irrigation engineering

1. Overview
Ethiopia has a vast water resource potential.
Yet only 1 % of the estimated annual surface water of 110
billion cubic meters is used for irrigation and hydropower.
Though the country’s irrigation potential is estimated at 3-4
million ha, only small percentage of this is utilized.
CHAPTER 8. WATER SOURCES AND IRRIGATION POTENTIAL OF
ETHIOPIA

2. 8.1. Water sources of Ethiopia
⚫Ethiopia is endowed with a substantial amount of
water resources.
⚫The surface water resource potential is
impressive, but little developed.
⚫The country possesses twelve major river basins,
which form four major drainage systems:

3. Drainage systems
⚫ The Nile basin (including Abbay or Blue Nile, Baro-
Akobo, Setit-Tekeze/Atbara and Mereb) covers 33
percent of the country and drains the northern and
central parts westwards;
⚫ The Rift Valley (including Awash, Denakil, Omo-
Gibe and Central Lakes) covers 28 percent of the
country;
⚫ The Shebelli−Juba basin (including Wabi-Shebelle
and Genale-Dawa) covers 33 percent of the country
and drains the southeastern mountains towards
Somalia and the Indian Ocean;
⚫ The North-East Coast (including the Ogaden and
Gulf of Aden basins) covers 6 percent of the country.

4. Table 1 Ethiopia’s surface water resources by major river basins
(km3)
Major drainage system River Basin Area (km2) As % of the total
area
Annual Runoff
(km3/yr)
As % of total
runoff
Nile Basin 368,812 32.40 84.55 69.0
Abbay 199,812 17.60 52.6 42.90
Baro-Akobo 74,100 6.50 23.6 19.30
Setit-Tekeze/Atbara 89,000 7.80 7.63 6.20
Mereb 5,900 0.50 0.5 0.60
Rift Valley 317,640 27.90 29.02 23.70
Awash 112,700 9.90 4.6 3.70
Denakil 74,000 6.50 0.86 0.70
Omo-Gibe 78,200 6.90 17.96 14.70
Central Lake 52,740 4.60 5.60 4.60
Shebelli-Juba 371,264 32.70 8.95 7.30
Wabe Shebele 200,214 17.60 3.15 2.60
Genale-Dawa 171,050 15.10 5.80 4.70
North East Coast 79,300
Ogaden 77,100 6.80 0
Aysha 2,200 0.20 0
Total 1,137,016 100.0 122.52 100.0

5. Water source of Ethiopia
⚫ Most of the rivers in Ethiopia are seasonal and about
70 percent of the total runoff is obtained during the
period June-August.
⚫ Dry season flow originates from springs which provide
base-flows for small-scale irrigation.
⚫ The groundwater potential of the country is estimated
at about 2.6 billion cubic meters of water, but so far
only a small fraction of it has been developed and this
mainly for local water supply purposes.
⚫ Traditional wells are widely used by nomads.
⚫ Neither desalinization nor treatment of wastewater is
practiced in Ethiopia

6. Water source of Ethiopia
⚫ Intense rainfall sometimes causes flooding particularly
along the Awash river and in the lower Baro-Akobo
and Wabe-Shebelle river basins, causing damage to
standing crops and infrastructures.
⚫ Ethiopia has several lakes (an area of about 7000
km2), a number of saline and crater lakes as well as
several wetland areas.
⚫ All the lakes, except Lake Tana which is the source of
Abbay River in the Nile Basin, are found in the Rift
Valley and
⚫ Among these lakes only Zway has fresh water while
the others are all saline.
⚫ Rising water levels in Lake Tana and Lake Hawassa
after intense rainfall have been creating concern.

7. Water source of Ethiopia
⚫Large wetlands serve as a source of water for
large rivers, flood retention and groundwater
recharge.
⚫They are critical resources because they are
areas of high biodiversity and vital to the
livelihood strategies of local communities through
the provision of environmental services and
socio-economic benefits.
⚫Ethiopia has so far put no emphasis on
developing and protecting the large wetlands,
although external initiatives are emerging.

8. Water source of Ethiopia
⚫Ethiopia has many small, medium and large
reservoir dams constructed for
⚫hydropower generation,
⚫irrigation and
⚫drinking water supply.
⚫Small dams are less than 15 m high and have a
capacity of less than 3 million m3.
⚫The height of the medium and large dams in
Ethiopia is 15−50 m and their capacity ranges
from 4 to 1900 million m3.

9. Water source of Ethiopia
⚫In total, there are nine medium and large dams
with a total capacity of almost 3.5 km3.
⚫Two large dams are used for hydropower
generation only,
⚫one dam is used both for hydropower generation
and irrigation supply,
⚫Two dams are used for irrigation supply only and
⚫The remaining four for water supply to the city of
Addis Ababa and the town of Gondar.
⚫Small dams (micro-dams) constructed for
irrigation supply are concentrated in the Amhara
and Tigray regional states.

10. Name
Installed
capacity
Commissioning Basin Remarks
Koka 42 MW 1960 Awash River
Awash II 36 MW 1966 Awash River
Awash III 36 MW 1971 Awash River
Fincha 134 MW 1973 Fincha (Blue Nile) also for irrigation
Gilgel Gibe I 180 MW 2004 Gilgel Gibe River
Tekezé 300 MW 2009 Tekeze (Atbara) producing 300 MW
Beles 460 MW 2010 Lake Tana (Blue Nile) Irrigation of 140,000 ha
Gilgel Gibe II 420 MW 2010
Omo River (no dam,
fed)
Gilgel Gibe III 1,870 MW 2015 Omo River
faces stiff environmental criticism but work in
progress (75% completed as of Oct. 2013)
Fincha Amerti Nesse (FAN) 100 MW 2012 Fincha (Blue Nile)
Halele Worabese 440 MW 2014 Omo River
Gilgel Gibe IV 2,000 MW 2015 Omo River
Chemoga Yeda 278 MW 2013
tributary of the Blue
Nile, near Debre
Markos
Will consist of 5 interconnected dams
Tendaho Irrigation Dam none 2014 Awash River No power, just irrigation and drinking water
Genale Dawa III 256 MW awarded in 2009
between Oromia and
Somali state
Feasibility study by Lahmeyer with funding from
theAfDB
Grand Ethiopian
Renaissance Dam
6000 MW 2018 Blue Nile River
Awarded without competitive bid (30% completed as
of Oct. 2013)
Koysha hydro 2,200MW --- Gibe River
secured a grant from an Italian credit firm to fund the
project 2016.

11. Water use
⚫ Written information on water use is not available, but
agriculture is obviously the main water-consuming
sector.
⚫ Based on the total irrigated area, cropping pattern and
calendar, annual agricultural water use is estimated to
be in the order of 5.2 km3, while domestic and
industrial water withdrawals are estimated to be about
0.33 and 0.02 km3 respectively.
⚫ Groundwater has not yet been considered for
irrigation development, mainly due to high investment
and running costs, but pilot schemes to use
groundwater for irrigation have been started
⚫ There is growing concern about water use because of
the conflict between the environment and agriculture
particularly in lowland rural areas, where total base
flows are diverted for irrigation without releasing water
for ecological conservation

12. International water issues
⚫ Most of the rivers of Ethiopia originate within the
country and flow across the borders to neighboring
countries, thus becoming trans-boundary rivers.
⚫ Sharing the water resources of these trans-boundary
rivers is very challenging, i.e. Nile tributaries (Abbay,
Tekeze and Baro-Akobo) with the downstream
riparian countries Sudan and Egypt.
⚫ Recently, under an international law supporting the
equitable utilization of the water resources, positive
progress has been observed now that riparian
countries are deciding on common water
development programs.
⚫ The Nile Basin Initiative has been created and a
Strategic Action Program prepared which consists of
two sub-programs: the Shared Vision Program (SVP)
and the Subsidiary Action Program (SAP).

13. International water issues
⚫ SVP is to help create an enabling environment for
action on the ground through building trust and skill,
while SAP is aimed at the delivery of actual
development projects involving two or more countries.
⚫ Projects are selected by individual riparian countries
for implementation and submitted to the Council of
Ministers of the Nile Basin Initiative for approval.
⚫ The council has already accepted four hydropower
and four irrigation development projects proposed by
Ethiopia.
⚫ Sudan, Ethiopia and Egypt have also adopted a
strategy of cooperation in which all projects to be
launched concerning the river should seek the
common benefit of all member states and this aspect
should be included in the accompanying feasibility
studies.

14. 8.2. Irrigation and drainage development
8.2.1. Evolution of irrigation development
Basins Potential irrigable area (ha) Actual irrigated area (ha) % Utilized
Abay (Blue Nile 977,915 21,010 2.10
Rift Valley Lakes 122,300 12,270 10.00
Awash 204,400 69,900 34.20
Omo-Ghibe 450,120 27,310 6.10
Genale-Dawa 435,300 80 0.02
Wabi-Shebele 204,000 20,290 9.90
Baro-Akobo 748,500 350 0.05
Tekeze 312,700 1,800 0.57
Afar 3,000 - -
Mereb 37,560 8,000 21.30
Total 3,495,795 161,010 4.07
Table 2 Potential irrigable and actual irrigated area of the drainage basins, Ethiopia

15. Irrigation
⚫Irrigation in Ethiopia dates back several centuries,
if not millennia, while “modern” irrigation was
started by the commercial irrigated sugar estate
established in the early 1950s during Imperial
Government of Ethiopia
⚫Therefore, the area under irrigation can be
considered more or less similar to the area
equipped for irrigation.
⚫Four categories of irrigation schemes can be
distinguished:

16. Such as:
⚫ Traditional irrigation schemes: These schemes are
constructed under self-help programmes carried out
by farmers on their own initiative and vary from less
than 1 ha to 100 ha.
⚫ Modern small-scale irrigation schemes: These
schemes use technologies for irrigating up to 200 ha
and are constructed by the government/NGOs with
farmer participation.
⚫ Modern private irrigation: Private investment in
irrigation has recently reemerged with the adoption of
a market-based economy policy in the early 1980s.
⚫ Public irrigation schemes: These schemes comprise
medium- and large-scale irrigation schemes with
areas of 200−3000 ha and above 3000 ha
respectively and a total estimated area of about
97,700 ha. They are constructed, owned and
operated by public enterprises.

17. Table 3 Existing irrigation schemes in Ethiopia by Region
Region Irrigation Potential (ha)
Current Irrigation activities
Traditional (ha)
Modern Irrigation (ha)
Small Mediurn & large
Oromia 1,350,000 56,807 17,690 31,980
Amhara 500,000 54,035 5,752 -
SNNP 700,000 2000 11,577 6,076
Tigrai 300,000 2,607 10,000 -
Afar 163,554 2,440 - 21,000
Ben Shangul Gumz 121,177 400 200 -
Gambella 600,000 46 70 -
Somalia 500,000 8,200 1,800 2,000
Hareri 19,200 812 125 -
Dire Dawa 2,000 640 860 -
Addis Ababa 526 352 - -
Total 4,256,457 138,339 48,074 61,057
Source: Tilahun and Paulos, 2004.

18. ⚫ About 62 percent of the area equipped for irrigation is located
in the Rift Valley, while 29 percent of the area equipped for
irrigation is located in the Nile basin.
⚫ The remaining 9 percent is located in the Shebelli-Juba
basin.
⚫ Region-wise, about 39 percent of the irrigated area is in
Oromia in central Ethiopia, followed by 24 percent in Amhara
in the north, 15 percent in Afar in the northeast and 12
percent in SNNPR, while the remaining 10 percent is in the
other regions.
⚫ Nearly 100 percent of the irrigated land is supplied from
surface water, while groundwater use has just been started
on a pilot scale in East Amhara.
⚫ Sprinkler irrigation is practiced on about 2 percent of the
irrigated area for sugar cane production by government
enterprises, while localized irrigation has recently started in
the Tigray and Amhara regions Pump irrigation by a group of
farm households and private farms is practiced in some
areas, while human-powered (treadle pump) irrigation has
also recently started in the Tigray and Amhara regions.
⚫ Though quantitative information is not available, spate

19. 8.2.2. Role of irrigation in agricultural production, economy
and society
⚫ Both irrigated and rainfed agriculture is important in
the Ethiopian economy.
⚫ Virtually all food crops in Ethiopia come from rainfed
agriculture with the irrigation sub-sector accounting
for only about 3 percent of the food crops.
⚫ Export crops such as coffee, oilseed and pulses are
also mostly rainfed, but industrial crops such as sugar
cane, cotton and fruit are irrigated.
⚫ Other important irrigated crops include vegetables
and fruit trees in medium- and large-scale schemes
and maize, wheat, vegetables, potatoes, sweet
potatoes and bananas in small-scale schemes.
⚫ There is a marked value added in irrigated agriculture

20. 8.3. Status and Evolution of Drainage
Systems
⚫ Drainage is as important as irrigation, particularly in the
highlands of Ethiopia.
⚫ However, except in irrigated lands, drainage is not given the
required attention in rainfed agriculture.
⚫ Because of irregularity in cross-sections and longitudinal slopes
as well as inadequate capacities, the drains are usually
converted to gullies if the same drains are adopted year after
year.
⚫ To avoid this happening, drain lines are changed every year.
⚫ Designs of small-scale irrigation schemes incorporate drainage
systems but these are not properly implemented.
⚫ The typology of the drainage system used in the country is the
surface drainage system (gravity drainage).
⚫ The construction of subsurface drainage systems was started for
one large-scale irrigation scheme in the Awash Valley for salinity
control, but was discontinued.
⚫ Separate information on the cost of drainage systems is not

21. 8.4. Water management, policies and legislation related to
water use in agriculture Institutions
⚫Several water sector institutions have been
established at federal and regional levels under
the regionalization and decentralization policy.
⚫ At the federal level, the public institutions
involved in water resources development include:
⚫The Ministry of Water Resources (MoWR)
⚫The Awash Basin Water Resources Management
Agency (ABWRMA)
⚫The Ministry of Agriculture (MoA)
⚫The Environmental Protection Authority

22. The regional/sub-national institutions involved in the water sector include:
⚫The Bureaus of Water, Mines and Energy
(BoWME) and/or Bureaus of Water Resources
Development (BoWRD)
⚫The Commissions for Sustainable Agriculture and
Environmental Rehabilitation (Co-SAER) and the
Irrigation Development Authorities
⚫The Bureaus of Agriculture (BoA)
⚫Several NGOs are involved in the water sector
 See the details on page 72

23. Water Management
⚫ Medium and large-scale irrigation schemes are
managed by government enterprises.
⚫ The water management of small-scale irrigation
schemes is the responsibility of the farmers
themselves, mainly through informal/traditional
community groups.
⚫ Some formal Water Users Associations (WUAs) have
been established.
⚫ Apart from the provision of extension and training
services to the WUAs on the part of the MoA/ BoA, no
institution is directly involved in water management in
smallholder-irrigated agriculture.
⚫ Once the construction of irrigation schemes is
completed, they are handed over to the beneficiaries
but maintenance remains within the responsibility of
the regional governments.

24. ⚫The absence of any appropriate local-level organs to
cater for small-scale irrigation has resulted in a lack of
guidance in irrigation operation and maintenance at a
community level.
⚫With an increase in irrigated areas and more users,
irrigation water management and rules for water
allocation are becoming more complex and problematic.
⚫Disputes are already common, especially between
upstream and downstream users.
⚫A decentralization process is under way with regional
and lower level administrative organs which are
becoming more autonomous in aspects related to
irrigation development and water management.
⚫The strategy is to establish WUAs before projects are
implemented and to strengthen them through both
training and involvement in the process so that they can
take over the responsibility of operation and water

25. 9. WATER HARVESTING: PRINCIPLES AND
PRACTICES
1. Definitions and classification
⚫ Water harvesting in its broadest sense will be defined as
the "collection of runoff for its productive use".
⚫ Runoff may be harvested from roofs and ground surfaces
as well as from intermittent or ephemeral watercourses.
⚫ Water harvesting techniques which harvest runoff from
roofs or ground surfaces fall under the term: RAINWATER
HARVESTING
⚫ while all systems which collect discharges from
watercourses are grouped under the term: FLOODWATER
HARVESTING
⚫ A wide variety of water harvesting techniques for many
different applications are known.
⚫ Productive uses include provision of domestic and stock
water, concentration of runoff for crops, fodder and tree

26. 9.2. Basic categories of water harvesting systems for plant
production
⚫The water harvesting techniques described in this
course fall under three basic categories :
1. Micro-catchments (rainwater harvesting):
(sometimes referred to as "Within-Field
Catchment System")
Main characteristics:
 overland flow harvested from short catchment length
 catchment length usually between 1 and 30 meters
 runoff stored in soil profile
 ratio catchment: cultivated area usually 1:1 to 3:1
 normally no provision for overflow
 plant growth is even

27. rainwater harvesting
⚫Typical Examples:
 Negarim Micro catchments (for trees)
 Contour Bunds (for trees)
 Contour Ridges (for crops)
 Semi-Circular Bunds (for range and fodder)
Figure 9.1. Micro-catchment
system: Negarim micro-
catchment for trees

28. 2. External catchment systems (rainwater
harvesting): (Long Slope Catchment
Technique)
 Main Characteristics:
overland flow or rill flow harvested
runoff stored in soil profile
catchment usually 30 - 200 metres in length
ratio catchment: cultivated area usually 2:1 to 10:1
provision for overflow of excess water
uneven plant growth unless land levelled
⚫Typical Examples:
⚫Trapezoidal Bunds (for crops)
⚫Contour Stone Bunds (for crops)

29. Figure 9.2. External catchment system: trapezoidal bunds for crops (Source:
Critchley and Reij 1989)

30. 3. Floodwater farming (floodwater harvesting):
(often referred to as "Water Spreading" and
sometimes "Spate Irrigation")
 Main Characteristics:
turbulent channel flow harvested either (a) by
diversion or (b) by spreading within channel
bed/valley floor
runoff stored in soil profile
catchment long (may be several kilometres)
ratio catchment: cultivated area above 10:1
provision for overflow of excess water
⚫Typical Examples:
⚫Permeable Rock Dams (for crops)
⚫Water Spreading Bunds (for crops)

31. Figure 9.3. Floodwater farming systems: (a) spreading within channel bed; (b)
diversion system

32. 9.3. Water requirements of crops
⚫For the design of water harvesting systems, it is
necessary to assess the water requirement of the
crop intended to be grown.
⚫There have been various methods developed to
determine the water requirements for specific
plants.
⚫An excellent guide to the details of these
calculations and different methods is the FAO
Irrigation and Drainage Paper 24 "Crop Water
Requirements".
⚫It should however be noted that formulae which
give high accuracy also require a high accuracy
of measured input data which in most places
where water harvesting is practiced will not be

33. 9.3.1. Factors influencing crop water
requirements
⚫Influence of climate
⚫Influence of crop type on crop water needs

34. 9.4. Soil requirements for water harvesting
⚫ Texture
⚫ Structure
⚫ Depth
⚫ Fertility
⚫ Salinity/sodicity
⚫ Infiltration rate
⚫ Available water capacity (AWC)
⚫ Constructional characteristics

35. ⚫Socio-economic factors
People's priorities
Participation
Adoption of systems
Area differences
Gender and equity
Land tenure
Village land use management