Field  works were undertaken  along selected  traverses in  different parts of the mapped  area,  with  the aim to  investigate the relationship between  the nature of different outcropping  lithological units and  tectonic patterns with hydrogeologic system.  Furthermore previous geological works made have also  been  referred  in  this study.
Based  on  the  fieldwork  and  studies  of  relevant  previous  works,  the  geological  formations  outcropped in the project area described below based on age and mode of origin.
> Precambrian basement rocks > Mesozoic sedimentary rocks > Tertiary igneous rocks
>    Quaternary deposits
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Figure 5. 6: Land Sat Image of the Project Area
5.6.2.1 Precambrian Rocks
The basement rocks of Ethiopia are considered to be the interface between the Mozambique Belt (MB) in the south and the Arabian-Nubian Shield (ANS) to the north The ANS (pan Africa 900 to 500 ma, characterized by low-grade volcano-sedimentary rocks with associated mafic to felsic intrusives, which is referred to as Upper Complex, all metamorphosed under green schist condition) and the MB (characterized by high-grade gneisses and  migmatites are referred  to  as Lower Complex  and  generally  consist of amphibolites facies (locally granulite facies) orthogenesis, parag-ncisses, migmatites, granulite and amphibolite with bands of marble) collectively  referred  to  as East African  Orogen  (EAO) (Stem,  1994).The northern  Ethiopian Precambrian rocks of which the study are belongs are characterized by the occurrence of low-grade volcanic, sedimentary', and plutonic rocks of typical Arabian-Nubian Shield assemblage
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5.6.2.2  Granitic Intrusion
This unit is out crops in the western part of the mapped area along of the western rift escarpment. It is the oldest unit underlying the sedimentary rock in the area. The unit exposed as circular outcrop unit on river bed and It is slightly weathered, pinkish to dark color, and coarse grained intrusion of quartz diorite, granodiorite and granite veined with quartz. The most extensive exposure is mapped at  Bada  town  near  to  Eritrea  border.  The  prominent  minerals  are  orthoclase  feldspar,  biotitic,  and quartz with intergranular texture.
Figure 5. 7: Granitic intrusion in the Project Area
5.6.2.3  Limestone Unit
A sequence of thick massive limestone crops out in the western part of the mapped area. It is closely folded, sheared, foliated and related with underlain slates and Phylites by an angular unconformity
It  is  brown  to  black  color,  well  bedded,  and  veined  with  calcite  In  some  places  it  is  highly  re crystallized Its age dates back to Precambrian to Pre-Triassic period.
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Figure 5. 8: Folded limestone unit
5.6.L4 Metasediments (Slates and Phyllites)
Metasediments represent the major and  oldest rock  formations in  the area These rocks are basically slates,  but in  some places significant amount of phylites and  interbeded  limestone are present and they  area belong  to  Tambien  group  of northern  Ethiopia.  They  are intruded  by  granite,  diorite,  and by  sills and  irregular masses of basalt and  andesite These rocks are exposed  in  the western  rift margin at the foot of major fault escarpment of in the mapped area. In fresh samples, it is greenish dark,  but dark  brown  in  weathered  ones,  and  has hard  and  compact in  appearance They  area highly foliated, sheared, foliated and tilted
Figure 5. 9: Foliated and tilted slaty cleavage exposed on the escarpment
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5.6.2.S Meta-Conglomerate
The study  area is dominated  and  characterized  by  low grade Meta-sedimentary  rocks The meta conglomerate unit in  the mapped  area exposed  in  and  along  river beds indicates evidence of shallow water origin.  The western  pan  of the mapped  area dominated  by  several conglomerates which  area composed  of not well rounded  or irregular shape clasts.  The clasts sizes are variable,  ranging  from millimeters up  few centimeters.  In  the study  area these rocks are associated  with  Meta-volcanic rocks and  interbedded  with  red  series It is coarse grained,  greenish  gray,  densely  welded  rock containing lithic fragments, marine clasts, and associated tuffs and lava flows.
Figure 5.10: Meta-Conglomerate
5.6.2.6 Meta-Greywacke
This unit is exposed  in  the western  part of the mapped  area Meta-Greywacke consists of crystals of feldspar and  quartz with  some intercalated  lithic fragments in  fine matrix.  It is light gray  to  light brown  fresh  samples and  yellowish  to  silver gray  in  weathered  ones.  Although  there are no petrographic and  chemical analysis,  field  visual inspection  confirms that these rocks derived  from pyroclastic deposits (rich  in  silica) ejected  during  the volcanism,  and  immediately  transported  and reworked by running water
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Figure 5. 11: Meta-Greywacke
5.6.X7 Meta-Volcanic Rocks
This unit is exposed  in  western  and  central part of the mapped  area occupying  Its composition ranges from basalts to  rhyolites and  associated  meta-sediments The major components of these sediments are of volcanic origins,  agglomerates,  breccias,  bedded  tuffs and  lavas.  These extensive low grade metamorphic rocks belong  to  Tsalit group  of northern  Ethiopia.  The meta-volcanic rocks are rich  in  acidic minerals,  dark  grey  to  brownish  color and  fine-medium grained.  The same change probably occurred further north in the study area.
Figure 5. 12; Meta-volcanics underlain by acidic materials
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5.6.2.8 Paleozoic Sediments
Non  metamorphosed  continental sedimentary  rocks are exposed  in  different parts of Ethiopia These rocks are considered to be Paleozoic in age mainly composed of sandstones and minor tillite, shale, siltstone and conglomerate. The Enticho sandstone and Edaga Arbi tillites in Tigray region, northern Ethiopia are one of them (Beyth,  1971; Dow et al.,  1971,  Levitte,  1972; Garland  1980).  These sediments are exposed at the very west and top part of the study area particularly in Senkata, Edaga- Hamus,  and  on  the Astbi plateau  They  are characterized  by  white,  coarse grained,  cross bedded calcareous sandstone with silty beds with some pebbles, cobble and boulders overlain by tillites.
5.6.2.9 Mesozoic Sedimentary Rocks
1 - Sandstone Unit
This unit is the oldest of the Mesozoic sediments exposed  the area It is a thick  sequence of sandstone which  is equivalent to  the Adigrat sandstone which  is also  believed  to  be of Triassic - Jurassic in age It rests unconformable on the Precambrian basement rocks of the area.
The maximum thickness of this unit reaches more than 800m in the region. It is exposed only at the northern  periphery  of the study  area.  The unit is pink  to  red,  coarse grained,  well sorted  arkosic sandstone with  conglomerate bed.  It has also  whitish  gray,  friable,  cross bedded  and  well sorted structure containing  rounded  quartz pebbles and  local shale beds.  Dykes and  Intrusion  of basalt and gabrro occur in the lower unit of this formation.
Figure 5.13: Sandstone unit, exposed at the eastern part of the Graben area
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2 Limestone Unit
This unit is composed  thinly  laminated  limestone,  marls and  calcareous Shales and  gypsum intercalation. It is the major sedimentary succession in the region. It is also a major Stratigraphic unit covering  large part of the mapped  area.  This formation  is characterized  by  thick  sequence of limestone layer,  intercalated  with  marl.  It is light to  yellowish  color in  fresh  sample and  yellowish gray color in weathered one. This limestone is characterized by thinly bedded intercalated shale. It is yellowish  color,  fossliferous and  well bedded  limestone.  These rocks and  the above described geological units form the western rift escarpment surrounding the depression or the salt plain
Figure S. 14: Thick limestone successions
5.6.2.10   Tertiary Rocks
The tertiary  rocks in  the study  area include pebble to  boulder size conglomerate,  fine to  coarse grained  sandstone,  sand,  shales and  variegated  color clay  beds,  with  interbedded  basaltic lavas and acidic intrusion.  These sediments are exposed  along  the margins of the Denakil depression  underlain by  basement and  Mesozoic rocks Lava flows of amigdaloidal basalts shows pillow structure and  the Amigdaloids are filled  with  secondary  minerals.  Acidic flows have also  observed  at the mouth  of the Sabba river a flow 10m thick of rhyolite was noted (Beyth 1971) and at Badda there is a thick bed of reddish ignimbrite containing olivine crystals. It is believed
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Figure 5.15: The Denakil red series exposure
(Garland  1972) that the series was formed  in  tropical climate in  an  oxidizing  environment in  the zones of fluvial outwash.  The age (Miocene-Pliocene in  age) of this series dates back  to  the formation of Danakil depression and the Afar as a whole.
5.6.2.11 Quaternary Deposits
Quaternary  deposits in  the study  area include volcanic and  sedimentary  rock  origin.  Despite their limited  areal coverage, these geological units play a significant role in understanding the surface and subsurface water movement and  occurrence in  the past and  at present at the project area.  Hence,  a brief account is given below for these rocks.
5.6.2.12 Sedimentary Deposits
The sedimentary  rocks in  the mapped  area include: the salt,  gypsum and  clay  deposits of the evaporate beds,  calcium precipitates,  and  alluvial deposits of unconsolidated  gravels,  sands,  and  silts which  form the alluvial fans.  Alluvium these sediments have limited  areal extent and  are found mainly in some depressions and flat basins.
Alluvial fans: the alluvial fans are extending from the foot of the escarpment in the west and spread eastwards over the flat floor of the depression.  These sediments occupy  flood  plains,  grabens,  rift floors,  and  the bases of escarpments and  cover the salt plains.  Mosley  fan,  Sabba fan  are the major alluvial fans in the area. These fans are composed of fluvial sediments of different size ranging from poorly  sorted  and  sub  rounded  pebbles and  boulders to  poorly  sorted  mixtures of gravel,  sand,  silt and  clay  Exposure of these sediments is found  along  river courses and  flood  plains and  graben regions of the study  area.  They  consist of all forms of reworked  materials of volcanic and sedimentary origin
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The rainfall amount in  the area is very  low and  the available water in  the area is due to  the runoff caused  by  the rainfall on  the escarpment during  rainy  seasons of July,  August,  and  September TTiis run  off accumulates large and  extensive alluvial deposits and  causes flooding  in  the salt plains.  Due to the scarcity of potable surface water in the area, the alluvial fans believed to hold huge amounts of fresh  water Test wells drilled  in  these deposits and  the lithologic logs indicate that the holes penetrated alluvial sediments of more than 100m thick and tap good quality of fresh water
Figure 5.16: The alluvial fan and boreholes drilled for test
Carbonate precipitates: Carbonate precipitates like travertine are formed  from the precipitation  of dissolved  calcium carbonates These precipitates are found  on  foots of western  escarpment and  they have light color and  fine grained.  The picture in  fig  5.16  depicts an  exposure of travertine deposits. They are very limited in size and spatial distribution.
Figures. 17: Travertine exposure
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5.6.2.13   Volcanic Rocks
The volcanic rocks in  the study  area are dominated  by  young  Quaternary  to  recent volcanic of dominantly  basaltic composition.  These volcanic rocks are composed  of basic lava flows,  lava fields and  related  spatter cones and  associated  thermal mineral springs.  They  are very  young,  dark  and  fine grained  basalt flows exposed  along  fissures and  faults.  These rocks are exposed  in  the eastern  part of the mapped  area occupying  the rift floor and  they  are exposed  over part of the salt plain.  The occurrence of central chain  of active volcanoes and  associated  hot springs in  a roughly  linear pattern indicates the existence of a fault.
Figure 5.18: Central chain of active Quaternary volcanoes
5.6.2.14  Evaporite Deposits
The evaporite beds in the mapped area cover the eastern most extension of the depression It occupies a large part of the depression and is surrounded by belt of marine sediments which were formed during invasion by the Red sea (Y. Arkin, 1969). The evaporites including potash, sulfur, gypsum, halite and other minerals present in these deposits. Recent lava flows and unconsolidated alluvials exposed over part of the salt plain and alluvial fans occur at higher levels in the mapped area
Dallol is located at the northern most extension of the Danakil depression in the center of salt plain It is the prominent feature in the area rising above the salt plain with an average elevation of 130m below sea level. It is a field of phreatic craters in the salt plain and it is the lowest and hottest area of the Danakil depression. Colorful hot brine springs and fumarolic deposits are found in the area There are hot yellow sulfur fields among the sparkling white salt beds.
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Geological Map of the Dallul Project area
Groundwater Potential Assessment ------- ------------------------------------------------------------------------------------------------------------------------------ .
30 area (Dal101) ■ Ma|n Report! Final), March 2014I
i               L L' L L L L L■
...1
.1 X
-u
X
X
X
X
XI
1
L
Ll:I
:lWaterworks Design and Supervision Enterpr.se ■ Dallol Area Groundwater assessment and Evaluation Project
The marginal grabens have developed  in  response to  extensional deformation  related  to  an  early phase in  the development of the western  margin  of the Afar Depression  as well as renewed  tensional
movement associated  with  magma injection  along  weak  zones (Zanettin  and  Justin-Visentiri 1975) Chorowicz et al.  (1999) and  Collet et al.  (2000) suggested  that the development of these basins is associated with Plio-Quatemary NNE-trending sinistral strike-slip faults.
Figure 5.25 Lelegehedi(Ayshet) graben bounded by uplifted fault blocks to the East
3  - Rift Floor Sector
The northern  rift floor of Afar are characterized  by  a system of faults trending  NW-SE.  This trend  is parallel to  the Red  Sea rift and  is considered  as its continuation  into  northeast Africa These NW-SE trending  structures are all normal faults developed  at different stages of evolution  of the rift accompanying  volcanic eruptions.  The faults are older on  the western  parts and  become younger towards the east.
The intersection of transverse faults in the Dallul and major fault paralleling the sides of the depression has resulted in a fractured zone through which the hot underground water rises to the surface Hot water nsing to the surface has earned salts with various colors in solution and redeposit them on the surface (the Ralph M Parsons Company, 1958)
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4     Foliation and Lineation
Older prominent small scale structures observed  tn  the basement complexes of the are.  are foliations
»d    lineations    These    are    penetrat.ve    planer    fabric    mainly    occur    in    meta-sed.men.s    and    nteu- volcanics,  the  latter  is  susceptible  to  deformation,  so  that  good  alignment  of  foltanon  more  present  tn meta-sediments   Very   closely   spaced   cleavage   planes   consisting   of   a   parallel   orientation   of   clays   and micas  represent  the  foliation  in  slates  in  the  study  area  Other  structures  observed  in  the  area,  are  the linear alignment of minerals and grains It is a fabric element represented by a line
Figure 5. 26: Strongly deformed and foliated basement rocks at the foot of the horst block
5 Joints and fractures
Fracture:   is   defined   by   Twiss   and   Moores   (1992)   as   “surfaces   along   which   rocks   or   minerals   have broken, they are therefore surfaces across which the materia) has lost cohesion.”
Joints: are fractures along  which  there has been  no  appreciable displacement parallel to  the fracture and  only  slight movement normal to  the fracture plane Most joints form by  extensional fracturing  of rock  in  the upper few kilometers of the Earth's crust.  These are the common  structures present in  all kind  of rocks in  the study  area.  Types of joints in  the mapped  area are columnar joints,  concentric
joints,   and   tiny   normal   joints   of   which   columnar   and   tiny   normal   joints   are   the   most   commonly observed
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Veins: are filled  joints and  shear fractures and  the filling  range from quartz and  feldspar to  quartz, calcite and  dolomite.  Quartz veins are observed  in  granitic and  granodioritic intrusions of the study area
Figure 5. 27: Columnar jointed basalts and quartz vein exposed in grano-doiorite intrusion Structural Map of the Study Area
Legend
Figure 5. 28: Structural map of the study area
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6. Geophysical Investigation
6.1 General
.
For Dallol area groundwater potential investigation, Geophysics has been taken as an important tool to  evaluate  the  groundwater  condition  from quality  and  quantity  point  of  view.  The  geophysical investigation method was planned to acquire data which help to map the fresh, brackish and salt water  interface  and  to  know  the  extension  of  fresh  and  brackish  water  zones both  in  depth  and laterally. For this, both the Transient electromagnetic survey (TEM), and Vertical electrical sounding (VES) was conducted where data were collected along the proposed traverses (NS) oriented across the Alluvial fan deposit. The geophysical investigation was done with the following objectives
■   To locate potential well sites for fresh groundwater
■    To  determine  the  depth  and  lateral  extension  of  fresh,  brackish  and  salt  water  interface  and accordingly thickness of the fresh and brackish water aquifers will be determined which helps for the quantitative estimation of volume of water in the aquifers
■     To  identify  structures  (Faults)  which  are  used  as  preferential  pathways  for  groundwater movement.
6.2 Methodology and Instrumentation
The Schlumberger electrode configuration  was used  for the Vertical Electrical Sounding measurements in  all the investigated  sites,  with  the maximum cunent electrode separation  used varying from sounding to sounding depending on the local conditions, but generally in the ranges of (AB/2) = 220m to 500m of electrode separation was utilized. Most of the VES data were collected with  NS azimuth  and  the intervals between  the sounding  points varies depending  on  the local conditions but mostly lined up in such a way that geolectrical sections can be prepared.
The Tetrameter SAS 4000, ABEM instrument is used for the VES surveys powered by 12volt and 70Ampare  car  battery  together  with  other  accessories  such  as  interconnecting  cables  with  reels.  At each VES shot, voltage (AV), current (I) and resistance (R) measurements were collected from the instruments  deploying  Schlumberger  array  at  distinct  location  on  the  ground.  From  the  resistance value  of  the  ground  and  the  corresponding  geometrical  factor  apparent  resistivity  of  the  ground  is computed.  The  data  is  feed  to  appropriate  software  on  the  computer.  The  one  dimensional  forward and   inverse   model   output   of   the   resistivity   interpretation   software   provides   the   observed   and computed  apparent  resistivity  curves  and  the  subsurface  layer  parameters  which  are  the  apparent resistivity  and  the  corresponding  thickness.  Litho  logical  logs  from  previously  drilled  boreholes  in proximity of the surveyed traverses have been used for calibration and further refining of the result.
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The geophysical (TEM) survey was carried out along and across the alluvial Ians. 1 he survey layout is 200m by  200m Tx  loop  size with  central loop  induction  method.  All the TEM soundings were made with  the same configuration.  Canada made GEONIX PROTEM instrument was used  in acquiring the data. The instrument incorporates a solid state memory hence, data were dump to the field  laptop  computer.  To  conduct the TEM sounding  an  electric cable is arranged  as square loop using  a hand  held  compass and  GPS with  length  of 200m by  200m on  the ground.  The TEM transmitter is placed  at one comer of the loop  and  connected  to  the receiver with  reference cable. Whereas circular coil is placed at the center of the Tx loop and connected to the Rx. The Tx is set to generate alternating  current in  the loop  and  the Rx  measures while the Tx  is in  off time.  The procedure is repeated  for three different sweeps and  stored  in  the solid  state memory  of the Rx. Thus, stored field data is dumped to the field lap top computer.
The field  TEM data is processed  using  TEM2IX1D and  IXID software packages.  Three sweeps H,M,L with different frequencies are selected and the Tx loop size is set on the TEM2IX1D software and  processed.  Then,  the output data is reprocessed  using  the IX1D.  The 41  soundings which  were processed have estimated RMS error bellow 5%.
The apparent resistivity Vs time model is displayed at the start of the processing and initial model is entered  which  contains the apparent resistivity  and  thickness parameters.  Then,  forward  model is run  at first and inversion is applied to get good fit of the observed and calculated curves. Then the final model is observed with apparent resistivity and thickness parameter.
6.3   Volume of Work
A total of 16  VES were conducted  on  the major fan  areas of Musley  and  adjacent fans and  the geophysical survey lines were oriented along the fan i.e west to east. Due to the problem of putting electrodes on  the surface because of hard  boulders covering  the fan,  it was not possible to  get sufficient data from the vertical electrical sounding  alone.  Therefore TEM (Transient Electromagnetic Survey) was conducted. A total of 41 TEM survey were conducted on the major fan areas of Musley,  Gehertu  and  Saba Out of these a total of 21  TEM survey  were carried  out for Musley  and  adjacent fans with  survey  lines oriented  along  and  across the fan  i.e North-South  and East to  West directions.  The location  and  raw data of vertical sounding  points and  magnetic profile data are annexed in the report.
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6.4  Results of VES and Transient Electromagnetic Survey
I) TEM interpretation on Gehertu and Musley fan area
In general, the model curves illustrate the presence of depleted apparent resistivity response at the top and bottom depths. Whereas, at intermediate depth there is enhancement in electrical parameter, Which illustrates the presence of clay at the top fresh ground water in coarse alluvial deposit at the middle and saline ground water at depth in evaporite and Clay beds.
The geo-electric sections reveal the presence of depleted  apparent resistivity  response at the top which  is attributed  to  plausible wet clay  and  enhanced  electrical response at the middle which  is interpreted  alluvial deposit with  fresh  ground  water.  Bellow this depth  is found  low apparent resistivity response which is caused by saline ground water in alluvium deposit.
From the geo electric section and calibrated model curves from test boreholes, it is observed that the fresh-salt water interface might goes 150-200m depth on the major fan areas like Gehertu fan. For Musley  fan  area,  the fresh-salt water interface exists 120-150m depth.  The fresh  water thickness decreases east wards from the center of the fan and the fresh salt water interface exists 50-60m depth below ground surface.
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Figure 6. 1: Location map for geophysical survey points and section linesWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Eiaiuat on J---------------------------
A) Gehcrtu fan selected TEM Model curves
Dallol TEM 09- Gehertu fan
Easting                 0626919
Northing                1576767
Elevation               17.9m
Figure 6. 2: TEM model Curves, and interpretations for Gehrtu and Musley fan area
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
140
15.7
15.7
Coarse sand .gravel with boulder fragments
2
129
20.9
36.6
Coarse sand
3
5
1.0
37.6
Clay
4
2087
86.0
ni23.6
Coarse sand and gravel ( water saturated below 108m
5
7
Saturated Fine to medium
sand
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Dallol TEM 10 - Gehertu fan Easting              0627124 Northing            1576740
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
148
7.5
7.5
Boulder and sand with Clay
2
137
13.3
20.8
Medium grained Sand
3
3
1.0
21.8
Clay
4
1990
96.7
118.5
Coarse Sand ,Gravel and Boulders
5
5
...
—
Saturated sand with clay and Silt
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Dallol TEM 11 - Gehertu fan
Easting                 0627527
Northing
Elevation
1576899 -10.6m
1.11 0.1 1
10 100
Tiw
,l ” 0.001 o.oi 01 i io ioo iddti
Rtiawr; iuta-ai
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
143
7.5
7.5
Boulder with sand and clay
2
132
15.7
23.2
Medium sand
3
3
2.0
25.2
Clay
4
2013
73.7
98.9
Water bearing coarse sand and gravel
5
5
Saturated fine sand with clay
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Dallol TEM 01 - Musley fan
Easting 0628633 Northing 1573132
Elevation
2.9m
V
(ohm-
on)
Thickness(m)
Depth(m)
Formation
1
7758
2.3
2.3
Boulders with Clay
2
2
18.3
20.6
Fine sand and Clay
3
23
1
21.6
Sand
4
2259
143.3
164.9
Coarse Sand Gravel and boulder fragments
5
2
““
—
Clay
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Dallol TEM 02 - Musley fan Easting              0630014 Northing             1572827 Elevation -54.7m
DALTEM02
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
229
2.3
2.3
Boulder with Clay
2
201
2.9
5.2
Boulder with Clay
3
5
9.9
15.1
Clay
4
2034
10.0
25.9
Dry Coarse gravel and Sand
5
5
Saturated fine Sand and Clay
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Dallol TEM 03 - Musley fan Easting 0630198 Northing 1572422 Elevation -64.8m
DALTEM03
1.01              o.i
I                         10                  100
••11.1           1 W IK UK*'
Pesfivit/ iGfaa-M)
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
121
6.5
6.5
Boulder with Clay
2
148
13.6
20.1
Sand and Gravel
3
5
2.8
22.9
Clay
4
1985
82.4
105.4
Sand , gravel and boulder fragments
5
5
...
Clay
_____________________________________________
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) Mam Report( Final) March 2014Waterworks Design and Supervision Enterprise
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Dallol TEM 04-Musley fan
Easting 0630123 Northing 1573263
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
131
6.1
6.1
Boulder with Clay
2
153
14.3
20.4
Coarse gravel and Sand
3
4
1.4
21.8
Clay
4
2175
92.9
114.7
Gravel and Boulder
fragments
5
6
—
Clay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Report! Final) March 2014Water Works Design and Superv.s.on Enterprise - Dallol Area Groundwater assessment and Eva.uafon Project
Dallol TEM 05 - Musley fan
Easting 0630082 Northing 1574092
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
133
6.0
6.0
Boulder with clay
2
154
14.5
20.5
Coarse gravel and Sand
3
3
1.2
21.7
Clay
4
2181
80.3
102.0
Boulder fragments with sand
5
5
Saturated clay ( Saline )
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Dallol TEM 06 - Musley fan
Easting 0630703 Northing 1573084 Elevation -79.3m
001 0.1 1 10 100 10«H
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
144
6.9
6.9
Boulder, gravel and Sand
2
137
12.7
19.6
Gravel and Sand
3
3
1.0
20.6
Clay
4
1984
66.5
87.1
Boulder, sand and gravel mix
5
5
Saturated Clay (Saline)
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Dallol TEM 07 -
Easting Northing Elevation
Musley fan
0630807 1572669 -80.4m
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
112
8.3
8.3
Boulders with clay
2
104
10.8
19.1
Sand and Gravel
3
3
1.8
20.9
^Clay
4
1985
54.7
75.6
Boulder fragments
5
4
Saturated Clay ( saline
________
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________________________________ area (Dallol) - Mam Report!
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Dallol TEM 08 - Musley fan
Easting 0630971 Northing 1572281 Elevation -87.7m
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
131
11.8
11.8
Boulder with gravel and sand
2
139
20.8
32.6
Coarse gravel with Sand
3
4
0.6
33.2
Clay
4
2041
52.1
85.3
Boulder fragments
5
5
—
Saturated Clay (Saline)
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Dallol TEM 12 - Gehertu fan Easting               0628588 Northing             1577437 Elevation            -69.5m
0ALTEM12
□
9
I —
K o00°
1
O
1
-------1—1 II1 111
1   1  1 1 1 1 II
0.11             0.1                     1                      10 Tu" IM
too
W.M1 <01 Q.1 1 10 ISO IOH
Poifivit; I'jUn-ri
ft
(ohm-m)
Thickness(m
)
Depth(m)
Formation
1
133
6.9
6.9
Boulder and Clay mix
2
124
13.2
20.1
Coarse gravel and Sand
3
3
2.0
22.1
Clay
4
1956
52.7
74.8
Gravel and rock fragments
5
5
—
Saturated clay (Saline)
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[I 1 1 1 1 1—1—1----------Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Dallol TEM 13 - Gehertu fan Easting               0628576 Northing              1577832 Elevation            -80.1m
DALTEI.I13
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
133
6.6
6.6
Boulder and Clay
2
185
12.9
19.5
Coarse gravel with Sand
3
7
2.0
21.5
Clay
4
1957
53.3
74.8
Coarse gravel, sand with rock framents
5
5
...
—
Clay
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Da Hol TEM 14 - South Musley (Bekerti) fan Easting             0633749
Northing            1565710 Elevation -50.6m
0.11 0.1
I
Tin H
10                 100
Mooi toi o.i 1 io too toil
Eeitrtt; iuluo-m.i
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
128
6.9
6.9
Boulder with Clay
2
138
15.1
22.0
Coarse sand and Gravel
3
5
1.0
23.0
Clay
4
2019
138.4
1614
Boulder  fragments  with  Sand and Gravel
5
7
22.2
183.6
Fine sand and Clay
6
26
Saturated fine Sand with
Clay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Reportf Final), March 2014Water Works Desi n and Supervision Enterprise - Oallol Area Groundwater assessment and Evaluation Project
C
Dallol TEM 15 - South Musley ( Bekerti) fan
Easting 0634089 Northing 1566268 Elevation -71.1m
1
1
J
J
J
"J
"J
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
131
6.6
6.6
Boulder with clay
2
141
15.2
21.8
Sand and Gravel
3
3
1.0
22.8
Clay
4             2029
116.4
139.2
Boulder fragments with sand and gravel
5
5
34.6
173.8
Clay
6
26
—
—
Saturated fine Sand and Clay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Reportf Final), March 2014
94Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Dallol TEM 16 - South Musley ( Bekerti) fan Easting               0633959
Northing              1566710
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
113
8.1
8.1
Coarse gravel and Sand
2
105
11.6
19.7
Fine to medium sand
31
5
1.0
20.7
Clay
4
1988
93.2
113.9
Boulder fragments with sand
5
7
14.1
128.0
Clay
6
50
—
Saturated fine Sand
1
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment ano Evaluation Project
Dallol TEM 17 - South Musley ( Bekerti) fan
Easting Northing Elevation
0632252 1568331 -72.3m
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
115
8.5
8.5
Boulder and Clay mix
2
107
11.2
19.7
Sand and Gravel
3
5
1.0
20.7
Clay
4
1994
85.2
105.9
Boulder fragments
5
6
25.7
131.6
Clay
6
49
Fine sand
Groundwater Potential Assessment and Evaluation of Musiey fan area (Dallol) - Main Report( Final), March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Dallol TEM 18 - South Musley ( Bekerty fan)
Easting Northing Elevation
0631873 1568842 -60.5m
DALTEM18
100
O
-
I
&
10
i
\°
\°
\°
V
•w
<£■
°\
a
□
1
QD
0
aS
1
a\
0\a
\p
----- r i rn rrr
1  1 I T JI IT
i i i nirr
1    1 1 1 11II
•JI               0.1                     1
Ito IM
10 100
0010.1 t 10 IM uh”
Ptiflvlt; (Otam)
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
116
8.4
8.4
Boulder with Clay
2
95
12.3
20.7
Sand and Gravel
3
4
1.0
21.7
Clay
4
2005
77.5
99.2
Boulder fragments
5
6
...
—
Clay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final), March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Dallol TEM 19- Easting Northing Elevation
Musley fan 0630041 1572213 -61.9m
o.ooi o.i i 10 too loci1
0.11 0.1 1 10 100
Tin* |m*|
PeKrtty lObwi-a)
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
101
8.6
8.6
Boulder with Clay
2
118
13.3
21.9
Sand and Gravel
3
7
1.0
22.9
Clay
4
2023
89.4
112.3
Boulder fragments
5
5
...
-—
relay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Repon( Final) March 2014
98
IDallol TEM 20-Musley fan
Easting 0630248
Northing 1572709
tt
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
83
8.2
8.2
Boulder with clay
2
99
12.4
20.6
Sand and Gravel
3
5
1.0
21.6
Clay
4
2035
90.1
111.7
Boulder fragments
5
8
---
_—
Clay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report( Final) March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Dallol TEM 21 - Musley fan
Easting 0631401
Northing
Elevation
1572614 -99.6m
6.01               0.1
I
Til" |a<(
10 100
0.010.1 ( 10 100 Ull'1
PeiHvir; (Cha n)
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
86
6.1
6.1
Boulder with clay
2
100
8.4
14.5
Gravel and Sand
3
5
1.7
16.2
Clay
4
2035
73.1
89.3
Boulder fragment
5
6
—
—
Clay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Reporr( Final) March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
J
J
Depth of Layers in meters
Clay and Fine Sediments
Resistivity (ohm-m)
J
0-10m
■]
]
1
25-30 m
40 - 150m
Fresh water Aquifer
Saline Water Zone
]
1
1
Saline
aquifer
Figure 6.3: Vertical Salinity Distribution at depth interpreted Trom TEM geophysical survey
J
1
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Repon( Final). March 2014------------------- 101naici t«wmj
DALLOL GEOELECTRIC SECTION 9
Apparent ReaBOvlty
(om-m)
Figure 6. 4: Interpreted TEM section on Gehertu fan area
Groundwater Potential Assessment and Evaluation of Musley fan area |Dallol) • Main Report! Final), March 2014
102Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
ii) VES interpretation on Gehertu fan area
The vertical electrical soundings and TEM survey conducted in different areas of the fan have been interpreted  in  this report.  The VES interpretations were calibrated  with  the test wells drilled  and additional borehole log data available in the vicinity of the VES points on the fan area.
The interpretation  of most VES model curves show that some areas in  the Musley  and  adjacent alluvial fan  are characterized  by  very  high  resistivity  top  layers which  could  be resulted  from boulders spread in the top soil. This depth could reach up to the depth of 2m to 4m. The second layer extending up to the depth of 70m is relatively less resistive layer. This could be due to the sand and gravel with clay deposit in the alluvial fan. Below this layer the resistivity of the subsurface is highly elevated in almost all of the sounding points. This is related to the presence of high resistive boulder fragments which  makes the sounding  difficult to acquire appropriate data at depth and that is why the TEM survey carried out efficiently to acquire appropriate subsurface data at depth. Most of the VES curves that looks promising for fresh ground water lays along large drainage pathways as it is also  visible on  the Google imagery.  Some of the interpreted  model curves and  pseudo  sections on Musley and Gehertu fans are presented below
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Repon( Final), March 2014
103Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation P—j
Figure 6.5: VES Mode) curves interpreted on Musley and South Musley fan areas
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
357.3
0.9
0.9
Top dry soil
2
215.3
2.5
3.4
Boulder fragments
3
423
30.1
33.5
Dry sand and gravel
4
141.9
93.8
127.3
Coarse gravel with Sand
5
67.6
Saturated sand and gravel ( Aquifer zone)
Groundwater Potent,al Assessment and Evaluate ot Musley fan area (Dallol) - Mam Report! F.nal). March 2014
104Appar. Resistivity [ohmm]
Water Works Oesign and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation ^rQJ
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
8525.1
1
1
Boulders with clay
2
633.1
5.4
6.4
Boulders with gravel and clay
3
332
71.7
78.1
Dry sand and gravel with clay
4
102.5
66.1
144.2
Saturated Coarse sand and gravel
5
2907.7
Boulder fragments with clay
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Repon( Final) March 2014
105Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Projea
#
(ohm-m)
Thickness(m)
Depth(m)
Formation
1
10864.3
0.5
0.5
Top dry soil
2
384.2
2.8
3.2
Boulders with clay
3
1103.3
7.5
10.7
dry sand with boulder fragments
4
92.4
32.4
43.0
Coarse sand
5
11.1
L
Fine sand and clay
1
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Report( final) March 2014
106Waterworks Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Projeo
Figure 6. 6: Photos taken during geophysical investigation on site
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) Main Report! Final) March 2014Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
7 - Hydrogeological Survey and Investigation Analysis
The following  hydro  geological survey  and  investigation  were carried  out to  assess the groundwater resource of Dallol area.  The major activities include water point inventory,  water quality  survey, geophysical investigation,  test wells drilling  and  pumping  test.  The next sections describe the results of the hydro geological surveys and investigation conducted in the area.
7.1 Water Point Inventory
7.1.1  Introduction and Field Work
The water point inventory  has been  commenced  at office level by  collecting  all available information and  data from different organizations.  These information  that are in  the form of reports and  data were evaluated  to  identify  the data gap  and  resolute what to  be done next.  Hence,  most of the obtained  information  and  data were found  to  be incomplete,  lacking  co-ordinate,  well log  and  others hydrodynamic parameters.  Thus,  the water point’s inventory  was planned  to  collect hydro  geological information  and  directly  measured  data such  as co-ordinates,  dynamic or static water level,  and  field water quality  measurements such  as specific electrical conductivity,  water temperature and  Ph. Representative Water samples were collected  and  analyzed  to  fill the data gap  and  upgrade the overall data base.
More than 110 water points were inventoried and collected and out of these 106 are boreholes with variable depth, very few hands dug wells and springs. The distribution of water points in the area is | given in fig 7.1 Water samples were collected from those representative water points for chemical
analysis. During the study 14 ( fourteen) samples from existing water points and ten ( 10) samples from test wells were taken and chemical analyses were conducted in Water Works Design &
Supervision   Enterprise   Laboratory   and   in   general   analysis   result   of   more   than   50   water   samples   (
| including results from other sources) were used for hydrochemical examination.
The analyses carried out are:
| 
' 
| 
• Main cation (NH4+, Na+, K+, Ca++, Mg++, Mn++)
Main anion (C1-, NO2-, NO3-, HCO3-, SO4-, and PO4—)
•            Water turbidity
•           Total dissolved Solids (mg/1)
•            Electrical Conductivity (pS/cm)
•            PH
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108
IWater Works Design and Supervision Enterprise - Da I lol Area Groundwater assessment and Evaluation Project
Total Hardness (mg/I Ca CO3)
• Alkalinity (mg/1 CaC03)
7.1.2  Characteristics of Water points
i)        Water Points distribution in the surface water basins
The water point’s inventory was carried out in the sub catchments of Saba, Ayshet, Musley and Adjacent fans and Figure 7.1 shows the distribution of collected water points from these basins.  More water points are surveyed  from Musley  and  adjacent catchments on  the fan areas where relatively  more boreholes have been  drilled  in  these areas for investigation  in relation to the potash mining
The water points in the project area include very few springs and hand dug wells with more boreholes of various depths ranging from shallow to deep wells out of which around 66.6 % of the water points are collected from Musley and Adjacent catchments. 20.4% from Ayshet catchment and 13% from Saba catchment.
109•10000
• 500      4 250        0
• 500 Meteo
.A-
"'1
Adoqua
I* •
Legend
★
Springs Wbter points
towns
— - -*
_ jgJFI \
•4
S. i*
i -•
, f X - *1
--------- Roads
Stream
[Al alluvial fans
| .Vater Shade boundary
/’/ J
‘ \“
- - J 4 7:
jJ
>-ri
LLOLAREA GROUNDWATER ASSESSMEN TAN D EVALUfA“ TLI 2O.N
PROJECT
INWNTORY MAP
170000
•20000
Figure 7. 1: Water points inventory Map
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) • Main Report( Final), March 2014
110
IWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
ii)     Water Points Inventory Data Availability
As discussed  above more than  100  water point data were collected  from different sub catchments of Dallol basins and  out of these the coverage of springs and  hand  dug  wells is minimum i.e less than  5% where the springs are situated  on  the foot of western  escarpment. The water wells with  different depth  occupy  more than  95  %.  The water wells are again categorized by their depth. Wells with less than 20 m as dug or (HDW), depths ranging from
20  -  60m  as  shallow  boreholes  (SBH)  and  depth  greater  than  60m  as  deep  borehole  (DBH). The deep boreholes covered 47.8% and the shallow boreholes covered 46.7%
a)   Springs
As stated  above,  the number of springs occupies less than  5  % of the total water point data, these springs are cold  springs and  gravity  type in  Meta volcanic and  meta sedimentary  rocks located  at the foot and  hill side of western  escarpment in  the upper water shade area of Saba catchment.  The yield  of these springs is more than  5  1/s.  However numerous hot springs exists in the salt plane of the lowest Dallol depression far to the east.
b)   Water Wells
Water well data with  different depth  range occupies around  95% of the total inventoried water point data .The deepest wells in  the project area are the test wells drilled  in  North Musley  fan  ( DTW-4,  Depth  250m) and  Saba fan  ( DTW-7,  depth  250m ) with  static water level of 132.8m and 44.6m below ground surface respectively.
Many  of the shallow and  deep  boreholes located  on  the fan  areas are drilled  in  coarse alluvial fan  sediments where as the very  few test boreholes on  the fan  area with  depth  greater than 200m like DTW-2  ,  DTW-4,  DTW-7  and  DTW-9  have been  drilled  in  Meta sedimentary' rocks below the fan sediment.
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111Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Figure 7. 2: Water point distributions in the river catchments of Dallol
iii)  Characteristics of Water wells
Out of the total boreholes inventoried, around 30 % are drilled in the upper catchments or
water shade areas of Dallol to the west. The depth to these boreholes ranges from 8 to 108m
Many of the boreholes in this area are drilled in fractured and weathered areas of the met-
volcanic and met- sedimentary rocks and some in pocket alluvial sediments in small grabens
A large number of Boreholes covering around 70% are drilled in the Alluvial fan and Dallol
plain to the east The boreholes are drilled for groundwater investigation purpose and for
water supply of potash mining in the past. The depth of boreholes ranges from 6m to 251m.
a) Depth to Static Water level
One of the vital hydraulic parameter that was collected  during  data collection  from both office and  field  was static water level of water wells.  Hence,  water levels measured  directly during  field  survey  when  the wells were operational are considered  as dynamic water level. Due to  this fact,  the static water levels considered,  were only  measured  from non-operational wells,  data obtained  from wells construction  completion  reports and  test wells,  the collected water levels data are categorized  by  geological formations where the wells are penetrating Additional wells data is obtained  from drilling  and  testing  of few mapping  wells completed and  located  at selected  positions to  complete the data gaps of inventory  and  archive data obtained from different sources
In  general,  water levels of boreholes in  different geological formations in  the sub  catchments vary  from places to  places However,  just to  have a general view,  the depth  to  water level for the boreholes in the upper water shade area of Dallol to the west ranges from 3m to 57m and
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112Water works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
the depth to static water level in the Alluvial fans and salt plain ranges from 1 12 ( on the salt plain) to 100m on the fan areas in Unconfined groundwater system. The deepest water level is recorded from test well ( DTW-2) on the fan area close to the escarpment to be 144m
This borehole penetrated the meta-sedimentary ( meta- limestone ) aquifer beneath the fan sediment
Attempts were also made to visualize the ground water depth variations with topographic set up. Hence, ground water levels( from selected boreholes 50-100m depth) and ground surface elevations used  to  plot a simple graph  from West ( upper water shade) to  East transects across the marginal Graben and fan structures to the salt plain ( fig 7.3 ). This graphs shows similar relation  between  the topography  and  groundwater level implying  that the groundwater surface is a replica of the topography
Figure 7.3: Variations to groundwater level elevation with topography
b) Borehole discharge and specific capacity
Bore holes discharge is one of the most commonly available data for characterizing the aquifers, 
but the well yield is the function of both the hydraulic capacity of the aquifer and the power of
the installed pump. The hydraulic capacity of the aquifer is expressed by its permeability and 
storage coefficient and well yields are less accurate to characterize water-bearing formations
However, it can give an indication of the aquifer’s hydraulic capacity
There is insufficient data of well discharge for the inventoried boreholes in the upper catchment of Dallol.  However well yield  is estimated  2-3  l/s from the existing  functioning  boreholes in Berehale,  Ayshet ( Elefenkule) and  Behaita i e DWP-02,  DWP-04  and  DWP-07  respectively from 6 production well casing and water table is shallow i e 3-40m depth.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Report! Final), March 2014
113Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
The wells are drilled in Meta -volcanic and Meta- sedimentary formations. These boreholes were drilled  for community  water supply  and  in  general the well discharge and  specific capacity  ol these wells is minimum as the boreholes are not fully penetrating the aquifers and are of small diameter.
Well discharge,  specific capacity  and  transmissivity  values are analyzed  from test boreholes drilled  on the major fan areas. The discharge of test boreholes is 2 - 60 1/s in the coarse fan sediments and  water level ranges from 4m to  99  m depth.  The specific capacity  ranges from 0.0822 to 39.63 1/s/m. On the other hand the discharge of boreholes that are drilled deep in to the meta-sedimentary rocks below the fan sediments is 10 -20 1/s and water level is deep 130m — 145m with specific capacity 0.51 - 1.54 1/s/m (Table-7.1)
Static water level, m
Discharge, 1/s
Specific capacity in 1/s/m
Geological formation
max
min
avg
max
min
avg
max
min
Coarse Alluvial fan formations
99
4
30
60
2
-
39.63
0.0822
Metasedimentary /
Metavolcanic rocks
145
130
20
10
15
1.54
0.51
Table 7.1: Ranges of Hydrualic parameters for different geologic formations
c)           Transmissivity
Transmissivity values represents a measure of the hydraulic capacity of the aquifer i.e. its ability to  transport groundwater.  In  the water points inventory  data there is no  such  enough  recorded available data of transmissivity.  Transmissivity  values are analyzed  from test boreholes pump testing  results.  Accordingly,  the transmissivity  data calculated  from these boreholes is grouped based on the nature of aquifer material the boreholes are penetrating.
Thus the transmissivity value of shallow alluvial fan aquifers of coarse sand and gravel as calculated from pump testing of test holes DTW-1 , DTW-3 and DTW-10 ranges from 2500m2 I day - 4000 m  / day . On the other hand, the transmissivity value of deep aquifers meta- sedimentary rocks beneath the fan sediments as calculated from DTW-2 and DTW- 4 
Ranges from 700 m ' day - 1000 m ' day.
2
2
2
7.2  Groundwater Quality Analysis and Evaluation
7.2.1 Objective and Methodology
Water samples are collected from existing water sources and enough samples from the proposed test drilling  wells where the samples are tested  and  analyzed  for physico-chemical to  characterize the chemical composition  of the aquifer.  Close monitoring  and  water sampling  for field  measurements were carried out to observe water quality variations (fresh, brackish and salt water) in depth and
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) Mam Repon( Final) March 2014
114Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
laterally  during  test wells drilling.  And  the depth  for the interface between  these different water quality  zones is recorded.  Water quality  data from test boreholes area also  used  to  calibrate the geophysical data.
7.2.2      Fieldwork Sampling and Analysis
A  total  of  57  water  samples  have  been  analyzed  and  compiled  for  geochemical  data  sampled  from shallow  and  deep  wells  in  the  upper  water  shade  areas  of  Dallol  and  on  the  fan  areas.  The  water sampling   includes   the   onsite   sampling   of   the   water   points   during   inventory   and   sampling   from completed   test   wells.   Analyzed   water   samples   from   previous   works   in   the   project   area   are   also compiled.  The  analyzed  hydrochemical  data  has  been  treated  and  evaluated  on  the  basis  of  the  nature of the hydro-geological setting where the samples are collected.
7.2.3       Major element geochemistry of the groundwater in Dallol groundwater basin
Water quality analysis data of different boreholes from upper water shade areas of Dallol has been 
evaluated and treated for major element geochemistry of the groundwater system separately from the
groundwater system on the Alluvial fan areas.
i) Water quality condition in the upper water shade areas of Dallol ( Metasedimentary
and Meta-volcanic terian )
The groundwater chemistry  of Dallol water shade areas is generally  characterized  as moderately fresh  water with  mean  TDS value of 957.7  mg/1.  the maximum value of total dissolved  solid  is around  2568  mg/1  and  the lowest value is 27  mg/1.  The topographic control on  the variation  of TDS is observed  with  increased  values towards the lower elevation  in  the upper water shade areas associated  with  high  sodium,  bicarbonate,  sulphate and  chloride ions.  In  the uplands the Higher TDS is related  to  higher calcium and  bicarbonate ions.  In  general the mean  values for Chlorides, Bicarbonate,  Calcium and  Sulfate is higher close to  the maximum allowable concentration  by  WHO. The higher values are related  to  the meta- sedimentary  ( meta- limestone formations in  the upper catchment areas.  Regarding  the Ph  of the groundwater,  almost all samples shows basic water with measured  Ph  value greater than  7  only  very  few 17  % of the total samples show Acid  water with  Ph less than 7 values and only very few samples show values close to neutral (6.95).
In   general   the   mean   fluoride   value   is   also   not   excessive   (0.8mg'l)   except   few   wells   with   2   mg/1 associated with meta- volcanic rocks in the area.
The   statistical   value   of   the   Physico-chemical   analysis   of   the   groundwater   for   water   shade   areas   in Dallol groundwater basin is given in the following table 7.2
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Report( F.nal) March 2014
115Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
indicator
pH
mg/l
TDS
Mg/l
MH.
Mg/l
Na
Mg/l
K
Mg/l
Total H Mg/l
Ca
Mg/l
Mg
Mg/l
Fe
Mg/l
F
Mg/l
a
Mg/l
NO,
Mg/l
HCO,
Mg/l
SO,
Mg/l
Maiomum
8.4
2568.0
3.5
500.0
26.5
22823
641.1
285.6
33
2.1
881.1
900.0
451.4
1398.6
Mint mum
1J0
27.0
02
15.1
1.0
191.9
47.1
53
0.0
02
24.6
02
1093
63.4
Mean
7.6
975.7
12
124.5
6.8
744.1
198.7
653
0.4
03
235.6
892
295.4
387.5
Median
73
960.0
0.5
92.0
5.4
608.0
160.2
59.7
0.0
0.6
125.7
16.3
292.4
2203
St dev
0.4
691.1
13
117.8
63
5773
159.7
66.6
1.1
03
257.4
205.4
973
412.7
No. of
Samples
19.0
19.0
13.0
193
193
19.0
19.0
19.0
113
18.0
183
19.0
183
183
Table 7. 2: Statistical value of physic-chemical analysis of the groundwater for water shade
areas.
Electrical Conductivity value for the water samples analyzed is discussed with respect to the major ions and parameters like Total Hardness as Calcium carbonate, Chlorides and sulfate. Accordingly, the Electrical conductivity shows good relationship with Total hardness, sulfates and chlorides and with some degree with Calcium and poorly related to the sulfate and chloride ions. Fig 7 4
Figure 7. 4: Relationship of Electrical conductivity with Total hard, Chloride, Sulphate and
Calcium
Topographic control on  the concentration  amount of Total dissolved  solid  of the groundwater is clearly  seen  from TDS versus well bottom elevation  relationship  where the TDS amount in  general declines as one goes from the higher elevation towards the lower topographic zone or away from the recharge areas as shown in Fig 7 5
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report) Final). March 2014Well bottom elev
Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Figure 7. 5: TDS versus well bottom elevation
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final) March 2014Figure 7. 6: Electrical Conductivity Map
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Reportf Final), March 2014
118Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
I
Total Hardness as Calcium Carbonate:
Because Hardness is a property  not attributable to  a single constituent some convention  is used  to  for expressing  concentration  in  quantitative terms.  Usually,  this consists of reporting  hardness in  terms of an  equivalent concentration  of Calcium carbonate.  Carbonate hardness,  where reported  includes that portion  of the hardness equivalent to  the bicarbonate + carbonate (Alkalinity).  More values ot Hardness can  be resulted  when  groundwater is in  contact with  limestone or gypsum.  Since the dominant geological formation  in  the water shade area of Dallol is meta- sedimentary,  the hardness
values  of  boreholes  samples  analyzed  is  high.  The  Hardness  values  range  from  minimum  value  192 
mg/1  to  maximum  value  of  2282  mg/1  where  all  the  water  samples  are  grouped  under  Hard  water (Hardness greater than 120 mg/1)
Chlorides:- Chloride is present in  all natural water ,  but mostly  the concentrations are low.  The chemical behavior of chloride in  natural water is tame and  subdued  compared  with  the other major ions.  The ions generally  show a conservative behavior and  do  not significantly  enter into  oxidation or reduction  reactions,  forms no  important solute complexes with  other ions unless the chloride concentration  is extremely  high  ,  do  not form salts of low solubility  and  not significantly  adsorbed on  mineral surfaces.  Among  the chloride bearing  minerals occurring  in  igneous rocks are the feldspathoid  sodality  and  the phosphate mineral apatite.  But on  the hole it must be concluded  that igneous rocks cannot yield  very  high  concentration  of chloride to  normally  circulating  natural water. Considerably  more important sources are associated  with  sedimentary  rocks particularly  the evaporites.
The geochemical control of the geological environment for the chloride concentration clearly seen 
.            from the relationship graph of well bottom elevation versus chloride concentration in Dallol basin (
I           Fig 7.7) where maximum values of chloride i.e concentration more than 60 000mg/l is recorded from
boreholes drilled  on  the fan  sediments with  evaporites close to  Dallol salt plain  .  Whereas the minimum values as low as 20-30  mg/1  concentration  is recorded  from shallow wells in  the upper catchments of Dallol in  the meta- sedimentary  rocks.  In  general the chloride concentration  in  the basin  ranges from 24.61  mg/1  to  64300  mg/1.  the topographic control for the Chloride concentration 
| is shown on a map Fig -- below
■   Similarly   the   same   trend   is   observed   for   the   topographic   and   geologic   control   on   the   sodium   ion concentration  as  we  go  to  the  lower  elevation  of  Dallol  salt  plain  from  the  western  water  shade  areas. Sodium  ion  concentration  in  general  ranges  from  minimum  value  of  15  mg/1  from  borehole  sample in  the  western  water  shade  area  of  Dallol  basin  to  a  maximum  value  36000  mg/1  from  boreholes  on the salt plain and fan sediments close to the salt plain.
I
1
I
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) ■ Mam Report final). March 2014
119Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
2400 1900 1400
< 900 -
400 < 100 J
►
* r >
•
i—------ ------ ----------------->
c             5000         10000        15000        20000        25000         30000         35000         40000 Na concentration mg/l
Figure 7. 7: Topographic Control on Sodium and Chloride concentration
Groundwater Potential Assessment and
Evaluation of Musley fan area (Dallol) - Main
Re P0*\i Final), March 2014
120Figure 7. 8: Chloride distribution map of Dallol Catchment related to Topographic effectWater Works Oesign and Supervision Enterprise - Dalloi Area Groundwater assessment and Evaluation Project
Sodium and  chloride ions shows positive relationships for the analyzed  water samples where high mean  sodium concentration  is also  seen  in  water samples with  higher chloride concentration  fig  7.8 The most common  type of water in  which  chloride is the dominant ion  is one in  which  Sodium is the predominant cation.
Figure 7. 9: Chloride and Sodium relationships
ii)       Groundwater Quality on the Alluvial fans of Musley and adjacent areas
The groundwater quality  on  the alluvial fan  of Musley  and  adjacent areas is evaluated  based  on the hydro- chemical data generated  from water quality  analysis results of test boreholes and existing  wells on  the fan  areas.  Hydro  chemical data of Water samples from 38  water points of (shallow to  deep  borehole including  test bore holes) have been  analyzed  and  mapped  to  observe the water quality variations on the fan areas in depth and laterally .
Water quality  analysis results from test boreholes on  the fan  areas shows all ranges of water quality  fresh,  brackish  and  highly  saline groundwater depending  on  the depth  of boreholes and nature or thickness of the fan  sediment.  Total dissolved  solid  ( TDS) values on  the fan  areas in general ranges from a minimum value of 790  mg/1  from test borehole ( DTW-1  depth  189m on Gehertu  fan  area) to  an  excessive value of 150,000mg/l from deep  test borehole ( Hydal 2- IIm/2012 Allana, Depth 157m) on south Musley fan area.
The groundwater quality analysis result of the two major fan areas of Musley and Gehertu ( North Musley) clearly shows the availability of fresh groundwater with TDS values less than 
1000 mg/1 with higher quantity of groundwater ( DTW-1, DTW-5 and DTW-10)
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) ■ Mam Report( Final) March 2014
122Water Works Design and Supervision Enterprise - Dalloi Area Groundwater assessment and evaluation Project
The depth  of drilling,  the litho  logy  of the fan  sediment (fine to  coarse material) and  thickness of the fan  are the major controlling  factors for the variation  of groundwater quality  at depth  and laterally.
Fresh  to  Saline  water  quality  variation  is  also  observed  as  one  goes  from  the  neck  of  the  Fan  to the toe of the fan (east wards) with uniform depth of drilling.
Table 7. 3: Statistical value of the Physico-chemical analysis of the groundwater for Dalloi
water shade areas
pH
Temp
C°
TDS
mg/1
NHj
mg/1
Na
mg/1
K mg/1
T.
Hardnes mg/1
Ca
mg/1
Mg
mg/1
Fe
mg/1
F
mg/1
Cl
mg/1
NO>
mg/1
HCOj
mg/1
SO.
mg/1
Max
8.0
52.4
150080.0
48.5
36000.0
4900.0
11130.0
15500.0
9100.0
0.9
1.8
64300.0
457.0
933.3
2110.0
Mln
6.8
41.3
790.0
0.1
82.9
8.3
400.0
123.5
7.5
0.0
0.5
49.2
0.1
48.8
11.5
Mean
7.4
44.5
33536.6
7.4
8687 7
823.1
2635.8
3613.0
1266.6
0.1
1.0
14479.5
67.6
2553
856 8
Med
7.4
43.1
6200.0
3.4
2500.0
111.0
950.0
8S2.0
133.0
0.0
0.9
3000.0
5.6
204.4
794.0
St
dev
0.4
3.4
43766.4
11.9
11399.8
1363.0
3351.2
4764.0
2238.2
0.3
0.5
19893.3
136.8
201.7
542.5
No.
ofS
11.0
15.0
37.0
19.0
20.0
20.0
11.0
24.0
25.0
10.0
11.0
25.0
13.0
27.0
25.0
The   statistical   value   of   the   Physico-chemical   analysis   of   the   groundwater   for   water   shade   areas   in Dalloi groundwater basin is given in the above table 7.3
From the above summary  of the water quality  analysis results ,  it is observed  that excessive mean concentration  values of TDS ( total dissolved  solid) is resulted  due to  excessive concentration values of Sodium,  Calcium and  Chloride ions which  resulted  from gypsum and  evaporites beds at depth  below the fan  sediment.  The Chloride ion  concentration  on  the fan  areas of Musley  and adjacent fan  ranges from a minimum value of49.2  mg/1  to  maximum value 64300  mg/1  with  mean value of 14479mg/l and  for sulfate the maximum value 2110  mg/1  and  the minimum value is 11.5 mg/1  with  mean  value 856.5  mg/1.  the mean  value of concentration  for Sodium,  Calcium and  Total hardness which  are the dominant parameters in  this analysis due to  excessive values is 8687.7  mg/1, 3613mg/l and 2635.8mg/l respectively.
All the minimum value concentrations of Cations and  Anions are recorded  from water samples of shallow and  deep  wells drilled  on  the major fan  areas of Musley  and  Gehcrtu  within  fresh groundwater zone.
Test boreholes where the bottom depth  of drilling  crossed  the fresh  and  salt water interface has yielded  highly  saline groundwater on  the fan  area.  The depth  for fresh  and  salt water interface on  the fan areas varies depending on the fan thickness and hydro lithology of the fan material.
In  the  middle  of  the  fan  structure  where  we  have  the  maximum  thickness  of  the  coarse  fan  materials the thickness of fresh groundwater zone is relatively higher than the toe or end areas of the fan and
Groundwater Potential Assessment and Evaluation o< Musley fan area (Dalloi) ■ Mam Report( Final) March 2014
123Water Works Design and Supervision Enterprise • Dallol Area Groundwater assessment and Evaluation Project
foot of the fan where the fan emerges. Accordingly the fresh and salt water interface for Musley major fan is located 130m-150m in the middle of the fan up to the foot of the escarpment ( DTW-5 & DTW-10 test drilling results) and Similarly the fresh and salt water interface in Gehertu major fan area goes up to 170m ( DTW-1 test drilling result at the middle of the fan). On the other hand the fresh and salt water interface is very shallow for the fan areas close to the salt plain i.e the toe of the fan. From test drilling result of DTW-3 in north Musley fan, the saline water zone appears at a very shallow depth around 50-60m and the thickness of fresh water zone is minimum 30-40m.
Groundwater Potent.al Assessment ano Evaluat.on of Musley fan area (Dallol) - Ma.n Report Final). March 2014
124— *ter Works Design ana Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Water quality (TDS)map of Musley fan and Adjacent ares
620000
630000
1
5
I
Figure 7. 10: Water Quality (TDS) Map of Musley fan and Adjacent area
"Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final) March 2014
125
IWater Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation P j —
The electrical conductivity (EC) and Salinity of the groundwater on the fan areas is a unctio depth of drilling on the same fan area under similar hydrogeological condition. This is clear y se from a relationship developed from TDS versus Well depth.
Figure 7. 11: TDS versus well depth
iii)  Water quality type in different hydro geologic environments
■ Water quality in Meta sedimentary and Meta volcanic rock aquifers
To  classify  the type of waters in  this geological formation  and  determine their relationship,  piper graphical method  of interpretation  of the chemical analysis is carried  out and  the piper diagram is plotted applying Aquachem computer software fig 7.11
The dominant water type covering  high  percentage for the groundwater in  general is Ca- Mg- Na- SO 4  with  35  % out of the total samples analyzed  and  from the piper diagram it is clearly  observed that the Calcium and  Magnesium are the dominant cat ions and  Bicarbonate and  Sulfate is also  the dominant anion.
Ca-Na- Mg -HCO3 Water Types = Ca- Mg- Na- SO   Water types
4
17 % =      35%
Na-Ca-Mg - HCO3 Water Type = Na-Ca-Mg- HC03-C1 water type = Mg-Ca-Na-SO  Water type =
4
Na-Ca-Mg-Cl
Ca-Mg-SO  - Cl- NO3 
4
=
. 
5 % 17% ] ] o/o
i]o/o 4<)/0
Groundwater Potent.al Assessment and Evaluate or Musley fan area (Dallol) - Mam R pon( F.nal)
C                           March 201/
126Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment ano E.uluo--------------------------------------- J-----
Figure 7.12: Piper plot for water samples in the water shade areas
■   Water Quality in Alluvial fan aquifers
Classifying  the  water  type  in  the  Alluvial  fan  aquifers  is  done  on  the  piper  plot  from  the  analyzed hydro chemical data compiled from test boreholes and existing wells on the fan area. Fig 7.12
The dominant water type covering high percentage for the groundwater in general is Na Ca Cl which covers around 46% . Chlorides and sulfates are the most dominant anions in the analyzed water samples from fan areas. Sodium and Calcium are the dominant cation from these samples Higher concentrations of chlorides and sulfate in the analyzed samples are originated from dissolution from evaporite and gypsum in the geologic environment.
The percentage coverage of the water types in the Alluvial fan aquifers is discussed below Na-Ca-Ch Water type -— 46%
Ca-Na-SO« Water type— 23% Ca - Na-Cl- SO  Water -—19 %
4
Na-Ca-HCCh Water ------------ 11%
Groundwater Potential Assessment and Evaluation of Muslev fan area (Dallol) Main Reportf final) , Match 2014
127
IViater Works Design ano Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Froject
Comparing  the water samples chemical composition  with  Ethiopian  Guidelines Specification  for Drinking  Water Quality  March  2002,  The groundwater sampled  from boreholes in  the upper catchment or water shade areas of Dallol basin  arc almost fresh  which  are drinkable except few boreholes with  higher concentration  of Sulfate,  Nitrate,  Total hardness and  iron  above Ethiopian guideline.
On the Alluvial fan aquifers, fresh groundwater for domestic use is only limited in shallow boreholes on  the major fan  areas of Muslcy,  Gehertu  and  adjacent fan  areas.  Groundwater quality  problems related  to  excessive Chloride,  Sulfate and  Sodium which  is much  higher than  the guideline is common for many of sampled boreholes.
Groundwater Potential Assessment ano Evaluation of Musley fan area (Dallol) Mam Report^ Final). March 2014
1?8Water Works Design and Supervision Enteiprise - Dallol Area Groundwater assessment and Evaluation Project_
Table 7. 4: Comparison of Dallol Area ground water qualities with Ethiopian Guidelines for
drinking water
Property
Ethiopian
Guidelines
Value (2002)
mg/l
-------------------------- --------------------------------------------- ----------------------------------------------------------------------
Geological formations
Alluvial fan sediments
Meata -
sediments/metavolcanics
Sodium (Na)
358
Min
82.9
Max
36000
Min
15.1
Max
500
Chloride (Cl)
49.2
64300
24.6
881.1
Boron (B)
0.3
Iron (Fe)
0.4
0.5
1.8
0.1
3.8
Manganese (Mn)
0.5
Sulphate (SO4)
483
11.5
2110.0
63.4
1398
------------------------------ —
Total Hardness (as CaCO3)
392
400
11130.0
191.9
2282.0
PH
6.S-8.5
6.8
8.0
7
8.4
Nitrate (NO3)
50
0.1
457.0
0.2
900
Fluoride (F)
3
0.5
1.8
0.2
2.1
1
Groundwater Potential Assessment and Evaluation of Muslcy fan area (Dallol) - Ma.n Repon( F.nal) March 2014
1297.3         Drilling of Test wells
i         Here the summary of drilling wells is given. The complete report on the drilling of test wells is given
*         in a separate report Annex -2 Well Accomplishment report of test wells
The main purposes of drilling of test wells are:
•    To understand Aquifer productivity and water quality variations in depth and lateral
•     To acquire subsurface data to calibrate the geophysical investigation results
•    To Obtain Aquifer parameters
The test wells are drilled at the major fan areas in the study area, moreover the depth of the wells were shallow to deep depending on the depth for Fresh and Salt water interface and the fan thickness The minimum depth of test well is 92m ( DTW-3) which is drilled north east of Gehertu fan close to the salt plain and the maximum depth of test well is 250m ( DTW-7 and DTW-9 ) drilled on Saba
| fan area.
The  test  well  drilling  in  the  proposed  nine sites  of the  project area  was  started  in  Feb.  2012  two months later after the signing of the Contract i.e Dec. 2012. The main Contractor is Ethiopotash BV Ethiopian  branch  and  the  Sub  Contractor  is  Raja  Mineral  and  Exploration  Techniques  Pic.  The contractual time for the drilling was six months however due to various problems related to casing supply and access roads the contract was extended for two months where a total of ten test boreholes (one extra test borehole added with amendments) are completed successfully.
The distribution of test boreholes was planned to test the potential of the major fan areas of Asabuye Musley, Gehertu ( North Musley) and Bekerti ( South Musley) and Saba fan areas. Accordingly one test borehole is drilled in Asabuye fan ( DTW-4), three test boreholes in Gehertu fans i.e DTW- 1,
DTW-2 and DTW-3, Two test boreholes in Musley fan ( DTW-5 and DTW-10 ) ,One test borehole in Bekerti fan (DTW-6) and three test wells in Saba fan area (DTW-7, DTW-8 and DTW-9).
The drilling and construction of all the test boreholes is completed successfully , out of these around six boreholes in Musley , Asabuye and Gehertu fan ( DTW-1, DTW-2,DTW-3,DTW-4 DTW-5 and
DTW-10  are pump  tested  with  constant discharge for 48  hours duration.  The remaining  three test wells in Saba area ( DTW-7, DTW-8 and DTW-9) and One test well in Bekerti or South Musley fan ( DTW-6) are not pump tested due to small yield 2-3 1/s as seen from pre test and this is not possible to  be tested  constantly  with  the available high  yield  pump  ( 20-50  1/s) which  is stated  in  the specification.
J
J
Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report Final) March 2014
130Water Works Design and Supervision Enterprise          - Dallol Area Groundwater assessment and Evaluation Project______________________
The major drilling  problems encountered  so  far are Bit damaged  repeatedly  due to  very  hard boulders of basement rocks transported from western escarpment areas and casing stacking in most of the test wells which was solved by continuous riming especially for the deep boreholes in North Musley (DTW-4) due to hard meta-sedimentary rocks and intercalated thick clay in Saba and Bekerti fan (DTW-7 and DTW-6) test boreholes.
According to the contract, the drilling work was agreed to be carried out with 20” drilling bit for the upper six  meter soft formation  where 17  “steel surface casing  is installed  and  the drilling  is continued with 14 “bit up to 150m with the installation of 10” casing and again drilling is continued to the bottom with 10 “bit where 6 “casing is installed. For some boreholes which are drilled up to 200-250m depth,  this design  is followed  (DTW-2,  DTW-4,  DTW-7,  DTW-9) .  However there are also  some local hydro-geological conditions where the drilling  with  large diameter is continued below 150m for some depth like DTW-4, DTW-2, DTW-6 and DTW-8.
In the center of the alluvial fan area, the drilling has encountered coarse gravel and sand formation up to 160m (DTW-1 and DTW-2 in Gehertu fan) with the intercalation of clay at different depth, but below 160 or 170 meter the drilling has encountered basement rocks of Meta sedimentary and meta- volcanic rocks.
The  distribution  of  mapping  wells  in  the  project  area  is  shown  in  fig  7.13  and  the  summary  of mapping well data is given in table 7.5 and table 7.6
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Reportf Final) March 2014
131Well ID
Location
UTME
UTM N
Elev
Depth
SWL
a
i/«
DD
T,
m2/d
Sc, l/s/m
Driller
Drillins
started
Drillins
completed
Remark
627462
1576873
DTW-1
Gehertu
-5
189
99 59
44
111
3890
39 64
RMS ( Sub
Contractor)
31/3/2013
15/4/2013
The groundwater is fresh and the well yields more than 44 l/s with little draw down during pump testing.
626691
1576283
DTW-2
Gehertu
39 22
223
144
10
647
714
1.56
RMS (Sub
Contractor)
22/4 /2013
1/5/2013
Drilling with large diameter (14* ) is done up to 170m and pump testing is completed The water is brackish.
DTW-3
North Gehertu
627337
1578555
-70.76
91
43 3
60
6 92
8.67
8.6
RMS (Sub
Contractor
7/5/2013
13/5/2013
The yield is very high 60 l/s and the water is brackish
1584222
DTW-4
Asabuye
622916
112 96
251
1328
10
1957
628
0 51
RMS (Sub
Contractor
16/5/203
5/6/2013
The well can yield more if higher head pump is available. The aquifer is fractured meta
sandstone
628438
1573114
S168
DTW-5
Musley
152
45 19
6
72.91
548
0 08229
RMS (Sub
Contractor
14/6/2013
17/6/2013
The water is fresh , the well is drilled very close to escarpment
631676
1564435
27107
DTW-6
Bekerti
160
40.7
RMS (Sub
Contractor
22/6/2013
25/6/2013
Continues pump
testing Is not conducted due to low discharge! 2-3 l/s) from pre test by the
available pump
627010
1547959
137.417
250
DTW-7
Saba
44 6
RMS (Sub
Contractor
1/7/2013
13/7/2013
Continues pump
testing is not conducted due to low discharge (2-3 l/s) from pre test by the available pump
628837
1548947
DTW-8
Saba
99 93
170
25.76
RMS (Sub
Contractor
24/7/2013
29/7/2013
Continues pump
testing Is not conducted due to low discharge ( 2 3l/s)from pre test by the
available pump
-J
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) • Main Report! Final), March 2014
132Well ID
location I       UTME
UTMN
Elev
Depth
SWl
a
i/i
DD
T,
m2/d
Sc, l/s/m
Driller
Drilling
started
Drilling
completed
Remark
DTW-9
Saba
630771
1546472
57 04
250
26.2
RMS (Sub
Contracto
7/8/2013
14/8/2013
Continues pump testing is not conducted due to low discharge (2-3l/s)from pre test by the available pump
DTW-10
Saba
629306
1573479
24
130
79 28
50
8.76
5190
570
RMS (Sub
Contractor
22/8/2013
29/8/2013
The well yields more than 50 l/s and the water quality is good
Table 7. 5: Summary of test wells drilling results
Station
PH
EC
TDS
NH4
Na
K
Total
Hard
Ca
Mg
Total
Iron
F
Cl
NO2
NO3
Alkalinity
HCO3
SO4
PO.
Date of
Anayisis
DTW-1
7.8
1107
790
86
15.5
409.5
123.48
24.19
0.01
0.7
71.93
21.25
40
48.8
434.84
01
DTW-2
7 99
15 590
11300
2500
120
4725
1848
25.2
0.1
1 18
5977.65
1.52
96
117.12
775.78
0 08
DTW-3
7 44
58400
43840
10500
770
11130
3738
428 4
0.05
1.82
26496.25
0.57
40
48.8
849.38
0 34
DTW-4
6 81
19700
13620
2575
111
5400
1440
432
0.21
1.84
8393.68
457
60
73.2
508.92
0.04
DTW-5
684
1394
910
154
235
400
144
96
0.02
0.63
65.43
5 15
352
429 44
28353
009
DTW-10
6 55
2410
1660
126
10 50
1240
384
67.20
0.01
0.65
178.38
0 67
1156
1410.32
181.45
0 34
Table 7. 6: Summary of Water Quality Analysis Results
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) • Main Report! Final), March 2014
133Legend
•       W&ter points
•------ tovwis
-------- Roads
Stream
[ lAI alluvial fans
[ ~ jwafr Shade boundary
NTAND EVALUATION
PROJECT
T> it W>IH DIXributlon Map j
Figure 7. 14: Test wells distribution Map
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final), March 2014
134Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation-------------j_
SOME SELECTED PHOTOGRAPHS TAKEN FROM DRILLING
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Repon( Final) March 2014
135Water Works Design and Supervision Enterprise - DaItol Area Groundwater assessment and Eva
■
Figure 7. 15: Photos taken from drilling and pump testing
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final) March 2014
136Water Works Design and Supervision Enterprise • Dallol Area Groundwater assessment and Evaluation Project
8 Aquifer Characterization of different geological formations
8.1 Alluvial fan aquifers of high productivity (Shallow Aquifer System) - Qpf
The Alluvial fans are unconsolidated  sedimentary  deposit that accumulates at the mouth  oi a mountain  Canyon  because of a dimunation  of sediment transported  by  the issuing  stream. Sediments on the higher parts of the Alluvial fan are rich in gravel with Cobble sand boulder sized rock fragments where as the toe of the alluvial fan typically consists of Sand, Silt and mud sized fractions. Some of the Alluvial fans in Dallol merge with other fans to form apron like structures along mountain fronts.
The shallow aquifers system in Dallol fan areas consists of inter- fingering layers and lenses of fine to coarse Sand, Gravel and pebbles which are porous and highly permeable beds that can store and transmit large quantities of Groundwater.  These aquifers exist commonly  in  unconfined  system. However in some parts of the fan there are thin impermeable clay beds interbeded with these course materials forming a confining system for the ground water in this aquifer. Groundwater trapped b/n impermeable layers within  the fan  exhibit artesian  flow as the groundwater builds up  pressure within  the fan.  The rise of water table to  shallow depth  i.e 44m in  test well DTW-5  near to escarpment in Musley fan is an implication of this condition.
The fresh  groundwater aquifer on  the fan  area has irregular thickness depending  on  the geomorphologic setting of the fan where the depth to the top of the aquifer is as deep as 90-100m for Gehrtu fan test boreholes ( DTW-1 with well depth 189m) and shallower 30-70m for Musley fan area( DTW-10 well depth 130m). The saturated average thickness of the alluvial aquifer with fresh groundwater is 50-60m as observed from test well logging and geophysical interpretations on the fan areas. The maximum thickness is observed in the major fan areas of Musley and Gehertu The thickness decrease as one goes from the escarpment towards the salt flat. The lateral extension of this aquifer is estimated to be around 12kms towards North and South Musley including Bekerti fan.
From analysis of pump  testing  of test boreholes drilled  on  the major fan  areas of Musley  and Gehertu  (DTW-10,  DTW-1),  the transmissivity  value calculated  is 3500  m2 / day.  The yield  of boreholes with  48  hours pumping  is 50  1/s which  is more than  4300  m3 I day  with  very  small drawdown. The Groundwater quality is fresh i.e less than 1000 micro S/cm.
From an observed wall section of stream channel that has cut down through alluvial fan deposit in Musley, the inter bedded layers of fine sand gravel and clay materials that confined the groundwater system in the upper reaches of the fan probably represents major storm events where flood flows contributed a new layer of sediment to the surface of the fan.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Reponf Final) March 2014
137r r r rJ'TJ'J
Water Works Design and Supervision Enterprise - Dalloi Area Groundwater assessment and Evaluation Project
570000
-----1—
600000
610000
630000
---------------------------------- *—
Legend
Hydro geologic units
Alluvial fan aquifers of high productivity Aluvium aquifers of moderate productivity
| Sedimentary aquifers of Moderate productivity ___ Basement aquifers of low productivity
H Aqududes and aquSards
— Regional Groundwater flow bne
■■ Groundwater Devide
--------- Groundwater contour Existing boreholes
towns
DALLOL AREA GROUNDWATER POTENTAL ASSESSMENT
PROJCT
Fig   Hydrogeological   Map   of   Dalloi and its Water Shade areas
1
o
<->
!P
—r—
570000
------- r—
600000
620000
630000
Figure   8. 1: Hydrogeological Map of Dalloi and its Water shade areas
Groundwater Potential Assessment and Evaluation of Musley fan area (Dalloi) - Main Report( Final), March 2014
138Water Works Design and Supervision Enterprise - Dallol              Groundwater.
and E»
Figure 8. 3: Hydro geological Section across Musley fan area
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Report( Final) , Marcn 2014
140Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
8.2 Alluvium Aquifers of Graben Areas and Intermountain plains of Moderate productivity — (Qp)
The intermountain pain and graben areas in the upper water shade areas west of Musley fan are filled by alluvium sediments of Sand , Gravel and Clay sediments transported from surrounding mountains of weathered Metasesimentary and metavolcanic composition. The exact thickness of this  aquifer  is  not  known  which  needs  some  deep  test  drilling  work.  However  the  alluvium  is underlain by basement rocks of low productivity from the prevailing hydrogeologic setting of the area. Groundwater data from existing boreholes inventoried in the area shows that the groundwater table is shallower 30-40 meter below surface with fresh quality TDS less-than 1100 mg/1. Water boreholes  of  small  diameter  drilled  for  community  water  supply  in  the  area  yields  4-51/s  with minimum drawdown. Good potential groundwater reservoir is supposed to exist in this area in the alluvium aquifer which can be more evaluated if large diameter test drilling is carried out.
8.3   Sedimentary Rock Aquifers of moderate productivity (Deep Fractured Aquifer System
near the Escarpments) - Ja + Jt + Nrs + Pzt
These are escarpment rocks of sedimentary origin mainly limestone ( Jt)and sandstone (Ja) and the Denakil red series that belongs to Tertiary and Mesozoic time. These are slightly metamorphosed with some degree of weathering and fracturing. Deep test well drilling on the fan area very close to the escarpments shows the existence of these aquifers at different depth beneath the fan sediments. In  DTW-2  test drilling  (depth  220m) highly  fractured  limestone aquifer appeared  below 160m depth yielding more than 10 1/s with brackish groundwater (TDS 11,000 mg/1) .Water table is deep 144m below ground  surface.  Similarly  in  deep test well drilling  DTW-4 (250m depth) in North Musley fan near the escarpments, the meta-sandstone aquifer appear at shallow depth 40m below ground surface. Groundwater in this aquifer exists in secondary openings along fracture zones with water table 132.8m below ground surface. The test Well drilled in this aquifer yields 12 1/s with minimum draw down  and  the water quality  is brackish  ( TDS around  13,600  mg/1).  The transmissivity  value in  these aquifers calculated  from pump  testing  in  general is around  700  m2 /day.  The aquifer is supposed  to  be recharged  from ground  water flow of water shade areas as subsurface flow along fracture and fault lines.
8.4  Basement Aquifers of low productivity ( Mtasedimentary and Metavolcanic rocks)- PR21 + PR2t)
These are consolidated rock aquifers of low productivity that forms wide areas of the western water shade parts of Dallol basin  .  Hydrogeological data from Existing  boreholes which  are drilled  for community water supply in the area shows that the aquifers yields 2-3 1/s in the basement rocks
with  moderately  fresh  groundwater  (  TDS  <  1500mg l
z
).  This  aquifer  gets  recharged  from  direct
rain fall and surface percolation from runoff through fracture zones in the upper water shade areas. Water supply boreholes drilled on and near the beds of wide river channels along fault and fracture
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report) Final) March 2014
141Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
zones    in    Berchale    and    surroundings    yield    less    than    5    1/s    from    6    diameter    wells    f
nrma
«i
ons
shallow around 20m and the groundwater quality is fresh (TDS < lOOOmg/1) . apart from fault or fracture zones or far away from river channel is more conso l fracturing displaying low permeability for the groundwater occurrence.
8.5 Aquicludes and Aqutards - ( Qh + Q + Cppt + grt)
o> *®v
lcss
These include localized  Aquicludes of Carbonate precipitates of travertine type and  intrusions to extensive mud  flats on  the salt plain  and  evaporite beds to  the east.  The permeability  of these formations is very  low due to  the occurrence of clay  beds which  retards the groundwater movement. The carbonate precipitates ( Cppt) and  granitic intrusion  ( grt ) serve as local groundwater divides for the shallow groundwater movement in the area.Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
9 Groundwater flow, Recharge and Discharge
9.1 Regional Ground water flow system
The regional groundwater flow system in Dallol Basin is in general controlled by the topographic setting, structures and hydraulic gradients. Much part of the deep Groundwater which is recharged from Dallol water shade areas of western plateau is supposed to drain towards the salt plain in the east.
Groundwater elevation  contours were generated  from water level data of existing  boreholes.  In Saba sub basin, the hydraulic gradient calculated from groundwater level elevation is steep in the water shade areas. The groundwater flow in Musley and Ayshet sub catchments is towards east and north east recharging the Alluvial fan areas in Musley and Gehertu fans. Here it is supposed from the map  that the fan  areas in  Musley  and  Gehertu  area in  addition  to  percolation  from surface recharge ,  gets deep  recharge from regional groundwater flow from western  highland  or water shades through deep structures beneath the Belakiya ridge which serves as a surface water divide in the area . The elevated Belakiya ridge or fault escarpment which is oriented north to south is made up  of meta- volcanic and  meta- sedimentary  complexes and  groundwater flow across these elongated  structures is along  fault lines which  form deep  river canyons and  drainage channels across the ridge towards the salt plain
Groundwater system in Saba catchment is separated from Ayshet and Musley groundwaterv system
by a groundwater divide west to east which coincides with the surface water divide. Here the
regional groundwater flow is tending more to south east.
Along the contact line of the basement rocks with the alluvial fan sediments, there exists granitic and granodiorite intrusions which intrude into the meta- volcanic and meta-sedimentary formations. These intrusive act as localized  groundwater and  surface water divide separating  the alluvial fan structures and sub catchments which contribute much run off into the fan areas.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Report( Final) March 2014
143Water works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Legend
1 Prospective Area, (Groundwater
■ — RegionalGroundeaier^°ne# )
Groundwater Devtde
---------- River
---------- Groundwater contour
•        Existing boreholes
•         towns Legend
Watershed boundary
| | Musley and Alacant area Catchment [ | Ayshet/ Lelegehedi River Catchment | | Saba River Catchment
DALLOL AREA GROUNDWATER POTENTIAL ASSESSMENT
PROJEC
Figure 9. 1: Groundwater flow Map of Dallol Catchment
Grounch         Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report) Final) March 2014
144Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment ano Evaluation Project
9.2 Groundwater flow in the Alluvial Fan Aquifers
Groundwater Contour map from Water table elevation of test wells drilled on the fan areas shows that in general the groundwater table slopes down wards from the escarpment towards the salt flats and this indicate that groundwater is moving from areas of recharge in the upper reaches of the fan to areas of discharge in the salt flat. Two groundwater systems are supposed to exist within the fan areas. The first is the shallow aquifer system in coarse unconsolidated formations of Gravel and Sand with boulders on the top. This aquifer is highly permeable and porous with average saturated thickness of around 50m in Musley and Gehertu major fan areas. Fresh groundwater circulates in this aquifer .The depth to the aquifer varies depending on the nature of the fan. The depth to the top of aquifer for Musley and South Musley fan areas is 60-70m and for Gehertu fan area, the depth to the top of the aquifer is around 98m. Transmissivity value calculated from this aquifer is around 3500 m2 / day. The second aquifer which exists beneath the coarse unconsolidated fan sediment is less permeable clay dominated and Saline aquifer which exist below 150-160m depth. Brackish to Saline groundwater exists in this formation.
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Mam Repon( Final) March 2014
145Water Works Design and Supervision Enterprise - Dallol Area Groundwater assessment and Evaluation Project
Groundwater flow map for Musley and adjacent fan Areas
Figure 9. 2: Groundwater flow Map of Musley and Adjacent fan Areas
Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report) Final), March 2014
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Ayshet
Recharge Model watershed
Sub-surface run of exponent y Sub-surface run of coficent a Sub-surface run of exponent e Maximum Storage Smax(mm) Initial Storage z
Direct runoff coefficent DRC Ground cover endex-G.C Base flow
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Groundwater Potential Assessment and Evaluation of Musley fan area (Dallol) - Main Report! Final) March 2014
211Waler Works Design and Supervision Enterprise Daliol Area Groundwater assessment and Iva labon Pr- ? .t
Year Jan FEB Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1996
1.5
0.6
19.9
19.9
2.3
0.6
19.9
19.9
54
52
15
08
1997
0.4
0.3
19.9
19.9
2.6
0.6
199
19.9
1.3
06
03
02
1998
0.1
0.1
0.0
19.9
2.3
0.6
2.9
19.9
7.0
IS
0.7
04
1999
0.3
0.2
0.1
19.9
0.9
0.3
19 9
19.9
21
08
04
0.3
2000
0.2
0.1
0.1
0.0
2.7
0.6
7.4
1.2
0.5
0.2
02
01
2001
0.1
0.1
19.9
19.9
1.0
0.3
19.9
19.9
4.S
1.2
06
04
2002
0.2
0.1
19.9
1.1
0.3
0.1
0.1
19.9
19.9
1.S
0.7
6.5
2003
1.7
0.7
2.3
4.9
0.9
0.3
2.1
19.9
3.3
1.0
O.S
0.3
2004          1.2          0.5          0.2         19.9          0.9           0.3           0.2          199            1.4           0 7             04             02
2005          0.2          0.1        19.9        19.9           6.8           1.0         19.9         19 9         19 9             IS            0.7            04
Mean 0.58 0.27 10.22 14.53 2.07 0.48 11.21 18 03 6 53 1.42 0 60
• • . •
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Groundwater Potential Assessment .nd  v.
?,-Water Works Design and Supervision Enterprise • Dalloi Area Groundv.^ter assessment and f vaud.
Year Jan FEB Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1996
1.5
0.6
19.9
19.9
2.3
0.6
19.9
19.9
54
5.2
1.5
08
1997
0.4
0.3
19.9
19.9
2.6
0.6
19.9
19.9
13
06
03
02
1998
0.1
0.1
0.0
19.9
2.3
0.6
2.9
19.9
7.0
1.5
0.7
04
1999
0.3
0.2
0.1
19.9
0.9
0.3
19 9
19.9
21
0.8
0.4
0.3
2000
0.2
0.1
0.1
0.0
2.7
0.6
7.4
1.2
0.5
0.2
0.2
0.1
2001
0.1
0.1
19.9
19.9
1.0
0.3
19.9
19.9
4.5
1.2
06
04
2002
0.2
0.1
19.9
1.1
0.3
0.1
0.1
19.9
19.9
1.5
0.7
6.5
2003
1.7
0.7
2.3
4.9
0.9
0.3
2.1
19.9
3.3
L0
0.5
03
2004
1.2
0.5
0.2
19.9
0.9
0.3
0.2
19 9
1.4
0.7
0.4
0.2
2005
0.2
0.1
19.9
19.9
6.8
1.0
19.9
19.9
19.9
1.5
07
0.4
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■S
0.27
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10.22      14.53         2.07         048
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11.21       18 03         6 53          1 42         0.60         097
Groundwater Potential Moment and Eva.uat.on of Mustev Ian 'are. (EWtol)
---------Water Woiks Design and Supervision Enterprise Dallol Area Groundwater assessment and Evaluation Project
Saba
Recharge Model watershed
Sub-surface run of exponent y Sub-surface run of coficent a Sub-surface run of exponent £ Maximum Storage Smax(mm) Initial Storage i
Direct runoff coefficent DRC Ground cover endex-G.C Base flow
R2
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2
56
005
360
05
0.1 0.7
0
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Groundwatei Potent.al Assessment and Lvaluatfon ot Musley fan a.ea (DaUoh Main Report) Final)
2014
?1?Water Works Design and Supervision Enterprise   - Dallul Area Groundwater assessment and Evacation P
Year
Jan
FEB
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
1996
0.00
0.00
0.00
56.04
0.00
0.00
56.04
56.04
0 00
062
0 22
0 11
1997
0.07
0.04
0.02
0.01
0.00
0.00
0.07
0.10
004
0.02
001
0 01
1998
0.01
0.00
0.00
0.00
0.00
0.00
0.01
0.07
006
003
0.02
0.01
1999
0.01
0.01
0.00
0.00
0.00
0.00
0.06
0.05
0.02
0.01
0 01
0.01
2000
0.00
0.00
0.00
0.00
0.00
0.00
0.01
0.00
0.00
0.00
0.00
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2001
0.00
0.00
0.01
0.06
0.02
0.01
0 01
0.10
0.07
0.03
0.02
0 01
2002
0.01
0.01
0.03
0.01
0.00
0.00
0.00
0.04
007
0.03
002
0 01
2003
0.01
0.01
0.01
0.00
0.00
0.00
0.01
0 09
0.04
0.02
001
001
2004
0.01
0.00
0.00
0.01
0.00
0.00
0.00
0.01
0.01
0.00
0.00
000
2005
0.00
0.00
0.01
0.01
0.03
001
0.05
o.os
0.06
003
0.02
0 01
Mean
0.01
0.01
0.01
5.61
0.01
0.00
5.63
5.66
0.04
0.08
0.03
0.02
Groundwater Potential Assessment and Evaluation of Musley fan area (Da’lnlt m--------------- Z--------------------------- ------- -----------------
e
V ran area (DaWol) - Mam Report! Ftotal) March \-4
214Water Works Design and Supervision Enterprise Dallol Area Groundwater assessment and E/aluot.ur 11
Dalol at saba catchment monthly watermodel result( 1996-2005
Groundwater Potential As.essment and Evaluabon ot Mosley tan area (Oa^'ir"

Summery

Project Overview

The document presents the final report (March 2014) of the Dallol Area Groundwater Potential Assessment Project conducted by the Water Works Design and Supervision Enterprise for the Ministry of Water, Irrigation and Energy of Ethiopia. The study focused on evaluating groundwater potential in the Musley and adjacent fan areas of the Dallol region in the Afar National Regional State.

Key Findings

Groundwater Potential

Two aquifer systems identified in Musley and Gehertu fans
Fresh groundwater found in shallow and deep aquifer systems within coarse alluvial formations
Test boreholes yielded >50 l/s of fresh water (TDS < 1000mg/L)
Estimated annual groundwater recharge: ~56 million m³ (Darcian approach) and ~40 million m³ (hydrological parameters)
Static groundwater potential reserve: ~225 million m³ (fresh water) and >400 million m³ (brackish water)

Hydrogeology

High aquifer transmissivity (3000-4000 m²/day) in major fans
Fresh water extends to 120-150m depth in fan centers
Brackish water found below fresh water zones and near salt plains (TDS 10,000-13,000 mg/l)
Highly saline water (TDS >40,000 mg/l) in fine sand and clay sediments with gypsum layers

Recharge Sources

Main recharge from infiltration of runoff from escarpments
Deep aquifers recharge from upper watershed areas
Estimated annual recharge from direct rainfall: ~10 million m³

Study Components

1. Hydro-meteorology

The study area has a monomodal rainfall pattern (July-September) with mean annual rainfall ranging from 152mm to 578mm. Water balance models (WATBAL) were used to estimate recharge.

Sub Basin	Catchment Area (km²)	Mean Annual Runoff (Mm³)
Musley and Adjacent	451	74.8
Ayshet/Lelegehedi	1000	174.6
Saba	1786	311.3

2. Geological Setting

The area lies within the Danakil depression, part of the East African Rift System. Four major physiographic regions were identified:

Western Highlands and Rift Escarpment
Graben Area
Alluvial Fans
Salt Plain

Key geological formations include Precambrian basement rocks, Mesozoic sedimentary rocks, Tertiary igneous rocks, and Quaternary deposits.

3. Geophysical Investigation

Methods used:

Transient Electromagnetic Survey (TEM) - 41 surveys
Vertical Electrical Sounding (VES) - 16 surveys

Findings:

Fresh-salt water interface at 150-200m depth in Gehertu fan
Fresh-salt water interface at 120-150m depth in Musley fan
Fresh water thickness decreases eastward from fan center

4. Hydrogeological Survey

Activities included:

Inventory of 110+ water points (mostly boreholes)
Water quality analysis (50+ samples)
Test well drilling and pump testing

Conclusions and Recommendations

The study identified significant fresh groundwater potential in the alluvial fan aquifers of Musley and Gehertu areas. The fans have been proposed as potential well fields with high productivity. Key recommendations include:

Development of production wells in identified potential areas
Proper groundwater management strategies
Further studies to better understand recharge mechanisms
Establishment of proper meteorological stations in the sub-basin