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CHAPTER ONE
INTRODUCTION
1.1 DEFINITION AND SCOPE OF IRRIGATION
Definition: Irrigation is the science of artificial application of water to the land, in accordance with the
crop requirements throughout the crop period for full nourishment of the crops.
It is the Engineering of controlling and harnessing the various natural sources of water, by
construction of dams & reservoirs, head works & canals and finally distributing the water to
agricultural fields. Water is normally supplied to the plants by nature through the rains. However, the
total rainfall in a particular area may be either insufficient, or ill-timed. In order to get the maximum
yield it is essential to supply the optimum quantity of water and to maintain correct timing of water.
This is possible only through systematic irrigation system by collecting water during the periods of
excess rainfall and releasing it to the crops as when it is needed. Generally the following are some of
the factors that necessitate irrigation.
- Inadequate rainfall
- Uneven distribution of Rainfall
- increasing the yield of the crops
- growing a number of crops
- insuring against drought.
- Growing perennial crops.
Scope of Irrigation Engineering
Irrigation Engineering is not only confined to the application of water to the land for raising crops. It
includes all aspects and problems extending from the watershed to the agricultural fields. It deals with
hydrology, river engineering, design and construction of dams, weirs, canals and various other
hydraulic and irrigation structures. It also deals with surface and sub surface drainage system, soil
reclamation, water-soil-crop relationships. Other allied sciences such as flood control, hydropower,
and inland navigation are also studied in irrigation engineering.
Various aspects of Irrigation Engineering are:
1. Water Resources and Hydrology Aspect – To locate various water sources and to study the
hydrology of the region. This includes study of meteorology, precipitation, stream flow, floods,
river engineering, reservoirs and flood control. The following information is required while
designing various irrigation structures.

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 The quantity of water that will be available at a reservoir site for storage.
 Maximum discharge at a river site.
 Reservoir capacity that ensures adequate Quantity of water for various purposes.
 Quantity of ground water which can be economically exploited.
2. Engineering Aspect - Involves the development of a source of water for irrigation and
construction of various irrigation structures.
 Dams and water power Engineering
 Diversion and Distribution structures
 Minor irrigation schemes (well, Tank / Pond, inundation Irrigation).
 Ground water development
3. Agricultural aspect – Involves irrigation practice and the study of agricultural characteristics of
the land.
4. Management Aspect- Deals with successful implementation and efficient management of
engineering aspects, water distribution, and agricultural works.
1.2 BENEFITS AND ILL- EFFECTS OF IRRIGATION
There are various direct and indirect advantages of irrigation.
- Increase in food production: Irrigation helps in increasing crop yields through controlled and
timely supply of water to the crop.
- Optimum benefits: optimal utilization of water is made possible by irrigation. Optimum
utilization implies obtaining maximum crop yield with any amount of water. In other words,
yield will be smaller for any quantity lesser than or in excess of optimum quantity.
- Elimination of mixed cropping in areas where irrigation is not ensured, generally mixed
cropping is adapted. Mixed cropping is growing two or more crops simultaneously in the same
field. If the weather condition is not suitable to one of the crops it may be suitable for the other;
and thus at least some yield is obtained. Mixed cropping can be adopted when irrigation
facilities are not available, but if irrigation is assured it can be eliminated. Mixed cropping is
generally not acceptable, because different crops require different types of field preparations
and different types of manures, amount of water etc.
- General prosperity: A Revenue return is sometimes quite high and helps in all round
development of the country.

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- Generation of hydroelectric power: cheaper power generation can be obtained on objects

primarily designed for irrigation alone. Also falls on irrigation channels can be utilized to
generate electricity which may help in industrializing the rural area and so in solving the
problem of fuel shortage.
- Domestic water supply: - irrigation helps in augmenting the town water supply where water is
available with great difficulty. It also provides water for swimming bathing, cattle drinking etc.
- Facilities of communication: Irrigation channels are generally provided with embankments
and inspection roads. These inspection paths provide a good road way to the villagers for
walking, cycling or even motoring.
- In land navigation
Ill-Effects of Irrigation
Ill-effects of irrigation occur only when the scheme is not properly designed and implemented. Most
of these are due to excess irrigation water application. Some of the common ill-effects are
1. Water logging: when cultivators apply more water than actually required by the crops, excess
water percolates in to the ground and raises the water table. Water logging occurs when the water
table reaches near the root zones of the crops. The soil pores become fully saturated and the
normal circulation of air in the root zones of the crop is stopped and the growth of the crops is
decreased. Thus crop yield considerably reduces. When the water table reaches the ground surface,
the land becomes saline.
2. Long term application of pesticides: under large scale irrigation system might have a negative
influence on soil microbial activities, on the quality of surface and sub surface water resources and
the survival of the surrounding vegetation. Irrigation may contribute in various ways to the
problem of pollution. One of these is the seepage in to the ground of the nitrates that has been
applied to the soil as fertilizer. Sometimes up to 50% of the nitrates applied to the soil sink in to
the underground reservoir. The under ground water thus get polluted.
3. Outbreak of disease: Irrigation may result in colder and damper climate causing outbreak of
disease like malaria.
4. Irrigation is complex and expensive in itself. Some times cheaper water is to be provided at the
cost of the government and revenue returns are low.

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1.3 IRRIGATION DEVELOPMENT IN ETHIOPIA

Ethiopia is the “water tower” of North Eastern Africa. Many rivers arising in Ethiopia are also the
sources of the major water resources in neighboring countries. The country is endowed with water
resources that could easily be tapped and used for irrigation. Ironically this country is already suffering
from food shortage because of the increasing population and chronic drought occurrence in most part
of the eastern and northern part of the country. There is an annual food deficit to the extent of 0.5 to
1.0 million tones in the country. During the period from 1984 to 1992 the food aid annually received
was around 0.9 to 1.0 tones (World Bank Report), to meet the demand of the ever growing population
(over 72 million). The need for utilizing these resources is most urgent, in particular, in areas of the
country where the length of the growing period is short and the precipitation is erratic. In Ethiopia,
rain fed agriculture contributes the largest share of the total production. However, over the past few
decades, irrigated agriculture has become more important.
Prior to the mid-1980s, irrigation in Ethiopia was concentrated on the production of commercial crops,
principally cotton and sugarcane on large state farms. By 1980 it was estimated that 85,000 ha. Mainly
in the Awash valley, had been developed under this form of production. In addition some 65,000 ha of
traditional irrigation was estimated to exist. Predominantly in the highlands and developed on the
farmer’s own initiative. These schemes were typically small runoff river diversion, with low
production levels. During this period government involvement in irrigation concentrated on the state
farms and was channeled through various agencies.
Historical Back Ground
 In 1956 water resource development (WRD) was established within Ministry of public works,
with responsibility for undertaking river basin development studies and such a study was
completed for the Blue Nile basin. However irrigation development remained concentrated in
the Awash valley and in 1962 Awash valley Authority (AVA) was established.
 In 1971 National Water Resources Commission (NWRC) was established.
 In 1977 Valleys agricultural development authority (VADA) was created to extend the
development of large scale irrigated agriculture beyond the Awash valley and AVA become
part of VADA.
 In 1981 NWRC strengthened to absorb functions of VADA. It comprised four authorities
including water resource development authority (WRDA), which became responsible for the

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study, design, and implementation of water resource development projects including large
scale irrigation.
The 1984 drought had a considerable impact on Ethiopia’s development policy, and the 1984 Ten-
Year perspective plan allocated top priority to agricultural development with objective of achieving
self sufficiency in food production, establishing a strategic reserve meeting the raw material
requirement of industries and expanding output of exportable agricultural products to increase foreign
exchange earnings.

The Water Sector Development program of MoWR (2002) organizes irrigation schemes in Ethiopia
under four different ways with sizes ranging from 50 to 85,000 ha

 Traditional small scale schemes: These includes up to 100 ha in area, built and operated by
farmers in local communities. Traditionally, farmers have built small scale schemes on their own
initiative with government technical and material support. They manage them in their own users’
associations or committees and irrigate areas from 50 to 100 ha with the average ranging from 70 to 90
ha. A total of 1,309 such schemes existed in 1992 covering an estimated area of 60,000ha.

Water users’ associations have long existed to operate and manage traditional schemes. They comprise
about 200 users who share a main or branch canal and further grouped in to several teams of 20 to 30
farmers each.

 Modern communal schemes: schemes up to 200 ha, built by government agencies with farmer
participation. Modern communal schemes were developed after the catastrophic drought of the 1973
as a means to improve food security and peasant livelihoods by providing cash incomes through
production and marketing of crops. Such schemes are capable of irrigating about 30,000ha of land.

These schemes are generally based on run-of - diversion of streams and rivers and may also involve
micro dams for storage. On-farm support from the respective agricultural departments and
maintenance of head works by water, mines and energy sections as well as technical support from the
authorized irrigation development Bureaus in different regions is giving supports and trying to
strengthen the system.

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 Modern private schemes: up to 2000 ha, owned and operated by private investors individually,
in partnership, or as corporations. Medium to large scale irrigation schemes in Ethiopia are private
enterprises. The private estates are the pioneers in the development of medium and large scale
irrigation development projects in the upper Awash during the 1950s and 1960s. During the 1990s
some private schemes, mostly in the form of limited companies re-emerged with the adoption of
market based economic policy but have expanded relatively slowly.

Currently 18 modern private irrigation projects are operating in some form over a total area of 6000 ha
in Oromiya, SNNPR, and Affar regions.
Public Schemes of over 3,000 ha, owned and operated by public enterprises as estate farms. They are
recently developed irrigation schemes during the late 1970s. Gode West, Omo Ratti and Alwero-
Abobo began late in the 1980s and early in the 1990s but have not yet been completed. Public
involvement towards large scale schemes was withdrawn due to government changes and most of such
schemes with the exception of Fincha sugare estate have been suspended. Large scale schemes being
operated by public enterprise extend over an area estimated at 61,000 ha. Oromiya and Affar account
nearly 87% of all irrigation schemes and about 73% of this is located in Awash valley. The SNNPR
and Somali regions contain 9.9 and 3.3 percent respectively, WSDP (2003).
Irrigation potential: In 1990 a team of consultants working for WAPCOS, a consultancy group in
India, prepared a preliminary water resource development master plan for Ethiopia. The potential for
medium and large scale irrigation projects was identified as 3.3 Mha. Areas having irrigation potential
were identified from 1:50,000 and 1:250,000 topographic maps and 1:1000:000 geomorphologic
maps. The study was carried out almost entirely as a desk exercise with minimal field verification. It
should be noted that the assessment of irrigation potential is to a large degree subjective as it is
dependent on the physical resources of land and water, but also on the economic and social feasibility
of their exploitation.
Another study conducted by FAO argues the estimation of the potential irrigable land by WAPCOS is
over estimated. From the total potential irrigable area identified by WAPCOS, some 3 Mha of the soils
or 90% were classified as only marginally suitable and in some case non-suitable with the technology
available. The main reason for this is the predominance of vertisols and nitosols in the areas identified.
Theses soils are characterized by high clay content, restricted damage and difficult workability. To
avoid water logging under irrigated conditions it is necessary to adopt a low cropping intensity or to

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install expensive sub-surface drainage. Either alternative significantly reduces the economic viability
of irrigation. However, such soils are frequently classified as highly suitable for rice production.
Ethiopia has a rich water resources potential, but water can be very short in many places. Except for
the Awash and the Omo, all the large rivers originating in Ethiopia flow into neighboring countries.
Unlike in the past Ethiopia is now taking genuine steps towards fostering close ties, joint planning and
harmonious relationships among riparian countries.
Table 1.1: The irrigation potential of the12 major river basins
Rivers Basin area Mean Ground water 1 2
(Km)2 annual potentialx109 m3 potential gross Net area
9 3
Vol.x10 m irrigable area(ha) Under irrigation(ha)
Awash 112696 4.60 0.14 205400 69900
Abay(Blue 204000 52.62 1.80 1001550 21010
Nile)
Baro-Akobo 75912 11.81 0.13 600000 350
Rift valley 52739 56.3 0.10 139300 12270
lakes
Omo-Gibe 79000 17.96 0.10 86520 27310
Genale- 17104 5.88 0.03 423300 80
dawa
Wabi- 202697 3.16 0.04 204000 20290
Shebelle
Tekeze 865000 8.20 0.02 189500 1800
Ogaden 72121 0.86 - - -
Denakil 62882 0.86 - 3000 -
Aysha 2223 0.22 - - -
Mereb-Gash 5700 0.65 0.05 67560 8000
Total 1127312 112.45 2.59 2920130 161010
Note 1= the data extracted from EARO and 2= the data from CSE
Ethiopia has not developed irrigation to the potential it has, i.e. according to the availability of
physical resources, land and water. At present only a little more than 3% of the irrigable land is
currently irrigated both in large and medium scale. The development of irrigated areas in the country

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has also been unevenly spread. Over 70% of the area developed for irrigation to date is in the Awash
River basin. Most of the development has been in the awash valley, which is the most accessible basin
to Addis and has the best infrastructure to support irrigation development.
The spells of drought during the last two decades have led to increased interest in irrigation
development. Irrigation is thus expanding in the Wabi-Shebelle and Genale rivers and in the Ziway-
Meki area of the rift valley. There are also a number of proposals for further irrigation schemes in
several of the other basins including the Omo River, Rift valley lakes and Baro-Akobo. Following the
decentralization of governance, there are now a number of regional initiatives to develop irrigation,
especially at the small and medium scales, building on existing traditional small-scale irrigation
systems, and augmenting them with the diversion of streams and the construction of earth dams.
Irrigation development in Ethiopia, as in other countries, has a number of ecological implications
because of its impact upon river regimes and downstream flows.
Some of the adverse effects of irrigation development on the environment are: The development of
medium and large scale irrigation projects causes a displacement of the indigenous population engaged
in pastoral modes of life. Clear examples include the displacement of 60,000 Afar pastoralists from the
Amibara irrigation project in the Middle Awash (Mac Donald, 1990) and unspecified number of
kereyou pastoralists during the establishment of the Metehara sugar plantation in the upper Awash.
With respect to the use of irrigation for crop production in the highlands, the success has been little.
The existence of small scales irrigation by small holders in parts of Shewa, Tigray Harerege, Gojjam,
North omo and few others is known. But the constraints of small scales of irrigation in the highlands
of Ethiopia are physical, know-how.
Until last year Ethiopia did not have a coherent water resource policy. Lack of an irrigation policy
precluded the preparation of a strategy for he sub-sector which would have identified development
targets and priorities. The large number of different agencies involved particularly in medium and
large scale irrigation created considerable difficulties in coordination of activities leading to overlap of
responsibilities and inefficient use of scarce human, financial and physical resources. Defined
institutional responsibilities and allowed rational planning of future manpower requirements and its
development. The sub-sector also suffered from unnecessary institutional and fragmentation.

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Functions of Irrigation water

The function of soil moisture in plant growth are diversified
1. It adds water to the soil to supply the moisture essential for plant growth
 It acts as a solvent for the nutrients. Water forms the solution of the nutrients and this
solution is absorbed by the roots. Thus water acts as a nutrient carrier.
 The irrigation water supplies moisture which is essential for the life of bacteria
beneficial to the plant growth.
 Irrigation water supplies the moisture which is essential for the chemical action within
the plant, leading to its growth.
2. Some salt present in soil react to produce nourishing food products only in the presence of
water
3. Water cools the soil and the atmosphere and thus makes more favorable environment for
healthy plant growth.
4. Irrigation water, with controlled supplies, washes out or dilutes salts in the soil
5. It reduces the hazard of soil piping.
6. It softens tillage pans
1.4 STANDARDS OF IRRIGATION WATER
All water is not suitable for irrigation. The quality of irrigation water is very much influenced by the
contents of the soil, which is to be irrigated. Particular water may be harmful for irrigation on a
particular soil but the same water may be tolerable or even useful on some other soil. Irrigation water
may be said to be unsatisfactory for its intended use if it contains:
 Chemicals toxic to plants or the persons using plant as food
 Chemicals that react with the soil to produce unsatisfactory moisture characteristics
 Bacteria injurious to persons or animals eating plants irrigated with water.
There are two main causes of salinity: Salinity caused by the supply of irrigation water and Salinity
caused by the upward movement of water and salts, related to high water tables and lack of drainage;
it is only indirectly related to salts in the irrigation water. The general solution to these problems is to
remove the salts from the soil by providing extra water, which dissolves the salts and percolates to the
saturated zone where it is removed by drainage. The process is called leaching. This is one of the
reasons why irrigation systems also require drainage systems.

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a. Sediment: its effect depends upon the type of irrigated land when fine sediment from water is
deposited on sandy soils the fertility is improved on the other hand if the sediment has been
derived from the eroded areas it may reduce the fertility or decrease the soil permeability.
Sediment water creates troubles in irrigation canals as it increases their siltation and
maintenance costs. In general ground water or surface water from reservoirs, etc does not have
sufficient sediment to cause any serious problems in irrigation.
b. Total concentration of soluble salts: Salts, when present in excessive quantities, reduce
osmotic activities of the plants and may prevent adequate aeration causing injuries to plant
growth. The effect of salts on plant growth depends largely upon the total amount of salts in
the soil solution.
c. Proportion of sodium ions to other cations: small quantities of sodium ions present in most soils
relative to other cations. If its percentage increases it has an influence on the aggregation of soil grains
i.e. it breaks down. The soil becomes less permeable and of poorer tilth. It starts crusting when dry and
its pH increases towards that of an alkaline soil. High sodium soils are therefore, plastic, sticky when
wet, and are prone to form clogs and they crust on drying.
The proportion of sodium ions present in the soil is generally measured by a factor called sodium-
absorption ratio (SAR) and represents the sodium hazards of water. SAR is defined as:
Na 
SAR =
 Ca    Mg   
 
 2 
When SAR between 0-10 it is low sodium water
10-18 medium ,
18-26 High ,
>26 very high ,
Low sodium water is suitable for irrigation except in crops which are sensitive to sodium like fruit
trees; avocados etc where as medium sodium water is hazardous in fine textured soils. Very high
sodium water is generally not suitable for irrigation. SAR value can be reduced by adding gypsum
(CaSo4).
d. pH :- The pH value of a soil or natural water is a measure of its alkalinity or acidity. More
accurately stated, the pH value is a measure of the hydrogen ion concentration in water.

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Mathematically this is the logarithm to the base 10 of the reciprocal of the hydrogen ion concentration
of the pure water.
e. Potentially toxic elements: elements like Boron, Selenium, etc may be toxic to plants.
Concentration of Boron exceeding 0.3 PPM may be toxic to certain plants.
>0.5 PPM, dangerous to nuts, citrus fruits.
Dates. Beets, asparagus are quite tolerant. Even for the most tolerant crops its concentration should not
exceed 4 PPM. Boron is present in various soaps. Wastewater containing soap, etc should be used with
great care in irrigation.
Table 1.2; Guidelines for the interpretation of water quality for irrigation water (FAO, 1976)
Irrigation problem Degree of problem
No Increasing Severe
problem problem problem
Salinity <0.75 0.75-3.0 >3.0
(affects water uptake)
Ecw (mmhos/cm)
Permeability (affects water
infiltration and availability)
Ecw (mmhos/cm) >0.5 0.5-0.2 <0.2
Adj.SAR
Montmorilonite Hlite- <6 6-9 >9
vermiculite <8 8-16 >16
Kaolimite-sesquioxides <10 16-24 >24
Specific ion toxicity
(affects sensitive crops)
sodium (adj. SAR) <3 3-9 >9
Chloride(meq/1) <4 4-10 >10
Boron (mg/1) 0.75 0.75-2.0 >12

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Miscellaneous effects
(affects susceptible crops)
No3-Nor NH4-N(mg/1) <5 5-30 >30
Hco3(meq/1) <1.5 1.5- 8.5 >8.5
PH
(Normal range 6.5- 8.4)

The following guidelines can be used in assessing the water quality for irrigation.
I. Salinity status: ECw and TDS
II. Infiltration capacity: this can be done by estimating SAR and ECw, salinity & sodium
content.
III. Specific ion Toxicity: Na , Cl, B ,
Other trace elements: Al, As, Be, Cd, Co, Cr, Cu, F, Fe, Li, Mn, Mo, Ni, Pb, Se, etc
iv. Miscellaneous effect: Nitrogen NO3 - N, Bicarbonate (HCO3) - for overhead irrigation
Some literatures provide different guidelines specified by FAO (1976) to interpret the irrigation water
quality parameters.
Table1.3: Laboratory determinations needed to evaluate common Irrigation water quality parameters
S.No Water Parameter Symbol Unit usual range in irrigation water
1. SALINITY:
1.1 Salt content
Electrical conductivity ECw dS/m 0-3
Total Dissolved Solids TDS mg/l 0-2000
1.2 Cations &Anions
Calcium Ca++ me/l 0-20
Magnesium Mg++ me/l 0-5
Sodium Na+ me/l 0-40
Carbonate CO3-- me/l 0-0.1
Bicarbonate HCO3- me/l 0-10
Chloride Cl- me/l 0-30
--
Sulphate SO4 me/l 0-20
2. NUTRIENTS
Nitrate- Nitrogen NO3 - N mg/l 0-10

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Ammonia – Nitrogen NH4 –N mg/l 0-5

Phosphate Phosphorus PO4-P mg/l 0-2
Potassium K+ mg/l 0-2

3. MISCELLANEOUS
Boron B mg/l 0-2
Acid /Basicity pH 1-14 6-8.5
Sodium adsorption ratio SAR me/l 0-15
Li , Fe
Source. FAO Irrigation &Drainage manual No. 29, Page 1-10

1.5 Feasibility studies of irrigation projects

Types of Irrigation projects
Any plan small or large, which ultimately aims at satisfying the paramount need of adequate water
provision for crop production, is an irrigation project.
Based on the scope of the irrigation project, irrigation projects can be classified as:
a) Large scale
b) Medium scale
c) Small scale
Table 1.4: Irrigation projects and their development costs
Type of project Command area Development cost*
(ha) U.S dollars/ha
Average cost Range in cost
Large scale >10,000 16,000 5,000-50,000
Medium scale 2,000-10,000 9,000 4,000-15,000
Small scale <2,000 4,000 1,000-6,500

* Source: FAO, 1995.

Note: In Ethiopia, Small scale irrigations are those which have command areas <200 ha, medium scale
200-3000 ha, and large scale >3000 ha.

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With this respect, Ethiopia has a total potentially irrigable area of about 3,637,000 ha. It is 27.55% of
the total cultivable area. From which
o For small scale irrigation 165,000-400,000 ha.
o For medium and large scale irrigation 3,300,000 ha.
Stages of investigation in the development of irrigation projects
 Basically, the development of water resources for irrigation requires the conception, planning,
design, construction, and operation of various facilities to utilize and control water and to maintain
water quality.
 Investigations of the development of irrigation projects need multi-disciplinary approach.
Specialists of different disciplines, such as, Soil and water specialist, Engineers (Irrigation and civil),
Agronomist, Geologist, and Socio-economist required.
 Investigations of water resources development projects are essentially aimed at collection of
basic data and analysis thereof for formulation of an optimum project. The extent of data to be
collected depends on the magnitude of the project and also on the stage of investigation.
The common procedures adopted in the development of an irrigation project are:
1. Sites are located on the toposheet.
2. The marked sites are inspected (reconnaissance) to decide their feasibility.
3. The feasibility investigations are carried out for one or more of the possible alternatives and
estimates based approximate details are prepared.
4. Detailed investigations are then taken up and technical sanctions are granted.
5. After the technical sanction, agency of execution (i.e., contractor) is fixed and construction
started.
Approaches of data collections:
The following questions should be answered
 What or which data are required?
 How they can be collected?
 Why are they needed?
 Is the cost of their collection worthwhile?

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Feasibility studies of irrigation projects

 Necessity for irrigation in the region: Normally Irrigation will be a necessity if there is
inadequacy of rainfall, uneven distribution of rainfall, etc. On the other hand it will be of a
paramount importance to alleviate food shortage due to population growth.
For instance, in Ethiopia,
In 2050 – population is expected to be 170 millions.
 Let 230-kg/person/year food grain is needed.
 Need of 400 mills. Quintal (which = 3x present)
 Let 200 mills. Quintal produced by rain-fed (which = 2x present)
Thus 200 million quintal should be produced by irrigation (which needs 80, 000 ha increment per
year).
 Availability of adequate water supply
 Topography of the area
 Cultural practices of the tract
 Adequacy of existing irrigation system it any
 Possibility of growing cash crops or other voluble crops after provision of irrigation
water
 Facilities regarding accessibility to the site and transportation of construction materials.
 Economical justification for implementing the irrigation scheme.
When the idea of an irrigation project is conceived (after reconnaissance survey), the data to be
collected at the feasibility study stage are
1. Physical data: Location, size, physiography (description of land form which includes only physical
aspects), climate, etc.
2. Hydrological data: Precipitation, Evaporation, transpiration, stream flow, sediment, water quality
etc.
3. Agricultural data: Land classification, crop water requirements, types of crops etc
4. Geological data: Rock & Soil types, ground water, minerals, erosion, etc.
5. Cartographic data: Topographic & other maps of the area.
6. Ecological data: Types of vegetation, fish & wild life.
7. Demographic data: Population statistics, data of people etc.
8. Economic data: Means of transportation, market, land taxes, etc.

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9. Legal data: Water rights, land ownership administrative pattern, etc

10. Data in existing project: Types of Location of various projects.
11. Data on public opinion: Opinions of different section of the society
12. Flood control data: Records of past flood, extent of damage caused, drainage requirements
Information to be collected includes;
Land resources
An evaluation of the suitability of land for alternative kinds of use requires a survey to define and map
the land units together with the collection of descriptive data of land characteristics and resources.
Land suitability is the fitness of a land-mapping unit for a defined use (in this case irrigation). Land
mapping units represent parts of a study area (ex. for irrigation) which are more or less homogeneous
with respect to certain land characteristics i.e. slope, rainfall, soil texture, soil type, etc).
Land evaluation provides information and recommendations for deciding ‘which crops to grow where’
and related questions. Land evaluation is the selection of suitable land, and suitable cropping,
irrigation and management alternatives that are physically and financially practicable and
economically viable. The main product of land evaluation investigations is a land classification that
indicates the suitability of various kinds of land for specific land uses, usually depicted on maps with
accompanying reports.
The four basic features of land suitability for irrigated agriculture are
 Irrigable terrain (land forms)
 Potentially fertile soil
 A climate in which the crop can thrive (develop well & be healthy)
 A reliable source of water of consistent quality
The classification of the suitability of a particular land – mapping unit depends on the extent to which
its land qualities satisfy the land use requirements. Definite specification (for land use requirements) is
established for an irrigation project area prior to land classification.

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Land suitability classification

Land suitability sub – classes. Examples

S2w – land moderately suitable (S2) because of lack of available water (w).
S2d – land moderately Suitable (S2) because of drainage deficiency (d).
 Land capability maps are used to delineate arable and non-arable lands.
 Land use and Vegetation maps of the catchments area are used to identify the present land use in
terms of cover and function.
Soil survey:
This includes

 Identification of soil types.

 Field observation of infiltration.
 Field observation of hydraulic conductivity.
 Water table depth and fluctuation.
 Workability of the soil.
 Absence or presence of soil salinity.
Soil survey recognizes the relation between terrain or physiography and soils.

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Table 1.5: Examples of the minimum grade of a number of land qualities and land suitability ratings
for irrigated rice
Land qualities Land suitability rating
S1 S2
Soil depth (cm) >60 >30
Soil fertility High low-medium
Soil salinity (ECin mmhos/cm) <4 <8
Rock outcrops (% of ground surface) <2 <25
Net field water requirements (mm/day) <20 <20
Slope (%) <2 <4
Field size medium-large small
Land development costs (US $ /ha <200 <600
Flooding nil or slight moderate

 Topographic Survey follows the soil survey and so is restricted mainly to the areas of irrigable
soils that have been delineated. Additional areas are included as necessary for the location of reservoir,
dams, head works, canals, buildings, roads, and hydraulic structures. etc.
Water resources
Hydrological survey and Hydro-geological are undertaken to asses surface and sub-surface water
resources of the catchments respectively. It may be carried out at: national level, river basin level,
project development level and at farm level.
Data sources
 Surface water supplies from long – term records of stream flows, by stream gauging and water
quality. If such data is not available, rainfall records for the catchments or stream flow records
of the neighboring rivers used.
 If the above two conditions didn’t exist, stream gauging and metrological stations are set up as
soon as possible on the principle that short – term records are better than none.
 For ground water supplies
Short – term yield is assessed by drilling and testing trial wells.
Long – term yield is estimated by a detailed study of the aquifers

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(Mathematical models, numerical models which simulate the non-steady state, two-dimensional,
ground water flows are used for such purposes.)
Agricultural and Engineering aspects
 In feasibility study the present state of Agriculture and agricultural society is assessed and the
future state, with irrigation, is predicted. I.e. the ‘with’ and ‘without’ conditions of irrigation.
Present farm practices
 The number of farms of different sizes
 Farming methods in use
 Land areas cultivated and irrigated
 Crop yield per hectare
 Total crop production and costs.
 Labor available for farming operation
 Existing skill in irrigated farming and attitudes to change.
 Assessment on the existing market & transport.
 Presence of noxious weeds
The future state of Agriculture
This assessment is much more difficult (numerous assumptions inevitably have to be made)
It should be demonstrated that.
The soils and the climate are suitable
 The rotation of crops is sound
 The water duties can be provided
 There will be accessible markets capable of absorbing the increased production at economic prices.
 The advising and training facilities will be adequate, etc.
The Engineering aspect mainly focuses on the development of a source of water for irrigation and
construction of various structures for storage, diversion, conveyance and application of water.
These includes investigations of
 Site selection and Design of a reservoir & a dam
 Site selection & Design of diversion head – works at point off takes.
 Alignment for canal system (lay outs for canal)
 Alignment for field channels.
 Study of sub–surface conditions that affect the design and construction of a proposed structures.

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 Concentrated on the mechanical properties of the sub soil at foundation levels.

 Construction materials including, soil and sand, rock and aggregate, cement, lime stone steel, etc.
 Tests should be carried out on the various construction materials.
 Any flood hazard so that provision of flood dyke protection is possible.
 If there is drainage requirements i.e. layouts of sub – surface drains.
 Other factors having bearing effects upon the design of engineering works.
Social and Economic aspects
The attitude of the people to the introduction of irrigation in that area should be investigated
thoroughly.
The Various items considered in benefit/cost relationships are.
a) Costs
 Capital cost of the project.
 Cost of preliminary and precise survey and investigation.
 Cost of a equitation of land
 Cost of various structures
 Cost of earthwork and lining for canal system. etc.
 Allowance made for foreseen and unforeseen contingencies.
 Interest on Capital
 Depreciation
 Operational and maintenance cost of project
b) Benefits.
 Agricultural production in the project area before and after taking up the project (irrigation).
 Cost of cultivation before and after irrigation (cost of inputs viz. Seeds, manure, labor,
irrigation machines and implement etc).
Then
Net annual benefit due to irrigation.
B. C ratio =
Annual Cost of Pr oject.
>1.5 for economically justified project.

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