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r k • d I ' ^> ■
GOVERNMENT OF ETHIOPIA MINISTRY OF WATER RESOURCES
AMIBARA DRAINAGE PROJECT PHASE-II
PREPARATION OF DETAILED DESIGNS, TENDER'DOCUMENTS,
PROJECT PREPARATION REPORT AND
ENVIRONMENTAL IMPACT ASSESSMENT REPORT
n        WATER AND POWER CONSULTANCY SERVICES (INDIA) LTD
(International Consultants in Water Resources)
'KAILASH', 26, KASTURBA GANDHI MARG.,
NEW DELHI - 110 001, INDIASection
HYDROGEOLOGICAL DATA/ANALYSIS TABLE OF CONTENTS
Dcscript ion TABLE OF CONTENTS
Page No
i
LIST
OF
LIST
OF
TABLES
FIGURES
LIST
OF
APPENDICES
iii
IV
iv
1.0 INTRODUCTION
1.1        Locat ion
1.2        Cli mate
1
1
1
1.3 
Soils and Geomorphology
1.4 
Geology and Hydrogeology
1.5 
Irrigation Practices
1.6 
Drainage
n
3
4
4
2.0 GROUNDWATER
2.1        Buckground
2.2        Review of Previous Studies
2.3        Review of the Available Data
2.4        Analysis of Data
2.4.1 Regression Analysis of Groundwater Data
2.4.2        Depth to Groundwater Nap
2.4.3        Identification of Priority Area of
Phase 11
2.4.4       Groundwater           Salinity Contour Map
6
6
6
11
11
15
16
16
19
2.4.5 
Groundwater
Level Contour Map
2.4.6 
Observation
Wells Hydrograph
2.4.7 
Piexometric
Sec t ions
19
20
2!
2.5 Perched Water Table
23Section
Description
2.6        Prediction of Future Groundwater 2.6.1       Rate of Expected Rise 2.6.2       Groundwater Depth 2.6.3       Groundwater Salinity 
2.7        Conclusions REFERENCES
Page No
Depths &. EC in Groundwater
24
29
29
31
31
33
iiTable No
LIST OF TABLES Description
1           Number of Observation wells/Piezometers Installed by Individual Organisation and Identifying Codes
2           Status of Observation Weils/Piezometers as on
August, 95
3          Wellwise Details of Data Availability
4           Priority Areas Delineated by Depth to Groundwater Contours (Phase-II )
5  Number of Wells Showing Rising or Falling Groundwater Trend
6           Predicted Future Groundwater Depths Below Absolute Zero
7           Predicted Future EC Values
8           Predicted Rate of Rise of Groundwater Level in Wells Having Rising Trend
i iiFig No 
LIST OF FIGURES Description
1                  Priority Areas for Sub-Surface Drainage (Phase -II)
2                  Groundwater Salinity Contour Map for August,95 EC values
3                  Groundwater Levels Contour Map for August 1995
4                   Piezometric Cross-Sections (Melka Sadi Area)
5
6
7
8
9
No.
1 
Piezometric Cross-Sections        (Amibara   Area)
Predicted  Groundwater          Depth          Contour   Map   for        year    2001
Pred icted  Groundwater          Depth          Contour   Map   for        year    2006
Predicted  Groundwater          Depth          Contour   Map  for        year    2011
Predicted  Groundwater         Depth          Contour  Map   for     year     2016
LIST OF APPENDICES
Description
Plot     of     Annual     Observed     Maximum,     Minimum     and     Mean 
Computed Groundwater Depths
2                        Plot of Annual Observed Maximum, Minimum and Mean Computed EC values
ivHYDROGEOLOGICAL DATA/ANALYSIS
1.0                     INTRODUCTION
1.1 Location
The area for the drainage study  is situated  in  the Northern Rift Valley  region  of Ethiopia on  the right bank  of river Awash.  The area covers mainly  the settlements in  the Melka Sadi and  Melka Warer and  also  includes the Amibara settlement project and  state farms.  The Addis Ababa-Hille highway  provides the access to  the project area via an  all- weather link  road.  The Rift Valley  Escarpments rise some distance to the east and west of the study area.
1.2 Climate
The climate of the project area can  be broadly  classified as semi-arid,  with  mean  annual rainfall of the order of 563  mm.  There are two  distinct rainfall pattern,  one in July-August covering  about 40% of annual rainfall and  the other in  February  - April covering  about 32% of the annual
rainfall.             Heavy 
intensity 
rainfall
occurs             during             the
rainfall       period       of       July-August       but       rainfall       as       high       as       100 
mm has been observed in one day on March 31,1982.
Mean  temperature in  the project area ranges between  23cC to 31°C with  mean  maximum temperature of 38°C in  June and  mean minimum temperature of 14.2°C in  December.  Mean  relative humidity  is maximum in  August (59% ) and  minimum in  June (38%).  Mean  daily  sunshine duration  is 8.46  hours on annual basis.  Mean  daily  evaporation  rates for class ’A* pan  is maximum in  June (9.49  inm) and  minimum in  December (6.03  mm).  The mean  daily  evaporation  is 7.17  mm on  annual basis.
11.3       Soils and Geomorphology
According  to  the Master Drainage Plan  for the Melka Sadi and  Amibara Area,  1985,  prepared  by  Halcrow,  three distinct
geomorphological
features,             namely             the
recent
alluvial
plain,        a        series        of        ancient        fluviatile        terraces        and        volcanic formations of varying age exist in the study area.
The alluvial plain  is a relatively  recent geomorphological feature and  shows abundant evidence of construction  by fluvial processes,  with  old  meanders and  levees being readily  identifiable.  Adjacent to  the alluvial plain  are a series of terraces which  are most pronounced  in  the south of the study  area,  where two  distinct terraces can  be clearly  seen.  The higher of these is separated  from the alluvial plain  by  a distinctive escarpment upto  10  metres high.  The lower terrace is less pronounced,  and  both terraces become discontinuous features towards the north  of the study  area,  where isolated  remnants are observed. Several irregular volcanic hills rise abruptly  from the otherwise flat alluvial plain,  and  recent lava flows are a common feature in the vicinity of the study area.
The generalised  soil distribution  within  the study  area
reflects
the
recent
geomorphological
history.             Coarser-
textured  levee soils occupy  a discontinuous belt adjacent to  the present river course,  with  finer textured  ’basin’ clays lying  beyond  this belt and  extending  towards the higher ground  and  river terraces in  the east.  Within  this overall pattern,  complex  soil associations occur,  and  there is considerable soil variability.  Adjacent to  the old terraces in  the east of the area,  occasional patches of saline soils remain,  but have largely  been  excluded  from the irrigation development.
V- Elsewhere         the         soils         are         of         variable         but         generally         low sal inity.
21.4       Geology and Hydrogeology
The northern  Rift Valley  was faulted  to  its present formation  during  tectonic activity  associated  with  the Tertiary  in  the late Paleocene - and  Eocene Epochs eras. During  the subsequent Plio-Pleistocene,  outwash  gravels containing  clay  lenses derived  from the breakdown  products of the elevated  areas on  the flanks of the Awash  River were deposited on the outwash plain adjacent to the river.
Intermittent            volcanic            activity            since
the            Eocene            and 
associated  outpourings of lavas has resulted  in  the deposition  of a gravel sequence interbedded  with  lavas. Towards the present flood  plain  of the Awash  River,  these deposits grade into  an  infill composed  of a complex sequence of silts,sandy  silts and  clays,  which  have in places been  laid  to  depths exceeding  100m.  The general geology  of the area has been  mapped  by  Halcrow while preparing  the Angelele-Bolhamo  Feasibility  Study  Report in October, 1975.
% o 
The available information  show that all formations in  the Awash  River flood  plain  are water bearing.  The sedimentary 
materials
are             consistently 
fine-grained             and             characterised 
by  a low horizontal permeability,  so  that they  appear to form an  aquifer that is essentially  without flow.  Aquifer type response is mainly  the result of inflow from rainfall and  irrigation  and  outflow by  evaporation.  Such  behaviour precludes the use of deep  disposal methods for lowering the water table.  Nevertheless,  where boreholes have penetrated  the gravels or fractured  volcanics,  water can  be
extracted 
in 
sufficient             quantities
for             water
supply 
purposes.  Although  confining  layers may  be encountered locally  in  fine grained  sequence,  the groundwater is believed  to  be in  hydraulic contact,  regardless of geological formation.
31•5 Irrigation Practices
Main  crop  in  the study  area is cotton  with  some banana, maize and  other crops.  These crops are generally  irrigated by  gravity  canal system taking  water from Amibara Irrigation  Project.  The areas around  old  Algeta,  Ambash and  Sublele State Farms,  producing  cotton  were utilizing pumped  supplies of irrigation  water directly  from Awash river through  3  pump  units,  but now only  one pump  unit is in working condition.
The gravity  irrigation  system,  comprising  a network  of secondary,  tertiary  and  field  canals,  designed  on  the basis of 24  hours operation,  takes the water from main  canal through  offtakes and  distribute to  the fields.  A limited number of flow control and  measurement devices have been provided to assist in water management practices.
The main  method  of irrigation  is by  furrows.  Very  accurate land  grading  is required  for this type of irrigation  system for efficient use of irrigation  water.  This method  of
irrigation           also           requires           services           of           skilled           irrigators
to 
maintain           correct           rates           of           flow           during           the period.
Basin irrigation system is being practised for the bananas, which require higher water round the year. Basin irrigation system is less sensitive to land grading and, requires less skilled irrigators than furrow method.
irrigation 
1.6 Drainage
A        well        planned        drainage        system        is        essential        to        dispose        off excess        water        from        the        irrigated        area        which        in        turn        will
ensure
sustained             agricultural
production.             Surface
drainage
is         required         to         dispose         of         excess         water         due         to         rainfall whereas sub-surface drainage system may be required to
4control high ground water table and remove excess ground 
water.
At the time of conversion  from pumped  to  gravity  irrigation system under Amibara Irrigation  Project II,  groundwater tables in  Melka Sadi-Amibara area were generally  at some depth  and  sub-surface system was not an  immediate requirement and  only  surface drainage system was designed and  installed  in  the project area.  Subsequently,  due to introduction  of irrigation  in  the study  area,  groundwater table started  rising  in  certain  areas and  need  for sub surface drainage was felt.  Halcrow in  1985  prepared  a Master Drainage Plan  for Melka Sadi and  Amibara Areas,identifying  the areas needing  immediate surface and sub-surface drainage system under Phase-I and  areas needing sub-surface drainage system subsequently  under Phase-II and III.  On  basis of this,  the Phase I drainage project was undertaken and is at an advanced stage of completion.
The present study  needs identifing  of the areas needing immediate sub-surface drainage and  plan  the drainage system for the study  areas under Phase II of Amibara Drainage Project.
52.0 GROUNDWATER
2.1 Background
Ground  Water level observations have been  started  on intermittent basis in  the study  area since 1970,since the piezometers were installed  by  Italconsult and  Awash  Valley Authority,
From       1980,       a       network       of       observation       wells       was       installed       as a       part       of       the       AIP       II       programme       to       systematically       monitor the         ground         water         levels         and         salinity         of         ground         water subsequent        to        the        introduction        of        gravity        irrigation        in        the study          area.          Since          the          installation          of          these          piezometers, number      of      them      have      been      damaged      and      become      unserviceable. Table          1          shows          the          information          about          the          piezometers installed        by        the        various        organizations        and        Table        2        shows the      status      of      the      piezometers      as      on      Aug      95,      which      indicates that      only      54      wells      are      presently      functioning      as      on      Aug,      95. Tn       the       Melka       Sadi       and       Amibara       areas,       all       observation       wells under      AIP      II      which      have      subsequently      been      damaged      should      be repaired or reinstalled and returned to use.
2.2 Review of Previous Studies
Italconsult,  during  the feasibility  study  of the Melka Sadi -Amibara area in  1969,  had  indicated  the presence of a trough  in  the water table on  the eastern  side of the Awash alluvial plain.  On  either side of this trough,  higher water table elevations were observed,  indicating  some recharge from the river and  from the hills bordering  the plain.  The alluvial plain  was believed  to  consist of a very  deep  and  uniform interbedded  sequence of silt,  sandy silt and silty sand.
6TABLE 1 - NUMBER OF OBSERVATION WELLS/PIEZOMETERS INSTALLED BY INDIVIDUAL ORGANISATIONS AND IDENTIFYING CODINGS
Organisation Which Installed observation Wells/ Piezometers
ILalconsult
Identifying Code
Number Installed
PPI,PP5 etc 4
P2,P3 etc 10
DW-ljDW-2 2
Remarks
Deep piezometric well (50 m)
Shallow piezometric well (15 m)
Deep  piezometric
well (100 m)
Awash Valley Authority (A.V.A.)
Wp Wj etc
4
No      information 
on
installation 
depths
available
Sir William lialcrow & Partners
Foraky S.A
ABS 1.2. etc
15
Piezometers
installed 
by Foraky S.A
Amibara Project
Irrigation 11
AIP 1.2 etc                       67
Piezometers installed to variable depths depending on position of water table.
AIP 3/1,3/2,3/3, 
10/1,10/2,10/3, 
etc.
15
Piezometers installed to variable depths
observation wells
AIP3, AIP 10 etc at a
distance of about 5m
each.
7TABLE 2. STATUS OF OBSERVATION WELLS/PIEZOMETERS AS ON AUGUST, 95
Observation/
Piezometer Type
Reference Number
No. of
Wells
StutUS
Italconsult
DW-l,DW-2
PPI,PP2,PP5,PP14 P1,P2,P9,P11
P3,4,6,7,8,10,13
2 
Not known
4 
Not    Functionil
4 
Functioning
7 
Not    Function:
or Not known 1
Awash Valley Authority (A.V.A)
WpWj
4
Sir     William     Halcrow
&. Partners
Foraky S.S
ABS1 to ABS 15
15 
Not Known
Amibara Irrigation
Project II
AIP 4 >9,13,15.20,26, 31,33,36,38,48,53, 
17
56,57,58,59,66 Rest AIP 1 to AIP 67 
50
Destroyed-0
of use
Functioning.
8Sections showing the piezometric grudient of the ground
water          were          plotted          by          Italconsult          which following:
indicated
the
(i)        A        low        hydraulic        gradient        towards        the        river        in        the Melka Sadi area.
ii)              A      low      hydraulic      gradient      away      from      the      river      in      the Amibara area.
iii)             A      hydraulic      gradient      of      about      .1%      in      a      southwest      - northeast direction across the Melka Sadi - Amibara
area.
It was also essentially response to evapotranspiration,
concluded         by         Italconsult         that         the         aquifer         was
without inflow
flow, varying in vertical sense in
from precipitation and outflow by 
♦s
velocity) is of the order of 10 permeability measuremets.
Q
as groundwater flow velocity(Darcy m/sec based on horizontal
Subseque
nt
studies
on 
geom
orphic, 
geol
ogical
and 
ground 
water
studies
in 
the
Awash 
Valley 
by 
FAO
indicated 
the
possible
exis
tence
of
two 
sets
of
aquifers
below
the
Amibara Plain.  The deeper,  unconfined  aquifer occupying gravel beds interbedded  with  lavas and  shallow aquifers of variable depth  occurring  in  alluvium above the combined aquifers,  recharged  by  rainfall,  floods,  the river and  from irrigation.
In  1975,  15  more piezometers were installed  for
hydrogeological feasibility 
investigations
during 
the               Angele-Bolhamo 
study.                 Hydrogeological
investigation 
largely 
confirmed the findings of Italconsult.
Drainage and  salinity  studies
of             Amibara            Irrigation 
I
I
Project-II          carried          out          by          Halcrow,          1982          indicated          the existence of perched water tables within 1 to 2m of the
9surface           in           Melka           Sadi           area           with           locally           artesian conditions.
Halcrow in  1985,  during  the study  of Master Drainage Plan for Melka Sadi and  Amibara areas,  carried  out analysis of the available piezometric data for the wells in  the study area.  They  identified  a total area of 3,844  ha ( 2,247  ha in Melka Sadi and  1,597  ha in  Amibara) as immediate priority area and  a total area of 7,990  ha (4,093  ha in  Melka Sadi and  3,897  ha in  Amibara area) as the next priority  area within  next 5  years,  based  on  the ground  water depths of 3m and  3  to  6  m respectively.  The findings as indicated  above were however stated  to  be indicative of ” the changes likely  to  take place rather than  a definititive statement and  should  be the subject of revisions as more data becomes available”.
Based on the ground water level hydrographs, they observed:
(i)              Sustained      overall      groundwater      rise      of      the      order      of      lm
per year
(ii)              The       aquifer       appears       to       be       responding       in       a       vertical sense to deep percolation losses.
The           piezometric           cross-sections           based           on           May,84           data indicated the following:
a)                The      piezometric      surface      slopes      towards      the      Awash      river with     a     gradient     in     the     range     of     1     in     400     to     1     in     900 in the Melka Sadi area.
b)                The       piezometric       surface       slopes       away       from       the       river, with     a     gradient     of     1     in     400     to     1     in     700     in     Amibara area.
10
.--2.3 Review of the Available Data
The monthly  piezometric observation  data of groundwater depths below absosute zero  of the piezometer and  electrical conductivity  below absolute of ground  water samples
collected        from        the        observation        wells        were        collected        for        79 
wells in  Melka Sadi and  Amibara areas for the period  from August,1980  to  August,1995,  with  some missing  data gaps. Table 3  gives the details of wellwise data availability  and the missing  data.  From Table 3,  is observed  that almost continuous data for a reasenably  long  period  are available for only  58  wells out of 79  wells.  These wells are located in  areas A &.  C (Phase I),  areas B & D (Phase II) and  area E  (Phase III) but with  no  well in  Area F of phase II,i.e Amibara-Angelele area,  where recent data are not available. As per recommendions of the Inception  Report accepted  by the client,  the area F Amibara-Angelele has been  excluded from the present study.
2.4 Analysis of Data
The consultant in the feasibility study of Melka-Sadi- Amibara Irrigation Project by Italconsult in July, 1969, concluded that the flood plain aquifer, with horizontal permeabilities of 10^m/day, was essentially without flow. The sedimentary materials are consistently fine-grained and characterised by a low horizontal permeability, so that
they appear to form an aquifer that is essentially without flow. Aquifer type responses is mainly the result of inflow from rainfall and irrigation and outflow by evaporation. Such behaviour precludes the use of deep disposal methods for lowering the water table.
It was further concluded that with ground flow velocities (Darcy’s velocity) in the order of 10’*m/sec (based on horizontal permeability measurements), the aquifer was essentially without flow varying in a vertical sense in response to inflow from precipitation and outflow by evapotranspiration.
11
iTABLE 3 - WELLWISE DETAILS OF DATA AVAILABILITY
Sheet 1 of 2
s.
NO
WELL
NO
GROUND WATER DEPTH
ELECTRICAL CONDUCTIVITY
AVAILABILITY FROM TO
FULL MISSING
YEAR
AVAILABILITY FROM TO
FULL WUSKING
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Al P-1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
8/80-95
8/80-95
8/80-95
10/80-6/90
8/80-95
8/80-95
8/80-95
8/80-95
8/80-11/91
8/80-95
8/80-95
10/80-95
8/80-9/82
8/80-95
8/80-10/91
8/80-95
8/80-95
8/80-95
8/80-95
8/80-1/95
8/80-95
8/80-95
11/83-95
2/84-95
2/84-95
2/84-94
11/83-95
2/84-95
2/84-95
11/83-95
5/84-2/85
10/80-95
8/80-12/83
9/80-95
8/80-95
8/80-1/89
8/80-95
8/80-6/90
8/80-95
11/83-95
8/80-95
8/80-95
2/84-95
8/80-95
8/80-95
10/80-95
8/80-95
8/80-2/95
8/80-5/95
10/80-95
1984-92
1982
1984
8/80-95
8/80-95
8/80-5/95
10/80-6/90
8/80-95
8/80-95
8/80-95
8/80-11/92
8/80-11/91
8/80-95
8/80-95
10/80-95
8/80-9/82
8/80-95
8/80-10/91
8/80-95
8/80-95
8/80-95
8/80-95
8/80-1/95
8/80-95
8/80-95
6/84-95
6/84-6/93
6/84-8/92
8/84-1/93
7/84-95
6/84-95
6/84-95
1/85-6/91
6/84-1/85
10/80-95
8/80-11/82
10/80-95
8/80-95
8/80-1/89
8/80-95
8/80-10/87
8/80-9/89
3/85-95
8/80-95
8/80-95
8/84-95
8/80-95
8/80-12/94
10/80-95
8/80-95
8/80-2/95
8/80-2/92
10/80-95
1984-92
1982
CM*
12TABLE 3 - WELLWISE DETAILS OF DATA AVAILABILITY
Sheet 2 of 2
s.
NO
WELL
NO
GROUND WATER DEPTH
ELECTRICAL CONDUCTIVITY
AVAILABILITY FROM TO
FULL MISSING
YEAR
AVAILABILITY FROM TO
FULL MISSING
YEAR
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
PPI
Pl
P2
C5
P8
P9
PIO
Pll
PP5
P13
PP2
PP9
8/80-95
10/80-95
8/80-1/88
10/80-95
10/80-95
No Data
10/80-4/91 1/85-11/89
No data
10/84-95
6/84-95
10/84-95
10/84-95
11/84-95
11/84-95
2/84-4/91
11/84-95
11/80-12/87
2/82-95
10/80-95
10/80-3/82
11/83-3/86
10/80-95
10/80-11/82 10/80-95
3/82-9/82
11/83
6/84-10/84
1/85-12/85
8/80-95
10/80-95
8/80-1/88
10/80-95
10/80-95
No Data
10/80-4/91
1/85-11/89
No data
10/84-95
6/84-95
10/84-95
10/84-95
11/84-8/93
11/84-95
11/84-4/91
11/84-6/94
12/80-11/84
1/85-7/95
10/80-95
10/80-3/82
1/85-6/85
10/80-95
10/80-11/82
10/80-95
3/82-9/82
No data
6/84-10/84
No data
»
Note :
(i) There are no Electrical Conductivity observations from Dec, 1982 to May, 1984.
(ii)       No observations are available for any of the wells in water depth and EC for the following periods :
a)            1981 -     July, August &. October.
respect of ground
b)            1982 -
January, April, July, August, October  & December
c)
1983 -
January to October
d)
1984 -
March for Groundwater depth
e)
1991 -
May & June
f)
1992 -
September
(iii)
In
addition
to the above missing data, there are
monthly data gaps in
the
case of
individual wells .
13Under such  trying  circumstances,  the mathematical model which  is to  reproduce the ground  water situation  at the regional scale,  would  not be sensitive enough  to  reproduce the seasonal variation  owing  to  changes in  hydrological parameters.
Therefore,  the available data of groundwater depth  were analyzed  primarily  to  delineate the area of immediate priority  for the subsurface drainage and  a further analysis
was       carried       out       to      predict      the      groundwater      depths      5,10      &.      20 
years         and         examine         the         nature         of         vertical         movement         of groundwater within aquifer.
The reassessment of the area needed  to  be included  in  the Phase II had  been  recommended  in  the Master Drainage Plan 
itself       as       per       the       following       extract       from       para       4.6,       page       40 
of Final Report July 1995.
”4.6 Guidelines for the Evaluation of Future Stages of
Development
The          timing          of          implementation          of          future          stages          of
subsurface
drainage             development
shall
be
directly 
related  to  the projected  rate of encroachment of high 
watertables.  Early  implementation  of such  work,  where
high  watertables are not imminent,  would  result in  a
low return  on  investment.  Conversely  an  excessively 
delayed  implementation  could  result in  lost production 
and  the need  for reclamation  of the resulting 
saturated 
land.             Delayed             implementation             could             also 
exacerbate the difficulties and cost of laying down at
14depth 
far
below
the
prevailing               watertable, 
particularly  in  areas of silts or very  fine sands where saturated  conditions under such  water pressures could induce instability.
A         systematic         approach         is         required         based         on         both monitoring         and         the         evaluation         of         results         leading         to the         timely         planning         and         implementation         of         subsequent stages of subsurface drainage."
2.4.1 Regression Analysis of Groundwater Data
Regression  analysis of the data of all the 58  wells, irrespective of the location  of the well in  phase I,  phase II and  phase III area,  for which  long  term data were available,  was carried  out to  fit the best fit curve.  As the groundwater depth  varies between  maximum and  minimum values in  the year,  the regression  was carried  out separately  for the annual maximum and  the minimum groundwater depths.  These annual maximum and  minimum groundwater depths were plotted  for each  year on  same plot and  type of regression,  linear (straight line) or non linear (log  curve),  was selected  on  the basis of the configuration  of the plot.  The regression  equation  so derived  was also  used  for the prediction  of the future annual mean  groundwater depths after 5,10  or 20  years
(years 2001, 
2006,       2016 ) .
Similar regression analysis was also carried out for
the EC data of water samples from each well.
Plots of maximum &.  minimum groundwater depths and  the mean computed  depth  are shown  in  Appendix  1  for each  well. Similar plots for EC are shown in Appendix 2.
152.4.2 Depth to Groundwater Contour Map
The        groundwater        depth        contour        map        for        the        August        1995 
available data (in  case no  data of August was available for a particular well then  data of previous available month,  was used) was prepared  to  identify  the areas of immediate priority.  The area of immediate priority  was taken  as the area where groundwater depth  is within  3  meters of the ground  surface.  As the groundwater depths are available below the absolute zero  at the top  of the piezometer, generally  about 30  cm above ground  level,  a contour of 3.30m was drawn  to  represent the groundwater depth  of 3m below the ground level.
2.4.3          Identification                  of Priority Area of Phase II
To  work  out the priority  areas,  the areas enclosed  within the contour of 3.30m were rationalized,  so  that full plot through  which  the contour is passing,  was considered  as the boundary  of the priority  area.  Fig  1  shows the priority area based  on  August 95  ground-water depth  contour map. 
The areas so  worked  out are given  below in  Table 4. Although  areas B,  D & F were to  be covered  in  the study  as per terms of reference,  the portions of area E also  with groundwater less than  3  m below the surface have been  shown in the Table 4.
Out of the total area of 1,550  ha in  Area B of Melka Sadi Area,  as per Table 4  above,  total 984  ha is proposed  to  be
included        as        priority        area        under        the        present        study        and 566      ha      excluded      from      the      study.      Out      of      this      566      ha,344      ha is        excluded        because        it        is        already        provided        with        sub-surface drainage         system         under         Phase-I.         The         balance         222         ha         is proposed       to       be       excluded       due       to       low       groundwater       table.       The areas        which        are        not        considered        for        inclusion        lie        in        the northwest part of Area B, where the depth of groundwater
16below the surface is more than  3m.  The neighbouring  wells in  this part of Area B,  namely  AIP 11,  AIP 16  and  AIP 19 have all a falling  trend  of groundwater vide Table 6  and hence the areas proposed  to  be excluded  from priority  under phase II,  do  not seem to  have any  possible high  groundwater level in future as per the present trend.
TABLE 4 - PRIORITY AREAS DELINEATED BY DEPTH TO GROUNDWATER CONTOURS (PHASE II)
Location
Area
Zone
Priority
Area (ha)
Remarks
Melka Sadi
B
B
A
A
B
-
Amibara
D
D
E
F
C
D
-
-
520
464*
38
Negligible
1552
1400
-
Western part of B
Eastern part of B Phase-I area where laterals have not
been provided
North Western
Zone of D
South Eastern
Zone of D
-
GWL considerably below surface as
per old records
Total
3974 
-1 2
* Excluding part of Area B already//dpv
The total area of
has been excluded
950 ha of area
ed under Phase-I
f 'Termss, of Reference
from the priority area of Phase  II, as
7
proposed client.
in the
Inception
The main         reason for
that        past        data        indicated        the
14m below surface,
there
17
Report and accepted by the the exclusion of area F were
groundwater level to be about were no tangible irrigatedagriculture       in       the       area       and       much       of       the       land       has       soil characteristics not favourable for sub-surface drainage.
The Area D has a total area of 3,050  ha,  out of which  as per Table 4  above,  1,552  ha is to  be included  under priority  area of Phase II.  The area proposed  to  be included  lies in  the south  eastern  part of Area D.  On  the other hand,  in  the Zone C in  the northwest of area D,  the groundwater level is more than  3  m below the surface,  and in  general the trend  is of falling  groundwater level.  In general the change in  the trend  of variation  in  groundwater level occurred  in  the year 1989-90.  The pumped  irrigation in  the area started  diminishing  since 1992-93  and  hence the trend  of falling  groundwater table cannot be attributed  to be solely due to the reduction of irrigated area.
The aforesaid  change in  the trend  seem to  be similar to  the gravity  irrigated  areas,  where the change in  trend  occurred 
on           introduction           of during the period 1989-90.
irrigation           through           alternate           furrows
It
is,         therefore,         debatable         as         to         whether         the         present
falling  trend  of groundwater level in  the zone C of area D
will reverse on  reintroduction  of pumped  irrigation  in  this
zone in  the coming  years.  Even  conceding  that there could 
be a change in  the trend  of falling  groundwater level on 
reintroduction            of            extensive            pumped 
irrigation, 
it
is
evident that it will take considerable time to  reach  the critical groundwater depth  of 3m below the surface.  It is found  that the observation  well readings in  1995  in  this zone are comparable with  readings during  1985  and  in  the Master Drainage Plan  1985  on  the basis of these readings it was concluded  that this zone did  not need  immediate subsurface drainage.  Hence there is every  justification  to exclude this zone from the priority area of Phase II.
18As per terms of reference,  the area E of 2,340  ha is not to be covered  under the present study.  However,  as per clients request,  the groundwater levels in  area E  were also studied  and  it was found  that a substantial area of 1,400 ha of area E  has grounwater level less than  3  m below surface and  this area is in  continuat-ion  of the priority area of Area D.  Hence,  the 1,400  ha of Area E  could  also be included under priority area of Phase II
2.4.4          Groundwater Salinity Contour Map
Groundwater salinity measurements are based on the
determination of the electrical conductivity of water
samples collected from the observation wells. The
availability  of EC data of groundwater wellwise is shown  in Table 3.  The continuous observation  of EC is available from June, 1984 onwards for almost all functioning wells.
Groundwater salinity  contour map  has been  prepared  for the August 1995  EC values (Fig  2).  From the map  it is
observed       that       EC       values       varies       in       the       range       of       4       to       12 
mmho/cm in  Melka Sadi area.  In  Melka Sadi Phase - II area, EC values varies in  the range of 4-8  mmho/cm.  In  Amibara area, EC values varies in the range of 2 to 12 mmho/cm.
2.4.5         Groundwater Contour Level Map
Groundwater levels for each well for August, 1995
were computed  by  subtracting  groundwater depth  below absolute zero  from the absolute zero  value of the corresponding  well.  Ground  water contour map  (Fig  3) for Aug  1995  levels was then  developed  to  study  the predominant flow directions.  In  the immediate vicinity  of Awash  river, the observation  well network  is such  that accurate positioning of groundwater contours was not possible.
19Therefore,  contours were not extended  upto  the river as it could  not be identified  definitely  as to  whether the river acts as a source of groundwater recharge or as a sink  for groundwater release.
From the groundwater contour map  (Fig  3),  it is observed that the groundwater gradient direction  is mainly  from the southern  part of the eastern  dyke towards the northwest part of the river dyke in the Melka Sadi area.
In  Amibara area,  from the groundwater contour map,  a hydraulic gradient line,  generally  parallel to  the eastern dyke can  be traced  as a minor trough,  almost from the southern  end  to  the northern  end,  water table on  east and west of which  are higher.  A low ground-water zone like a sink  can  be located  around  observation  well no.  AIP 63  in the Amibara Settlement Project Area.  The hydraulic gradient line of ground-water slopes towards this sink  both from river side in  the south  and  west as well as from the land  side on  the east and  north.  Unlike Melka Sadi area,  in the Amibara area,  there is no  general slope of the groundwater towards the river.
2.4.6           Observation Well Hydrographs
As         already         mentioned         in         section         2.4.1,         observation         well hydrographs       were       drawn       for       the       annual       maximum       and       minimum groundwater        depth        and        groundwater        EC        values        to        analyze        the variation       of       the       groundwater       depths       and       EC       values       from       year to       year       and       also       to       carry       out       regression       analysis       for       the
prediction          under          future          scenarios.          The          hydrographs          for          58 
wells,  for which  long  term data from 1980  to  1995  were available and  regression  analysis carried  out,  have been 
shown       in       Appendix       1       for       groundwater       depth       and       Appendix       2 
for groundwater EC values.
20From the observation  well hydrographs,  it is observed  that for 42  number of wells,  groundwater depth  is increasing  or groundwater level is having  a falling  trend.  For most of the wells the falling  groundwater trend  has started  from the year 1989/90.  In  case of EC values,  20  number of wells show the falling  trend  of groundwater salinity.  Areawise details of wells showing  rising  or falling  groundwater trend is given in Table 5.
The change in  the trend  of groundwater level variation  from 1989/90  onwards in  most of the cases of Appendix  1  may  be
attributed           to           the           changes
in           the           irrigation           practices
introduced  during  this period  by  supplying  water to 
alternate furrow instead  of each  furrow,  thereby  reducing 
the total quantity  of irrigation  water supplied  and  to  some
extent also  due to  area being  not cultivated.  The yearwise
quantity           of
irrigation           water           supplied           offtakewise           along 
with  area irrigated  are reviewed  in  Annex  12,  dealing  with Data on  Agricultural Aspects.  From this,  it is observed that in  recent years,  total water applied  per hectare has reduced,  which  seems to  be one of the main  reasons for falling  groundwater trend.  This is discussed  in  more detail in Annex 12.
From the items A3  and  B7a of Table 5,  it can  be seen  that in  Phase I areas,  almost all the observation  wells show falling  groundwater level trend,  indicating  that the sub surface drainage provided  under Phase I are proving e f fect ive.
2.4.7         Piezometric Sections
In          the          Master          Drainage          Plan          (Halcrow,1985),          piezometric
section,             approximately             perpendicular
to 
the             groundwater
contours           and           intersecting           selected           observation           wells           were plotted for both Melka Sadi & Amibara areas (Fig 4 & 5)*
21TABLE 5 - NUMBER OF WELLS SHOWING RISING OR FALLING GROUNDWATER TREND
s.
No
Area 8c Zone
Number of
Wells    With    GW Trend
Well No.
Rise-
ing
Fall
ing
A
1
2
3
Melka Sadi
Zone A of Area B
Zone B of Area B
Other Area
a) Phase I
3
1
1
5
1
16
B
4
5
6
7
*
b) Outside Phase I&II
Anibara
Zone C of Area D
Zone D of Area D
Zone E of Area E
Other Area
a) Phase I
b) Outside Phase II
1
AIP 5,9,11,30
AIP 18,19,20,21,
22, PP1/P1
AIP 2,3,6,7,8. 
10,12,14,17,23, 24,25,26,27,28,
29, Pll
AIP 16
3
-
5
2
8
2
1
7
1
1
AIP 44, 49, 
55,62, P9
AIP 34,35,37,
41,42, 43,64,65
AIP 46,47,50,51 
52,54,67
AIP 32,39,40,45,
60,61, 63,P2
AIP 48,57
Total
15
43
22based       on       May       1984       observat       ion       wells       data       with       river       bed 
levels            based            on            available            topographic            surveys,            Identical
piezometric
cross-sections              were
taken              from              groundwater
contour        map        discussed        in        section        2.4.5        and        superimposed        on Figure 4 & 5.
The        following        observations        can        be        made        from        the        piezometric cross-section :
(1)         In         Melka         Sadi         area,         the         piezometric         surface         slopes towards        river        Awash        with        a        gradient        approximately        in the     range     of     1     in     600     to     1     in     2500     along     the     selected cross-sections.
With  the assumed  average depth  of 6  m above bed  level at Melka Warer site for August for the flood condition,  the ground  water flow direction  will be away  from the river and  positive head  is available for recharge from river to groundwater.
(ii) In Amibara area, the piezometric surface slopes away from the river along section D-D and section F-F with a gradient in the range of 1 in 600 to 1 in 1000. Along section EE, the piezometric surface slopes from southern side (eastern dyke side) towards river on northern side.
2.5 Perched Water Tables
Within the Melka Sadi area, the possibly-existence perched water tables, separated from true deeper ground water by an impermeable layer of varying thickness was noted in previous studies on Drainage & Salinity of AIP II carried out by Halcrow (1982). The field soil survey conducted by Halcrow (1985), while preparing Master
r.f
'
Drainage Plan of Melka Sadi &. Amibara areas, has indicated 23that the relatively  impermeable layer was such  that perched 
water tables extending  over a considerable area exists in 
Melka Sadi area.  In  Amibara area occurrence of perched 
water table was indicted  to  be of very  limited  extent. 
Relatively  impermeable layer was defined  as one whose
hydraulic conductivity  is less than  ten  times that of the
soil
horizon            immediately            above            irrespective            of            soil
textural group. 
In a highly stratified soils the
relatively impermeable layer can be readily identified 
as a compact layer of silty clay or clay of considerable
continuous lateral extent.
The detailed  soil survey  of the identified  priority  areas in  Melka Sadi and  Amibara was also  carried  out by  the consultants! the detailed  description  of which  is given  in Annex  4  dealing  with  Soil Survey/Soil Classification data/Analysis.  The field  soil survey  has indicated  the existence of perched water table as discussed in Annex D.
2.6        Prediction of Future                       Groundwater Depths and EC
As already  mentioned  in  section  2.4.1,  regression  analysis was carried  out for all the 58  wells for which  long  term data were available,  irrespective of whether the well is located in phase- II area or outside it.
The regression  analysis was carried  out for both groundwater depth  as well as groundwater EC values.  Based on  the regression  equation,  predictions were done for a period  of 20  years hence( ie upto  2016.  The extrapolation was terminated  either at 20  year or when  the predicted depth  to  ground  water reaches near surface or EC values become almost zero.
Table        6        shows        the        mean        predicted        groundwater        depths        for
each well for the years 1996, 
2001,       2006,       2011 and 2016.
24TABLE 6 - PREDICTED FUTURE GROUNDWATER DEPTHS BELOW ABSOLUTE ZERO
s.
No
Well
No
Absolute
Zero 
Value
(■)
GW Depth for the Year (■)
Area
Location
1996
2001
2006
2011
2016
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
42
44
Al P-2 
”   -3 
"   -5 
”   -6 
"   -7 
”   -8 
”   -9 
"   -10 
"   -11 
”   -12 
"   -14 
”   -16 
”   -17 
"   -18 
”   -19 
"   -20 
"   -21 
”   -22 
”   -23 
"   -24 
”   -25 
”   -26 
"   -27 
"   -28 
"   -29 
"   -30 
"   -32 
"   -34 
"   -35 
”   -37 
"   -39 
”   -40 
"   -41 
"   -42 
"   -43 
”   -44 
"   -45 
”   -46 
" -47
"   -48 
”   -49 
"   -50 
"   -51 
” -52
743.82 
743.60
741.42 
744.40 
740.96 
740.996 
739.89 741.233 739.89
738.64
742.32 
739.20
739.83
741.48 
738.94 
738.75 
737.30 
737.72
740.58
740.12
740.26 
741.03 
746.09
744.58
742.65
735.53
735.48
734.12 
733.52 
733.44
732.66 
732.56 
731.64
731.43 
732.09
730.26
731.33 
730.15
735.875
729.13 
728.74 
727.86
730.14
2.77
2.17 
2.44 
2.47 
3.73 
4.86 
0.80 
3.30 
4.42 
3.71
3.18
7.94 3.22 
3.06 
4.07
3.23
3.77 
2.52 
3.65
3.85
5.19 5.05 3.01 3.63 
4.09
1.49
6.86 
3.38 
2.61
2.23 
7.32 
5.79 
6.21 3.13 
2.5
5.49
5.64 
4.91 
2.11
3.20 
2.35
3.95 
3.16
7.24
4.1 
2.43
2.41 
2.26
4.96 
5.99 
0.36 
3.90
5.74
5.97 
4.24
11.39
4.39 
3.58 
4.63 
3.90 
4.88 
2.71
4.97
4.85
7.65
7.51 
2.68
4.98 
5.61
1.65 
8.87
4.33 
3.3
2.29
7.42
8.21
9.60
3.85
2.74
7.39 
8.45
6.42 
0.36 
(1998)
2.21
1.60
5.52
0.13 
5.28
5.43 
2.70 
2.38 
2.05
6.79
7.12 
0.16
4.49 
7.06
8.23 
5.3 
14.84
5.57 
4.10 
5.18
4.57
5.98 
2.90 
6.29 
5.85
10.12
9.97 
2.34
6.33 
7.13
1.80
10.89
5.28
3.99
2.34 
7.53
10.63
12.99
4.58
2.99
9.29 11.25 
7.93
1.23 
1.09 
7.08
3.31
6.76 
2.96
2.35
1.84
7.42 
8.24 
0.08 
5.09
8.38 
10.48
6.36
18.29 
6.75
4.62 
5.74
5.23 
7.09 
3.09 
7.61
6.85 
12.58 12.42 
2.01
7.68 
8.65
I. 95 
12.91
6.23
4.68
2.39
7.63 
13.05 16.37 
5.31
3.23 II.   18 14.06 
9.45
0.32 
0.75 
£.64
1.35
8.09 
3.23 
2.31 
1.63 
8.65
9.37 
0.04
5.69
9.70
12.74
7.41
21.74
7.92 
5.14 
6.29 
5.90 
8.20
3.28
8.93 
7.85 
15.05 14.88 
1.68 
9.04 
10.17
2.10
14.92 
7.18
5.37 
2.44
7.74 
15.47 19.76 
6.03 
3.48 
13.08
16.87
10.96
0.52
10.21
A
A
B
A
A
A
B
A
B
A
A
B
A
B
B
B
B
B
A
A
A
A
A
A
A
B
C
D
D
D
C
c
D
D
D
D
C
E
E
Outside
D
E
E
E
25TABLE 6 - PREDICTED FUTURE GROUNDWATER DEPTHS BELOW ABSOLUTE ZERO
s.
No
Well
No
Absolute
Zero Value
(■)
GW Depth   for the       Year (■)
Sheet  2 of 2                   n
1996
2001
2006
2011
Area
Location
2016
45
46
47
48
49
50
51
52
53
54
55
56
57
58
A1P-54 
“   -55 
11    -57 
"    -60 
"    -61 
"    -62 
"    -63 
"   -64 
"    -65 
"    -67 
" -Pl ’’ -P2 ” -P9 
” -Pll
728.30
726.99
726.17 
735.02 
731.03 
728.14
734.52
732.96
733.26
729.83
738.27
735.55
728.27
741.96
9.39 
4.87 
4.68
3.91
3.92 
3.89 12.23 
2.81
5.79 
4.37 
3.97 10.73 
5.46
3.32
7.20 
6.36 
3.04 
1.14 
5.35 
5.34 
16.38 
3.57 
8.9 
6.23 
2.88
14.11 
5.3 
4.77
5.02 
7.84 
1.99
6.77
6.79
20.53 
4.32 
12.02
8.09
1.79 
17.49 
5.14 
6.22
2.84 
9.32
1.30
8.2
8.23
24.67 
5.07 
15.14 
9.96
1.31 
20.86
4.99
7.67
0.87 
10.8
0.86
9.62 
9.68 
28.82
5.82
18.26
11.82
0.91
24.24
4.83 
9.11
E 
b 
outside
C
C
D
C
D
D
E 
B
C
D
A
n
ii
ii
li
26TABLE 7 - PREDICTED FUTURE EC VALUES
I S.
No
Well
No
Absolute
Zero Value
(■)
EC Value for the Year (aaho/Ca)
1996
2001
2006
2011
2016
Sheet 1 of 2
Area Location
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
Al P-2
” -3
" -5
” -6
" -7
" -8
" -9
" -10
" -11
" -12
" -14
" -16
” -17
” -18
” -19
” -20
" -21
" -22
" -23
” -24
” -25
" -26
” -27
” -28
" -29
” -30
" -32
” -34
" -35
" -37
” -39
" -40
" -41
" -42
" -43
" -44
" -45
" -46
" -47
" -48
” -49
" -50
743.82
743.60
741.42
744.40
740.97
740.996
739.89
741.233
739.89
738.64
742.32
739.20
739.83
741.48
738.94
738.75
737.30
737.72
740.58
740.12
740.26
741.03
746.09
744.58
742.65
-
735.53
735.48
734.12
733.52
733.44
732.66
732.56
731.64
731.43
732.09
730.26
731.33
730.15
735.875
729.13
728.74
1.87
2.37
4.80
3.44
13.72 18.56 29.43
7.66
8.27
5.39
6.8
8.66
1.95
10.10
7.22
1.54
6.62
12.92
7.11
1.30
2.23
1.59
7.25
5.23
15.97
2.21
5.44
2.97
5.41
4.04
28.42
7.41
6.15
10.85
7.94
12.36
2.21
5.41
10.15
3.38
5.68
9.11
2.24
2.91
5.56
4.04
11.99
26.56
36.03
9.33
10.88
8.55
7.98
10.13
1.89
11.13
7.22
10.0
6.68
13.88
7.02
0.69
2.68
1.92
8.27
7.08
23.37
2.73
7.36
2.93
0.62 
(2000)
4.68
39.05
9.83
5.43
8.65
9.38
7.37
2.67
0.39 
(1998)
9.46
2.31
1.16
(1999)
4.57
2.62
3.45
6.33
4.65
10.26
34.55
42.63
11.00
13.49
11.71
9.16
11.59
1.83
12.17
7.22
-
6.75
14.85
6.93
0.76
3.14
2.25
9.29
8.93
30.77
3.26
9.28
2.89
-
5.33
49.69 12.25
4.71
6.45
10.82
3.32
3.14
-
8.76
2.51
-
1.33
2.99
3.99
7.09
5.25
8.52
42.55
49.24
12.68
16.10
14.87
10.34
13.06
1.77
13.20
7.22
-
6.81
15.82
7.02
0.83
3.59
2.59
10.3
10.79
38.17
3.78
11.2
2.88
-
5.98
60.32
14.66
4.31
4.25
12.26
0.84
3.60
-
8.06
2.72
-
0.69
3.37
4.53
7.86
5.86
6.79
50.55 55.84
14.35
18.71
18.03
11.52
14.52
1.71
14.24
7.22
-
6.88
16.79
8.17
0.90
4.04
2.91
11.3
12.64 45.57
4.30
13.11
3.01
-
6.62
70.96
17.08
4.51
2.05
13.7
—
4.07
-
70.36
2.93
-
0.36
A
B
A
A
A
B
A
B
A
A
B
A
B
B
B
B
B
A
A
A
A
A
A
A
B
C
D
D
D
C
C
D
D
D
D
C
E
E
Outside
D
E
27TABLE 7 - PREDICTED FUTURE EC VALUES
Sheet 2 of 2
s.
No
Well
No
Absolute
Zero 
Value (■)
EC Value for the year (anho/ca)
Area
Location
199G
2001
2006
2011
2016
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
Al P-51
"    -52 
"    -54 
"    -55 
’   -57 
"    -60 
”   -61 
”    -62 
11    -63 
"    -64 
”    -65 
"    -67 
" -Pl ” -P2 ” -P9 
" -Pll
727.86
730.14
728.30
726.99
726.17 
735.02 
731.03
720.14
734.52
732.96
733.26
729.83
738.27
735.55
728.27
741.96
8.73
6.84
6.66
3.33 
34.48 
3.63 
5.92 
6.42 
5.18 
3.69 
4.55
1.34
3.44 
3.9 
2.88
7.47
1.51
4.47
7.82
3.86
43.9
3.46 
8.14
8.48 
5.37 
3.72 
5.04 
0.52
4.48 
3.41
0.42
5.49
0.1 
(2004)
2.1
8.98 
4.39 
53.26 
3.29 
10.36 
10.55 
5.56 
5.08 
5.54 
0.19
5.51 
4.11 
0.13 
(2003)
3.51
0.47
10.15 
4.93 
62.66 
3.12 
12.58 
12.61
5.75 
6.43 
6.03 
0.05 
(2008)
6.54 
4.81
1.52
0.1 
(2013)
11.31 
5.46 
72.05 
2.95 
14.8 
14.68 
5.94 
7.79 
6.53
7.57 
5.51
0.92
E
E
E
D
outside
C
C
D
C
D
D
E
B
C
D
A
20Table 7  shows the mean  predicted  EC values for the same years.  Based  on  the above predicted  values,  contour maps have been  prepared  for the years 2001,  2006,  2011  and  2016 for groundwater depths (Fig  6  to  9).  Prediction  for future years has been done on the present trend and the assumption
that similar trend will continue in future also.
2.6.1         Rate of Expected               Rise in Groundwater
Out of the 58  number of wells in  Table 6,  only  14  number of wells have indicated  a trend  of rise in  groundwater level and  the remaining  44  number of wells have a trend  of falling groundwater level.
Thus only  24  percent of the wells have a trend  of rising groundwater level.  In  Table 8  the annual rate of rise in groundwater level have been  worked  out which  is maximum 0.88  m/year,  minimum 0.01  m/year and  average 0.29  m/year. This finding  is considerably  different from the assessment made in  the Master Drainage Plan  1985  where it was assessed that the overall rate of rise in  groundwater level shall be lm/year.  This modified  rate of rise in  groundwater level means that areas,  where the groundwater is at 3  m below the surface and  there is a rising  trend,  in  general the groundwater level shall attain  a critical depth  of 2m below the surface in  a period  of 3  to  4  years.  With  the experience of the time needed  to  complete the implementation  of the Phase I which  has an  area comparable with  Phase II area,  it would  be reasonable to  consider area with  groundwater level upto  3m below the surface,  as the priority area.
2.6.2 Groundwater Depth
From the groundwater depth contour maps it   is observed that 29TABLE 8 PREDICTED RATE Ob' RISE OF GROUNDWATER LEVEL IN WELLS HAVING RISING
Well  No
Ground Water depth for the
year
1996
2001
Rise in Ground Water level in 
5 years
(■)
Annual
rate of
rise
■/year
A1P    5
A1P    6
Al P    9
Al P  27
AIP  47
AIP  48
AIP  49
AIP  51
AIP  52
AIP  54
AIP  57
AIP  60
P1
P9
2.44
2.47
0.80
3.01
2.11
3.20
2.35
3.16
7.24
9.39
4.68
3.91
3.97
5.46
2.41
2.26
0.36
2.68
0.36
2.21
1.60
0.13
5.28
7.20
3.04
1.14
2.88
5.30
0.03
0.21
0.44
0.33
1.75
0.99
0.75
3.03
1.96
2.19
1.64
2.77
1.09
0.16
0.01
0.04
0.09
0.07
0.88
0.20
0.15
0.61
0.39
0.44
0.33
0.55
0.22
0.03
Total
4.01
Average
0.29
30most of the area in  Melka Sadi,  which  at present have groundwater at 3  m below ground  will have prog-ressively increasing  groundwater depth  from year to  year.  In  case of Amibara area also,  areas having  groundwater depth  within  3m will reduce in Area D Zone C and Area D Zone D.
Some additional area in  Area E around  wells AIP 47,  51  ,  52, 54  & 57  will have groundwater depths within  3  m range in future,  which  will require sub-surface drainage system if the present trend  of rising  groundwater continues but that situation  will arrive only  after about 5-15  years from now and  hence can  not be included  in  the priority  area of Phase JI .
2.6.3          Ground Water Salinity
From the Table 7,  it is observed  that 13  wells out of 22 wells in  Phase II area have rising  groundwater salinity trend.  Groundwater salinity  will increase in  the entire Area B-Zone A.  In  Area B-Zone B,  except wells AIP 19  &.  20 others wells have shown  rising  EC trend.  In  Zone C-Aree D, wells AIP 55  &.  62  have shown  the marginal rise in  EC values.  In  Zone D-Area D,  wells AIP 37,  43  &.  65  have shown 
the      small      increase      in      EC      values.      In      Area      E      except      well      54 
alL      the      wells      have      shown      falling      EC      trend      and      EC      reducing to almost zero in most of the case.
2.7 Conclusions
The
magn
itude
of
sub-surface
field 
drainage
priorit
y 
areas
within 
the
phase
-II
(Area       B
and       Area
D)       asse
ssed 
on 
the
basis
of
August, 
95 
groundwater
depths
is      2,536 
ha
which
is
much 
less
than 
the
area     shown 
in     TOR
as     5,000 
-
6,000 
ha. 
Even         if         some         additional         area         requiring         sub-surface         drainage in Area A and E, which is outside the scope of TOR, is also
31included  then  total area for sub-surface drainage works out to  3,974  ha only  for which  consultants propose to  design the sub-surface drainage system.  Attempt to  increase the aforesaid  area identified  as priority  area by  adding  to  it some areas having  groundwater more than  3m below the surface will adversely  affect the economic viability  of the Phase II project due to  the reason  quoted  from the Master Drainage Plan 1985, at section 2.4.
32REFERENCES
(I) Master Drainage Plan for Melka Sadi and Amibara Areas, Final Report, Vol 1-8, Sir William Halcrow & Partners, July, 1985 .
33DEPTH(m)
■■aas■
G.W. DEPTHS
FOR WELL-2
1980            1984            1988            1992 e"
□         MAX                    +
1996            2000           2004            2008            2012            201 l YEAR
MIN
X         MEAN(C).DEPTH(m)
□     MAX
YEAR Mlbl
MEAN(C)DEPTH(m)
MAX.& MIN.DEPTHS FOR WELL-5
YEAR
□         MAX.
+ MIN
X COMP(MEAN)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
FOR WELL-6
8
1980             1984             1988             1992            1996 YEAR
2000            2004             2008              2012             2016
□         MAX                     +         MIN                      X         MEAN(C)G.W.D.(m)
MAXIMUM & MINIMUM G.W.DEP'THS
YEAR
□
MAXIMUM
+ MINIMUM
X      COMP (MEAN)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
10
□ MAX
YEAR MIN
X MEAN(C)EC(mmho/cm)
MAX.& MIN. EC VALUES<.'LUO/oqujLU)03
MAXIMUM &
EC VALUES
/'J
1984
20U*d
o      MAX
1988             1992            1996 Y E-
+        MillEC(mmho/ zcrrQ
MAXIMUM & MINIMUM EC VALUES
FOR WELL—1 1
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
1980            1934             1988             1992            1996            2000               2004            2003             2012               2016 YEAR
□         MAXIMUM
+
MINIMUM
O          MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
-.FOR WELL-12
1980             1984             1988             1992            1 996             2000            2004             2003               20 I 2                20 It YEAR
□         MAX
MiH
X         MEAN(C)EC(mmho/cm)
MAX.& MIN. EC VALUES
12
YEAR
□ MAX
+ MIN
X MEAN(C)EC(rnmho/'cm)
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
+ MIN
X MEAN(C;EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
12
□         MAX
YEAR MIN
X MEAN(C)(IJJO/OLI LU 1X1)023
MAXIMUM & MINIMUM EC VALUES
FOR WELL-18 18 --------------------------------------------------------------------------------------------
1          ii
iI—|---------- i------ ii—II---------1------- i------ i—i---------- 1-------1-- f----- ii-1II-1i—i------------------ii—iI--------- 1--- 1----- l—|---------- II—i»---------1------]—i
»       •       | —l r
1980              1984             I 988             1992             1996             2000            2004             2008              201 2              2016 YEAR
□         MAX                      +
MIN
X          MEAN(O)EC(rnmho/cm)
MAXIMUM & MINIMUM EC VALUES
12
□ MAXIMUM
YEAR + MINIMUM
X MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
45
□         MAXIMUM
YEAR
MINIMUM
X         MEAM(C)EC(mmho/'cm)
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
-I- MIN
X MEAN(C)EC(rnmho/cm)
MAXIMUM & MINIMUM EC VALUES
FOR WELL—22
23
3------------- i----- t----- r----- 1-----1---- tr—IIr—II------ Tr—1t-----t----- j----- t----- tr—it------ |------ T---- t------ t----- 1-----t------ t------ t |-------------t------ t t |
tr—it          r
1984
1988 f *'
1992                1996              2000               2004               2008                 2012                2016 YEAR
□         MAX                     H-
MIN
X         MEAN(C)
fffEVKIIIIIIEC(mmho/crn)
MAXIMUM & MINIMUM EC VALUES
34
□         MAX
YEAR MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
+ MIN
X MEAM(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
+ MIN
X MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
3
□         MAX
YEAR MIN
X         MEAN(C)(UJ 5/O 4 LULU ) 03
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
+ MIN
X MEAN(C)( ijj o/o q lulu ) 03
MAXIMUM & MINIMUM EC VALUES
FOB WELL—28
0               r " i [ i : i | i i i |" r r i" | i i i j i i | I I i i “j i i » j i ■ i
1980             193 +            1988             1992            1995             2000            2004             2008              2012               2016 YEAR
□         MAX                      +
MIN
X         MEAN(C)
BKBBBBBSSS(LU 0/0 4 LU LU ) 03
MAXIMUM & MINIMUM EC VALUES
60
MAX
YEAR MIN
X MEAN(C)(LUO/OULU LU) 03
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
+ MIN
X MEAM(C)(luo/0 4luuj)03
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
+ MIN
X MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
14
□         MAXIMUM
YEAR
MINIMUM
X         MEAN(C)(uuo/oqLuuj)03
MAXIMUM & MINIMUM EC VALUES
26
□         MAX
YEAR MIN
X MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
□         MAX
YEAR MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
so
□         MAX
YEAR MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
1980              1984             1988            1992             1996             2000            2004             2008              2012              2016 YEAR
D         MAX                     +
MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
11
□         MAX
YEAR MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
□         MAX
YEAR MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
MAX
YEAR + MIN
X         MEAM(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
FOR WELL-44
40 --- ----------------------------------------------------------------------------------------------------------------------------------
0-------- 1—i—i—|—i------ 1—i—j—»—’—i—|—’—'—i—|—’—»—i—j—•—'—’—|—’                 1       ’ i ’           * T T 1980              1984             1988             1992            1996             2000                   2004 2008                    2012
YEAR
2016
□          MAX                     +
MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
FOR WELL—45
□         MAX                     +
YEAR MIN
MEAN(C)EC(mmho/cm)
!
MAXIMUM & MINIMUM EC VALUES
2000
□ MAX
+ MIN
X MEAM(C)
I f I ■ ■ s a a uux ■
-DEPTH(m)
MAXIMUM & MINIMUM G.W. DEPTHS
□ MAXIMUM
+ MINIMUM
X COMP(MEAN)DEPTH (m)
MAXIMUM 8c MINIMUM G.W.DEPTHS
6
□          MAX
YEAR MIN
X          MEAN(C)DEPTH (ni}
MAXIMUM & MINIMUM G.W.DEPTHS
MAX
YEAR 4- MIN
X          MEAN(C)DEFTH(m)
MAXIMUM & MINIMUM G.W.DEPTHSDEPTH
MAXIMUM MINIMUM G.W.DEPTHS
c
□     MAX                    4- MIN
X        MEAN(C)DEPTH(m)
KIUIU*4J
IMUM &c. MINIMUM G.W.DEPTHS
FOR WELL-16
22-------- 21 -
20 -
19 -
18 -
17 -
16 -
15 -
14 -
13 -
12 -
11
10 ip-Q,
9
8-
7-
6-
5-
4 H.
1980
T
1996            2000 YEAR
MIN
X         MEAN(C)DEPTH(m)
MAX
YEAR MIN
X        MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
□         MAX
YEAR MIN
X        MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.'//.DEPTHS
FOR WELL-19
10 -i------------------------------------------------------------------------------------- -------------------------------------------
1         ’ i---------- 1----- ]------1-1-’1'-—'  ----11---'-- J----- J----- 1----------11--------- ]1---------- 11------rr——it------ j1---i--1----- tr-—1 ---- 1-----1j-—I ----- 1----- 1—1 -----—1 1---—f -- 1-—1 ---- 1—1----—1 - 1-—1 - 1—-- j------ 1----- 1----- 11-----Jj------ 11-----1—r 1
1984            1988 e--
1992           1996 YEAR
2000
2004           2008
2012             2016
□         MAX                   +     MIN                     X        MEAN(C)DEPTH(m)
MAXIMUM &. MINIMUM G.W. DEPTHS
YEAR
+ MIN
X MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W. DEPTHS
FOR WELL-21
13
1
’
’I'
1r]
’
1
1
|
’
1
' i |----------------- T---------- 1
----- 1----- 1----- 1-----
1----- 1-----
1----- 1----- 1----- 1----- 1------1----- 1
----- 1----- 1----- 1----- r
1980
1934
1988
1992
1996
2000
2004
2008
2012
2016
□
MAX
+
YEAR
MIN
X
MEAN
(C)DEPTH(m)
MAXIMUM & .MINIMUM G.W.DEPTHS
YEAR + WIN
X MEAN(C)DEPTH(m)
MAXIMUM
G.W. DEPTH
c_ '.y
FOR WELL—23
9 -i— 8-
7-
X
X
6-
X
5-
4-
3-
2-
i -H
1980
1984
1988
1992
1996
2000
2004
2008
2012
2016
*
□     MAX                    +     MIN                      X         MEAN(C)
YEARDEPTH(m)
>                      Alt-J* - ■■
MAXIMUM & MINIMUM G.W.DEPTHSDEPTH(m)
1980            1984           1988           1992           1996            2000           2004            2008             2012             201c
r-'
□     MAX                   4-        MIN                     X        MEAN(C)
YEARDEPTH(m)
G.W.DEPTH
FOR WELL-26
15
1980            1984            1988            1992            1996            2000           2004            2008             2012             2016 f *'
D         MAX
YEAR MIN
X         MEAN(C)DEPTH(m)
FOR WELL—27
5 4.8 4.6 4.4
4.2
4 3.8 3.6 3.4
3.2
3 2.8 2.6 2.4
2.2
2 1.8
1.6
1980            1984
1988
□ MAX
1992            1996 YEAR
MIN
2000
2004
2008
2012            2016
X        MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
13
1980            1934           1938            1992            1996            2000            2004             2008              2012              2016 YEAR
□        MAX
MIN
X         MEAN(G)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
11
MAX
YEAR MIN
X        MEAN(C)
__DEPTH(m)
MAXIMUM & MINIMUM G.W. DEPTHS
6
□     MAX
YEAR MIN
X         MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
FOR WELL-34
10
.
1         ’ I' I
ir—“ii      | i----------- ir—ii------- j--------i------ 1----- 1----- |------ r
1980           1984            1988            1992           1996            2000           2004            2008              2012             2016
□     MAX                    4-
YEAR MIN
x      MEAM(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
YEAR
X        MEAN(C)DEPTH(m)
MAXIMUM &                        G.W. DEPTHS
□     MAX
YEAR MIN
X        MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
FOR WELL—37
1
---
’ I ' 
—.
|
r—i
------ 1----- j------ 1----- r —
'—1—1—r 1996
YEAR
—I—1— —
i—j—i—i—i—
|—i—
T-- t--- J 
«
1980
1934
1988
1992
2000
2004
2008
2012
——
2016
□
MAX
+
MIN
X
MEAN(C)DEPTH(m)
1980             1984              1988             1992        '.-.'1996              2000             2004             2008       •     2012             201c YEAR
□ MAX
+ MIN
X MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
FOR WELL-40
16 -- 15 - 14 - 13 - 12 - 11- 10 -
9- 8- 7- 6- 5- 4- 3- 2-
-Lx
X
5 ••
X
1 4-
1930
1996             2000 YEAR
2004 X         MEAN(C)
•r-----1---- j----- 1-----1---- 1---- 1----- 1i—ii r
2003              2012
2016DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHSDEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
14
□     MAX
YEAR MIN
mean(c)DEPTH(m).
MAXIMUM & MINIMUM G.W.DEPTHS
12
□     MAX
YEAR MIN
X          MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
FHR WFLI-44
14
MAX
YEAR + MIN
X          MEAN(C)DEPTH (rrr)
MAXIMUM & MINIMUM G.W. DEPTHS
FOR WELL—45
1177 16 15 14 13 12 1111 10
9 B 7 6 5 4 33 2 11 0
1980
1984             1988             11999922
11999966              22000000              22000044               22000088
22001122
1
n
YEAR MIN
MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
17
□ MAX
YEAR + MIN
X MEAN(C)
■r U w g B H sDEPTH(rn)
MAXIMUM & MINIMUM G.W.DEPTHS
YEAR
□ MAX
+ MIN
X MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
FOR WELL—48
7
2-
1
1980
1            I             1            1    -n------- 1-----t---- —1—1—'—r      —--------1---- 1---- r —'—1—’—  —»—iiiiiiiiiii
||—i—
1934
1988
1992
1995 YEAR
MIN
2000
2004              2008
i | f—n
2012
2016
□     MAX                       +
X          MEAN(C)DEPTH(m)
MAX
YEAR -I- MIN
X         MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W. DEPTHS
13
YEAR
□ MAX
+ MIN
X MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
16
□          MAX                      +
YEAR MIN
X            MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W. DEPTHS
14
YEAR
□ MAX
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X MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
17
FOR WELL—54
1980               1984              1988              1992              1996              2000            2004             2008                2012 '            2016
YEAR
□     MAX                      4-
MIN
X         MEAN(C)DEFTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
□     MAX
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X          MEA.N(C)DEPTH(m)
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1980
1984
1988
1992
1996
2004
2008
2012
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YEAR
□
MAX
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MIN
X
MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
9
□     MAX
YEAR MIN
X          MEAM(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
MAX
YEAR + MIN
X          MEAN(C)DEPTH (m)
MAXIMUM & MINIMUM G.W.DEPTHS
10
MAX
+ MIN
X          MEAN(C)DEPTH (m)
MAXIMUM & MINIMUM G.W.DEPTHS
30
MAX
YEAR MIN
X         MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
8
FOR WELL—64
1996             2000 YEAR
MIN
2008
X MEAN(C)
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MAXIMUM & MINIMUM G.W.DEPTHS
1980             1984             1988               1992 .        1996             2000            2004             2008 YEAR
2012 2016
□                        MAX                    4-*
MIN
X         MEAN(C)
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MAXIMUM & MINIMUM G.W.DEPTHS
□         MAX
YEAR MIN
X         MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
12
YEAR
□ MAX
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X MEAN(C)DEPTH (m)
I
MAXIMUM & MINIMUM G.W.DEPTH
□     MAX
YEAR MIN
X         MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
13
□         MAX
YEAR MIN
X         MEAN(C)DEPTH(m)
MAXIMUM & MINIMUM G.W.DEPTHS
10
□     MAX                     +
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MAXIMUM & MINIMUM EC '/CLUES
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MAXIMUM & MINIMUM EC VALUESEC(mmho/crn)
MAXIMUM & MINIMUM EC VALUES
YEAREC (mmho/cm)
MAXIMUM & MINIMUM EC VALUES
30
YEAR
□ MAXIMUM
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X COMP(MEAN)EC(mmho/crn)
MAXIMUM & MINIMUM EC VALUES
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MAX.& MIN. EC VALUES
YEAR
□ MAX
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X        COMP (MEAN)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
FOR WELL—47
1980             1984             1988            1992            1996            2000             2004             2008              2012              2016 YEAR
□         MAX                     +
MIN
X         MEAN(C)EC(mmho / c m )
MAXIMUM MINIMUM EC VALUES
FOR WELL—48
1980              1934             1983             1992            1996             2000            2004             2008              2012              2016 YEAR
□       MAX                      +
MIN
X         MEAN(C)(uj0/oqujuj)33
MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
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X MEAN(C)( LU D/O q ULJUJ ) Q3
MAXIMUM & MINIMUM EC VALUES
FOR WELL—50
1980              1934             1988             1992             1996            2000            20G4            2003 YEAR
2012 f_. 2016
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MIN
X         MEAN(C)EC(mmho/cm)
MAXIMUM & MINIMUM EC VALUES
MAX
YEAR + MIN
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MAXIMUM & MINIMUM EC VALUES
16
□          MAX
YEAR MIN
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MAXIMUM & MINIMUM EC VALUES
12
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MAXIMUM & MINIMUM EC VALUES
YEAR
□ MAX
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MAXIMUM & MINIMUM EC VALUES
15
YEAR
□ MAX
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FOR WELL—64
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1980              1984             1988             1992            1996             2000            2004             2008              2012              2016 YEAR
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Summery

Amibara Drainage Project Phase-II Summary

Amibara Drainage Project Phase-II: Hydrogeological Data Analysis Summary

Project Overview

The Amibara Drainage Project Phase-II is a hydrogeological study conducted in Ethiopia's Northern Rift Valley region, focusing on the right bank of the Awash River. The project aims to prepare detailed designs, tender documents, and environmental impact assessments for subsurface drainage systems in areas affected by rising groundwater tables due to irrigation practices.

Key Findings

1. Location and Climate

Semi-arid climate with mean annual rainfall of 563mm
Two distinct rainfall patterns: July-August (40% of annual) and February-April (32%)
Mean temperature ranges between 23°C to 31°C

2. Geology and Hydrogeology

Area consists of alluvial plain, ancient fluviatile terraces, and volcanic formations
Aquifer is essentially without flow, responding vertically to precipitation and evapotranspiration
Low horizontal permeability (10^-6 m/day) precludes deep disposal methods

3. Groundwater Analysis

54 functioning observation wells as of August 1995 (from original 79)
Regression analysis used to predict future groundwater depths and salinity
Priority areas identified where groundwater is within 3m of surface

Priority Areas for Subsurface Drainage

Location	Area	Priority Area (ha)	Remarks
Melka Sadi	B	984	Western and Eastern parts of Area B
Amibara	D	1,552	South Eastern Zone of Area D
Additional Areas	E	1,400	Outside original scope but showing critical groundwater levels
Total Priority Area		3,974 ha	Significantly less than original estimate of 5,000-6,000 ha

Groundwater Trends and Predictions

1. Groundwater Level Trends

Only 24% of wells show rising groundwater trend (average 0.29 m/year)
76% show falling groundwater levels, attributed to changes in irrigation practices
Significant change in trend observed since 1989-90

2. Future Predictions (1996-2016)

Most areas in Melka Sadi show progressively increasing groundwater depth
Some areas in Amibara (Zone D) will maintain critical groundwater levels
Additional areas in Zone E may require drainage in 5-15 years

3. Groundwater Salinity

13 of 22 wells in Phase II area show rising salinity trend
EC values range from 4-12 mmho/cm in Melka Sadi and 2-12 mmho/cm in Amibara

Conclusions and Recommendations

        The priority area for subsurface drainage is 3,974 ha, significantly less than originally estimated
The rate of groundwater rise (average 0.29 m/year) is much lower than previous estimates (1 m/year)
Areas with groundwater within 3m of surface should be prioritized for drainage implementation
Phase I drainage systems have proven effective in reducing groundwater levels
Future monitoring is recommended to verify trends and adjust implementation plans

    

Project Details

Client: Government of Ethiopia, Ministry of Water Resources

Consultant: Water and Power Consultancy Services (India) Ltd.

Report Date: August 1995 (data coverage from 1980-1995)