MELKA SADI-AM1BARA PROPOSED IRRIGATION PROJECT
FEASIBILITY STUDY
PART II
I STUDIES AND SURVEYS
VOL 3 - Gl-’OLOGY AND HYDROGEOLOGY
^3
I I ALCON SU LI K"fhc July |%9
tCONTENTS
PART I -         GENERAL REPORT
PART II -       STUDIES AND SURVEYS
VOL. I - HYDROLOGY AND CLIMATOLOGY VOL. 2 - SOIL SCIENCE
VOL. 1 - GEOLOGY AND HYDROLOGY
VOL. 4 - IRRIGATION ENGINEERING
VOL. 5 - AGRICULTURE AND LIVESTOCK
VOL. 6 - ECONOMIC AND FINANCIAL ASPECTS VOL. 7 - SOCIOLOGICAL AND HEALTH ASPECTS
PART III- OUTLINE OF THE PROJECTIMPERIAL ETHIOPIAN GOVERNMENT
AWASH VALLEY AUTHORITY
ADDIS ABABA
MELKA SADI-AMIBARA PROPOSED IRRIGATION PROJECT’
FEASIBILITY STUDY
PART 11
STUDIES AND SURVEYS
VOL 3 - GEOLOGY AND HYDROGEOLOGY
H \ I < o \ s I | |
July l%9CONTENTS
Page
1
1.   SCOPE
work perfomed
2.             ORGANIZATION OF THE INVESTIGATIONS
2.2           INVESTIGATIONS PERFORMED IN THE VARIOUS
AREAS
2.3           DOCUMENTS AND MAPS SUBMITTED
3. results of investigations
*
7
3.1 general geological outline of the region 8 3.2           STUDY OF GEOLOGICAL AND ENGINEERING
CONDITIONS IN THE MELKA SADI AREA
3.           2, 1 Geological Conditions
3.2.2      Choice of Site for Weir
3. 2. 3 Examination of Section A-A
3. 2. 4 Conclusions
3.3           STUDY OF GEOLOGICAL AND ENGINEERING CONDITIONS IN THE MELKA WARAR AREA
3. 3. 1        Geological Conditions
3. 3. 2        Choice of Site for Weir
3. 3. 3        Examination of Site for Weir
3.3.4          Conclusions
3.4           ENGINEERING PROPERTIES OF THE GROUND ALONG THE LINE OF THE DYKE
3.5           NATURE AND HYDRAULIC BEHAVIOUR OF THE PLAIN ALLUVIALS
3.5.1         Nature of Ground Encountered
3.5.2         Permeability
3.5.3         Water Absorption Capacity 
3.5.4         Piezometric Map
3.5.5         Chemical Quality of the Waters
3.6            POSSIBILITY OF FINDING GROUND WATERS 4.        CONCLUSIONS
9
9
1 0
1 1
1 3
1 3
1 3
14
14
1
J7
18
18
19
20
20
22TABLES
I     - CHEMICAL ANALYSIS OF THE WATERS
ANNEXES
1     - PETROLOGICAL EXAMINATION OF ROCK SAMPLES FROM BOREHOLES MW-1E, MW-1C, MS-3BAND MS-3D
2     - ANALYSES RUN BY THE ADDIS ABABA COLLEGE OF TECHNOLOGY
3  - ANALYSES RUN BY SAUTI CONSULTING ENGINEERS OF ADDIS ABABA
4     - ANALYSES RUN BY THE INSTITUTE OF FOUNDATION TECHNOLOGY, NAPLES UNIVERSITYfigures
location of piezometric wells and dam sites 1:2, 000, 000 GEOLOGICAL MAP
MELKA SADI GEOLOGICAL MAP SCALE 1:5, 000 GEOLOGIC profile through rodio boreholes LOCATION OF BOREHOLES SCALE 1:1, 000
LOGS OF 7 BOREHOLES DRILLED BY KELLER AT MELKA SADI
GEOLOGIC PROFILE AT INTAKE STRUCTURE MELKA WAR AR GEOLOGICAL MAP SCALE 1:5,000 STUDY AREA MELKA WARAR SCALE 1:1,000 PROBABLE EXTENT OF SURFACE LAVA FLOW PROBABLE EXTENT OF DEEP LAVA FLOW
LOGS OF 10 BOREHOLES DRILLED BY KELLER
GEOLOGIC PROFILES THROUGH KELLER AND RODIO BOREHOLES
LOCATION OF HAND-DUG PITS
PIEZOMETRIC MAP
LOGS OF 14 PIEZOMETRIC WELLS
SECTIONS SHOWING PIEZOMETRIC GRADIENT LOGS OF DEEP PIEZOMETRIC WELLS1.     SCOPE
Geological and hydrogeological investigations have been carried out within the framework of the Melka  Sadi Amibara  irrigation project for the Middle Awash Valley.
The objectives of these investigations were:
1) To chose the most favourable sections for siting the two weirs at Mel
ka Sadi and Melka Warar, and determination of the stability and water
lightness conditions at the sites.
Z)     To     assess     the     engineering     properties     of     the     ground     along     the     line     of     the river dyke;
3)          To     ascertain     the     nature     and     hydraulic     behaviour     of     the     plain     alluvials, in order to assess the consequences of irrigation.
4)      To determine the possibility of finding ground waters.- 2 -
2.     WORK PERFORMED
ORGANIZATION OF THE INVESTIGATIONS
Supervision of works and coordination of the investigations, to
gether with the geological surveys, were the responsibility of
Italconsult. The Company assigned a geologist to undertake the
field work between 5/1/69 and 15/5/69.
2. 1. 2          Drilling, the taking of undisturbed samples from the holes dril
led, and water absorption tests were performed by the Johann
Keller Drilling Company between 28/12/68 and 31/5/69. This
company also dug 2-4 metre pits along the alignment of the dyke.
A total of 986 m was drilled, 114 undisturbed samples were tak
en, 26 Standard Penetration Tests and 96 water absorption tests
were run and 58 pits dug.
2. 1. 3 The laboratory analyses of disturbed and undisturbed samples
taken over the whole area were conducted partly in Addis Ababa
at the Ethio-Swedish Institute of Building Technology and by
Sauti Consulting Engineers, and partly in Italy at the Institute
of Foundation Technology of Naples University. The results of
these tests are given in the annexes.
Below is a summary of the quantities and types of analyses run:
At the Ethio-Swedish Institute of Building Technology
The     following     tests     were     run     on     51     undisturbed     samples
.        Natural moisture content (51 tests)
•        Permeability (38 tests)
.        Grain size analysis (50 tests)- 3 -
26      undisturbed      samples      from      the      exploratory      boreholes      were subjected to the following checks:
Specific gravity (22 tests)
Grain size analysis (24 tests)
, Unit weight (13 tests)
.        Consolidation (20 tests)
.        Angle of internal friction                     (2 tests)
.        Cohesion (2 tests)
.        Liquid limit (9 tests)
.       Plastic limit (9 tests)
The following tests were run on                       108 the hand-dug pits:
.        Liquid limit
.        Plastic limit
.        Natural moisture content
.        % finer than No. 200 sieve
.        Free swell (25 tests)
.        Grain size analysis (3 tests)
disturbed samples from
Twenty  eight disturbed samples taken from the hand-dug  pits were dealt with by  Sauti Consulting  Engineers,  Addis Ababa the following tests being run:
•         Swelling
•         Liquid limit
. Plastic limit
•         Moisture content
. Wet sieve analysis.
They      also      carried      out      11      consolidation      tests taken from hand-dug pits.
on undisturbed samples- 4 -
Seventeen undisturbed samples were examined by the Institute Foundation Technology, Naples University. These came
Tholes in Melka Warar and Melka tests were run:
Specific weight (7 tests) Grain size analysis (7 tests) Plasticity index (7 tests) Breaking strength (4 tests) Consolidation strength (6 tests).
and the following
Unfortunately, only on 4 samples (4 boreholes) was it possible
to run a Slow Triaxial Test (1), due to the lengthy period of time between the date of collection and date of delivery to the labora tory, and because of the poor state of conservation of the samples.
2. 1. 4         Chemical analyses of 10 samples of water collected in the piezo- metric wells were run by the Ethio-Swedish Institute of Building T echnology.
The petrological analysis of 4 samples of rock was performed by Italconsult’s geologists in Rome.
2. 2. 1
INVESTIGATIONS PERFORMED IN THE VARIOUS AREAS The locations of the investigations performed are shown in Fig. 1. To study the stability and watertightness conditions at the weirs.
tCStS sh°uld have been carried out by the Ethio-Swedish Institute, which however wa  unable to deal with them in the
required time.
s-J
LOCATION   OF PIEZOMETRIC WELLS AND DAM SITES
SCALE 1 100.000
A A
PIO
LEGEND
PP12
▲
SHALLOW PIEZOMETRIC WELL (15m)
DEEP PIEZOMETRIC WELL (50m)
DEEP PIEZOMETRIC WELL ( 100 m)
INTAKE STRUCTURE AREA
M«rA
P5
Melka Sadi:
Melka Warar: -
Geological survey of the zone.
7 holes drilled totalling 164.85 m, by the rotary method with continuous coring (diameters 146- 76mm). These holes were set out on two align ments running N-S and E-W.
Twenty three undisturbed samples taken.
The following laboratory tests were run on these undisturbed samples: consolidation, grain size distribution, liquid limit, plastic limit, unit weight, wet sieve analysis, slow triaxial.
7 standard penetration tests.
5 permeability tests (Lugeon method).
7 permeability tests (Open End method).
Geological survey of the zone.
10 holes drilled for a total of 262.50 m, of which one borehole inclined at 25°, by the rotary meth od with continuous coring (diameters from 146 to 76mm). These holes were concentrated in the weir site area.
Thirty six undisturbed samples taken.
The same laboratory tests as listed for Melka Sadi were performed.
19 standard penetration tests.
-     18 permeability tests (Lugeon method).
-     3 permeability tests (Open End method).
To assess the engineering properties of the ground along the line of the dyke.
Twenty pits were hand-dug to a depth of between 3.50 and 4. 00 m.
Thirty eight pits were hand-dug to a depth of about 2.00 m. One hundred and thirty five disturbed samples were taken.- 6 -
Seventeen undisturbed samples were taken.
The following laboratory tests were run on the above samples:
liquid limit, plastic limit, natural moisture content, wet
sieve analysis, swelling, grain size distribution, consolida
tion.
2.  2. 3 To ascertain the nature and hydraulic behaviour of the plain al-
luvials:
Fourteen    piezometric    wells    were    sunk    for    a    total    depth    of
357.  55  m;  10  reached  a  depth  of  about  15  m  and  4  a  depth
of about 50 m.
These    holes    were    drilled    by    the    rotary    method    with    continuous coring (dia. 146-86 mm).
They    were    cased    with    50    mm    galvanized    iron    piping    slotted against the water-bearing levels.
Fifty five undisturbed samples were taken.
The following laboratory tests were run on the above samples: grain size distribution, natural moisture content, permeabi
lity.
4 permeability tests were run by the Le Franc method
13 permeability tests were run by the L»ugeon method.
27 permeability tests were run by the Open End method.
Ten samples of water were taken and the following tests were carried out: pH, total dissolved solids, temporary hardness as CaCO^.
2.   2. 4 To determine the possibility of finding ground waters. Two piezometric wells were sunk to a total depth of 201. 60 m, by the rotary method (diameter 146-76 mm).
Two permeability tests were run using the Lugeon method.- 7 -
documents and maps submitted
The results of the laboratory tests are shown in the annexes
The results of the investigations set out in the following para
graphs are illustrated by a series of figures in the text, namely:
Fig.       1 -        Location      of      piezometric      wells      and      dam      sites, scale 1:100, 000
Fig.       2 -        1:2, 000, 000 geological map
Fig.       3 -        Melka Sadi geological map, scale 1:5, 000
Fig.       4 -        Geologic profile through Rodio boreholes. Melka
Sadi
Fig.       5 -        Location of boreholes, scale 1:500
Fig.
6
Logs of 7 boreholes drilled by Keller at Melka Sadi
Fig.
7 -
Geologic profile at intake structure
Fig.
8 -
Melka Warar geological map, scale 1:5, 000
Fig.
9 -
Study area, scale 1:1,000
Fig.
10 -
Probable extent of surface lava flow, scale I
: I. 000
Fig.     ll -
Probable extent of deep lava flow, scale 1:1,000
Fig.    12 -        Loga of 10 boreholes drilled by Keller
Fig.    13 -        5      geologic      profiles      through      Keller      and      Rodio  Bore- holos
Fig.    14 -         Location of hand-dug pits, scale 1:100,000 Fig.    15 .     Piesometrlc map. scale 1:100,000
Fig.    16 -         Logs of 14 pioaoinotric wells
Fig.    17 .
' sections showing piesonietric gradient
Fig.    18 .         Logs of 2 ileop pieaometric wells- 8 -
3.           RESULTS OF INVESTIGATIONS
3.  1 general GEOLOGICAL OUTLINE OF THE REGION
The vast plain where the project is sited consists essentially of very thick alluvial deposits (over 100 m) (1). Deposition probably started at the end of the Pliocene and is still in progress. These deposits oc cur in terraces which reflect their age (these terraces are crossed along the road from Awash Station to Melka Sadi). They consist es sentially of very fine silty material though interbedded gravels and coarse sands are also present; these are sometimes slightly cement ed by argillaceous silt. They are to be seen in the area south of Melka Sadi.
This alluvial cover probably overlies the basic volcanic complex outcropping along the margins of the plain (2). It should be noted that volcanic activity continued into the Quaternary at the time the alluvial silts were being deposited so some flows are encountered in the alluvial cover (as observed at Melka Sadi and Melka Warar). The various ridges rising from the plain (Asada, Bahadamu, Ghed- diaro) are also manifestations of this recent volcanic activity, as are the hot mineral springs at Unda Bilen and in the sector west of Melka Sadi.
The area is still subject to volcanic activity though conditions are quiescent at the moment. The explosions of Mount Fentale and of the adjacent cones occurred only 100 years ago.
(1)     Boreholes DW-1 and DW-Z sunk during the project reached a depth of 100 m and were still in alluvium.
(2)     However, the presence of Mesozoic limestones and sandstones analogous to those present in the Abbai River and Webi River areas is not altogether to be excluded.GEOLOGICAL MAP
-LEGEND
'LIOCENE abATERNARV
OllGOCtME MIOCENE
O"
CRETACEOUS
Upper Hndiltnt faciei (llmeihm in Semiha
1 Secetral
AMaie limeaiene
SCALE I 2.000.000
No. 28 138the Kin valley 
C.inagnivuwv                       —---------------- -, y.
It is observed that several stretches of the Awash River run in the
same NS direction as the principal faults, while other shorter sec
tions run in a perpendicular direction, denoting an orthogonal system of faults. The risk of instability is probably greatest at the points
where the two systems meet.
In the hight of the foregoing, allowance must be made for seismic activity when designing the works (in particular the wrirsl It is considered that a series of expansion joints should suffice to guar
antee stability since the thick alluvial cover should considerably attenuate theenergy transmitted.
STUDY     OF     GEOLOGICAL     AND     ENGINEERING     CONDITIONS     IN     THE MELKA SADI AREA
Geological Conditions
Fig. 3 shows the surface geology of the area.
The following formations are present (2): Recent alluvium: silts and sandy siltsFIG. 3
MELKA SADI GEOLOGICAL MAP
SCALE 1:5,000
LEGEND
I       RECENT       ALLUVIUM       SANDY       SILTS J AND SILTS
OLD ALLUVIUM. ALTERNATIONS OF CONGLOMERATES WITH SANDY-SILTY CEMENT, SILTS, SANDY SILTS AND SANDS BASALTS
MS 2
O
2
KELLER BOREHOLES RODIO BOREHOLES
No 28139
{ ITALCONSULT-10-
OLd       alluvium:       alternating       conglomerates silts, sandy silts and sands
Basalts
with sandy-silty cement,
- Old clayey silts (whichoutcrop only on the east of the map under
a basalt flow).
The boreholes have shown the recent alluvials to vary from 5 and
10 m in thickness.
The old alluvium overlying the basalt flow has a thickness of between
5 m and a few dozen metres.
The basalt flows may be up to 20 m thick.
Under these flows it is probable that the same formations repeat for
some hundreds of metres in varying alternations.
It is probable that there is a series of N-S and E-W faults or fractures along the course of the river and in particular a N-S fract ire between the profiles of boreholes A-A and M, and E-W fractures to the north of
AA transversally to B-B.
3. 2. 2 Choice of Site for Weir
Prior to this study, an initial position explored by Rodio boreholes had been chosen as the site for the weir. This lay to the south of the area explored by Italconsult. Fig. 4 shows the geologic profile as evidenced by these boreholes. The an-a chosen by Rodio however had the following disadvantages:
Position lay  at an elbow in the Awash; this is
origin
probably of tectonic
The    formations    on    the    right    and    left    banks (alluvials on right, basalts on left).
are not homogeneous
The basalt       outcrops on the left bank               are very jointed.FIG. A
MELKA SADI
GEOLOGIC PROFILE THROUGH RODIO BOREHOLES
1
ma «I -756
754 752 750
-748 -746
■74 4 -74 2 -740
•73 8 736 734 732 -730
728
LEGEND
SILT AND SANDY SILT
FINE CLAYEY SANDY SILT
CONGLOMERATE    WITH    SILTY- SANDY CEMENT
BASALT
—--------------- FAULT
SCALES
HORIZONTAL VERTICAL
I. 500
1:200
No, 28140- 11
Therefore, investigations were concentrated on the straight section north of this position, the whole length of which was explored (circa 350 m). A series of boreholes was sunk parallel to the river with
a view to locating soils having suitable mechanical characteristics for a dam site. Naturally, morphological characteristics were also borne in mind when deciding on the location of the weir and the di version canal.
The section described below fulfills both requirements.
3. 2. 3 Examination of Section A-A
The results obtained from the 5 boreholes drilled are set forth in the logs in Fig. 6 and in the profile in Fig. 7.
Succe sjsi on_of_be d s_
Under a 5-m layer of recent silts outcropping on both banks there is a bed of conglomerates increasing in thickness from 5 m in the east to over 1 5 m in the west (this bed is absent in borehole MS-3). Tin- conglomerate rests on a basalt flow about 7 m thick to the east and wedges out to the west. The whole overlies old silts metamor phosed along the line of contact with the flow.
Meehan ica 1_ characteristics—
Standard Penetration Tests run on the surface silts gave N valu. s of between 3 and 5. They thus have very low bearing strength .iud are to be considered absolutely unsuitable for the foundations of the
weir.
The    conglomerates    and    the    basalt    flow,    on    the    other    hand,    are    com pact and thus form an excellent foundation.FIG 5
MELKA - SADI
LOCATION OF BOREHOLESMELKA SADI BOREHOLES
NOTES
- In the Lugeon tests, the absorption and permeability
values obtained at 1 .5 kg/sq. cm are shown on the left
of the column, while those obtained at 3 kg/sq ..cm
are shown on the right. When the test was run at at --
mospheric pressure, only one value is shown.
In the absorption diagrams the broken Line indicates values recorded at L.5  kg/sq.cm and the unbroken line those recorded at 3 kg/sq, cm.FIG 6-1FEATURE MELKA SADI____________________________________________ BOREHOLE No MS-2FEATURE MELKA SADI
DEPTH
m. BELOW GROUND LEVEL
DESCRIPTION AND CLASSIFICATION OF MATERIAL
BOREHOLE No MS-3
CORE
RECOVERY
LUOEON
lit./minAnt.
PERMEABILITY TESTS
OPEN END TEST lit/min./mt
DIAGRAM
lit /min./mt.
Clayey Silt
Silty Sand
Sandy SH?
Fin* Silt
Sandy Silt
Conglomerate with Silty-Bandy Cement
Fine Clayey Silt
Compact Baaalt
Veeicular Basalt, 
Jointed
Fine Clayey Silt
"Till
mo
ICI5
FIG 6-3s>l 8? N
FEATURE MELKA SADI
BOREHOLE No MS-3o
30
FIG 6-FEATURE MELKA SADI
BOREHOLE No MS-3 b
DEPTH
m. BELOW
GROUNO LEVEL
DESCRIPTION AND CLASSIFICATION
CORE
RECOVERY
OF MATERIAL
LUGEON
lil./min/mt.
PERMEABILITY TESTS
OPEN
ABSORPTION
END TEST
lit/mirv/rnt
OIAGRAM ht./minJmt
Large and Medium Grain Look Gr
avel
Medium     and     Fine     Grain
Conglomerate
■
with Silly-Bandy Cement
L _n«ti
Fine Silt with Pebble*
Compact Basalt
Fine Clayey Silt
Silty Sand
Fine Clayey Sill
21 )5
Sandy Silt
n io
Silty Sand
Fine, Clayey SiltITALCOSSI11| L'l (-ISNO31V LI 1
8
INK N
ELEVATION
g CUMUL SIMPLE
C m°
r-Oz
ml
TrrrrrTi
i yjnf
im i i i mn i
ii; Ji nr hfii 111
1,11111 (twini
iiinni   hit    in
iiiiiiiiriii.iiiii
nmm
diameter
□rilling
method
IIIH-I
mini!.
WATER LEVEL
m. b. g. I.
UNDISTURBED SAMPLES
PENETRATION
RESISTANCE
(blows per foot)
WATER
LOSSES
Z-9 9IJ
FEATURE MELKA SADI
BOREHOLE No MS-3d2814912 -
Pe,rmeabilitie_s (1)
The Open End Teets carried out in the conglomerates indicated per meability values of between 3 and 5x10 cm/sec. Thus the forma
tion is practically impermeable. During drilling operations, in fact
the total absence of water from this formation was noted.
The Lugeon tests run in the basalts (with a pressure of L 5 atmo»- spheres) indicated permeability values of between 2x10’ and
8x1 0"1 * * 4 * * * * * cm/sec which^although higher than in the preceding case, is still very low in the absolute sense.
(1) Note on permeability me»urtm«nH
Various types of teste were run. depending on the nature at the aolla and the type of permeability to be assessed (horizontal or vertical).
In the basalts and compact, dry alluviala (silts). the Lugeon method was applied.
In the basalts two successive
re run at prtnure, of 1. 5 and J. 0 kg/sqcm.
In the alluviala the Lugeon testa were run at atmoapheric prenure. The Le Franc method waa adopted in the loose alluviala and where there was a water table. The Open End method was applied to determine vertical permeability.
The valuea of permeability coefficients K were calculated with the following for-
mulae:
U£ ing.Pl®-Lugeon_ Method
K•
Q 1  . a+c
p TnC lo« -R-
K
permeability in m/aec
Q
P
injected discharge in cu. m/aec
real pressure existing in the section in m of water
a
R
half the length of the section in m
radiue in m
c
L’ l.lDg Lt f X*n_£ ^Method.
C «
Q
DKh
C
pocket coefficient
Q * discharge in cu. m/aec
D
K
h
diameter of the pocket in m
permeability in m/iec
difference in m between static level and dynamic level
Vg*BgOpen End. JeejMethod
K =
5. 5H
K « permeability In m/aec
Q ■ absorbed discharge in cu. m/aec
r  ■ radius of casing in. m
H • height of column of water In m.- 13 -
3.2.4 Conclusions
The     weir     should     be     sited     exclusively     on     the     conglomerates     which     have excellent mechanical characteristics and aero permeabtlity.
The structure should incorporate a serie, oi Joints to allow lor the seismic nature oi the region and the probable presence oi a fault or fracture which here run parallel to the course of the river.
3.3 STUDY OF GEOLOGICAL AND ENGINEERING CONDITIONS IN I HE
MELKA WARAR AREA
3.3.1 Geological Conditions
Fig.     8     shows     the     surface     geology     of     the     area.     The     following     forma tions are present:
Recent alluvium: silts and sandy silts
Old alluvium:                fine clayey sandy silts
Various basalt flows interbedded with the older silts.
The Recent silts cover the whole of the valley bottom for a width of
250-300     m,     while     the     old     silts     outcrop     on     both     hills     bordering     the valley.
There appear to be three or four basalt flows. The most recent covers the crest of the hills, the middle one occurs at the foot of these and the oldest outcrop in the river.
These latter have been picked up in various boreholes and the pro bable extent of the surface flow is shown in Fig. 10. The top of the flow lies at an elevation of between 726 and 734 m and it dips from north to south. It varies from 70 cm to 1 0 m in thickness. Beneath this flow the boreholes have picked up yet another which is even old er. The extent of this is shown in Fig. 11. It appears to be border ed to the west by a fault which follows the course of the river. The top elevations are 728 m to the north and 714 m to the west.FIG. 8
MELKA WARAR
GEOLOGICAL MAP
SCALE 1:5,000
legend
o
“I      RECENT      ALLUVIUM      SANDY      SILTS J AND SILTS
OLD ALLUVIUM ALTERNATIONS OF CONGLOMERATES WITH SANDY-SILTY CEMENT. SILTS, SANDY SILTS AND SANDS
BASALTS
MW I KELLER BOREHOLES
O
2              RODIO BOREHOLES
28150
Qtalconsii ltJMELKA WARAR
FIG. 9
STUDY             AREA
LEGEND
RECENT ALLUVIUM SANDY SILTS
AND SILTS
OLD ALLUVIUM ALTERNATIONS OF CONGLOMERATES WITH SANDY - SILTY CEMENT. SILTS. SANOV SILTS ANO SANDS BASALTS
MW1O KELLER BOREHOLES RODIO    BOREHOLES CROSS    SECTIONS
SCALE        I 1.000
28151
italcomsl i 1melka warar
FIG. 10
probable
EXTENT          OF SURFACE LAVA F LOW
W
L 721W
LEGEND
KELLER
BOREHOLES
CROSS   SECTIONS
ELEVATION   TOP OF BASALT FLOW THICKNESS
BASALT FLOW
SCALE
I ITALCOMSULTMELKA WARAR
FIG. 11
LEGEND
rnjt
RODIO BOREHOLES
CROSS SECTIONS ELEVATION TOP OF BASALT PROBABLE FAULT- 14 -
The profiles in Fig. 1 3 show the trend of the two flows and of the
silts lying above, below and between them in the Study Area.
3. 3. 2 Choice of Site for Weir
An initial line of holes run across the valley by Rodio indicated a pos
sible position forthe weir some 100 m south of the island in the river, How-eve r, it has been necessary to discard this because of the low load bearing capacity of the silts (S. P. T. gave N value of 19 as shown by the Ro-
dio boreholes). Furthermore, from the design aspect the weir must be sited in a wider part of the river so as to keep the height of the dykes to a minimum and to provide a better site for the intake works (see Vol. IV).
Thus the survey was concentrated a little farther north where the river broadens out considerably (to about 60 m as against the 3 0 it. to the south). Boreholes have been put down here to ascertain the nature of the subsoil.
3. 3. 3 Examination of Site for Weir
The results obtained from the 9 boreholes drilled at the site for the weir (plus an additional hole outside this zone) are set forth in the logs in Fig. 12 and in the profiles in Figs. 13-1 and 13-2.
Suc$ es_s_ion_of_Be_^ s
<
The cross sections indicate the following sequence of beds:
Recent silts on the banks to a depth of 6-8 m
First basalt flow some 4 m thick. This wedges out on the left
Fine     sandy     clayey     and     sandy     silts,     very     well     develon.rf     -
^ Unk' Th"e P‘"Ch betw"  '”<>
n
Oo»> on the right
Second     flow,     or     series     of     flows basalts are over 10 m thick.
with interbedded silts.
The seMELKA WARAR BOREHOLES
In the Lugeon tests,  the absorption and permeability values obtained at 1  .5  kg/sq.cm are shown on the left of the column,  while those obtained at 3  kg/sq.cm are shown on the right.  When the test was run at at mospheric pressure, only one value is shown.
In the absorption diagrams the broken line indicates values recorded at 1.5  kg/sq.cm and the unbroken line those recorded at 3 kg/sq.cm.m O A3 rn
o
r~
m
z
*FEATURE MELKA WARAR
DEPTH
m. BELOW
GROUND LEVEL
PERMEABILITY tests
DESCRIPT'Chl AND CLASSIFICATION OF MATERIAL
BOREHOLE No MW la
CORE
RECOVE
-
I
b
LUGEON | lit /mir\/ml
OPEN
ENO TEST
Irt./mirk/mt'
K
cm/wc
Iabsorpt
1 DIAGRAM
*hl /mir\ /ml
Jim___ Lui___ DUI__ L
lit »•
-Z1LM____ I
Fine SU£
Finn   Silt   with   Basalt   Boulder* Jointed Ba salt
Silty Sand with Ba a a Lt Bouldere Sandy Slit
.1-1 “ fflM’
_ Silty Sand___________________
.leSiIi with BaiaIi BoulAcxa Clayey Sandy Silt
rinri | :*2i rnir
nurFEATURE MELKA WARAR
DEPTH m BELOW
GROUND LEVEL
PERMEABILITY TESTS
CfSCRiF'lOh A.*«D C.iSSlFlCA’.ON OF MATERIAL
BOREHOLE No MW 1b
CORE RECOVERY
LUGEON
litJmmhnt.
1r
| OPEN | iEMO TE5T
id/min,/mi
K
cm /*♦€
I ABSDRrT'
Compact Baath
Cki
Joint ad Baaalt otaad with Clay Slightly VaalcuUr Compact Basalt Flna Silt with Baaalt Bo airfare
Fine Silt
5*ady SIU with Baoalt P^bblaa
Mainly Jolntod Baiallmuinx yvMrxMrt
DEPTH
m BELOW
GROUND LEVEL
BOREHOLE No MW 1c
DESCRIPTION AND CLASSiF.CAl CN
OF MATERIAL
permeability tests
CORE
recover*
LUGEON
hl /rnin/nM
r
*I
cm/wc
*fiSORFTicd DIAGRAM
lit /mirUrnt
Fine Sill
7JS 73
W*
22 ILL __ .ZiLM
Sandy Slit
Sih
Mae Sih with Basalt Pebble a Jointed Basalt
Fine Clayey Slit Compact Basalt Fine Clayey Slit Compact Ba oall
Jointed Basalt
Compact Ba tail
30’ HSNQ3 IV XI
FEATURE MELKA WARAR
DEPTH
m BELOW GROUND LEVEL
DESCRIPTION AND CLASSIFICATION OF MATERIAL
BOREHOLE No MW 1 d
CCRE
RECO.ERY
’ERMEABIUTY TESTS
LUGEON ' °PEN
Lil /min/rnt
END TEST 1
nr
lil/rrwin /ml
ern/wc
ABSORPT
1 DIAGRAM
1 (it /min/ml
Fine Silt
Silty Sand
Salt with Bae a It Pebble*
Fine Clayey Sill
Ok
• H--
Sandy Silt
Silty very Fine Sand
Silly SAnd
Lint Sill wUFFclhl
J,
—
Fine      Clarey
Sill
_
_____
JLmr Surer Sill *tth
Peb
ble*
Very Fine Silt
Fine Clayey Silt
Fine Silt
Silty Sand
30
FIG 12-530
FIG 12-6Elevation
: cuMui
simple
om.*
r-Ox
Pl*
<
m
diameiea
oriuing
method
I X] X)
WATER LEVEL m b q.i
UNDISTURBED SAMPLES
PENE1RATION RESISTANCE
I bhwi p*« *0<>tl
WATER
LOSSES
ri
r?
m
2o
o -U
-5
rn z
U»
m
X
c
m
►
L-Z\ OUaFEATURE MEL KA WAR AR
DEPTH
m BELOW GROUND LEVEL
BOREHOLE No MW 1 i
25*1
DESCRIPTION AND CLASSIFICATION OF MATERIAL
CORE
RECOVERY
LUOEON
iit/minJmt
OPEN
END TES1
lit/min./ml
Vaaicular Basalt
*’X-
Fina Clayey Silt
Basalt
FIG. 12-9Fl G. 13-1
MEL KA WARAR
geologic     PROFILES THROUGH KELLER AND RODIO BOREHOLESFIG. 13-2
MELKA WARAR
GEOLOGIC PROFILES THROUGH KELLER AND RODIO BOREHOLES
o
mail. 740 735 730 725 720 7 15
□
ma.s.l
735
730
725
720
715
RECENT ALLUVIUM. SANDY SILTS AND SILTS
OLD ALLUVIUM. ALTERNATIONS OF CONGLOMERATES
WITH SANDY -SILTY CEMENT . SILT 5
(
SANDY
SILTS AND SANDS
BASALTS
■ I TALCOMCLT j
o- 15 .
As indicated in Fig- U» it is possible that a fault runs along the line
of the river, truncating the old lava flows to the west.
Mechanical Chara ct$ r istics.
Standard Penetration Tests run on the surface silts gave N values
of between 12 and 20. With thesefigures the safe loading is assessed
to be less than 1 kg/sqxm.
At the expected level of the foundation - 728 m a. s.l. - N was 40
to 60 and the safe load could thus be over 2 kg/sqcm. Despite the
great number of undisturbed samples taken at around this elevation from holes MW1A, MW1B and MW1D, there are not sufficient reliable triaxial compression test results available because the Contractor
did not carry out his obligations as regard the performance of labo- ratory tests.
The results of the samples taken from MW1B at elevations of 724. 50 and 721 m have been assumed to be indicative.
The.se are:
26°
C = 0.37 kg/sq£tn
Itisnot considered prudent to consul*’ tion of 728 m since the va
e
■Jy = 1.64 kg, c-udii'.
suits obtained from the
. ampl
e taK.n tram MW1D
ot tp(39°Z0') is well above • « 
due Io the state of preservatton oi
is well above the average. This high figure may well b<
e  Thl. h.gh
le  which'»»» “ot
until four months after it had een
a Frohlich’s formulae
to
Applying      Terzaghi's,           *   "    *”  ’
Ca<   uot   Ker      1
the results from the NW IB samp
it
enS
ues
85 kg/sq» cm ( ^rO 1
that      the      safe
^V^^8
,
load lies somewhere between 1. an
g range is in g°od
Caquot-Kerisel       1.47,       Terzaghi       1.85h       Siandard           Penetration       Test       . ment with the figures derived from
F rom the series of N values available or
f  the three holes it is noted
i
alwayS over
 40. Th
uS
^at the value beneath the 728 m elevat^
U  '"Quid seem that a load of 1 kg. sq. 
Permissible     (the     N     value     would     even     £ but in view of the incomplete know e
“ would not be prudent to adopt this f gure). * 
more w
ould be
con
* loading of 2 kg/ Q-
ditions in this are
i The basalts seern .
reasonably compact and capable of taki g
least Zkg^-cui.- 16 -
Pe rme^b il
Le  Franc tests run on the Recent silts gave values of between 1 and 5 x IO"  cm/sec. These tests and Open End Tests run on the old
4
silts gave values of between 3 x 1 0-5 and 1 x 10-6 
cm 8ec>
/      Thus
while the permeability of the Recent silts is very low, the old silts are virtually impermeable.
Luge on Tests run on the ba salts at a pressure of 1 • 5 kg/sq. cm in dicate permeabilities of between 1 x 10-3 and j x 10-4 crn/gcc.
With permeabilities of this kind, there could be serious losses from the reservoir if extensive areas of basalts were involved. However, as only limited areas of outcrop will be under water, this eventuality appears unlikely.
3.3.4       Conclusions
The Recent surface silts must be eliminated from the foundations. The weir will lie partly on the basalts, on the right bank, and part ly on the old silts on the left. It is held that both formations have suitable mechanical properties. However, during the Final Design sta ge it would be as well to supplement the data through sinking
r er boreholes and running geophysical surveys to determine
e  thickness and extent of the basalt flows and to learn more about e  Mechanical properties of the silts.
The
tions Anri r
bo 
possible presence of an erosion surface between the two forma
° f a fault in the western part of the section should also be
in     mind.     A     sufficient     number    of     construction     joints    should     be t T>Ora^ed    in    the    weir    to    allow    for    the    seismicity    of    the    region    and Probable presence of a fault or a fracture.
The
any ter-retention properties of the reservoir do not give rise to perr^ cause for concern since the old silts are virtually im-
a pat.^able while the more permeable basalts do not outcrop over great lcularly large area. Even if losses occur, they will not be
i
i
ng
 ’ Ho*ever, the basalts could be rendered watertight by grout-R2 • SHALLOW PITS- 18 -
It may be concluded that the stability of the dykes will be satis factory provided that sufficient freeboard is left between the maximum water level and the top of the dyke to take account of the expected 30 cm of settlement.
nature AND HYDRAULIC behaviour OF THE plain alluvials
The 14 piezometric wells which are sunk provide information
on the nature, permeability and water absorption capacity of
the plain alluvials to a depth of 50 m, and on the configuration
of the water table.
3.5.1 Nature of Ground Encountered
As will be seen from the 14  logs given in Fig.  16,  the plain alluvials consist of an alternation of silts,  sandy  silts,  clay silts and silty sands.
The cover is extremely uniform, the only exceptions being noted ln  Piezometer P.9 which encountered basalt (12 m from ground lev el) and in P. P. 12 where a bed of conglomerate was picked up.
r^'igeon and Le Franc testa indicate an average horizontal per- ^  bility of 2.4   10-4  m/sec while the Open End Test points
ea
xC
Ve
rtical permeability being 1 x 10‘  cm/sec.
5
whi'°rat°ry tests
 gave an average figure of 3.2 x 10’  cm/sec
4
i             *8 in good agreement with the results obtained by the geon method.FIG. 15
I ITALCONSUI.
PIEZOMETRIC MAP
SCALE I 100.000
LEGEND
A-------- CROSS SECTIONS
72444 ELEVATION OF WATER TABLE
P2 •
PIEZOMETRIC WELLS
WATER TABLE CONTOURSPIEZOMETERS« III
CUMUL
SIMPLE
O
30
33
o_
c:
z (Dm o m-xj
r- OI
s*
r~
r
r
diameter
ROTARY
DRILLING
METHOO
rm t 11 t ’ • i ’’ TV''VJJ
r
rrrrrrrrrnTn
urriTrirn
TTxr.tr tritn tiitjiit
IIIIIIIIIII III
LOG
ENO TEST I *5
WATER LEVEL m, fc. j. I.
CASINO
UNDISTURBED SAMPLES
LUGEON liMmtrv /rvW
OPEN
M cm/s«c.t Lt'4 M LUM
/           :t
«*
*
**
t
— -4
X«
1
1.       I
I; £
'■b
»
**
M
*•
1
-
*O II"w 1
CUMUl
M
■>
-
o
M
U
o
I1
»     >P
•                1 -j       '     ■
i: 1 ~ i ~
SIMPLE
lr
I »- Dl
im
>
.--------------------------------------------------------------------------------- ------------- 1 ------------------------------------------------------------------------------------------------------------------------------------------------- ----------------------------- --------------
1
M 1J2
Jff KI
ROTARY
i■
DIAMETER
DRILLING
METHOD
niri in Illi' i i.r.i ii -111 • • i.i.r r i
!ll 1 IIIilll hl 11,11,11',111
'llllll i 1,1 |H 1111111 11' II.LH 1 1IH , JUJJl 1 111 1J J HI 1 .IHII.I
11
THTTTI IITIU III 11' , , I ,*' ■ 1 I 1 III 1,1,1 1
,1 1,11,1
’
'..',-'111!............ .. ill '• 1 H-1 rl 1 !.l IH.'II-I JH JI 11 <i
,r, ' » r in lllll'li
II Illi II llllll!i|
1 ' '?• 1 ' 1.7'1 ■ IT r 1^ UMiWulJ I I'l 1
ijimipHt; irtnn J innu'FtdHUNrn
1111*111,111111
IIHI 111 Hill 1
Itlllll II, II '
1 II 11,11
JI III
■■■ ■ ■ 11 LI 1
111111' 1
1 rih ii
g
Qf
1
IE
?
■
*
a.
g
5.
«
E
■<
I
K
g.
•*
f?
5®
_
______________
WATER LEveL
M »
I | Jf CASINO
• uwoisiuReco 1
S SAMPLES |
LUGEON
■‘fW
□ PEN
E*C 1 ES1 litjmiri/rnl,
H
v.| c
-A   —
IMPEKM£A®L£
h cm ^»«c.PIEZOMETERNoPi
>-
»—
_1
*—
$&
>*9f U>3 H
I
a
MJ
CL
Uj
'JUJ/AjaUiriH iS3i gm
NUdO
ILLI/ Ulul/|1| Noasni
I
SlldHVS
ajaamsiQNn
I fl q uj 1JAI1 HliVM
:■/          Hh          II.IIJIIHILIII J lU.ih:: liiii i ii I ii'^ .
1
111 I HI
* >J * L i j H
XI CD
D0HX3W
0NH1IM0
H313MVI0
I 31dH15
CL LU !---------------------------
. Uiffl I
o\Ot|\ ™wn:i
Hcnmii'aPIEZOMETERN0PP5
n~ a      *-
? jjo
L Sts
ar, **-
cr:
i iuj
ft
IWfUlWHII
ON}
N'ltfO
p<w/ iif
NOaom
SairfHYS
aiogrusrahtn
ONlSr? g
"1 * q uj
| 13A31 W31TM 1
rnrrni 1111 iiiti  i ir. 1111 in i uuri
■ytm mu uiiiiiiiiiii min
1111 u rn ii
ktit          n        rrmnT
• umini ii uiufl
TTTTTrt
1,1 ij'iiAmiii:
I V
aoHia*
oniiw
y vaOci
Amann
I, H  ■! MW
MmiWKTTlCUMUL \o3 o\*
I f ® Hl \ —
------------- A a <11 Tile
SIMPLE
1 *■
!
Irn
1V
ror*h*
□ 1AME1ER
DRILLING
METHOD
III11111,1,1 111 I.IIH.I IIMJI1IIHIIIIIIIIJHII SHUli 111 llil III Ilfi!llJilJ[IJ[llJUJ]llJ
UNO IS FURBED SAMPLES
IUGCON
7.1 i IQ
h< i MrR. /ftiI1
OWN END TEST
h CiM /aifC.m
i
•j_h
1 *" Jt
■/ un H
bwu'.ufrr
iSli int
NlrfO
B .ai* • •■
|
I£
[ ■ft
W
_ 51 * • t
__ni. ■!£
1
|
1
1
|LU|> UIU/ ||| i
NQJQni 1
j
]
i J ' ■ P i Nirr,;-
QO'H 13H
OHJYliaO
»B*J  ML        Lid.l »
----------------------------------------?o------------------- r.~d3r i
SIMPLE yjs.
□ UMEIEH
DRILLING METHOD
koi
/
1
__________________________________________________________ J-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
,
0 132
Ul
Ji------------------------------------------------------------------------------------------- —---------------------------------------------------------------------------------------------------------------------------------------------- 1 ROTARY
’ri i ■ j n. j
• 1 r J. i — f i' -               »l l i ' ,- ' ; |' r 11' 1111I 11:1 i '  'nN,'  i||UI,'ir:|f||  IMilHH  1  lit,  ,'|lli  111  11  llllllll
ki’Hii'i’1 H'm I' t'iii'JiUii . tniii iji nun r11it
11
11
1
.1 .in , i'.ir mmmi ii mmiif Jim.iiminmi
1t I  i 1.1 i    i|i i 11 i ,ii I 1111 I ill r r 111 111111 ii i ii ii ii 11 Ilin 11 il,,l 111 mmiiim ii iniiiiiiiiiiiiur.iiii in iiiii-
■ i1111111-111.111 mu i mill 11ii ii11111H iiiiiii'irmi m
ihhih mu..!....................... .. iiiunmimiiim j
J.!  1  IL.  11  Illi ULh'IlH'-:
1UBII1H II1
• Ji HI’H
11
us
e1
I
If
Ma.
b—■
*■
a
k-
'
1
1
B
a
n
S'
■3
=F"
Ln
n
it
■*<
MS
L.
1
wAiLK irrfl
m6$1
2 CASJMQ I
UNDlSTUfcUL'O SAMPLES
LLTGfQN
h l /min Anf f m
rd
-D |
1 ft * 10
k-bnlQ ’
-
PPEN
ENTi TEST
LA £ 1
Cl J o
J?
l<! Jnsi n/ml |
a t *ia
I 4 HD-4
j
A cm/nre. 1
I ffs
>
3/ ?»*/ui9 W
I | iuvui*/ irh 1531 0H3
I Nl«*0 I
| ILUjl U4uj;|'|l I
i *ozinnT J
S J UHVJ OJHwnjsiaNn
ONisra £
t ,oi 4
T
# Ol»w L
t <H*%C
-----------------------------1—
1
I-
— 
<-•••' _d
3I
sth
TF=»--------
;a
1
T
r_J
LH
LU
Q
o
■«
O
v*
un z
O
v5
t>
r
tZ
-n
H
■
W
•M
A
2
■r*
ia»
>-.
TJ
S
w
’ ■ n iiFrrrrrrn ii i i.j n J ii. i 'Tti i' 111  ■■".,,••,. ;
■i
1
001
□0H13W owmua
U3L3VAVLQ
iiiillii  11  11  mmir'llIUk11LiJ3Wi1i--i  mi'  in■:II1  111  ■  I  lUri  a
r . T| TJ H-T ■ 'IT          • ~r
' 1 P1 mmim I- I;- ||, 1 'i'li'
iii;iii,ir111Hi,ii,ijn lii,i J 111,1,11,ii.'ii n.iii, i111n
i^
!1
1
l
1  J AU J J A JA W .M.U. JAM
1 1-1 ,______ ______ ______ L_____ Li_____ i______ L _ _ 1
1
1                     L     nr1
.• jK . U 0 A V . k ' V f l\ ,H,i
r
;H i
r' n ri" ■: i ri 11.      ■ ii 11 1    1 III II H'UUllilll 1,1
1
<iHii: hur1n1...■..:..i....i..i i!i' ,i .in 1 . I1I I1I >i LI J. . 1...11H 1 1
in .iilii.■n■il ilittwii'll,l iiil1Nl ll('■iiii j1i.rm1I.M1
kHTldfc
,— 
-1
—------------------------------------ 1-------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------ -f
i
SV
. Jfl
ftl ff
1
\tq _i i SI I’>lk tp 3 '.
\
\ 3i’i TldHlS
I
-----------
f
/
□rd'. 22*"'3
i|
/
/
•*
HQH* '*"!■ *
■ *i
1
1
•
-7 
/ r
.L'£I-------------------------------------------------- ]--------------------------------- -
3BC/U43 X mi on3
HldO
Uiuin11
Noaoni
S3?dHV5 (oa«rusiONn 0NISV3
I fq w
1
n-------------------
•im
i-
01 M I
>■
»«c r
t-
I 0,01
*I3A3l MllVM
□OH  I3H ON'TIIBO
diiawvia
W
ITdKlS
AM
z>
>
Ixl
.ID _J
*5 Itio
lanna
HC1LYAT4 3
ii
o
u.
I..
J«|J UJ3 W
kuQ uimnq
1531 □Nl
N3d0
Noisim
SlldWVS niiiMftisrONn
I B q lu UA31
Q0H13W
□ NIUIMO z        d3i3HVin
3UHIS
z^'|
men *
, PT?
, I I: Jl Illi I' 11.1 n
r u rj..11ri'111 | uh
■IHiil1Id.1-—i l ii i, il.h( Il. niLirI.,lxliJr11■ lji
a a * l0 b
.
inwrii
*jl
«l
<1 -     •'I     •            = |
L.      1
1|
i, st m                                               1
:'l
h □! LV fr J11
1
11
1 4l
■>
"      3   T.     r             S>
1
l'FIG.17
MELKA WARAR
SECTIONS SHOWING PIEZOMETRIC GRADIENT
B
AWASH_ RIVER
p PIO
B mo.L
i$o-
740-
-700
P11
740
*—[------------------------------------------------------------
—- -qr
720-
. 710
LEGEND
PIEZOMETRIC LINE
0
]
Km 1
700-
k
TOO
c
AWASH RIVER
c
ma.o.l
700-
740
710
700-
440
PP 12
n
p 11
u_
---------
7
/
s----------------
P3
---------------n------- *
P6
P9
r
II
Ir
tI-I--------
--------------- Il--------------------- ----------------- U-
1*0 tl -700
•7<i
•710
-700
■too
• I Al CONSULT
1112
1
1
1
1
1
1
1
1
1
1
jj- 20 -
It will also be seen that there is a Low hydraulic gradient running southwest-northeast (l%>). Hence with a horizontal permeability of 10 cm/sec the flow rate is around 10“9 m/sec. The aquifer
is thus virtually without flow and in all probability merely varies in a vertical sense with inflow from the rain and outflow by evapo transpiration.
3.5.5 Chemical Quality of the Waters
The analyses show (see Table 1) that the waters generally have a high salt content (from 0.4 to 10 gpl \ This iB no doubt due to the static nature of the aquifer and associated evaporation.
3.6 POSSIBILITY OF FINDING GROUND WATERS
The two deep piezometric weils(logs given in Fig. 18) drilled near the volcanic hill9 at Melka Warar encountered various horizons of sand and gravelly sand which are water bearing. Permeability tests run on DW-1 indicate an average value of 2.5 x 1 O'  cm/sec. In theory a maximum discharge of around
3
5 Utres per second could be obtained (1). However, before making any plans to exploit these ground waters, investigations would have to be performed to ascertain recharge possibilities and to determine the chemical nature of the waters themselves.
(1) Discharge calculated by means of Sichard’s formula
Q = Vc x S
where:
Q is the discharge
Vc is the critical velocity
S = well diameter, assumed in this case to be 300 mm.CHEMICAL ANALYSIS OF THE WATERS
Sample Marked as
Total Dissolved Solids
at 110°C
Temporary Hardness
as CaCOj
PH
Well N° p. p. 1
Hole N° p. 2
Borehole N. P. 4
Borehole N. P. P. 5
Hole P. 8
P. 9
Hole P, 10
P. 11
P. P. 12
P. P. 14
1. 130 mg/1
I. 644 mg/l
1 0, 624 mg/1
932 mg/1
1, 390 mg/1
486 mg/1
5, 854 mg/1
396 mg/1
41 2 mg/1
740 mg/1
38 mg/1
I 08 mg/1
395 mg/1
14 mg/1
68 mg/l
1 06 mg/1
769 mg/1
96 mg/1
104 mg/l
8,8 mg/1
8. 75
7. 68
7. 03
8. 65
7. 60
8. 10
7. 48
8. 05
5. 25
8. 40
17
Table 1EZOMETER
3X/UJ3 X
IHl QN.7
N3d0
luv v«ui/)i|
N03001
saidHvs
OJOHfUSiONn
ONISVO h
i n tj <m
1JA31 M31VM
Z
Q
Z
<
T
O
o
•<
tn
<n
o
o
Q.
001
00M13H
0NI11IW0
fc3A3HVI0
31dWfS
1
•w x
<Ci >
—
—14 ‘
4-
1
O
Q
<
T
<
2
1 M3
-
■                    5 1 5                   3        3
 - s J
J
?
innno                2                    s ----------- 1-
_________ _ 
5
5'
5 ' A3    5
R
L
S
R3
S
i Ifi 1
±
51
1
N0I1VA313
E
•» | |
>1eature
melka warar                PIEZOMETER No DW-2
depth
m BELOW
grouno level
FIG 18-2
-j
o
i
3
u
kJ
a.
I
in
DESCRIPTION ANO
CLASSIFICATION
OF MATERIAL
PERMEABILITY
TESTS
si -* -
«g| :
oyi g
IM 2 M
Sandy Silt
fine Clayey Silt
Joint ad Barak with Silt
Vaalcular Basalt
Compact Baiak
Vary Joi a tad Baaali rdlaad
with Silly Sand
F«aa Clayey Silt
Sandy Silt
Fine Clayay Silt
silty Sand witfi Ba^all_Frag
SLfhdy Silty Sand
Slightly Silty Sand
IT A LC O S 5 (_ y- Il.
4 - CONCLUSIONS
The Melfa S»« intake will lie
o . Co„glom„atfs whic„ h„, 
bearing properties and are impermeable.
At Melka Warar part of the intake will lie on basalts (right side) and 
part on old alluvium (left side) below an elevation of 728. The safe
bearing capacity here is a little over 1 kg/sq.cm. Permeability is
virtually nil in the alluvium and low in the basalts.
At both Melka Sadi and Melka IVarar provision must be made for con
struction joints to allow for the seismicity of the region and the pre
sence of fractures running parallel to the river. At Melka Warar ac
count should also be taken of the non-homogeneous nature of the forma
tions on the two banks.
Examination of the soils which occur along the line of the dykes indicates
these to be suitable for construction (safety factor greater than two, and 
settlement in the region of 30 cm over a period in excess of 6 years).
The   plain   soils   have   .1   very   low   permeability   both   in   a   vertical   and   a horizontal     direction.     The     aquifer     may     be     considered     as     practically static.
The dry  ground  above the water table will,  it is thought,  become Saturat ed  with  irrigation  water in  5-6  years,  hence a drainage system should  be built in the years immediately after the land is brought into cultivation.
Ground waters may be found near the Melka Warar volcanic hills how
ever, discharge tests must be run and more information obtained as to recharge and water quality. By and large it would seem that the wells
would have to go to a depth of 1 00 m or more; they would have a delivery of 5 It/sec.ANNEXESANNEX I
PETROLOGICAL EXAMINATION OF ROCK SAMPLES FROM BOREHOLES MW-IE. MW-1G, MS-3B AND MS-3D
4.
1Al-I
e
a
■   frnm MW-1E at 4J0_in
u croscopieally the rock is grey la dark grey in colour and haa small roundish or ovalish vesicles which tend to be elongated m one direction 
nd are Lined with secondary minerals. The cavities vary from 0 5 to 
r
5 mm in diameter.
Under the microscope the rock is seen to consist basically of calc-alkali felspars and pyroxene, It has a porphyritic structure. There are oc casional phenocrysts of olivine, labradorite and augite having an average diameter of 400-500 microns. These are set in a ground mass of micro- lithic felspars and pyroxene grains.
A fair number of opaque granules of iron oxides and hydroxide. - occur evenly throughout the rock* Calcite is also present in places as an ac cessory mineral. The olivine which is always rather rounded has a thin reddish brown fringe of iddingsite.
The rock may be classed as olivine basalt.
1
13.50 m
The     rock     is     grey     to     dark     grey     in     coJcnrwith     some     small     roundish     vesicles °<5to 5 mrn j  diameter.
n
Coder the microscope it is seen to consist of a few phenocrysts of caLc -
J lkali felspar and olivine having an average diameter of around 700-
00  mi trQna These are set essentially in a ground mass of labradorite
* lth subsidiary augite, olivine and opaque iron hydroxide grains. The
^*«rage dimensions of the ground mass crystals is around 2 00 microns. olivine crystals are generally rounded and partially decomposed to id-
iroutid the margins and along the fractures.
e f ock
be classed as basalt.Al-2
I * from MS’3B at 8»_ Q m
5jj23Pl - ~—------ —
The       rock     is     dark     grey     and     has     numerous     small     vesicles     with     a     rounded or        elongated     section,     varying     in     diameter     from     a     lew     hundred     microns to  several millimetres.
7
jn thin section the rock is seen to consist of a few phenocrysts of ralc- alkali felspar and olivine, whose dimensions are of the order of a few hundred microns, set in a minutely vesicular groundmass consisting mainly of closely interknit calc-alkali felspars with a markedly tabular elongated habit. The interstices between the felspar crystals are filled mainly with more or less isometric crystals of pyroxene and subordinate- ly with, opaque granules and glassy materials. The olivine always has a reddish border of iddingsite.
The rock may be classed as basalt.
Sample from MS-3D_al 17.60 m
Dark grey or black compact rock with a few vugs partially filled with secondary minerals. In the sample examined, one of these vugs was about one centitnei re in diameter, the others were all much smaller (around a millimetre).
In thin section the rock is seen to have a porphyritic structure and a sub- ophitic texture. Crystals of pyroxene are present; these partially en-
^lose felspar crystals and also occur interstitially (I).
fn Order of magnitude, the rock consists of Labradorite augite, olivine
iron oxides and hydroxides. Chlorite is also present in a fair amount ‘ ls ri secondary mineral and is frequently associated with calcite,
T h
r ock may be classed as basalt.
Pyroxene crystals may be from 200 microns to 1 mm in siste, ^hlle the felspars arc normally around 500-600 microns.
aANNEX 2
ANALYSES RUN BY THE ADDIS ABABA COLLEGE OF TECHNOLOGYADDITIONAL COPIES ARE AVAILABLE ON REQUESTANNEX 3
ANALYSES RUN BY SAUTI CONSULTING ENGINEERS OF ADDIS .ABABAADDITIONAL COPIES ARE AVAILABLE ON REQUEST*
ANNEX 4
ANALYSES RUN BY THE INSTITUTE OF :-X)UNDATlON TECHNOLOGY, NAPLES UNIVERSITYADDITIONAL COPIES ARE AVAILABLE ON REQUEST

< <

Summery

Summary of Melka Sadi-Amibara Irrigation Project Feasibility Study

Melka Sadi-Amibara Irrigation Project Feasibility Study

Geology and Hydrogeology Report Summary

Project Overview

This document is Volume 3 (Geology and Hydrogeology) of a feasibility study conducted in 1969 for the proposed Melka Sadi-Amibara Irrigation Project in Ethiopia's Awash Valley. The study was commissioned by the Imperial Ethiopian Government's Awash Valley Authority and conducted by Italconsult.

Key Objectives

Select optimal sites for weirs at Melka Sadi and Melka Warar
Assess engineering properties of ground along the river dyke
Evaluate hydraulic behavior of plain alluvials
Investigate groundwater potential

Main Findings

Melka Sadi Area

Geology consists of recent alluvium (sandy silts), old alluvium (conglomerates with sandy-silty cement), and basalts
Recommended weir site has conglomerates with excellent mechanical properties (safe load >2 kg/cm²) and zero permeability
Construction joints recommended due to seismic activity in the region

Melka Warar Area

Geology features recent alluvium, old alluvium, and multiple basalt flows
Weir will be partially on basalts (right bank) and old alluvium (left bank)
Safe bearing capacity approximately 1 kg/cm²
Potential water losses through basalts (permeability 1×10⁻³ to 1×10⁻⁴ cm/sec)

Plain Alluvials

Consist of alternating silts, sandy silts, clay silts and silty sands
Average horizontal permeability: 2.4×10⁻⁴ cm/sec
Vertical permeability: 1×10⁻⁵ cm/sec
Aquifer is virtually static with low hydraulic gradient

Groundwater Potential

Water-bearing sand and gravelly sand horizons found near Melka Warar volcanic hills
Potential maximum discharge: ~5 liters/second
High salt content in waters (0.4 to 10 g/l) due to static nature of aquifer

Key Recommendations

Incorporate construction joints in weirs to accommodate seismic activity
Implement drainage system within 5-6 years of irrigation commencement
Conduct further tests before exploiting groundwater resources
Consider grouting basalts at Melka Warar to reduce water losses

Investigation Methods

Method	Description	Quantity
Boreholes	Rotary drilling with continuous coring	986 meters total
Undisturbed samples	Collected for laboratory testing	114 samples
Standard Penetration Tests	Soil strength assessment	26 tests
Permeability tests	Lugeon, Open End, and Le Franc methods	96 tests
Hand-dug pits	Along dyke alignment	58 pits

Laboratory Analyses

Tests were conducted at multiple institutions including:

Ethio-Swedish Institute of Building Technology (Addis Ababa)
Sauti Consulting Engineers (Addis Ababa)
Institute of Foundation Technology, Naples University