CANAL NETWORKING AND DRAINAGE SYSTEM

DESIGN ON RIBB IRRIGATION PROJECT

ARBAMINCH UNIVERSITY

WATER RESOURCES & IRRIGATION

ENGINEERING DEPARTMENT

JUNE, 2011

ARBAMINCH
CANAL NETWORKING AND DRAINAG SYSTEM
DESIGN
ON RIBB IRRGATION PROJECT
SUBMITTED BY:
ABIY ALEMU

BETELHEM W/RUFEAL

ESHETU TSEGA

FIREZER GETACHEW

GETAHUN ALAMNEH

MATEWOS WOMA

MOHAMED EBRAHEM

TARIKU DEGEFA

IN PARTIAL FULFILMENTS FOR THE AWARD DEGREE OF:

BACHILOR OF SCIENCE, B.SC

IN

WATER RESOURCES & IRRIGATION ENGINEERING

ARBAMINCH UNIVERSITY

UNDER THE GUIDANCE OF :

TADDESSE SHIMELES (M.SC)

AND

HABTE GEBEYEHU (B.SC) JUNE ARBAMINCH

THIS IS TO CERTIFY THAT THIS REPORT ENTITELED DESIGN OF CANAL
NETWORKING AND DRAINAGE SYSTEM ON RIBB IRRIGATION PROJECT

SUBMITTED BY:
ABIY ALEMU

BETELHEM W/RUFEAL

ESHETU TSEGA

FIREZER GETACHEW

GETAHUN ALAMNEH

MATEWOS WOMA

MOHAMED EBRAHEM

TARIKU DEGEFA

IN PARTI AL FULFILMENTS FOR THE AWARD DEGREE OF:

BACHILOR OF SCIENCE (B.SC)

IN

WATER RESOURCES & IRRIGATION ENGINEERING

ARBAMINCH UNIVERSITY

UNDER THE GUIDANCE OF:

TADDESSE SHIMELES (M.SC)

AND

HABTE GEBEYEW (B.SC)

JUNE 2011

ARBAMINCH
 Acknowledgement
About all, we would like to express our deepest heartfelt thank to Eternal God whose hand
support us in all our study and careers in AMU.

We would like to express our sincere gratitude and indebtedness to our advisors Ato
Taddesse Shimelis (M.Sc) and Ato Habte Gebeyehu (B.Sc) who support and cooperated us
by providing the necessary data what we need, and for their intelligent guidance to solve
varieties of difficulties in the process of our work.

We would like also like to express our thanks to librarian for their generous cooperation in
providing us the necessary books, sample project when required.

Finally, we thanks our families, friends communities of AMU and all others who have
helped us in our activities through moral, financial and material in our four year study in
AMU.
 ABSTRACT
The report on canal networking and drainage design system project consists of genuine
work on the design of the irrigation scheme for 1000ha of land of which will be effectual
through diversion of Ribb River.

The report consists of background information of the project area, such as soil, crop water
demand assessment for the selected crops, design of canal and canal structures, irrigation
water application design, design of drainage system, environmental impact assessment,
economic analysis of the project, conclusion and recommendation and annexes have been
provided.

The project consists of eight chapters and each chapter has its own content to deal with.

Chapter One-deals about the introduction, General situation of the area, Project area,
Location, Topography, Climate, and Soil type of the area, and Scope of the project.

Chapter Two – Irrigation water demand assessment, calculation method of ETO, crop
selection, cropping pattern, land allocation of the selected area, calculation of K C,
calculation of ETC, irrigation requirement, effective rainfall, NIWR, GIR, irrigation schedule,
depth of irrigation and irrigation interval.

Chapter Three – irrigation canal system, canal alignment, design of canal structure(such as
culvert, canal drop, stilling basin, canal outlet, division box, and aqueduct.

Chapter Four – about water application system, surface irrigation system, furrow
irrigation system, designs of siphon tube and irrigation system management.

Chapter Five - deals about system design of drainage under this it deals , selection of
drainage system, surface and sub surface drainage system design .

Chapter Six - deals about economic analysis and estimation the project benefit.

Chapter - Seven - deals about EIA, potential impact and mitigation measures, negative
impact, positive impact and mitigation measure.

Chapter – Eight deals about conclusion and recommendation of the project.

 List of abbreviation
AMU-Arbaminch University

B/C-Cost benefit ratio

CBL-canal bed level

CEL-canal elevation level

CWR- crop water requirement

EIA-environmental impact assessment

FAO-food and agriculture organization

FSL-full supply level

GIR-gross irrigation requirement

GW-ground water

MAD- management allowable depletion

MAR-mean annual rain fall

NIR-net irrigation requirement

NIWR-net irrigation requirement

OGL-original ground level

RAM-readily available moisture

Rad-radiation

TAW-total available water

USDA-united states of development of agriculture

 Canal Network Design on Ribb Irrigation Project

CHAPTER ONE

INTRODUCTION

1.1 General
Ethiopia is one of the developing countries and around 85% of the total population
depends on agriculture most of the agricultural practice is rain fed crop production.

However, due to the back ward method farming, unreliable rainfall, including population
and drought. The nation faced series food shortage. These food shortages were followed by
sever famines that resulted in the loss of the lives of millions of citizens.

Hence, it is obvious that the agricultural system has to be improved and irrigation practice
should be spread extensively to bring about sustainable food self-sufficiency and to earn
foreign exchange.

Fortunately, Ethiopia is luck of in that it has got ample source of surface and subsurface
water which it is known as” The water tower of east Africa.”

Moreover, the irrigation potential is estimated to be about 4025 million hectare of which
only 5.8% is irrigated. (Source; study carried out by international water management
institute-IWMI. In this project it is aimed to irrigate 1000ha i.e. small scale irrigation
project.

1.2 Project area

1.2.1 Location and Topography

Ribb irrigation network canal and drainage is located, on the eastern side of Lake Tana
Basin, in the South Gondar Zone of Amhara National Regional State. It is located in altitude
of 2020m, latitude 12.110N and Longitude 37.860E.

Lake Tana Basin is one of the major agricultural areas of the country. However, this
potential area is under threat. The ever-increasing devastation of the natural vegetation, the

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gentle slopes, and traditional land management practices, poorly adapted to land
conservation under the prevailing conditions, have resulted in dramatic soil erosion in the
area.

The basin population is expected to triple over the next fifty years. This will place enormous
additional pressure on the land base in the highlands, where it is already fully utilized.
Indeed, it is clear that the land as a whole cannot possibly absorb the expected population,
and alternate means of livelihood must be created.

Lake Tana's shore is characterized by flat low-lying land with poor drainage conditions. In
these low-lying lands, the rivers have inadequate flood-carrying capacity due to mild slope
and shallow cross-sections caused by sediment deposition in the riverbed. Surface inflows
overtopping the riverbanks, direct rainfall on the area, poor drained soil and Lake Tana
backwater effect also contribute to flooding in the area. This has even hampered the
development of rain fed crops during the main season.

The introduction of irrigation will make farmers feel more secure about their basic food
supply and enable them to diversify their crops based on local market demand and export
opportunities.

The land and water resources in the area are suitable for irrigation development.
Experience from small-scale irrigation schemes has demonstrated that a range of crops
could be grown profitably during the dry season, without affecting the production of staple
food crops during the rainy season.

To enhance the economic viability of investments in infrastructure, it is important that

irrigation development efforts be focused on achievement of the benefits described above.
The proposed irrigation canal & derange project will develop one thousands of hectares of
irrigated agriculture, thereby generating a demand for agricultural support services, and
will enable farmers to fully benefit from more reliable access to sources of water.

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Tertiary unit

figure1. 1 Topography of Ribb irrigation project

1.2.2 Climate
The climate of the Ribb Basin is marked by bimodal rainy season the first round extend
from March to June, with monthly rainfall varying from 74.6 mm in March to 148.9 mm in
April; the second round extends from August to November with monthly rainfall varying
from 74.1mm in August to 124.9mm in October . The dry season is from December to
February. Dependable rainfall varies from less than 51.1 mm during the dry season to 74.1–
148.9 mm/month during the period of rainy season. The average minimum and maximum
temperature variations throughout the year are extending from 16.49 ºC to 29.85 ºC
respectively. Humidity varies between 44% in Feb and 66% in May. Wind speed is low, it
varies from 0.8m/s in Dec to 1.17m/s in June the average Sunshine duration varies from
4.7-9.1hours during July and January

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Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

figure1. 2 Average climatic data graphically

1.2.3 Soil Composition

Soil is a dynamic natural body composed of minerals, organic materials and living forms in
which plants grow. It is the collection of natural bodies occupying parts of earth’s surface
that supports plants and has properties due to integrated effects of climate and living
matter acting upon parent materials, as conditioned by relief, over periods of time. The soil

type for this small scale irrigation project is medium soil.

1.3 Socio Economic study

Farming with traditional cultural practices forms the livelihood of the community. Around
the project area rain fed agriculture is the existing means of survival for the farmers, which
is supported by live stock production. Because of the poor performance of agricultural
production system and its consequent results, the farmers are exposed to food shortage
and forced to live below the subsistence level. Irrigation development is the option to

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improve the living standard of the area. This ensures food self-sufficiency and reduces
poverty.
The area being very near to the three big towns Gonder, Addiss Zemen and Bahir Dar, the
agricultural product has good marketing facilities.

1.4 Objective of the project

1.4.1 General objective

 To generates cash incomes for the targeted and non targeted beneficiaries

 To utilize existing resources in a better way and reduce the wastage of materials and
human dependency on rainfall

 Finally to improve the socio economic life of the community, by increasing per
capital incomes too.

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CHAPTER TWO

IRRIGATION WATER DEMAND ASSESMENT

2.1 General
Water is one of the most important agricultural inputs which plays vital role in the process
of plant growth. Crops need water, starting from the time of sowing until they got matured.
However, the rate of use of water is affected by various factors such as

 Type of soil
 Type of crop
 Length of growing season
 Meteorological variables like sun shine, temperature humidity, rainfall and wind
speed.

Irrigation water is a major source of water supply that ensures the required, Irrigation
water requirement is the total quantity of water required to be supplied by irrigation to
meet crop needs for consumptive use and additional needs like leaching and unavoidable
losses. The total quantity of water sizing of a reservoir

There is no vital requirement other than water for crops. It has a number of functions in the
process of growth.
The function of water with respect to growth of plant and its yield are:
1. Solvent for gaseous, minerals and other soluble food.
2. Conduct and translocation of solutions in cell and tissues.
3. as an active reagent in photosynthesis and hydrolysis.
The factors that affect the water requirement of plants are: type of soil, type of plant,
metrological variables like sunshine, temperature, humidity, rainfall and wind etc.

2.2 Crop water requirement

Crop water requirement is defined as” the depth of water needed to meet the water loss
through evapotranspiration (ETcrop) of a disease free, growing in large fields, under non-

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restricting conditions including soil water and fertility and achieving full production
potential under the given growing environment.
The water requirement of crops may be contributed from different sources such as
irrigation requirement, effective rainfall, soil moisture storage and ground water
contributions.
CWR=IR+ER+S+GW
Where, CWR=crop water requirement
IR=irrigation requirement
ER=effective rainfall
S=carry over soil moisture in the root zone
GW=ground water contribution

2.3 Calculation method of reference evapotranspiration (ETo)

The methods to calculate ETo are as follows
 Blaney-criddle,
 Thornthwaite,
 Hardgrave’s class A pan evaporation,
 modified penman and
 pen-man monteith methods
The choice of the method must be based on the type of climatic data available and on the
accuracy required in determining water needs.
The effect of crop characteristics, is given by the crop coefficient (Kc) which presents the
relationship between ETo and ETcrop

Where ETcrop=crop evapotranspiration

Kc=crop coefficient
ETo=reference evapotranspiration
The value of Kc varies with the type of crop, its stage of growth, growing season and the
prevailing weather condition.

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So, Blaney-criddle and Thornthwaite methods use temperature data only so that the other
climatic conditions are ignored. Hardgrave’s and Modified penman methods are over
estimated.
The FAO penman method was found to frequently overestimate ET o while the other FAO
recommended equations, namely the radiation, the Blaney-Criddle the evaporation
methods, showed variable adherence to the grass reference cop evapotranspiration. As
result, the FAO penman-Monteith method is recommended. As the sole method for
determining reference evapotranspiration, the method has been selected because it closely
approximates grass ETo at the location evaluated. However, procedures have been
developed for estimating climatic data based on given metrological data.

Penman-monteith method (direct estimation of ETo)

Penman equation has been adopted to estimate evapotranspiration in mm/day as follows;

Where, ETo=reference evapotranspiration in mm/day

=psychometric constant=0.49mmHg/oc
∆=the slop of the saturated vapor pressure vs temp. curve at mean temp.
u2=mean wind speed in km/day measured 2m above the ground.
es =saturated vapor pressure at mean air temp. in mmHg.
ea =actual vapor pressure in the air in mmHg.
G = soil heat flux ( MJ/m2day)
Rn=net radiation at crop surface (MJ/m2d)

U = wind speed in km/day

z = elevation from sea level, m

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Penman-monteith method using cropWat 8 soft wear

The pen-man monteith method is done using the computer software cropWat 8 windows
by using metrological data of the project area as follows for the available climatic data’s.
Country Ethiopia Station Addis zemen
Altitude 2020m Longitude 37.860E
Latitude 12.110N
table 2. 1 ETo determination using pen-man montieth method
Month Min Max Humidity Wind Sunshine Rad ETo
Temp Temp % speed hours MJ/m?/day mm
°C °C m/s /day

January 15.9 30.8 49 0.8 9.1 20.1 4.01

February 16.5 32.0 44 0.9 9.0 21.5 4.51
March 17.3 32.0 50 1.0 8.3 21.8 4.84
April 17.1 30.3 62 0.9 7.5 21.1 4.58
May 16.9 28.9 66 1.1 8.1 21.7 4.62
June 16.8 28.4 63 1.2 6.5 19.0 4.23
July 16.6 28.0 62 1.1 4.7 16.4 3.78
August 16.8 28.4 61 1.1 5.3 17.5 3.97
September 16.9 29.5 58 1.0 7.0 19.9 4.33
October 16.5 29.4 63 0.8 7.5 19.6 4.14
November 15.5 29.9 58 0.8 8.8 20.0 4.07
December33 15.1 30.6 50 0.8 9.0 19.4 3.97
3
Average 16.5 29.9 57 1.0 7.6 19.8 4.25

2.4 Crop selection

To select the type of crops to be grown in certain area, the following points have to be
considered

 Adaptability to climate

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 Socio-economic aspect
 Marketing value of crop (priority should be given to those with higher market
value).
 Based on the above criteria Potato, Maze, Tomato, Barely, & Pepper crop was
selected to grow in the project area

2.5 Cropping Pattern

Crop using pattern is the sequence of different crops growing in a regular order in any
particular field. To determine the irrigation requirement of the crops under project area, an
assessment should be made for different crops grown under irrigation with moreover
information on the crop characteristics, such as length of growth cycle, rooting depth, crop
coefficient etc. In Ribb irrigation project there is command area of 1000ha. The proposed
command area has medium soil type.

2.6 Land Allocation for Selected Crop

This project attempts to make use of the optimization techniques while apportioning the
land for different crops with surface irrigation

2.6.1 Optimization Technique

Optimization is the art of obtaining the best result under the given circumstances in design,
construction and maintenance of any irrigation system. The ultimate goal of all is either to
minimize the effort required or maximize the desired benefit or to decide what amount of
area out of the total irrigable land; a certain crop should occupy so as to give maximum
benefit.
In this project, the goal is to maximize the benefit by optimally allocating the area for each
crop. Therefore, optimization refers to an economical decision.
Assumptions required during optimization:
 Large area is given to crops serving as staple food and maximum benefit
 Optimization is done for two season simultaneously
 To solve optimization technique linear programming method is used.

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The following points are considered on the generation of the objective function
of the optimization problem.
 Project yields of each crop taken from local information and yield response to
water, FAO 1986.
 Price of the products taken from local market of the project area.
 Input costs for seeds, fertilizers and chemical protection such as herbicides are
taken from feasibility report of the project area.
Labor required adopted from local information;
 Labor costs are 20 birr/day for the project area, obtained from local information.
 Irrigation system operation and maintenance costs are difficult to estimate.
However, the estimation has been taken from previously done projects (i.e. 100
Birr/ha).
 Overhead cost is usually taken as a certain percentage of the total cost. For this
project 10% of the total cost is adopted.
table 2. 2 Optimization Techniques
Types of Yield Price Selling Input Labor Labor Tillage Total Over Profit
crops Qui/ha per Birr/ha cost red’s cost O&M cost cost head Birr/ha
Qui Birr/ha man- Birr/ha Costs Birr/ha Birr/ha cost
day/ha Birr
Potato 210 400 84000 1500 100 2000 100 250 3850 385 79765
Maize 75 500 37500 4000 90 1800 100 400 6300 630 30570
Tomato 400 500 20000 2000 100 2000 100 300 4400 440 15160
Barely 85 500 42500 900 45 900 100 450 2350 235 39915
Pepper 225 600 13500 2000 100 2000 100 280 4380 438 8682

Season one crops are potato, maize Tomato, barely and pepper. For the second season
these crops use too. By considering the most staple food for the local people, profitability of
the crops and water requirements of the crops, take 100% of total area which is irrigated
by surface irrigation method.
Let X1 = amount of hectares of land for potato
X2 = amount of hectares of land for maize

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X3 = amount of hectares of land for tomato

X4 = amount of hectares of land for barely
X5 = amount of hectares of land for pepper
Optimization for season one crops
Season one surface irrigation
Objective function
Maximization of profit

Constraint functions

<= 1000ha (total available area irrigated by furrow irrigation)

X1>=299ha (profitable crop)

X2>=250ha
X3>=200ha
X4>=150ha
X5>=100ha
Non negative constraints
X1, X2, X3, X4, X5>= 0
Optimization by liner programming
X1>=300ha (profitable crop)
X2>=250ha
X3>=200ha
X4>=150ha
X5>=100ha
If this much area is used , the profit is maximized to 4145950.
When the calculated area changed in percent it will become like the following table.

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table 2. 3 Area of each crop

Types of crops Area (ha) Area in %
Potato 300 30%
Maize 250 25%
Tomato 200 20%
Barely 150 15%
Pepper 100 10%
Total 1000 100%

2.7 Crop evapotranspiration (ETC)

Mathematically, it can be calculated as:

Where, ETo= Initial crop evapotranspiration

For this project we adopt the Penman-Monitith equation to calculate the reference crop
evapotranspiration. This equation considers the climatic parameters such as maximum
and minimum temperature, relative humidity, wind speed and sunshine hour. We
calculate ETc based on cropwat 8 program package and kcvalue.
The calculation procedure for crop evapotranspiration, ETc, consists of:
 Identifying the growth stages, determining their length and selecting the
corresponding Kc coefficient.
 Adjusting the selected Kc coefficient from frequency wetting or climatic conditions
during the stage.
 Constructing the crop coefficient curve (allowing) one to determine Kc values for
any period during the growing period.
Calculating ETc as the product of ETo and Kc

2.7.1 Crop Coefficient (KC)

The crop coefficient is used to relate the potential evapotranspiration (ETo) to the
evapotranspiration of the crop (ETc). The Kc value varies predominantly with the specific
crop characteristics and only to a limited extent with climate. This enables the transfer of

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standard value for Kc between location and climates. Different crops have different crop
coefficients. The changing characteristics of crop cover the growing season also affect the
crop coefficient, Kc. The following are factors affecting crop coefficient.
 Crop type
 Climate
 Soil evaporation
 Crop growth stage

figure 2. 1 Crop coefficient curve

Calculation of crop evapotranspiration using crop coefficient (KC)

The crop coefficient incorporates crop characteristics and averaged effects of evaporation
from the soil.
The Kc values with their corresponding base period of different crops that grown on the
Ribb irrigation project are tabulated as follows (according to cropWat8 ).

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table 2. 4 Kc values for the selected crops

Crop Planting Harvesting Kc values
Date Date Total Crop
Kc Kc Kc
period (Days)
initial mid End
Potato 02/03/201 09/07/201 0.5 1.15 0.75 130
2 2
Maize 05/03/201 07/07/201 0.3 1.2 0.35 125
2 2
Tomato 07/03/201 29/07/201 0.6 1.15 0.8 145
2 2
Barely 09/03/201 06/07/201 0.3 1.15 0.25 120
2 2
Pepper 11/03/201 13/07/201 0.6 1.05 0.9 125
2 2

Since we use similar crop for season 2 we have the same Kc value
But the values for Kc(initial), Kc (mid) and Kc (end) in the above table represents those for
sub humid climate with an average day time minimum relative humidity (RH min) of about
44%.

2.8 Irrigation requirement of crops (IR)

It is defined as the part of water requirement of crops that should be fulfilled by
irrigation.
IR=CWR-(ER+S+GW)

2.8.1 Effective rainfall

It is defined as the rainfall that is stored in the root zone and can be utilized by crops. All
the rainfall that falls is not useful or effective. The different methods used to calculate ER
from monthly total rainfall data are as follows;

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1. Fixed percentage effective rainfall

The effective rainfall is taken as affixed percentage of the monthly rainfall
ER=80% of total rainfall
2. Dependable rainfall
An empirical formula developed by FAO based on analysis for different arid and sub-humid
climates. This formula is as follows
ER=0.6*total rainfall -10 ----------------for total rainfall<70mm
ER=0.8*total rainfall-24 ----------------for total rainfall>70mm
3. Empirical formula for effective rainfall
This formula is similar to FAO formula (see dependable rainfall method above) with some
parameters left to the user to define. The formula is as follows;
ER=a*total rainfall-b ----------------total rainfall<Z mm
ER=c*total rainfall-d ----------------total rainfall>Z mm
Where a, b, c, d and Z are variables to be defined by the user.
4. Method of USDA soil conservation service
The effective rainfall is calculated according to the formula developed by USDA soil
conservation service which is as follows.
ER=total rainfall*(125-0.2*total rain fall)/125-------total rainfall<250mm
ER=125+0.1*total rainfall -------total rainfall>250mm
table 2. 5 Determination of ER through different methods in mm
Month Total rainfall, mm Dependable USDA Fixed,(use 80%)
Jan 46.1 17.66 42.70 36.88
Feb 44.3 16.58 41.16 35.44
Mar 74.6 35.68 65.70 59.68
Apr 148.9 95.12 113.43 119.12
May 140.6 88.48 108.97 112.48
Jun 76.9 37.52 67.44 61.52
Jul 69.5 31.7 61.77 55.6
Aug 74.1 35.28 65.31 59.28
Sep 99.0 55.2 83.32 79.2
Oct 124.9 75.92 99.94 99.92

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Nov 75.0 36 66.00 60.0

Dec 51.1 20.66 46.92 40.88
From the above different methods, the dependable is preferable to find the ER for safe
design because it is the smallest of all other ERF calculation method which enables to
design the canal for the worst condition.

2.8.2 Ground water contribution (GW)

The actual contribution from the ground water table is dependent on the depth of ground
water table below the root zone and capillary characteristics of soil. For clayey soils the
rate of movement is low and distance of upward movement is high whole for a light
textured soil the rate is high and the distance of movement is low. In this project the soil is
medium but there is no information about the ground water contribution of the project
area.

2.8.3 Stored soil water

It is the moisture stored in the root zone depth in the soil before the crop is planted. The
source this moisture is either from the rain fall that occur before sawing or it may be the
moisture that remained in the soil from past irrigation. It is also available for meeting the
evapotranspiration need of a plant and contributes to the consumptive use of water and
should be considered from the water requirements of crops in determining irrigation
requirements. However, it could be neglected in the planting stage as it is difficult to
estimate and its contribution is not generally significant.

2.9 Net irrigation requirement (NIR)

The irrigation water requirement (IR), is the water which must be supplied to the crop
plant to ensure that it received its full water requirement or a predetermined portion of
it. If irrigation is the sole source of water, the irrigation requirement will be at least equal
to the water requirement. (ETcrop) and may often have to be greater to allow for possible
losses in the irrigation system, such as leaching, deep percolation or uneven distribution.

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On the other hand, if the plant is receiving some of its water from other sources such as
rainfall, stored water in the soil, or underground seepage, the irrigation requirement may
be considerably less than the water requirement.

Mathematically, it can be expressed as

Where ETc= crop evapotranspiration

Peff = effective rain fall

Gw = ground water contribution

Sw= stored soil water

The project has two cropping seasons. The first season is from to and the second
season is from to .
Sample calculation of weighted NIR season one crop
WeightedNIR=[(Area%)*NIR(mm/day)](Potato)+[(Area%)*NIR(mm/day)](Maize)+[(Area
%)*NIR(mm/day)](Tomato)+[(Area%)*NIR(mm/day)](Barely)+[(Area%)*
NIR(mm/day)](Pepper)
The Area in percentage is calculated from the optimization calculation.(Refer table 2.3)
Weighted NIR= 2.9*0.3+1.6*0.25+2.3*0.2+2.6*0.15+3.0*0.1=2.42mm/day
Similarly, for season two for the same crop
Weighted NIR=1.0*0.3+1.9*0.25+2.6*0.2+3.1*0.15+3.4*0.1=2.1mm/day

2.10 Irrigation efficiency

To account for losses of water during conveyance and application to the field an efficiency
factor should be incurred when calculating the irrigation water requirement.

Field application efficiency (Ea)

This is the ratio of water directly available to crop and that received at the field inlet.

Field canal efficiency ( Eb)

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This is the ratio between water received at the field in let and that received at the inlet of
the blocks of the fields

Conveyance Efficiency (Ec):-

This is the ratio between water received at the inlet to the block of fields and that released
at the project headwork

Project Efficiency:

It indicates the overall efficiency of the system from the head work to the finall use by
plants for consumptive use.

EP= Ea*Eb*Ec

The values of Ea,Eb&Ec are recommended for different conditions as shown below

table 2. 6 Recommended values of efficiency

Field application efficiency…………………………………………….. ( Ea)
Surface method of irrigation
-Light soil …………………………………………………………………Ea=0.55
-Medium soil………………………………………………………………Ea= 0.7
-Heavy soil…………………………………………………………………Ea= 0.6
2) Field canal efficiency………………………………………………… ( Eb)
For blocks larger the 20 ha
Unlined …………………………………………………………………..Eb=0.8
Lined ……………………………………………………………………...Eb= 0.9

-For blocks upto 20 ha

Unlined ……………………………………………………………………Eb=0.7
Lined ……………………………………………………………………….Eb=0.8

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Conveyance efficiency………………………………………………… ( Ec)

-For command are >10,000ha
Based on predetermined schedule …………………………………..Ec=0.7
Based on adcance request ……………………………………………Ec=0.65
For 1000ha command area …………………………………………...Ec = 0.8
(Source ICID / ILrI Recommendations (From FAO))

Assumption to select the efficiencies;

The irrigation method is surface irrigation method on medium soil.

Blocks above 20ha unlined and lined

For command area 1 000ha & predetermined schedule.

Based on the above assumptions,

Ea = 0.7 & Eb=0.8 for unlined and Eb=0.9 for lined Ec=0.8

Project efficiency, Ep = Ea*Eb*Ec

For unlined canal=0.7*0.8*0.8= 0.448

For lined canal= 0.7*0.9*0.8=0.50

2.11 Gross irrigation requirement (GIR)

The quantity of water that should be diverted from a given source to irrigation field or it is
the amount of water required to fulfill the field irrigation requirement plus the amount of
irrigation water loss in conveyance through the canal or pipes system and in water
application and can be obtained by the following equation :-

Where: - GIR- Gross Irrigation Requirement

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NIR- Net Irrigation requirement

EP- Project Efficiency

For unlined canal=0.7*0.8*0.8= 0.448

Season one=

Season two=

For lined canal= 0.7*0.9*0.8=0.504

Season one=

Season two =

2.12 Irrigation Schedule

Irrigation scheduling is the practice of fixing irrigation depth and irrigation interval based
on water balance of the field. Scheduling is affected by a number of factors, for example,
during early stage of growth plants need less irrigation depth but frequently application;
whereas during late stage of growth they require more depth but can be applied less
frequently. This is mainly due to variation in rooting depth, evapotranspiration and other
factors.

Scheduling is affected also by soil characteristics because different soils have different
water holding capacities. The soil moisture is not allowed to be depleted up to the wilting

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point, as it would result inconsiderable fall in crop yield. In other words, the total available
water (i.e. water held in the soil b/n field capacity and permanent wilting point) is not
readily available for plant use but only a certain fraction of it.

RAM= (FC-PWP)*P=290mm/m*60=174mm/meter

Where, RAM- readily available moisture, mm

P – depletion factor, %

FC-PWP – the total available water, mm/m (taken from cropwatt8 version)

Irrigation should be supplied as soon as the moisture falls up to optimum level known as
MAD or moment allowable deficit (hence, fixing irrigation frequency) and its quantity
should be just sufficient to bring the soil moisture up to field capacity (hence, fixing
irrigation depth).

2.12.1 Depth of irrigation (d)

It is the quantity of water that should be applied to bring the soil moisture to field capacity.
Hence it is the depth of water that can be stored in the root zone between the allowable
level of soil depletion for the given crop and the field capacity.

Depth of irrigation applied (d) is equal to the readily available soil water times the root
depth (D). An application efficiency (Ea.) is always added to account for uneven application
over the field.

d= D * (FC - PWP) * P

2.12.2 Irrigation interval (I)

It is the time gap between two successive or consecutive irrigations. Irrigation should be
applied time because delayed irrigation could cause considerable reduction in crop yield,
particularly at stages when the crop is sensitive to water stress. Irrigation interval should
take into account the soil water depletion requirement of the crops which vary with
evaporative demand, rooting depth, soil type and other factors.

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Where, I- irrigation interval

P- Fraction of available soil water = 60%

(FC-PWP) – The total available water, 290 mm/m

ETc (peak)- peak crop water requirement

The irrigation interval will be calculated in the following table

table 2. 7 Irrigation interval calculation

Crop season Root RAM dnet ETc Interval
depth (mm/m) (mm) peak I
(m) mm/day (day)
Potato 1 0.6 104.4 5.19 20
2 0.6 104.4 5.19 20
Maize 1 1.0 174 5.36 32
2 1.0 174 4.82 36
Tomato 1 1.0 174 5.13 33
2 1.0 174 174 4.59 37
Barely 1 1.1 191.4 5.17 37
2 1.1 191.4 4.64 41
Pepper 1 0.8 139.2 4.68 29
2 0.8 139.2 4.19 33

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The peak net scheme irrigation requirement has been found to be 0.39l/s/ha from crop
watt. The total irrigable land of area was fixed as 1000ha during the feasibility study of the
project. The design discharge in the main canal is calculated as follows.

Where project efficiency(Ep)=Eb*Ec*Ea.

As Ea has already have been considered in the calculation of net irrigation requirement in
the cropwat8 computer package, only the values of Ec and Eb are taken for design
discharge calculation. The crop watt computer package considers Ea of 70% in computing
net irrigation requirement. Thus,

`Ep=Eb*Ec

For lined………………….0.9*0.8=0.72

For unlined………………0.8*0.8=0.64

Since the main canal is unlined, its design discharge is calculated as follows.

Since the irrigation water is not applied for 24hr, it needs to multiply the design discharge
by the working time factor, adopting 16hours of irrigation, the design discharge becomes,

Design discharge

2.12.3 Rotational irrigation

To be economical the canal should be decreased. This is done by applying rotational
irrigation method; to do this take a minimum irrigation interval to satisfy the water need of
the other selected crop.

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The minimum irrigation interval is 20 day. The irrigable land is divided in to 5 blocks.
Each block covers 200ha of land.

The design discharge for the gross area is 0.9141m3/s.

dnet for the crop which have minimum irrigation interval is 104.4mm.

The volume of water for each block is calculated as follows

Where, A= the area of one block(ha)=200ha

V=volume of water for one block(m3)

dnet= the depth net of irrigation(mm)=104.4mm

From this volume the time of irrigation for each block is calculated as follows.

Where; Q= discharge of the gross area.

V=volume of water for one block (m3)

t=the required time for a unit block

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So adopt 4 days for one block.

Each block irrigate for 4 day and one day for operation and maintenance for the system.
The irrigation return to the first 200ha block is after 20day; so water stress is not formed in
the soil.

CHAPTER THREE

IRRIGATION CANAL SYSTEM DESIGN

3.1 General
Irrigation scheme which utilize weir, a barrage or a storage reservoir necessitates the construction
of network of canals. The entire system of canals (main and branches) distributed over the field are
to be designed properly for certain realistic value of maximum discharge, that must pass through
them so as to provide sufficient irrigation water to the command area; the success of the flow
irrigation depends on the perfect design of the network of canals

The design of canals is carried out in considerations of Kennedy’s and Lacey’s theory which are
based on the characteristics of sediment load i.e. (silt) in canal water.

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The design consideration of irrigation canals naturally varies according to the type of soil, again the
velocity of flow in the canal should be critical (i.e., none silting and scouring).

3.2 Canal Alignment

A canal has to be aligned in such a way that it covers the entire area proposed to be irrigated. It is
clear that irrigation water, (in flow type) should reach the field by gravity to accomplish the
requirement. Irrigation canal is always aligned in such a way that the water gets proper command
over the whole irrigable area.

General Consideration for Canal Alignment

The following points should be kept in mind in alignment of canals

 The alignment should not pass through the valuable lands, religious places, villages, etc. to
avoid unnecessary compensation and unwanted conflict.
 The alignment should be short as far as possible, but to make it short the alignment should
not be taken through the area where irrigation is not yet all possible.
 The alignment should be straight as far as possible.
 The alignment should cross the natural stream, drainage, etc approximately at the right
angles. At the crossing point, the width of the drainage should be minimum and the banks
should be well defined.
 The alignment should not involve heavy cutting or banking.
 The alignment along the ridge line or water shade line is very good as the water shed canal
can irrigate the area on both the side. Moreover, cross drainage work may be avoided.
 The alignment should be such that the maximum area may be irrigated with minimum
length of the canal.
 The alignment should not pass through the water logged area because the canal may be
collapsed due to the heavy moisture in the area.
 The alignment should not pass through the sandy soil as the percolation in the loss soil will
be more and the duty of the soil will be less.
 The average slope of a main canal is flatter than the average slope of a branch canals.
Having the above considerations the proper canal alignments have been made for the given
topographical map.

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The main canal starts from the weir site and divided in to five secondary canals and then each
secondary canal divide in to five tertiary canals depending on topography of the irrigable area. All
field canals are supplied by branched canals; which are generally governed by the orientation and
direction of field, and the method of irrigation.

3.2.1 Main canal alignment

The layout of the primary canal is based on the minimum drawdown level of the storage,
topography of the command area, and expected maximum cultivable command area. In addition,
the length of the canal should be small as much as possible. Main canal is the longest and the largest
canal in the system and it takes off from headwork.

3.2.2 Secondary canal alignment

The layouts of secondary canals depend on the layout of the tertiary and primary canals. Major
considerations of the choice of layout of secondary canals are:

 Divide the command area in to suitable size for layout and management
 Convey water in efficient way to each tertiary canal perpendicularly
 To cover all suitable command area even in hills
 Minimum length of canals
 Minimum number of falls, cross drainage structures.

3.2.3 Tertiary canal alignment

Tertiary canals are smaller canals in Ribb irrigation system network, which supply water to field
canals. At the same time, it carries the full supply water to irrigate the field. The tertiary canal
layout is designed by considering

 The method of irrigation

 The easiness of operation and management
 The slope of cultivable land
 Minimum number of tertiary canals
 The irrigation of more area in gross command
 Minimum drainage and canal infrastructures
 And a canal should be aligned on a watershed or ridge as far as possible because it
ensures irrigation on both sides of the canal and avoids cross drainage works.

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By using the above considerations, the tertiary canal layout is best to be across contour. It has the
advantage of irrigating both sides of the canal. Thus, the number of tertiary canals decreases per
unit area of land. And by using contour field canals, the minimum slope and enough length of
furrow is assigned. The tertiary canals have fall in each stripe of cultivatable area. However, the
design of fall is small and economical than fall exist in secondary and main canal.

Cultivable field area by tertiary canal

The alignment of tertiary canals as discussed in the above paragraphs is aligned across contour, to
irrigate both sides. To minimize the number of canal density in the cultivated area, the length of
tertiary canals is the maximum length.

The length of furrow and topography of land govern the space between tertiary canals. According to
FAO, the maximum allowable length of furrow for loam and loam soil is 300m.

3.3 Canal design

3.3.1 General
To take away water from the canal headwork such as weir, barrage, storage reservoir or storage
dam to the field; a well-designed distribution consisting of a network of canals is required.

Based on the water requirements of crops on the area to be irrigated, the entire system of main
canal, secondary canal, tertiary canal and field distributaries should be designed properly. The
canals are designed for a certain realistic value of peak discharge that must pass through them, to
provide sufficient irrigation water to the command area. Therefore, the design of canal is based on
the irrigation water requirement and irrigable area. Depending upon the soil type in Ribb irrigation
project unlined canal was recommended.

Design parameters

Duty: - Duty is the capacity of water to irrigate the land. It is the ratio of the area of the land to be
irrigated to the quantity of water required. The field water supply of the project estimated by using
“cropWat8 ”. The duty of canal is 0.39l/s/ha.

Time factor:-Time factor is the ratio of the number of days the canal actually runs during a
watering period to the total number of days of the watering. Take 16hr working time out of the 24
hr. of the day and the rest 8hr. used for to drain the irrigable land and other purposes.

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Slope: - Slope is fixed by the design discharge and silt factor or velocity. A steeper slope with
maximum permissible velocity will be more economical, but the FSL will be lower. Additionally the
design slop is flatter than the natural available slope. Fall is provided to adjust the slope, but the
number of falls must be of minimum.

Side slope for unlined canal

The slope to be given to the sides depends on the angle of the internal friction for a particular
soil .in other word the slope adopted should also be remembered that the side slopes adopted in
cutting and filling are not the same.

table 3. 1 Side Slope for Various Soils

Soil type Side slope (Horizontal : vertical )

Cutting Embankment

Sound rock 0.125 :1 1.5: 1

Poor rock 0.5: 1 1.5: 1

Gravelly soil 0.75 : 1 1.5: 1

Compact clay 1 : 1 1 .5 : 1
soil

Clay soil 1.5: 1 2:1

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Loam soil 1.5: 1 2:1

Sandy loam 2:1 to 3:1 2:1 to 3:1

soil

Sandy soil 3 :1 4:1

(Sahasrabudhe, 1994 page 197)

Longitudinal slope

Canal bed slope depends up on the slope of the natural ground for economy in the earth work, and
for structural safety it depends on the permissible velocity.

Roughness Coefficient

The roughness of the canal bed affects the velocity of the flow. The roughness is caused due to the
ripple s formed on the bed of the canal. So the roughness coefficient was introduced by the R.G
Kennedy to calculate the mean velocity flow.

table 3. 2 The Value of n for different type Of bed material.

Material Roughness coefficient (n)

Wood 0.013 to 0.0165

Steel 0.0123 to 0.018

Concrete 0.013 to 0.018

Masonry 0.02 to 0.036

Earth 0.0225 to 0.035

[Sahasrabudhe, 1984 page 136]

Design discharge

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Discharge capacity of canal is fixed by considering the irrigation area, duty, application or working
time, and efficiency of conveyance and application. The design capacity of main canal is to irrigate
200ha at time, by assuming rotational water application by dividing the total irrigable area in to five
roots (blocks).

For future expansion and safety 12% allowance discharge

Qd=0.12*0.183m3/s=0.205m3/s

Bed width to Depth ratio for Q > 0.2m3/s is

B/D = 1.76 * Q0.35

Free board from Lacey’s equation

FB = 0.2 + 0.15 * Q0.35

Efficiencies on the project, conveyance efficiency, EC = 0.8,

Distribution efficiency, Ed = 0.8 and application efficiency, Ea= 0.7

Permissible velocity

Permissible velocity is the one which can be resisted by the canal boundary surfaces. This velocity
is taken depending on the soil type. The velocity of design canal should be self-cleaning; in other
word, it should not deposit silt on canal, and should not also scour the bed and sides of the canal.
The maximum value of mean velocity must be safe against erosion. Based on soil type that is found
in the irrigable area.

table 3. 3 Permissible velocity (unlined canal)

S.no Type of material Permissible velocity(m/sec)

1 Loam clay soil or loam 0.38 to1.37

2 Clay soil 0.41 to 1.67

4 Sandy clay 0.52 to 1.83

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5 Ordinary 0.60 to 0.90

6 Gravel hard rock >3

[Arora 2003]

The maximum value of mean velocity must be safe against erosion. Based on soil type that is found
in the irrigable area i.e. loam clay or loam soil the permissible velocity lies from 0.38m/s to
1.37m/s.

3.3.2 Main canal design

Take permissible velocity 0.4m/s (for loamy clay soil)

B=1.011D

0.5125=2.511 D=0.45m

B=1.011*0.45=0.46m

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S=0.000635=

Take approximately S

Where: B = the bottom width of the main canal

D = the depth of water in the main canal

m = the side slope of the main canal

R = the mean hydraulic radius of main canal

A = the area of main canal section.

P = the wetted perimeter of the canal section

S = the bed slope of the main canal.

n=roughness coefficient=0.025(for earth material table)

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figure 3. 1 Cross section of unlined main canal

3.3.3 Secondary canal design

The design principle of the secondary canal is the same as that of the main canal using the Kennedy
theory. The secondary canal is designed, so that it can have the capacity to irrigate the respective
command area. Since the irrigation system is rotational the discharge of the main canal is the same
with that of the secondary canal. There for the depth, bed width and slope are similar with that of
main canal. However; the length of the main canal greater than the length of the secondary canal.
This used for full rotational system of irrigable land. To facilitate this activity there are five
secondary canals with the same parameter. Each secondary canal has a capacity to irrigate 200ha.

3.3.4 Tertiary canal design

The design principle of tertiary canal is the same as that of the secondary canal. There are 25
tertiary canals along the entire area. The cross sectional dimensions is calculated as follows. Since
there are 5 tertiary canals in each secondary canals the design discharge of tertiary canal is one five
of the secondary canal.

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Take permissible velocity=0.38m/s

B=0.575D

0.108=2.075

D=0.23m

B=0.575D =0.575*0.23=0.13m

S=0.00162=

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Take approximately S

Where: B = the bottom width of the tertiary canal

D = the depth of water in the tertiary canal

m = the side slope of the tertiary canal

R = the mean hydraulic radius of tertiary canal

A = the area of tertiary canal section.

P = the wetted perimeter of the canal section

S = the bed slope of the tertiary canal.

n=roughness coefficient=0.025(for earth material table)

figure 3. 2 cross section of tertiary canal

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3.4 Access Roads

Access roads are provided in irrigation schemes layout for the purpose of facilities for the
movement of machine and the farm from the irrigation command area.

Main access road:

The main access road may be laid parallel to the primary canal starting from the diversion weir site
up to the end of the irrigation command area; this access road will have sub base and gravel
surfacing

Secondary and Tertiary access roads

These access roads are close to each plots of area which are parallel to all secondary and tertiary
canals.

Generally

Inspection road is used for the purpose of inspection, repair and maintenance of canal; in addition,
it is also used for community transport facility. The Inspection road is provided at 0.5m higher than
the FSL of canal. It has been constructed by compacting and filling the excavated soil of the canal.

3.5 Appurtenant structure

3.5.1 Culverts
Culverts are the structures constructed at the crossing of roads, drainages & irrigation canals.

Making the water flow freely .It consists of a barrel which can be circular or rectangular on entrance
and exit flow in culverts can be either free flow (open channel) or pipe flow (pressure flow).

Whenever road has to cross on existing drain or canal or some times when a drain has to cross an
existing road small bridge, culvert is constructed at the point of crossing .

Design of Culvert along main canal

The design of culvert is based on orifices formula.

table 3. 4 Available Data’s for the design of culvert

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Discharge( Bed width Depth(m) Side Velocity(v) Velocity Roughn

m3/s) slope(z) head, hv ess(n)
(m) (m/s)
(m)

0.205 0.46 0.45 1.5 0.4 0.013 0.025

The difference in elevation between the u/s culvert, the inlet and d/s out let is equal to the friction
head loss through the pipe.

hf = L*S2

Where L= 6m culvert length which is equal to main access road, width, adopted standard width of
gravel road for all main national standard (RR30)

Design Procedure

a) Hydraulic flow of culvert

Select culvert dimensions, width b2=0.46m

Depth d2=0.45

Velocity in the culvert,V2

, A=b2*d2=0.46*0.45=0.207m2

V2=0.20/0.207=0.97m/s

V22 0.97 2
Velocity head in the culvert,hv2=  0.048m
2 g 19.62
Wetted perimeter, P2=b2+2d2=0.46+2(0.45) =1.36m
A 0.45 * 0.46
Hydraulic mean radius, R=  0.152m
P2 1.36
Longitudinal bed slop,s
For uniform slope is the same as energy slope
n * V2 2 0.014 * 0.97 2
Bed slope in culvert, S 2 ( 2/3
) ( ) 0.0023
R 0.152 2 / 3

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Where n=0.014, manning roughing coefficient for concrete (Garg, 2003)

The difference in elevation between the u/s culvert, the inlet and d/s out let is equal to the friction
head loss through the pipe.

hf = L*S2

Where L= 6m culvert length which is equal to main access road, width, adopted standard width of
gravel road for all main national standard

hf = 6*0.0023m=0.0138

b) Drop of water surface at U/S and D/S of culvert

V22 _ V12
Drop of water surface at the inlet of the culvert h1 1.5( )
2g

Where, V2-velocity of flow in culvert

V1-velocity of flow in canal

0.97 2  0.4 2
h1 1.5( ) 0.059
2 * 9.81

Drop of water surface at D/S of canal section

0.3(V22  V12 ) 0.3(0.97 2  0.4 2 )

h2   0.0119
2g 19.62

c) Elevation

Canal bed elevation at U/S of canal =1792.7m from top map

Water surface elevation at U/s canal =1792.7m+0.45m=1793.15m

Water surface elevation at the culvert inlet=1793.15m-⩟h =1793.15-0.059=1793.091m

 Bed elevation at culvert Inlet: 1793.091m-d2=1793.091m-0.45m=1792.64m

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 Bed elevation at culvert outlet: 1792.64m-hf=1792.64m-0.0138m=1792.63m

 Water surface elevation at culvert outlet: =1792.63m+ d2=1792.63m+0.45m=1793.077m
 Water surface elevation at D/S canal,=1793.077+∆h2 =1793.077 +0.0119=1793.09m
 Bed elevation at d/s canal= 1793.09 –d1 =1793.09 -0.45=1792.64m

d) Total head loss, HT

HT =Entrance loss+ friction loss in culvert +Exit loss

HT = 0.5∆hv+hf+0.7∆h +hf=

e) Check water surface elevation difference between u/s & d/s canals,

HT =1793.15-1793.09 =0.06m ok

3.5.2 Canal Drop

Whenever the available natural ground slope is steeper than the designed bed slope of the channel,
the difference is adjusted by constructing vertical falls or drops in the canal bed at suitable interval
[Garge, 1999 page, 615]

Canal drop is a structure Constructed on a channel to lower down the water level and the bed level
of the channel. Because of the drop of the water at the fall, the potential energy of the water is
converted in to the kinetic energy, which may damage the D/S portion of the canal by scouring
action.

The canal fall is therefore designed to dissipate the surplus energy. [Arora, 2002]

For this project, a rectangular weir with raised crest from the category of vertical drop has been
adopted.

Available data for the design of canal drop;

Discharge U/S, Qd = 0.205m3/s

Discharge D/S, Qd = 0.205m3/s

Drop , adopted , HL=1m

Bed width U/S b=0.46m

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Bed width D/S =0.46m

Full supply level U/S=1793.15m

Full supply level D/S =1792.15m

Bed level U/S =1792.7m

Bed level D/S=1791.7m

Water depth U/S, D1 =0.45m

Water depth D/S, D2 = 0.45m and neglect the velocity of approach

Design Procedure of canal drop

1) For rectangular crest (discharge less than 14m3/s)p

Length of crest, L= bed width = b1=0.46m

Assume top width, B=0.2m

H 1/ 6
Q 1.835L( H ) 3 / 2 * ( )
B

H 1/ 6
0.205 1.835 * 0.46( H ) 3 / 2 * ( ) → H = 0.36m
0.2

R.L of crest =U/S FSL-H = 1793.15-0.36=1792.79m

Height of crest above D/S bed, d= crest level - D/S bed level = 1792.79-1791.7=1.09m

Top width of crest wall,

The assumed top width is correct and to be provided.

Bottom width, m

Where G = 2.24m

2) Cistern

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The depth of cistern;

RL of cistern = d/s bed level –x = 1791.7-0.31=1791.39m

1/ 2 1/ 2
The length of cistern, LC 5 * ( H  H L ) 5 * (0.364  1.0) 5.84m

Impervious floor design

Maximum seepage heads Hs =Crest level- D/S bed level

Hs= 1792.79-1791.7=1.09m

Total creep length, L= Take Bligh creep coefficient, c=8

L= 8*1.09=8.72m

D1 0.45
Depth of U/S cut off =  0 .6   0.6 0.75
3 3

D2 0.45
Depth of D/S cut off =  0 .6   0.6 0.825
2 2

Vertical creep length =2(0.75+0.825) =3.15m

Length of impervious floor, b= L-3.15=8.72-3.15=5.57m

Minimum length of D/S floor

Ld=2(d2+L2)+HL=2(0.45+0.825)+1=3.05m

Length of U/S floor =b-Ld-D1=5.57-3.05-0.75=1.77m

3) Thickness of impervious floor

a) Residual head as the D/S toe of the crest wall

Water Resources And Irrigation Engineering Final Year Project 2011 Page 43
 Canal Network Design on Ribb Irrigation Project

Thickness of the floor

b) Residual head at 2m from the toe of the crest wall

Hr 3.45
Thickness of the floor   2.79
G  1 1.24

c) Residual head at end of D/S floor

Hr 0.375
Thickness of the floor,  0.302m
G  1 1.24

Providing nominal thickness for U/S floor=0.4m

4) U/S wing wall

Top level of U/S wing wall = 1793.15+0.5 =1793.65m

Top level of D/S wing wall =1792.15+0.5= 1792.65m

figure 3. 3 Cross section of vertical drop

Water Resources And Irrigation Engineering Final Year Project 2011 Page 44
 Canal Network Design on Ribb Irrigation Project

3.5.3 Settling Basin

Settling basin is a basin of relatively large cross section than the canal and is provided to remove
sand and heavier silts from irrigation water.

It provided just downstream of weir structure to remove sediments and flushed back to the natural
drainage through the settling sluice (gated structure).

The size of a basin depends on discharge and velocity. Flow velocity in the basin should is 0.38m.
The deposited sediment in the basin will be disposed off natural drainage.

Dimensions are determined by manning equation:

V = 1/n*R2/3S1/2

For simplicity of construction in Ribb Irrigation Project rectangular silting basin is selected

Where; V – Recommended velocity = 0.4m/se

b − Width of settling basin

d – Depth of settling basin

S – Longitudinal slope of the basin (1/1500 from wood’s table based on discharge and
topography)

n – Roughness coefficient (n=0.016 for concrete see)

For Q < 0.2m3/sec, b/d = 1

For Q > 0.2m3/sec, b/d = 1.76*Q0.35 [USBR]

The discharge enter to the settling basin is equal to 0.205m3/sec

Therefore b/d = 1.76*0.2050.35 =1.011 → b=1.011d

From the above equations 0.4m/s=1/0.016* (bd/b+2d)2/3*s1/2

0.4m/s=1/0.016* (1.011d2/1.011d+2d)2/3*(1/1500)1/2

Water Resources And Irrigation Engineering Final Year Project 2011 Page 45
 Canal Network Design on Ribb Irrigation Project

d = 0.51m take d =1m because it should be greater than the depth of the main canal to accumulate
the flow discharge.

b = 1.011d b = 1.011*1m = 1.011m

The length of the settling basin L = 2.5*b = 2.5*1.011m = 2.53m [Basak]

figure 3. 4 Sections of settling basin

3.5.4 Canal out Let
· Canal out let is the structure built on the bank of the distribution channel through which
water is supplied to a field channel , it can be also be used for discharge measurement being
supplied to the crops .

· Semi modular out lets or flexible out lets is selected for the project because of its
discharge depend only on the water surface level .

· Canal out lets are provided for tertiary canals.

Design procedure of canal outlet:

Typically all sample calculation for tertiary canal TC1-1

Pipe out let discharges free

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 Canal Network Design on Ribb Irrigation Project

Data input:

Qd= 0.041m3/s

C = 0.62 (for free falling).

Assume h = 0.5m

= 0.62*a*(2*9.81*0.5)1/2 =0.041

If 9cm diameter pipe is selected 0.041m3/sec = 0.62*3.14*0.092*(2*9.81*h)1/2/4

h= 0.344 <0.5hence OK!

The design of out let have the same procedure as that of tertiary canal calculated

3.5.5 Division box

Division box is used to divert water from one canal to another subcanal.

Sample calculation

Station at the end of main canal

To divided main canal into two secondary canals

Water Resources And Irrigation Engineering Final Year Project 2011 Page 47
 Canal Network Design on Ribb Irrigation Project

figure 3. 5 Division box

Available data

QO = QMC = Discharge through main canal = 0.205m3/s

Q1 = QSC1 = Discharge through secondary canal-2.1 = 0.205m3/s

Q2 = QSC2 = Discharge through secondary canal-2 = 0.205m3/s

A broad crest formula to divide proportionally is used

3
Q C * L * H 2

Where: Q = discharge over rectangular weir sill (m3/s)

C = discharge coefficient = 1.79

L = effective length of the crest opening in m

H = over flow depth (m)

Assuming that

-crest level and form are in the same direction

-equal coefficient of discharge and sill height for the divide canal

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 Canal Network Design on Ribb Irrigation Project

Assume dead height = 0.20m

Sill height = 0.20m

H = 0.40m

Q 0.205
L1 = 3 = 3
= 0.45m
1.79 * 0.40
2
CH 2

L2 Q1 Q1
= => L2 = L1
L Q2 Q2

0.205
= 0.45 * = 0.45m
0.205

B b  2 * mD

Where: b = width of main canal = 0.46m

M = side slope = 1.5:1

D = depth of main canal = 0.45m

B = width of division box

B 0.46m  2 * 1.5 * 0.45m

B= 1.81m

Division box at secondary canals

Q = 0.205m3/s

B = 0.46m

M = 1.5:1

D = 0.45m

Dead height = 0.20m

Water Resources And Irrigation Engineering Final Year Project 2011 Page 49
 Canal Network Design on Ribb Irrigation Project

Sill height = 0.10m

H = 0.30m

Q 0.205
L1 = 3 = 3 = 0.45m
C*H 2
1.79 * 0.40 2

L2 Q1 Q
L1 1
L1 Q Q2 = 0.45m.
= 2 => L2 =

B b  2 * mD

B 0.46m  2 * 1.5 * 0.45m =1.81m

All other division boxes at the inlet of tertiary canals are designed in the same way and size.
There are 25 total number of division boxes on secondary canals.

Note: In our case, to regulate the discharge, manually operating gates called vertical gate
made up of steel are installed at openings of L1 and L2 designed for division box

3.5.6 Design of cross drainage structures

The primary canal cross the river along its path at chain age of 0+900 and its design is shown below
and the design data are taken from previous work.

table 3. 5 Given data for the design of cross drainage structures

Canal Canal water depth=0.45m

Full supply discharge = 0.205m3/s Canal elevation level 1792.2

Full supply level = 1791.95 Drainage

Canal bed level = 1791.5 Bed level=1792.3m

Canal bed width = 0.46m

Canal side slope=1.5

Water Resources And Irrigation Engineering Final Year Project 2011 Page 50
Since the bed level of the canal is below the river bed level and the full supply level of the canal is
sufficiently below the bed level of the drainage bed level, hence the cross drainage work to be
constructed at the crossing will be a super passage. The design of super passage is to be done as
follow.

Step1 design of main canal water way

V=Q/A=0.205/0.5125=0.5m/s these show that the velocity is low which does not create further
erosion so that it can be earthen canal but to be economical we have to provide splay on the canal.

Providing a splay of 2:1 contraction on the upstream side, the length of contraction transition

= (0.46-0.3)/2*2=0.16m

Providing a splay of 3:1 on the downstream expansion the length of expansion transition

=(0.46-0.3)/2*3=0.225m

Length of flumed rectangular section of canal will be equal to the width of the drainage through as
worked out in the next step.

Step2 Design of drainage waterway

The length of drainage waterway should be determined by lacey’s equation, but the discharge of the
drain is not known and its width from the contour map to be 1.5m, providing piers having
thickness 0.5m on both side of the canal. Thus the length of rectangular portion of canal will be
2.5m.

Since the drainage has also been slightly flumed and kept lesser than its previous width, so let us
design its contraction and expansion length.

Assuming 2:1 convergence, we have the length of contraction transition

=1.5-1/2*2=0.5m

Assuming 3:1 splay in expansion we have the length of expansion transition

=1.5-1/2*3=0.75m
 figure 3. 6 Indicative plan of super passage crossing

Design of transitions for the drainage

a)Contraction transition

The transition is designed by on the basis of mitra’s hyperbolic transition equation

Bn.Bf .Lf
Bx = where Bf=1m
Lf .Bn  X ( Bn  Bf )

Bn=1.5m

Lf=0.5m

0.75
Bx=width at any distance from the flumed section=
0.75  0.5 x

For various value of x between 0 to 0.5m, values of b are worked as shown below
X 0 0.1 0.2 0.3 0.4 0.5

1 1.071 1.154 0.125 1.364 1.5

A) Expansion transition

The transition is designed by on the basis of Mitra’s hyperbolic transition equation

Bn.Bf .Lf
Bx = where Bf=1m Bn=1.5m and Lf=0.75m
Lf .Bn  X ( Bn  Bf )

1.125
Bx=width at any distance from the flumed section=
1.125  0.5 x

For various value of x between 0 to 0.5m, values of b are worked as shown below

X 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.75

1.125 1 1.047 1.098 0.154 1.216 1.285 1.364 1.452 1.5

Bx=
1.125  0.5 x 5 6

Structural design of supper-passage

figure 3. 7 Aqueduct
Use C-30MPa & =9.81KN/m3

Deformed steel bar with S-300MPa

Allowable stress in concrete and steel are:

For strength design

fc,allowable=11N/mm2 for compression due to bending

fs,allowable=(direct tension and bending)=130N/mm2

to control cracks

fct, allowable=1.44n/mm2 -for direct tension

2.02N/mm2 -for bending

-design constant of balanced section for flexural member

Design of vertical side wall h=0.75m

-maximum vertical movement developed at the base of the wall,

tension on water face

Then thickness of wall required by flexure

Consider thickness of side wall about twice that required by flexure

1st trial

T (wall) = 200mm

Effective depth of wall assuming bars and 40mm cover

Then, area of vertical tension steel required by flexure

Spacing of vertical bars required on water face

Provide vertical bar at 200mm c/c placed on water inner face of wall

Design of horizontal slab

1st trial

T (wall) = 200mm

Effective span of wall =2.5+0.2=2.7m

Weight of slab =0.25m*25KN/m2=6.25KN/m2

Weight of water on slab =0.75m*9.81KN/m3=7.36KN/m2

KN/m2

Net moment developed at the center of the slab (l=2.5m and h=0.75m)
Check thickness of slab for flexure

Therefore , trial thickness is adequate for flexure 25KN/m2

Then effective depth of slab assuming bars and 40mm clear cover

Area of tension steel required by flexure

Spacing of bars required on outer face at bottom

Provide bars at 450mmc/c place at the outer face of slab at bottom

Design of side wall as beams

Load from slab =

Self weight of side wall=0.2m*1.5m*25KN/m3=7.5KN/m

Total service design load on each wall =17.01+7.5=24.51KN/m

Then maximum moment 0f side wall as simply supported beam l=3m

Check depth of beam for flexure!

The required depth of beam with cover of 60mm

Effective depth of beam with cover of 60mm

and the area of tension steel required by flexure

Number of required= take 6bars

Therefore provide 2 bars in two layers placed at the bottom of the wall.
 CHAPTER FOUR

WATER APPLICATION SYSTEM

4.1 General
The term surface irrigation refers to water application methods in which the soil surface conveys
and distributes water over the irrigated field, and into the soil within usable range of the roots of
the growing plant. It is the oldest and still the most widely used method of water application to
agricultural land. The scientific approach of irrigation in recent years is water control, to make the
best use of both water, labor, and avoid the hazards of water logging and salinity. Most commonly,
surface irrigation methods applied in the forms of:

* Wild flooding

* Basin irrigation

* Border irrigation

* Furrow irrigation

4.2 Criteria for the Selection of Surface Irrigation Methods

Generally, selection of an irrigation method is based on, technical feasibility and economy. Surface
methods are mostly the cheapest to install, and where conditions are suitable there is little point in
considering other methods.

However, where high value cash crops are to be grown there may be economic justification for
considering other types of irrigation especially where conditions are not ideal (or costly
amendments are required) for surface irrigation.

Some of the limiting conditions to determine the choice of surface irrigation systems are:

-natural circumstances (slope, soil type)

-type of crop

-required depth of application

-level of technology
-previous experiences with irrigation

-required labor input

-Farming operations (land preparation, cultivation and harvesting etc.)

In case of Ribb irrigation project most of the crops selected are row crops, which can be irrigated by
furrow systems. The other conditions are also, almost favorable for furrow irrigation method to be
employed. Therefore, furrow irrigation system, is selected for this particular project.

Distinct advantage of furrow irrigation over other methods

 As the area wetted some percentage of the cropped area of the field, puddling and
crusting of the soil, is minimum, and men and machines can work in the field sooner
after the end of water application.
 Loss of water due to deep percolation and evaporation (due to the lesser open water
surface) is restricted.
 Furrows do not put hindrance in use of field machinery or other farming methods.
 In this method plants in there early tender age are not damaged by flow of water.
 By laying the furrows along the contours, across the slope of land, soil erosion
minimization is possible.
 Furrow making is a simple and cheap method and working expenses are minimal.
 Land between the rows of plants is utilized to construct furrows; therefore, useful
irrigable land is not wasted.

4.3 Furrow Irrigation System Design Considerations

Generally, there are two types of design data inputs in surface irrigation: field parameters and field
decision variables. The designer can manipulate decision variables. They include flow rate, field
dimensions, and cut-off time. On the other hand, the designer cannot influence field parameters;
they are measured or assumed properties of the given situation. They primarily consist of the soil
infiltration characteristics, the flow resistance, the required net application depth, and the field
slopes.
 4.3.1 System (field) parameters
 Required amount of application (Zr):-It is the amount of water, which needs to be stored in
the crop root zone during irrigation, in order to sustain normal crop growth.
Zr=MAD=TAW*P

 Maximum allowable flow velocity (Vmax):-non-erosive flow velocity, to estimate the non-
erosive flow rate, Qmax.

 Manning’s roughness coefficient (n):-It is the measure of the resistance effects, which flow
might encounter, as it moves down the furrow. Generally, for furrow irrigation system
design, n is taken as 0.04.

 Channel bed slope (So):-It is the average slope in the direction of irrigation (furrow slope).

 Infiltration parameter (I):-It is critically important for evaluation, design, or management of

a furrow irrigation system.

 Channel geometry: - Furrows can have parabolic, triangular, or trapezoidal cross-sections.

For our case, a trapezoidal furrow cross-section is selected, considering construction
easiness.

4.3.2 System variables

 Channel (furrow) length (L):- The length of furrow should be determined considering the
soil type, from previous studies to estimate advance and recession over the length of the
channel, the resulting distribution of infiltrated water, volume of runoff and the
performance indices. For our case, furrow length is taken as 150m.

 Unit inlet flow rate (Qo):- this is the discharge diverted into a furrow.

 Cut-off time (Tco):- It is the time at which the supply is turned- off, measured from the onset
of irrigation. The most important effect of cut-off is reflected on the amount of losses, deep
percolation and surface runoff, and hence adequacy and efficiency of irrigation.

4.4 Design of Furrow Irrigation System

Efficient irrigation by furrow method is obtained by selecting proper combinations of spacing,
length, and slope of furrows and suitable size of the irrigation stream and duration of water
application.
 4.4.1 Furrow spacing
The size and shape of the furrow depends on the crop grown, equipment used and spacing between
crop rows. Furrows can be spaced to fit the crops grown and the standard machines used for
planting and cultivating. Furrows should be spaced close enough to ensure that water spreads to
the sides into the ridge and root zone of the crop before it moves down below the root zone. Crops
like maize, sorghum, groundnut, potatoes, cotton etc. Have furrows between all rows. Vegetable
crops like onion, carrots, and some shallow rooted crops like bean have two rows between furrows.
To obtain a complete wetting of uniform clay soils to depths of 1 to 1.5 meters a furrow spacing of
one meter or more is required. Many crops are planted in single rows of 75 to 105 cm apart.

table 4. 1 Spacing between rows and plants

Suggested space between

Crop Rows and plants(cm)

Maize 75 x 30

Potato 80 x 30

Tomato 150 x 20

Pepper 60 x 40

Onion 60 x 40

(Michael, 1994)
 table 4. 2 Furrow infiltration and inflow rate
Soil texture Infiltration rate Furrow inflow

(mm/hr) (l/s/1000m length)

Clay 1-5 0.03-0.15

Clay loam 5-10 0.15-0.3

Silt loam 10-20 0.3-0.5

Sandy loam 20-30 0.5-0.8

Sand 30-100 0.8-2.7

4.4.2 Furrow length

The optimum length of furrow is usually the longest furrow that can be irrigated safely and
efficiently. Proper furrow length depends largely on the hydraulic conductivity of the soil. Furrows
must be shorter on a porous sandy soil than on a tight clay soil. It may be as short as 45m on soils
which take up water rapidly or as much as 300m or longer on the soils with low infiltration rate.
The length of the furrow may often be limited by the size and shape of the field.
 table 4. 3 Recommended length and depth of furrows for different soil types
Furrow Net depth of water application
slope
Clay soils Loam soils Sandy soils
(%)
75mm 150mm 50mm 100mm 50mm 75mm 100mm

-------------------------------------------meters------------------------------------------

0.05 300 400 120 270 60 90 150

0.1 350 440 180 330 90 120 190

0.2 370 470 220 370 120 190 250

0.3 390 500 280 400 150 125 280

0.4 380 500 280 370 120 190 250

0.5 270 400 250 300 90 150 220

In the case of Rib irrigation area the most of the soils are silt loam soils.
Based on the slope and soil type, furrow length is considered equal to 300m.

4.4.3 Furrow Stream

The size of the furrow stream is the one factor which can be varied after the furrow irrigation
system has been installed. The size of the stream usually varies from 0.5 to 2.5 liters per second. To
obtain the most uniform irrigation, the largest stream of water that will not cause erosion is used in
each furrow at the beginning of irrigation. Its purpose is to wet the entire length of each furrow as
quickly as possible, thus enabling the soil to absorb water evenly through the entire furrow length.
The maximum size of irrigation stream that can be used at the start of the irrigation limited by
consideration of erosion in furrows, over topping of furrows and prevention of run-off at the down
steam end.
The maximum non-erosive flow rate is estimated by the following empirical equation.
Qm = 0.6/s [Micheal 1978]
Where Qm =maximum non-erosive stream, l/s
S=slope of furrow expressed as percent for furrow slope =0.5%
Qm = 0.6/0.5 = 1.2 l/s
Design of furrow system
The following parameters are used for design of the furrow system.
The parameter of the intake families: soil with similar infiltration characteristics is based
on one – dimension infiltration families. The classification is based on one –dimension
infiltration furrow irrigation by taking in to account the wetted perimeter of the furrow and
the furrow spacing. This purpose the adjusted wetted perimeter is used for design.
Reduced inflow perimeter (P2): This is the furrow perimeter corresponding to cut –back
stream.
Advanced time (Ta): The time at which the advance water front (run in stream) reaches a
particular point.
Opportunity time (To): It is the difference of between the water fronts reaches a particular
point along the furrow and the time at which the tail records from the same point.
Recession time (Tr): The time for out flow of water to stop after inflow at the head of the
furrow has ended in recession time.
Infiltration in furrow system and calculation of required infiltration time must be handled
differently than for other types of surface system. This is because infiltration takes place on the
wetted perimeter of the furrow and the adjusted wetted perimeter is given by the following
equation.

P = 0.265 + 0.227

Where Q - volumetric inflow rate, l/s

n - Manning roughness coefficient
s - Furrow slop or hydraulic gradient (m/m)
In most cases, after the flow has stabilized and gets uniform, the hydraulic gradient is equal to the
furrow slop. A roughness coefficient of 0.04 is normally used for design of furrow irrigation system.
[Cuenca 1989]
The advanced time (Tt): for a stream of water moving down the furrow is given by

Ta =

Where Tt – advance time (minute)

L - Distance down the furrow (m)
Q - Volumetric inflow rate (l/s)
S - Slope, m/m
The net infiltration time or opportunity time (Tn):

Where dn - net irrigation depth (application depth) = RAM*P*D

RAM-readily available moisture from CROPWAT4window version

P - Depletion factor of sugarcane

D - Root depth of the sugarcane and C is constant.

Cut of time (Tco):Tco reflects an irrigation management decision made by the former and
designer. It should be an adequate length of time to infiltrate a satisfactory depth of water over the
length of the furrow without causing excessive deep percolation.
Tco = Ta+Tn-Tr, min
Where Tr is recession time is assumed zero for open–ended gradient furrow (i.e. for
furrows whose slope is not equal to zero) without loss of accuracy.
Therefore Tco = Ta + Tn
 The average infiltration opportunity time

Toavg = Tco -

Where =

 Gross application depth (Ig)

 Average infiltration depth (Iavg)

 Surface run off (dro)

dro = Ig - Iavg
 Deep percolation (dp) dp= Iavg-In
 Percentage of dp = * 100 (< 10%)

 Distribution pattern efficiency, Ed

Ed = * 100 (>50%)

If the value of distribution efficiency is less than the standard specification value, cut-back condition
is necessary to minimize the deep percolation of the water .In this condition some formulas are
modified.
 Cut back stream Q2: means flow after the water reaches the lower end of furrow; the
stream is reduced or cut back. Cut back stream size is equal to half initial stream flow

Q2 = = = 0.6l/s

 Reduced inflow perimeter

P2 = 0.265* + 0.277

Where Q2 - is cut back stream

Net application time is the time water must remain on the surface at the end of the field and equal
to Tn under reduced flow condition

Tn =

Time of cut back Tcb, is the time of advance at full flow, Tcb = Ta

 Time of cut off, Tco Tco = Tn + Tcb

Where Tn = Net application time under reduced flow condition. The average
infiltration time during the advanced period is the absolute value of the second term of the equation

Tavg= ; Where =

The average infiltration depth Iavg under cut-back condition

Iavg = [a +c] +[a( +c]

 Gross application depth

Ig = [Q1(Ta) + Q2(Tn)]

 Surface run off depth, dro, dro = Ig – Iavg

 Deep percolation depth, dp, dp = Iavg – In
 Distribution efficiency, Ed - under cut-back condition

Ed =

table 4. 4 Intake and advance coefficients for furrow intake family equation
Soil type Intake family

Clay loam 0.05-0.4

Fine Silt loam 0.45-0.5

Moderately silt 0.6

loam

Coarse silt loam 0.7-0.8

Sand loam 0.9-1.0

Coarse sandy 2

Fine sandy 2
table 4. 5 Kostiakov-Lewis intake family number
Intake family A B C F g*10-4

0.05 0.5334 0.168 7.0 7.16 1.088

0.10 06198 0.661 7.0 7.25 1.251

0.20 0.7772 0.699 7.0 7.43 1.578

0.30 0.9246 0.720 7.0 7.61 1.904

0.40 1.064 0.736 7.0 7.79 2.230

0.50 1.1961 0.748 7.0 7.97 2.556

0.60 1.321 0.757 7.0 8.15 2.883

0.70 1.443 0.766 7.0 8.33 3.209

0.80 1.560 0.773 7.0 8.50 3.535

0.90 1.674 0.779 7.0 8.68 3.852

1.0 1.786 0.785 7.0 8.86 4.188

1.5 2.284 0.799 7.0 9.76 5.819

2.0 2.753 0.808 7.0 10.65 7.451

Design parameter
Sample calculation for potato
Intake families IF: 0.60(silt loam soil)

a = 1.321 b = 0.757 c=7 g = 2.883* f = 8.15

Furrow length, L = 300m

Furrow slope, S = 0.005m/m
Inflow rate, Q =1.2l/s
Roughness coefficient, n = 0.04
Net irrigation depth, dn = 104.4mm (From crop water requirement)
Furrow space, w = 0.80m
Advance time (Ta)

Ta =

= exp ( *300) =102.0min

Adjusted wetted perimeter

P1 = 0.265( +0.227

= 0.265 +0.227

= 0.452m
Net infiltration time, Tn

Tn

= 649.2min
Cut off time, Tco
Tco = Ta + Tn = 102.0+649.2 = 751.2min
The average infiltration opportunity time
Tavg= Tco- ;

  gx / Q2 s 0.5 = =1.02

=751.2 = 751.2– 54.92 = 696.28min

Gross application depth, dg

dg = = = 225.36mm

Average infiltration depth, davg

davg =[a +c] = [1.321( +7] = 109.86mm

Surface run off, dro

dro= dg - davg = 225.36mm – 109.86mm =115.49mm
Deep percolation, Ddp
Ddp = davg– dn = 109.86mm – 104.4mm = 5.46mm

% dp =dp/davg= *100% =4.97% 10% ------------------------- ok

Distribution pattern efficiency, Ed

Ed = *100% = *100% = 46.33% < 50% ------------------------- not ok!

The distribution pattern efficiency is less than 50%, therefore we use cut back condition.
Cut back stream, Q2

Q2 = = = 0.6l/s
Reduced inflow perimeter

P2 = 0.265 + 0.227

P2 = 0.265 + 0.227= 0.32m

Net application time under cut back condition

Tn =

Tn = =1040.12min

Time of cut back,Tcb = Ta=102.0min

Time of cut off Tco = Tn + Tcb=1040.12+ 102.0 = 1142.12min
Average infiltration time

Tavg= ; Where = =2.04

Tavg = =79.48min

Average infiltration depth under cut back condition

davg = 106.06+7.543=113.603mm
Gross application depth

=186.62mm
Surface run off dro = dg -davg= 186.62-113.603 =73.015mm
Deep percolation depthddp= davg –dn= 113.603- 104.4 =9.203mm

Distribution pattern efficiency, Ed = ok

table 4. 6 Summary of furrow system

Parameters Crops
Potato Maize Tomato Barley Pepper
Required application 104.4 174 174 191.4 139.2
depth dn (mm)
Advance time Tt (min.) 102 102 102 102 102
Net infiltration time Tn 1040.2 2072.21 4082 1599.8 1040.12
(min.)
Time of cut-off Tco (min.) 1142.12 2174.2 4904 1701.8 1142.12
Inflow Q (l/sec.) 1.2 1.2 1.2 1.2 1.2
Cutback inflow (l/sec.) 0.6 0.6 0.6 0.6 0.6
Furrow spacing w (m) 0.80 0.75 1.5 0.6 0.6
Furrow length L (m) 300 300 300 300 300
Gross depth dg (mm) 186.62 364.19 342.88 360.76 248.82
Average depth dava (mm) 113.603 189.04 175.99 201.38 143.7
Surface runoff depth dro 73.015 175.15 166.89 159.38 105.12
(mm)
Deep percolation 9.203 15.04 1.99 9.98 4.5
depth ddp (mm)
Distribution pattern 55.94 51.43 50.8 53.06 55.9
efficiency Ed (%)

Furrows are aligned along the contour, slightly decreasing in elevation; and supplied from a head
ditch (tertiary canal). A tail ditch at the end of the run collects water for re-use or disposal at the
lower levels. The old practice of breaching canal banks to release water from the head tertiary canal
should be avoided in a modern irrigation system. The canal banks are scarred and likely to leak
after the breach has been closed, and there is no control or measure of the flow on to the field.
Instead, plastic or aluminum siphon tubes are used, which are light, simple to use, give a control
flow, and preserve the canal bank.
 4.5 Design of siphon tubes
Siphons of plastic tubing are used in field irrigation to transfer water from the tertiary canal to the
head of a furrow at a known rate. The siphon is particularly useful in irrigation work as a simple
and robust device for discharging at known rate from a farm channel onto a field. The design of
siphon tubes is a simple task, provided that, the maximum discharge required by a furrow is
known.

Flow through a siphon is a function of the difference in water level between its ends, i.e. hydraulic
gradient line (slope). Assuming that the minimum head difference between its ends is equal to the
furrow slope, the maximum size of the siphon tube can be determined.

From manning equation

2 1
A
Q = *R3 *S 2
n

3
Where: Q = maximum stream size of furrow, =1.20 l s = .0012 m s

D 2
A = cross sectional area of the siphon tube, =
4

D 2
A D
R = hydraulic radius of the siphon tube, = = 4 =
P 4
D

D=diameter of siphon tube

S = furrow slope, 0.005

n = roughness coefficient of the siphon tube; it is equal to 0.008 for the smoothest plastic
pipe

Substituting all the values except D in the above equation, gives

After rearranging and simplifying

 8
0.00043558 = D3

D = 0.05491m = 54.91 mm  80 mm

Comparing this with the standard products of plastic tubes, an appropriate 80mm diameter of
siphon tubes will be selected.
 CHAPTER FIVE

DESIEGN OF DRAINAGE CANAL SYSTEM

5.1 General
Drainage is the term applied to systems for dealing with excess water that describe all the
processes where by surplus water is removed from the land. It includes both internal drainage of
soil and the collection and dispersal of surface runoff.

By its nature, irrigation creates periodically saturation condition of upper layers of soil formation
over a long period where intensive irrigation is practiced; even deep soil layers tend to become
saturated and consequently underground water table rises in absence of adequate drainage
facilities. The knowledge of drainage engineering is very essential to solve this problem.

Water logged land is of little use; however, it can be utilized after providing proper drainage
arrangement. Usually in undulating country, the surface slopes are sufficient to carry off this
surplus water into the ditches and stream without any engineering construction. Low lying flat
areas are usually invariably near or below the flood level of the river. In order to prevent the area
from flooding the river must be trained; it is usually done by constructing of embankments. Like
this, we must construct drainage canal in order to prevent the irrigation canal from silting.

5.2 Requirement of drainage

Irrigation system design without drainage is incomplete. Soil has the capacity of holding water,
which enables plant to grow by drawing water and nutrient in solution in the water from the soils
through their root system. The structure of the soil consists of framework of solid materials
enclosed by complex system of pore and channel that provide a space within the soil for air and
water.

When all this space is filled with water, the soil is termed as saturated. A soil can only remain in a
saturated condition, if it is below water table and cannot drain truly. It may be temporarily
saturated during and immediately after irrigation or heavy rainfall. Saturation capacity is maximum
amount of water or moisture that a soil can hold at saturation, it depends on the volume of its pore
space.
In order for plant to grow, apart from availability of water, air also is needed, and hence soil should
be permanently saturated with water. A good soil, therefore, has internal drainage characteristic,
which means water must be able to move fairly and easily through the soil, that excess water can
remove when required.

So far irrigated lands are concerned the following benefits may be achieved from adequate drainage
scheme.

Those are:

1. It facilitates early ploughing and in turn early sowing crop

2. It actually extends the crop root zone. Thus, more soil moisture is made available crop
growth
3. It maintains higher soil temperature. Soils that are water logged take more time for
warming up. The reason is, water logged soil require more heat to raise the temperature of
a given of water by 1°c than to raise the temperature of value of air by 1°c.
4. It helps in maintaining proper area of upper soil. The aeration and higher temperature
increased the bacteriological activities in the soil.
5. In the processes of draining the land, harmful salts are leached out
6. It also improves the sanitary conditions and makes surrounding

5.3 Selections of drainage systems

Drainage may be artificial or natural. Drains are termed artificial when they are constructed after
proper consideration of existing conditions and function to be served. Artificial drains are generally
constructed to dispose of surplus water quickly, before it gets absorbed deep into the soil. Drainage
can be classified into two main systems.

Those are: - 1 -Surface drainage system

2 -Subsurface drainage system

5.3.1 Surface drainage systems

Surface drainage problem occur in nearly flat area, uneven land surface with depression or ridges
preventing natural runoff and in areas without outlet. Soils with low infiltration rates are
susceptible to surface drainage problem. Surface drainage is intended for safe removal of excess
water from the land surface through land shaping and canal construction. Function of the system
may be considered as:

-Collection systems

-conveying systems

-Outlet system

Water from the individual field is collected and is then removed through a system to the outlet.
Generally, surface drainage is required for-

1. The removal of storm rainfall where the subsurface drainage is not economically feasible

2. The collection and disposal of surface irrigation runoff

5.3.2 Subsurface drainage system

Subsurface drainages are required for soils with poor internal drainage and a high water table. This
type of drain does not hinder movement in the field but they have high initial investment cost.

However, here in our case we have recommended to use the surface drainage system because of the
fact that our project is small scale and low cost of installation.

5.4 Alignment of surface drainage

The following points should be given great consideration in marking an alignment of drain.

Firstly, alignment should follow a natural drainage line that is the lowest contouring in the valley.
To reduce the cost of drainage scheme the drain should have minimum length. It can be achieved by
taking alignment straight rather than zigzag.

Secondly, alignment of drain should not pass through ponds or marshes. The reason is that such
drain may act as feeder line to the marsh and the pond will go on expanding. The solution to the
situation is to align the drain clear off the pond.

Thirdly, so far as possible drains should not cross irrigation canals. The reason is that some
expensive structures will have to be constructed at the crossing point. It increases the cost of
drainage scheme.
 5.5 Design of surface drainage
When we design surface drainage for a given irrigable command area, the following parameters are
to be considered.

Capacity of drainage

Drainage should be designed to carry the maximum anticipated flood efficiently.

Longitudinal (bed) slope

Longitudinal slope of the drain is given by the general slope of natural ground; of course slope
should be fixed in correlation to the permissible velocity. An efficient drain is one, which is so
designed as not to produce velocity, which may induce either silting or scouring. Economy and
efficiency should be the main considerations in designing drainage systems. Generally, the bed
slope is determined from Top map of the irrigable area.

From the top map of Ribb irrigation project, the following result is found.

–The longitudinal slope of main drainage canal, S = 1/1250

–The longitudinal slope of secondary drainage canal, S = 1/1000

–The longitudinal slope of tertiary drainage canal, S = 1/500

–The longitudinal slope of filed drainage canal, S = 1/300

Drainage coefficient (DC)

The drainage coefficient is the amount of water that must be removed from soil surface in order to
have sustainable agriculture. It depends, on depth of irrigations, method of irrigation, leaching
requirement and soil characteristics. There are different methods for estimating drainage
coefficient. Those are:

#1 1%MAR method; Where: MAR= mean annual rainfall

For Ribb irrigable area, MAR = 1024.9mm

DC = 1%*1024.9 mm= 10.249 mm

#2 Hudson (1983)’s method; In this method the following two conditions are considered
 If MAR <1000 mm, DC = 10 mm/day

If MAR >1000 mm, DC = MAR/100 mm/day

Since MAR = 1024.9 mm, DC =1024.9/100=10.249 mm/day

#3 Muzumdor methods; In this method, the following table is provided for estimation of drainage
coefficient from MAR.

table 5. 1 Estimation of drainage Coefficients

MAR(mm) DC(mm/day)
1 <750 5.0-7.5
2 750-1000 7.5-9.0
3 1000-1250 9.0-12.0
4 1250-1500 12.0-25.0

Since MAR = 1024.9 mm;

DCmax= 12.0 mm/day

From the above three methods the value of the drainage coefficient (Dc) for the maximum one is
taken for design of the drainage canal. DC = 12mm/day

5.6 Types of drainage canals

From different types of drainage canals, the trapezoidal drainage canal is selected. The reason is
that trapezoidal canal is more stable than the other channels. In addition, it is more economical.

5.6.1 Design of field drain

Available data

-Drainage area, Adr= 8 ha

-Drainage coefficient, DC =12mm/day

-Drainage discharge, Qdr= DC*Adr= 12 mm/day*8ha= 0.011m3/sec

Let assume D= 0.18m

 Where = 33.69o

For m =1.5m ,B= 0.109

= 0.758m

= 0.068m2

= 0.090m

-Bed slope of field drain is determine from topo map

S = 1/300 = 0.0033

-Side slope, m = 1.5

-Manning roughness coefficient, n= 0.025

V= 1.213m/s

= 0.082m3/s Qdr ok!

Free Board (FB)

The top of canal banks has to be maintained higher than the level to allow for waves and possible
fluctuation in supply. The vertical distance between the top of drainage canal banks and the full
supply level of drainage canal, known as free board. For this case, take a free board of 0.1m.

For the trapezoidal drainage canal

B = 0.109m

D = 0.18m

DT = D + FB = 0.18m + 0.1m = 0.19m

 Where: DT=the total depth of canal including free board.

figure 5. 1 Cross-section of field drain

Number of filed drain are 125
Length of filed drain is 200m

5.6.2 Design of collector drain

Available data: -Drainage area, Adr = 40ha
-Drainage coefficient, DC = 12 mm/day
-Drainage discharge, Qdr= DC*Adr= 12 mm/day*40 ha= 0.056m3/sec
Let assume D= 0.3m

Where = 33.69o

For m =1.5m
B= 0.18m

= 1.26m

= 0.189m2

= 0.15m

-Bed slope of field drain is determine from topo map

S = 1/500 = 0.002
-Side slope, m = 1.5
-Manning roughness coefficient, n= 0.025
V= 0.511m/s

= 0.097m3/s Qdr ok!

For the trapezoidal drainage canal
 Assuming FB = 0.2m
B = 0.18m
D = 0.3m
DT = D + FB = 0.3+0.2 = 0.5m

figure 5. 2 Cross section of collector drain

Number of collector drain are 25

Length of collector drain is 1000m

5.6.3 Design of secondary drainage canal)

Upstream drainage is designed for the purpose of protecting silt entry in to secondary canals.

Available data

-Drainage area, Adr= 200 ha

-Drainage coefficient, DC = 12 mm/day

-Drainage discharge, Qdr= DC*Adr= 12 mm/day*200 ha= 0.278m3/sec

Let assume D= 0.55m

Where = 33.69o

For m =1.5m

B= 0.333m

= 2.316m

= 0.637m2
 = 0.275m

-Bed slope of field drain is determine from topo map

S = 1/1000 = 0.001
-Side slope, m = 1.5
-Manning roughness coefficient, n= 0.025
V= 0.540m/s

= 0.344m3/s Qdr ok!

For the trapezoidal drainage canal
Assuming FB = 0.25m
B = 0.333m
D = 0.55m
DT = D + FB = 0.55m + 0.2m = 0.75m

figure 5. 3 Cross-section of upstream drainage (secondary canal)

Number secondary canal are 5
Length of secondary canal is 2000m

5.6.4 Design of main drainage canal

Upstream drainage is designed for the purpose of protecting silt entry in to main canal.
Available data:
-Drainage area, Adr= 1000 ha
-Drainage coefficient, DC = 12mm/day
-Drainage discharge, Qdr= DC*Adr=12 mm/day*1000 ha= 0.556m3/sec
Let assume D= 0.70m
Where = 33.69o

For m =1.5m
B= 0.424m

= 2.948m

= 1.032m2

= 0.35m

-Bed slope of field drain is determine from topo map

S = 1/1250 = 0.0008
-Side slope, m = 1.5 and n= 0.025
V= 0.566m/s

= 0.584m3/s Qdr ok!

For the trapezoidal drainage canal
Assuming FB = 0.25m
B = 0.424m
D = 0.70m
DT = D + FB = 0.70m + 0.25 m = 0.95m

figure 5. 4 Cross-section of upstream drainage (main canal)

Number secondary canal are 5 and length of each secondary canal is 2000m.
 CHAPTER SIX

ECONOMIC ANALYSIS

6.1 General
Economic analysis is helpful to know the schemes cost to the farmers (beneficiaries) and how it will
be interpreted in terms of the farm products. It is also helpful for selecting alternative design and
construction materials.

A project is economically feasible if the benefit, which results from the project, exceeds the total
cost spent to implement the project.

6.2 Estimation of the project cost

Initial investment cost and bill of quantities are summarized below

table 6. 1 Economic analyses

s.no work description Unit Quantity Unit Total cost (Birr)
cost(Birr)
1 Excavation in soil for
canal work
1.1 Cut m3 345368 20 6907360
1.2 Fill m3 800 25 20000
1.3 Site clearance M2 10024000 12 12028800
1.4 Access rods
Cut M3 410657 20 8213140
Fill M3 100876.3 25 2521907.5
2 Canal structure

2.1 Drops
Concrete m3 0.2006 2728 547.24

Masonry m3 0.4 640 256

Plastering M2 1.003 130 130.39

 2.2 Sayphn

Reinforced bar

Φ=16mm Kg 8 765.3 6122.4

Φ=10mm Kg 12 478.3 5739.6

Concrete m3 4.8 2728 13094.4

Masonry m3 9.6 640 6144

2
Plastering M 44 130 5720
2.3 Calvert
Concrete m3 8.1 1765 14296.5
Masonry m3 16.2 640 10368
Plastering M2 40.5 130 5265
2.4 Division box
Concrete m3 16.375 1765 28901.875
Masonry m3 31.761 640 20327.04
Plastering M2 81.903 130 10647.39
2.5 Siphon NO 25 50 1250
Grand total 3097087.335

6.3 Estimation of the project benefit

Since irrigation systems are implemented for the purpose of producing agricultural product
through the year. The benefit of the project is obtained by assuming if all the agricultural out puts
obtained are sold for the assumed life time of the project for 15 years analysis.
 table 6. 2 Optimization Techniques
Types of Yield Price Selling Input Labor Labor Tillage Total Over Profit
crops Qui/ha per Birr/ha cost red’s cost O&M cost cost head Birr/ha
Qui Birr/ha man- Birr/ha Costs Birr/ha Birr/ha cost
day/ha Birr
Potato 210 400 84000 1500 100 2000 100 250 3850 385 79765
Maize 75 500 37500 4000 90 1800 100 400 6300 630 30570
Tomato 400 500 20000 2000 100 2000 100 300 4400 440 15160
Barely 85 500 42500 900 45 900 100 450 2350 235 39915
Pepper 225 600 13500 2000 100 2000 100 280 4380 438 8682
If this much are is used, the profit is maximized to 4145950 birr
Analysis
The useful life of the project (n) and the interest rate (i) are assumed to be 15 and 10%
respectively. The present worth of the project (P) is 4145950 birr
The annual worth (A) is given by

Reasonably assuming the annual operation and maintenance cost of the project to be 10% of the
annual cost (A),
The Operation and Maintenance cost (Mn) = 0.1* A=54508.37Birr/year
Using the modified benefit cost ratio method

Where:
Bn- net capital saving
Mn- net Operation and Maintenance cost
Cn- capital cost of replacing the present facility with the future facility.
B/C - benefit cost ratio
The result of the above equation of benefit cost ratio is
B/C=13.36>1.0
Hence the project is feasible!
 CHAPTER SEVEN

ENVIRONMENTAL IMPACT ASSESSMENT

7.1 General
The environment is composed of various systems comprising of physical, biological and socio-
economic sub systems, which are subjected to construction of development works, like water
resource development projects. These changes may shape the environment for the better or worse
condition. It necessitates that they should be analyzed in the design of the project. Environmental
impact assessment is therefore a systematic structured, identification, prediction and evaluation of
the environmental consequences of proposed actions.
The impact of the proposed action will be identified by using the existing environment as a control.
A change in the environment is the difference in the environment between the control, the existing
environment and the new environment, the altered condition caused by a project. How good or
adverse the condition, is depend on what happened to the environment after the change has taken
places.
EIA is a set of activities under taken to ensure that a development project not only brings out the
intended economic development but also mitigates the likely negative environmental impacts of
implementing such projects.

7.2 Potential environmental impact and mitigation measures

Implementation of the Ribb irrigation development project would involve land clearing and
earthwork activities for building conveyance canal, irrigation canals, drains, and farm access roads.
These and other activities related to the implementation of the project will bring the following
environmental impacts.

The aim of environmental impact assessment

 To understand the likely environmental consequences of new development
 To understand the implication of proposed interventions
 To identify the measures by which the impact can be mitigated
 To present the result in such a way that they can provide answers needed by stake holders.

7.3 Impact of the project

The impacts of the project are classified in to two groups
 1. Negative impacts
2. Positive impacts

7.3.1 Negative impacts of the project

Negative impacts of the project are:
-pollution of water quality
-adverse soil modification
-impact on vegetation and soil
-soil erosion
-loss of land
-impact on socio-economic environment
Some Negative impacts of the project are discussed below.
Water quality
Irrigation may contribute to the problem of water pollution in various ways. During construction
period, earthwork activities for construction of the proposed conveyance canal and irrigation
infrastructure are likely to yield high sediment loads. All these changes may bring changes to the
water quality.
Mitigation measures:
(Establishments of biological and physical water quality criterion for agricultural water use
(Improving awareness of the community about effect of fertilizers and chemicals on water
quality
(Proper disposal of swages from agricultural water i.e. drainage system should be adopted

Negative impacts of water logging

( Reduction in crop yield because of stoppage of air circulation
( Difficulty in ploughing and other filling practices
( Salt efflorescence
( Increase in growth of aquatic weeds causing moving filling expense
Mitigation measures:
( Lining of canals and watercourses
( Reducing the intensity of irrigation
( Exercising economical and scientific use of water system( Using proper drainage system)
 7.3.2 Positive impacts of the project
The important benefits and Positive impacts of the project are the following
 Increase of crop production
 Increasing the reliability of agricultural production
 Famine relief – famine follows drought. Irrigation helps in alters the drought.
 Rise in social standards – with increased food production and assured supplies of food and
water, more money is available with farmers and raises their standard of living.
 Flood control
Thus, it is important to realize the close interaction between development and their environmental
consequences and incorporate environmental impact assessment into decision making as an
integral component in the design of the project, rather than something utilized after the design
phase is completed

CHAPTER EIGHT

CONCLUSION AND RECOMMENDATION

8.1 Conclusion
Based on the study and the results obtained from the Ribb irrigation project in the area no more
drought. The climatic condition indicates in the area there is binomial rainfall; the annual rainfall is
about 1024.9mm. Even though this rainfall is fairly enough for crop growth; but from the
background of the project area and living standard of the people irrigation project is required, to
harvest more than one in a year.
 As we see from different background of field history, it can be concluded that the majority of the
soil and its topography is suitable for the production of crops such as potato, maize, tomato, barely,
pepper and other edible fruits.
 The result of cropwatt shows extra water is required for additional production.
 For safe design we have to use dependable ERF because it is the smallest of all other ERF
calculation method which enables us to design our canal for the worst condition.
 From topographical nature of command area, suitable canal alignment was done and
trapezoidal unlined canal section is selected based on soil criteria. The design of the cross section
of the canal fixed by using Kennedy theory. And also different components of canal structures such
as culverts, drops, diversion box.
 For supplying faire amount of water to the command area, surface irrigation method i.e. furrow
irrigation is designed appropriate.
 To improve existing drainage condition, internal drainage system, which remove the excess
irrigation or rainwater, is designed.
 During the design of drainage system surface drainage system is preferable than the subsurface
drainage system because the subsurface drainage system is very cost than the surface drainage
system.
 The cost of the project is approximately estimated by considering the dimension of the
structure and the materials used for construction of the structure. The approximant cost of the
project was estimated to be 3097087.335Birr.
Some environmental effects of the scheme, which have direct impact on the environment, have
discussed, and valuable remedial measures are provided for each effect, which have negative
impact on environment.

8.2 Recommendation
 The farmers should organize for efficient use of water.
 Since most of the canals are unlined, frequent maintenance or silt removal is needed that makes
the canals serve durably.
 The maintenance condition, embankment condition and general performance of the main canal
should have maintained periodically.
 It should have been very much nice, had the university sought some means for final year project
group to have a visit to their respective project site.
 Since no information is given about irrigation water quality and it is just assumed that the
available water is good for irrigation apart from erosion during rainy season due to steeping slope
of land of command area. These results rapid silting up of canals which nesses sits soil conservation
activities.
 Most of the beneficiaries have no enough knowledge of irrigation. Thus education and training
should be given to the farmers for adopting practice of conservative use of water on scientific line.

REFERENCES
 ARORA,K.R, (2002). Irrigation, Water Power And Water Resources Engineering, Standard
Publishers, NAIA Saraf,Delhi.
 FAO,(1996). Guide Lines for computing crop water requirement, Irrigation And Drainage
Project Paper 56, FAO,Roma.
 Garge, S.K, (2003). Irrigation Engineering And Hydraulic Structures, 12th edition, Khanna
Publisher, New Delhi.
 Michael A.M ,(1997). Irrigation Theory and Practice, (publisher)
 Novac, (1996). P.Hydraulic Structures
 Sahasrabudhe, J.K, Irrigation Engineering and Hydraulic Structures,1994
 CropWAT 8 software version.