GOVERNMENT OF ETHIOPIA
WATER RESOURCES DEVELOPMENT AUTHORITY
MASTER DRAINAGE PLAN FOR
MELKA SADI AND AMIBARA AREAS
FINAL REPORT
July 1985
VOLUME 7 ANNEX D : ENGINEERING
Water Resources Development Authority
P 0 Box 5673
Addis Ababa
Ethiopia
Sir William Haicrow & Partners
Consulting Engineers
Burderop Park
Swindon
Wiltshire SN4 OQD
United KingdomGOVERNME
ETHIOPIA
WATER RESOURCES DEVELOPMENT AUTHORITY
MASTER DRAINAGE PLAN FOR
MELKA SADI AND AMIBARA AREAS
FINAL REPORT
July 1985
VOLUME 7 ANNEX D : ENGINEERING
Water Resources Development Authority
P 0 Box 5673
Addis Ababa
Ethiopia
Sir William Hal crow & Partners
Consulting Engineers
Qurderop Park
Swindon
Wiltshire SN4 OQD
United KingdomMASTER DRAINAGE PLAN FOR MELKA SADI 4 AMI3ARA AREAS FINAL REPORT
VOL 1 
VOL 2
VOL 3
VOL 4
VOL 5
VOL 6
-
VOL 7 
VOL 3
VOL 9
-
—
VOL 10
SUMMARY
MAIN REPORT
ANNEX Al : SOILS AND DRAINABILITY CLASSES
ANNEX A2 : SOILS AND DRALNABIL1TY CLASS MAPS ANNEX A3             DESCRIPTION OF AUGER BORES ANNEX B               groundwater and salinity ANNEX C : HYDROLOGY
ANNEX D : ENGINEERING
ANNEX E : AGRICULTURE
ANNEX F        : MARKETING AND PRICES
ANNEX G        : PROJECT COST ESTIMATES
ANNEX H        : FINANCIAL AND ECONOMIC EVALUATION ANNEX I : EVALUATION METHODOLOGY - GUIDELINES ANNEX J : ENVIRONMENT AND HEALTHANNEX D - ENGINEERING
CONTENTS LIST
Page No
1.        INTRODUCTION
1.1       Background
1.2       Data, Maps and Surveys
2.        PRESENT IRRIGATION SYSTEM AND PRACTICES
2.1         Water  Distribution and Control.
2.2       Present Deficiencies and Recommendations for Improvement 2.2,1        Distribution Deficiencies
2.2.2        Seepage Losses
2.2.3        Counnunicat ions
2.3        Water   Measurement
2.4           Field   Irrigation Practices
2.4.1        Furrow Irrigation
2.4.2        Land Planing
2,4.3        Irrigation Scheduling
3.      DRAINAGE PLANNING AND THE MASTER PLAN
3.1    Drainage Requirements of Che Study Area
3.1,1          Existing Surface Drainage
3.1.2          Existing Subsurface Drainage Situation 3.1.3          The Drainage Requirement
3.2      Alternative Drainage Proposals
3.2.1          Main Drainage Options
3.2.2          FieLd and Collector Drain Options 3.2.3          Vertical or Well Point Drainage
3.3    The Master Drainage Plan
1
2
5
5
7
9
10
13
13
14
15
17
17
17
18
19
20
20
23
25
25
3,3.1
Introduction
25
3.3.2
The Drainage Network
26
3.3.3
The Development Programme?
27
3.3.4          Further Survey Work Requirement?
29
li)Page No
4. DESIGN OF THE DRAINAGE SYSTEM
4.1        Surface      Drainage Network - Melka Sadi Area 
4.2        Surface      Drainage Network - Amibara Area 
4.3        Main Drain 2 Design
4.3.1           Outfal 1 Design
4.3.2             Main Drain 2 Alignment
4.3.3             Siltation in Main Drain 2 
4.4        Drainage Design Criteria 
4.4.1             Subsurface Drainage Rate
4*4.2          Surface Drainage Design Criteria 
4.5        Sub-surface Drainage Network
4*5.1          Field Lateral Design
4.5.2             Collector Drain Design
4.6        Drainage Structures
.
4.6.1   ,        Major Culverts
.
4.6.2              Bridges
4.6.3  Surface Drainage Culverts
4.6.4             Surface Drain Outfalls
31
31
32
34
35
33
39
39
40
41
42
45
47
49
50 50
4.6.5 
Sub-surface Drainage Structures
51
4.7 
Flood
Protection Works
52
4.7.1 
Western Flood Dyke
52
4.7.2 
Eastern Flood Dyke and Drain
53
4.0 
Bilen
Swamp
55
4.9 
Water
Harvesting 
^7
4.10      Health and Environmental Implications
5. IMPLEMENTATION
Method     of Construction
61.
61
5.1.1
Alternatives for Pipe-laying
61
5.1.2
Pipes for Sub-soil Drainage
62
5.1.3
The RacofflBsended Method of Construction
57
5.1*4            Construction by Contract
5B5*2 Implementation Programme
5-2.1 General Aspects
5.2*2 Rate and Method of Subsurface Drainage Installation 5.3 Supervision of Project Implementation
6.        OPERATION AND MAINTENANCE
6.1        Irrigation Water Management
6.2       Operation and Maintenance of Drainage System
Page No
59
71
76
79
79
60
6.2.1        Operation and
Maintenance
Responsibilities
80
6*2.2 Operation and
Maintenance
Requirements
81
6*2.3 Organisational Strengthening Co Project Control Centre 33
7.      COST  ESTIMATES FOR STAGE I DEVELOPMENT
85
7.1
Unit Kates and Capital Costs
85
7*2
Recurrent Casts
57
7*3
Disbursement Schedule
88
3. COST ESTIMATES FOR MASTERPLAN
REFERENCES
89
I
i
(iii)FIGURES
1* Water Measurement Provisions at Secondary Canal Offtakes
2.          Master Drainage Plan Layout
3.          Master Drainage Plan Indicative Developinent Programme
4.           Melka Sadi Stage I Area - Surface and Sub-surface Drainage Layout
5* Main Drain I - Longitudinal Profile and Typical Cross Sections
6.          Ami bar4 Stage I Area - Surface and Sub-surface Drainage Layout
7.                Secondary      Drains      SD7      and      SD5      Longitudinal      Profile      and      Cross      Section B. Secondary Dram SD4 and SD6 Longitudinal Profile and Cross Section
9.        Subelele Drainage Pump Station
10.       MD2 Outfall - Awash River Stage Duration
11.       MD2 Longitudinal Profile and Cross Section
12.        Typical Sub-surface Drainage Layout
13.        Field Lateral Spacings for Stage I Areas
14.        Typical Sections through Sub-surface Drainage Pipes 15.        Typical Layouts for Replacement Culverts
16.       Typical Main Drain Culvert Details
17.       Main Drain (MD1/MD2) Cross-Drainage Structure
(iv)23. Typical Surface Drainage Culvert
19.      Typical Surface Drain OutfalL into Main Drain
20.       Typical Sub-surface Drainage Structure Details
21.      Western Dyke Longitudinal Profile and Typical Cross Sections
22.       Eastern Dyke Extension Longitudinal Profile and Cross Section
23.       Proposed Conservation Works for Water Harvesting Pilot Area
24* Proposed Implementation Schedule for Stage 1
25.     Middle Awash Agricultural Enterprise - Organisational Strengthening
26.       Project Control Centre - Organisational Strengthening for Additional
Drainage Works
27.       Illustration of Typical Trencher Machine
28.       Proposed Organisation for Site Supervision
APPENDICES
A Maintenance of Subsurface Drains
Monitoring      of      Irrigation      Practices      in      Melka      Sadi     Farm     Units     1      and     2, including Tables 31 - BL2
C Design Criteria
Subsoil       Drainage       Pipes       Alternative       Methods       of       Laying       -       Discussion       Paper,, March 1984E Job Descriptions: Middle Awash Agricultural Development Enterprise and State Farms
J
F Transport Considerations q£ Imported Pipes
G        Survey Equipment for Implementation Supervision H        Specification of Additional HousinR for PCC
I Production of PVC Pipes on Site
(vi)TABLES
1. Additional Operation and Maintenance Plant for the Project Control Cent
2. Additional Operation and Maintenance Personnel for the Project Control
Cen t r e
3.
Costs of Additional Housing for Project Control Centre
Plant and Equipment Cost Summary 5,         Selected Unit Rates
6
Melka
Sadi     Stage
I
Bills
of    Quantities
- Project
Year
2
7.
Melka
Sadi     Stage
[
Bills
of    quantities
- Project
Year
3
8.
Melka
Sad i    Stage
I
Bills
of    Quant ities
- Project
Year
4
9.
Afflihara
Stage      1
Bills
of
Quantities
- Project
Y ear   4
10
An ibara
Stage      I
Bills
of
Quantities
- Project
Year    5
11
Amibara
Stage      I
Bills
of
Quanti ties
- Project
Y ear   6
12,      Annual Recurrent Costa
13. Disbursement Schedule for Engineering Cost Estimates
14.      Master Drainage Plan Cost Estimate1. INTRODUCTION
1.1     Background
The engineering studies which have been carried out as part of the Master Drainage Plan have been reporced on in stages in the Discussion Paper (Ref 1) submitted in August 1984 and in the Interim Report (Ref 2) of November 1984.
The Discussion Paper presented the Outline Masterplan for the drainage of the study area, essentially recommending a system of gravity drainage leading the study area flows northwards into Angelele, through Kortume Swamp and back into the Awash. A cost comparison between pumped and gravity drainage systems was made at that stage and indicated that the pumped option was not favourable on cost grounds. This option has not been pursued further.
At the Interim Report stage a schedule for the implementation in three Phases of the surface and subsurface drainage works was outlined, with the individual Phases relating to the utilisation of drainage outfalls constructed
progressively downstream as the need for subsurface drainage extended northwards. A tentative implementation programme for the development of the Phase I works, using the existing primary drain outfall, was proposed. The
first stage of development within this programme identified an area of 5200 ha gross within the Melka Sadi and Amibara areas, for which detailed design and tender documents would be prepared.
The field studies have been concerned with the evaluation of existing irrigation practices and the assessment of drainage returns flows on the existing Amibara Irrigation Project; evaluation of seepage losses in canals; determination of drain and flood dyke alignments and associated topographical survey work. Outline designs, quantities and costs for the assessment of the various drainage options were also prepared during the field study phase. These have been further developed and refined during the latter part of the study.
11-2 Data, Maps and Surveys
The following maps and photographs were made available for the study;
Ci) Topographical maps of the entire study area at 1 in 20,000 scale, 0.5 m
vertical interval contour, based on 1966 aerial photography. These maps
have also been produced at 1 in 5,000 scale.
(ii)         Regatta maps, 1 in 2500 scale with 0.1 m vertical interval contours of the
Melka Warer Research Station the Amibara Settlement Project and Amibara
State Farm Units 1, 2 and 3.
(iii)       As constructed drawings for the Amibara Irrigation Project.
( iv) Ethiopian Mapping Agency Series 3 maps at 1 in 250,000 scale, 50 m vertical
interval contours of the Eastern Catchment area and Aledeghi Plains.
(v) Aerial photographs at 1 in 20,000 and 1 in 50,000 scales, based on 1966
aerial photography. These are currently being supplemented by photographs
and mosaics based on 1984 photography.
Field topographical surveys were carried out during the study period on the
fol lowing
(i)         Western        (Awash)        Flood        dyke        extending   from Amibara Settlement Farm to the northern limit of the dyke (24 km).
(ii) Alignment of proposed Main Drain No 2, from the existing main drain
extension to the northern boundary of the study area (9 km).
(ii i) Alignment of new secondary drain SD7, from the Melka Warer Research Station to SD5 near Ambash Farm (12 km).
(iv)       Awash River Cross sections; 18 sections were surveyed.
2(v)    Limited supplementary surveys were also carried out on parts of the proposed Eastern Dyke Extension and at Bilen and Kortume Swamps.
Data on irrigation water releases at Primary Canal Offtakes were obtained from the Project Control Centre. These were supplemented by information on planting and irrigation schedules obtained from State Farms.
All relevant reports on previous studies were also made available; those referred to in this Annex are listed in a Table of References attached to this report.
32. PRESENT IRRIGATION SYSTEMS AND PRACTICES
The present irrigation systems and practices were evaluated to assess any contribution they may be making to Che overall drainage problems within the study area. In particular improvements to the water distribution and control structures were investigated as well as the existing field irrigation practices
to reduce water wastage and over irrigation, contributory factors to the raising of Che groundwater tables.
2.1      Water Distribution and Control
Gravity irrigation is provided for the Amibara Irrigation Project State Farms, Melka Sadi Banana Unit, Melka Warer Research Station and Amibara Settlement Project. The old State Farms of Algeta, Ambash, Subelele and the Angelele Units LI and III in the Amibara Extension area have a pumped irrigation system chough in Che future it is proposed this will be converted to a gravity system
(Ref 3).
For rhe gravity irrigation system water is diverted at Che Melka Sadi weir and conveyed along 25.5 km of primary canal with water distribution regulated by six check drop structures, thirteen primary offtakes and five rejection spillways. The primary offtakes which incorporate constant head orifice measurement facilities control flow of water into the secondary canals.
Within Che Melka Warer Research Station and the Melka Sadi Banana Unit a formalised distribution system exists with under and over-shot gates controlling the flow of water into field canals. A less formalised system exists for the Amibara Settlement Project with very few control structures.
Within the Amibara Irrigation Project duckbill weirs and secondary offtakes regulate water distribution into Che tertiary canals. Smaller duckbill weirs and field offtakes control the flow of water into field canals where distribution of water to furrows is through syphons. Rejection and runoff from the furrows is disposed of via field, tertiary and secondary drains into the main drain.
aThe pumped irrigated system comprises 6 pump station sites situated along the Awash River with a total of 16 pumping units in operation. Measurements taken in October 1984 showed that individual pumping units were delivering between 200-250 l/sec with a 6 metre suction lift from the Awash River. A distribution system of tertiary and field canals delivers the water to furrows with control being achieved by earth check dams and movable syphons. No drainage system is provided.
2• 2 Present Deficiences and Recommendations for Improvement
2.2.1                   Distribution Deficiences
The present control of irrigation water within the Amibara Settlement Project and the old State Farms of Algeta, Ambash, Subelele and Angelele is not satisfactory. However improvements to the old State Farm systems will be implemented in conjunction with their conversion to a gravity fed system which
is Che subject of a separate study being presently undertaken by Nedeco.
Field visits Co the Amibara Settlement Project (ASP) during the study phase have indicated the following specific deficiencies in the present irrigation of the
Lands there:-
(a)        Poor land levelling resulting in uneven distribution of water over the fields and in some cases fields being out of command.
(b)        No permanent control structures along the tertiary canal or at the head of the field canals to regulate irrigation flows.
(c)         Inadequate regulating structures along the main supply canals. Most have no permanent gates to control water distribution and several structures are in need of repair.
(d)        Except for two parshall flumes and a constant head orifice offtake from the Primary canal no other water measurement facilities exist throughout the ASP area.
5(e)      There are no drainage facilities at all to remove irrigation rejection
flows or storm runoff.
All of the above factors will have contributed to the rising water cable
problems within the ASP. Whilst Che Master Drainage Plan includes a complete surface and sub-surface drainage layout for this entire area, the improvement o the present irrigation system is also considered essential.
Though the design of an improved irrigation network for the Amibara Settlement Project lies outside Che scope of Chis study, it is reconmended that
consideration should be given to the design and implementation of at least the minimal improvements noted below:-
(a)       Land planing within alL fields and for Chose fields
problems land
grades within
levelling        should        be        first        carried        out
the fields.
with more serious
to achieve the correct
(b)       Gated offtake            structures           Co control          flow into field                  canals.
(c) Water measurement/regu1ating structures at secondary offtakes. The Romijn
weir type as recommended by Nedeco (Ref 3) would be appropriate.
Lt is estimated chat the cost for these improvements would be in the order of
Birr 4.0 million of which some 2 million has been allocated for structures.
The distribution and control of water within the remaining irrigated areas is
satisfactory, except for the lack of adequate water measurement facilities at
the secondary and tertiary canal level within the Amibara Irrigation Project
area as discussed later,
Inefficiences        and        water        losses        also        occur        in        the        irrigation        distribution        system due to poor maintenance and inadequate repairs. Such would account for:
Water leaks through structures and gates,
Siltation and weed growth reducing the capacity of canals, Seepage through broken or poorly compacted embankmentsThe importance of regular maintenance for all canals and structures cannot be over-emphasised to restrict these losses.
2.2.2                 Seepage Losses
The contribution to the groundwater of seepage losses through canal banks and beds was investigated during the study phase. Ponding trials lasting from 3 to 5 days were carried out along the following canal reaches:-
Canal
Ponded reach length
(m)
Seepage loss
(l/sec/1000 m2 wetted perimeter
Primary Canal between
PCD4 and PCD5                                                             2000
Primary Canal between
PCD5 and PCD6                                                             1250
Primary Canal between
AVSA box culvert and
end of canaL                                                                    2750
Tertiary Canal T4/3                                                      1000
Pilot drainage area
supply canal                                                                       380
The results from these ponding trials indicate a seepage loss of the order of
0.20 l/sec/1000 m  wetted perimeter. The trials were undertaken in canals which had been in regular use, thereby it was assumed that:
(a)       the hydraulic gradient between the canal and the underlying water table was stab le
0.20
0.16
0.17
0.21
0.18
2
7(b)       deposition of silt along Che canal sides and bed would have helped seal the canal
The seepage loss rate obtained can therefore be considered the long term seepage value for design purposes though higher values could well be achieved for short periods on initial filling of canals.
In Che determination of the sub-surface drainage discharge coefficient a seepage component of 0.2 mm/day was taken. This is adequate to allow for all seepage from canals based on the seepage loss rate of 0.20 L/sec/1000 of
wetted perimeter.
An analysis of Che relative contributions of each canal co the overall seepage
loss indicated that some 40Z of the total seepage loss was contributed by the Primary canal due to its considerably larger wetted perimeter. To provide further information on the actual nature of Che seepage loss from the Primary canal two series of augerings were completed with auger borings to 5.0 metres over a distance from 1.0 to 50 metres from the canal's water edge. These augerings were completed along the primary canal adjacent to Melka Sadi village. The first site showed a direct connection, in a localised area of permeable sandy strata, between the water level in Che canal and the adjacent water table, 3.5 metres below ground at a distance of 50 metres from the canal. The second site showed no evidence of lateral seepage between the canal and the water Cable some 3.5 metres below the ground adjacent to the canal. No specific conclusions can be reached from the limited data although the two results confirm the variable nature of seepage from the canal, as can be expected in an area of such heterogeneous soils.
Whilst it is anticipated from the above results, that the estimated seepage from the Main Canal will not cause significant overloading of the drainage system, the proposed enlargement to this canal could prove problematic. The increase in duty to 28 m^/s which the Angelele Bolhamo extension requires (Ref 3) would result in an appreciable enlargement to the canal section and increase the present seepage losses. The aspect of canal lining will have been considered
in the current studies being undertaken by Nedeco. Should it be decided to retain an unlined section then the resultant seepage could increase by up to
850Z and may cause excessive surcharging of the adjacent field lateral drains.
It is reconmiended however that no special action be taken unless such surcharging is observed to be occurring. Should such occur then a sub-surface interceptor drain may be required to be installed along Che irrigated side of
the canal. This drain would be installed at or near a depth of 2.0 metres as
further deepening could effectively increase the seepage. To cover for the
possible occurrence of excessive seepage an allowance of Birr 1.9 million at 1984/85 prices is included in the Masterplan cost estimate (Table 14), This
would provide for the installation alongside Che enlarged canal section of some
23 km of interceptor drains of diameters 150 nm, 225 mm and 350 mm with a red ash surround, discharging into the nearest deep open drains.
2.2.3                   Communications
During the study phase, field observations showed that usually there was a rejection flow from at least one secondary or tertiary canal within each farm
unit. The cumulative effect of these rejection flows over the whole drainage
system resulted in average main drain flows of between 500 to 1500 1/sec being recorded at the main drain outfall. Though some rejections are unavoidable a contributory factor appears to be the existing poor communication facilities, which at present does not enable a quick response to sudden changes in water requirements at the field level.
For example the lack of radio facilities between the various parties and
sometimes shortages of transport can result in a request from the Unit Farm's Irrigation Supervisor in the field through the Unit Manager, Water Management Engineer, Water Bailiff and then to the gate operators taking up to 24 hours. Normally the Unit Farm's Irrigation Supervisor and Manager are requested to programme in advance what their daily requirements will be. However unexpected events such as heavy rainfall, canal breaches or irrigation teams not turning
up, could upset their scheduling. A quicker response therefore to these sudden events by the relevant parties possessing walkie talkie sets as recommended in the Operations Manual (Ref 4) could help to reduce rejection flows.
Q2.3      Water Measurement
Adequate water measurement facilities are essential to permit the correct distribution of water throughout an irrigation system from headworks to field.
Such facilities also enable the relationship between water applications and crop
yield to be monitored thereby improving the water application efficiencies and reducing wastage of water. Ideally direct water measurement should be provided
as an integral part of the control of all regulating structures. Due to
hydraulic and cost considerations this is not practicable and a compromise
solution is adopted.
The existing situation regarding flow measurement for the areas outside the Amibara Irrigation Project is as follows:-
(a)       The Melka Sadi Banana Unit has a fairly comprehensive measurement sytem with Parshall flumes at the secondary canal offtakes and calibrated sharp crested weir plates at the tertiary offtakes into the field canals.
(b)       The Melka Warer Research Station and the Amibara Settlement Project have limited measurement facilities with a few Parshall flumes only in secondary canals.
(c)       The old farms of the Amibara and Angelele Units have water meters on Che delivery pipe systems of nine pump units along the Awash River. In October only one meter (at Algeta) appeared to be functioning.
For the Amibara Irrigation Project water measurement facilities were provided at each offtake from the Primary canal such chat flows into secondary canals could be accurately determined. Flows at secondary offtakes into tertiary canals are controlled by a single lift gate which permits only approximate calibration. In practice an acceptably accurate flow division into these tertiaries has not been achieved. At tertiary offtakes into field canals similar difficulties have been experienced with apportionment of flows. These difficulties cannot be wholly attributed to the inadequacy of the system for any improvements in the
facilities must be parallelled by an improvement in the skill and technical appreciation of the gate operators and irrigation supervisors. To facilitate
10the operation of the present system it is recommended that direct water measurement devices should be provided at all secondary offtakes, combined with low cost improvements at tertiary offtakes.
At the existing secondary offtakes within the Amibara Irrigation Project two adaptations of the existing structures are possible for the provision of flow measurement facilities. These are outlined in Figure 1 and described below.
(a) Pressure Gauge Measurement
This requires the provision of pressure taps upstream and downstream of the existing culvert control gates with stilling wells in which water levels would be read using a portable differential gauge. Discharge would be estimated using a chart of discharge versus differential head over a range of gate openings.
(b) Free Flow Sluice Gate
This requires the provision of an adjustable free flow sluice gate in the approach channel. To obtain stable flow conditions (requiring a minimum gate submergence) a specially shaped gate, based on the standard Crump de Guyter type (Ref 5) would be combined with a 10 cm increase in upstream head. This increase could be obtained either by lowering the approach channel floor or by raising Che secondary canal check weir crest. The latter course would be that recommended since it avoids difficult demolition and rebuilding of reinforced concrete. Some check crests have already been raised and excavated silt deposits can be used for raising secondary canal banks where necessary.
A third alternative relating to the operation of the intake as a constant head orifice using an additional gate would require excessive head which is not available, and is therefore not pursued further.
Of the above methods the use of an adjustable free flow gate is preferred as it would give the most direct and accurate measurement. It would also be applicable to both the pipe and channel type secondary offtakes.
11For the pipe type secondary offtake the measurement gace would be installed at the position of the upstream stoplog slots. The existing control gace would be retained. To improve the upstream flow conditions the wing walls would be built up and provided with rounded pier noses and the bed approach extended and also rounded as shown on Figure 1. Similar modifications would be made at the channel type secondary offtake except Chat the existing gate can be modified in its present location.
The improvement in the discharge capacity and accuracy is largely achieved by the radial profile of the lower gace section made from 3 mm thick miLd steel plate. Measurement of the flows would be made from a staff gauge situated upstream from the gate in conjunction with a calibration chart. Modular discharge across the gace is assumed to ensure accurate flow measurement.
As Che geometry of the secondary canal offtake structure is different to that of the standard Crump de Guyter weir/gate configuration the standard rating curves cannot be utilised. Calibration of the structure would therefore be required using a standard Parshall type flume constructed in Che downstream channel.
It is recommended Chat prototypes for a pipe type offtake and a channel type are constructed and tested throughout the required discharge range. Apart from calibrating the structure it is particularly important to establish, for Che
pipe offtake type, Chat reflected waves from the pipe headwall do not influence free flow conditions under the gate. AI90 a check can be made on whether the proposed 10 cm rise at the secondary canal check weir is in fact necesary as is indicated by calculations. Apart from the above points no other operating difficulties are anticipated. In particular Che high silt content of the
irrigation water should not in itself adversely influence the performance of the gate. The calibrations derived from the prototypes would be appropriate to the other proposed structures.
With the ability to reliably estimate the discharge at the head of the tertiary canal it is considered that less sophisticated measurement facilities would be required at the field canal level. The installation of clear and accurately levelled staff gauges upstream and downstream of the tertiary offtake pipe culverts are therefore reconmended. a number of culverts would be calibrated 
12using a portable measuring flume and charts prepared of discharge versus head difference. The Water Management unit of the PCC would be responsible for
these tests and for the resultant calibration of the structures.
Within the existing drainage system a Parshall flume for measurement of the
total drainage flows is already located close to the Main Drain's outfall into 
the Awash river. It is proposed chat this be supplemented by a further Parshall
flume in Main Drain 1 at the existing drop structure near the Amibara State Farm Headquarters. This structure would allow measurement of sub-surface and 
rejection flows from the Melka Sadi area.
2.4 Field Irrigation Practices
2.4.1              Furrow Irrigation
Furrow irrigation is the most common practice throughout the study area with 
water being syphoned directly into the furrow from the field canals. Furrow
lengths are typically 200-250 mm with slopes of 0.052 - 0.3Z. Earthen closure
bunds are constructed at approximately 50 m intervals along the field canal to 
pond up the flow. The continual rebuilding of these bunds causes low spots in 
the adjacent fields and weakens the canal banks. Several units farms within the Amibara Irrigation Project now use heavy duty polythene portable checks; this practice should be extended to all farms.
To achieve a uniform water distribution down a furrow, the initial stream
applied should be the maximum non erosive flow for the furrow such that Che advance flow reaches the end of the furrow as quickly as possible. This should 
be within one hour approximately under normal conditions, using between three
and five syphons per furrow. Thereafter Che flow should be cut back to equal
the furrow intake rate and continue for the scheduled duration of the
irrigation, without any water escaping from the end of Che furrow. The Water Management Manual (Ref 6) and the Operations Manual (Ref 4) advise on the number of syphons to be employed and the application times. These latter range from
about 19 hours for the pre-planting irrigation to 5 hours for post planting irrigations, with applied amounts of 314 and 130 ram gross respectively.
13During this study, detailed observations were made over a two week period of the irrigation practices in Melka Sadi Units 1 and 2. The results are given in Appendix B. These observations indicated that the actual applications times
were usually dictated by the time taken for the advance stream in the 'slower' furrows to reach the end of the furrow, rather than by any predetermined time schedule. The rates of advance between furrows ranged widely, largely as a result of appreciable microtopographical variations. Advance streams were generally provided by two, occassiona1ly three, siphons with one siphon being used for the cut-back stream. Very few irrigation teams possessed watches so that accurate adherence to application times would not have been possible. Apart from the need to provide watches, as recommended in previous reports, and to adhere to the recommended streams and application rimes, the uniform distribution of water in furrows will not be achieved without improvements to microtopography.
2.4.2              Land PLaning
The immediate requirement, co permit uniformity of irrigation application, is to achieve and maintain the correct furrow gradients. During the construction of the Amibara Irrigation Project extensive land Levelling operations were carried out Co Che stipulated specifications and design gradients before being approved and accepted by the project. The resultant levels and gradients would not be expected to remain constant, especially during the initial post-construction years, due to settlement of the fill areas and to Che loosening and movement of soil during agricultural operations. Subsequent land planing is an essential
and regularly required operation to maintain uniformity.
Apart from the observations above of flow behaviour in furrows indicating irregular microtopography, a series of profiles along furrows were surveyed during the agronomic field work, confirming the appreciable variations in microtopography (Annex E), and concluding that the current land planing operations are not successful. Recommendations for obtaining an improved uniformity of land levels are given in Annex E. Until such improvements are achieved the uniformity of water applications will remain low.
142.4.3               Irrigation Schedules
Irrigation schedules for the Amibara Irrigation Project area are prepared in advance each year by the Water Management Engineer, based on proposed planting dates supplied by the State Farm Units. These schedules and their stipulated application amounts have been based on the recommendations given in the Water Management Manual (Ref 6).
The recorded irrigation schedules, showing dates of irrigation over the past
three years, were obtained for Che Melka Sadi and Melka Warer Units 1 and 2 as well as the pumped supply for State Farms, Algeta, Ambash, Subelele and Angelele. These showed the Amibara Irrigation Project unit farms to have received an average of six post-plant irrigations per season whiLsc the pumped areas only received four irrigations. The recommended schedule proposed seven irrigations.
As discussed in Annex C, it is recommended that Che median rainfall (SOX exceedence) is used instead of the previously advocated 75X monthly exceedence value. The proposed new irrigation schedules given in Annex E are based on median rainfall amounts.
Continuous review of the irrigation schedule should be made during the growing season to take into account the rainfall received and the date of previous irrigation. Such review will require a good level of understanding of crop 
water requirements and how these are derived and applied. State Farms will therefore need to recruit and retain experienced irrigation staff as described 
in Section 6.1 herein.
In the Melka Sadi Banana Unit Che stipulated irrigation schedule is 100 mm gross every 15 days applied in small basins. An analysis of irrigation records for
1983/84 shows wide divergences from this interval, the most frequent intervals employed being in Che range of 20-25 days. Similarly the tentative water balance for bananas, computed in Annex C indicates appreciable application deficits. In the particular circumstances of this Unit, where water tables are already high, it would appear unwise to recoanend an increase in application 
15without Che provision of attendant sub-surface drainage. Under drained conditions a revised irrigation regime is given in Annex E proposing reduced irrigation intervals. In view of Che high sensitivity of this crop to water shortages it is strongly advised that rainfall amounts are taken into account in adjusting the irrigation applications.
163. DRAINAGE PLANNING & THE MASTER PLAN
3.1      Drainage Requirements of the Study Area
3.1.1              Existing Surface Drainage
The study area comprises the right bank flood plains of the Middle Awash River. It is bounded on the west by Che levee formation of the Awash and is protected from river flooding by a continuous dyke of some 55 km length which runs northwards from the diversion weir at Melka Sadi, past the Melka Sadi and Amibara Areas, to Che upper part of the Angelele Plain.
To the east lies the Aledeghi escarpment, part of which drains towards the Awash across the project area. The eastern catchment dyke extending over 32 km from Melka Sadi to Che northern limit of the existing Amibara Irrigation Project
(AlP)j protects the project from flood flows and diverts these into the
presently uncultivated lands of the Amibara Extension area.
A series of ill-defined natural drainage lines run northwards through the study 
area and continue into the Angelele Plains leading towards Kortume Swamp which forms the natural drainage sump for the entire flood plains. Excess flows from
the swamp are reputed to drain northwards through a series of faults towards Lake Hertale, a saline lake which lies a further 30 km to the north.
Surface drainage of the Amibara Irrigation Project is effected by the existing Primary Drain, constructed in 1980, which runs from the northern boundary of the Melka Sadi Banana Unit through Melka Sadi and then skirts the eastern edge of the Amibara section of A1P. This drain formerly discharged into uncultivated lands at the northern limit of the AIP area resulting in the creation of a perennial swamp with its attendant health hazards (Annex J). In 1983 the drain was extended across the flood plain to discharge into the Awash River through a gravity flap sluice structure. Under the intermittent conditions of high river
levels the flap remains closed and excess drainage flows are discharged over an emergency spiLlweir into uncultivated lands downstream.
17In-field, tertiary and secondary surface drainage channels were constructed 
within the AIP area, and conduct storm runoff, excess flows from irrigation and 
irrigation canal rejection flows into the Main Drain. A less formal system of
surface drainage exists within the Melka Sadi Banana Unit, primarily constructed 
to accept irrigation canal rejection flows.
There     is     no     existing     system     of     surface     drainage     within     the     Melka     Water     Research Station                the Amibara Settlement Farm, Ami bar a Units 1, 2 and 3 (Algeta and
Arab ash) and Angelele Unit 1 (Subelele). Similarly the Angelele Units 2 and 3, lying in the northern part of the study area possess no drainage system. All the above units are essentially a ‘closed cell* arrangement, being wholly encircled by flood dykes, roads or canal banks. The remaining lands forming the northern sector of the study area are presently uncultivated but are scheduled for development in the near future as part of the Angelele-Bolhamo project.
3.1.2              Existing Subsurface Drainage Situation
With the exception of the Pilot Drainage Scheme (35 ha) there are no sub-surface drains within the Study Area. Earlier studies, carried out prior to the implementation of the Amibara Irrigation Project LI, concluded that the natural hydrogeological characteristics of the area would not be capable of absorbing the deep percolation losses induced by surface irrigation and that Che groundwater tables could be expected to rapidly rise to a level which would require the installation of sub-surface drains (Ref 7). Actual rates of rise of groundwater sustained since the onset of irrigation have confirmed these predictions. In Che Melka Sadi Banana Unit high groundwater levels were observed by 1976, five years after irrigation had commenced in that area. The current study findings indicate chat groundwater tables are rising at about 1 metre per year and currently lie within 3 metres of ground surface over some 2200 ha in Melka Sadi and 1600 ha in Amibara.
1/ An interim arrangement for pumping canal rejection flows from the Research Station into the Awash is currently being installed.
183.1.3               The Drainage Requirement
The lack of surface drainage facilities within the irrigated entities adjacent
to the Amibara Irrigation Project prevents the evacuation of excess storm runoff, excess irrigation applications and of rejection flows with the latter being applied directly on to the fields. Apart from the adverse effect that the consequent waterlogging has on crop yields the contribution to groundwater recharge is enhanced, resulting in a more rapid rise of the groundwater tables.
Trial water balances, based on records of actual gross water applications for a selected area in Melka Sadi with deep water tables indicate that, for cotton,
the contribution to groundwater recharge has been in excess of 200 ms per season, in spice of the actual application amounts during the period being less than chose recommended (Annex C).
Conversely with high water cables, within say 1.5 m of ground level, the evaporation from the water tables during the fallow season for cotton could equal or exceed the contribution to groundwater during the irrigation season resulting in the water table fluctuating seasonally about an annual mean constant level. Under such conditions the crop would suffer from high water tables in the irrigation season combined with a high degree of secondary salinisacion during the fallow (Annex E).
In the Melka Sadi Banana Unit, where Che present water tables generally lie within 1 m of ground surface, Che trial water balances indicate that due to significant annual under-applications of irrigation water Che net contribution Co Che groundwater may have been effectively at or near zero, with Che deficiency in application amount being partially offset by plant withdrawal from the high groundwater tables.
With irrigation regimes recommended to achieve optimum yield under project conditions and with low water tables it is unlikely that the net losses to the groundwater table would fall below 25Z of the gross field irrigation applications, assuming an in-field application efficiency of 70Z with limited surface runoff losses. This would represent annual contributions to the groundwater of some 250-300 mm for cotton and 750-900 mm for bananas.
19Projections of the current rate of rise of groundwater indicate that within 14 years, that is, by 1999, the water table will have risen to within 1 metre below ground over the entire Melka Sadi area and over approximately half of the Amibara area, if drainage is not provided (Annex B).
The essential requirements to effect adequate drainage within the study area are the provision of subsurface drains in areas of high watertables together with an extended surface drainage network to cater for the currently irrigated areas without such a facility, as well as those further areas scheduled for irrigated development within the study boundary.
3.2      Alternative Drainage Proposals
3.2.1                Main Drainage Options
During the initial, Identification phase of this study a series of options
available for the surface and sub-surface drainage of the study area were investigated. Two main approaches are available:
( i-) Gravity diversion of drainage flows, through lands lying downstream of the study area
and
(ii) Pumping drainage flows back into the river from one or more collection points, together with a gravity discharge facility operating at low river levels.
The combined pumping/gravicy option was based on a pumping station with low level gravity flap sluice outlets, located at the northern end of Che study 
area. The costs of Chis option in terms of both initial capital and subsequent operating expenditure were unfavourable relative to gravity only alternatives.
20A number of gravity drainage sub-options were also investigated with consideration given to returning to the Awash all or part of the drainage flows derived internally from the study area as well as flood flows derived from the Eastern Catchment area.
The conclusions of these initial studies clearly favoured the all-gravity 
options and in particular Chose which featured the diversion into lower Angelele of the intermittent flood flows, derived from the Eastern Catchment, as opposed to Che alternative of diverting these floods, through a high level bunded channel, back into the Awash. It was further concluded that the existing drainage system within Che upper sections of the Amibara Irrigation Project could be deepened to effect both surface and sub-surface drainage through the present Primary Drain Outfall. Due to limitations of drainage levels at this
outfall into the Awash it cannot effect gravity drainage of the lands adjacent
to its lower reaches and flows resulting from these areas would be directed northwards into the Lower part of the study areas.
Within Angelele the options available are the discharge of drainage flows into or through Kortume Swamp or, alternatively, the conveyance of these flows back into the river through an elevated drainage channel. For the latter option a drainage facility similar to the existing Primary Drain outfall structure was considered, incorporating a gravity flap sluice and a rejection spillway to discharge excess flows into Kortume Swamp during high river levels.
During the study phase the further investigations carried out indicated the unsuitability of using Kortume Swamp as a drainage sump. The continuous discharge of drainage flows into this low lying area would effectively create a perennial body of water. This would provide ideal conditions for the breeding of Che bilharzia snail vectors and would also destroy the main dry season grazing ground available to and extensively used by the Afar tribesmen. In view of Che low level of the swamp relative to the river, gravity drainage from the area back into the river is not practicable.
21Adverse conditions in Kortume could also be caused by excessive rejection of drainage flows during periods of drain outfall closure induced by sustained high river levels. The outfall would accordingly require to be located sufficiently downstream of the study area to minimise the incidence and duration of closures.
An alternative solution for the unrestricted release of drainage flows into the
Awash was developed such that the rejection of these flows into Kortume during high river stages would not occur. This alternative comprises a drain, aligned along the higher ground adjacent to the river level, which flows directly into 
the Awash without an outfall structure. High flow levels from Che river are confined within the drain banks, the confluence with the river being located sufficiently far downstream of the study area to minimise the backwater effects induced by such levels. Ln view of its advantages and its lower associated 
costs, this alternative has been adopted and its operation is more fully 
described in Section 4.3 herein.
The discharge of the intermittent flood flows generated from the Eastern Catchment would, conversely, be of benefit to Kortume and to the intervening Angelele lands over which these flows would spread by supplementing the limited rainfall in these areas. The frequency and duration of these flows would be insufficient to induce perennial swamp conditions. The existing eastern catchment drain freely discharges its rare flows into the uncultivated section 
of the Amibara Extension area. As observed during the study phase, these intermittent flows have enhanced the dry land grazing without having any appreciable negative health impact. The proposed system would operate in a similar manner so that there would appear to be no justification for the major investment which would be required in constructing high level guide bunds to convey these flows directly back into the Awash.
Similarly once past the northern limit of the study area, that is, north of
Bilen Swamp, there is no requirement to further guide the eastern catchment flows which will spread towards the natural drainage path in Angelele. The flood dyke has accordingly been terminated just beyond the study area boundary.
223.2.2               Field and Collector Drain Options (a) Shallow versus Deep Drains
% *
The required depths for in-field drains is governed by the need to ensure good water table control in the root zone during cropping and also, in the case of non-perennia1 crops, to limit the degree of secondary salinisation during the fallow or similar periods when the land is not being irrigated. Detailed discussion of the aspect of water table control is given in Annex E (Section 5.1) and of secondary salinisation in Annex 0 (Section 3.8). An analysis of water table response to irrigation indicated that drains as shallow as 1.0 metre were ineffective in controlling the fluctuation of the water table in the crop root zone such that yields would be seriously reduced. For adequate water table control, providing optimal yield response in cotton, a drain depth of 1.6 tn was required. A more stringent criterion on drain depth is imposed by the need to minimise the level of secondary salination. Based on this criterion a drain depth of 1.8 m was chosen.
Using a nominal depth of 1.0 metre a9 the maximum in defining a shallow drain then such drains would not be appropriate for the drainage of cotton or other annual crops. Similarly, for perennially irrigated bananas, the desirable maximum height of water table would be approximately 1.0 metre below ground. (Annex E, Section 5.1.2). Under the heavy irrigation regime required by this crop such control is achieved, but not exceeded, by drains at a depth of 1.8 m.
(b) Covered versus Open Drains
(i)           Field laterals
Field laterals are installed at a depth of 1.8 metres, with spacing varying from 30 m to 110 m (Section 4.5.1). The unit cost of supply and installation for a 60 :nm diameter corrugated PVC pipe including filter surround is estimated at 8.1 birr/linear metre. Unit rates are discussed 
in Section 7. An open drain of the same depth would require some 6 m^ of
23excavations per linear metre costing an estimated 38 birr. On cost grounds alone there can be no justification for using open lateral drains.
Of more importance would be the very appreciable loss in land area which would result from the use of open lateral drains. With the predominant
spacing of 45 metres the loss in land area would be in excess of 12Z within each field. Open drains are not therefore considered to be a viabLe
alternative co buried lateral pipes.
(ii)     Collector drains
The estimated cost per Linear metre for a 300 mm dia corrugated PVC pipe, supplied, laid and backfilled is 58 Birr. The costs of a deep open drain would range from 67 to 95 Birr for depths 2.5 m to 3.0 m respectively, assuming spoil can be directly disposed adjacent to Che excavation. Any restriction on the disposal of spoil would increase the costs of the open drain. As noted in Section 4.5.2 a single 300 mm dia collector, laid at
the minimum gradient of 0.052, will serve a drainage area of 102 ha. For drainage units of less than 100 ha the use of buried collectors is
preferable to deep open drains.
For drainage units larger than 100 ha the consideration of using buried or deep open drains would be based on local factors such as:- natural ground slope along collector alignment (at 0.12 slope a 300 am diameter buried 
pipe couLd serve some 140 ha); number of crossing points which a deep open drain may necessitate; required depth of collector; need to remove
excavated material to disposal areas; maintenance costs; health considerations, etc.
A further consideration lies in the achievement of a desirable minimum velocity in deep open drains. Under normal design flows (Section 4.4,2) with a channel invert gradient of 0.052, a contributing drainage area of some 300 ha is required co achieve a channel velocity of 0.3 ra/s, based on a bed width 0.5 m, Manning’s n - 0.025, and side slopes of 1 in 1.5.
24Where consideration is given to the above factors it is generally preferable to use a double pipe collector instead of a deep open drain; in some circumstances a triple pipe collector could be warranted although no individual drainage units in the present study area exceeded 200 ha.
3.2.3 Vertical or Well Point Drainage
In Annex B it is noted that the underlying aquifers appear to be essentially without flow and are also virtually hydraulically continuous. The use of
vertical drains for deep disposal methods is precluded under these
circums tances.
The sedimentary materials in the study area are consistently fine grained and characterised by low horizontal permeability. This factor, combined with the presence of relatively impermeable layers at comparatively shallow depths (less than 5 metres), would also disfavour the use of well point drainage, in that
very close spacing of wells would be required in order to effect adequate
water-table control. This option has accordingly not been pursued further.
3.3 The Master Drainage Plan
3.3.1 Introduction
The purpose of the Master Drainage Plan is to provide a comprehensive plan and schedule for the drainage development, both surface and subsurface, of the entire study area. In its scope the Masterplan comprises the outline design of
the major drainage network for the study area together with the detailed design of the surface and subsurface drainage works required to alleviate those areas currently being affected by high water Cables or likely to become so affected in the near future. The plan includes protection of the developed areas from river floods or adjacent catchment runoff.3.3.2                The Drainage Network
The      engineering      features      of      the      drainage      network      required      to      achieve      surface      and sub-surface drainage of the entire study area are as follows:-
(i)       The installation of buried field lateral drains, at an average depth of 1.8 
metres below ground, to achieve adequate control of the groundwater table.
The recommended spacing of field laterals varies from 30 m to 110 m within 
the area surveyed for drainability classification.
(ii)      The conveyance of lateral drain flows in buried collector drains to 
appropriate discharge points in deep open drains.
(iii)     The construction of in-field and tertiary surface drains to remove canal
rejection flows and excess field runoff resulting from irrigation or storm
rainfall.
(iv)     The deepening and widening, as appropriate, of existing secondary drains
and che Main Drain as well as the construction of new deep open drains to 
carry subsurface flows, rejection flows and storm runoff.
(v)      The construction of a drainage outfall into the Awash, in Angelele, with 
its associated Western (Awash) flood dyke extension.
(vi)     The realignment and heightening of parts of the Western (Awash) flood dyke
between Algeta and the northern limit of the study area as well as the
extension of rhe Eastern Catchment flood dyke and drain to the northern
limit of the            study area.
An     outline     of     the     proposed     drainage     network     for     the     entire     study     area     is     shown in Figure 2.
263.3.3              The Development Programme
AC the Interim Report stage it was considered Chat the implementation of the Masterplan appeared to divide naturally into three Phases. Phase I related to 
the development of drainage works in those areas which could utilise the existing primary drain outfall for discharge of flows into the Awash. Phase III reLated to the construction of a drainage outfall in Lower Angelele which would permit subsurface drainage down to the study area boundary. This phase accordingly provided for the surface and subsurface drainage of the entire study area at full development.
Phase II referred to the construction of an intermediate outfall which would cater for the development of subsurface works up to some, as then unspecified limit, which would be determined by projected rates of encroachment of high water tables. A further criterion in assessing the location of and required 
timing for the Phase II outfall was the need for the immediate provision of such a facility on implementation of Che proposed development in the Amibara Extension Area to serve its surface drainage requirements.
Further studies and designs have confirmed that, as a result of Che extremely mild land gradients in upper Angelele, the location of an outfall to achieve the surface drainage of the study area is substantially similar to that required for the subsurface drainage, such that one new outfall only need be constructed.
Additionally the implementation schedule proposed by Nedeco for the Angelele- Bolhamo project (Ref 3) infers that surface drainage works in the Amibara Extension area could be constructed during 1987/88. These surface drainage works would require the construction of the new outfall which could thus be available for utilisation in the near future even before rhe required subsurface drainage works utilising the existing primary drain outfall would be
construct ed.
The need to sub-divide the development into distinct Phases related to each outfall, is thus obviated and this distinction has not been maintained in this Report.The subsurface development of the Melka Sadi area, including the MeLka Sadi Banana Unit can be carried out utilising the existing drain outfall. Groundwater projections (Annex B) indicate that virtually this entire area could be affected by the early 1990's, with up to 2800 ha (gross) being affected by 
1988.
Similarily in the western part of Amibara the groundwater projections indicate that the Settlement Farm together with substantial sections of the Research Station and Algeta Farm could be affected by 1988/89, the affected area possibly extending along the western part of Amibara through Subelele by 1990/91. Subsurface drainage of the former mentioned areas can be effected through the existing outfall whilst subsurface drainage of the latter areas, including Subelele would utilise the new proposed outfall. Based on these projections a Stage I area of approximately 5200 ha gross was delineated for immediate development.
In the subsequent design of the requisite subsurface and surface drainage works the boundary of the Stage I area was 'rationalised' to accord with existing 
field boundaries and natural drainage units, encompassing a total gross area of 6200 ha, with corresponding gross and net cultivable areas of 5450 ha and 4740 ha approximately. The construction of the surface and subsurface drainage works within this area would require a four to five year implementation period.
Projections of the rates of encroachment of high water tables in the north eastern parts of the Melka Warer State Farm indicate that these areas may not be affected for a further 20 years or more. However these projections relate to comparatively recently developed areas which lie adjacent to the largely uncultivated Amibara Extension Area. With the onset of irrigation in the Extension Area the rate of rise of groundwater can be expected to increase significantly. Lt is considered prudent to limit the implementation period for subsurface drainage throughout the study area to the forthcoming 15 years, that is, from 1985 to 2000. An indicative programme for the implementation of these works and corresponding areas are delineated in Figure 3. Due to the tentative nature of the drainage projections the sub-divisions of the implementation schedule into individual entities has not been carried out beyond Stage I.
29The detailed implementation programme for Che development of the Stage I area is given in Section 5. The preparation of detaiLed designs, tender documents, assessment of agricultural returns and the financial and economic appraisal
relate to Chis development.
3.3.4 Further Survey Work Requirements
Data for any raodifications co drains and structures within the Amibara
Irrigation Project areas can be obtained from the Project's as-constructed drawings. The 1:2,500 Regalta maps with 0.1 m vertical interval contours
provide adequate ground data for the design of the additional surface and 
sub-surface drainage works within the Ambash and Subelele State Farms. The design of drainage works within the Amibara Extension area will make use of topographic data collected for Che present on-going design of the new irrigation system for chat area.
Within the .Melka Sadi Banana Unit the only survey available is based on Che 1 in 20,000 scale, 0.5 m vertical interval, survey maps, prepared from Che 1966 
aerial photography. The accuracy of this mapping within the Banana Unit should be confirmed prior to the determination of setting out levels for sub-surface drainage. It is suggested that sample area surveys, within the abandoned sections of Che Unit are conducted for this purpose. A minimum of three blocks of 100 ha each should be surveyed. A grid interval of 40 m would be appropriate to the production of 0.1 m contours.
Cross sections at 200 m intervals are also required along proposed Secondary Drains SD8 and SD9 and also along these existing drains which will be utilised as tertiary drains under the proposed system.
Should the sample surveys confirm the adequacy of Che existing mapping then further survey will not be necessary. Conversely should the existing survey data be inaccurate then the entire area will require detailed surveying.
29Additional survey requirements to enable completion of the full Master D
g
Plan designs are required for the following specific components.-
(i)    Main    Drain    2    alignment    along    the    Awash    levee    from    the    end    of    the    present study area to Main Drain 2’s outfall
(ii)     Eastern     dyke     extension     from     its     present     end     to     the     natural     watercourse     just to the north of the study area boundary.
304. DESIGN OF THE DRAINAGE SYSTEM
The proposed layout for the surface and sub-surface drains has been made to conform with the existing irrigation and drainage systems to minimise disruption and reduce costs. The only exception is in the Amibara Extension Area where it is not practicable to incorporate the existing state farm layouts into the
proposed developments for the surrounding lands. The Master Drainage Plan layout is shown in Figure 2.
4. 1 Surface Drainage Network - Melka Sadi Area
For the Melka Sadi Banana Unit the proposed surface drainage improvements comprise the provision of field drains for each field, conveying surface runoff into tertiary drains which will run parallel to the supply canals. Some
tertiary drains already exist. These will be supplemented by new tertiary 
drains excavated along field boundaries with new culverts being provided at field access road crossing points as necessary. See Figure 4.
Two short deep open drains have already been constructed within the Unit in connection with the Pilot Drainage Project. Two further deep drains (SD8 and SD9) are proposed, to carry the sub-surface drainage flows and surface runoff. SD8 will be formed by deepening the existing Unit main drain, whilst SD9 will involve the deeping of an existing drain through the middle of the Unit. It is envisaged that where SD8 (the existing Unit main drain) runs parallel with SDl these two drains will be combined into one. As limited disposal areas exist adjacent to this drain an allowance has been made for 90Z of the excavated material from these drains to be trucked away to spoil tips alongside the
western dyke and SD2.
For the Stage I area sub-surface drainage requirements, the Primary Drain and Secondary Drains Nos SD2 and SD3 will be deepened and existing culverts along SD2 lowered. The Primary Drain will only be deepened as far as Che primary canal cross drainage structure. See Figure 4. As there are wide reserves
alongside these drains very little trucking of the excess spoil material is required.
31Also during the implementation of Stage I a tertiary drain will be constructed 
to allow the passage of the rejection flows from the end of the tertiary canal
T 1/3 back into the Main Drain near Dinile Hill. This will remove the present
stagnant pond of water downstream of this tertiary and alleviate the associated 
health hazard.
When subsurface drainage of those areas in the western part of Melka Sadi,
adjacent to the Western Dyke, becomes necessary in a subsequent stage of
development then SDl will be realigned following a more direct northerly 
alignment to join the Main Drain near Dinile Hill. This will permit the
sub-surface drainage of fields within the area served by this secondary. At
this stage the Main Drain deepening will be extended into the Amibara area as
far as the first culvert. See Figure 5. The primary canal cross drainage
culvert and link road culvert will also be lowered at this time.
4.2 Surface Drainage Network - Amibara Area
Surface drainage improvements for the Amibara area will include the provision of
field drains for each field within the Melka Warer Research Station, Amibara
Settlement Project and the ALgeta, Ambash and Subelele State Farms. To suit the
average existing field sizes of 4 ha for the Melka Warer Research Station, and 
18 ha for the Awash Settlement Project area, field drain lengths of 400 and 600 
metres respectively will be required. For the old state farm areas it has been 
assumed that the exisiting approximate 60 ha blocks will be sub-divided into
12     ha     fields     250     metres     wide,     thereby     requiring     600     metres     length     of     field     drain per field.
Within the Amibara Extension area the drainage network proposed differs from that outlined by Nedeco (Ref 3). This is due to the field layouts now being aligned relative to the existing ground contours to ensure the direction of furrow irrigation follows the natural ground slope. This also conforms with the layouts adopted during the latter half of construction of the Amibara irrigation 
Project which resulted in reduced land levelling requirements per field.
32In Stage I a new deep Secondary Drain SD7 will be excavated, starting from the Melka Warer Research Station, passing through the middle of the Awash Settlement Project and Algeta and Ambash State rarms to connect up with the existing SD5 drain. SD5 will be deepened as far as its outfall into Main Drain 1. See
Figures 6 and 7. The existing SD4 drain will be deepened and connected to SD6 by a new deep drain along the alignment of Che existing tertiary drain TD 11/3. See Figure 8. A new deep open drain SD 4/2 will be built to discharge drainage from Che Awash Settlement Project Extension area into SD4. Due to inadequate reserves alongside SD4 and SD7 most of the excavated material from these drains will be trucked away to spoil tips along nearby cattle corridors or outside the Project area. The existing outfaLl of SD4 into the Main Drain will be blocked 
off. New culverts will be constructed along SD7 where it crosses existing canal and road lines and the existing culverts along SD4 will be lowered to accommodate the deeper drain. The remainder of the Amibara Irrigation Project surface drainage system will operate as designed.
At present, excess drainage flows passing over Che emergency spillweir when Che main drain outfall is closed, pond in the low lying area between the Main Drain and Angelele Unit II State Farm. As a temporary expedient for the immediate alleviation of this problem it is recommended that a flood drain and dyke be constructed to guide drainage flows to the east of the Angelele Unit II. The
dyke will join up with the existing dyke running along the eastern side of the
Unit II farm and guide drainage flows away along natural drainage paths to the north.
During further proposed developments utilising the existing drain outfall (MDl) the Awash Settlement Project Extension surface drainage requirements will be completed and a new deep open drain SD 4/1 excavated between Tertiary canal TC 5B/2 and SD4 to facilitate sub-surface drainage of Unit I of the Melka Warer State Farm. SD6 will be deepened as far as its outfall into Main Drain 1. The surface drainage of the remaining areas not completed in Stage I within the Algeta, Ambash and Subelele State Farms, will be undertaken and the upper reach of SD5 to its proposed junction with SD7 deepened. Drain culverts will be constructed as required.
33Within the Subelele area however the ground levels are too low to permit gravity drainage into Main Drain 1. Therefore the immediate surface drainage requirements of the area can only be met by constructing a small pumping station near the road crossing of the main drain extension. The pump station would consist of two 80 1/sec diesel driven pumps as detailed in Figure 9. This pump station would become defunct on the construction of the proposed new main drain and outfalll (Main Drain 2).
The head of Main Drain 2 will be located at the confluence of SD5 and SD6. Lt will initially run parallel to and then pass under MDl by means of a cross
drainage culvert near
the existing Parshall flume road culvert. Main Drain 2
will
continue through the Amibara Extension area before
joining the              Awash River
at     an     outfall     adjacent     to     the     Southern     end     of     Korturae     Swamp.     Tertiary     drain     TD
10/2 part
will be deepened to form drain SD6/1 to facilitate of Unit 6 of the Melka Warer State Farm. Tertiary 
sub-surface
drains will be
drainage of
constructed      through      the      whole      of      the      Amibara      Extension      area      during      this      Phase. Drain culverts will also be constructed as required.
With the development of the Amibara Extension area the flood dyke and drain as discussed above, to carry drainage flows away from the emergency spillweir, will become obsolete. It will be replaced by a flood drain constructed parallel to 
Main Drain 1 to carry discharges passing over the spillweir directly into Main 
Drain 2. This flood drain will outfall into MD2 just downstream of its exit
from the cross drainage culvert under MDl.
4.3 Main Drain 2 Design
Main Drain 2 will provide drainage for those parts of the Amibara area too low
to achieve surface and sub-surface drainage through the present Main Drain 1 
outfall. It will command a net area of 9700 ha. It will also take overspill
from Main Drain 1 (which would have a command area of 4500 ha net) when the Main Drain 1 outfall is closed by high river levels. It will allow surface and 
sub-surface drainage for the Amibara Extension area.
344.3.1               Outfall Design
Several alternatives were considered for the discharge into the Awash River of drainage flows passing through Main Drain 2. AU had the objective of returning 
at least the normal drain flows to the Awash River.
(a)      Flap-gated pumped outfall
This type of outfall would allow normal drainage by gravity during low
river levels and by pumping at other times. To limit the pumps to an acceptable size, a spillweir would be required to reject the stormwater
flows which would then pass through the Angelele area into Kortume swamp.
For this alternative Che outfall could be located anywhere downstream of the drained area, depending on how many months of the year it was considered acceptable to operate the pumps.
This alternative relies on the continual use of pumps throughout the life
of the project. Cost analyses showed that the initial capital costs could marginaLly favour this alternative. However the subsequent high operation and maintenance costs of the pump units makes the option unattractive and it was not pursued further.
(b)      Gravity Flap-gated outfall
This would be similar in operation co the existing outfall of main drain 1 such chat during high river levels the normal drainage flows would pass over a rejection spillweir into the Angelele area.
This alternative may only provide a partial solution to the drainage of the entire area including Angelele, as spillage into Che Angelele area could pose problems for future irrigation development there. Also the possible sustained rejection of drainage flows during closure of the outfall due to high river levels could create unfavourable conditions within-the Kortume area which is environmentally unacceptable.(c)      Natural confluence with no structure
For this alternative all drainage Elows would be returned to the Awash 
River. Left and right drain banks would be such as not to be overtopped 
during the 1:20 year river flood. Silt deposited in the drain during 
backing up of water during floods would be scoured out again as the river
recedes. (See Section 4.3.3). This alternative is preferred.
The location of MD2 outfall was chosen to make the drain as short as possible
while satisfying the following requirements:-
3
(i)       A minimum velocity of 0.4 m/sec at the normal discharge of 3.7 m /sec
assuming no spillage from MDl, giving a minimum slope of 1:10,000.
3
(ii)      Water levels at the normal discharge of 5.2 m /sec , which assumes rejection 
spillage from MDL, to be sufficiently low to allow subsurface drainage
of the northern part of the study area.
3
(iii)Water levels at the storm discharge of 22.2 m /sec, including storm
spillage from MDl, to be below ground level in the Amibara Extension area.
(iv)          Temporary     rises     in     flow     level     during     high     river     levels     to     be     of     acceptable magnitude,      duration      and      frequency      so      as      not      to      affect      sub-surface      drainage within the Amibara Extension area.
At the selected outfall location two flood level/discharge conditions in the Awash were chosen to assess the backwater response which would be induced in Main Drain 2. These were:.
(i)        Bank full discharge at the outfall, estimated to be in the order of
260 tn^/s, and
(ii)       Flow at a nominal 0.65 m below bank full, estimated to be in the order of 175 m3/s
36These flow Levels in the river result in increases of flow level in the drain,
above its normal level, of 1.78 m and 1.13 ni respectively at the drain outfall, decreasing to 0.78 m and 0.33 m at the northern end of the project area, some 12 kilometres upstream of the outfall.
Daily flow records at Melka Warer from August 1972 to December 1982 showed that Che chosen river discharges were, on average, exceeded for a total of 5 days and 28 days per year, mostly for periods of one Co three days at a time. See
Figure 10. It is considered Chat such occurrences would have a virtually negligable effect on crop growth and are acceptable.
Similarly it is not anticipated Chat the temporary retention or holding back of
the drainage flows in the collectors would in itself induce any unfavourable siltation probLems in these pipes and no special provision needs to be made for additional maintenance.
4.3.2 Main Drain 2 Alignment
Main Drain 2 will follow the natural drainage path from the Main Drain 1 cross drainage culvert to a point adjacent to the Angelele Unit III farm boundary.
MD2 will then follow an alignment 50 metres to the east of the western dyke extension, itself a minimum of 100 metres from the river bank. Longitudinal profiles and cross sections of MD2 are given in Figure 11.
The point of departure from the natural drainage path was chosen where this path becomes closest to the river levee, thereafter the drainage path again diverges trom the levee. Continuation of the drain, along the natural drainage path, beyond this point would require it to loop back towards the river, thereby enclosing an isolated area of land between the river and the drain which would render its future development more difficult. A further disadvantage is that
spoil excavated from the drain would have to be hauled back to the levee to construct the flood dyke whereas forming the drain on or adjacent to the levee obviates the need for haulage.
37Subsurface drainage of part of the remaining area enclosed within the study boundary line cannot be achieved without an appreciable lowering of the HD2 bed level. As the drain is designed to run at the minimum gradient, commensurate with Che requirement to maintain a normal flow velocity of 0.4 m/s, this
lowering in bed level would extend throughout MD2 to its outfall thereby increasing the earthworks quantities and requiring an outfall further
downstream. The area affected is shown on Figure 2 and is in the order of only 100 ha. Thus it is recommended chat provision is not made for its subsurface
drainage into MD2. Should such drainage prove necessary it could be combined with the further drainage of Angelele lands outside Che project area.
4.3.3                 Siltation in Main                 Drain 2
Siltation of MD2 will be of three types: drainwater silt, river silt supplied by reverse flow into the drain and river silt supplied by eddies at Che drain 
outfal 1.
The amount of silt deposited by the drainage water itself will be slight,
especially during normal flow originating from the pipe drains, and should be
well within the capacity of the usual maintenance plant.
Deposition of silt in the drain by Che river requires either a continuous or an alternating supply of river water. An alternating supply results from reverse
flow into Che drain during rapid rises in river level followed by evacuation during recession. The normal drain discharge of 3.7 m^/s would be checked by a river level rising at a rate of around 2 ra in 24 hours. When the river rises
faster than this, river water will start co flow back into the drain, pushing 
the drainage flow back. If the river rises 4 m in 24 hours, the river water
will extend some 6 km into the drain by the end of the period, depositing its
silt load to a depth of the order of 1 cm. Such large rises are infrequent, and 
the total silt load deposited by this mechanism will again be small.
The third type of siltation will be much more rapid. When the river is in 
flood, eddies at the mouth of the outfall extending at most a few hundred 
metres into the drain will provide a continous supply of silt. Experience with 
the flushing channel downstream of the Melka Sadi headworks has shown deposition
38rates of the order of a metre per day. It is expected that a plug of silt will form in the drain outfall during every large flood. The depth of this plug would be related to river level, leaving sufficient depths over the plug to allow the passage of the drain discharge itself. This plug will be well within the steep final reach of the drain at a slope of 1 in 1000. On flood recession the drainage flow, assisted by the release of the water backed up in the drain, will scour down into the plug as in any natural stream confluence.
4.4 Drainage Design Criteria
4.4.1              Subsurface Drainage Rate
The relevant subsurface design parameters are discussed in detail in Annex A, Section 5. The design subsurface drainage rate is based on the estimated drainable excess resulting from the irrigation regime for a particular crop.
The       average       in-field       drainable       excess       recorded trials ranged from 202 - 302. Expected values
in the Pilot
Drainage Scheme
for surface irrigation with an
assumed     application     efficiency     of     302     would     normally     be     in     the     order     of     252, the remaining 52 being direct surface run-off.
For design purposes the following values have been assumed;
Bananas : drainable excess =• 252 - 27.52 
Cotton        : drainable excess => 252
Based on the recommended irrigation regimes the resulting excesses are in the
range of 3.1-3.4 rnm/day for bananas, at the peak irrigation cycle of 100 mm
gross every 8 days and 2.2 mm/day for cotton. The comparative excess for
cotton, derived from the present practice of 130 mm gross every 14 days, is
2.3 mm/day.
With  a nominal allowance for seepage contribution  from distributary  canals, estimated  in  Annex  C to  be in  the order of 0.15  mm/day, Che design  drainage rates are taken as 3.4 mm per day for bananas and 2.5 mm per day for cotton.
39The value chosen for cotton would also be sufficient for Che drainage of most
other Likely irrigated crops in Che area.
4.4.2 Surface Drainage Design Criteria
Field drains were designed as a minimum section of 0.5 metre bed width, 0.50 
metre deep and l:li side slopes and can be constructed using a shaped ditching 
bucket.
Tertiary  drains were designed  to  cater for the full rejection  from a tertiary canal giving  a drain  design  capacity  of 400  l/sec. Minimum bed  width  of 0.75 metre, with 1:1.5 side slopes were chosen.
The deep open secondary and main drains were designed for normal flow velocities being greater than 0.3 m/sec. For Bilharzia control the velocities should preferably be greater than 0.4 m/sec (Annex J). Where the ground slopes were favourable and discharges adequate these higher velocities were achieved. Elsewhere these are not possible to achieve without significantly increasing 
drain depths and hence costs.
The normal flow level io the deep open drains was set 15 cm below the centreline of the sub-surface collector drain outfall level. Normal flow discharges were made up of two components
(a)       Sub-surface drainage flows
(b)       Rejection fLows
The sub-surface drainage flows into surface drains were estimated by applying a factor of 0.2 1/sec/ha to the drained area. This factor was derived by taking the sub-surface drainage race of 2.5 nxn/day and applying an areal reduction factor of 0.7. This factor relates to the fraction of the total area that is
being irrigated at any one time being 10Z or less (Ref 8).
•pie rejection flows were estimated by applying a.factor of 0.15 l/sec/ha. This factor was derived from field data collected on rejection flows during the study phase. The data indicated that the sum of both direct canal rejection and field 
40rejections     varied     from     some     10     to     20     1/sec     per     100     ha,     with     an     overall     average of 12 1/sec per 100 ha. Therefore a design figure of 0.15 l/sec/ha was chosen.
Combining      the      rejection      and      sub-surface      drainage      components      gave      a      design      normal flow discharge coefficient to 0.35 l/sec/ha.
Where possible the depth of the deep open drains were kept less than 3.5 metre
below the existing ground level. 3ed width and depth ratios were optimised to 
ensure minimum cut sections compatible with the minimum velocity and flow
criteria. Where the depth of the drain was greater than 3.5 metre, then a 4.0 
metre wide berm was included in the drain section for stability reasons. As the
controlling criteria for Che design of Che deep open drains was normal flow
conditions being maintained below sub-surface drainage outfall levels, an 
appreciable margin of spare capacity was available in these drains during flood 
flow conditions.
However     fLood     flow     discharges     were     used     in     the     design     of     structures     along     the deep open drains. As discussed in Annex C a drainage coefficient of
1.0 l/sec/ha was derived based on a I in 5 year rainfall occurrence. To this drainage duty was added, for example, in Che case of a main drain receiving sub-surface drainage flows as well, Che normal flow discharge coefficient to give an overall flood flow coefficient of 1.35 l/sec/ha.
A summary of Che design criteria is given in Appendix C.
4.5 Sub-Surface Drainage Network
The sub-surface drainage network consists of slotted corrugated PVC pipes forming the buried field lateral drains. The field laterals connect to collector drains also of corrugated PVC pipe which discharge drainage water directly into deep open drains. The collector drains serve one or two sets of laterals as appropriate. See Figure 12 for a typical sub-surface drainage layout.
414.5.1                 Field Lateral Design
The depth of the field lateral pipe has to be compatible with satisfying the following criteria:-
(a)       Control of the groundwater cable so as not crop during the irrigation season.
to cause waterlogging of the
(b) Control of the groundwater table to minimise capilliary salinisation of the
crop root zone during the fallow season.
The depth should also be such as to be within the economical operating range of conventional pipe laying equipment as well as permitting, in this instance,
gravity discharge into the river without excessively deep open drains extending unnecessarily far downstream of the study area.
As discussed in Annex A consideration of these factors resulted in an average field lateral depth of 1.8 metres being chosen.
The ideal alignment for the field laterals is parallel to the direction of
irrigation so that disturbance to the furrows is minimised and preferential drainage paths reduced. The laterals are also most generally placed at right
angles to the collector drains. In order to minimise the depth of the collector outfalls below ground level, especially in the flatter parts of the area, the collector drains run parallel to the maximum ground slope (Section 4.5.2). The LateraLs therefore run parallel to the contour which is also for much of the
ALP 11 area, the direction of the furrow irrigation.
Ln order to limit machine excavation requirements a maximum lateral depth of 2.0 metres has been taken, with a minimum depth at the head of a lateral, or at the lowest point in a field, of 1.6 metres. A design slope of 0.1Z has been chosen 
as the minimum appropriate for laterals. Such a slope should limit siltation and also will allow for some tolerances in pipe-laying.
42As    discussed    in    Annex of soil drainabilicy.
A field  lateral spacings have been  optimised  on  the basis
Four       soil       drainability       sub-classes       have       been       identified 
for both coarse and fine textured soils to give the following design field lateral spacings:
Soil Type
Drainability Class
La
Coarse Textured
lb
Ic
Id
Ila
Fine Textured
lib
lie
lid
Design Spacing (metres)
45
65
85
110
30 45 60 75
The soil surveys chat have been completed within the Stage I areas of both Melka Sadi and Amibara indicated Chat fine textured soils predominated. Therefore the field lateral spacings will vary from 30 to 75 metres. Rationalisation of Che boundaries on the drainability class map for the Stage I works gave the areas
for the different drain spacings as shown in Figure 13.
The field lateral pipe size was chosen to ensure Chat it would discharge the equivalent of 2.5 mm/day (the drainage rate for cotton), assuming 20Z reduction in the capacity of the pipe due to silting and a maximum lateral spacing of 70 metres. A lateral length of 300 metres was assumed with the lateral laid at a gradient of 0.1Z. Taking the non uniform flow equation for corrugated pipes (Ref 9) as Q - 38d 2.667 £ 0.5  where Q is in Lit/sec, and d is in mm.
#
then                d       2.667.
x 70 x 300 x 1000 0  5 x 1000
0.8 x 38 x (0.00L) -
60 ora (id)A     60     aim     internal     diameter     pipe     was     therefore     taken     as     the     standard     size     for     the field laterals within the cotton area.
For the bananas the maximum drainage coefficient was taken as 3.4 nnn/day, based on the peak water application regime (Annex A). Within the Melka Sadi Banana Unit the average field lateral length is 250 metres and applying the same
equation as above with average lateral spacings and slopes of 60 metres and 0.1Z respectively gives a required pipe diameter also of 60 ram (id).
Surrounding the field lateral pipes will be a red ash envelope of minimum thickness 75 mm. This envelope will not only reduce the entry resistance of water into the pipe but with a suitable grading will assist in preventing fine
soil particles entering the pipes. A filter gradation as given below based on criteria recommended by Winger and Ryan (Ref 11) gives a coarse filter and was considered appropriate for the design of the envelope material used in the Pilot Drainage Project. Results from the Pilot Drainage Project to date indicate that the use of Chis red ash envelope reduced the amount of silt found in the pipes.
The natural grading of samples of red ash material taken during the Pilot Drainage Study trials conform well with the design criteria on removal by screening of the coarse fraction (> 38 am) and fioe fraction (< 0.07 mm). No further crushing or sieving proved necessary. The obvious economies that would result from using this locally available material without the need for extensive crushing or sieving make it an ideal envelope material for the sub-surface
drains. However to confirm its longer term suitability it is recommended that its performance is monitored by sampling over a period of time. The filter should be exposed and its condition assessed as well as carrying out a sieve anaLysis and inspecting the pipe perforations for blockage.
44The recommended grading, as us               ed in the Pilot Drainage trials, is listed below:
Z Passing Sieve
100 85 50 15
0
Particle Size Lower Limit
(mm) 10
5 1.5
0.4 0.07
Particle Size Upper Limit
(mm) 38
20
8 3 0.6
Supplies of red  ash  material are plentiful with  recommended  sources being  Dinile Hill in  the Melka Sadi area and  the volcanic hills at Amibara village and  Ambash in the Amibara area.
4.5.2              Collector Drain Design
The subsurface collector drains are aligned parallel to the general land slope
so that they can take maximum advantage of the naturaL fall without requiring excessive deepening. With most of the area having the direction of field irrigation parallel to the contour, this makes it possible for Che collector drains’ alignment to be parallel to and alongside field or tertiary drains. However, in some instances, for example Melka Sadi Unit 5, the direction of field irrigation is at right angles to the contour. For this situation the
collector drains will have co run through the fields to ensure the field lateral lengths do not exceed 400 metres. For maintenance purposes access to the collector drains will be from manholes situated where the collector drains cross field boundaries.
A minimum gradient of 0.05Z was assumed along the collector drains to reduce their outfall depths. Three pipe sizes have been chosen; 150, 225 and 300 mm internal diameter. Using the same drainage coefficients as above; a 20Z reduction in the capacity of the pipe due to silting; areal drainage reduction factors of 0.8 for 150 ram, and 0.7 for 225 and 300 mm diameter pipes; a reduction factor of 0.75 to give appropriate lengths at which transition from
45one size to another takes place, and applying the non-uniform equation for corrugated pipes of Q « 38 d 2.667 £ 0.5 (R f 9)1) gave areas served by each 
e
collector as follows:- Pipe diameter
(mm)
------ Area - hectares ------ Cotton Crop 
Banana Crop
150 
14 
10
225 
47 
35
300 
102 
75
Where the area served is greater than the above limits for 300 mm pipes, then 
two collectors would be laid in parallel trenches. No envelope material is
required around the collector drain pipes.
4.6 Drainage Structures
The Locations of major structures are shown in Figures 2, 4 and 6, (Layouts) and 
Figures 5, 7, 8 and 11, (Longitudinal Sections). The following general types
are required:
Culverts and cross-drainage structures in deep drains
- Bridges over deep drains
Surface drainage culverts and cross-drainage structures
Surface drain outfalls and drops
Sub-surface drain manholes and outfalls
The       functions       and       outline       designs       for       these       structures       are       discussed       briefly below, with design criteria listed in Appendix C.
1/ Where Q is in lit/sec and d in mm
464.6.1              Major Culverts
Major culverts are required to carry roads or canals or both over deep main drains, and roads over deep secondary and tertiary drains. The structures will be located both on new drains (eg SD7) and on existing drains which are required to be deepened (eg MDl).
On main drains (MDl) the possibility was considered of modifying the existing structures to accept, with a lower bed level, the increased discharges resulting from review of the surface drainage coefficient and the addition of sub-surface drainage discharge. For the existing standard drain culvert, comprising masonry abutments on a reinforced concrete base slab, the modification which would best reduce the risk of collapse during construction would be the installation of a 1 metre diameter pipe under the base slab in a heading (small tunnel). However, in most cases the difference between proposed bed level and existing bed and culvert floor level is such that the single pipe would be required to carry all
of the peak discharge, necessitating downstream energy dissipation provisions to cater for Che high pipe velocities. Additionally, although the apparent cost of such a modification would be comparable with the alternative discussed below, it is difficult to estimate the amount which a Contractor might include to cover
his risk element in such an unusual construction method. Lt was therefore concluded that Che best solution in most instances would be replacement of existing culverts.
The arrangements for construction of culverts in deepened main drains will have to cater for a continuous drain discharge, since even in the closed season for cotton sub-surface drainage flows will continue from the Melka Sadi Banana Unit and rejection flows will arise from the current (undesirable) practice of supplying drinking water through the canal system. To avoid the necessity for construction of a temporary diversion channel it is therefore proposed that the replacement culverts be built in the dry, alongside the existing structures,
with a minor drain diversion on completion. Schematic arrangements for such work are shown in Figure 15.
47In the case of the existing standard culverts at the tail of drain SDl and on 
MD1 in Melka Sadi, deepened drain bed levels would be such that the flow level
at peak discharge would not reach the invert levels of the existing culverts and 
all flow would therefore .be carried by the replacement structure. The same
applies to the existing culverts MDC 1/2 and HOC 1/3. With the culverts on MDl under the primary canal and the link road, the difference between existing and proposed bed levels is less (see MDl Longitudinal Section - Figure 5) and the existing culverts would carry a proportion of the peak discharge. Normal
discharge, comprising sub-surface and rejection flow, would be carried entirely 
by the new supplementary culverts situated in by-pass channels.
The standard reinforced concrete/masonry ’bridge’ type culvert design was previously adopted for use on Amibara Irrigation Project works since it was less costly than a pipe culvert both in terras of material use and additional drain excavation depth required as a result of head loss. A similar design has not
been adopted for the proposed culverts, for Che following reasons:
Proposed drain depths are generally between 3 and 4 metres (compared with original main drain depths up to about 2 metres) and at this depth the cost
of masonry in abutments and sidewalls compares unfavourably with the cost of concrete pipes.
A significant number of the new structures are required to carry watercourses over the deep drains and for this purpose a culvert type structure is preferable to the alternative of a flumed watercourse combined with the bridge deck. Given the necessity for pipe production for these structures, there is merit in standardisation by using pipe structures elsewhere; the unit cost of pre-cast pipe will reduce as the total number required increases.
Head loss through the proposed culverts is of significance at normal discharge, when subsurface drain outfalls must remain un-submerged. At this discharge the head loss is negligible with an acceptable number of pipe barrels. During the short duration peak discharge periods much higher headloss can be accepted through the proposed pipe culverts, (there being 
48more than adequate freeboard in the deep drains) consistent with adequate protection at the pipe outlet.
Outline standard details for the proposed culverts are shown in Figure 16. The structures carrying watercourses across the deep drain would differ tros the standard road crossing structures in respect of length of pipe and the provision 
of pipe collars and toe drains to cater for seepage.
Culvert hydraulic design provides for the pipe velocity to be no less than the
drain velocity at all discharges, with a maximum at peak discharge of approximately 3.0 metres/sec. Head loss is generally of the order of 2-5 cm at normal discharge and 50 cm for short durations at peak discharge. Pipe inverts
are depressed below bed level to allow for possible downstream bed 
retrogression; to provide for adequate submergence under conditions of rapid inflow (eg from rejection) and co provide for energy dissipation ar high discharges.
For Che cross-drainage structure carrying main drain MD2 under the existing primary drain extension (MDl) in Amibara, costing of alternatives showed an advantage in the use of a reinforced concrete box culvert rather than a large number of pipes. Outline details of the structure, with 2 no 1.5 m square
boxes, are shown in Figure 17.
During construction of this crossing it will be necessary to divert the MDl
flows around the structure or alternatively to pump. The diversion duty can be minimised by ensuring that the diversion is carried out in the non irrigation 
season and/or by arranging for any short duration high flows in MDl co be diverted through the existing rejection spillway.
4.6.2              Bridges
Four crossings of MD2 would be required when this drain is constructed downstream of the present primary drain extension. Three of the crossings would be for roads only, and the southern-most for a road together with a future secondary canal, as proposed by Nedeco (Ref 3), for the eastern side of the Amibara Extension area. The drain peak discharge would be some 22 cumec with a
49depth of the order of 5 metres and top width of 19 metres. With these
parameters the most economical type of crossings would be bridges and costs have been estimated on the basis of two 9pan simply supported structures of the same basic design as those constructed during the Amibara Irrigation Project at the
link road and at Melka Sadi village. In the one case where a canal crossing is required, this would be achieved in a reinforced concrete rectangular flume alongside, and on the same piers as, the bridge traffic deck.
4.6.3                Surface Drainage Culverts
Tertiary level culverts and cross drainage culverts will be required as part of surface drainage development in the Awash Settlement Project, Ambash, Algeta and Subelele State Farms. The designs proposed are based on standard details developed during construction of the Amibara Irrigation Project, using 600 mm internal diameter pre-cast concrete pipes and masonry headwalls as shown in Figure 18. Cross drainage culverts would be provided with pipe collars to 
prevent erosion by seepage from watercourses crossing over the drain. At locations where an access crack crosses the downstream ends of field drains, small culverts, using 450 ram (id) pre cast concrete pipes, would be required and details would again be as Chose adopted for the Amibara Irrigation Project works.
4.6.4                Surface Drain Outfalls
To avoid unacceptable erosion, small structures are required to discharge tertiary and secondary drain flows through falls of up to 3 metres into deep main drains. The most severe operating conditions for such structures occurs with little flow in the main drain and a sudden inflow from the minor drain, as might result from canal rejection. The outfall structures have therefore been designed to cater for 100X rejection from either tertiary or secondary canals discharging into tertiary or secondary drains. Details of these structures are shown in Figure 19, with construction comprising a lightly reinforced concrete glacis slab with masonry sidewalls carried to a suitable depth below main drain bed level to allow for stable energy dissipation. Alternative modes of construction considered were rip-rap and cemented pitching sloping aprons, both of which have been used only with moderate success in previous works. Rip-rap
50protected falls would be extensive in area with the relatively high drops and mild slopes required; additionally they rely on very careful design and installation of the underlying filter layers. Cemented pitching suffers from cracking due to uplift pressures as can be seen with some of the exiscing structures. Hence it is considered chat the design outlined in Figure 19 provides the best solution.
Drops are required at the head of deepened sections of secondary or tertiary drains, ie, immediately upstream respectively of the first collector drain or tertiary drain outfall. In most cases these structures will be the same as those described above. In a few instances more substantial structures (although designed on the same principle) are required where the secondary drain is designed to accept large rejection flows direct from the primary canal (eg SD2 on the Melka Sadi Agricultural Estate southern boundary).
4.6.5               Sub-Surface Drainage Structures
Outline details of these structure are shown in Figure 20. Manholes will be provided at maximum spacings of 300 metres along Che collector drains, to facilitate drain maintenance and assist in flushing of field laterals. They 
will also be provided at sharp bends along the collector drains. The manhole
will be sited alongside surface drains or canals where farm machinery should not interfere with them. They will be made from standard precast concrete sections and assembled on site.
The collector drain outfalls will be protected by rip-rap placed over a selected gravel filter co prevent scour of the adjacent drain bed and banks. Where field laterals discharge directly into deep open ditches no protection will be necessary as the discharge will be small. However it is recommended that marker posts are erected at each outfall site along the deep open drains so that
machine operators can locate them during maintenance operations.
To facilitate jetting of the field laterals an extension will be made tp the
field lateral pipe just upstream of its junction to the collector drain. The extension pipe will be brought to the surface and tied to a marker post some 1.5 metres high. The end of the pipe will be sealed off with a cap.
51^•7 Flood Protection Works
A component of the study is to look at the present flood protection works and to make recommendations on any improvements that may be required. Also additional flood protection works are required to the East of the Amibara Extension Area
and along the Awash to protect the new main drain and outfall.
4,7.1                Western Flood Dyke
In order to check the adequacy of the existing western dyke heights and provide data for the extension of the dyke to the proposed main drain 2 outfall, flood routing of selected flow hydrographs was carried out. This is discussed in 
detail in Annex C.
As reported by both Halcrow (Ref 10) and Nedeco (Ref 3) a 1:20 year return 
period flood was regarded the optimum for use in the design of the Awash River flood dyke. A freeboard of 1.0 m was added to Che calculated flood levels.
A check of the 1 in 20 year flood levels together with the 1.0 metre freeboard allowance showed that the existing Western Dyke was of adequate height except for a 5.0 km stretch between the Northern end of Subelele and a point 3.6 km to the north of the existing main drain outfall. The dyke over this length needs
to be raised by an average of 0.5 metres.
In addition the alignment of the dyke was checked to ensure that there was a minimum reserve distance of 100 metres between the toe of the embankment and the bank of the river. Six reaches of dyke were identified as requiring re-aligning with a total realignment of some 4.2 km. See Figure 21. These locations were
at the South Ambash, North Ambash and Subelele pump station sites and at three locations within the Amibara Extension area. At present the dykes come close to the river at the pump station sites to protect the pumps which are alongside the river. Because of their present importance the dykes at these locations are regularly maintained and strengthened. However when gravity irrigation replaces the pumped scheme Chen these locations will receive very little maintenance and 
hence become weak points in Che dyke system as well as restricting the floodway.
52The existing dyke ends just to the North of the study area boundary. The last
3 km of Che dyke which is of low height and in poor condition will be abandoned 
and a new dyke constructed parallel to the Main Drain 2 alignment. This new
dyke will connect up with the existing dyke near the old Angelele Unit III pump 
station site. The new dyke will continue downstream to the proposed outfall
site and will be constructed with excavated material from Main Drain 2 which 
runs parallel with it. See Figure 11.
The     top     width     of     the     new     and     strengthened     lengths     of     dyke     will     be     3.0     metres     to allow for vehicular access for inspection and maintenance.
4.7.2                   Eastern    Flood    Dyke    and    Drain 
(i) Existing Dyke
Since its completion in 1980 the existing eastern catchment dyke has been subjected to two severe flood events. These occurred in 1980 and in 1981 with the bulk of the flows being contributed from the southern part of the catchment, such that flows in the order of 100 m^/s passed under the link road bridge on both occassions. On the first occasion the flood water reportedly reached the top of the dyke at one point in Amibara but did not breach. On the second occasion several breaches occurred over a reach of approximately 1 kilometre in Amibara, downstream of the Melka War er Farm Headquarters. No significant damage was incurred in the Primary Drain and adjacent fields. The dyke has been subsequently strengthened and raised along this reach and also further downstream.
This type of information, provided by actual flood events, is of great vaiue in indicating what works are required, where calculations in themselves would only provide an indicative guide. The strengthening already carried out to the existing dyke should now be sufficient to ensure its adequacy against the proposed design flood (see below).
There are however some other features of the existing dyke which could endanger its safety. These are:
53(i)        Che presence of minor spoil dumps in Che floodway, adjacent Co the dyke, and
(ii)       the proximity of the interceptor drain channel to Che dyke itself.
The localised spoil dumps could, under high flow conditions, interfere with the flow pattern and possibly direct the flow towards the dyke itself. Similarly any actively scouring sections of the drain, where adjacent to 
the dyke, couLd endanger its stability.
It is recoamended that all minor spoil dumps are levelled such that no irregularities remain within the immediate vicinity of the dyke, say within 50 metres. Also where Che interceptor drain comes wichin 20 metres of the dyke a new channel should be cut at a distance of 50 m from the toe of the dyke and the former channel infilled. Such recommendations involve only limited small scale works which can be carried out as part of the project maintenance activities. Visual inspection will be sufficient to locate the relevant sections requiring such works.
(ii) Dyke Extension
Ln conjunction with the proposed developments of irrigated agriculture in the Amibara Extension area there will be a requirement to prevent storm runoff from the Eastern escarpment entering into this area. The existing Eastern drain and dyke will therefore need to be extended northwards along the alignment of existing drainage paths to a point to the south west of Cada Bilen Swamp. The alignment will then continue at a gradient just off the contour until the end of the study area is reached. The eastern drain will continue for a further 0.8 km towards a natural drainage line which will direct any runoff flows through Angelele towards Kortume Swamp. As noted in Section 3-2.1 there appears to be no justification to extend the dyke beyond the planned expansion area, nor to convey the intermittent flows back into the river. However should the development of the Angelele area be considered at a later stage the dyke could be extended, into Angelele, to run adjacent to the scarp and directing the flows further northwards, as required. Such an extension through Angelele would result
543
3
3
in     only     a     minor     increase     in     catchment     area     and     would     be     unlikely     to     affect the current flood flow estimates.
As noted in Annex C, Section 6.3 the Eastern drain is designed for a 1 in 
10 year return period flood of 94 m /s, rounded upto 100 m /s, with a
freeboard allowance of 0.5 metres. The 1 in 25 year return period flood,
estimated at 130 m /s, would result in a water level rise above the
100     m3/s     level     of     some     0.24     metres,     well     within     the     allocated     freeboard allowance.
The dyke will be formed by excavating a channel and using the material to build the adjacent embankment leaving a minimum reserve of about 50 m between the two. The dyke will be positioned a minimum distance of 150 metres from the toe of the adjacent foothills. Longitudinal and cross sections are shown on Figure 22.
The bed width of the channel was varied according to the local ground levels to give a constant water surface slope during Che design flood in order to make the channeL as stable as possible. Dyke top leveLs atyJ channel bed levels were chosen to equalise cut and fill.
4.8      Bilen Swamp
The Bilen Swamp is fed by a series of hot volcanic springs located at the toe of the eastern escarpment. The springs are perennial. Seasonal flow variations,
if any, are not known. A flow of some 500 lit/s was observed at Cada Bilen, the larger spring, whilst the flow at Unda Bilen was some 5 lit/sec. The
electrical conductivity of the water was approximately 1 mS/cm, which is the medium salinity range, unsuitable for senaitive crops.
The 9wamp occupies some 250-300 ha and supports in its centre a dense growth of marsh grasses and reeds whilst its fringes are extensively grazed grasses used 
by the local nomadic tribesmen for their herds. Ln the dry season when grazing is limited elsewhere a high concentration of animals is found adjacent to the swamp which provides one of the few reliable watering points in the area.
55Although surface salinity is evident in the adjacent escarpment the dense vegetation within the swamp itself indicates that a leaching mechanism must
exist in the absence of surface outflow from the swamp. It is suspected that
surface outflow only rarely occurs in times of overland flood flows from the escarpment catchment, through the swamp. If it is assumed that the inflow to 
the swamp is constant at 500 lit/s, with no surface outflow, Chen the seepage
loss would be in the order of 200-300 lit/s, with the balance going to 
evaporation or evapotranspiration. Despite such an apparently large
contribution to the ground water there is no evidence of salinity or
waterlogging in the area immediately downhill of the swamp. It is possible however that the seepage contribution may be channelled through preferential
flow paths in the underlying rock as is reputed to occur downstream of Kortume Swamp. Two of the proposed observation wells (Annex B, Figure 9) are located in the future irrigation area downstream of the swamp. Observations on these
wells, when available, will provide an indication of the localised influence on the ground water table.
Unless such observations indicate that the swamp is significantly contributing to the groundwater levels in the future irrigation area, it is recommended that the swamp and it environs be left unchanged thereby retaining one of the few remaining natural watering and grazing points in this area.
Consideration was also given co the utlisation of Bilen Swamp as an attenuation pond for Eastern catchment flood flows. However the ratio of storage area in Bilen, relative to the total catchment area is very small
(2.5 km/800 km - 0.3Z). Significant attenuation can normally only be expected from ratios above 5Z or 10Z. Additionally it would appear from existing contour maps that a substantial portion of Bilen swamp would be above the level of the eastern drain at that point. Equally no requirement exists for
attenuation as the flood flows can be accommodated in the eastern catchment drain and will be naturally dispersed in the Angelele area. The subject has therefore not been pursued further.
562
2
2
4.9      Water Harvesting
The derivation of flood flow estimates for the Eastern catchment is described in Annex C. It is considered unlikely that contributions to the flood flows would occur simultaneously from all parts of the 800 km  catchment. Therefore possible contributing areas of 317 km  and 590 km  were assessed, producing 1 in 10 year flood peaks of 90-95 m^/sec. Ln view of the large areas of catchment which could contribute to these flows it is unlikely that significant
attenuation could be achieved unless very extensive water harvesting measures were to be undertaken. This would constitute a large project in itself and 
would not be warranted solely from the point of view of protecting the project area from flood flows. Water harvesting measures have accordingly not been incorporated into the Masterplan.
Nonetheless there are other significant benefits to be gained from water harvesting both in reducing erosion of the catchment area and in stimulating the growth of vegetation. In view of these benefits it is recommended that consideration be given to the development of a small pilot area to demonstrate these benefits and to determine the most appropriate measures for the particular conditions prevailing between the eastern escarpment and the project flood protection dyke. A suitable area was identified during the study phase some 500 metres co the north of the link road. Here the ground rises gently at an 
average gradient of 1:100 from the Eastern dyke until a steep escarpment is reached some 2 km to the East. The area is covered with sparse bush and is subjected to surface and gully erosion along the natural watercourses.
The conservation works envisaged are the construction of 1.0 metre high bunds along the contour spaced at vertical intervals of 2.0 metres. They will stretch across a small catchment area some 1000 metre wide. The top most bund nearest the escarpment will be made into a catchment drain with a sufficient grade on it to remove any runoff from upstream away from the pilot area. Sheet runoff originating between the bunds would pond up against each bund and infiltrate, depositing any sediment. The infiltration opportunity afforded would assist in establishing and sustaining vegetation.
57These minor works could be constructed by a small dozer (equivalent to a Caterpillar D4 or D6), with material being pushed down the slope to form the bunds with a top width of 1.0 m. Suggested details of these conservation works are shown on Figure 23. Should the pilot scheme be considered for implementation it would be necessary to conduct a detailed topographical survey to determine the existing ground contours and align the bunds accordingly.
Although the costs of implementing the pilot
scheme are not
included in the
Masterplan an estimate of the required
works
is given below:
Description
Cost (Birr)
Bush Clearance (along bunds), 20 ha
66,000
Construct bunds 25,000 m^
175.000
Fencing 6 km
150,000
Access Gates 4 No
4,000
Sub-total
395,000
Contingencies, say 10Z
40,000
TOTAL
435,000 Birr
The costs given above assume that the
works
are carried out
as part of a
contract.     It     is     possible     however     that     some,     if     not     all     of     these     works     could     be undertaken by the PCC utilising the existing plant.
4.10    Health and Environmental Implications
A     study     of     the     Health     and     Environmental     implications     of     the     Master     Drainage     Plan was     carried     out     by     the     Environmental     Health     Unit     of     WRDA     in     association     with     the Inter-Institutional         Committee.         The         findings,         conclusions         and         recommendations         of this 9tudy are presented as Annex J to this report.
The study considered the principal health hazards to be schistosomiasis and malaria and placed particular emphasis on the need to eliminate all bodies of stagnant water and to avoid the creation of swamp conditions through the discharge of excess drainage flows. Among other recommendations directly related to the engineering design and layout were the improvement of water
58management and maintenance, the increase in design velocities in drains to
0.4 m/sec, the alignment of open drains away from centres of populations and provision for a reduction in salinity of drainage return flows.
The masterplan provides for the return of all drainage flows, originating in the
study area, to the Awash river such that the need to discharge excess flows into Angelele lands and into Kortume Swamp is obviated. The creation of perennial or even temporary swamp conditions will accordingly not arise under these
proposals. Similarly the provision of a comprehensive drainage network, both surface and sub-surface, will be effective in the rapid evacuation of excess
flows within the study area thereby preventing the build up of isolated pools of water. This network will include a drain leading the rejection flows from
tertiary canal Tl-3 in Melka Sadi, to the main drain, replacing the existing unsatisfactory arrangement of uncontrolled rejections with its resultant
ponding.
Pending the construction of Main Drain 2, the excess fLows from the rejection spillweir on Main Drain 1 (primary drain extension) would be diverted in a temporary earth channel routed to the east of the Angelele Unit 3 flood dyke
from which point the flows would naturally spread northwards.
Flood flows from the Eastern Catchment drain will provide a degree of natural recharge in Angelele lands and in Kortume. With the extension of the Awash flood dyke in Angelele, forming the flood retaining bank for Main Drain- 2, the incidence of river flooding across the levee in upper Angelele will be
eliminated such that river recharge to Kortume will be reduced. Although beneficial from the point of view of reducing the schistosomiasis snail habitat
in Kortume it may ultimately prove necessary to supplement Che Kortume inflows to ensure adequate provision for pasture.
The recommended design velocity of 0.4 m/sec for drainage flows has been adopted where practicable for the normal flow conditions in these drains. Such velocity 
will not be achieved under low flow conditions or where drainage maintenance is inadequate to ensure removal of excessive weed growth. Velocities in the lower reaches of the Main Drains near their outfalls into the river will also be
retarded at high river flow conditions.
59The major realignment of existing drains in the vicinity of centres of
population is not practicable within reasonable limits of expenditure and would also entail realignment of the associated irrigation layouts. Also where such drains are aligned along natural drainage courses their realignment would leave the existing Low lying areas undrained as well as require further deepening to accommodate Che higher ground levels away from such drainage lines.
An alternative of burying the main drains adjacent to village areas would also be very expensive; eg, at Melka Sadi Satellite village approximately 1.5 km of drain would need to be buried with an estimated cost of Birr 1.5 million. Such a measure would be likely to divert attention onto other adjacent canals and drains.
Fencing the drains themselves would pose difficulties for their maintenance by machine. Such fencing could, however, be provided to the adjacent sections of vilLage boundaries such that access to the drains is discouraged. Such measures would only ultimately be effective if adequate provision exists for potable drinking water supplies, latrines, Laundries, showers and protected swimming pools, together with appropriate health and hygiene education. Within the context of the Master Drainage Plan no provision has been made for such facilities. It is suggested that a detailed study of the measures necessary to improve the village health and sanitation facilities should be carried out in order to ensure that the problem of disease transmission is most effectively tackled.
As a minimum and immediate recommendation it is suggested that latrines and washing facilities be provided in the satellite villages. Without such minimal provision the relocation of drains away from population centres, or any other such measures, would not be effective.
605. IMPLEMENTATION
5.1      Method of Construction
5.1.1              Alternatives for Pipe-laying
Alternative methods of pipe installation have previously been considered and a discussion paper was submitted to the Amibara Irrigation Project office in March
1984, This paper is included herein as Appendix D.
This paper considered and compared the three principal methods by which drains could be installed. These were:-
a)        Using   a special pipelaying machine
b)        Using   conventional construction plant
c)        Using   labour intensively
There are two main types of special pipe laying machine, known as trenchers and trenchless. The latter relies on a plough being pulled through the ground and a pipe being laid in the resulting hole. This technique is not recommended for
this project due to the "smearing" effect that could occur below the critical
depth. This is the depth below which the plough ceases to move the soil by heaving it upward and instead compresses the soil radially and with the action 
of pulling a plough through the ground seals the walls of the drain and effectively prevents the ingress of water.
The trencher machine is one that cuts a narrow open trench with an endless chain cutter and lays a pipe at the bottom, if required, with a filter surround. Soil disturbance is minimal and outputs are high resulting in low unit costs and minimum disturbance to cropping.
Drainage pipes cannot be laid with conventional construction equipment, only the excavation for them can be done this way. The pipes have to be laid by hand which mean9 men working at the bottom of the excavation in waterlogged ground. In a vertically sided trench this would be very dangerous unless trench supports are used. This process is slow. The alternative would be to excavate safe side
61slopes which results in a large quantity of excavation and disturbance to the
soil over a wide strip. It is also slow. It was estimated Chat fifteen 
hydraulic excavators would be required to do Che same amount of work as one specialised trencher. Each excavator would cost about as much to buy and operate as a trencher.
If labour intensive methods were used without any machinery it was estimated Chat about 21,000 men would be required Co achieve the same output as one trenching machine. In addition more men would be required for trench timbering, pipelaying, supervising etc. This large number of people would have to be transported, housed, fed, provided with a water supply and sanitation. It would pose a considerable logistics problem.
Comparative costs on an area of 1,000 hectares were estimated, these have been updated to mid 1985 prices and are given below.
a)
using 
trenching machine
-     Birr
855,600
b)
using 
conventional plant
-     Birr
8,176,000
c)
using 
labour only 
-     Birr
5,202,000
These figures were not intended co show the total cost of the drainage installations as they did not include for collector drains, or for any other engineering work required. Nor did they include for General items. They were intended to show only the comparison between estimated costs of excavating for, supplying, laying and backfilling field drains. They showed quite clearly that
the use of a specialised trenching machine provided the only economic and realistic way of laying the large lengths of drainage pipe that would be involved.
5.1.2                Pipes for Sub-soil Drainage
The largest quantity of pipes required will be those for the field drains and these will have the smallest diameter of 60 mm ID. Pipes for the collector drains will be required in larger diameters up to 300 mm ID. The choice of Che number of sizes used will depend in part on how the pipes are obtained. An assessment of the suitability of different types of drainage materials which are
62available for conditions at Amibara was made in the Consultants report of August 1983, entitled, 'Report on Subsoil Drainage Pipes, Materials Costs and Methods of Installation’, (Ref 14). Of the different materials available, which include bituminised fibre, asbestos cement, aluminium alloy and steel pipes it was considered that only concrete, clay and plastic pipes were potentially 
suitable. For the field drains there are two choices of material, clay or
plastic with the latter being imported or manufactured locally. For the larger collector drains the choice is between plastic and concrete. These alternatives have been considered and are commented upon below.
(a)     Clay Pipes
The following is abstracted from Che Consultants’ Report on Subsoil Drainage (Ref 14);
’’General
Clay pipes have been used traditionally in Europe since the inid-19th century and have shown themselves to be very reliable and durable. The drains are laid in "tiles” of usually 0.3 m length with Che tile ends butted against one another.
The general flow towards a drain is largely horizontal but in the last stages becomes radial. In a clay pipe the water entry is concentrated at the
butt-joints; the porosity of the pipe walls is of no practical significance. Manufacture of clay pipes requires a great deal of skill and a well-equipped factory, in order to produce tiles of good quality that are straight,
square-ended, homogeneous and with no cracks.
Advantages of Clay Pipes:-
(a)      Clay pipes are durable
(b)      They are highly resistant to chemical attacks and do not deteriorate in the soil
(c)      Clay pipes have good hydraulic characteristicsDisadvantages of Clay Pipes:-
(a)       They are not locally obtainable for the Melka Sadi drainage scheme
(b)      Owing to their weight and volume the cost of import is not considered feasible for the final full scheme
(c)      They are not as convenient for laying by machine as
pipes".
A further, and major, drawback in the production of clay pipes is the high energy requirement in firing the clay. It is also not known whether or not the clays at Amibara are suitable; to establish such would require specialised testing as was noted in the Consultants’ Report. (Ref 14)
In view of the serious disadvantages of clay pipes and the total lack of Local experience in their production it is concluded that they should not be recommended for the Amibara project and the subject is not pursued further.
(b) Importation of manufactured PVC corrugated pipes; All the PVC corrugated pipes, of whatever size, could be purchased from European manufacturers, shipped to Assab and transported overland to site. This can be done quite economically for the small diameter field drain pipes but for the larger pipes the cost of transport and shipping escalates rapidly as the pipe diameter increases and the cost of the pipes quickly becomes prohibitive. To illustrate this the cost of various PVC pipe sizes delivered to site has been estimated to be as follows:
are flexible plastic
Pipe size
51 mm   I.D
60  11 Uli     I.D
100  [[HL     O.D
150   mw      O.D
225   mm      O.D
Cost, Birr/metre 2.11 2.86
6.29
17.41
58.74
64The estimate for 300 am pipes has not been done as it would clearly have shown an unacceptably high price.
(c)      Fabrication of PVC corrugated pipes in Ethiopia; An alternative to the above would be to make the PVC pipes on site using plant designed for this purpose. Such plant is presently being used in countries such as Egypt and Iraq, in other words where hot and dusty conditions are encountered, as they are at Amibara. This method will avoid shipping and transporting large volumes of bulky pipes but on the other hand it will entail the purchase of expensive and quite sophisticated machinery and a considerable lead time would be required in order co obtain, ship, install and commission the plant before any pipes could be available. Another disadvantage is that the plant would be considerably under-utilised on account of its high output capability. Lt could on the other hand be used 
to provide pipes for other irrigated agricultural developments should this be considered necessary.
In spite of these drawbacks the plant would still be able Co produce Che small diameter pipes for field drains at about the same cost as importing them but the larger diameter collector pipes could be produced for considerably less. The cost of producing PVC pipes on site has been estimated as follows
Pipe Size
60 mm I.D
71.5 am I.D.
Cost, Birr/metres 2.72
3.17
160 nan 0.D
200   mm 0. D
300 nan O.D
8.40 10.84 27.60
If production requirements can be increased by providing pipes to other schemes these unit costs could be reduced.
65(d)      Fabrication of Concrete collector pipes on site: the third alternative
would be to import the small diameter PVC pipes and to make the larger diameter ones on site in concrete. In order to achieve the required rates
of production and quality specially designed concrete pipe making equipment has been identified and Che associated cost estimates derived. The equipment is designed and made in Denmark and is widely used in a large number of countries round the world. This alternative would appear to be quite a feasible one and would make use of local concrete materials, cement, stone and sand as well as local labour.
The pipes made by this technique could be laid by a trenching machine so the economic benefits of this type of pipe laying can still be obtained.
The estimated cost of producing concrete pipes on site using OPC is as fol lows:*
Pipe Size
Cost, Birr/metres
100  mm I.D
7.75
150  mm I.D.
9.32
225  OTD I.D
11.21
300  mm I.D
13.51
It would be necessary to provide a substantial building to house the pipe making equipment and to store newly finished pipes for up to 48 hours during which time they would otherwise be particularly susceptible to the effects of direct sun and drying winds.
A considerable
lead time would be required to order, ship, install and 
commission the
equipment and to construct the factory building before any 
concrete pipes
could be produced for use on site.
Although this alternative is comparable, on cost grounds, to Chat of fabricating corrugated PVC pipes on site, rhe prevalence of high sulphate ion concentrations in selected samples of observation well water and in drainage water from the Pilot Drainage Scheme (Annex C) would render the
66concrete liable to deterioration. Such sulphate rich water may not extend 
throughout the study area and it may also be possible that sustained 
leaching under drained conditions would reduce the sulphate concentration 
to tolerable levels. Nevertheless it considered that this alternative is
not suitable and it has not been pursued further.
5.1.3               The Recommended Method of Construction
The installation of the deep subsoil pipes both in field drains and collector
drains should be carried out by trenching machines specially developed and made
for the purpose. The use of such machines al Lows the pipes to be laid much 
faster and cheaper than by any other method and also results in far less
disturbance to Che soil. These machines should be provided with laser equipment
to control Che depth of pipe installation as Chis will result in accurate depths
and grades being maintained. Lt is envisaged that two trenching machines will
be required.
The      cost      estimates      and      construction      programme      have      been      prepared      on      the assumption that the above mentioned equipment will be used.
As mentioned  in  Section  5.1.2  the corrugated  PVC pipes can  be made on  site with equipment made for Che purpose. The comparative estimates made with  other ways of providing  pipes show this to  be economically  attractive and  technically  good and  the cost estimates have been  based  on  this method  of pipe manufacture being adopted.
At the request of the Water Resources Development Authority the possibility of using the same pipe manufacturing plant for the production of smooth walled PVC pressure pipes for water supply has been investigated in outline. The projected annual demand in Ethiopia for the rural sector alone is in the order of
1000 km 1). Demand values for the urban sector were not available to the Consultants but are reportedly likely to equal the rural demand. Currently these pipes are imported and are costly. The conclusions of this outline
1/ Source: Annual demand values provided by WRDA
67investigation indicates that the manufacturing plant can be adapted for the production of both corrugated and smooth walled pipes, additional components being required for the latter. A summary of these initial findings and costs is enclosed as Appendix I herein.
Manholes would be made up of precast segments made on vibrating tables and installed with the aid of an excavator. This would allow good control of the quality of the segments and the transportation of them round the site would be
an easy matter. The tops would be heavy enough to prevent their removal and unauthorised entry into the manhole. Excavation would be carried out by hydraulic backactor or JCB type of machine which could also do the bulk of Che backfilling.
Open drainage channels would be normally excavated by hydraulic backactor and trimmed by hand. The excavated material will be placed as near the drain as possible to reduce haulage costs. However where no suitable spoil area
adjacent to the drain was available, allowance has been made for the material to be trucked away for distances up to 5 km.
For the Eastern Catchment drains and dyke and Main Drain 2, which lie outside the scope of the Stage I works, the use of motorised scrapers may be more appropriate to permit construction of their associated dykes.
5.1.4 Construction by Contract
It is recommended that the Stage I works are undertaken by contract with an appropriate construction organisation rather than by direct labour supervised by the Client's own staff. Direct labour construction would require an appreciable body of technical, supervisory and administrative staff to be assembled and to become fully effective in a very limited period and the diversion of such staff from their current activities would place severe strain on the resources of WKDA. The rapid build up required in the rate of implementation would also be difficult to achieve in such a newly formed organisation.
68An appropriate contracting organisation would have Che required resources
readily available and could undertake the construction under the supervision of
the Client’s staff, assisted by internationally recruited Consultants where
necessary. Although several Ethiopian contractors have gained experience in Che
construction of the Amibara Irrigation Project these have now become
re-organised and their likely workload or potential is not known. The Ethiopian 
Water Works Construction Authority would appear to have both the resources and 
staff to undertake such works and it is considered appropriate that this
Authority, and other local construction entities, should be invited to 
prequalify for tendering. It is also considered necessary to attract
international tenderers so that an adequate number of bids can be obtained.
This will require that a substantial amount of work is included in the contract.
It is recommended therefore that the whole of the Stage I works be awarded as a
single contract as this would provide a large enough package to attract
international bids. As well as being desirable Chis may be essential depending 
upon the financing arrangements that are ultimately required.
It is also suggested chat the purchase, installation and commissioning of the
major items of plant and equipment be made the responsibility of the main 
contractor and that adequate lead time be built into the construction programme.
Contractually it would be much simpler Co make these provisions the
responsibility of rhe main contractor otherwise the alternatives are likely to 
lead to difficulties and claims whenever there is a breakdown and consequent
standing time.
5.2 Implementation Programme
5.2.1 General Aspects
An      indicative      implementation      programme      for      the      entire      Master      Drainage      Plan      area is given in Section 3.3.
The proposed programme of construction for the Stage I areas, which require immediate implementation, is shown in Figure 24. In this progranme a five year construction period is envisaged with much of the first construction year being 
69taken up with purchasing and commissioning on site the special equipment and plant required. This would also include the crushing and screening plant necessary for processing the filter material for the field drain surround.
It will be necessary to allow at least six months in order to get the trenching machines to site and working as they are usually only made to special order. Similarly, enough time will have to be allowed to get the pipe making machine to site, if this is the ultimate choice for obtaining the necessary pipes. In 
addition a building would have to be provided and this of course would have to be constructed before the equipment can be installed.
The earthworks and structure modifications to the open drainage network would aLso commence in the first year to permit the subsequent installation of the subsurface drains. During each of the subsequent years the total net subsurface drainage area of 4740 ha would be installed, the peak annual installation rate
of approximately 1600 ha being achieved during the third year of construction (Project Year 4). This maximum rate of progress is based on the utilisation of the trenching machines for a period of seven months in each year, thereby leaving adequate allowances for interruption in machine operations during the greater part of the cotton growing season and the main wet seasons, as well as provision for delays due to any other circumstances.
In view of the rapidly deteriorating situation in Melka Sadi it is envisaged that Che works would be initially carried out in this area, with rhe Amibara section of Che Stage 1 area being carried out thereafter. The anticipated rate of construction per entity during Stage I, for the subsurface drainage works, is as follows:
70Entity
Melka Sadi Banana Unit
Melka Sadi State Farm
Project Year
1  3 4 5 6 Total
1                 Net Areas       in Hectares
|  410 918 1328
1  650 682 1332
Melka Warer State Farm
1
111
111
Melka Warer Research Station
1
229
229 *
Amibara Settlement Project
1
1219
no
1329
Algeta Farm
1
1
411
411
TOTAL
I 1060
1600
1330
750
4740
Prior to Che commencement of
construction          a period        of one      year     (Project Year 1)
has been allocated for the Government Co arrange the necessary funding for the project, co call for and receive tenders and Co award the contract. This very 
tight schedule has been proposed in view of the urgency to implement the works. Any significant slippages could result in the need Co extend the implementation areas and/or an acceleration of the rate of progress either by mobilising 
additional machinery or by working for a more extended period within each year. 5.2.2 Rate and Method of Subsurface Drainage Installations
(i)      Race of Installation
To assist in an understanding of rhe proposed development, a brief description of the method of machine installation is given below. The trenching machines required for the installation will have a high rate of output and advantage should be taken of this to lay as much of the drains as possible during the fallow season (for cotton) when no crops are growing and the ground is not being irrigated. The non irrigation period is the
time when ground conditions will be at their most appropriate for trenching activities and, except for limited periods during the short rains, easy access can be expected at most times.
71A     conservative     estimate     of     the     amount     of     drain     laying     that     could     be     done     by one trenching machine per month is as follows:-
Assume - 6 day week
8 hour day
0.8 (802) machine availability
0.8 (802) logistics efficiency (supply of fuel and pipes to machine & supply of filter)
Therefore - productive machine time per day
« 8 x 0.8 x 0.8 ■ 5.12 hours
Assuming conservative production rate of 2,000 metres per day (390 m per hour), then the monthly output would be -
2 kms x 6 x 4.33 ■ 51.96, say 52 km
For cotton Che period during which drains could be installed without
causing damage to growing crops wouLd be from about Che end of November, when the first fields would be fully harvested, to the end of June when the
last     of     the     fields     would     be     required     for     planting, months 52 x 7 km « 364 km of drains could be laid.
drain spacing of 45 m, requiring 222 metres/ha, this output would cover some 1640 ha in 7 months.
Thus in these seven With an average lateral
The present programme for drainage has an annual maximum installation rate of 1600 ha/year in project year 4, with an average annual rate over the 42 month (Fig 24) period of approximately 1350 ha. This indicates that all of the year's work could be done without interfering with the growing cotton. Some interference with cultivation operations will however occur which could cause delays in cotton planting. Similarly, it is advisable to 
provide some allowance for delays in installation which could lead to encroachment into the cotton growing season. The effect of drain laying through crops is thus considered below.(ii)      Installation through crops
A technique known as ’’through the crop installation” is now practised whereby the hopper of the trenching/drain laying machine is supplied via forward facing conveyors with filter envelope material from a tracked gravel delivery trailer which runs in the same tracks as the trenching machine, straddling the trench. As the delivery trailer runs in the same tracks it does not damage any additional land. Assuming that slippages or delays in the implementation schedule were to occur such that the installation period overlapped the cotton growing season by one month, then approximately 52 km of drain would be laid in cotton, corresponding to some 230 ha or 14X of a full years production (1640 ha). The corresponding area of cotton affected, expressed as a percentage of the annual drained total, assuming an affected swathe of ground some 6 metres wide per drain run, would be:
Spacing (m)
Affected Area
30
20Z of 14Z
- 2.8Z
45
13.3Z of 14Z
- 1.9X
60
10Z of 14Z
- 1.4X
75
8Z of 14Z
= 1.1Z
In summary, it is apparent that even were machine operations co encroach on the early or latter part of the growing season, then overall losses would 
not be appreciable. Additionally, other means of reducing losses could be achieved. At the beginning of the season planting could be delayed if expedient, resulting possibly in a yield reduction from late planting. At
Che latter end of the season the drainage could be installed following the initial picking, losses being incurred on subsequent pickings only. In the evaluation of the project a conservative allowance of 5X yield reduction overall was made for each installation year.
In bananas there is no particular period during which damage can be avoided co the growing crop unless replanting were necessary in any event. The damage resulting to the crop would range from 20X loss to 8X loss for drain spacings of 30 m and 75 tn respectively. However, only a limited portion of
73the Melka Sadi Banana Unit is actively producing bananas with no losses being incurred in the abandoned areas. The yields have accordingly been adjusted downwards by a Lesser value, averaging 5Z.
(iii)Sequence of Drainlaying Operations
The sequence of operations required in laying collector and lateral drains would be:-
1.
Set out lines of collector drains.
2.
Dig ’starter trench' from edge of completed open drains to enable
trencher machine to cornnence along alignment of collector. Starter
trench can be dug by hydraulic excavator.
3.
Set up laser transmitter for required grade and depth.
4.
Collector pipe laid as continuous line up to specified location of
change in diameter where a further starter trench is dug and sequence
is repeated using smaller diameter pipe. The 300 mm (id) pipes are not coiled and would be laid out in front of the machine, sleeve joint coupled to form a continuous line, picked up by the trencher and fed continuously into the trench bottom. The smaller diameter pipe (225 ram and 150 ram) are pre-coiled and would be carried on Che trencher.
5.         'Starter trenches' would also be required at all changes in direction, manholes would be subsequently located at these points.
6.
For field lateral lines a 'starter trench' would be dug, exposing the
collector at one end of the trench.
7.
Required depth and grade set on laser transmitter.
8.
Trenching machine lays field lateral pipe and filter surround as a
single operation.
749.        The gravel delivery trailer follows immediately behind pipe laying trencher and provides a continuous supply of filter into the filter hopper by a forward facing conveyor.
10.     Backfilling, partly done by angled blades mounted below the filter carrier, is completed as specified and compacted.
11.      The jetting connection and junction at the lower end of the lateral is positioned by hand and lateral/co1lector connections are also completed by hand.
12.      Backfilling of ’starter trench' is carried out.
13.     Manholes on collector pipes, located at a nominal 250 m spacing, would be positioned to intercept the nearest lateral which would then 
connect directly into rhe manhole itself. At such points the jetting connection would be omitted.
14.     Marker posts to be located at jetting outlets.
An illustration of a conventional trenching machine, pipelaying with a gravel surround, is given in Fig 27. Details of machine type are also given in the Consultants' Report on Subsoil Drainage Pipes, Materials, Costs and Methods of Installation, submitted to AIP in August 1983 
(Ref 14).
During that part of the year when drainlaying was not taking place, work would be concentrated on providing sufficient materials for the next following drainlaying season. Thus sufficient pipes would be made and stored, stocks of filter material would be built up in strategic places, plans would be made for the survey work required, and any bench marks established. During this period the machinery would be serviced, repaired or overhauled as necessary and stocks of spares re-built as required.
755.3 Supervision of Project Implementation
As noted in Section 5.1.4 it is anticipated that WRDA staff would supervise Che implementation, assisted by internationally recruited consultants with experience in drainage and in contract supervision.
A proposed organisation chart for site supervision is enclosed as Figure 28. It
is suggested that the Resident Engineer and his deputy be initially recruited from Consultants who would provide the experience and training to the section engineers. During the execution of the contract it should be possible to 
replace the Deputy Resident Engineer by internal promotion of a Section Engineer. Five field inspectors are envisaged, one of whom would be responsible for quality control of pipes manufactured on site, two would be in continuous attendance on the trenching machines with the latter two supervising structures and earthworks respectively. One of the inspectors, assuming the role of Chief Inspector, should have previous experience of subsurface drain installation by trenching machine. Accordingly it may be necessary to recruit this post
through/from consultants. A chief surveyor with two survey teams would ensure that all set out works are checked and approved.
A 1 L3C of surveying equipment for such supervision is given in Appendix G.
The intermittent services of a laboratory technician would be required for sieve analysis of filter material, cube testing, soil particle size determination etc. The existing facilities of the PCC site laboratory are adequate for these purposes.Brief job descriptions of the professional supervisory staff are given below:
Post
Task
Experience Required
Resident Engineer
Contract Administration.                                Qualified         civil         engineer
Liaison with WRDA, PCC and                      minimum 10 years
affected entities. Overall
experience in design and 
technical supervision of
construction of irri
works and administrative                                gation and drainage with 
supervision of staff.
specialised knowledge of
Deputy Resident Engineer
Assist RE in above duties and carry out in field supervision and training of section engineers and staff.
Section Engineer -
Subsurface Drains
Responsible for field supervision of drainage installation, design of variations, measurements and control.
Section Engineers - Earthworks and Structures
Responsible for field supervision of construction, design activities measurement and control.
subsurface drainage.
Qualified civil engineer minimum 8 years experience, to include site experience of irrigation and drainage construction.
Graduate, civil engineer with minimum of 5 years experience, to include constructon supervision, preferably in
irrigation/drainage works.
Graduate civil engineer minimum 2 years experience in design with preferably some construction experience.Chief Surveyor
Drain and dyke alignment/ cross-9ection surveys for measurement/supervision purposes. Check surveys of proposed/executed works as directed.
Qualifed surveyor with minimum of 10 years experience in field survey techniques and preferably familiar with the project area.
It is envisaged that the costs of the above staff would be covered within the construction supervision allowance of 10Z.
Both housing and office accommodation should be made available from the existing facilities, supplemented by the additional housing proposed for the additional operation and maintenance staff which PCC will require (Section 6.2.3).
Additional equipment proposed for the survey section to be purchased under the Contract is listed in Appendix G herein.
The construction programme (Figure 24) envisages the commencement of site works by mid 1986, the successful tenderer having been nominated during early 1986. The Clients site supervision staff should also be recruited before mid 1986. Similarly Consultants should be selected and appointed by this time. It is
assumed that WRDA will ensure that the pre-con9truction survey work (Section 3.3.4) will be completed by the commencement of construction so that sufficient time is available to the site supervision team to refine details of Levels and alignments as appropriate.
786. OPERATION AND MAINTENANCE
6.1    Irrigation Water Management
The Water Management Unit (WMU) of the Project Control Centre (PCC) is responsible for the supply and distribution of irrigation water to the various
entities. This unit, its organisation and operation has formed the subject of various reports (Ref 4, 12 and 13) and would appear to be operating 
satisfactorily, provided always Chat its staffing levels are achieved and 
maintained. Such proviso applies more particularly to the PCC itself which 
must, in order to adequately dispense its obligations, permanently maintain with experienced personnel, the three key posts of Manager, Operations and
Maintenance Engineer and Water Management Engineer.
The distribution of irrigation water in tertiary canals and its application on 
the field is the responsibility of the receiving entities, which are the State
Farms in the Aiaibara Irrigation Project. During the course of this study the
detailed observations carried out on field irrigation practices in Melka Sadi
Units 1 and 2, and random observations elsewhere, confirmed that significant
scope remains for improvements to these practices. Only limited improvements in water measurement can be achieved without excessive investment (Section 2). Of more fundamental importance would be the improvements which could only be obtained by strengthening the organisation of the State Farm entities and of the MiddLe Awash Agricultural Development Enterprise (MAADE) such that experienced senior irrigation personnel are put in charge of the irrigation operations. In 
the 'Operations Manual, Irrigation and Drainage Works’ prepared by the Consultants for WRDA in November 1983 (Ref 4) it was recommended that each State Farm should recruit an Irrigation Manager, directly responsible to the Farm
Manager. This Manual proposed job descriptions for the Irrigation Manager and also for a Water Management Engineer and a Land Development and Irrigation Engineer, both of the latter being attached to MAADE.
To illustrate the strengthening which is required an organisation chart of MAADE is given in Figure 25. This chart shows the existing Divisional Organisation 
and indicates the proposed strengthening to both the Agricultural and Technical Services Divisions. The essential strengthening co the Agricultural Division is
79the creation of a Water Management Section. This section, reporting to the Agricultural Division Manager, would be responsible for the adoption of improved irrigation and drainage practices throughout the State Farm Units. An 
experienced Water Management Engineer should be recruited so that the appropriate advice, guidance and training can be given to the Irrigation 
Managers of each state farm. A brief job description for the Water Management Engineer, based on that given in the "Operations Manual" is included herein as Appendix E.
Within the Technical Services Division the Land Development, Irrigation and Drainage aspects should be recognised as a specific section, headed by an Irrigation and Drainage Engineer. The latter post can be filled by a lesser experienced engineer who would also benefit from training given by the Water Management Engineer. A brief job description for this post is also included in Appendix E together with that for the post of State Farm Irrigation Manager. A detailed description of the improvements recommended for strengthening the State Farms is given in the "Operation Manual" and is not repeated herein.
It is suggested that such fundamental reorganisation is essential if
significant improvements in water management are to be achieved.
b.2 Operation and Maintenance of Drainage System
6.2.1               Operation and Maintenance Responsibilities
The operations and maintenance of the existing network of the primary and secondary drains within the Amibara Irrigation Project is the responsibility of the Project Control Centre (PCC) whilst that of the field drain and tertiaries is retained by the benefitting entity, for example, the State Farms. It is suggested that this broad apportionment of responsibility should be retained with Che following clarifications to accord with changes in the nature of the works resulting from subsurface drainage installation.
All deep open drains
existing primary and
to    be    the s econdary
Che Melka Sadi Banana Unit and
responsibility of PCC. These include Che
drains as well as the proposed deep drains within the new secondary drain through the Research
80Station, Settlement Farm and Algeta (designated SD7). The maintenance of the
existing sections of these drains is carried out by hydraulic excavator.
Similar plant would carry out these works on the new and deepened drains.
All subsurface laterals and collector pipes to become the responsibility of PCC.
The maintenance of these is a specialised operation with specific plant which 
would be most effectively controlled centrally rather than individually within 
the various entities.
All      surface      fieLd      drains      and      tertiaries      to      remain      Che      responsibility      of      the individual entities.
6.2.2               Operation and Maintenance Requirements
The       estimated       operations       and       maintenance       requirements       of       the       various       components of the installed drainage works are discussed below.
(a)      Piped Drainage System
The piped drainage system is likely to consist of inert material buried sufficiently deep to be unaffected by agricultural activities on the
surface for most of its length and apart from periodic checks on silt in the pipes it is unlikely that they will require anything much in the way of ma intenance.
The life expectancy of buried PVC pipes is not known but is thought to be considerable. Pipes that have been tested in UK before laying and dug up and tested again ten years later show no sign of deterioration. Similarly pipes that have been in use in Holland for 20 years are found to be in perfectly good condition. Lt is not expected therefore Chat pipes will require replacing in Che foreseeable future.
In the early stages of their operation the piped drains should each be cleared of silt about once a year to ensure the satisfactory functioning of the system. It is likely that this interval could extend co a four or five year or more cleaning frequency within a few years of their installation.
31This operation is carried out using special drain jetting equipment using either a low pressure pump delivering 100 1/min at 40 bar or a high pressure pump delivering 36 l/min at 170 bar pressure. In either case the water is delivered through a high pressure hose with one forward facing jet and a number of rear facing ones. The direction of the jets enables the
hose to be driven along the drain pipes by the water pressure. However the low pressure equipment will not be capable of travelling the full length of
a field lateral without some manual assistance especially if a bend is encountered at the entry to the field lateral. As detailed in Figure 20 it
is proposed the jetting equipment will enter the lateral just upstream of
the collector drain by means of an access tube from the ground surface. To be able to cope with this bend high pressure jetting equipment is recommended. A further advantage is Chat such equipment requires smaller vcLames of water. The pump will be towed by an agricultural tractor which also provides the power to drive the pump. A 6000 litre capacity bowser
will al9O be required to provide a supply of water should this not be available from a nearby canal.
Based on an estimated output of some 900 metres of pipe cleaned per day by each set of equipment it would be expedient to purchase a total of four
sets for the initial years of the project, replacing only two of these for subsequent years. This quantity will have to be reviewed in the light of experience of the actual accumulation of silt in the drains after several years operation. Further details on desilting requirements and methods of operation are given in Appendix A.
In addition to the desilting requirements of these drains a provision will also be required to keep in repair the exposed ends of the pipes, markers, manholes and outfalls as well as to effect repairs or replacement of isolated section of pipes or junctions. The additional items of plant and equipment assessed for this committment are listed in Table 1. A nominal allowance of 0.5 percent of the capital cost of pipe materials is recommended for the purpose of annual budgetting to cover material replaceraents,
823
(b)      Deep Open Drains
An additional length of some 23 km of deep open drains will be implemented during Stage I, comprising the Melka Sadi Banana Unit secondary drains SD8 and SD9 and the Amibara secondary drain SD7. Based on an estimated quantity of deposited silt of 1.5 m  per metre run of drain to be removed annually, it will be necessary to provide an additional hydraulic excavator
of 13-14 m reach to supplement the existing PCC fleet. The bulk of the material excavated will require to be carted away to spoil and supporting tipper trucks will also be required. This additional equipment is also 
listed in Table 1.
(c)      Surface field drains and tertiaries
The maintenance of these drains will be carried out both by hand and by agricultural machinery under the responsibility of each of the benefitting entities, that is, Melka Sadi Banana Unit, Melka Warer Research Station, Amibara Settlement Farm and Algeta. To cover the cost of the individual plant and labour inputs required for these activities an allowance of 2.5Z
of the total capital cost has been included in the financial estimates.
6.2.3              Organisational Strengthening to Project Control Centre
In order to carry out its additional operation and maintenance obligations the existing staff, operators and labour force of the Project Control Centre would require strengthening. It is envisaged that responsibility for these additional
works would naturally be that of the Operation and Maintenance Engineer, already in post, and that the existing administrative staff would not require
strengthening.
A suggested list of additional personnel is given in Table 2. A new Subsurface Drainage Section would be formed within the Operation and Maintenance Division of PCC. The Assistant Drainage Engineer, directly answerable to Che O&M engineer, wouLd be responsible for this section, assisted by a Sub—surface Drainage Supervisor. It is desirable that both of the above mentioned new staff would have participated in the supervision of drainage installation and thereby
B3be familiar with Che works and their operation. The proposed organisational strengthening is shown on Figure 26. The remaining additionally recruited personnel, indicated on Table 2, would be absorbed directly into the existing sections of Earthworks and Heavy Plant Workshop without any changes to the organisation structure. These personnel have not therefore been shown on Figure 26.
Additional housing requirements, are also listed in Table 2 and the associated costs for these houses are noted in Table 3.
847.       COST ESTIMATES FOR STAGE I DEVELOPMENT
7.1     Unit Races and Capital Coats
As noted in Section 5.1 it is assumed that the engineering works would be carried out by Contractors and the unit rates derived are based on this. Unit
rates for construction of major components of the work were built up from estimated basic requirements of materials, plant and labour. Current prices of the subsurface pipe manufacturing, pipe laying equipment and appropriate construction plant were obtained from the specialist suppliers and appropriate allowances made for shipping, spares, fuel etc. These prices are summarised in Table 4.
Rates entered by contractors on the Amibara Irrigation Project, updated to 1985 prices, together with appropriate rates from other contracts were also used to derive unit rates and provide an indication of allowances used for overheads and general and preliminary items.
The total costs of implementing each item of work were derived from the direct cost, based on considerations of plant, materials and labour, together with additions for the following:-
(i) Overheads, including supervision, head office costs, purchasing, documentation and financing; 55Z of direct cost.
(ii) General and Preliminary Items, including insurances, guarantees, mobilisation, transport, housing etc; 25Z of direct and overhead costs.
A 10Z allowance was added to the above costs for minor items not individually identified or estimated.
For the purposes of the economic evaluation the unit costs derived on the above basis were subdivided into plant, materials, skilled and unskilled labour, on-costs (overheads and general and preliminary items excluding profit) andprofit. The Latter was taken as 10Z of the total cost of each item. Foreign exchange components of unit rates were apportioned on the above subdivisions as fol Lows;
Plant Materials
:        64Z
: Imported into Assab; 1002 on CIF
Cement; 60Z
Reinforcing steel; 60Z
Timber formwork; 20Z
Contractor's on costs:                         202 local, 502 foreign
Contractor's profits :                           02 local, 1002 foreign
The above foreign exchange components used for plant and materials are based on 
those derived in previous studies (Ref 15, 16), taking into account initial
purchase cost, local taxes and operation and maintenance costs of plant and 
transport. Further details of foreign exchange components were abstracted from
the ’’Feasibility Study on Irrigation for Expansion at Wonji/Shoa", Tate and Lyle
Technical Services Ltd, November 1983, as provided by WRDA.
For Contractors on-costs, using a local contractor the foreign exchange
components relate principally to transport, housing and other items required for
establishment. The local exchange component relates to wages, overheads etc.
An overall component of 20Z is considered to be representative. Using a foreign 
contractor the expatriate staff wages, overheads and insurances etc would have
appreciable foreign exchange components, increasing the overall value to an 
estimated 50Z.
Profits accrueing to a local contractor would be entirely in local currency.
Conversely those accrueing to a foreign contractor may be totally in foreign 
currency, the allocations of OX and 1002 respectively have accordingly been 
made.
A    summary    of    selected    unit    rates    is    given    in    Table    5    and    the    make-up    of    total annual      expenditures      for      Stage      I,      based      on      quantities      of      work      implemented,      are given in Tables 6 to 11.
967.2     Recurrent Costs
The recurrent costs have been built up from consideration of the additional
operation and maintenance inputs which the Stage I implementation will require
as noted in Section 6 herein.
The costs of the additional plant which would be purchased and operated by the
Project Control Centre has been determined from suppliers quotations and from
PCC annual budgets (Table 4). A plant replacement cycle of six years has been 
assumed. Annual running costs, including spares have been taken as one third of
the capital cost of each item.
The     total     annual     costs     of     the     staff,     machine     operators     and     labour     force     has     been based on those prevailing in Amibara as paid by the PCC.
Annual maintenance costs for materials imported to site have been estimated as a percentage of the total capital investment on these materials. The following percentages have been used;
PVC pipes, laterals and collectors
: 0.52 of materials capital cost
Other materials, cement, reinforcement, etc: 2.52 of materials capital cost
The annual recurrent costs for the operations and maintenance of the in field 
and shallow surface drains, the responsibility for which would be retained by 
the farming entity, were also estimated as percentages of their initial capital
costs, at 2.52 for earthworks and 12 for structures.
For the purposes of the economic appraisal the foreign exchange and unskilled 
labour components of these annual costs were based on the capital cost
components.
A    summary    of    these    recurrent    costs,    over    a    25    year    period,    is    given    in Table 12.7.3      Disbursement Schedule
The amounts entered in the Bills of Quantities, given in Tables 6 to 11, are
based on quantities of work executed annually for Stage I together with their appropriate unit rates. To these amounts must be added the additional costs of supervision of the construction. Based on our appreciation of the supervision costs incurred in projects of this nature, including the overheads and direct
costs of the Client's and Consultant's supervisory staff, an allowance of 10Z of Che construction total is proposed. A further allocation of 10Z is included for physical contingencies.
The resulting annual investment cost stream has been adjusted to allow for the Contractor's advance mobilisation payment, taken as 20Z of the total tender value, that is, excluding supervision and physical contingencies. This advance payment has been nominally deducted in four equal amounts over the remaining four years of implementation. The resultant disbursement schedule is given in Table 13.
888.       COST ESTIMATES FOR MASTERPLAN
Based on the implementation programme given in Figure 3 cost estimates were
prepared for the full development of the Masterplan works using the rates
derived for the Stage I development. These are given in Table 14 and are at
1984/85 prices without provision for construction supervision nor an allowance
for physical contingencies, nor for inflation.
The cost for the Stage I development works during the construction period
1985-90 is Birr 28,407,000 which include a provision of Birr 1,300,000 for
housing additional operation and maintenance personnel. With a 10Z allowance
for contingencies together with a further 10Z for supervision of construction 
the total Stage I cost would be Birr 7252/ha (USS 3502/ha). This cost excludes
the substantial investments which have already been made in the existing surface
drainage works within the AIP area.
During this period the following costs are also added for priority works to be
undertaken as part of the general Masterplan development, but outside the Stage
1 area works:-
(a)      Birr 63,000 for the provision of a temporary pumping station to alleviate
the immediate surface drainage problems in Subelele.
(b)      Birr 318,000 for the temporary diversion of the flood flows from the
emergency spillweir on Main drain I.
(c)      Birr 120,000 for the installation of 10 number boreholes within the Amibara
Extension area.
This     gives     a     total     cost     for     the     Masterplan     development     during     the     period     1985-90 of Birr 28,908,000 excluding contingencies and supervision costs.
89The total cost for the Masterplan development during the construction period 1990-1995 is Birr 42,227,000. The works constructed during this period would include the following main components:-
(i) Sub-surface drainage for the remaining areas within the Melka Sadi State Farm
(ii) Surface and
Farm
sub-surface drainage                within      Algeta,       Ambash  and       Subelele   State
( iii)Sub-surface              drainage within Units 1, 2, State Farm
(iv)      Surface and         sub-surface drainage Amibara Extension area
(v)      The Eastern Dyke extension
3 and 8      (part)       of        the Melka  Warer to the      west of       Main Drain            2 within   the
(vi)     Western Dyke realignment and strengthening along the Awash River (vii)All associated                  structures
The remaining works within the study area would be completed during the construction period 1995-2000 at a total cost of Birr 15,024,000. The grand total cost for the Masterplan as shown in Table 14 is therefore estimated at Birr 84,859,000 or Birr 88,959,000 including for additional housing. This total however does not include for the possible construction of interceptor drains along the primary canal. To cover for this work an additional Birr 1.9 million should be allowed which gives a final estimated cost for the Masterplan of Birr 90,859,000.
90REFERENCES
1.         ’Discussion Paper on Outline Masterplan , Halcrow, August 198m
2.         ’Master Drainage Plan for Amibara and Melka Sadi Areas, Interim Report*,
Halcrow, November 1984
3.         ’Angelele-Bolhamo and Amibara Irrigation Expansion Project', Final Report,
Nedeco, June 1982
4.        Amibara Irrigation Project II, ’Operations Manual Irrigation and Drainage
Works', Halcrow, November 1983
5.        'Discharge Measurement Structures’, ILRI Publication No 20
6.         Amibara   Irrigation         Project       II.          ’Water Management   Manua1 *,      Halcrow,   July 1983
7. Amibara Irr igat ion Project II, * Hydropedological Studies' , Halcrow, , October 1975
8.
'Drainage Design Factors’,   FAO Publication No 38
9.         'Drainage Principles and Applications, Vol IV, 'Design and Management of Drainage Systems’, ILRI Publication No 16
10.       ’Angelele-Bolhamo Feasibility Study Report’, HaLcrow, October 1975
11.      'Drainage Testing’ FAO Publication No 28, 1976
12.      Amibara Irrigation Project II, ’Project Control Centre, Part A, Staff Recruitment for field Operations and Maintenance (Parc A) and for Heavy Plant Workshop (Part B) ', Halcrow, March 1984
13.      Amibara Irrigation Project II, ’Maintenance Manual for Civil Engineering Works', Halcrow, November 1984
9114.
Amibara Irrigation Project II, ’Report on Subsoil drainage pipes, Materials, Costs and Methods of Installation*, Halcrow, August 1983
15. Water Resources Development Authority, 'Dabus Irrigation Project,
Feasibility Study Report*, Halcrow-ULG Ltd, February 1982
16.
Water Resources Development Authority, 'Weito Irrigation Project, Feasibility Study Report’, Ralcrow-ULG Ltd, January 1982
92I
I
I
N
D
nFIGURE
SIR WILLJAM HALCROW 8 PARTNERS JULY 1985
Ms  measurement gate and frame
Secondary Canal check crest raised IOO opprox
mass concrete
Gote guides installed in nQ 75 * 75 sl°p-‘og
11
Alternative woter meosurement
■J?2  'iv   US,ng   d|ff   er  entiai  gouge ond  pressure  tops  eoch  side  of
existing control gote
Sand cement rendering
ttoo rpvrnouv.idd.esmooth opprooch
flow
Estimated heod loss
210 with free flow
under measurement gate with discharge
concrete
450 I/sec
y
^77777
Moss concrete
Existing rc
Structure
control gate
Existing 750 i d
pipe culvert
Existing re
structure
77*777
6OQ
Existing  stone  ft  filter reploced on completion
300 i d concrete or plostic pipe stilling wells with 30dia plostic pipe inlets
777> I
SLGII QN A-A
300 i.d. pipe with moss
concrete infill to provide
opprooch nosing
MASS
CONCRETE
LONGITUDINAL SECT I ON THROUGH PIPE OFFTAKE
Downstreom stilling well needed only if Conslont
---------- Heod Orifice meosurement
is to be used
Notes-
Existing control gate con be removed if desired if measurement gale free flow method is odopted
Estimated heod losses relative to gaiMing check crest level ore 110mm, for free flow and 40mm for CHO measurement of 450 I/sec Dimensions in mm,
Sond/
cement
morin.-
infill
lOOOnvr,
MASTER DRAINAGE PLAN FOR MELKA SADI AND AMIBARA AREAS
PART ■ PLAN
WATER MEASUREMENT PROVISIONS
AT SECONDARY CANAL OFFTAKES■ ■ ■ ■ Uli a as ■B B B B B B
KEY
IMPLEMENTATION periods
1985 -1990
(STAGE I)
1990 - 1995
BLOCK ©MELKA SA0I © AMlBARA
©MELKA SAOl
© AMlBARA
N£T ARgA$
- 2660 ho T - 2060 he J
- 1550 hoi
H 740 ho
- 5050 r>o T 5550 ho
MASTER DRAINAGE PLAN FOR MELKA SADI
©AMlBARA EXTENSION
- 950 hoj
AND AMlBARA AREAS
1995 -2000
©AMlBARA
©AMlBARA EXTENSION
-2340 hoi
•1570 he J
L 3910 he
MASTER DRAINAGE PLAN
INDICATIVE DEVELOPMENT PROGRAMME
TOTAL 14.200 ha
Sir William Hole row I Portrait
July 1985
FIGURE 3FIGURE 4
misting works
canals drains
AELO BOUNDARIES ACCESS ROAOS
DYKE settlements
VILLAGE
NEW WORKS
SUB - SURFACE COLLECTOR DRAINS
DIRECT.    ON    OF    sue    -SURFACE    AELO    LATERALS DEEP OPEN DRAINS
NEW TERTIARY DRAINS
MASTER DRAINAGE PLAN FOR MELKA SADI
STAGE 1 AREA BOUNDARY
AND AMIBARA AREAS
CULVERT
MELKA SADI STAGE I AREA
SURFACE ANO SUB-SURFACE DRAINAGE LAYOUT
Sir WtlUtwn Halcrow A Partner*
July 1985FIGURE 5
-DO
■V’T*-.
MASTER DRAINAGE PLAN FOR MELKA SADI
AND AMIBARA AREAS
MAIN DRAIN 1
LONGITUOINAL PROALE AND TYPICAL CROSS SECTIONS
Sir William Halcrow ft Partners
July 1985AM I BARA VILLAGE
farm
AM8ASH FARM
FIGURE 6
^SETTLEMENT
&
AWASH SETTLEMENT
PROJECT EXTENSION
Eilstinc
mam
dram (M
Dl) outfall
10
1
2
__  3 km
CANALS
DRAINS
helo boundaries
ACCESS ROADS
dyke
SETTLEMENTS
PUMP STATION
SUB - SURFACE COLLECTOR DRAINS
DIRECTION OF SUB'SURFACE r
Elo LATERALS
DEEP OPEN DRAINS
NEW TERTIARY DRAWS STAGE I AREA BOUNDARY
CULVERT
roncc. HRA inage cvi’EAr
SCALE 1 40000-
MASTER drainage plan for melka saoi
ANO AMIBARA AREAS
AMIBARA STAGE 1 AREA
surface ano sub-surface drainage layout
Sir Wlllld* Ha’crow ft Partner*
July IW5FIGURE 7
1 ONGrtUDHW, PWQfllE_SD_7_ CHAgUGF C TJ 12QK
'I’wJu*• ‘
•A:
e«
Jt.          **** -*>Xj>c m           cuv'-u *i
; ,lMl
•».          ’’"“'‘■'’■mil
-rP<AL CPOSS CTK> GF SO? ChAJMAGE 9<00 TO W3C
%CA4f •
yul *
master drainage plan for MELKA SADI
ANO AMI BAR A AREAS
SECONDARY DRAINS SO7 AND SD5 longituoinal PROFILE AND TYPICAL CROSS SECTION
Sir William Malcrow & Partnart
July 19851 
u 
M
■
FIGURE 8
trx.* a
KAlX •
MASTER ORAINAGE PLAN FOR MELKA SAD!
AND AMI BARA AREAS
SECONDARY ORAINS SD4 AND S06
longitudinal PROFILE AND TYPICAL CROSS SECTION
Sir WiUiom Hotcrow a Rxtntrs
July 1985I I I I V
M
BFIGURE 9
SIR WILLIAM HALCROW 8 PARTNERS JULY 1965
Isolating
Joint
elan
Air cooled di etel engine close coupled to pump
Cenlrefugal or mixed flow punuj designed to deliver 80 I /tec ogointt o 6 0m head
Trash rock - 15mm bort al
5Omm in ter volt
£725 25
Cone filler with gale volve
main drain
fliter
ilching
I 1500        , py
Sind bolted
Io concrete boee Mo 5s concrete------ Filter  with
flop valve
2500
Spiroilv welded steel Dips - 150mm dia with Ranged joints
*OQQ
Di meat i one in mm levels in metres
Scale:
OI
2 metre*
500 IOOO              2000 mm
longitudinal section
MASTER DRAINAGE PLAN FOR MELKA SADI ANO AMIBARA AREAS
SUBELELE DRAINAGE PUMP STATIONI
IFIGURE IO
MASTER DRAINAGE PLAN FOR MELKASADl AND AMIBARA AREAS
MD2 OUTFALL - AWASH RIVER STAGE : DURATION
Number of exceedances between August 1972 and December 1982
SIR WILLIAM HALCROW 8 PARTNERS
JULY 1985
Length of exceedance (days)FIGURE II
.QNGlTUOlNA
777 1
r?i
r?« -
r»
171
TK<
5
» TttJt                  nooc u«i.
”* -------------------------------------- ?r» -
»'D Hvt.
n* -
ZJ .
~pV
Z?V
fZ2 *3
5rt ji M14
mt--------------
nr *0__
----- —hT«£     ZZ___
^Tod— -^ZZZTESE
t.ttt—  :__ p* ~~~
------  — 
- ran
Z ’•• m — 
7
----------- ------ ------------------------- --------___________ tf r=vr
- --------  —~---------------------- - _ M -ST
icm •
MAIN DRAIN 2 longitudinal profile and cross section
Sir William Halcrow 3 Partners
July *985I I
I I
w
a a
MASTER DRAINAGE PLAN FOR MELKA SADI AND AMIBARA AREAS
typical sub-surface drainage layout
Sir Williom Holcrow B Portners July 1985FIGURE 13
LEG ENQ
Lafaroi
Spacing
Rat ionol ixod Oroinobility
Do**
f
E3
3Om HO
45m Hb
6Om nc
TSm                  no
Limit   0f    toll   turv«y S’OQ* 1 Oreo bovndory
MASTER DRAINAGE PLAN FOR MELKA SADI
AND AMI BARA AREAS
FIELD LATERAL SPACINGS FOR
STAGE I AREAS
Sir Wilborn Holcrow & Portner*
July 1985w |-z
FIGURE 14
MASTER DRAINAGE PLAN FOR MELKA SADI AND AMI0ARA AREAS
TYPICAL SECTIONS THROUGH SUB-SURFACE DRAINAGE PIPES
FIELD LATERAL PIPE
COLLECTOR PIPE
SIR WILLIAM HALCROW a PARTNERS
JULY 1965FIGURE 15
SIR william halcrow a par™
JULY 1'
Replacement or low
How culvert
Diverted channel excavated
to final bed level in
Stage 1 construction
Temporary  stepdown  la  diverled
chomel bed level after
Stage 1 construction
ded step up Io existing culvert invert level after Main Dram excavation la final level (MDCl/5) Rip* rap prelection ns required
L1..1 LI L
Existing culvert and drain bockfilfcd (MDC 1/3) or
Approx. Over oil Length 180 m
reigned for (MDG 1/5)
peak flow*
GENERAL ARRANGEMENT (EXAMPLES MDCI/3 ft MOC 1/5)
MOC 1/2
FOR
SD2/I a MDC l/i
MASTER ORAINAGE PLAN MELKA SADI AND AMIBARA AREAS
TYPICAL LAYOUTS
SCHEMATIC LAYOUTS AT SPECIFIC LOCATIONS
(Not to Scale)
FOR REPLACEMENT CULVERTSFIGURE 16
SIR WILLIAM HALCROW 8 PARTNERS JULY 1985
nBW■■
I of 2 no lOOOmm i d precast concrete pipes on concrete bed and
hountfi- expansion joints os required
ROAD
SECONDARY OR
tertiary canal
field
ACCESS
Graded filters 500 thick
ond rip-ropmin 500 thick
to loe droinage and protection
heodwali
Compcx.ltd backfill
7^7
L metres (see Schedule)
Movemen I
Reinforced concrete
wall base
5000
TYPICAL LONGITUDINAL SECTION
REF Nos
No OF
PIPES
LENGTH
L
REF Nos
STAGE I      MELKA S
ADI
SDC 8/2
9/1,9/2,9/3
SDC 2/1 and MOC l/i
MDC I/2BI/3 STAGE I
1
o
2
- AMI0AR
14
16
18
A
SDC 7/11 SDC 4/1.4/2 SDC 4/3
No OF
PIPES
2
1
2
LENGTH
L
14
14
28
UTILIZATION
Reptocemenl for rood Xing
Replacement for rood Xing
New, for rood 8COnol Xings
NOTE
Pipe collars ond toe dromoge required only on X-dramoge culverts Other culverts to have bed and bank protection 300 rip-rop on 150 filters
SUBSEQUEN
T STAGE -
MELKA
5*121
SOC 7/1
SDC 7/2
SDC 7/3
SOC 7/4
SDC 7/5
SDC 7/6,7/7
SDC 7/8
SOC 7/9.7/10
1
1
1
1
2
2
2
2
14
26
16
15
15
26
31
14
UTILIZATION
Replacements for rood Xings Replacements for rood Xings Replacements for rood X mgs
New, for road X mg
New. for road 6 canol Xings
New, for rood Xing
New, for rood Xing
New, for rood Xing
New,for road & conol Xings New,lor road 8 2 x canals
New,for road Xings
SDC l/l, 1/2
MDC 1/4
MDC 1/5
1
2
2
14
36
18
Replacement for road Xing
Low-flow by-pass under
Primary Canal
Low-flow by-poss under
Link Road
Dimensions in mm
Scale
metre* 500      2000           4000mm
SCHEDULE OF MAJOR CULVERTS
MASTER DRAINAGE PLAN FOR MELKA SADI AND AMI0ARA AREAS
TYPICAL MAIN DRAIN CULVERT DETAILSFIGURE 17
SIR WILLIAM HALCROW B PARTNERS JULY I9B5
B B K B ■ ■■ B «
*
MAIN DRAIN (MDI/MD2) CROSS - DRAINAGE STRUCTURE«
ft I I
I IFIGURE 18
SIR WILLIAM HALCROW 8
Mosonry haod^all
300  rip-rap  on  150 coarse grovel bed
600 dm pre-cost
concrete pipe -
SECTION THROUGH P'P£
Dimensions m mm
Scale
9 _L
500 IOOO           2000 nun
FOR
MASTER DRAINAGE PLAN MELKA SADI AND AMIBARA AREAS
TYPICAL SURFACE DRAINAGE CULVERT0021
main drain
Di mannans tn mm
Scold
&00 IOOO
2m«rr«i
=1
ZCOOmm
MASTER DRAINAGE PLAN
FOR MELKA SADI AND AM I BARA AREAS
T YPICAL SURFACE DRAIN OUTFALL INTO MAIN DRAIN
FIGURE !9K
H
0
I
IFIGURE 20
MASTER DRAINAGE PLAN FOR MELKA SADI ANO AMlBARA AREAS
TYPICAL SUBSURFACE DRAINAGE STRUCTURE DETAILS
Lifting eyes cast
into cover
OGL
I
Cost ron steps
Eorth mound
1
'50 wide
3C0 deep
Moke up pieces
m multiples of
250
Red
marker
post
Kies
Cement mortor
seal around pipe
8
MANHOLE SECTION
Collector pipe 150,
225 or 300 dio.
Corrugated field lateral
60mm ID, m a red ash
envelope
Y Junction
I
Red morker
Corrugated collector pipe
150- 300mm ID
I
FIELD LATERAL
CONNECTIONS
Collector pipe
outfall with
concrete surround
300mm thick rip-rap on
150mm. thick coarse grovel
Not to Scale
Dimensions in mm
SUBSURFACE DRAINAGE
OUTFALL
SIR WILLIAM HALCROW 5 PARTNERS
JULY 1905FIGURE 21
VMI •
master drainage plan for MELKA SADI
AND AMI BAR A AREAS
WESTERN CWKE
LONGITUDINAL PROFILE AND TYPICAL CROSS SECTIONS
$  Wllliom Halcrow & Partner*
ir
ISWLONGITUDINAL PROFILE
Horixoniol icalt A                    Vtrlicol Icole 0
BED WIDTH VARIES
J
2000m«M«i
TYPICAL CROSS SECTION
Scot* 0
50 Mllll
SCQlt A
Scolf 0
MASTER QRAINAGE PLAN
FOR MELKA SADI AND AMlBARA AREAS EASTERN DYKE EXTENSION
LONGITUDINAL PROFILE a CROSS SECTION
FIGURE 22*FIGURE 23
MASTER DRAINAGE PLAN FOR MELKA SAOI AND AMI0ARA AREAS
PROPOSED CONSERVATION WORKS FOR WATER HARVESTING PILOT AREA
SIR WILLIAM HALCROW a PARTNERS
JULY I9&5FIGURE 2-3
SIR WILLIAM HALCROW 8 PARTNERS JULY 1905
PROPOSED IMPLEMENTATION SCHEDULE FOR STAGE IFIGURE 25
MASTER pmilNACI PLAN To MELIA SADI MW MCTMA ARXKJ
KTDCLX ^WA5«_ AaiICXrL7Tn<AL CTTPWIgt
tEirtlng DL»l«lexMU ’3r<MdJ*tlaa
iiird-HAlj
MANAGER          1 1 J 1 
1
1
I_
----------------- i
1
11 adeinisttiation mic i I ’ERSOWtL DIVISION     |    |
. _l 1
-t:uncz
SWISIOH
11
1 1          STORES ANO
I  i supply orroiOH I I II
1
1 AGRICULTURAL 1
Dtvwsw
1
I TECHNICAL 5ZJWTCZS
DIVISION
11
I
1
1 _
I-------------
STATE FAWS
I_________________ I
Streg<fcih"«JLnj, to ■HgylculWrfLX BHhriLadLon.
Propoyad Stawi<th<nln< to T^ciwUal S^cta Dlvlxlcm
TECHNICAL SERVICES I
omswN
CON5TOCTIOri
I
I
I
■rfCRKShnps
.
I rAKM MECHANISATION |
I_________________________ I
SIR WILLIAM HALCROW a PARTNERS
JULY 1985I
I I V
VIFIGURE 26
SIR WILLIAM HALCROW & PARTNERS JULY 1985
MASTKR DRAINAGE PLAN FOR MELKA SADI AND AMI BARA AREAS PCC - ORGANISATION STRENGTHENING FOR ADDITIONAL DRAINAGE WORKS
Operation and Halntennnce DivInion OPERATION AND MAINTENANCE |
ENGINEER 
I
1
I
SUB SURFACE
DRAINAGE
| EARTHWORKS
I
II_____________ I
I
11
SURVEYING 1 1 TECHNICAL
1 1     SERVICES 11
1
STRUCTURES 1
1 1
I
I
| HEAVY PLANT | | WORKSHOP
I___________ II
I
New Section
——\/
Existing. SecLiona
PLANT OPERATORS (5)
DRIVERS
GANG CHIEFS
LABOURERS
(1)
(2)
(10)
j FIELD CLERKS (2)FIGURE 27
MASTER DRAINAGE PLAN FOR MELKA SADI ANO AMIBARA AREAS
illustration of typical trencher machine
(Not to scole)
SIR WILLIAM halcrow a PARTNERS
JULY 1985FIGURE 29
SIR WILLIAM HALCROW ft PARTNERS JULY 1985
MASTER DRAINAGE PLAN FOR MELKA SADI AND AMI BARA AREAS Proponed Orgnnlsatioii for Site SuperviaLonAFPENDLX A
MAINTENANCE OF SUBSURFACE DRAINSAPPEND LX A
MAINTENANCE OF SUBSURFACE DRAINS
Within one year after ins tai lation Lt is recommended that ill the piped drains
be cleaned out to remove any silt or sediment deposited in than. This destining, requirement is essential in the early stages of the operation of a piped
drainage system due to the envelope material and surrounding soil requiring tine to settle and reach a stabilised condition* Thereafter the requirement for
desilting will be determined primarily on the performance of the drains and from the results of observe tions curried. out on the Pilot Deal nags Arsa. To assess
the drains  performance it is reomended that annually one drain per 100
hectares approximately throughout the drained area is jetted. To enabLe monitoring of the sediment removed, only drains which Lead into a manhole should be jetted at this time. lf» during these operations, it appears the drains are
heavily silted then this will indicate that regular desilting is still required for these areas, A limited number of trial pits should also be dug co expose sections of the laterals in such areas. However, it is anticipated that siltatian will be minimal and with time the desilting requirements should be reduced to a minimum interval of five years at least.
1
To facilitate desiLting of the sub-surface drains access
provided for in the designs. Along the collector drains manholes are spaced a
to each drain has been
maximum distance apart of 300 metres and at every bend. The manholes are also situated so as to coincide with a field lateral connection to the collector
drain- At all other connections between field Laterals and collector drains, provision has been made just upstream of the connection for an access tube to be brought to the surface to provide access to the individual field lateral.
Desilting of the drains will be undertaken by specialised drain jetting
equipment* This consists of a;-
( 1) High pressure pump,
(ii)      Hose of up to 450 metres length wrapped on a reel,
(iii)     NozEle at the end of the hose witn rear facing jets tor hydraulic drive and one forward jet for clearing the sediment.The   equipment   can   be   either   mounted   on   the   three   points   linkage   at   the   rear   of   a tractor or on a separate trailer.
Power for the pumping unit can come from either a tractor power take off unit or
a separate power unit attached to the trailer supporting the reel. As some of
the access points for desilting will be away from a ready source of water it is
recommended that a water bowser of up co 6000 litres capacity is used to supply
the water for the jetting equipment.
Two types of jetting equipment are available:-
(i)       A high pressure (up to 170 bar)* low volume (36 litre/min) unit,
(ii)      A low pressure (40 bar), high volume (100 litre/min) unit.
It    is    recommended    that    Che    high    pressure    low    volume    unit    is    used    for    the following reasons:-
(i)       The movement of Che jetting nozzle up the drain is by hydraulic drive. To
overcome the friction developed against the hose at the bend between Che
access tube and the field lateral and still ensure that the nozzle can
travel the full length of the field lateral the higher pressure unit is
required.
(ii)         Due   to   the   lack   of   a   ready   source   of   water   at   each   jetting   point   the   low volume unit will use less water.
(iii)     The higher pressures will be more effective in breaking up tough dried out deposits within the pipes, should these occur.
BMJH
'
*
jSj
I BK'B
fl
If regular maintenance is carried out as recommended the drains should never
1
become heavily silted. The jetting nozzle would be fed into the drains at a
constant rate thereby loosening the sediment deposits as it progresses. As the
nozzle is withdrawn it will flush out the sediment in front of it which will
then be either deposited in the sediment traps at the bottom of the manholes or
washed out through the drain outfall. It is recommended that the drains be
u
nflushed from the collector drains working upstream into the adjoining field laterals, returning to clean collector drams again if found to be necessary.
Should a drain ever become completely bLocked and the jetting cannot remove Che blockage then a radio transmitter can be fixed to Che head of rhe nozzle.
Walking above the drain with Che aid of a receiver will locate the precise position of the blockage for Chis point to be dug out by machine. Although Chis additional transmitter/receiver is not expensive its purchase is not recommended unless blockages were found to be frequent, which is considered to be extremely unlikely.
After the jetting operation is completed the sediment traps at the bottom of each manhole are co be cleaned out manually.APPENDIX 3
MONITORING OF IRRIGATION PRACTICES IN MELKA SADI UNITS 1 AND 2APPENDIX 0
MONITORING OF IRRIGATION PRACTICES [N HELKA SADI UNITS 1 AND 2
During the study phaseT observations were made over a two week period at the end
□ f September on the irrigation practices within the Melka Sadi Units I and 2. The observations were carried out daily on each field .md in some cases repeat observations were aade an the same day in. order to monitor the progress at the irrigation. During this time irrigations were undertaken on twelve fields a® follows; Field Nos 1/lA, 1/1B, 1/3, 1/4, 1/5a, 1/5B, 1/6A, 1/6B, 3/17. 3/13,
3/22A and 3722B. Each set of observations included the following information:-
(a)      The Location along a field canal of the start and end of an irrigation
(b)      Th«- number of syphons operating
(c)      The operating head under which the sypnons were wording
(d)      Estimate of the total flow entering the head of the field canal
(e)      Estimate of the rejection flows from Che field canal, and at the end of Che furrows into the field drain
The data collected is summarised in Table Nos Bl to Bl2.
The data showed the high variability on a daily basis between the irrigation application over different sections in any one field* A contributory factor to
this variability was the ease or difficulty experienced in irrigating a field.
The usual practice was to lay out between 80 co 140 number 2.5 cm diameter syphons over an approximate 50 metre length of field canal. Initially two
syphons would be provided per furrow, being reduced to one per furrow when the advance stream reached the end of the furrow* However irregularities in the slopes both across and down the field resulted in uneven rates of advance and in cases ponding up of water over Large areas before water could be forced to advance further across the field. The irrigators helped the rate of advance by building up the furrows Locally in low spots. An irrigation would be considered complete within j block, when water had reached the end of all furrows. For the "slow irrigated furrows, this could result in no cut—back stream 'being used , and
hence possible over-irrigation. Therefore the actual time of irrigation wasrelated to how quickly the irrigation water moved across the field and not to any pre-determined time allocation.
Rejection flows from rhe end of furrows were minimal due to the practice of bunding off the end of the furrows to pond water up on the fields* However due to poor site supervision excessive amounts of water would sometimes pond up at the end of a field causing these bunds to be breached. This would result in
short duration high rejection flows until the breach was repaired* Selection flows would also be experienced on completion of irrigation ot 3 particular
field. Water flow would often continue into the field canal until the
Irrigation Supervisor or Unit Manager instructed the diversion of water to another field canal.
The collected data also indicated the variability between total gross field applications. They varied from under-irrigation of some 210Z in field 1/LB to an over-irrigation of some 77X in field 1/60 from the required irrigation amount of 130 mm. However the low irrigation amounts were intentionally applied to fields 1/1a and L/IB as the cotton in the fields had already received the first pick and this was the seventh and final irrigation. The over-irrigation in
field 1/6B highlighted the difficulty in irrigating this field, which took some 12 days, due to its uneven microtopography,QATA SHUT FOE FIELD IRRIGATION PRACTICE STVOJES
Field He                 < / < <*_________
POSl  PLANT IRRIGATIQM
NUHntH
l‘ u
|           GATE
IRRIGATION duration
(hri)
AREA
[RRIGAIEO (h.)
TOTAL 5YPHDB DISCHARGES
(1/MC)
ESriMAICO
REJECIIOM FiWS
(l/itc)
VOLUME OF
WATER APPLIED
(1/kc)
DEPTH Of
appljcatiom
(«l
RAINFALL
{«>
•ores
I
1
1
2?/*i/SI)
2 0/1A k
J*
2k
2k
30
1006
JifU
1         1017
3O/Z5f/
2 5^
if 00
6-62
20
<<o
12
52
NIL
NIL
AJrfi*
(MIL
5t)t
21
111
2b
85
J6-RB
j / in
66
■ 4
• -
♦
*
1
1
table atn*TA SHECT FOB FIELD IRRIGAT1QII PRACTICE STUDIES
POST PLANT | IRRIGA7EOM |
ndhber
DATE
IRRIGATION
DURATION
(hra)
AREA           TTCI At SY PHO R ] ESTIMATED 1 VOLUME OF
| DEPTH Of
TRRIGATEO j DISCHARGES (REJECTION FLONS|tfATER APPLIED | APPLICATION
(hi) 1  (l/»c) 1  (i/»d
1
(1/iec)
Ik                      3 56
i 20
1
24
14
30
J 60      1 ^2
11
4-43                    61 1 |
(MIL
AHL
1„1 1i11
NIL
/ooe
27t5
| S7<t6
1
i
1
i      i26        | 1
i
^■55
23         >     NIL
2627
II 47
I2O4B
•• ! 62 |DATA $HEE1 fu« FIT LU lftRlGAT!€■ PRACTICE STUOIES
field <o *V*/3________________
1 [POST Pl ART
| IRRIGATION        |            DATE 1 |1NUUlIMn futlfMQ,              1
IRRIGA1101 DURATION
(hr»)
AREA
IRRIGATED
(he)
ICTAL SYPHON DISCHARGES
(l/«0
ESTIMATED
REJECTION FLOWS
(l/lic)
VOLUME OF
MATER APPLIED
( l/»*G )
DEPTH OF APPLICATION
(»)
RAINFALL
(■•)
NOTES T|
1
II
II
II LLU
11
1
1
I h/i/s4
2l/ Y«4
22/^/^
23/1/ 84
f  24/y
2s/l/v4
2&/1/&4
9
24
24
12
>4
2<f
24
- 12
2 33
2-<11
2/o
5 9/
/■is
2-4*1
*51
2-51
12
32
24
to
40
21
34
33
NIL
MIL
NIL
NIL
2
NIL
AZ2
27tS
2071/
1120
I<4I5
/«Hf
2139
IM26
40
is
*11
21
1(7
13
/0S
57
IS
IQ 0
1
1
1
1
1
I
1
1
1
Mqia caiAoJ  mcx&xl 1 fcr 23 hotLxs Ui |
" blcci-to^c cd iUti
ketAcl,LocvUu
ML
NIL
2©
/ 5SB 2
1-
1
1
1
1
1
11
1
1
1
1
1
1
|
III
II
1
1
I
TABLE 33DAM SHUT FOR FIELD IMlGAHOI PRACTICE STUDIES
[POST PLAN! II IPS JG*r ION II NUkBCR
DATE
IRRIGATION AAEA
DURATION         | IRRtHAfED
TOTAL  StPHOU             ESTIMATED
| VOLUME OF                     OEPTH OF
NOTES
I
DISCHARGES         ftfJECTIOU FLOWS   |WATER APPLIED     | APPLICATION
(hrs)
(hi)
(1/iec)                       (1/secJ
(»}
RAINFALL (»)
II
II ttu
II
II
II
II
II
II
II
II
II
1
1
1 ‘
1
1
IS
20/^/t^                  21/
2I/T/S*
2"
22/1/SV               u 23/q/84               14 21|/ ’/^               24/
/Oft                 52
1
2 6g I 52 I nil
IM
363
2GS
21
1
1
1 NIL
NIL
1
4^3 ' ,1i>
I
! no
I
•)CT7
2'
38                       N/U                         ms                  72
C
I
2S/^ / 8* .z |
1
-
1
1
1
1
1
1
1
1
4-3*? 5S
2 2*i                 53
2O-SS
N/L
N't-
1
1
1
22^0
JDS
joO
I
20 03b               A7
11
11
11
1!
11
11
11
I
1
1
Mate canal -{Ibll
hou.fi cCujl 'to | blockaaa. at £Ue |
adujOrUii
i
II II II II II II II II II II 11 II II
IIOATA ShCH FOR FIELD IRRIGATION PRACIICE STUDIES
Fiild Na Ffr/l/ga______________________
POST   PLANI IRRIGATION
NUMBER
DATE
IRRIGATION DURATION
(hrs.)
AREA             | TQf*L MPHQH
IRRIGATED
(ha)              I
U ISCHAkGESJ
ESTIMATED
REJECTION ELONS
(l/ssd
VOLUME OF
WAIER APPLIED
(!/»«>
DEPTH OF APPLICATION
(-.)
RAINFALL
l-M
NOTES            ‘
£tu
26/^/SQ
3o
20
2 TS
393 1
1
2 25
jWIL
AJH.
^2QO
2512
3(<«6
in
is
ISO
*#-©1
<1 2 fiSd
/c?3
1
1
1
1
1
11
II
> Direct
5€ 310UJPAIA SHEET FOR FIELD IRRIGATION PRACTICE STUDIES Field No Fl/l/Sb_______________________
POST    PIAUI IRRIGATION
NUMBER
DATE
IRRIGATION DURATION
. (hrs)
AREA
IRRIGATED
(ha)
]"lOI*L         SIPHON | DISCHARGES
ESTIMATED         | VOLUME Of
DEPTH OF
NOTES
Irejeciion flomsImaier applied | APPLICATION
1
1
1 (■■)
1
SiU
20/1/8 2l/ l/80
e
/o
1
1274
1
1
RAINFALL
(■■)
14 O
11 2* 1
| 22/1/84
2^/84
n
1
1
■* l»-71 2 67
112
ZI7 / 68
|S
41
53
16                     4G66 15              1     1778
1|
17
62
II II II II II II II II 1
25/l/?* 1
29
12
bi
61
2
NIL
121  1 1
3
2318
6270
1
2SO|
1
| 17 VIZ
1
1
1
1
1
1
1
\Mam <c*.noJ            cvc^d (for 23 hours ilut U
( HccUciq«. uA 4L<* J UeuduiOkks
m
111
1
1
1
1
1
1
1
TABLE 06DATA SHEET FOR FIELD IRRIGATION PRACTICE STUDIES Fit Id No M|/>/
|POST     PL*kT |lRfiU*f LOH
NUH6ER
|            DATE
IRRIGATION DURATION
(hri)
AREA
IRRIGATED
(h*)
TOTAL SYPHON
DISCHARGES t
|l/itc>
ESIINAIEO
REJECTION FLOWS
VOLUME OF
MAIER APPLIED
( 1/bbg)
DEPTH OF APPLICATION
(»)
RA1BFMI.L
NOTES
1
(..) |
20/1 /tfif 18
2|/‘I/fe’9 2H
22/-?/E*                13
2\/^/Vk               /<j
/‘t/vti
2 n                    n
0                        in
0 ?t                  II
/ 52                IB
174                   A
1 71
I 74 33 I
2^1
]
1 08                   so
1 u                 bl*
1
2-tO 1
D-tZ               33
1
2203
1 2 jo
5*5
507
2 sot
25*12
2S5t
3S1C
1120
4 LbG
37*5
2l3b
ZO2
123
b6
40
1*4
1*7
*64
mi
MOD
ztb
103
-26/
I
2 6/<?/*«
2»
2*
27/<? A*            2 li
Zb/B/gZ/              2*
2M/7 /W          ■ 24
loh /UH               21
1 f>a/W              <6           1
1
!
1
NlL.
NIL.
N/U
NIL
NIL
NIL
NIL
N»L
N *l_
h/lL
rd>L
NlU
1
U0 1
1
1
1 ■ Main can<J                cqcls<i 1 ■ fcr 2 3 houL<s tCtAjk to
1   blockage at ik«.
1   heexd UXjrks ,
1
1
1
1
1
20
1
1
1
JO m
fll
K threat Ice-Ji r\g mlo
LUDATA SHEET FOR FIELD IftflI GA t ton PRACTICE STUDIES
Field Mo F »/> /& b
____ ____
IRRIGATION DURATION
(hrs)
ARC A
IRRIGATED (ha)
(01*1 SYPHON
DISCHARGES
(SHMAIED REJECTION FICKS
(1/iec)
VOLUME OF
MATER APPLIED
(1/secl
DEPTH OF
APPLICATION
(■»)
RAINFALL
(■■)
NOTES
1
RPOSI PLAMl ■
| IRRIGATION
1 NUMBER
1
1 btu
1
MIE
20/ ’i /&«
1 2\/<a/i»i
1
1                      22/^/^
1
II
II 111
Zlf /‘l/M
2 78
1 BQ
0 31
JO|
0 82
2 IS
i bi
fO7
163
D'%
0 It
ro3
207^
337 0
1 3S7
a SAB
4141
£1*17
Son
£270
25*11
3 370
3183
j a I/O
75
i®3
t|J«
111
5Ot
1                     2$/°l /ill
11
1                     2G/l/*4
27/^/314
28 /9 /«4 |
16
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13
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14
• 14
1 /1O/84 !
1
1
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}2
31
21
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46
33
68
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21
38
3°
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MIL
MIL
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Mu
rHL
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lh o
j Main tonal jlu-i
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Lea<J<-jor ,
1
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413
SSI
3Q2
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1
II
n 0?
JH71
210
!■DAU SHEET FOR FIELD 1RH1GMICR PRACTICE STUDIES Field Mo F Q / *3 /1 7_____________
[|POST PLABT ||IRHIG*1 ION || NUMBER
DATE
1RRTGAUOI DOflATiOl
(hr*)
MEA
IRRIGATED
{hi)
TOTAL SIPHON DISCHARGES
(1/sec)
EST1MATED
REJECTION FLOMS
(Vl«)
VOLUME OF
MATER APPlKO
U/l«)
DEPTH OF APPLICiriOl
(••)
rainfall
MOTES                               1
I
[««; I
II
II
II 4*u
II
II
1
2 5/ 1/»I|
21
2y/1/8« 21/f/^
24
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2-01
ION
IPM
4 41
J Hl
4i
11
5
NIL
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6SE26
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327
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h AU Ck(oi\<j flclc 1
fJC 1 A Al Cr Or
NO IftRlfrflT
24
IB
ST
36
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NIL
75)7
2333
i 70
<23
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II
II
II
1 11
II
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1
1
1
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H-/7
20 itie
•
■*
•
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II
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I nxiud U^d
I  ixrittoAc.
R/1/in
I
I
I
I
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I
I
I
I
I
I
I
TABLE 59DATA SHEET FOR FIELD IRRIGATION PRACTICE STUDIES Fiald lo F4 / 3/<8______________________
JfPOST PLANT
||lRRIGAIION j
|| NUMBER
DAIE
IRRIGATION OURATION
(hrs)
AREA IRRIGATED
(ha)
]   IOTAL   SYPHON | DISCHARGES
ESTIMATED
VOLUME Of
(REJECTION FLOW! >|MATER APPLIED
DEPTH OF APPLICAIIOM |
1
1 (I/mc)
(1/mc)
1
RAINFALL
(•■)
NOUS
II                1
11
51                    NIL                        5010
1
11
II II II II II
1
1
1
1
26/1/84
1
NIL
426 122 |
Tl
1
1
1
1
1
1 27/’/W
24
24
24
1 2o
2 4o
4 oB
34
123
1     NIL
2138
| /O627
260 |
II                1
11
II
II
II
II
II
II
||
1
1
2B/1/84          24               3 12
NIL                          1850
1
1
1
1 2VWi
260                        3,
1
[
1
1
1
2678      |      <03
1
1
1
»O/1/S|
1 IB I 1 1
2 11
44
NIL
II
II
II
II
1
1
1
1
285/
34042
130
l»7
1 1
11
1 1 1
|
• *
II                1
II                1
II                1
II                1
II                1
II                1
II                1
1 1
1
111
1
1
1
1
1
1
11
11
11
11
11
11
11
11
11
11
11
11
11
11
11
TABLE bioDATA SHEET FOR FIELD IRRIGATION PRACTICE STUDIES
Field Ao FI / 3 / 2 2 o
[JpOSI    PLANT 11IRRIGAII0A
|| RUNNER
DATE
| IRRIGATION
1 duration
(hrs )
AREA            |  TOTAL  STPHON
IRRIGATED       j     DISCHARGES
(hi)                I (l/..c)
ESI1AATED        ]  VOLUME  OF
(rejection flows jwAIER APPLIED
(1/mc)             1      (l/>«c)
DEPTH OF
APPLICATION
(■•)
RAINFALL
(••)
MOTES
1
le/A/g/j
1 24                                                                                1      1 4
11
IbR                34
•
12
Aoiu
1
27CS
107
HS
32
1
2 o/<9 /9if | NO IKKiC-/
2 91                2
H/V** 1  1 ‘
r/o a/
11
11
16
KO
Stopped olu« tu
rain folk
l | 2M U 39 58
1
1      1 '•
1
Zl/l/W
2 2/‘f/fc|, 13
23/Vw Ik
2«/V»| .e
2 4>S
1 10
1
I
MIL
MW
U*
I
I
I
I
I
11
2 94 MIL
|
I •‘13      1
Am-
3623
It
32
H
118
) HatA conul
( fa             V^oais cUa* tc [ blccUo^e cA Ike
1 beudvcc.Ls
• •                                / 6 3S
13 036
tfo
•
I
1
1
1
1
31BC1□AT* SHEET FOR F[£LO IflPIGATJON PRACTICE STUDIES
Hildlo 'll 3/22 b_____________
I |POST PLANT || IRRIGATION H MUMPER
DATE
IRRIGATED* DURATION
•• (hrs)
AREA
| IRRIGATED j
|hi)
rOTAL SYPHON             ESTIMATED               NOLUxFof I DEPTH OF
-
NOTES
DISCHARGES       (REJECTION FLOWS
|WATER APPLIED | APPLICATION
(1/lBc)
[1/mcJ        1                      I       («)
RAINFALL
(■«)
II
II
II
1!
II
II
II
II
II
II
II
I8|A /«k 2k
.2
..... 1
' 52
2 kt
|
1 2o/V^
1
1
1 AJO lARltrA
TlON
4                       ML
1
26           |           |WL
1
11
1
|1
1
776                 5^ H23                kfc
I
11
467“) 130 7o2 3H
I £
HO
II II II
II
il
I
)
Stepped due tc ra^|alV
2i/V^ 2k
22/^/n
352 63 nil
1
II II 1
>
1
1
1
1
1
1
1
1
1
1
1
IQ
16
1
302  1 30
1 1
118  | IS
1
1          W,U
h  Hom  cuncA  |  tcu>  ccusvJ  I
1
tc
NIL               1
1
ins
I
1
2k
oil          :     2H
3
31
I £>£5
t3
222  1
i -for 23 hours 
| blcclca^Q. at 4k« |J ktodvsorUs
12-66 |
i
1 1 1 1 1 1
I
1
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10 782
gk
Zie 91flHAPPENDIX c
DESIGN CRITERIA’PPENDEX C - CESICM CRITERIA
C.l FLOOD PYXES
C.I.l             Iwnnh River Flood Protection Dyke
Criterion
(i)                 River    dyke    to    withstand    return period florid of
(ii)                   Minuam Tree baa rd
(Hi)
Dyke top width
Ci*)             Side sldQe^
(*) Cross Fall ta dyke top (toworcta river) (H) Tnpwoil stripping undec embankment
(nuniam)
(vic)             Compaction  to  embankment
(Proctor density)
(*iu)            Minimum   reserve   between   dyke   and adjacent riverway
ABsiqrad
Value
20 yearn
0*5 w
3*0 a
1 in 2
1 in JO
Design Consideration
□ptlmlaed coat/berwfit
Cant lngency/’M fat y factor Vehicular access
Stability
Surface drainage
0.15 m                           Elimination         of         preferential leepqqe pash/staoiIIty
95%
100 n
C.l.2.
(D
%
Eastern Catchment Flood Dyke and Drain
Dyke to withstand return period
riood af
10 year
Stability/acepaqe
Flood reserve for
attenuation, safety reserve nqainst high velocity/
erosion oT dyke
Qualitative      asaesKsaEnt      of appropriate period.
(11)             Minimum TreeOnard
(ill)              Dyke top width
Cl*)          Side slopes
(*) Minimum reserve between dyke and drain
0.5 m                             Cent ingoncy/safety factor
3.0 ■
1 in 2
50 >
Vehicular access
Stability
Limit
veioeity/erosion
1*1)
(vii)
(vin)
Minimus   reserve   between   dyke   end   Coe   of adjacent foothills
r op sail stripping under CTfibonkmciint (minimio)
Compaction    to    embankment    (Proctor Density)
(ix>              Minim lm width Of flood channel
(*)               Miniain    depth    of    flood    channel (cut and fill balance)
C.2 SUB-SUflFACE CHAIN Ad
C.23              In Field Pipe Drama
15D a
0.15 •
955
20 m
a.5 a>
adjacent to dyke
Flood reserve
Elimination         or         preferential seepage pa th/stability
S tab 11 i ty /ae spa ge
Provision        of        prferentiel
flow path
Provision        af        preferential
flow path
(1)               Drainage Races
(ii) Minimum pipe gradient
- Cotton
- Banania
Z.5 XR/dny                    □rainable excess frexn
3.4 mm/day
□ .15
irrigation, including
canal seepages
Siltat    ion    and    laying tolerance (small diameters)
(Hi)
Slltation allowance
20% reduction             Pilot drainage scheme
in rapacity
reaulta/FAO       irrigation       nnd Drainage Paper 3fiCriterion
C iv)              Mexia urn Length of pipe run
(v)                 Hinimisa    depth    of    draire.    at    heed    of lateral or low point along lateral
Abh igraed;
Value
400 is
(Jeaiqn Consideration
Access far maintenance,
practical limit
1.6 m Water table/eelini ty
control
tvi)
Pipe filter surround
C.2.2             Collector Pipa Drains
(i)                  Drainage Rates
(U)                Minimus pipe gradient (iii)                Siltntion allowance
- Cotton
- Bananas
75 mm minimum
thickness
2.5 mu/day
3.4 nw-' day
0.055
20% reduction
in capacity
Civ)
Maximum Length of pipe rui, between
inspection chambers
(v)
Areal reduction factor -225 4 300 «w(id)
-150 mm(id) C.3 SURFACE DRAINAGE
C.3.1              Shallow Surface Drains
(1)                  Fleld draina
Drain section determined by construction considerations (using ditcher bucket). This criterion
exceeds rmoff considerations.
Dimensions:            Bed width
D e p th
Side slopes Minimum gradient
Mannings 'n*
(U)                 Tertiary Drains
Drainage coefficient
300 «
0.7
0.8
Enhanced hydraulic entry/
soil stability
Ad above
5iltation and laying
tolerance
FAO, Irrigation and Drainage
Paper 30
Access for maintenance,
practical limit
FAO, Irrigation and Drainage
Papera, Na 28 and 38
*
0.5 m                              Minimus practical for 0.5 m                              mechanical excavation
1 in 1.5
C.Q5X
0,03
Soils stability
Hydraulic capacity
Coefficient for grass
/weeds-*1
1.2 1/ sec /ha ar             1 in 5 year rainfall/
Bed width Minimum gradient
Mannings ’n! Minimun Freeboard
tertiary canal
rejection Row
(1003 design)
D+75 m
0.055
0.03
0.25 m
runoff estimate
Nominal atandards for
velocity roijqhneao and
contingency allowance
(in freeboard)
(ill)                 Secondary Drains
Drainage coefficient
(iv)                 Main Drain
Mannings 1 n' Hinimun freeboard Drainaqc coefficient
MunnIngs • n1 Mlnumja freeboard
1.2 1/Bee/ha or
secondary canal     Ab CJ»L(li), roughness rejection flow                coefficient baaed on
( IDO * tfealg n) maintained flow section
0.025
0.Z5 m
1.0 l/sec/hs or     1 in 5 year 24 hour
sum of canal
rejection flaw
1100* cfeaiqp)
0.025
0.50 n
ralnfal 1/runoff estimate
Maintained flaw section
Contingency
V "Open Channel Hydraulica’1 Ven te Cha*, McGraw-Hill, 1959enter ion
Assigned
Design Consideration
/ a i ue
0.5.2            Deep Surface Drain*! (corivey i rg s ub-a urface
(i)                 Normal flow discharge coefficient
Mannings 1 n' Secondary and Main drain Normal flow level | helo* centre-line of sih-surface pipe outlets
Maximin drain depth witrxjut berm
S i tfe s Lopes
Sere width (where required)
' ii)               Oeai^i flood FI cw t sum of design
normal How and surface storm
runoff (or rejection) flows for
Secondary or Main Drains
Minimus Freeboard             Hain Drain Secondary Drain
C. J. 3         Desirable Velocities in Open-Drains
Minim ui (for Normal flow)
Maximum (for Peak flew)
C.4 DRAINAGE STRUCTURES
Maximum   culvert   headlowa   at   normal   flow Minimum pipe velocity
Maximin pipa velocity
Factor   of   Safety   an.   snapaqn   (exit gradients)
Angle     of     internal     friction     of     backfill Cohosion of backfill
Safe bearing capacity of fomdatiorwj
AflsuMed   nooLLnsl   concrete   strength   at   28
days
Filter gradings (far rip-rap)
drainage flows)
0.55 1/aec/ha Cm bl he d rejection and
0.025
0.15 ■
3.5 «
1 in 1.5
subsurface (^mlnage flows Maintained flew section Operational contingency
a 1 lawanci*/ fee ilit ate
inspection
Stability/accexe far
maintenance Soils stability
4.0 m                             Mini SMB access for maintenance
□. 35 V see/ha
* 1.0 1/snc/ha
= 1. 35 1/sec/ha
0.5 m
0 Z5 m
S    up    st    inpO'Sing    flood    runoff an norntfil □perating
condition
Contingency allowances
+
0.4 m/sec
0.0 m/sec
0.05 □
Not less than
Srain velocity
J.O   m/sec
5.0
50°
0
100      W-i*
20 N/wa*
Designed to
USSR
Prevention of bilharzia
eratil
Scaur velocity
Cost        minimisation
Silt pravsntian
Energy dissipation
Soil stability
Standard strength class
S ta blli ty/pe rfteubiLity
□f Ml deFlying sail
recos
ndatignsiAPPENDIX D
SUBSOIL DRAINAGE PIPES - ALTERNATIVE METHODS OF LAYING DISCUSSION PAPER ’ MARCH 1984ICOPY
HW/MSA 615
Executive Director
Aaibara Irrigation Project II
PO Box 2338
Addis Ababa
Ethiopia
6 March 1934
Dear Dr Zewdie
AMIBARA IRRIGATION PROJECT
SUBSOIL DRAINAGE PIPES ~ ALTERNATIVE METHODS OF LAYING
During my recent visit to Addis Ababa you requested a discussion paper on alternative methods of laying deep subsoil drainage pipes. We now have pleasure in enclosing the paper which we trust will be found co cover adequately all Che points you had in mind. If there is any
further io format ion you require, or if you need amplification of any of the points contained in the paper no doubt you will let us know.
Yours sincerely
D G GLENNIE
EnclDISCUSSION paper on alternative methods of laying subsoil drainage pipes
This paper sets out and discusses the alterantiv* ways in which deep subsoil
pipes could be laid and Che advantages and disadvantages of each and sets out
sone comparative costs, Reference has been made to the following reports
prepared by the Consultant:-
Interim      Report      on      Subsoil      Drainage      Pipes:-      Types      available,      costs      and      methods      of installation - March 1983.
Report      on      Subsoil      Drainage      Pipes.      Materials,      costs      and      methods      of      installation      - August 1983.
A* SUMMARY
Three principal methods of laying pipes are discussed, namely:-
a)        Using a special pipeLaying machine
b)        Using conventional construction plant
c)        Using labour intensively
The last two methods mentioned above are too slow and too costly to merit
serious consideration. Using Labour only requires such a large number of men
that it would raise serious logistics problems*
Comparative     costs     of     Laying     field     drains     only     on     an     area     of     1000     hectares     are     as follows:-
a)        Using special pipelaying machine
b) Using conventional construction equipment -
c)        Using labour only
Birr 760,500
Birr 7.267,500
Birr 4,623,750
Methods b) and c) above also introduce problems of the safety of workers and disturbance of the topsoil, and in the opinion of the consultants do not merit further consideration.B. METHODS OF LAYING
Bl. Using Special Pipe Laying Machine
Since the 1950’s pipe laying machines have been developed with ever increasing degrees of sophistication. There are now two main types available. One is the trenching machine which forms a narrow trench using an endless chain excavator. The other is the so-called trenchless machine which tows a mole through the ground and a continuous slotted plastic pipe is inserted through the mole. Trenching machines have been developed that will cut a trench up to 3 metres in depth in favourable conditions. As it progresses a continuous plastic slotted
pipe is laid on the trench bottom. The installation of the granular bed and surround can also be carried out at the same time if required. Backfilling can be carried out by hand or by a simple archimedes screw mounted on the front of an agricultural tractor.
Details of a number of trenching machines are contained in the Consultants report on Subsoil Drainage Pipes, Materials, Costs and Methods of Installation dated August 1983.
Trenchless machines have, until recently had a limited satisfactory depth of operation due to the ’’smearing” effect below the critical depth in certain clay soils. The recent introduction of Che Delta or 'V’ plough, so called because it has two digging legs joined at the bottom to form a V-shaped cutting tool, is one of Che lastest developments in trenchless drainage machinery technology. The legs and joining piece are hollow co allow for the passage of plastic drainage pipe and gravel Co surround the pipe if required. As the tool is dragged through the ground, a wedge of soil is lifted for long enough to allow the pipe to be installed. One of the main advantages of this mode of operation is that it avoids the disadvantage of conventional trenching machines when digging at depths greater than critical (about 1.5m), chat of soil being compacted or smeared around the drain in certain soil conditions, although this problem can be alleviated by the use of special cutting teeth.Both these techniques provide a fast rare of pipelaying with a race of 3000 metres being an achievable daily rate given reasonable conditions. This becomes an important consideration when drainage installation is planned for the season when no irrigation is required and the land is consequently dry. Drain laying
at that time of year would also cause the Lea*t disruption to growing cotton and would consequently reduce cotton losses due to drain laying activities. This period should be about four months long and is assumed to be Che preferred period for drain Laying operations.
One of the objections that has been raised against the use of a pipe laying machine is its cost and heavy dependence on foreign spare parts
requiring foreign currency to purchase cho). But in fact the owning and operating of one of these machines is Che same in principle as for any other item of heavy construction plant in Ethiopia. They all require foreign currency to purchase and for spares.
Their specialised design allows low unit installation costs as will be seen
later. It also means that men do not have to work in deep trenches with the attendant dangers that brings.
B2. Using Conventional Construction Equipment
If conventional construction equipment is to be used the only item that could be realistically considered is a backaetor, either wheeled or tracked. Such a machine can dig a trench easily enough to a wide range of widths depending on the bucket width fitted.
The main difficulty then is that men have to work in the bottom of the trench in order to lay the pipes. Since the trenches, by reason of the drainage need,
will usually be m ground that is largely saturated they will consequently be liable to collapse. This would obviously be a danger to human Life and could not be accepted. The solution would be either to shore the trench* sides or to excavate trenches with safe side slopes. Shoring trench sides is a slow and expensive operation and excavating to safe side slopes involves a large quantity of excavation and back filling per metre of drain laid and this too will be expensive. On top of this there would be extensive disturbance to the topsoiland unless this was excavated, set aside an
lost with the consequent effects this may a Setting it aside seperately would add further to
backfilled seperately it would be
,ubseouently
. .... nn crops grown subsequently.
Che cost*
A backactor,
Pilot Scheme
requried for
74 metres of
land laying  of of pipes without the
for the installation of 7000  metres
use of shoring was used in the
h
of pipe. T e total time
this installation was
pipe were laid per day.
about four months which means that an average
The variation order items covering
drains
amounted to Birr 151,872, which is equivalent
excluding the cost of the
contractor.
pipes which were delivered
excavation to field drains and laying field
to      Bir      21.7      per      metre
free of charge to the
One Akerman backacter was used for the Pilot Scheme. It is thought Chat about 2/3 of its time was spent on digging open collector drains which means that its rate of digging field drains, had it worked all the time on them, might have been about 220 metres per day. Thus to match Che rate of laying of a specialised pipe lyaing machine about 15 Akermans would be required, each one costing about £156,000 cif Assab with spares. This clearly would not be a
realistic solution.
B3. Labour Intensive
It is understood that one of the objectives of drain installation
operation labour
intensive. The ultimate in labour intensiveness
use no machinery st all and do all the excavation and backfilling
is to make the
would be to
by hand. It
is       not       certain       whether       this       degree       of       labour       intensiveness       is       what       is       intended but if not there are many degrees of intensivenes. that could be practiced
between this and full mechanisation. However ™ what is required further conanents can be made.
It is assumed chat the trenches will be ? n
cba, our Ub.ur.ru.., „u„. . „ b.ubHn 
t
would be required to double handle the mater 1 Therefore at least 7 men would be rea„i. . 
nowever, on the assumption that this
is
U0
n,eCre per day and cwo
and
more
fr °W th* trench ed8e-
excavate and backfill each metreof pipe per day. To achieve the saae output as a trenching machine at least
21,000 men would be required and possibly more. On top of this, further men
would be required for trench timbering, pipe laying, supervising etc. This
large number of people would have to be recruited, transported to site, housed,
fed, provided with a water supply and sanitation, transport to and from their
place of work etc. The logistics of such an operation would be formidable and
the cost considerable.
Even if the labour intensive work were spread over 12 months rather chan 4, the
force required would be in excess of 7,000 which is probably about the number
required co pick the cotton crop by hand. It is also thought likely that more
foreign currency would be used transporting this number of men than would be
involved in buying and operating a trenching machine.
Therefore this solution would seem to be quite unrealistic and untenable.
C. COSTS
Cl. Using Special Pipe Laying Machine
The following is reproduced from the August 1983 Report on Subsoil Drainage
Pipes.
ESTIMATED COSTS OF INSTALLATION OF FIELD 6 COLLECTOR DRAINS BY CONTINUOUS TRENCHING MACHINE FOR A TOTAL AREA OF 5000 HECTARES AT THE RATE OF 1000 HA PER YEAR
GENERAL
Unit rates are based on the following:
1.       April 1983 Plant costs, Material prices and labour rates with no allowance for future escalation.
2.       Exchange Races US $ 1.60 - Birr 3.25 - DM 4.04 = £1.0 Sterling.1
3.         The whole of the “Works'  for an area of 5000 HA to be completed as a series of 5 No Contracts of twelve months duration for 1000 HA each let to local contractors over a period of 5 years.
4.         Installation of field and collector drains in any one area of 1000 HA completed during the six months period December to May of each year.
5.         A total quantity of work per 1000 HA of 250,000 lin m of 44 mm I/D field
drains and 33,000 lin m of 80 mm I/D collector drains.
6. Field drains with and without filter media surround of either graded
crushed rock or as dug volvanic ash both available within 20 km one way of
work site.
7. An allowance of 30* of the direct cost is included to cover Contractor's
on-costs.
METHOD STATEMENT
Field and Collector Drains
Excavation,  and laying  of drains (with or without filter media  surround) by Hoes-Gigant 2000  trenching  machine or Mastenbroek 25/20  V plough trenchless machine.
The drainage machine will need to be supported by a filter media feeding hopper loaded by a craxcavator front end loader/back hoe. The backfilling of the trench and local disposal of surplus material will be carried out part labour,
part machine.
UNIT RATES Per lin meter.
a) Supply deliver and lay 44 m I/D field drains without gravel surround with Hoes-Gigant trenching machine per lin meter.Mobilisation of Plant from port Asab to site
Birr
0.03
Commission drainage machine
0.07
Excavate and lay 44 tmn I/D pipe and backfill
1.37
Supply and deliver 44 rmn l/D pipe
1.13
Total Direct Cost
Birr
2.60
Add for On-cost 30t of Direct Cost
0.78
Selling Race
Birr
3.38
b)
Supply deliver and ley 44 zta i/E field rains without gravel   >urround with Mastenbroek 25/20 V plough per lin zneter
Mobilisation of Plant from Port Asab to site
Ctramission drainage machine
Excavate and Lay 44 snn I/D pipe
Supply and deliver to site 44 I/D pipe
Total Direct Cost
Add for On-Cost 303 of Direct Cost
Selling Race
c)      Filter media surround to field drain
1.      Crushed rock delivered to work site per cu m for trench of cross sectional area 0.210m x 0.210m
Direct cost per lin tn
Add for On-Cost 30Z of Direct Cost
Birr         0.03
0.07
1. 18
1.13
Birr         2.41
0.72
Birr 3. 13
Birr          28.0   cu m
*
» Birr                 1.23
0.37
SellinR Rate
■ Birr
1.50
per Lin a
2-
As dug volcanic ash delivered co site per cu m
- Birr
15-0
cu m
For trench of cross sectional area 0.210m X 0.21On Direct cost per lin m
■ Birr
0.66
Add for On-Coat 303 of Direct Coat
-
.20
Stolling Rate
» Birr
0.86
per lin md) Supply deliver and lay 80 mm I/D collector drain without gravel surround with Hoes Gigant trenching machine per lin m.
Mobilisation of Plant Port Asab to site
Birr 0.03
Commission
drainage
machine
0.07
Excavate          and          lay          80          mm          l/D          pipe          and          backfill          1.37
Supply               and               deliver               80               ram               I/D               pipe
Total
Direct
Cost
4.32
5.79
Add               for               On-Cost               30X
Selling Rate 7.53
Add to total cost per 1000 Hectare a 10/Z Contingency to cover
x               Direct               Cost               1.74
1)
field drain/collector drain connection
2)
pressure cleaning bend and flushing bend
3)
marker posts
A further allowance will have to be made for structures and manholes once the
scheme has been designed.
C2. Using Conventional Construction Equipment
The       following       cost       estimates       have       been       taken       from       the       Interim       Report       on       Subsoil Drains dated March 1983.
Excavate       for       field       drains       to       depth       and       gradient       and       backfill       on       completion       and remove surplus to tip.
First Stage - Excavate of drain trench to a depth of 1.94 metres ie top level
of filter envelope with Akerman H 16 supported by Cat D 7 Dozer. Side slopes 1.5 to 1.0.Second Stage - Excavation of drain trench 0-46 metres x 0-46 metres manually
Production           150 Lin m per 8              hr day
Labour
Excavate & backfill Stage 1 (Machine)
Removal of Surplus
Excavate & backfill Stage 2 (Labour)
Dewatering by pumping
TOTALS
Total DIRECT COST - Birr 20-63/lin metre
2.99
L.00
3.99
Plant (Incl Operator) 12.32
2.84
1,48
16.64
Add for On-Cost 502
(includes Profit
and Bond)
head Office Costs,
Sice Costs,
Insurance
Selling Rate - Birr 30.95 say 31-OO/liu metreGraded Material
Graded Material ex stockpile
Transport to site
TOTALS
Total     DIRECT     COST     -     Birr     0.86     *     27.89     - Add for On Cost 50Z
SelLing Rate
Add for waste 10Z, Selling Rate - Birr
10.92/lin m.
Red Volcanic Ash (as dug)
Labour
0.86
-
0.86
Birr          28.75
14.37
Birr 43.12 per cu m
Plant
14.12 (Incl Operator)
13.77 (Incl Operator)
27.89
7.50      per cu w,            equivalent to Birr
Labour
Load 6 transport to site
TOTALS
NIL
Plant
10.33 (Incl Operator)
10.33
Total DIRE
CT COST -
Birr 10.33
- Birr
10.33
Add for
On-Cost 50Z
5.17
Selling
Rate
Birr
15. 50      per cu m
Add for waste 10Z, Selling Rate ■ say Birr 17.00, equivalent to Birr 3.91/lin m
Labour
Lay pipes and place
Toral DIRECT COST =
Add for On-Cost 50Z
Selling Rate
filter material by hand
2.63
Plant
1.00
Birr 2.63 + 1.00 - Birr 3.63
1.81
Birr 4.33/mThe drainage aachine will ^eed to be supported by a hopper and a CAT 9'7 front end Loader co load filter material into the accompanying hopper*
It is not known how much work the drainage machine will ultimately have to do but if it is asusmed that 5000 ha will eventually have to be drained and that on average the length of drain per hectare will be 225 metres the machine cost per metre laid would be as follows:-
Time required for machine to complete ls 5000 x 225 
3000
assuming 8 hour day ■ 375 x 8 - 3000 hours.
“ 3 75 days working
At 2000 hours per year this
spread over several years,
over this time, would be:-
Trenching machine 33,000 x 5
is equivalent to 1.5 years, although this will be
The monthly cost of the machine, assumed written off
1.5
CAT 977
Trailer
120,000
60.000
say 20,000
Birr 200,000
If       production       race       when       machine       is      working       is      75.000       metres/monrh      the       plant       cost per metre becomes Birr 2.67,
Labour                Plant
Excavate and lay pipe and surround
0.05
2. 67Total DIRECT COST - Birr 0.05 ♦ 2.67 -
Add for On-Cost 50X
Selling Rate
Birr 2.72
1.36
4.08 per lin m
Labour
Plant
Supply and transport to site of
Graded Material
0.86 
27.89 (Incl Operator)
Total     DIRECT     COST     •     Birr     0.86     *     27.89     ■     Birr     28.75     or     0.86     *     22.64     «     22.50
Add
for
On-Cost5 
50Z
14.37 
11.75
Selling Rate 43.12 35.25
Add for waste 5X, Selling Rate - Birr 45.00 per cu m or 37.35 per cu m, equivalent to Birr 10.35/lin m-
Labour
Plant
Supply and transport to site of
Red Volcanic Ash (see Sheet 2)
Total    DIRECT    COST    «    Birr    10.33
Add       for       On-Costs       50Z       5.       17
Selling Rate 15.50
Add for waste 5Z Selling Rate = say Birr 16.25 equivalent to Birr 3.74/lin m.
SUMMARY
1.         Estimated cost of laying drains in open channel, from above:- A Crushed Filter material
10.33 (Incl Operator)
Excavate and backfill on completion Provide crushed filter material
Lay pipes and place filter material by hand
TOTAL
Birr
31.00/lin   m
Birr
10.92/Lin  m
Bxrr
5.44/lin  m
Birr
47.36/lin  mB        Red Volcanic Ash (as dug)
Excavate and backfill on completion
Birr
31.00/lin  m
Provide red ash filter material
Lay pipes and place filter material by
TOTAL
Birr
3.91/lin  m
hand
Birr
5.44/lin  a
Birr
40.35/lin m
2.        Estimated cost of laying drains by trenching machine A Crushed filter material
Excavace, lay pipes, place filter
Birr
4.08/lin m
Backfill
Birr
1.50/lin m
Crushed filter material
Birr
10.92/lin m
TOTAL
Birr
16.50/lin a
B Red Volcanic Ash (as dug)
Excavate, lay pipes, place filter
Birr
4.08/lin  a
Backfill
Birr
1.50/lin  m
Red ash filter material
Birr
3.74/lia  m
TOTAL
Birr
9.32/lin  m
C3. Using Labour Only
in Section A3 it was assumed at best that a labourer could excavace 2/j cubic metre per day but from the bottom half of a deep trench this is unlikely. Also
the material would almost certainly have to be double handled away from the trench edge. Therefore assume 3 man days to excavate one metre run, 2 man days to double handle the material and a further 2 man days to backfill.
Total 7 man days 3 2.75 Birr
Add for supply and deliver 44 urn pipe • 1.13 Birr
• 19.25 Birr
.17 Birr
TOTAL
Birr 10.55/lin metreSUMMARY
It      cm      be      seen      from      Section      B      above      chat      the      comparative      prices      for      supplying and Laying mm diameter pipes are:-
a)
Using trenching machine
-       Birr
3*38/metre
b)
Using conventional plant Excavate and backfill
-       Birr
31.00
Supply 4 deliver pipe
-       Birr
1.13
Lay pipe say 
-       Birr
0.17
ci Using labour only 
Birr 32.3/metre
- Birr 20.55/metre
Total      costs      on      an      area      of      1000      ha,      assuming      225t000      metres      of      pipe      on      this      area would be:-
a)
Using trenching machine
- Birr
760,500
b)
Using conventional plant
- Birr
7,267,500
c)
Using labour only
- Birr
4,623,750
These figures are not intended to show the total cost of the drainage installations as they do not include for collector drains, or for any other engineering work required. Nor do they include for General items. They are intended to show only the comparison between estimated costs of excavating for, supplying, laying and backfilling field drains. They show quite clearly chat
che use of a specialised trenching machine provides Che only economic and realistic way of Laying the large lengths of drainage pipe chat will be
involved.APPENDIX £
JOB DESCRIPTIONS: MIDDLE AWASH AGRICULTURAL ENTERPRISE AND STATE FARMSJOB DESCRIPT TON: WATER MANAGEMENT ENGINEER
MIDDLE AWASH AGRICULTURAL ENTERPRISE
The Water Managetrent Engineer will be an exper tented irrigation/agricultural
engineer with a knowledge of soiL-plan" relationships. He will be respon*ibte
to the Manager, Agricultural Division of the Enterprise. His duties will
include: -
Preparation           monitoring        and updating irrigation schedules tor State pareis.
2- Advising Farm Irrigation Managers on proper methods of furrow irrigation to achieve maximum efficiencies.
3.        Ensuring Farm Irrigation Managers ire actively engaged in limiting
■innecessary rejection of water, as surface run-off at end of furrows etc.
4.         Ensuring each irrigation crew of the Farms has been provided with a pocket watch for timing irrigations.
5.        Monitoring application efficiencies etc.
6.        Monitoring rainfall data sc the irrigation schedules or application amounts can be altered co suit actual conditions.
7.        Developing and introducing water budgeting methods ot irrigation.
6.
Training State
Farm Irrigation Managers and other irrigation staif.
9.         Arranging soil            sampling for salinity monitoring.
LO. Liaising with the Water Management and Operation and Maintenance Engineers of the Project Control Centre.JOB DESCRIPTION: LAND DEVELOPMENT, IRRIGATION AND DRAINAGE ENGINEER
MIDDLE AWASH AGRICDLTDRAL ENTERPRISE
The Land Development, Irrigation and Drainage Engineer will be a graduate civil engineer with a minimum of two years experience in the design and construction
of irrigation and drainage works. He will be responsible to the Manager,
Technical Services Section of the Enterprise. His duties will include:-
1.         Design of small irrigation structures, canals and drains.
2.         Land development for extension to existing schemes or small new schemes.
3.         Advising Farm Irrigation Managers on proper maintenance of structures,
canals and drains.
4.          Ensuring Farm Irrigation Managers carry out maintenance of irrigation
canals and drains according to design to prevent overtopping, seepage and breaches during the cropping season.
5.         Ensuring Farm Irrigation Managers compile and execute a maintenance program for the closed season to be completed before mid April.
6- Advising and liaLsing with the Farm Mechanisation Section on proper laud smoothing methods to eliminate waterlogging.
7. Liaising with the Water Management Engineer of the Agricultural Division.JOB DESCRIPTION: IRRIGATION MANAGER
STATE FARMS
The Irrigation Manager will be a graduate with two to three years experience io irrigation and water management. He will be administratively responsible to the Farm Manager but in direct contact with the Land Development and Irrigation Engineer and Water Management Engineer of the Enterprise. His duties will include:-
1.       Advising Irrigation Supervisors, group leaders and Irrigators on proper methods of furrow irrigation to ensure even application depths and minimise rejection and run-off.
2.        Advising Irrigation Supervisors and group leaders on reading graphs provided for water measuring structures.
3.        Ensuring group leaders are timing all irrigations to avoid over irrigation or under irrigation.
4.        Preparing maintenance schedules for canals and drains and ensuring proper maintenance is carried out during the closed season and where necessary during the cropping season. This will prevent overtopping or breaches due to silting and grass growth during the cropping season and fields becoming water logged due to lack of field drains.
5.        Ensuring secondary offtake gates are cleaned and lubricated once a month and tertiary offtake gates are not mishandled by irrigators.
6.        Maintaining a water budgeting method of scheduling for each field when introduced.
7.       Monitoring efficiency of distribution system and field application.8.          Requesting the Water Management Unit, Project Control Centre for water issues.
9.         Computing water issues through each offtake on a monthly basis for the cropping season.appendix f
TRANSPORT CONSIDERATIONS OF IMPORTED PIPESAPPENDIX F
TRAMSPORT CONSIDERATIONS OF IMPORTED PVC DRAINAGE PIPES
The study of the alternative means of providing drainage pipes indicates the preferred solution, on cost grounds, is the manufacture of PVC pipes on site. Should it be decided, for reasons other than cost, that the drainage pipes were
to be imported into Ethiopia rather chan manufactured locally then their transport tram AssaD to Amibara would be required.
For the Stage I area the total requirement Eor pipe drams is approximately
1020 km of 60 oei diameter PVC laterals and 141 km of PVC coLLector drains, ranging from 150 am to 300 san di-tmeter,
Laterals would normally be shipped in 'Jumbo* coils, each containing 3 km of 60 rxn (id) pipe and occupying approximately 10 volume per coil, with a total
of sone 340 coils being required. Allowing a minimum carriage of 6 coils per truck and trailer combination a total of 57 truck journeys would be required-
The 150 na and 225 nm (id) collector pipes are shipped in coils of lengths
360 metres and LOO metres respectively* The 300 mm (id) collector pipes can be shipped in nominal 10 metre lengths to suit the long base trucks Ln use in Ethiopia. With an imposed height restriction of 3 metres D on the truck bed some 40 pipes could be carried, that is, 400 metres per load. The required lengths of each size of collector, together with the cor respondsing number of vehicle journeys is tabulated below:
Collector Diameter m
150
Required Length km
43’
Number of Journeys
20
225
65
ioa
300
33
33
TOTALS
141
211
1) Total height not to exceed 4.2   under proposed regulation (update of Legal
m
Notice 7261 (1962)The      Cotai      number      of      vehicle      journeys      would      thus      be      268      o£      which      185      number      would be truck/traiI er combination and 83 would be Long base trucks.
The proposed installation period for Stage I subsurface drainage is three years and a conservative allowance of delivery of pipes to site could be taken as, say, two years, ignoring storage considerations at Assab Port. With an assumed potential capacity of two trips per truck per week a minimum fleet of two trucks would be required continuously at an assumed 60Z operational factor. If necessary this fleet could be provided by the contractor within the contract such that no constraint on delivery is anticipated. However in practice such a low race of haulage would probably involve an unacceptably high storage requirement at Assab, with its associated high cost. It would accordingly be preferable to mobilise a larger transport fleet to ensure the rapid clearance from storage at the port. The preferred transport fleet size would be a
function of the number oE ship deliveries and the acceptable storage time for each delivery. If, for example, four deliveries were made, with clearance from the port storage being achieved in I month for each delivery, a fleet of 12 vehicles wouLd be required, with a 601 operational factor.
In conclusion it is considered that no delay to construction would be incurred, under normal circumstances, in transporting the subsurface drainage pipes from Assab to site as transport requirements to avoid such delay are minimal and could if necessary be provided under the contract. However a constraint on shipping through Assab is Likely to be imposed by the need to reduce storage requirements at the port itself, necessitating the mobilisation of a large transport fleet, possibly in the order of 12 vehicles.APPENDIX G
SURVEYING EQUIPMENT FOR IMPLEMENTATION SUPEV1SIONAPPENDIX G
SURVEYING EQUIPMENT FOR IMPLEMENTATION SUPERVISION
Description
Electronic Calculating Machines with print out (raains/batlery operated)
No Req u i
Naina charger/adaptor for Quickset Levels + tripod Precise Levels + tripod 
above
3
3
J
1
Tacheoraetric theodolite reading directly to twenty seconds nf angle + tripod
Ditto reading to one second of anlge
5 metre levelling staff
Calibrated steel bands 100 tn long + detachable handles roller grip and spring balance
Abney Level ar inclinometer Prismatic compasses
Steel tape ( 3Q m Long) Linin/fibreglass tape (30 m long) 3tn steel, tape (pocket type) Survey umbrellas
Tape Repair Kit Spirit level (I metre) Planimeter
2
[
4
3 
1■
■
H
U
a
■
Rappendix h
SPECIFICATION OF ADDITIONAL, HOUSING FOR PCCAPPENDIX H
i
3
2
SPECIFICATION OF ADDITIONAL SOUSING FOR PCC
HOUSE TYPE B
1.       Consist! of a black of 2 semi-detached single storey units. Approximate
2
floor area of 120 m2, including a verandah. (60 m  per individual unit).
2.        Two bedrooms per unit of approximately 12 tn  floor area each. Each bedroom to be provided with 2 single 13a electric wall switch socket and a ceiling tight controlled by 2-way switch near door. Approximately 2 m  fitted cupboard space per bedroom to be installed.
3.        One kitchen per unit of approximately ti n  fluor area. It shall bo 
provided with single drainer stainless steel sink with hoc and cold water and waste plumbing. Space is to be made available for an electric cooker and electric refrigerator within the kitchen. Approximately 1 fitted cupboard space co be installed within the kitchen. 2 double 13A electric wall switch sockets and a ceiling light controlled by 2-way switch near door.
4.        Living area per unit of approximately 16 in* floor area. IL shall be provided with 2 ceiling lights controlled by switcch near door and 2 double 13A electric wall switched socket outlets, and one ceiling fan.
5.       One toilet/shower room per unit of approximately 5 floor area. It shall
be fitted with modern wc and low-level cistern, a shower tray and shower fitments, hand wash basin and co have all pipework for hoc, cold and waste water plumbed in. Ceiling light controlled by pull switch near door. Mirror with a viewpoint light and shaver socket. Window to be glazed in obscure gLass. 6
6.        One main entrance per unit with approximately 4 m2 £lO0r area for verandah. 
One rear entrance per unit.7.        One block of 4 individual service quarters to be shared by two Type B houses. Each individual service quarters to have 10 approximate floor area and comprise a pit latrine and shower area, living room, one bedroom and open cooking area.
HOUSE TYPE D
1. 
Consists of a block of 4 semi-detached single storey units. Approximate
floor area of 96 m2 (24 m^ per unit).
2. 
One bedroom per unit of approximately 12 m          floor area, Bedroom to be
1 2 3 4 5
provided with 2 single 13a electric wall switch socket outlets and a
ceiling light controlled by 2-way switch near door.
3. 
One living room per unit of approximately 12 floor area. Living room to be provided with 2 single 13a electric wall switch socket outlets and a
ceiling light controlled by 2-way switch near door.
4. 
One main entrance per unit.
5. 
Provided in separate block per house one kitchen per unit with shower and pic latrines shared communal per house. Shower to have all pipework for
cold and waste water plumbed in.APPENDIX I
PRODUCTION OF PVC PIPES ON SITEAPPENDIX I
PRODUCTION OF PVC PIPES ON SITE
in the course of prepari ng the cost estimate for th.*! ins t a 1I at ion of drainage
pipes in the proposed Stage I of the Drainage Project it quickly became apparent
that the cost of importing the corrugated PVC drainage pipes from Western Europe would be very high. This was almost entirely due to the cost ot transport and 
the bigger the pipe diameter the more rapidly did the cost rise.
It was consequently decided to Look into the possibility of making the pipes on 
site usmg machinery designed for the purpose and using imported raw materials. 
The Consultant contacted a Eirm named OLtmann at West Germany, who were known to market the machinery and knowhow, and budget prices were obtained. An exercise
was carried out and this showed an appreciable saving in costs, something which has later been confirmed by Oltmann.
Ta      make      the      four      sizes      of      corrugated      pipes      required      for Che following special equipment would be required. The
0 Itmanns factory in Germany.
Stage      1      of      the      project prices are ex-works
Casing head 
ri
ii
Extruder die
II           M
II
«l
II           II Corrugator
ii
Mould chain ir           ii
l«                   14
II          II Perforator
ii
Perforating tool
So A 150 :nm
225  &  300  inm 6G nnu
1 50 rum
225 m
300 mm
50 4 150 in
225   4   30u   Un ‘60 m
150 inn
225 mn
300 uiei
SO & 150 uni 225 & 300 an 60 Tim
DM           7,153
141,200
16,427
21,102 79,416 38,100
183,566
253,209
104.505
136,952
248,316 275.654
88,166 91.069
9,746Perforating cool Cutting device Working table
150 mm
225 & 300 mm
225 6 300 mm
13,318 124,112
8,230
DM 1,890,241
In addition, certain items of general equipment would be required which could be used for the production of other pipe sizes and types. These items and their prices, ex-works West Germany, are:-
1.        Extruder
2.         PVC conveying plant
3.         Refrigeration unit
4.         Diesel generator and fuel tank
5.         Compressor
6.         Control Panel
7.         Tool cupboard and tools
8.         Pipes and fittings
DM 401,724 28,430 61,015 74,011
6,422 53,270
1,979 4,870
TOTAL                          DM 631,721
In response to a later enquiry from WRDA the Consultant made enquiries, this time with two firms, Oltmann of West Germany and Wavin of Holland, to see whether the machinery purchased for the production of corrugated PVC pipes could be used for producing smooth walled pipes for water supply. The information we obtained and passed to the plant manufacturers concerning the likely requirement of smooth PVC pipes for local water supply in rural areas was as follows:-
Total      annual       requirement Split       into:-
-
1000 km
50 mm dia
75 mm dia
100 nxn dia
150 mm dia
-
-
-
-
402
402
102
102
The      two      smaller      sizes      would      be      to      6      bar      normal      working      pressure;      the      two      larger sizes to 10 bar.Bath     firiu     said     that     certain     additional     items     of     equipment     would     be     needed, these being:-
1.        Casing head
2,        Extrusion dies diameter 50, 75, 100 & 150 non
1.      Vacuum calibrator
4,       Calibrator cases (all diameters)
5*      Discharging chain
6,        Cutting device
7,       Marking appratus
8,        Length control instrument
9,        Socket machine (sleeve sockets)
10,     Cooling unit
For this Oltaann have given an indicative lump sum price ex—works of DM 722,234 At an exchange rate of DM 3.90 ■ El, this is equivalent to El98 000. The Dutch 
a
company's indicative price, which is less detailed, amounts co about £148,000 ax-works.
Production costs have not been assessed at this stage nor do we know what the material consumption would be in the manufacture of smooth walled pipes, but it would be considerably greater than for the corrugated pipes owing to the need for greater thickness to withstand pressure.
The     projected     demand     for with production capacity
both     corrugated     and     smooth     walled     pipes     could     be     met, in hand, with the type of plant investigated.
The Consultant remains of the opinion that the cost of making PVC corrugated pipes on site provides for coat savings over the importation of pipes from Western Europe even allowing for the building to house rhe plant and store finished pipes and for operation and spares. This view relates to the area reconnended for drainage in Stage I* if further stages are subsequently drained, the unit costs will fal^. and future cost savings would be even greaterThe Consultant re cosine nds that before a decision is finally taken on the
purchase of such machinery and equipment more detailed discussions are held with both the manufacturers, including if necessary visits to the respective
factories in Holland and Germany, and that more detailed quotations are sought from each company. This work is outside rhe scope of the present study and design work and as stated in WRDA's telex of 10 July 1985, the Consultant is not expected to da any further work an the matter.0
g
I
i
i*TABLE 1          ADDITIONAL OPERATION AND MAINTENANCE PLANT FOR THE PROJECT CONTROL CENTRE
Project Year
Plant 3 4  5  8
7'
SnalL Hydraulic Excavator, Wheeled                                             1
I111
Tipper Trucks 1 3 3 3 3
SWA, 4x4 Vehicles                                                                         2                  2               2               2               2
Hydraulic Excavator (14 m reach)
Pipe Jectitig Unit
(Tractor, Pimp, Bowser) Miscellaneous Small Tools
-
I
1111
2 3 4 4 1
As      required
1) Only two jetting units replaced, operators reduce to 8 at year 9 and 7 at year 10TABLE 2     ADDITIONAL OPERATION AND MAINTENANCE PERSONNEL FOR THE PROJECT CONTROL CENTRE
PERSONNEL
PROJECT YEAR 34567
HOUSING ALLOCATION
TYPE
Assistant Engineer
Subsurface Drainage Supervisor Field Technician
Field Clerks
Machine Operators
Drivers/Light Plant Operators Gang Chiefs
Labour
. Mechanics
0.5 1 1 1 1
0.5 1 1 1 1
11111
I2222
12222
25677
12222
5 10 10 10 10
12222
IB
IB
ID
2D
2D
-
-
-
2DTABLE 3 - COSTS OF ADDITIONAL HOUSING FOR PROJECT CONTROL CENTRE (OPERATION & MAINTENANCE STAFF)
I ITEM I
DESCRIPTION
I UNIT I QUANTITY I
T
RATE  I  AMOUNT BIRR I BIRR
1 Housing
I
1 Type B house
I Service quarter for ditto
I Type D house
i Service quarters for ditto
I External services 3 40Z
Bill 1, General Items (3 35Z
I Contingency 3 LSI
I Furnishings
I
I Type B I Type D
I II
i Block : Block! I Block!
124.000
151,000
115,000
124,000 75,500
201,250
1 1.75
Contingency @ 15Z
Housing and Furnishings
I Note: Unit costs based on AL? II Contract Prices with allowance for inflation
Block Block!
|
I I 1
----- r I
i
[
i i
i Subtotal T
I TOTAL I Say
I
i
i
)
i
i
I
I
ITABLE 4 PLANT AND EQUIPMENT COST SUMMARY
All prices refer Co equipment delivered to site (excluding spares)
1
I       No 1
1
1 
| 
1
1
1 
1
Description
1 UNIT PRICE                 I BIRR            |
TOTAL BIRR
1 
1
1 1 1 1 1
1
I CONSTRUCTION PLANT 1
1
I 275 HP Trenching Machine
1 1                1 350 HP Trenching Machine
1 1 I Set of Laser Equipment for Trenching
1 1
1 1
1 1
1 1
I             270,000 324,000 
1 1
1                   ■ Machines                                                                                            1               72,000 
|
|
1 3                I Front End Loaders
1 2 I Sets of Mobile Crushing and Screening
1 68,000 | 1 1
1
I Plant                                                                                                     1 
78,000 
1 1 I Conveyor at Screening Site 1  27,000 
1 2 Self-Propelled Gravel Trailers 1  104,000 
1 1                   Tractor with Backfilling Screw Auger
49,000 
|
|
|
I
1 1 1 1 1 1 1 1 1
1 PVC Pipe Manufacturing Plant                                                          1                                       1
1 (including Commissioning * Training)
1
1
I OPERATION AND MAINTENANCE PLANT
2,449,000 
| 1
270,000
324,000
72,000
204,000
156,000
27,000
208,000
49,000
2,449,000
1 1 1 1 1
1
1
Hydraulic Excavator                                                                          1            170,000
1 1 I Small Wheeled Hydraulic Excavator 1  85,000 
1 3 1 Tipper Trucks 1  70,000 
1 2                 1 Short Wheel Based Landrovers 1 4                 I Sets of Jetting Equipment
1 1                    Concrete Mixer
1               24,000 1 120,000 |
1 20,000 1 10,000 1 
|
|
|
1 1 1
I Set of Miscellaneous Tools 1
170,000
85,000
210,000
48,000
480,000
20,000
10,000
ITAHLF 5 SELECTED 1*11 RATES
DESCRIPTION
1
1 1*11
1
I
11
1 ITEM 1
11
|
I
II           1
1
11
121
MATERIALS I PLANT ANO | AND SERVICES 1 TRANSPORT I
skilled
LABOUR
1--------
1     total I         COST
IfOREI® 1
1 EXPUNGE I
------- !
IXSAHLEO I I. AMUR l
!
1 1         BIW
j_______
BIRR 1 BIRR |
1
|         HIRR
1-------------------
'«1 ------- 1
-------------- r
Excavate for structures
Excavate for drains and place in embankments
1
i
(□  □)2)
1 9.4 1 0.6
1 (6.0) | (0)
0.B
(0)
11.9 |
(6.6) 1
1
8.9
(1.8p>
1
1
U
(0)
0
(0)
1          3.1 I 1          (1.98)1 11
0.1
(0)
0.13
(0)
25
(0)
0.05                     3.6       1            2.7
11
|
|
! ■’
1
(0)
(2.0) 1
1
(0.54)
11
1 3 I Cunpact Fill in ere bank nen tn
11
11
Reinforced Concrete
1‘1
1
11
1   5      1 Reinforcement Steel
11
11
Masonry
85
(51)
1.4
(0.8)
(0.4)
16 1
11
11
17    1 11
Reinforced Concrete Pipe - «IU m
•*
1
1
1
1
1
1 Kg
1
1.
1
1
1
1
1•
1
11•
•
1
1
1•
1
1
0.06                     2.5       1            1.9
(0)
(1.43) 1
1
17                   284
(0)
0.2
(0)
(148.3) 1
1
(0.4)
212.9
(42.6)
1
2.9 | 2.2
(1.1) 1
1
26
(15.6)
36
(21.6)
2.08 1
1        (1.3) 1
1     131
1     (83.B) 1
J
0., 1
1 <B-” 1
1»1
1  1 (34.6) 1
11 I 169 1
1 (121.0) 1
0.7
(0)
55
(0)
165           1         123.8
(0)
(55.2) 1
1
(24.8)
10
(0)
1
284           1         212.9 (156.9) |           (42.6)
I     2B2           1 1 (180.5) 1
11
23
(0)
>5
(0)
16                  426           1         319.3
(0)
(234.2) 1
1
(63.9)
(199.5)
826 (29B.1 )
1    B    1  Supply    end    install    60    mm    id    PVC    field    laterals
1 11 11
- 1500
54
(32.4)
and
0.7
(□.7)
2.1
(2.0)
| 3.3 1
1 (2.9)
0.1
(0) 1
0.1
(0)
4.6        1            3.5
surromda
(4.0) 1
1
(0.7)
1
||
11
19 1
11
Supply and install PVC collector pipes
- 150     an           1 -
1
1       6.5 1
| (6.1) 1
0.1                     10.8 1                   8.1
(0)
0.2
(0)
(9.8) 1
1
l
(1.62)
(11 .A)
1i
11
11
- 225 mm
1
1 n>
1
4.3
(4.2)
I 10.4 1
I (9.9) 1
0.2
(0)
0.3
(0)
19.6       |           14.7
(18.0) 1
1
(2.9)
- WO an 1 a
1
9.4
(9.3)
| 19.8 1
(18.8) 1
0.5
(0)
0.3                     33.0       1           24.8
(0)
(30.9) 1             (5.0)
64.1
(35.9)
11
_________
Includes IOS allowance Tor ■Inor items
Foreign exchange component given in brackets
Forel<F exchange component assies local contractorLTABLE 6 - MELXA SADI STAGE I Bills of Quantities - Project Year 2
i        r-
[
1 ITEM | 
II
DESCRIPTION
“ T“------------------ RATE |  AMOUNT BIRR I BIRR
r~------------------------—-------------------------
I DEE? OPEN DRAINS
I Earthworks
II
11. I Exc-ivate deep open drain
I
I 2.          | EO [tern for haulage up to 1 km
| UNIT I  QUANTITY I
I        I_______ I
1       !"            T
II II
m3 | 1
I
I
I
I
I
188      600 | 1
i
7 .0              1 1 320   200
m3 |         12
20D I        3      .96 I
48   300
II                                                                                 1
Structures
I
1 
i
3.         | Replace cuLverts                                                                                       1
I
I        | In MSAE area Na 8/2 la    SD2    area In    MD2   ar ea
1 No 1 
1
I
1
1
1
1
1
1
1
1t
l 1i 1 1
57      252 ;
•1
57    252
I 4.         | Lower existing
No 2/1
No 1/1
No 1/2
Na 1/3
drainage outfalls
No 1           1            1
i! No
1
j
1
1
110   889               no  889
1
1
1
1
110   889
i 1
no  889
No [
1
1
1
1
1
141 711 I
1
141   711
No |          1 K
No |         17
141
711 1
141
711
5
|
671 |
96
407
| TOTAL FOR YEAR
027     355TABLE 7 - MELKA SADI STAGE I Bills of Quantities - Project Year 3
1           'l 1 ITEM 11
i1
DESCRIPTION
■ 1 1 ] UNIT I
1 1
1 1 1
1
QUANTITY I
1
1
RATE    I BIRR 1
1
AMOUNT I
BIRR            I
1           1 SUBSURFACE DRAINS
I1
1 I- I Lay 60 wi ID slotted corrugated 1 1 field lateral pipe including red-
1
1
1
[
“I
1 1
1 1                      1 ash !                   1                    1
1
I
1 1
1 2. i
i ftnveLope i
i
!           711      1
225 970
1
|
1 1 1
■ 9.0 I
L I
2 033 730
1
1
Lay collector pipe 150 mm (ID)
1 m 1               10 250
21.0 1
215 250 1
i
225 nun (ID) 300 mm CtD}
18 100 I         38.0        1           687 800
1            1 
i1
1
1  m | 1  m 1 1
7 950 1 1
1
64.1        |        509 59 5 I
1 3.       « Manholes
1
i
1 1
No
178 597
I
1
1
1
14 5              1 1
1
1231,7          | l
1
,1
1
1 1 4.
i
1 ( 6. i1 1
i
1
1 DEEP OPEN DRAINS
| Earthworks
|1
Excavate deep open drain
1
I,
I EO Ltem 4 for haulage up to 2 km
i
1
1 ;            1                        1                         1
1
1
1
1
■
L
I m3  1      59 boo I 1
1
7.0 !
1
1 m3 |
b
1
35 300 1 1
1
3.96
2.0
1      418 600
l
139 788
|    EO    item    4    for    haulage    2    to    5    km 1
I
' STRUCTURES 1
1
| m3 1
1
1       19 600 1 1
1
11
1 7. i1
1 i1 1 i1 1 [
1 Replace culverts                                                                           1
i
i               No a/i 1
No 9/1 1
i               No 9/2 1
J
1
I1
i1
1 
111 1 1 11
1 11 1 1
1
1
1         39 200
1
1 1
No
1
1
i1 1
11
40 865
No
1 1
1 No
1 1 1
1
I1
;   57   252 1
1
1 57 252 1
40 865 i
1
1        57 252 i
1
11
]          57 252
1
J
1              No 9/3 1
i
1 Ko 1
1
1
1
1
1 57 252           1         57 252
1 s. 1
i
1         Lower         existing         drainage         outfalls I
1
1 SURFACE DRAINAGE
No
1
1
1            5 1
1 1
i
5 671 1
1
1
1
1         28 355 1
1
1 1
1 1 9.
1
1
1
1 Earthworks                                                                                  1            1
1
1
1
1
i
1
1
1
Excavate for tertiary drain 
I
|
1 m3   1      30 300        1         7.0
I
1
i
1 212 100
1 10,
| Excavate for field drain
l
|
i1
1     40 400
7.0
282 800
1
11
1
1
1
1
1 11.
| EO tttsn 9 & 10 for haulage up to
2 krri
rn^
1     63 600
I
1 
3.96      1 
251 856
11
Il
ii
1
1 22-     I EO item 9 4 10 for haulage 2 to
5 km |           n>3 1     35 400
2,0
70 BOOTABLE 7 - MELKA SADI STAGE I Bills of Quantities - Project Tear 3
ITEM
DESCRIPTION
CM LT |
QUANTITY 1
RATE ■
1
11
1       BIBB
AMOUNT
BIEK
IJ ,
ST&UCTUKES Tertiary drain culvert
i
n i
i 1 Na 1
1 1
1 1
1J
1
1
1
1
14,         Drainage culvert with □utfall into deep drain
11
15.      1 Field c□1vert r
1
1
I? 130          ]            Z23 444 1 1
1      No 1 1
No 1 1
1           1
1           1
[    No    1 
1           1| I
I1
5             |’12 359 1
119 Z95
*0 1
1 1 
I
11 1
1
1 1 1
1
68              I i|
1 1             I
*
6 39 3        1 11
i
255 720
16.
17 .
18.
19.
20.
i MudiCteations to secondary offtakes i tor measurement purposes
r
I
■ Main drain flume
11
. Field canal gauges
1
1 Portable flume for field canal 1 discharge measurement
1
1 Tertiary canal flume
1 6 862 | 
I 11
ao ooo |
?
1 1 1
1 No 1
1  1
1  1
1
1   Ti*   1 
2D0 2 000
| 
1 |1 1 No I
i
1
I
1
1 1   20 000
4ft 034 40 000 13 600
1 - ’
1 2 000 1 20 000
TOTAL FOft YEA ft 3TABLE B - MELKA SADI STAGE I Bills □£ Quantities - Project Year 4
1
! ITEM I
[
i
DESCRIPTION
n--------- i 1 UNIT I 11
“T
QUANTITY I
RATE
1
1 AMOUNT
11
1
1 1
11.
1      BIRR       1    BIRR
T l
11
I SUBSURFACE DRAINAGE
1
, Lay 60 mm ID slotted corrugated
1 
I
1
1
I1
11
f"
l
1
1
1              1 field lateral pipe including red-                                                    1
11               1
1
ash envelope
I U1
1 
319 931 !
9-0
11
11
2 879 379
ii
1I
1
1
1 2.
| Lay collector pipe 150 mm (ID)
1 
rn
l1
I
1 
13 250 1
21,0
If
L1
1      278 250
i
1
1
1 
225 mm (ID)
1 
m
20 300 !
i1
1
1
| 1 
i1
38.0
i
1
771 400
1 1 3.
JOO zm (ID)
I
1 Manholes
f     to 1
I
1 No
1 
9 650 1 1
1 
1
64. L      1      681 565 1
1               173 1       1231.7
231 084
TOTAL FOR YEAH 4TABLE 9 - AHIBARA STAGE 1
Bills of Quantities - Project Year 4
ITEM
1
1
1
DESCRIPTION
| LTN IT I QUANTITY i
---- r------- “i
SATE I AMOUNT I BLRR I BIRR___________ I
1.
DEEP OPEN DRAINS
Earthworks
I1
1 Excavate deep open drain
al |       222   600 i|
7 .0 I
1
1 558     200
2.         1    £0    item    4    Ear    hauLage    up    to    2    km 1
a 3 |
1
i
178    loo
3      .96 1          705     276
3<
l 1 1 1 1
EO item 4 for haulage 2 to 5 kra                                                                                                   2         .0 |
66   aoo
133    600
Structures
|
1
1
1
1
1
4.         I Construct new cross drainage culvert                                                                                                         1
i   including road crossing
1
I
11
1  No 7/2
1
1
1  No 7/7 i 7/8
5, I Construct new cross drainage culvert
1  !lu 7/1                                                                                                                                          52      047 I
1
1
1
No | 
11
I
No | 
11
1
Ho I
2
52 047 101 44 9 287 626
1
1
<
1
No
1
j
101 449 [
ji
143 813 |
1 1 1 1
1
I No 7/6                                                                                                                                        143
143    813
1
1
313 1 1
6- Construct new bridge over main drain I No 7/3
I
| No 7/4
I
I Nq 7/5
No 7/9 f. 7/10
1
No | 
Ii
1
Ho I
1
1
1
No | 
1
1i
I
No | 
l
1
2
i
1
59 628 |
11
56 642 1 
1
79      306 I [
32       649 [ i
J
58   628
56   642
79   806
165 298
No |
7. I Lover existing culverts No 5/1 82 649 | 82 649
. I
1
I
I
I j I I
I
TOTAL FUR YEAR 4
I
I 3 425 034TABLE 10- AMIBARA STAGE I
Bills of Quantities - Project Year 5
1
1. ITEM
DESCRIPTION
UNIT 1
1
QUANTITY 1
1 RATE i
1
1         BIRR
AMOUNT
BIRR
i-----------
1 SUBSURFACE DRAINAGE 1
1
1
“T
1 I 1.
1
Lay 60 mm ID slotted corrugated
1
1
i
i
i
1               field lateral pipe including red-ash |                                                            1                          1
1
1
1
1
i
1
1
1 1 2, i
1
1
1
1
1
•
1 3. 1
I
1
I
1
1 1 4, i
1
envelope                                                                                       1 1 '
ra | 1
i
296 799.71 1
1
9,0 1 1
i
2 671 197 1 1
i
I Lay collector pipe 150 mm (ID) L
1 
1 1 1
225 mm (ID)                            1 300 mta ClDi
m | I
l
12 175          1 1
1
21.0 I
I
255 675 I
mI
11
16 389          1 i
m |      10 111 1
i
38.0 1 1
1
64. 1 I 1
1
622 592
648 115
1
1 Manholes                                                                                       1
I
J
| DEEP OPEN DRAINS
! Earthworks 1
No            155            1 l
1 I 1
1 1
1231*7         1             190 914
| Excavate deep open drain 
|1
I EO item 4 for haulage up to 2 km |
I
m3
i
29 000          | 1 l1
1 5. I
1 6. 1
I
1   23 200          1
1
7*0
3.96
203 000 91 872
I EO item 4 tor haulage 2 to 5 km 1
i
m3 1
I
1      m-3 1
1
1 I
1
1
1
i
1 7.
1 STRUCTURES 1
1
1 1 1 11 1 1 1 1
I Construct new cross drainage culvert                                            1
1
1
1
1
1
1 1
1 8, I
including road crossing
i
i
1 No 4/3
1
. Lower existing drainage outfall I
1
1
4
•
1 1 1
1 No   1 1 11
160 089
1
1
1
|        No 1
1
1 11 1
1
5 67 1
160 089
62 381
1 9.        | Construct new bridge on main drain 
i 1
1
1
1
I
1 1
1 No 1 1
k
1 No 4/2/1 |
-
| 10. I1
1 1
Lower existing culverts <
1 No 4/1 & 4/2 1
k
1
■
1
I
I
1
1
1
1
t
40 865 1  40 865
1
1
1            1 SURFACE DRAINAGE
I No I
I
1
. 1
1
1
2 
57 252
1
1 111.
[1
1 Earthworks
i
I
I Excavate for tertiary drain
1I
1
1 m3   1      72 DOO 1
I
l1
|  114 504
|. 1
|
1
1
7,0
I 12.          Excavate for field drain
1
I 13. | EO item 9 4 10 for haulage up to
1
1 m3
.     127 000
11
I1
7,0
1
1
1       504 00Q
1
1   889 000 i
1
1
[
| 2 km
1
11
1
l
1 m3   1    179 100        1     3.96
I
1
1
1 14.         E0 item 9 & IQ tor haulage 2 to 5 km
1 1:13 km  1 59 700
2*0
709 236 1
I
1   119 400TABLE 10- AMI BARA STAGE I
Billa af Quantities - Project Year 5
ir
I ITEM | 
II r-------T-
1
DESCRIPTION
I UNIT I       QUANTITY       I RRAATTEE I AMOUNT I
I
i              1l
1----------■------------------- 1------------ T---------------1
I|
I     BIRR 1       BIRR I
i
i
I
;
15
I
I .16.
I
I
I
I
STRUCTURES Tertiary drain culvert
II
II
1,1 Na |
1
16
I
1
17 138  1 27 5 008 i
I
I
I
I
I
I
Drainage culvert with outfall into 1 deep drain
15                 6
1
1
393 1 1          95   895 l
I
I
I
I
Cross drainage culvert
Modificati.ua         to         tertiary 
3
6
41 6
950 1 1
1
862 | 1
1
125   850
I 19.
I
I 20. I
o£ t'takes
1 No | 
||
1
No 1 No | 
i 1
Na 1 1 1
1
1
1
1
21 1   22   859       1
480   039
i
1
17.          Field culvert
18.
I Field canal gauges
I
No |             7
200
41  172 I    400
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I I I I I ! I I I I I 1 I
I
I
I
I
I
I
I
I
i
1
I
I
1
I
I
I
)
I
I
I
I
I
I
I
I
I
I
302 204 I
1
I
I
I
I
I
TOTAL FOR YEAR 5
I
ITABLE 11- AMIBARA STAGE I
Bills of Quantities - Project Year 6
i
r
”1         i             1
1
: ITEM 1
1i
DESCRIPTION
1 UNIT 1 QUANTITY 1 RATE I
1 1 1     BIRR 1
1
AMOUNT I BIRR
I
SUBSURFACE DRALNAGE
I
1.
I
I Lay  60  mm ID slotted  corrugated 
I
I
I
I
I
I
I
I
field lateral envelope
Lay collector
pipe
pipe
including red-ash 1                                         1               1
1          rtl | 
179 900 |           9           *1  1  619    100
i
2.
150 ram (ID) 225 mm (ID) 300 cxm ( ID)
1 1 
m | 1
1
1 I
7 525 1 i
1
21.0
I
I
m 1 II
10 016 |          38.0
1
1
I 158   025 i
1
1       380     608 I
1 
I
1
5 089
i1
3.
I
im 1
i
i
60.1 1  326 20 5
1
I
Manholes
I
1
No |
90 I1 1231.9
110   853
TOTAL FOR YEAR 6
.2
I
594
1TAHLE 12 - ***<UAL RECURRENT C0SI5
ANNUAL COST (N BIRK ‘00(1 1 2
__________ |
I
I
1
1 HCM
1
PROJECT YEAR | ] 2 J 4 5 6 7 8 9 ID 11 12 13 14 15 16 17 18 19 20 21 22 23 24
1- 1
1
I
1           | FOREIGN IlMSKIllEDI
25 | TOTAL | EXCHANGE 1 LABOUR I
I 5!1
1             11
1
1
I (a) Subsurfa
ce A deep open drains
|
1
11
1
1
1
1
1
1
1
Plant: Capital A reploceawnt coats | -
-
3J3
410    1211    120
-
213
310
120    12C     -
213      310     120     120
-
213     310     120     120
- I 3292
1
97
1
01
I
1
|
|
|
1
Plant: Annual Operating costa
|-
-
111
254     294     534
334
334     294
254
254    as year 11
1 6019
1 60
|
01
11
|
||
1
Staff, Operators and Labour
I-
-
71
133     144     155
155
155     144
in
133    as year 11
I M85
101
10 1
|
||
1
1
1
Materials )
|1
I- 1
|
11
1
|-
--
211      W       40     as year 6
1 B5Q     1 88 1                         0 1
11
i
1 b) In-field and uhalluw aurface ar a inn 
1
1
1
1
1
1
11
11
11
1
1
1
1
1
1
|
11
Annual recurrent roots^)
-         20       40       75       93     as year 6
1 1995     1        M         I           5          1
1
1
1
1
1
1
•
1
1
1
11
1
1 (c)
Additional Housing Tor PCC*)
1-
20       20       20       20     ns year 6
I 460
1        33
|
3.5
1
1 ____________________________________ 1___                                                                                                                                                                                          1                      1 1                                          1
1
|
1
1
11
1
COMBINED TOTALS
_
I (J ____ L
0       555     09/     683     762     642 M2           904       850     660    660    540     540     753     850     660     66U    540    540    753    850     s60     660
5AQ | 15701 |          54        |
11
1
1
31
J
1) 0.5% of imported materials cost for aub-aurTscr pipes and 2.0% of imported materials for • tructureg
2)          2.5% of earthworks and 1.0% of structures
J) 1.5% of capital cost1J - a!58i*”7*M SDCtilJ. rm FWCIKIR[*C CWT l5Tn*res
lire ;«
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11    .-3
Iiarwr^ M tota. com ..clxirq k^r.Liiar contlng^r . |n r.«r J,
mi » lt t«ual «u-Ls ,.
3
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4 I'eiL-lMH
2) .r xin-.rs Lira* Ccriractac. re *m!h r-irup Contract*TABLE 14 - MASTER ORAINAtt PLAN COST ESTIMATE
11
1 CONSTRICTION PER 100 1
•1
1985 -
1990
1
|
------------------ L
1990 - 1995 1995
___
- 20U0
1
1 LOCATION
1
1
1 block
1___
1
L—L
I
TCLKA SADI |
I
AM IBARA |
1
c1
1
1
»€LKA SADI 1
1
1
1
AM I BAR A
1
| AMI BAR A
1
1
i
EXT I AM IBAHA
L
1
1
i
1
AI
1
|
L
1
L
B10
1
F                   1
L
E1
1
1
1
1
1
AM IB AR A EXT |
1
1
C1
1
11
1
’L
I
1
1
<T AREA (Ha)
1
2650
1
1
1
2091)
|
1
1550
1
1
1
3050
950
2340
1
I
L
15 70
1
1
I
I
I
1
1
1
1
1
1
1
1
.L
1
1
1
1
Qty 1
Coat
|
Qty |
C
oot I
Qty 1
Coat
1
Qty 1
Coot
Qty 1
Coot
1
Qty |
Ccet
1
Qty 1
Cost
|
COMPONENT
1
1 Birr x
10*1
Birr x
10*1
iBirr x 10
*|
1 Birr
a 10*1
I Birr x
10* I
1 Birr x 10*
1
1 Birr
x 10*|
L
11
1
1
1
1
1
11
1
1
11
1
I
1
1
1
I
1
1
1
I
1
i
1
I
1
|
1
1
1
1
1
1 SUB-SURFACE DRAINAGE
1
|
I
1
1
1
|
1
i
I
1
1
1
1
1
3371
1
1
1
1
1
1
1
1
1
1 F in Id laterals
(km)
546 |
A,913
|
477 I
4,290
|
3,033
I
650 I
5,850 I
3)2 |
1,
818 |
499 |
4.491
|
>35 1
3
,015 I
1 Collector drama
(km)
1
BO |
3,
472 I
61 1
2,695
1
37|
1.572
1
92 1
3,858 I
29 1
1.307
1
70 I
2,972
1
47|
1,990
|
| Deep open drains
I ModlFy existing culverts
I Modify existing fra in outfalls
I Build drainage culverts
I Build road bridges
1 Oteervation Nells *•'
r
(■* x       IO*) |       248 |         1,966       |      252 1         2,692       1   112 1             784     |     1170 I          12,051 I           52 1             366      1          61
63 |            - 1                          1
(No)                1          91             775      |           31             197     |         41             430      |           21             163      1          - 1                        1
II                  111 1             - I                          1
(No)                1         22|
125      |         111                   62 1        23|             145     |         191               94      |           - 1                        1           41                23     |            - 1                          1
(No)                1          - 1                        1        12 1         1,147 I
- 1                        1           21             %A I                11              342     1          - 1                         1             - I
1
(No)                1          - 1                        1           - 1                        1         - 1                       1           - 1                        1           31              789     |           - 1                         1           - 1                          1
(No) 1 - 1 1 10 1 120 1 - 1
|
1
|
-1
|
-1
|
1
|
|
1 -1
1
1
1
I S UH FACE DRAINAGE                                                                                       1            1                         1             1                       1        1                        1             1                                        1                        1               1                       1              1                         1
1
| Tertiary and Field drains
I Build tertiary and Elaid drain
1 Build Pug) Station A/
| Modify canal offtakes for measurement *'
1
1
(ha) 1
1
1328 f
1
817 |
1
19 74 |
1
2,222 1
1
-1
1
1
1
1189 | 1,094
1
950 |
1
874 |
1
-1
1
1
1
1570 |
1
1.446 |
culverts
(No)
1        58 |             593      |        55 1             976      1        - 1.
1        42 1             623                 33|             498      |           - 1                        1          55|              824      |
(No)               1           - 1                        1           11               63      1        - 1                        1           - 1           -
-1                         1           -1                        1           -1                          1
(No) 1
|
71
i
124 | 6 1 43 1
|
Al
I
1
27 |
|
1
1
10 1
|
1
|
69
1
|
1
|
DI
|
I
89 |
|
I flood dykes 1
|
1
|
1
|
1
1
1
|1
-1
|
1
I
-1
1
1
«1
I
1
|
1
1
1
1
1
1 Eimsrgency Spillway Oykc
| AMieh Western Dyke
| Earn tern Dyke
I
(km)              1           - 1                         1           41              318     1        - 1                        1           - 1
I       -                                1           -1                         1
(km)              1           - 1                         1           - 1                        1          - 1                        1        17 1           3,DI                    21             451      |       -
-1
-1
(km)              1
I
-1
I
-1
1
.1
L
-1
L
Bl
II1
-
1
J|
1
1
1 total cost                     1
1
1
1 CUMULATIVE TOTAL
1
I
1
"1 L
1
1
1
12,785 |
|
1
12,785 |
1
1
.L
1
14,823 1
1
1
27,608 1
L
1
1
1
5,992 I
1
1
33,600 |
27,477
61,077
1
1
J
1
1
J
2,433 |
1
1
8,758
69,835
7,749
77,564
------------L
1
1
1
1
7,275 |
|
1
84 , 859 2/|
I
NOTES 1/ AB cost* are at 1984/85 prices without provision for constructs aiporvieion, nor m allowance for physical contingencics nor for inflation
2/ This grand total does not inclulo Birr 1.9 aillion to cover for the possible constriction of interceptor frame along the primary canal (See Section 2.2.2)
V      For elisting Ami boro Irrigation Project Areas only
V       Not included In Stage I development costs
5/ Moving coots for additional operation and maintenance staff »x)t included in above total" Ueaed nn an estimated coat of Birr l.J million for Stage 1 ^ly, the pro-rate eoet of housing for the entire development would te in tte order of Birr 4.1 "ll lOnRESERVED

< <

Summery

Summary: Master Drainage Plan for Melka Sadi and Amibara Areas

Master Drainage Plan for Melka Sadi and Amibara Areas - Final Report (July 1985)

1. Introduction

This engineering annex (Volume 7, Annex D) presents the Master Drainage Plan for the Melka Sadi and Amibara areas in Ethiopia. The study was conducted by the Water Resources Development Authority of Ethiopia in collaboration with consulting engineers Sir William Halcrow & Partners.

            Key Background Information:
            The study area comprises the right bank flood plains of the Middle Awash River
Existing problems include rising groundwater tables and inadequate drainage systems
The plan addresses both surface and subsurface drainage requirements
Implementation is proposed in stages, with Stage I covering 6,200 ha gross area

        

2. Current Irrigation Systems and Deficiencies

2.1 Existing Irrigation Practices

The area has both gravity-fed and pumped irrigation systems serving various state farms and research stations. Key observations include:

Water distribution is regulated through various structures including check drops, primary offtakes, and spillways
Furrow irrigation is the predominant method with typical furrow lengths of 200-250m
Measurement facilities are inadequate in many areas

2.2 Major Deficiencies

Deficiency	Impact	Recommended Improvement
Poor land leveling	Uneven water distribution, fields out of command	Land planing and leveling
Lack of control structures	Inefficient water distribution	Installation of gated offtake structures
Inadequate water measurement	Poor water management	Installation of measurement devices
Seepage losses (0.20 l/sec/1000m²)	Water wastage, rising water tables	Potential canal lining

3. Drainage Planning and Master Plan

3.1 Drainage Requirements

The study identified critical drainage needs:

Existing surface drainage is inadequate with ill-defined natural drainage lines
Subsurface drainage is virtually non-existent except for a small pilot area
Groundwater tables are rising at about 1m/year in affected areas
Projections indicate water tables will rise to within 1m of surface over 2,200ha in Melka Sadi and 1,600ha in Amibara by 1988

3.2 Master Drainage Plan Components

Buried field lateral drains at 1.8m depth with spacings from 30-110m
Buried collector drains conveying water to deep open drains
In-field and tertiary surface drains
Deepening and widening of existing secondary and main drains
New drainage outfall into the Awash River
Flood protection works including dyke realignment

Implementation Strategy:

The plan proposes a 15-year implementation period (1985-2000) with Stage I covering 6,200 ha (gross) requiring 4-5 years. The implementation schedule is designed to address the most critical areas first, particularly in Melka Sadi where conditions are deteriorating rapidly.

4. Key Design Elements

4.1 Drainage Network Design

The design includes:

Surface Drainage: Field drains, tertiary drains (400 l/sec capacity), and deep open secondary/main drains
Subsurface Drainage: 60mm corrugated PVC pipes for laterals with red ash envelopes; 150-300mm pipes for collectors
Structures: Culverts, bridges, outfalls, and manholes

4.2 Design Criteria

Parameter	Value
Subsurface drainage rate (bananas)	3.4 mm/day
Subsurface drainage rate (cotton)	2.5 mm/day
Tertiary drain capacity	400 l/sec
Minimum drain velocity	0.3 m/s (preferably 0.4 m/s for bilharzia control)

4.3 Flood Protection

The plan includes:

Western (Awash) flood dyke - 55km length requiring heightening in some sections
Eastern catchment dyke extension - 32km length designed for 1:10 year flood
Realignment of 4.2km of dyke at critical locations

5. Implementation and Costs

5.1 Construction Methods

The plan recommends:

Specialized trenching machines for pipe installation (estimated output: 52km/month/machine)
On-site production of PVC pipes (estimated cost: 2.72 Birr/m for 60mm pipe)
Contract-based implementation rather than direct labor

5.2 Cost Estimates

Component	Cost (Birr)
Stage I Development (1985-90)	28,407,000
Full Masterplan (1985-2000)	90,859,000
Unit cost (Stage I)	7,252/ha (US$ 3,502/ha)

5.3 Operation and Maintenance

Key requirements include:

Specialized drain jetting equipment for subsurface maintenance
Additional hydraulic excavators for open drain maintenance
Strengthening of the Project Control Centre organization
Estimated annual recurrent costs: 2.5% of capital cost for surface drains, 0.5% for pipes

6. Conclusions and Recommendations

            Key Recommendations:
            Immediate implementation of Stage I works in the most affected areas
Improvements to irrigation water management practices
Strengthening of organizational structures for water management
Contract-based implementation using specialized equipment
Comprehensive monitoring and maintenance program

        

The Master Drainage Plan presents a comprehensive solution to the drainage problems in the Melka Sadi and Amibara areas, addressing both immediate needs and long-term requirements through a phased implementation approach.