GOVERNMENT OF ETHIOPIA
WATER RESOURCES DEVELOPMENT AUTHORITY
AMIBARA IRRIGATION PROJECT II
DRAINAGE & SALINITY STUDY AND RECOMMENDATIONS FOR
FIELD DRAINAGE
VOLUME 3-ADDENDUM
JANUARY 1983
Sir William Halcrow & Partners Consulting Engineers
Burderop Park Swindon
Wiltshire SN4 OQD United KingdomI
GOVERNMENT OF ETHIOPIA
WATER RESOURCES DEVELOPMENT AUTHORITY
AMIBARA IRRIGATION
ROJECT II
DRAINAGE & SALINITY STUDY AND RECOMMENDATIONS FOR
FIELD DRAINAGE
VOLUME 3-ADDENDUM
JANUARY 1983
Sir William Halcrow & Partners Consulting Engineers
Burderop Park Swindon
Wiltshire SN4 OQD United KingdomAMIBARA IRRIGATION PROJECT II
Drainage & Salinity Study
and Recommendations for Field Drainage Volume 3 - Addendum
CONTENTS
1              Introduction
2  Replies to IDA Comments
3               Objectives of Pilot Area
Figures
Figure 13
Figure 14
Figure 15
Appendices
Page
1
1
6
A
IDA Comments, May 1982
B
Proposals for Pilot Area
C
IDA Comments, August 1982
Maps
Map 6A - Amibara Area
Map 7  - Depth to Water Table - Melka Sadi Area1 INTRODUCTION
i. • This report forms an addendum to the report entitled ’’Drainage and Salinity-
Study and Recommendations for Field Drainage” dated April 1982. At the ’Donors
Conference’ in May/June 1982 some comments on this report were presented by the
IDA representatives. These comments, which were included as Annex III of the
Record of the Donors Conference, are included here as Appendix A of this report.
Each of the comments             is discussed in Section 2 of this report.
1.2     Section 3 of this report then discusses the objectives of the pilot area.
A copy of a separate document which gives the logistical and manpower
requirements      for      design      and      supervision      of      the      pilot      area,      together      with      guidelines of the aspects to be investigated, is included as Appendix B of this report.
2 REPLIES TO IDA COMMENTS
2.1      Depth to Ground Water
2.1.1          This information had in fact been prepared during the study, but it was.. decided to exclude it from the report to reduce the number of maps presented.
Two maps are now included.
These are: •
Map 7      - Depth to Water Table - Melka Sadi Area Map 6A - Soil Salinity Study - Amibara Area
For    the latter map the additional
previous Map 6.
In       addition,       three       cross       sections drawn and are included as Figures
information has been superimposed on the
through the Melka Sadi Area have been 13 to 15 inclusive.2.1.2       For the Melka Sadi Area within the former Maesco farm, the map is drawn using water table data from open auger holes. These water levels were measured some hours after boring to allow the water to stabilize.
Outside the farm area the water table levels are based on readings of the AIP observation wells.
There appears to be a perched water table within the farm area which is separated from the main ground water body by a layer of impermeable or
slowly permeable clay of variable thickness which has a characteristic
10 YR 3/1, very dark grey colour and was extremely firm and barely moist. The water tables are shown on the sections together with the location of
the impermeable layers, where known, and other pertinent data.
2.1.3       For the Amibara area contours of depth to ground water have been superimposed on the existing map which summarises the results of the investigations. It
can be seen that the highest water levels are in close to the river where irrigation has been carried out for some years. In the north east of the
area, the water table is more than 10 m below ground level.
2.2          Observation Wells
2.2.1       Drawings of the two types of observation wells installed prior to 1981 
were included to demonstrate their shortcomings. These wells were installed to monitor the main ground water body and as such have been successful. These wells have mainly been installed prior to irrigation. The location and occurrence of perched water tables resulting from irrigation could not
have been easily predicted.
2.2.2       As part of the investigations in 1981 the depth to ground water within the former MAESCO farm area was checked by drilling open holes and adjacent
2to the existing observation wells. The differences in water levels and salinities (EC) are shown by Table 2 on page 5 of Volume 1. It can be seen tha fairly similar water levels were recorded although usually those in the observation wells were the deeper. The salinity levels recorded for water
in the open bores were up to four times those measured for water from the observation wells.
2.2.3      It is worthwhile recording the method used for the installation of the AIP
series of observation wells. In general the piezometer tip was installed
3            m below the water table at the time of drilling. This was to provide for the possibility that the water table could drop since to install the
piezometer close to the water table could result in the water dropping out of observation range. On completion of the installation of an observation well
the driller was then required to demonstrate that it functioned correctly 
by filling it with water which was then expected to - drop down to the water table within a reasonable period of time. This technique would then result in the piezometer standpipe containing the water used for the test. Unless this water is removed, water sampled will not be representative of the ground water and will tend to remain constant (see Observation Well Records in Volume 2 Annex 1).
2.2.4         The shallow water table within the MAESCO farm area is free and overlies
an impermeable or slowly permeable clay layer. This water table is highly saline with measured conductivities of up to 60 mmhos/cm. The deeper aquifers are slightly confined by the clay layers and at most sites there was a slight
rise in the water level after the bore had been drilled. Sometimes the deeper waters are very saline (see Volume 1 pages 4 & 6).
2.2.5         The interaction of the two aquifer systems can be studied by installing piezometers and recording the different levels over a period of time. This would require a          series of piezometers at each site with their tips at
3different depths. Piezometer studies are recommended for the pilot
drainage area.
2.3            Vertical Hydraulic Conductivity
2.3.1         Tests on the vertical hydraulic conductivity of the impermeable or slowly
permeable      clay      layers      were      impractical      with      the      available      equipment      since      these layers were below the water table.
2.3.2          The appearance of specimens of the clay layers as obtained by hand augering was such that a zero or very low permeability could be expected. In particular at some sites the clay was only just moist although it was
cverlain by coarser more permeable and saturated material.
2.3.3           The hydraulic conductivity values obtained from the pour-in method were lower than the values from the pump-out method (below the water table). The latter method tends to measure horizontal permeability and it is this horizontal movement of water above the impermeable layer, generally deeper than 2 m below ground level, which will contribute to the water entering the drains.
2.3.4        Much of the former MAESCO farm has one or more horizontal layers of coarser material m the subsoil and this was taken into account when selecting a
’k* value for each of areas (See figure 5 on page 28, volume 1). However, the assumed porosities have been reduced from the values expected as for soils with the higher hydraulic conductivities to take account of the variable vertical hydraulic conductivity (ref p27, Volume 1).
2.4 
Required Drainage Depths
2.4.1 
A major factor affecting the selection of the design drain depths was the
saline groundwater conditions. FAO Irrigation and Drainage Paper 38 states
on p24 "Considerations of water table and salinity control yield the
4shallowest possible design drain depth .... and it is generally in the range
of 1.5 - 2.0 m below ground surface. Where water management conditions are poor, the drain depth should be closer to the lower limit".
2.4.2         Although banana is the main crop of the former MAESCO farm, the proposed drainage arrangements should be applicable for elsewhere in the project, 
for which cotton is the main crop. It is considered advisable that ground water should be kept clear of the root zone and hence the design guidelines set out in Volume 1, page 25, were established. After irrigation, the maximum design water table is 1.5 m below the surface (1.2 m in areas of shallow permeable soil) and not the 1.8 m stated on page 23 of Volume 1).
2.4.3 
The presence of some stratification of the soil, with more and less permeable
layers, has to be considered in the drainage design. It is this factor
combined with the different hydraulic conductivities, which has resulted in a total of 8 different drain types being proposed (see Table 6, Volume 1, page 31). There is therefore little scope for comparing different
alternatives to establish the least cost solution.
2.5 
Pilot Tests
1
2.5.1 Detailed proposals for the drainage pilot area, including the purpose of
the trials, alternatives to be considered and the logistical and manpower requirements for the design and supervision are given in the document
‘Proposals for Pilot Area  which is attached as Appendix B . The reasons for selection of the pilot area are given in Section 3.1 of this report.
2.5.2         It is agreed that initial trials with open drains may provide useful data
on performance and this is now included in the proposals for the pilot area
!f
(Appendix ’B ). Design depths for open drains are already given on Table 6, 
1
(Volume 1 page 31). The use of open drains would enable a commencement of studies prior to the purchase of pipes which may have to be imported.
5The main reservation about open drains is the side stability. If it is
feasible to excavate temporary open drains with side slopes in the order
of 1 vertical to 0.5 horizontal then the quantities of excavation required 
will be reasonable. The excavation of side slopes flatter than 1:1 will
involve substantial quantities of earthmoving. The presence of substantial spoil banks alongside the drains will encroach on the areas available for irrigation. A further complication associated with open drains is that the areas available for water application and leaching trials will be limited. These disadvantages are outweighed by the attraction of permitting an early start to the trials and enabling a visual examination of the effects.
Calcareous Soils
It was appreciated during the investigation that the highly calcareous soils would pose a problem for the soil analyst but, after discussions at the Holetta Laboratory, it was agreed to use the normal testing procedures in the knowledge that the results could be affected by the calcium content. 
It was in fact the first time that saline/alkaline calcareous soils had 
been tested at that laboratory.
2 The presence of gypsum in the soil profile was observed. The gypsum tended to occur at the sites which had a high exchangeable sodium percentage, 
ie AIP6, AIP10.
OBJECTIVES OF PILOT AREA
Selection of Area
The main factors influencing the selection of the pilot area were:-
i)           The proposed area was close to the main drainage network and the least amount of initial additional excavation would be required to enable gravity drainage.
6ii) The proposed area consisted partly of land which was already 
abandoned and the remainder was becoming saline.
iii) The area contained several 3oil classes with different salinity
levels and depths to the
impermeable layer.
iv)           Access from the existing                 project road network would be good
(subject to construction
of a secondary drain
crossing).
v)            The pilot area would be at the downstream end of the largest
single block of saline land, which could then be progressively
drained, working up slope.
vi)           By including both moderately and highly saline land, it will be
possible to assess the effects of drainage in:
(a)        controlling salinity build up in land still under irrigation, 
and
(b)        reclaiming highly saline land.
vii)          Irrigation water would be available from the existing adjacent canal
system for leaching trials.
3.2            design Considerations
3.2.1 There would be considerable attraction in constructing trial open drains
which  would  enable an  early  start to  be made while procurement of pipes was still in  progress.  These drains could  be constructed  at a range of spacings to check the performance of the designs.
3.2.2         The type of pipe selected will depend on availability. It is not known whether clay pipes are manufactured in the required quantities within Ethiopia, but this source of supply will be investigated thoroughly before any decision is made to import pipes.
73.2.3       Pipe drains should be installed both with and without the filter surround and alternative materials for the filter surround should be tested.
3.2.4       Although trials with open drains may demonstrate that the design spacings could be changed these results would only be directly applicable to the pilot area. The results would, however, provide an overall indication of the effect of the more permeable layers on the soil drainage properties.
It would be prudent to supplement the existing investigation with more exploratory holes before changing the drainage design in areas of different soil types.
3.3              Construction
The pipe drains for the pilot area will probably be installed in a trench. Some sort of moveable shuttering will be required to protect people working in the trench on pipe laying.
~ -2 9 
• •—       For drainage installation on a large scale some quicker method of drain installation will be required. A range of specialist drain installation machines is available and one will have to be selected to suit the chosen type of pipes.
3.4             Performance
3.4.1       It is essential that all aspects of the pilot area drains are carefully monitored. Initially, a network of piezometers must be installed to measure the water table prior to drainage works being commenced.
3.4.2       Drainage flows and water quality must also be measured, particularly during irrigation and leaching trials.
8* Kk»U 3
Elv m
MELKA SADI FARM BOUNDARY
745 -
744 -j
MELKA   SADI   FARM boundary AND DRAIN
kT
X  Wmeot> or tkMTli
DRH22
PILOT AREA
742 - 741 - 740- 739 738 - 737 - 736- 735 - 734 - 733 - 732
73l - 730 -
7 29
726 727
Horizonioi Scolp I 5Q QQQ 216 E C , mmhos/cm, of water
AIP20
WATER LEVEL
IN OPEN BORES
1/ if
AIP2I
GROUND LEVEL m
Projected water toble
based on Map 7
-see note below
I
^-4-6 35
\
\
X
\
\
\
WATER TABLE X OBS WELLS
I
I
I
I
I
Note
Mop 7 indicates that there appears to be g perched woter toble within the Maesco form area which issepcrated from the mom ground water body by a loyer of impermeable or slowly permeable clay of vorioble thickness More enplorotory holes ore required in this particular area to define fte woter fables more occurotely
9 20
\
\
\
\
\
\
\I
\ I \'
J_ll 58
---- Il'1 **• ’
FIG-JPE 4
EI v m 747- 746- 745 - 744 - 743 - 742 - 741 - 740- 739 - 738- 737 - 736 - 735 - 734 - 733 - 732- 731 - 730-
LEGEND
Impermeoble  or  slowly permeable loyer
051
2               3km
i_______i______ i----------- i------------ 1-----------1------------ •
Horizontal Scale 1.50,000
7 8 E.C., mmhos/cm, of wafer
Note
Map 7 indicates that there appears to be
729-
728-
727-
a perched water table within the Maesco
farm area which is separated from the
CROSS SECTION E-W
main ground water body by a layer of
impermeable or slowly permeable clay of
Through Melka Sadi Area
variable thickness. More exploratory holes 
are required in this particular area to
define the woter tables more accurately.
726-jElv.m MAIN CANAL
74 6 -
745 -
744 -
743 -
742 -
St tHt
I
741
740-
739-;
738-
737 -
736-
735 -
734
733
7 3?
I
r*
Projected water table
based on Map 7
;
;
731
- see note below.
;
—■>—'7—7 ? WATER TABLE
"
OBS. WELLS
.b
Moi 7 ndtcotes mot there oppeors to be
c ^tsirhac water table within the Moesco
torn oiec whKt it separated from the
iitou gtoui.C woter body by a layer ot
CROSS SECTION SSE-NNW
impermeable ex stowiy permeable cloy of
wui.al c tlur Hcbt M(.it etplorotory holes
Through Melka Sadi Area
ait iCMM.ieC .1 tint purtKulOr area toAPPENDIX A
IDA Comments
(Annex III of Record of
Donors Conference 31 May - 1 June 1982)ANNEX III
AMIBARA IRRIGATION PROJECT II
Comments by IDA on the Report prepared by SWH&P entitled "Drainage and Salinity Study and Recoirmendatians for Field Drainage, Vols.l
and 2, April 1982
1.       Depth to Ground Water. While map no.l gives ground water (g.w.) contours, no map shows depth to g.w. (or depth to piezcmatric surface, as appropriate). The data is available but has not been assembled
in nap form. It is difficult to visualize the drainage plan and to identify the more critical areas without such a nap. A couple of
cross-sectional views also would be very helpful in ’understanding the relationships among impervious layers, perched, free and artesian zones, and the proposed drains.
2.       Observation Wells, pp. 9,10. At sites with seme impermeable layers, neither type shewn will show the actual "water table”. This is especially inportant if perched water tables exist, as they apparently do at some locations in the area. The consultants should identify clearly the differences among the free ground water table and piezcnetric surface. There nay be more than one of the latter. The Section 3.2 description is vague as to whether or not the shallow aquifers are all free, or a mixture of free and confined layers.
3.      Vertical Hydraulic Conductivity. No tests are reported on vertical hydraulic conductivity of the various underlying layers. Only surface infiltration is reported. Since layering exists, vertical hydraulic conductivity tests should be performed at the top of important layers where vertical conductivity changes are suspected. These tests should be as per U.S. Bu. Rec. Ring Permeameter tests (pp. 81-93, Drainage Manual) which approximates saturated flow. Alternatively, sene correlation between horizontal and vertical permeabilities should 
be justified.
U. Required Drainage Depths, p. 23 Section 11 and 11(a) and p.25.
The minimum water table depth of 1.8m seems high for the projected crops. See pp. 21-23 of FAO I& D Paper No. 38, Drainage resign Factors, enclosed. Having established the water table depth, depth to drain and spacing are interrelated, and a matter of economic analysis to get a least-cost solution.
5.       Pilot Tests. Rather than importing expensive tile-laying systems initially, why not consider test plots with open drains, where flows ran be easily observed? Depths and spacing used would be the same as estimated for the cal culled least-cost tile solution, but the(Annex III)
tests would confirm the estimates as far as water table performance and drain flows. Some closer and larger spacings also should be tested. When the better design is apparent, tiles can be installed.
Such tests can be quickly installed by project forces or contractors, and the info can be used for the final designs and construction.
In the long run, tile drainage orobably will be the best answer, but pilot work should be commenced now.
6. Calcareous Soils. Peters has noted on Sheet 3, next-to-last page,
Volume 2, that the values for calcium are suspect since the usual
test methodology is not applicable to these calcareous soils. ESP
must be obtained by other methods. He also suspects that gypsum may be present.
7. Miscellaneous. Other notes on seme of the pages of Vol.l have been made, mostly relating to the soil chemistry. We would be happy to discuss these further with the consultant, preferably in Washington,D.C(Annex III)
tests would confirm the estimates as far as water table performance and drain flows. Some closer and larger spacings also should be tested. When the better design is apparent, tiles can be installed.
Such tests can be quickly installed by project forces or contractors,
and the info can be used for the final designs and construction.
In the long run, tile drainage orobably will be the best answer, but
pilot work should be commenced now.
6. Calcareous Soils. Peters has noted on Sheet 3, next-to-last page,
Volume 2, that the values for calcium are suspect since the usual
test methodology is not applicable to these calcareous soils. ESP
must be obtained by other methods. He also suspects that gypsum may be present.
7.      Miscellaneous. Other notes on seme of the pages of Vol.l have been mde, mostly relating to the soil chemistry. We would be happy to discuss these further with the consultant, preferably in Washington, D.CAPPENDIX B
Proposals for Pilot AreaAMIBARA IRRIGATION PROJECT II
SUB-SOIL DRAINAGE
PROPOSALS FOR PILOT AREA
REVISED DRAFT
Sir Willia® Halcrow & Partners Burderop Park
Swindon SNA SQL Wilts
England
July 1982AMIBARA IRRIGATION PROJECT II
SUB-SOIL DRAINAGE PROPOSALS rCP PILOT AREA
CONTENTS
Page
INTRODUCTION
2     OBJECTIVES OF PILOT AREA
3     ASSESSMENT OF PERFORMANCE 
2
4     DIVISION OF RESPONSIBILITIES 
2
STAFF REQUIREMENTS 
3
EQUIPMENT AND MATERIALS REQUIREMENTS 
3
7    STAFF DUTIES 
5
Figure               Activity N«twoi*k Diagram1  INTRODUCTION
Following
submission of the Drainage and Salinity Study and Recommendations
for Field Drainage Report (April
1982), it has been decided that the installation
of drains within a pilot area of
some 50 ha should be carried out at an early date.
The Report outlined drain design and a programme of construction was proposed. This document provides additional guidelines on the objectives of the pilot area and details the resources required for the design and supervision.
OBJECTIVES OF PILOT AREA
The pilot area is to establish the most appropriate method of subsoil drainage and salinity control for the Amibara Irrigation Project.
The design of the pilot area should take into account the following objectives a)    To check the theoretical designs and establish the most appropriate 
drain spacings and depths*;
h1
V)
To determine the most appropriate type of drainage pipe;
c)    To establish whether a filter surround is required for the pipes and locate a suitable source of the filter if required;
d)
To carry out leaching and irrigation trials and monitor the performance of the drains;
e)
To enable the effectiveness of drainage in water and salinity control within the project area;
f)
To permit a more accurate co3t estimate to be made for future drainage works for the project.
* This may be best carried out by installing temporary open drains at various spacings.3 ASSESSMENT OF PERFORMANCE
In order that the performance of the drainage works can be assessed, the following will need to be monitored:-
a)    Groundwater levels prior to drainage, during installation of the works and during leaching and irrigation trials;
b)    Groundwater and soil salinity levels prior to drainage, during the works and after leaching and irrigation trials;
c)    Rainfall and open pan evaporation during the course of the trials;
d)   Drainage outflows and salinity levels during the course of the trials.
4 DIVISION OF RESPONSIBILITIES
If. order to allow for flexibility in the choice of who is to perform the construction, a division of responsibilities has been assumed. Activities such as site survey, design, supervision, will be assigned to the*Engineer’(including Air staff), and the main constructional activities have been grouped within the responsibilities of the ’Contractor’. These activities are broadly as follows
Mobilise
Survey
Install measuring devices Monitor measuring devices Prepare design details Issue design details Obtain tenders
Check setting out Supervise construction Review design
Contractor
Mobilise
Purchase/Fabricate pipes
Purchase/Fabricate travelling shutter Excavate open drains
Install pipe drains Construct structure
22/
1 Photocopier—
1 Dyeline Print Machine
Sundry Office Consumables (paper, pencils, pens, etc)
Survey Equipment.—
1  Theodolite  with tripod
1  Automatic level with tripod
2   5m staves
1  100 m tape
1  30 m tape
Sundry surveying consumables (survey books, marking pens, pegs, etc)
Vehicles (with drivers)
1  for Engineer
1  for Inspector
1  for Surveyor and Survey  Team
Monitorir.g/Testing Equipment
2   Discharge recorders  for attachment to drain outlets
4 Calibrated buckets and stopwatches for measurement of drain discharge
1   tfater sampler to recover samples from within observation well tubes ana oelow water level
2   Water sounding tapes with electric indicators
NOTES: 2/ It is proposed to obtain a year'3 supply of paper for existing photocopier instead of purchasing a new copier.
3/ It is expected that the survey equipment can be made available from existing stocks.3   Spare probes for above
1  Spare cable for above
4   Spare batteries for above
1  Auger hole kit
1  Class A evaporation pan complete with gauge and cover
2   Soil moisture probes - walking stick type
1 Top pan balance, 500 gm capacity
1 Drying oven
24 Soil sample rings with plastic caps and carrying case
1 Ring holder for above for sampling above the water table
1  ditto for sampling below the water table
2   Munsell soil colour charts
400 m of 50 mm dia galvanised or plastic pipe for observation wells 50 Sockets for above
50 end plugs for above
100 m of 25 mm internal dia rigid plastic pipe for piezometers 1 screw type auger head 25 mm dia
Shutters for forming Parshall flumes in concrete 1 Rain gauge
7 STAFF DUTIES 
7.1 Drainage Engineer
a)    The Drainage Engineer shall be responsible, under the overall direction of the Resident Engineer, for the design and supervision of the drainage works.
b)    He shall be responsible for arranging the acquisition of the materials and equipment required for the drainage design and supervision, and the setting up of the office. He should give particular attention to establishing at an early stage what items are already available and which may need to be imported.
57.2
c)    He shall, in conjunction with the surveyor, co-ordinate the survey work and establish priorities.
d)    He shall make arrangements for the installation of additional piezometers and observation wells and other instrumentation within the pilot area.
e)    He shall prepare setting out information, designs, bills of quantities and specifications for issue to the Contractor.
f)    He shall, in conjunction with the Inspector, be responsible for the day to day supervision of the construction of the works-.
g)    He shall ensure that regular readings are made of water levels and that records are kept of all observations.
He shall be responsible for summarising all data and interpreting the results.
He shall, as directed by the Resident Engineer,  prepare reports on the progress of the works.
Drainage Expert
8
The Drainage Expert shall review the design for  the works.
He snail visit the works at the commencement of construction and advise on any difficulties.
c) He shall visit the site about two months after completion of the drainage wonts and shall prepare, in conjunction with the Drainage Engineer, an Interim Report on the pilot area drainage.
d) He would advise on any other aspects of the works from the Consultant’s Head Office as considered necessary by the Resident Engineer.
7.3 Surveyor
a)      The Surveyor shall agree with the Drainage Engineer the nature and sequence of the survey work required and how the results are to be presented.
6d) He shall check the Contractor's setting out.
c) He shall, as notified by the Drainage Engineer or Inspector, carry out checks on the line and level of drains being installed by the Contractor
7.A    Inspector
a)    The Inspector shall, in conjunction with the Drainage Engineer, be responsible for the installation and reading of the monitoring instrumentation.
b)    He shall be responsible for witnessing the Contractor's operations, drawing the Contractor's attention to any shortcomings and advising the Drainage or Resident Engineer if the works are failing to conform with the designs or specifications.
c)    He shall notify the Surveyor when checks on the Contractor's setting out or drain installations are required.
d)    He shall ensure that either himself or the Junior Inspector is present at all times when work is being carried out.
Junior Inspector
a)    He shall assist the Inspector and the Drainage Engineer as directed. b)    He shall normally be responsible for making regular observations of 
the monitoring instruments and keeping the records up-to-date. c)    He shall stand in for the Inspector when directed.
7Obtoln I Vehicle
For Inspector
Assist With Inslollolion 01 PniomiH'i Etc
4
Obtoln
Ifot Piezometers                 Test Gear
Obtain
Moteciols
/Obtoln
All Other p.
(l(
/ For Piezometer M                Monitoring* y
Monitor Existing^________________________________________ ______________________
Monitor Existing And Oromed Areos ] iMio.,
Woter Table
/ (Port)
/'/
Equipment
To Be           1
Installed |
/1
/ Obtoin 1 1
/\/ /I / / /
1 Vehicle
Instoll
Instoll Monitoring Equipment (Remolndor Of Piezometer Etc.) And Sei Ud Pcrshoil Flumes
/ For Engineer Piezometers''-''
(Port)
Procure Suitable z-x             Set Up
Office
Design
Existing
Obto«r Ottic
Survey let Field And p\ Survey 2ndField And Adiocent Block DroinlsP^ Adjocent Block Droln(s)''
/ Adjocent Block
Drain (s')'
Survey 4th Field Andfcp\ Survey 5th Field An Adjacent Block Drain (s)''"'' Adjacent Block Drain(s
1Ik
,I
(Surveyors Concurrent Activities)
Check Setting Out
II
'
Check Setting Out
' l'1
Check Setting Out
Check Setting Out
Check Setting Out
Works
Eacovote Moin And
Collector Orolns
/
For 2nd
(Concurrent Activities)
1 (Concurrent Activities)
Excavate Drains For 3rd Field
Loy Pipes
Excavate
, Drains
For 4th Fiel
t QLoy Pipe^Q Loy Pipe^Q
Backtll
I.
x>
Bocktill
GOVERNMENT OF ETHIOPIA
AWASH VALLEY
DEVELOPMENT AGENCY
AMIBARA IRRIGATION PROJECT II ACTIVITY NETWORK DIAGRAM
FOR INSTALLATION OF DRAINS IN PILOT AREAAPPENDIX 'C' Comments from IDA dated August 9, 1-982rLEGEND
Ground Water Contour (Outside Melko Sodi Farm)
Ground Water Contour (Inside Melko Sadi Farm)
Perched   Water   Table   Contour (Inside Melko Sodi Farm)
k / i Line of Cross Section
Primary Canal Secondary Canal Primary Drain Secondary Drain
Dyke

< <

Summery

Amibara Irrigation Project II - Summary

Amibara Irrigation Project II - Drainage & Salinity Study

Prepared by: Sir William Halcrow & Partners
Date: January 1983
Location: Amibara, Ethiopia

1. Introduction

This addendum to the April 1982 report addresses comments from IDA representatives at the May/June 1982 Donors Conference. The study focuses on drainage and salinity control for the Amibara Irrigation Project II, with particular emphasis on establishing a pilot area for testing drainage solutions.

2. Key Findings

2.1 Groundwater Conditions

Two distinct aquifer systems identified:
- A shallow, highly saline perched water table (up to 60 mmhos/cm conductivity)
- A deeper aquifer system separated by impermeable clay layers
Water table closest to surface near river areas with long-term irrigation
In northeast areas, water table >10m below ground level

2.2 Drainage Design Considerations

8 different drain types proposed based on soil stratification and hydraulic conductivity
Design drain depths recommended at 1.5-2.0m (FAO guidelines)
Maximum post-irrigation water table should be 1.5m below surface (1.2m in shallow permeable soils)

3. Pilot Area Proposal

3.1 Selection Criteria

50ha area near main drainage network
Includes both abandoned and becoming-saline land
Multiple soil classes with varying salinity levels
Good road access
Downstream location allowing progressive drainage upslope
Includes both moderately and highly saline land
Existing canal system for leaching trials

3.2 Pilot Area Objectives

Objective	Description
Design Validation	Check theoretical drain spacings and depths
Material Testing	Determine optimal drainage pipe type and filter surround
Performance Monitoring	Assess drainage effectiveness in water and salinity control
Leaching Trials	Test irrigation and leaching methods
Cost Estimation	Provide accurate cost data for full-scale implementation

3.3 Implementation Approach

Initial Phase: Temporary open drains at various spacings to enable early start while pipe procurement continues

Subsequent Phase: Pipe drains with different configurations (with/without filter surrounds)

4. Monitoring Requirements

Groundwater levels: Before, during, and after drainage installation
Salinity levels: In both groundwater and soil
Climate data: Rainfall and evaporation measurements
Drain performance: Outflow quantities and salinity levels
Piezometer network: To measure water table dynamics

5. Challenges and Considerations

Highly calcareous soils complicate soil analysis
Presence of gypsum in soil profile (especially in high sodium areas)
Open drain stability concerns (side slope stability, spoil bank encroachment)
Need for specialized equipment for large-scale drain installation
Potential need for imported drainage pipes if local supply insufficient

6. Recommendations

Proceed with pilot area implementation to validate drainage designs
Begin with open drains to gather early performance data
Install comprehensive monitoring network before drainage works begin
Investigate local sources for drainage pipes before considering imports
Conduct additional soil investigations in areas with different soil types
Develop specialized testing procedures for calcareous soils