ADDIS ABABA UNIVERSITY

INSTITUTE OF TECHNOLOGY
SCHOOL OF CIVIL AND ENVIRONMENTAL ENGINEERING

Design of Small-Scale Surface Irrigation

The Case of Jalele, Ethiopia
By Gurmu Madessa Ija

A Project Submitted to the School of Graduate Studies of Addis Ababa

University Institute of Technology in Partial Fulfilment of the
Requirements for the Degree of Master of Engineering in Hydraulic
Engineering

April 2021

Addis Ababa, Ethiopia

 Addis Ababa, Ethiopia
April 2021
Addis Ababa University
Institute of Technology
School of Civil and Environmental Engineering

This is to certify that the project prepared by Gurmu Madessa Ija, entitled: Design of
Small-Scale Surface Irrigation, the Case of Jalele and submitted in partial fulfilment of the
requirements for the Degree of Master of Engineering (Hydraulic Engineering) complies with
the regulations of the university and meets the accepted standards with respect to originality
and quality.

Approved by the Examining Committee:

Daneal Fekersillassie (PhD) _________________ ________________

Advisor Signature Date

Yenesew Mengiste (PhD) __________________ ________________

Internal Examiner Signature Date

___________________________________
School Chairperson

I
ACKNOWLEDGMENTS

First of all, I would like to thank my GOD for giving me the strength to finish this project.

I would like to express my sincere gratitude to Ethiopian Road Authority, ERA for
Scholarship award and all the university teachers and staff members in Universities.

Special thanks to my advisor Dr. Daneal Fekersillassie for his valuable guidance,
encouragement, suggestions and constructive comments from beginning to the completion of
this research work.

I would like to thank my wife w/ro Aberash Kebede for her unreserved effort during my
project work.

I would also thank my families (parents, sisters, and brothers) for their never-ending concern,
support and encouragement.

Last but not least; I would like to forward my thanks to my kids for their patience and
support during my studies.

II
ACRONYMS AND ABBREVIATIONS

E East
PA Peasants Association
N North
FAO Food, Agriculture Organization
MoWR Ministry of Water Resource
MoA Ministry of Agriculture

III
ABSTRACT
The project Jalele small scale irrigation is located in East Wollega Zone, Sibu Sire Ana, at a
distance of about 37km away from Nekemte, nearby Nekemte-Finfinne high way. The area of
the catchment (watershed) is 17km2 and the project is intending to develop 60 hectares of
land by surface irrigation.

The overall objective of the project is to design and analyze of small-scale surface irrigation
by using river water (Jalele river). Specifically, design of surface irrigation, design of head
work (weir), and selection of weir type will be the major one performed in this project.

The necessary data that was collected and used for this study were primary and secondary
data. Data essential for this project work was collected from different sources. The collected
data include soil, agronomy, hydrology, geology, surveying that is used for headwork, main
canal, and irrigation system design.

During peak flow, the water level attained is equivalent to 0.90m. The water level is obtained
from stage ~ discharge curve. After preparing stage ~ discharge curve, the tail water depth is
estimated as 0.90m. For stage ~ discharge curve, the discharge was calculated by using
Manning equation, Q = (A/n)*(R2/3 I 1/2).

Expected maximum flow for Jalele catchments is estimated by Rational Method Qp =

0.00216 CIA0.73 = 0.00216 * 0.63 * 96mm * (1700ha)0.73 = 29.8 m3/s ≈ 30m3/sec, based on
field data observation, i.e. land slope classification, coverage of the area, and value of runoff
coefficient, C. Thus, high flood level of the river (HFL) before construction of the structure
is, HFL = river bed level + tail water depth = 1861.30 + 0.90 = 1862.20.

Ogee weir is selected from broad crested weir for big boulders are coming from upstream
mountainous area. Other reason for selecting ogee weir is due to its high coefficient of
discharge. Ogee weir is used to pass boulders coming from upstream easily.

Furrow surface irrigation, the most common method of surface irrigation, is recommended
for this project, for the following reasons; it is suitable to the soil type of the project area; it
has been traditionally exercised by the farmers of the project area; it is easily manageable at
farmer’s level; and it is suitable to irrigate all crops, which are recommended for the project.

IV
TABLE OF CONTENTS
ACKNOWLEDGMENTS ........................................................................................................ II
ACRONYMS AND ABBREVIATIONS ................................................................................ III
ABSTRACT .............................................................................................................................IV
1. INTRODUCTION .............................................................................................................. 1
1.1. Background ................................................................................................................. 1
1.2. Objective of the Study ................................................................................................. 1
1.2.1. General Objective .................................................................................................... 1
1.2.2. Specific Objectives .................................................................................................. 1
2. LITERATURE REVIEW ................................................................................................... 2
2.1 General ........................................................................................................................ 2
2.2 Small Scale Irrigation in Ethiopia ............................................................................... 4
3. METHODS AND MATERIALS ....................................................................................... 6
3.1 Description of the Study Area ..................................................................................... 6
3.2 Approach and Methodology ........................................................................................ 7
3.2.1 Soil ....................................................................................................................... 7
3.2.2 Agronomy ............................................................................................................ 8
3.2.3 Geology ................................................................................................................ 8
4. HEAD WORK, AND IRRIGATION SYSTEM DESIGN ................................................ 9
4.1. Head Work Design ...................................................................................................... 9
4.1.1 Weir Type Selection and Weir Design ................................................................ 9
4.1.2 Determination of Weir Crest Level.................................................................... 10
4.1.3 Estimation of Tail Water Depth ......................................................................... 11
4.1.4 Peak Flood of the River ..................................................................................... 14
4.1.5 Surface Hydraulics ............................................................................................. 16
4.1.6 Stability Analysis ............................................................................................... 19
4.1.7 Design of Stilling Basin ..................................................................................... 22
4.2. Surface Irrigation and Drainage System Design ....................................................... 26
4.2.1 Field Irrigation Method ...................................................................................... 26
4.2.2 Proposed Water Distribution and Scheduling .................................................... 27

V
 4.2.3 Water Duty ......................................................................................................... 29
4.2.4 Main Canal Design ............................................................................................ 30
4.2.5 Secondary Canals Design .................................................................................. 33
4.2.6 Field Canals Design ........................................................................................... 34
4.2.7 Canal Structures Design ..................................................................................... 34
4.2.8 Cross Drainage Structures Design ..................................................................... 41
4.2.9 Drainage Canals Design ..................................................................................... 42
4.2.10 Catch Drains....................................................................................................... 42
5. RESULTS AND DISCUSSIONS .................................................................................... 43
6. CONCLUSION AND RECOMMENDATIONS ............................................................. 50
7. REFERENCES ................................................................................................................. 52

VI
LIST OF TABLES
Table 1: Selection of an irrigation method based on soil type and net irrigation depth (Source:
Jensen, 1983).............................................................................................................................. 3
Table 2: Furrow lengths in meters as related to soil type, slope, stream size and irrigation
depth (Source: Kay, 1986) ......................................................................................................... 4
Table 3: Practical values of maximum furrow lengths in meters depending on soil type, slope,
stream size and irrigation depth for small-scale irrigation (Source: FAO, 1988) ...................... 4
Table 4: Average River Bed Slope Estimation ........................................................................ 11
Table 5: Elevation and depth data ............................................................................................ 14
Table 6: List of turnouts available in the project ..................................................................... 29
Table 7: List of secondary canals location and length ............................................................. 33
Table 8: List of culverts on main and secondary canals .......................................................... 35
Table 9: Location of Turnouts ................................................................................................. 38
Table 10: Location and length of chutes of secondary canals ................................................. 39
Table 11: Cross drainage structures and their locations .......................................................... 42

VII
1. INTRODUCTION
1.1. Background
The rapidly increasing population of our country can no longer be fed by food crops, which
are through traditional and backward agricultural activities. The uneven and erratic
distribution of rainfall and the unusual weather changes are among the main reasons for the
failure of agricultural productivity.

To overcome the shortage of food crops, proper management and utilization of the existing
resources is one of the best solutions.

Jalele Small Scale Irrigation Development Project is proposed on the bases of these facts.
Besides producing more food crops for family consumption, the cash income of the
beneficiaries is expected to increase; and thus, their living standard would be raised, after the
implementation of the project.

The project is located in East Wollega Zone, Sibu Sire Ana, at a distance of about 37km away
from Nekemte, nearby Nekemte-Finfinne high way.

The main motivating force to do this project work goes to the benefit of small-scale
irrigation. Small scale irrigation is little developed in Jalele area. As a result, designing and
analysing small scale irrigation for Jalele is considered. By doing so, the local community
particularly small farm holders of the area will be benefit from the project if the project is
implemented.

1.2. Objective of the Study

1.2.1. General Objective
The general objective of the project is to design and analyze of small-scale surface irrigation.

1.2.2. Specific Objectives

The specific objectives of the project are:
➢ designing surface irrigation of Jalele small scale,
➢ designing head work (weir) for Jalele small scale,
➢ selecting weir type for Jalele small scale

1
2. LITERATURE REVIEW
2.1 General
Irrigation is defined as application of artificial water to the living plants for the purpose of
food production and overcoming shortage of rainfall and help to stabilize agricultural
production and productivity (FAO, 2005). Irrigation in Ethiopia is considered as a basic
strategy to alleviate poverty and hence food security. It is useful to transform the rain-fed
agricultural system which depends on rainfall into the combined rain-fed and irrigation
agricultural system. According MoWR (2012) modern irrigation has been documented in the
1960s where the government designed large irrigation projects in the Awash Valley to
produce food crops for domestic consumption and industrial crops for exports. Irrigation
development is being suggested as a key strategy to improve agricultural productivity and to
encourage economic development (Bhattarai et al., 2007). The adoption of new technology
(e.g., irrigation) is the major powerful for agricultural growth and poverty reduction (Norton
et al, 2010). The most commonly used and most ancient type is surface irrigation methods
(FAO, 2002) through the usage of gravity forces. This was used especially across river sides
and it does not depend on mechanized equipments. Nowadays, modernized irrigation
systems are mostly used which works based on the pressurized energy system (FAO, 2001).

In order to be in a position to select an irrigation system for a given area, it is important to

look at the types of irrigation systems commonly used. Based on the method of applying
water to the land, there are four broad classes of irrigation systems: (1) surface irrigation
systems, (2) sprinkler irrigation systems, (3) localized irrigation systems and (4) sub-surface
irrigation systems.

Surface irrigation is the oldest and most common method of applying water to crops. It
involves moving water over the soil in order to wet it completely or partially. The water
flows over or ponds on the soil surface and gradually infiltrates to the desired depth. Surface
irrigation methods are best suited to soils with low to moderate infiltration capacities and to
lands with relatively uniform terrain with slopes less than 2-3% (FAO, 1974).

According to FAO (1989), 95% of the irrigated area in the world is under surface irrigation.
Some of the major advantages of surface irrigation systems over other systems are that they
are easy to operate and maintain with skilled labour, they are not affected by windy
conditions and, with the exception of furrow irrigation, they are good for the leaching of the
salts from the root zone. Generally, they are associated with low energy costs.

2
 Soil Rooting Net irrigation depth
Surface irrigation method
type depth of crop per application (mm)
Shallow 20-30 Short furrows
Sand Medium 30-40 Medium furrows, short borders
Deep 40-50 Long furrows, medium borders, small basins
Shallow 30-40 Medium furrows, short borders
Loam Medium 40-50 Long furrows, medium borders, small basins
Deep 50-60 Long borders, medium basins
Shallow 40-50 Long furrows, medium borders, small basins
Clay Medium 50-60 Long borders, medium basins
Deep 60-70 Large basins
Table 1: Selection of an irrigation method based on soil type and net irrigation depth (Source:
Jensen, 1983)

An engineer may have an opportunity to design a surface irrigation system as part of a new
irrigation project where surface methods have been selected or when the performance of an
existing irrigation system requires improvement by redesign. In either case, the data required
fall into six general categories (Walker and Skogerboe, 1987):
I. the nature of irrigation water supply in terms of the annual allotment, method of
delivery and charge, discharge and duration, frequency of use and the quality of the
water;
II. the topography of the land with particular emphasis on major slopes, undulations,
locations of water delivery and surface drainage outlets;
III. the physical and chemical characteristics of the soil, especially the infiltration
characteristics, moisture-holding capacities, salinity and internal drainage;
IV. the cropping pattern, its water requirements, and special considerations given to
assure that the irrigation system is workable within the harvesting and cultivation
schedule, germination period and the critical growth periods;
V. the marketing conditions in the area as well as the availability and skill of labour,
maintenance and replacement services, funding for construction and operation, and
energy, fertilizers, seeds, pesticides, etc.; and
VI. the cultural practices employed in the farming region especially where they may
prohibit a specific element of the design or operation of the system.

According to Michael (1994), rational procedures for predicting the water front advance and
tail water recession in furrows, which are applicable to field designs, have not been
developed. Various workers have proposed a number of quasi-rational procedures with
varying degrees of adaptability. In the absence of more precise information on predicting the

3
water advance and recession in furrows, general principles regarding stream size, furrow
length and furrow slope to obtain efficient irrigation are followed in field design.

Soil type Clay Loam Sand

Average irrigation depth (mm)
Furrow slope % Maximum stream size (l/sec) 75 150 50 100 150 50 75 100
0.05 3.0 300 400 120 270 400 60 90 150
0.10 3.0 340 440 180 340 440 90 120 190
0.20 2.5 370 470 220 370 470 120 190 250
0.30 2.0 400 500 280 400 500 150 220 280
0.50 1.2 400 500 280 370 470 120 190 250
1.00 0.6 280 400 250 300 370 90 150 220
1.50 0.5 250 340 220 280 340 80 120 190
2.00 3.0 220 270 180 250 300 60 90 150
Table 2: Furrow lengths in meters as related to soil type, slope, stream size and irrigation
depth (Source: Kay, 1986)

Soil type Clay Loam Sand

Average irrigation depth (mm)
Furrow slope % Maximum stream size per furrow (l/sec)
50 75 50 75 50 75
0.00 3.0 100 150 60 90 30 45
0.10 3.0 120 170 90 125 45 60
0.20 2.5 130 180 110 150 60 95
0.30 2.0 150 200 130 170 75 110
0.50 1.2 150 200 130 170 75 110

Table 3: Practical values of maximum furrow lengths in meters depending on soil type, slope,
stream size and irrigation depth for small-scale irrigation (Source: FAO, 1988)

2.2 Small Scale Irrigation in Ethiopia

In Ethiopia, traditional irrigation was practiced before centuries (Bekele et al., 2012).
Moreover, in the highlands of Ethiopia, irrigation practices have long been in use since
ancient times for producing subsistence food crops (Awulachew et al., 2007; Bacha et al.,
2011; MoA, 2011a). Different authors such as Awlachew et al (2007), Makombe et al.
(2007), Hagos et al. (2009), Bacha et al. (2011) stressed that supplementary irrigation has
been practiced by smallholder farmers of Ethiopia for centuries to solve their livelihood
challenges.
Irrigated agriculture is being practiced under smallholders, medium and large-scale farming.
Many authors such as Awlachew et al. (2007), Makomb et al., (2007), Hagos et al. (2009),
Bacha et al. (2011) were used government based irrigation schemes classification systems

4
for their description during their studies. According to Ministry of Water Resources of
Ethiopia (MoWR, 2002), irrigation development in Ethiopia is classified based on the size of
the command area, in three types:

1. Small-scale irrigation systems (<200 hectares ha)

2. Medium-scale irrigation systems (200-3,000 ha)
3. Large-scale irrigation systems (>3,000 ha)

This classification system is the most common in Ethiopia. Accordingly, 46% of proposed
irrigation developments are in the small-scale irrigation category (Makombe et al., 2011).

Small scale irrigation is a type of irrigation defined as irrigation, on small plots, in which
farmers have the controlling influence and must be involved in the design process and
decisions about boundaries (Tafesse, 2007). Small scale irrigation is an important strategy in
reducing risks associated with rainfall variability and increasing income of rural farm
households.

5
3. METHODS AND MATERIALS
3.1 Description of the Study Area
Climatic Characteristics
The study area is categorized under warm sub-humid agro climatic zone with average annual
rain fall of 1342mm. The daily average maximum temperature and average minimum
temperature are 28c and 18c respectively. The dry months of the year are from December
to March whereas the rain months are from April to October. The elevation of the project is
about 1875m a.m.s.l.

Hydrologic Characteristics
The area has available water resources in the form of surface and ground water. River and
small streams are the main surface water resource of the area. Jalele is one of the catchments
of Didesa river basin, which drains from north to south direction crossing the way of main
asphalt road of Addis Ababa to Nekemte.

Grid coordinate is 90 04’ N ~ 90 08’N latitude, 360 44’E ~ 360 48’E longitude from the upper
most divide to the out let (the proposed weir site.) The area of the enclosed drainage is about
17Km2 with large number of perennial springs, which enhance good flow potential to the
main stream of Jalele (it has high stream density).

6
 Project Site

Figure 1: Study area location

3.2 Approach and Methodology

The necessary data that was collected and used for this study were classified into two:
primary and secondary data. Data necessary for this project work was collected from different
sources. Data collection include: soil, agronomy, hydrology, geology, surveying that is used
for headwork, main canal, and irrigation system design.

3.2.1 Soil

For the study of physical and chemical properties of the command area and other associated
studies, general field visit and reconnaissance was made and the command area has been
divided into three soil units and field and laboratory studies have been carried out.

7
Concerning the main canal route (to know textural composition, infiltration, seepage
condition and other associated studies), the laboratory and field studies of the samples have
been carried out.

At every 200m distance, soil samples for laboratory analysis were collected at 0 ~ 30cm and
30 ~ 60cm depth. The samples collected are expected to represent the whole canal line. The
vegetation, slope change, geology and other conditions of the area have been considered to
collect the representative samples.

3.2.2 Agronomy

The project area farmers are practicing mixed system of farming, crop production and animal
husbandry. Improved agricultural practices and mechanized agricultural technology are not
well developed. However, fertilizer applications and using selected seed (package) are
practiced by some farmers only on some crops.

3.2.3 Geology

It was not possible to get any written material about Jalele River in general and about the
project site in particular.

To study and describe the geology of the site top- map of the area (scale 1:50,000) geological
compass and geological hammer were used. Observations were made in the catchment,
command area and streams and along the main canal. Geologic test pits were dug at right and
left side edge of the river along the weir axis.

Information was gathered from the Zonal Water, Mines and Energy Resources Development
Department concerning the boreholes dug in the areas so as to have information about the
ground water.

8
4. HEAD WORK, AND IRRIGATION SYSTEM DESIGN

Head work, irrigation and drainage system design involves determination of more efficient
and reliable hydraulic structures of the headwork including weir, stilling basin, and design of
on farm structures.

4.1. Head Work Design

A weir is a concrete or masonry structure which is constructed across the open channel (such
as a river) to change its water flow characteristics. Weirs are constructed as an obstruction to
flow of water. In my project, the weir is a concrete structure constructed across Jalele river.

Weirs are classified according to shape of the opening, shape of the crest and effect of the
sides on the emerging nappe.

1) Types of weirs based on shape of the opening

a. Rectangular weir
b. Triangular weir
c. Trapezoidal weir

2) Types of weirs based on shape of the crest

a. Sharp-crested weir
b. Broad- crested weir
c. Narrow-crested weir
d. Ogee-shaped weir: type of weir for Jalele project.

3) Types of weirs based on effect of the sides on the emerging nappe

a. Weir with end contraction (contracted weir)
b. Weir without end contraction (suppressed weir)

4.1.1 Weir Type Selection and Weir Design

The geology of the weir site is composed of alluvial deposits from the size of boulders up to
small sized gravel around the riverbed. From the test pits taken on the axis of the weir (on
both edges of the river), the profile is characterized by boulders with admixture of silty clay.

The upstream of the weir site that is catchment area is v ~ shaped valley and there are
mountains of domes cliff forms. There are big boulders that comes from the catchment area.

9
Ogee weir is selected for the reason that big boulders are coming from upstream mountainous
area. Ogee weir is the appropriate weir in transporting boulders from upstream to downstream
smoothly. Other reason for selecting ogee weir is due to its high coefficient of discharge, as
flow over an ogee weir is dependent on the discharge coefficient. Ogee weir, as the name
says, represents the shape of the downstream face of the weir. The downstream face of the
weir is constructed corresponding to the shape of lower nappe of freely falling water jet
which is in ogee shape. The ogee shape of the downstream face is designed on the basis of
the principle of a projectile. In general, the shape of lower nappe of the water jet is not
constant for all water heads hence, the shape obtained for the maximum head is taken into
account while designing ogee weir.

Data used for Design

➢ Peak Flood Discharge: The maximum probable flood discharge is 30.0m3/sec.
➢ Rating Curve: The water level attained during the floods before the construction of
the weir is obtained from the stage-discharge curve, and the depth is equal to 0.90m.
➢ Cross Section of the River: The width of the river at the weir axis is measured to be
12.0m.
➢ Weir Crest Length: From field observations and design considerations, a weir length
of 16.0m is fixed.
➢ The shape of the ogee weir depends upon the head, the inclination of the upstream
face of the overflow section, and the height of the overflow section above the floor of
the entrance channel.

4.1.2 Determination of Weir Crest Level

Average elevation of the highest field in the command area = 1860.70.

Water depth required = 0.31m.
Head loss across head regulator = 0.15m.
Head loss along the main canal =0.807m.
Head loss at turnout = 0.05m.
Entrance, friction and exit loss = 0.0803m.
Free board = 0.10m.
Average river bed elevation = 1861.30m.
Total head loss = 1.50m.
Therefore, weir crest level = 1860.70 + 1.50 = 1862.20.
Therefore, crest height, h = 1862.20 – 1861.30 = 0.90m.

10
 4.1.3 Estimation of Tail Water Depth

The design peak flood discharge for the specific catchment is 30.0m3/sec.

No. Station Relative Dist (m) Elevation Cumulative Ht (m) Area (m2) Remark
1 0+00 0 1859.53 0.00 0.000
2 0+03 3 1859.83 0.30 0.450
3 0+10 7 1860.24 0.71 3.535
4 0+25 15 1860.75 1.22 14.475
5 0+34 9 1860.82 1.29 11.295
6 0+37 3 1861.02 1.49 4.170
7 0+41 4 1861.36 1.83 6.640 Weir Axis
8 0+49 8 1861.77 2.24 16.280
9 0+54 5 1862.24 2.71 12.375
10 0+62 8 1862.52 2.99 22.800
11 0+75 13 1862.68 3.15 39.910
12 0+84 9 1862.69 3.16 28.395
13 0+94 10 1863.41 3.88 35.200
Total 94 195.525
Table 4: Average River Bed Slope Estimation

Individual Area, An = {[Hn + H(n-1)]/2}*Ln

Cumulative Height, Eln – El0
Average Height, Hav =2A/2 = (2*195.525m2)/94 = 4.16m.
Average River Bed Slope, Iav = Hav/L =4.16m/94m = 0.04425 = 4.425%

11
12
 Transversal Cross Section of Jalele River(Weir Axis)

1868

1867

1866
Elevation(m.a.m.s.l)

1865

1864

1863

1862

1861
0 5 10 15 20 25 30 35 40 45
Distance(m)

13
 4.1.4 Peak Flood of the River

Elevation Depth, d (m) Water Area, Wetted Hydraulic Velocity, Discharge, Remark
A (m2) Perimeter, Radius, R V Q (m3/sec)
P (m) (m) (m/sec)
1861.30 0.00 0.000 0.000 0.000 0.000 0.000 Center of River
1861.52 0.22 0.558 5.090 0.109 1.371 0.765
1861.72 0.42 1.867 8.066 0.231 2.265 4.236
1861.98 0.68 4.233 10.379 0.408 3.305 13.991
1864.08 2.78 25.614 14.579 1.756 8.751 224.146
Table 5: Elevation and depth data

The discharge is calculated from the Manning’s Equation,

Q = (A/n)*(R2/3 I 1/2)
Where Q = Discharge (m3/sec)
A = Water Area (m2)
N = Manning’s Roughness Coefficient
R = Hydraulic Radius (m)
I = Average River Bed Slope

After preparing the Rating Curve (plotting discharge versus depth from table 5), the tail
water depth (depth of water during the expected maximum flow) is estimated as 0.90m.

Therefore, high flood level of the river (HFL) before construction of the structure is:
HFL = 1861.30 + 0.90 = 1862.20

14
 THE RATING CURVE

1864.5

1864

1863.5
ELEVATION

1863

1862.5
Twl=0.90m
1862

1861.5 Q=30m3/s

1861
-50 0 50 100 150 200 250
3
DISCHARGE (M /SEC)

15
 4.1.5 Surface Hydraulics

Water Depth on the Crest

Shape of the Weir: Considering boulder coming from the upstream of the weir and taking into
account its high discharge coefficient it is decided to design an ogee shaped weir with inclined
upstream face.

Crest Length of the Weir: From physical field observations, the weir crest length should be equal to
16.0m.

Discharge over the weir is generally expressed as:

Q = CLHe3/2, where Q = Peak flood (m3/sec)/50 years return period/
L = Weir crest length (m)
C = Coefficient of discharge = 2.22
He = Height of energy line above the crest (m)

Therefore, He = [Q/CL] 2/3 ⇒ He = [30/(2.22*16)] = 0.893m.

He = 0.893m
Velocity of approach, Va = Q/A = {Q/[L(h-P)+Hd]}, where P = Silt height
Va = {30/[16(0.9 – 0.4) + Hd]} = [1.875/(0.5 +Hd)]
Therefore, hv = Va /2g = {(30)2/[(16(0.5 +H d )]2}* 1/2g
2

⇒ hv =[0.17918/(0.5+Hd)2] ------------------------------------- (i)

But He = Hd + hv ⇒ hv = He – Hd
⇒ hv = 0.893 – Hd --------------------- (ii)
Equating (i) & (ii),
[0.17918/(0.5+Hd)2] = 0.893 – Hd

Hd Left Side Right Side Remark

0.75 0.1146 0.143
0.78 0.109 0.113
0.785 0.108 0.108 Ok

Therefore, Hd = 0.785m, hv = 0.108m.

16
The equation of ogee- shaped weirs as of the Water Ways Experiment Station is expressed as:
Xn = K0Hdn-1Y,
Where:
X and Y are co-ordinates of the crest profile with the origin at the highest point of the crest, Hd is
the design head excluding the head due to the velocity of approach and, K0 and n are parameters
depending on the slope of the upstream face. For our case,
The upstream face has a slope of 3Vertical:2Horizontal.
K0 = 1.939
n = 1.810
Substituting the values in the above equation, we get the following formula for the weir crest
geometry;
Y = -X1.810/1.5937
The shape can be determined by assigning different values to X and calculating the corresponding
co-ordinate, Y.

No. X Y = -X1.810/1.5937
1 0.000 0.000
2 0.250 -0.051
3 0.500 -0.179
4 0.750 -0.372
5 1.000 -0.627
6 1.225 -0.905

Determination of the Radius of the Base Bucket

The toe of the weir should be connected to the base by a circular curve.
V = √[2g(h + 0.5Hd)], where V = velocity at the toe of the weir
H= weir height = 0.90m.
Hd = design head = 0.785m.
⇒V = √[2*9.81(0.90 + 0.5*0.785)] = 5.035m/sec

K = [(V + 6.40H + 4.88)/(3.6Hd + 19.50)]

= [(5.035+6.40*0.893 + 4.88)/(3.60*0.785 + 19.50

17
 ⇒K = 0.70

R0 = 0.305*10k = 0.305*10 0.70

⇒R0 = 1.528m

The arc at the base should be tangent to the weir face (slope of the tangent is 1V:0.75H).

In considering the reverse, the ogee curve is continuous up to the value of X = 1.225; thus the Y
value becomes –0.905.
Let f(X) = -X1.810/1.5937 and g(X) = -0.905.
f and g are continuous on [0,1.225] and f(X) ≥ g(X). Then the area A of the region R between the
graphs of f and g on [0,1.225] is given by:
A = ∫[f(X) – g(X)]dx
1.225

= ∫ [(-X 1.810/1.5937) – (-0.90)]dx

0
1.225 1.225

= (-1/1.5937) ∫ X 1.810
dx + 0.905∫dx
0 0
1.225
(1.810+1)
=(-1/1.5937)[X + 0.905X]
0

= -0.3949 + 1.108
⇒ A = 0.713m2
Then the moments Mx and My about the axes are given by:
1.225

Mx = ∫1/2{[f(X)] – [g(X)]2}dx
2

0
1.225 1.225

= ∫1/2{[-X 1.810
/1.5937)] dx – 1/2∫(-0.905) dx
2 2

0 0
1.225

=(1/5.079)[(X 3.62+1
)/(3.62+1) – (1/2)(0.819)]
0

_ ⇒Mx = -0.3928
Y = Mx/A = -0.3928/0.713 = -0.55m.

18
 1.225

My = ∫X[f(X) – g(X)]dx
0

1.225

My = ∫X[-X 1.810/1.5937 + 0.905]dx

0

= -0.3568 +0.679
⇒My = 0.322m.
_
X = My /A = 0.322/0.713 = 0.451m
_ _
Therefore, Center of Gravity of the ogee geometry, (X,Y) = (0.451,-0.55)

4.1.6 Stability Analysis

For the analysis of stability, the following parameters are considered:

Unit weight of concrete = 2.3T/M3
Unit weight of Masonry = 2.1T/M3
Unit weight of Water = 1.0T/M3
Unit weight of Silt = 1.36T/M3

I. Static Case

No. Name &Description of Force Magnitude of Force (T) Arm Length Moment about Toe (TM)
Vertical Horizontal (M) MR (+) MO0(-)
1 Self-Weight – W1 0.529 - 2.840 1.502 -
2 Self-Weight – W2 0.388 - 2.530 0.983 -
3 Self-Weight – W3 0.015 - 2.490 0.037 -
4 Self-Weight – W4 1.640 - 1.969 3.229 -
5 Self-Weight – W5 1.050 - 2.990 3.139 -
6 Self-Weight – W6 1.622 - 1.967 3.199 -
7 Self-Weight – W7 0.158 - 2.640 0.416 -
8 Self-Weight – W8 0.040 - 1.078 0.043 -
9 Self-Weight – W9 0.110 - 1.080 0.120 -

19
10 Self-Weight – W10 0.839 - 1.250 1.046 -
11 Self-Weight – W11 0.166 - 0.860 0.142 -
12 Self-Weight – W12 0.074 - 0.780 0.058 -
13 Self-Weight – W13 0.048 - 0.260 0.013 -
14 Self-Weight – W14 2.100 - 0.500 1.050 -
14 Water Pressure -Wp - 0.405 1.873 - 0.758
15 Silt Pressure – SP1 - 0.109 1.706 - 0.186
16 Water Weight – WW1 0.405 - 2.940 1.191 -
17 Uplift Pressure – UP1 3.771 - 1.620 - 6.109
18 Uplift Pressure – UP2 1.019 - 2.160 - 2.201

Summation of all Vertical Forces, Fv = 4.393 T.

Summation of all Horizontal Forces, Fh = 0.5138 T.
Summation of all Balancing Moments, M(r) =16.167 T.M.
Summation of all Overturning Moments, M(o) = 9.2536 T.M.
Summation of all Moments, M = 6.913 T.M.
Check for Stability
Check for Sliding
Factor of safety against sliding, F.S/s = μFv/Fh >1.50.
F.S/s = 0.65(4.393)/0.5138 = 5.55 >1.50. ------------------ Ok.

Check for Overturning

Factor of safety against overturning, F.S/ot = M(r)/ M(o) > 1.50.
F.S/ot = 16.167/9.2536 = 1.747 > 1.50. ------------------- Ok.

Check for Overstress

X = M/Fv = 6.913/4.393 = 1.573m.

Eccentricity, e = /1.573 – L/2/ = /1.573 – 3.24/2/ = 0.047m.
Allowable Eccentricity, e = L/6 = 3.24/6 = 0.54m.
0.047 < 0.54. Hence, no tension will develop anywhere in the structure.

20
 II. Dynamic Case

No. Name &Description of Force Magnitude of Force (T) Arm Length Moment about Toe (TM)
Vertical Horizontal (M) MR (+) MO (-)
1 Self-Weight – W1 0.529 - 2.840 1.502 -
2 Self-Weight – W2 0.388 - 2.530 0.983 -
3 Self-Weight – W3 0.015 - 2.490 0.037 -
4 Self-Weight – W4 1.640 - 1.969 3.229 -
5 Self-Weight – W5 1.050 - 2.990 3.139 -
6 Self-Weight – W6 1.622 - 1.967 3.199 -
7 Self-Weight – W7 0.158 - 2.640 0.416 -
8 Self-Weight – W8 0. 402 - 1.078 0.043 -
9 Self-Weight – W9 0.110 - 1.080 0.120 -
10 Self-Weight – W10 0.839 - 1.250 1.046 -
11 Self-Weight – W11 0.166 - 0.860 0.142 -
12 Self-Weight – W12 0. 739 - 0.780 0.058 -
13 Self-Weight – W13 2.100 - 0.260 0.013 -
14 Self-Weight – W14 3.295 - 0.500 1.050
15 Up lift pressure – UP1 - - 1.620 - 5.338
16 Up lift pressure – UP2 1.082 - 2.160 - 2.337
17 Weight of water – WW1 0.405 - 1.873 1.191 -
18 Water pressure – WP1 - 0.707 2.023 - 1.429
19 Water pressure – WP2 - 0.405 1.873 - 0.758
20 Silt pressure -SP - 0.109 1.973 - 0.21

Summation of all Vertical Forces, Fv = 5.1685 T.

Summation of all Horizontal Forces, Fh = 1.220 T.
Summation of all Balancing Moments, M(r) =16.16738 T.M.
Summation of all Overturning Moments, M(o) = 10.0766 T.M.
Summation of all Moments, M = 6.0907 T.M.

Check for Stability

i. Check for Sliding
Factor of safety against sliding, F.S/s = μFv/Fh >1.50.
21
 F.S/s = 0.65(5.1685)/1.22 = 2.75. >1.50. ------------------ Ok.
ii. Check for Overturning
Factor of safety against overturning, F.S/ot = M(r)/ M(o) > 1.50.
F.S/ot = 16.16738/10.0766 = 1.604 > 1.50. ------------------- Ok.

iii. Check for Overstress

X = M/Fv = 6.0907/5.1685 = 1.1.178m.

Eccentricity, e = /1.178 – L/2/ = /1.178 – 3.24/2/ = 0.441m.
Allowable Eccentricity, e = L/6 = 3.24/6 = 0.54m.
0.441 < 0.54. Hence, no tension will develop anywhere in the structure

4.1.7 Design of Stilling Basin

Design Information of Stilling Basin

Hydraulic Jump

Average Riverbed Elevation = 1861.30.

Weir Crest Level = 1862.20.
Downstream Water Level = 1862.0.
The bed level of stilling basin can be determined by trial-and-error method. Assume the floor level
is 0.80m lower than the riverbed level.
Therefore, assume EL1 = EL3 – 0.80m.
= 1861.30 – 0.80.
= 1860.50.
Total energy head, He = E0 = E1
Z = EL0 – Assumed EL1
= 1862.20 – 1860.50.
= 1.70m.
H = He + Z
= 0.893 + 1.70.
= 2.593m.
Discharge intensity over the weir crest, q = 1.875m3/sec/m.
E0 = E1 = d1 + hv1 = d1 + v12/2g

22
 But v1 = q/d1.
By the principle of conservation of energy,
d1 + v12/2g = 2.593.
d1 = 2.593 – 0.17918/d12

d1 2.593 – 0.17918/d12 Remark

0.270 0.135
0.278 0.274 OK
0.280 0.307
Therefore, d1 = 0.278m.
V1 = q/d1 = 1.875/0.278 = 6.744m/sec.
Froud Number, Fr = v1/√(gd1) = 6.744/√ (9.81*0.278) = 4.084.
d2 = (d1/2) √[(1+8Fr2) – 1] =1.473m.
If the water surface of the jump is 0.20m higher than the downstream water level,
EL = WL3 + 0.20 = 1862.20 + 0.20 = 1862.40.
1862.40 – 1.473 = 1860.972 > 1860.500.
The sequent depth, d2 is greater than the tail water depth by 0.573m. Hence, it is decided to depress
the floor level to an elevation of 1860.727.
Length of basin, L = 5(d2 – d1)
= 5(1.473 – 0.278)
= 5.975m. ≈ 6.0m.
Scour Depth

The depth of scour may be calculated from Lacey’s Formula, as follows:

R = 1.35[q2/f]1/3, Where R = Depth of scour below the highest flood in meter.
q = highest flood discharge of the river in m3/sec per meter
length of the point of consideration.
f = silt factor = 1.
R = 1.35[(1.875)2/ 1]1/3 = 2.05m.
- Upstream scour depth = 1.25*R = 2.566m. ≈ 2.57m.
- Downstream scour depth = 1.5*R = 3.075m ≈ 3.08m.

23
Exit Gradient

The factor of safety for exit gradient for soil types of our case (as of the geologic information of the
weir axis) is selected to be 1/5.
The general formula adopted for exit gradient is

EG = (H/d) *1/(π√ λ)
A graph based on Khosla’s theory is placed to indicate the correction between the floor length, b
and cut off depth, d i.e,

Ժ and 1/(л√ λ) to determine exit gradient.

λ =(1+√ 1+ Ժ2 )/2 , Ժ=b/d

for b=9.24 and d=1.00m.

Ժ=9.24/1.00=9.24
For Ժ = 9.24 from the graph , 1/(л√ λ) =0.146
Hmax – is for the static case and equal to 0.90m.

EG = 0.90/1.00*1/(л√ λ)
=0.90*0.146
=0.1314 < 0.20-------------------safe.

Thickness of the floor

For the downstream apron the thickness to be determined depends on whether a static or dynamic
case is being considered.

1. Static case:
Head on the structure
= 1862.200-1861.300
= 0.900m
2. Dynamic case
Head on the structure
= Upstream TEL – Downstream TEL

24
 = 1863.093 – 1862.282
= 0.810m
The Maximum static head should be used for designing purposes.

Weighted creep length

According to Lane’s method, weighted creep ratio is recommended in the form,
L>CH where L: percolation distance (m.)
H: maximum head, = 0.90
C: Lane’s creep ratio = 3.20
L> 3.20x0.90
L> 2.880
L= Σlv+1/3lh ≥ CH
Lc = (1.00+-.50+1.08+1.10)+(0.50+0.70+1.00+6)1/3
= 3.68+2.733
= 6.413
Weighted creep ratio =L c/head on the structure
= 6.413/0.90 = 7.720
Static case (Hmax = 0.90)
Point Weight creep length Hmax [1-LA/LC] (TWL-WLA) t(Safety factor/rm-1)
Case H V L
A 2.200 2.580 3.313 0.435 0.200 0.635
B 4.200 2.580 3.979 0.341 0.200 0.541
C 0.000 2.580 4.646 0.247 0.200 0.447
Dynamic case (Hmax=0.81)
A 2.30 2.58 3.313 0.392 0.598 0.989 ≈ 1.000
B 2.58 0.306 0.000 0.306
C 2.58 0.222 0.000 0.222

Checking the thickness at each point

Point A 1.00 > 0.989--------------- Ok (dynamic case)
Point B 0.55 > 0.540--------------- Ok (static case)
Point C 0.45> 0.447 --------------- Ok (static case)

25
 4.2. Surface Irrigation and Drainage System Design

In order to be in a position to select an irrigation system for a given area, it is important to look at
the types of irrigation systems commonly used. Based on the method of applying water to the land,
there are four broad classes of irrigation systems:
1) Surface irrigation systems,
2) Sprinkler irrigation systems,
3) Localized irrigation systems and
4) Sub-surface irrigation systems.

Surface irrigation is the application of water by gravity flow to the surface of the field. Either the
entire field is flooded (basin irrigation) or the water is fed into small channels (furrows) or strips of
land (borders).

In sprinkler irrigation systems, water is conveyed and distributed through pressurized pipe networks
before being sprayed onto the land. There are several sprinkler irrigation systems, which can
broadly be divided into set systems and continuous move systems.

In localized irrigation systems, a pipe distribution network is used to distribute and deliver filtered
water (and fertilizer) to a predetermined point. The three main categories of localized irrigation
methods are drip, spray and bubbler. More recently, drip irrigation systems have been developed
whereby the laterals are buried in the root zone of the crop.

Sub-surface irrigation systems rely on the raising or lowering of the water table in order to effect
groundwater flow to the root zone. As such, they are drainage flow systems.

4.2.1 Field Irrigation Method

Surface irrigation schemes are designed and operated to satisfy the irrigation water requirements of
each field while controlling deep percolation, runoff, evaporation and operational losses. The
performance of the system is determined by the efficiency with which water is conveyed to the
scheme from the headworks, distributed within the scheme and applied to the field, and by the
adequacy and uniformity of application in each field.

26
The classification of surface methods is perhaps somewhat arbitrary in technical literature. This has
been compounded by the fact that a single method is often referred to with different names. Surface
methods are classified by the slope, the size and shape of the field, the end conditions, and how
water flows into and over the field. Each surface system has unique advantages and disadvantages
depending on such factors like:
1) Initial cost;
2) Size and shape of fields;
3) Soil characteristics;
4) Nature and availability of the water supply;
5) Climate;
6) Cropping patterns;
7) Social preferences and structures;
8) Historical experiences; and
9) Influences external to the surface irrigation system.

Furrow irrigation, the most traditional method of surface irrigation, is recommended for this project,
for the following reasons; it is suitable to the soil type of the project area; it has been traditionally
exercised by the farmers of the project area; it is easily manageable at farmer’s level; it is suitable to
irrigate all crops, which are recommended for the project. Furthermore, furrow irrigation avoids
flooding the entire field surface by channelling the flow along the primary direction of the field
using 'furrows,' 'creases,' or 'corrugations'. Water infiltrates through the wetted perimeter and
spreads vertically and horizontally to refill the soil reservoir. Furrows are often employed in basins
and borders to reduce the effects of topographical variation and crusting. The distinctive feature of
furrow irrigation is that the flow into each furrow is independently set and controlled as opposed to
borders and basins where the flow is set and controlled on a border by border or basin by basin
basis.

4.2.2 Proposed Water Distribution and Scheduling

Unit Flow
The water duty of the project is calculated as 2.16lit/sec/ha. By multiplying this figure by the unit
area of land under each turnout, the unit flow is obtained.

27
Scheduling
The average irrigation interval (recommended by the agronomist) is 7 days. If we have to irrigate
60ha of land in seven days, therefore, we have to irrigate 60/7 = 8.57ha/day. Therefore, the supply
of water would be:
130lt/sec/8.57ha = 15.17lt/sec/ha.

In order to satisfy this condition, the command area is divided into 7 blocks with areas nearly equal
to 8.57ha each, and turnouts with the same schedule of irrigation are identified by similar symbols
(♠, ♣, ♥, etc). See the table 6 below.

Canal Turnout No Area (ha) Discharge, (m3/sec) Remark

Main Canal T-1 0.45 0.97 ♠

Main Canal T-2 1.29 2.79 ♠
Main Canal T-3 1.07 2.31 ♠
Main Canal T-4 1.49 3.22 ♠
Main Canal T-5 0.42 0.91 ♠
Main Canal T-6 0-17 0.37 ♠
Main Canal T-7 2.03 4.38 ♠
Main Canal T-8 1.69 3.65 ♠
Main Canal T-9 1.47 3.18 ♣
Main Canal T-10 0.71 1.53 ♣
Main Canal T-11 0.32 0.69 ♣
Main Canal T-12 1.16 2.51 ♣
Main Canal T-13 2.02 4.36 ♣
Main Canal T-14 3.54 7.65 ♣
Main Canal T-15 3.58 7.73 ♥
Main Canal T-16 2.5 5.4 ♥
Secondary Canal-1 T-1,1 1.5 3.24 ♥
Secondary Canal-1 T-1,2 1.98 4.28 ♦
Secondary Canal-1 T-1,3 0.82 1.77 ♥
Secondary Canal-1 T-1,4 1.29 2.79 ♦
Secondary Canal-1 T-1,5 0.69 1.49 ♦
Secondary Canal-1 T-1,6 0.65 1.4 ♦
Secondary Canal-1 T-1,7 0.55 1.19 ♦
Secondary Canal-1 T-1,8 0.53 1.15 ♦
Secondary Canal-1 T-1,9 0.91 1.97 ♦
Secondary Canal-1 T-1,10 0.37 0.8 ♦

28
 Secondary Canal-1 T-1,11 0.55 1.19 ♦
Secondary Canal-2 T-2,1 0.17 0.37 ♦
Secondary Canal-2 T-2,2 0.23 0.5 ♦
Secondary Canal-2 T-2,3 0.51 1.1 ♦
Secondary Canal-2 T-2,4 0.48 1.04 ▲
Secondary Canal-2 T-2,5 0.2 0.43 ▲
Secondary Canal-2 T-2,6 0.35 0.76 ▲
Secondary Canal-2 T-2,8 0.27 0.58 ▲
Secondary Canal-2 T-2,9 0.39 0.84 ▲
Secondary Canal-2 T-2,10 0.43 0.93 ▲
Secondary Canal-2 T-2,11 1.99 4.3 ▲
Secondary Canal-2 T-2,12 0.59 1.27 ▲
Secondary Canal-2 T-2,13 0.97 2.1 ▲
Secondary Canal-2 T-2,14 0.67 1.45 ▲
Secondary Canal-2 T-2,15 0.85 1.84 ▲
Secondary Canal-2 T-2,16 1.93 4.17 ■
Secondary Canal-2 T-2,17 0.62 1.34 ▲
Secondary Canal-2 T-2,18 2.29 4.95 ■
Secondary Canal-2 T-2,19 1.95 4.21 ■
Secondary Canal-2 T-2,20 2.26 4.88 ■
Secondary Canal-2 T-2-21 1 2.16 ☻
Secondary Canal -3 T-3,1 1.48 3.2 ☻
Secondary Canal -3 T-3,2 1.73 3.74 ☻
Secondary Canal -3 T-3,3 1.36 2.94 ☻
Secondary Canal -3 T-3,4 1.42 3.07 ☻
Secondary Canal -3 T-3,5 1 2.16 ☻

Table 6: List of turnouts available in the project

4.2.3 Water Duty

The maximum total irrigation water requirement (for Onion) is calculated as 6,760m3/ha for the
growing period of 5 months. But the maximum irrigation water requirement (in the month of
March) is 2,340m3/ha. This figure is used to calculate the water duty of the project.

Taking the farmers past experience in to consideration, 10 hours irrigation per day is considered to
calculate the water duty.

29
Hence, the water duty would be 2340m3/hax103lt/m3/month = 234 x 104lt/ha/30 x 24 x 60 x 60 =
0.9lt/sec/ha. This figure is for 24 hours irrigation.

Therefore, for 10 hours irrigation, Q = 0.9x24/10 = 2.16lt/sec/ha. This figure satisfies all of the
crops recommended for this project.

4.2.4 Main Canal Design

The main canal has a total length of 3.54km. Of this length, 12.00m is closed conduit (diameter of
pipe = 50cm), 38.00m is box canal (a box with masonry lining), 65.00m is box conduit (with cover
slab), 524.50m is line canal (masonry lining), and 2900.50m is earthen canal with a longitudinal
slope of 1/560. The Manning’s Equation is used to design the canal.

The main canal is a contour canal throughout its length unless otherwise unavoidable obstacles are
reached, it is tried to maintain a constant depth of cut of 0.60m. The new canal joins the old main
canal at a chainage of 2+750. Drop structures are provided on the canal after it joins the old main
canal so as to maintain the alignment of the later.

Dry discharge of Jalele River is estimated as 125lt/sec (by floating method). Releasing 20lt/sec. For
downstream users, the can portion from the head structure up to Leku River is designed for a
discharge of 105lt/sec.

Q = 105lt/sec
S = 1/560 (for the carton part of the canal)
n = 0.025
b:d= 1:1
Canal side slope = 1:1 (for the earthen part)
A=(b+T)/(2) d = (b+b+b+b)/(a) b = 4b2/2 = 2b2 = 2d2

P= 2√b2+b2+b = 2√2b2+b = 2b√2+b = 2d√2+d

R= A/P = 2d2/d(2√2+1 = 2/(2√2+1) d
Q= VA, V=1/n R 2/3 5 1/2.A
= 1/0.225x2/(2√2+1 d) 2/3 (1/560) 1/2.A
= 1.096.d2/3 2d2

30
0.13 = 2x1.09 d8/3.
D = 0.347 ≈ 0.35m
Free board, f= 0.25m
 D= 0.60m
 A= 0.24m2, P= 1.327m, R= 0.181m
V= 1/0.025 (0.181) 2/3 (1/560) 1/2
= 0.54m/sec

Design of Lined Canal

(0+12+0+50)
Q = 130lt/sec
S = 0.1/38 = 1/380
N = 0.017
B:d = 1

A= bd= 1.5d2
P= 2d+1.5d= 3.5d
R= A/P = 1.5d2/3.5d = 0.429d

Q= A/n R2/3 S1/2

0.13 = 1.5d2/0.017 (0.429d) 2/3 (1/380) 1/3
0.051 = d8/3
 d= 0.33m
 b= 1.5d= 0.49m ≈ 0.50m
Q= VA V= Q/A = 0.13/0.33x0.49 = 0.80m/sec

Let free board, f= 0.17m

 D= 0.50m
0+50-0+115

Box contract (Box with cover slab)

Q= 130lt/sec
S=1/25
n=0.017

31
b:d = 1.5
A= bd= 1.5d2
R= 0.429d
Q= a/n R2/d  0.13 1.5d2/0.017 (0.429d) 2/3 (1/250) 1/2
 0.041 = d8/3
 d=0.30m
 b= 1.5d = 0.45m
Q= VAV = Q/A = 0.13/0.30x0.45 = 0.96m/sec
Let free board, f = 0.20m
 D= 0.50m

Design of Lined canal (629-1125,1575-1610.50)

Q= 130lt/sec
S= 1/560
n= 0.017
b:d = 1.5
b=1.5d
A= bd= 1.5d2
P= 2d+1.5d = 3.5d
R= A/P = 1.5d2/3.5d = 0.429d
Q= A/n R2/3 51/2
0.13 = 1.5d2/0.017 (0.429d) 2/3 (1/560)1/2
 d= 0.35m
b= 0.52m
Free board, f= 0.15m
 Total depth of lined canal = 0.50m
Q= VAV= Q/A = 0.13/0.35x0.52
= 0.72m/sec

32
 4.2.5 Secondary Canals Design

Three secondary canals, namely secondary canal -1, 2 & 3 are designed for the scheme. The points
at which these canals depart from the main canal and their respective lengths are shown on table 7.

No Type of secondary Canal Length Point of Departure from the

(km) main canal
1 Secondary Canal -1 0.800 1+750
2 Secondary Canal -2 2.581 2+345
3 Secondary Canal -3 0.636 2+870

Table 7: List of secondary canals location and length

Towards the beginning of them, all of the secondary canals run on steeply slope. Therefore, they are
equipped with chute structures. And secondary canals 1 and 2 have got chute structures at the
middle of their lengths due to the unavoidable steeply slope which they run through.

The Manning Equation is used to design the secondary canals, too. The hydraulic parameters of the
canals are shown on the following sketches.

Design of Secondary Canal-1

Secondary canal 2 and 3 are also designed in the same way as secondary canal 1.
Design slope, S= 1/400
n= 0.025
b:d = 1
Canal side slope = 1
A= (b+ T)/(2) d = 2d2
P= 2√2b2+b = 2b√2+6 = 2d√2+d
R= A/P = 2/2√2+1d
Q= VA V= 1/n R2/3 S1/2
= 1.30d2/3
0.02125 = 2d2 (1.3d2/3)
= 2.50 d8/3
d = 0.17m. Mane b= 0.20m for the sake of ease of construction
Fb = 0.13m

33
 D= 0.30m
R= 2/2r2+1 d = 0.089m
V= 1/0.025 (0.089) 2/3 (1/400)1/2 = 0.40m/sec

Lined canal on secondary canal-1

(0+650-0+800)
Length = 150m
Slope = 1805.50-1799.7/150 = 0.0387 3.87%
Q = 0.02125m3/sec
n = 0.017
b = 2d
A = bd=2d2
P = 2d+d= 4d
R = A/P = 2d2/4d= d/2
Q = A/n R2/3 5 ½
0.02125= 2d2/(0.017) (d/2)2/3 (0.0387)1/2
0.00146 = d8/3
D = 0.086m
b = 2d = 0.17m
Free board, fb = 0.114m
D= 0.20m

4.2.6 Field Canals Design

The amount of water supplied to the field through turnouts is very small (not more than 4.88lt/sec).
Therefore, it is believed that the farmer’s furrow field canals without any slope-adjusting structures
are sufficient for this purpose.

4.2.7 Canal Structures Design

A. Drop Structures

There are eight (8) vertical drops of 1.0m height (USBR Type) on the main canal. These are
provided to make the slope of the old main canal compatible with our design slope.
➢ On Secondary canal-1, there is one drop of 0.50m height.

34
 ➢ On secondary canal –2, there are eight drops of 0.80m height, two drops of 0.10m height
and one drops of 0.50m height, which amounts to the total of eleven drops.
➢ On secondary canal –3, there are four drops of 0.80m height. All of the drops are vertical
drops (USBR type).

Design of vertical drops (H=1m) (Main canal)

Remaining drops are done in the same manner on main and secondary canals.
Design discharge, Q= 0.130m3/sec
Height of drop, H= 1.0m
Width of drop, bc = 0.734Q/(d1)3/2 = 0.734(0.13)/(0.313)3/2 = 0.55m
Unit discharge, q = Q/bc = 0.236m3/sec/m
Critical depth, dc = [q2/q]1/3 = 0.18m

Stilling basin
Lip height, a= dc/∂ = 0.09m use a= 0.15m
Length, L = [2-5+1.1dc/H+0.7(dc/H)3]√Hdc = 1.15m ≈ 1.2m
Width , B= 18.46√Q/Q+9.91 = 0.66m = 0.70m

B. Culverts
The culverts on the main and secondary canals with their structural dimension are described by
table 8

No Canal Length of culvert Pipe Diameter Number of

(m) (cm) culverts
1 Main canal 6 40 4
2 Main canal 5 40 7
3 SC-1 6 20 1
4 SC-2 5 30 6
5 SC-3 6 20 1

Table 8: List of culverts on main and secondary canals

Design of 5 m culvert-Main Canal

Remaining culverts on main and secondary canals are designed in the same.
Design velocity in canal = 0.535m/sec

35
Pipe diameter = 0.40m
Area of pipe, H/r = 1.6  A/r 2.694 A= 0.10776m2
Velocity of water in pipe = Q/A = 0.130/0.10776 = 1.21m/sec
Velocity head in pipe = V2/2g = 0.075m
Wetted perimeter, H/r = 1.6 P/r = 4.428 P= 0.8856m
Hydraulic radius, H/r = 1.6 R/r= 0.608R=0.1216m
Value of n = 0.018

Frictional loss in pipe, hf = (Vn/R2/3)2x L

H= 0.8D
= 0.32m
H/r = 0.32/0.2 = 1.6
 P= 0.8856m
H/r = 1.6 R/r = 0.608
 R=0.1216m
 hf = [0.46x0.018/(0.23) 2/3] 2x5= 0.04m

Water surface change at the u/s 8 d/s of culvert

Drop of water surface at the inlet of the culvert
Dh1 = 1.5(V22- V12/2g) = 0.09m ≈ 0.10m
Rise of water surface at d/s of canal section
Dh2 = 0.3 (V22/2g) = 0.0.018m ≈ 0.02m

C. Turnouts
A free pipe outlet is designed. The discharge can be computed by using the equation
Q = CaA√2gHo, where
Cd = Coefficient of discharge = 0.62
HO = Head on upstream side measured from FSL of distributary up to center of pipe outlet.
A = Area of cross section of pipe.

The calculation is made for the maximum area of land served by a single turnout, and this one is
adopted for the rest of the outlets. The maximum area of land served by a single turnout is 3.58ha
(T-15)
q = Duty x3.58 = 2.16lt/sec/hax3.58ha

36
 = 7.73lt/sec
Let HO = 17cm = 0.17m (for outlets on the main canal)
7.73x10-3 = 0.62A√2x9.81x0.17
 A = 6.83x10-3 m2
  = 0.05m.
Therefore, a pipe out let (concrete pipe) of diameter 10cm would be used moreover; a check
structure of 5.10cm height is arranged in front of every outlet in order to assure continuous and
sufficient supply of water into the field. The discharge of the off taken would be controlled by
wooden/steel gates of specified dimensions.

Secondary canals-1 and 3 take off by a pipe of diameter 15 cm, while secondary canal-2 takes off
by a pipe of diameter 20cm.

The following table (table 9) describes the location of turnouts on each type of canal (i.e., main and
secondary canals).

Turnout Turnout
No Canal Location No Canal Location
No No
1 MC SC-1 1+075 29 SC-1 T-1,10 0+700
2 MC SC-2 2+345 30 SC-1 T-1,11 0+800
3 MC SC-3 2+870 31 SC-2 T-2,1 0+225
4 MC T-1 0+350 32 SC-2 T-2,2 0+325
5 MC T-2 0+425 33 SC-2 T-2,3 0+425
6 MC T-3 0+525 34 SC-2 T-2,4 0+475
7 MC T-4 1+175 35 SC-2 T-2,5 0+575
8 MC T-5 1+275 36 SC-2 T-2,6 0+725
9 MC T-6 1+950 37 SC-2 T-2,7 0+875
10 MC T-7 2+095 38 SC-2 T-2,8 1+025
11 MC T-8 2+300 39 SC-2 T-2,9 1+075
12 MC T-9 2+400 40 SC-2 T-2,10 1+100
13 MC T-10 2+545 41 SC-2 T-2,11 1+175
14 MC T-11 2+600 42 SC-2 T-2,12 1+30
15 MC T-12 2+900 43 SC-2 T-2,13 1+375
16 MC T-13 3+100 44 SC-2 T-2,14 1+485
17 MC T-14 3+300 45 SC-2 T-2,15 1+656
18 MC T-15 3+400 46 SC-2 T-2,16 1+906

37
 19 MC T-16 3+523 47 SC-2 T-2,17 2+006
20 SC-1 T-1,1 0+175 48 SC-2 T-2,18 2+181
21 SC-1 T-1,2 0+325 49 SC-2 T-2,19 2+256
22 SC-1 T-1,3 0+450 50 SC-2 T-2,20 2+331
23 SC-1 T-1,4 0+450 51 SC-2 T-2,21 2+431
24 SC-1 T-1,5 0+525 52 SC3 T-3,1 0+211
25 SC-1 T-1,6 0+525 53 SC3 T-3,2 0+286
26 SC-1 T-1,7 0+600 54 SC3 T-3,3 0+386
27 SC-1 T-1,8 0+600 55 SC3 T-3,4 0+486
28 SC-1 T-1,9 0+700 56 SC3 T-3,5 0+586
Table 9: Location of Turnouts

D. Chutes

Towards their beginning and at some of their middle chainage, the secondary canals run through
profiles of steeply slopes. Therefore, chute structures are provided to these canals at these steeply
slope profiles. The lengths and chainages of the chute structures on the secondary canals are
described by the following table (table 10):

No. Canal Chute No. Location Length (m)

1 SC-1 Ch-1,1 0+000-0+075 75
2 SC-1 Ch-1,2 0+275-0+320 45
3 SC-1 Ch-1,3 0+400-0+450 50
4 SC-1 Ch-1,4 0+450-0+525 75
5 SC-1 Ch-1,5 0+525-0+600 75
6 SC-1 Ch-1,6 0+600-0+650 50
7 SC-2 Ch-2,1 0+000-0+125 125
8 SC-2 Ch-2,2 0+125-0+169 44
9 SC-2 Ch-2,3 0+430-0+457 27
10 SC-2 Ch-2,4 0+475-0+525 50
11 SC-2 Ch-2,5 0+575-0+625 50
12 SC-2 Ch-s,6 0+575-0+625 50
13 SC-2 Ch-2,7 0+625-0+720 95
14 SC-2 Ch-2,8 0+725-0+750 25
15 SC-2 Ch-2,9 1+220-1+300 80
16 SC-2 Ch-2,10 1+300-1+341 41

38
17 SC-3 Ch-3,1 0+000-0+061 61
18 SC-3 Ch-3,2 0+061-0+136 75
19 SC-3 Ch-3,3 0+136-0+211 75
Table 10: Location and length of chutes of secondary canals

Design of chute 1, 1 (secondary canal 1) (D+00-0+75)

Remaining chutes are designed in the same way as this one.
Discharge, Q= 0.02125m3/sec
Width of notch, bc= 0.734Q/(d)3/2 = 0.22m
Unit discharge, q= Q/bc = 0.096m3/sec/m
Critical depth, dc = [q2/q]1/3 = 0.098m
Critical velocity, Ac = q/dc = 0.98m/sec
Velocity head, hvc = Vc2/2g = 0.049m
Water area, Ac = bcdc = 0.0216m2
Wetted perimeter, Pc = bc+2dc = 0.416m
Hydraulic radius, Rc = Ac/Pc = 0.052m
Water surface, Ic = [(nvc) /(Rc) 2/3 ] 2 0.0143

Chute

Energy calculation
At section (c)
F= EL.A-EL.B= 1858.13-1840.10= 18.03m
Ec = dc+ hvc + F= 0.098+0.049+18.03= 18.177m

39
Energy at section (C)

Designation Results of the calculation

Trial Number 1 2 3
Assumed depth,d1 0.05 0.03 0.02975
b1= bc 0.22 0.22 0.22
A1= b1dc 0.011 0.0066 0.006545
V1= Q/A1 1.932 3.22 3.247
Hv1= V12/2g 0.19 0.528 0.537
P1= b1+2d1 0.32 0.28 0.2795
R1 = A1/P1 0.0344 0.0236 0.0234
I1=(nv1/R12/3)2 0.0964 0.443 0.455
Im= (Ic+I1)/2 0.0554 0.229 0.235
Hfl = Im . L 4.152 17.159 17.589
E1 = 18.177 4.392 17.718 18.156

Froud Number, Fr = (v1/gd1) = [3.247/(9.81*0.02975)] = 6.01

Conjugate Depth, d2 = {(d1/2)*[(1+8Fr2) –1]} = 0.24m

Stilling Basin
Length, L = 4d2 = 0.96m 1m.
Width, B = 18.4bQ/Q+9.91 = 0.27m
Bottom Elevation (EL.C)
V2 = q/d2 = 0.096/0.24= 0.4m/sec
Hv2 = V22 /2g = 0.0082m
E2 = d2+hv2 = 0.25m
a= E2-E3= 0.25-0.174= 0.08m = 0.10m

Design of chute 2, 1 (0+00-0+125)

Q= 0.04161m3/sec
Width of notch, bc = 0.734Q/(d0)3/2 = 0.30m
Q= Q/bc = 0.141m3/sec/m

40
 dc= (q2/g)1/3 = 0.126m
Vc = q/dc = 1.12m/sec
2
hvc = Vc /2g = 0.064m
Ac = bcdc = 0.0378m2
Pc = bc+2dc = 0.552m
Rc = Ac/Pc = 0.069m
Ic = [nvc/(Rc)2/3]2 = 0.0129

Energy calculation
F= 1855.19- 1837-40 = 17.79m
Ec = dc+hvc+F= 17.98m

Energy at section (1)

D1 is solved by trial and error as
D1= 0.0437m
 V1= 3.174m/sec
Fr = V1/√gd1 = 4.848
D2 = d1/2 (√1+8Fr2 –1) = 0.28m
Stilling basin, L= 4d2 = 1.12m ≈ 1.20m
B= (18.46) √Q/(Q+9.91)= 0.38
Bottom elevation (EL.C)
V2 = q/d2= 0.141/0.28 = 0.504m/sec.
hv2 = V22/2g = 0.013m
E2 = d2+hv2= 0.293m
E3 = d3+hv3 = 0.22+(0.468) 2 /2x9.81 = 0.23m
A = E2-E3 = 0.63m, make a= 0.10m

4.2.8 Cross Drainage Structures Design

As it was mentioned above, the main canal is contour canal throughout its length. The drainage
water, which comes from uphill, will be intercepted by interceptor drain and it will be safely passed
down wards through cross drainages structures. The same arrangement of cross drainages is
performed for secondary canals, too.

41
The cross-drainage arrangement is in such a way that the irrigation water will be passing through a
culvert of 5m length, while the drainage water will be passing over the culvert. The design
calculation of a 5m culvert which had been performed for a crossing culvert of the same length will
apply for this case.

The location of cross drainage structure on each canal is described by the following table (table 11).

No. Canal Cross Drainage No. Location

1 Main canal CD-1 0+800
2 Main canal CD-2 2+500
3 Secondary Canal ~ 2 CD-2,1 0+350
4 Secondary Canal ~ 2 CD-2,2 0+875
5 Secondary Canal ~ 2 CD-2,3 1+670
6 Secondary Canal ~ 2 CD-2,4 2+097

Table 11: Cross drainage structures and their locations

4.2.9 Drainage Canals Design

The alignment of field drains and main drain is shown on the irrigation system layout. The water
drained out of the field, i.e., water which is surplus of the irrigation requirement, is very small, and
hence it is not necessary to design a field drain. The farmers’ furrows like drains are believed to be
able to safely drain out the surplus water out of the field.

On the other hand, the main drain is aligned along natural drainage lines of the area. Therefore,
these too do not require special design procedure.

4.2.10 Catch Drains

As it is already stated above, the main canal runs along a hill side of a ridge, i.e. it is a contour
canal. Therefore, a catch drain facility should be arranged in order to safe guard the canals and the
command area against flood hazards of the uphill land.

42
5. RESULTS AND DISCUSSIONS

Surface irrigation scheme is designed and operated to satisfy the irrigation water requirements of
each field while controlling deep percolation, runoff, evaporation and operational losses. The
performance of the system is determined by the efficiency with which water is conveyed to the
scheme from the headworks, distributed within the scheme and applied to the field, and by the
adequacy and uniformity of application in each field. A furrow irrigation system consists of furrows
and ridges. The water is applied by means of small channels or furrows, which follow a uniform
longitudinal slope. The method is best suited to row crops proposed on the project such as maize,
potatoes, onions, tomatoes.

The project consists of 7,567m length of canal of which 3,540m is main canal (contour canal) and
the remaining is secondary canals. Concerning main canal 12m is closed conduit, 38m is box canal,
65m is box conduit, 524.50m is masonry lined canal, and 2900.50m is earthen canal. For both main
and secondary canals designing, Manning’s Equation is used.

On main canal, a change of ground level encountered at eight different locations that necessities the
provision of eight vertical drops (falls) to lower down its bed level to maintain the designed slope.
Eleven drops of different heights are provided on secondary canals to keep the designed slope of the
canals. Towards their beginning and at some of their middle chainages, the secondary canals run
through profiles of steeply slopes. Therefore, chutes are required to reduce the bottom slope of
canals lying on steeply sloping land in order to avoid high velocity of the flow and risk of erosion.
Out of nineteen chutes of different length, six are located on secondary canal one, ten on secondary
canal two and three on secondary canal three.

Turnouts are provided to divert irrigation water from main and secondary canals to field. The
calculation is made for the maximum area of land served by a single turnout, and this one is
adopted for the rest of the outlets. The maximum area of land served by a single turnout is 3.58ha
(T-15). Therefore, a pipe outlet of diameter 10cm would be used. Moreover, a check structure of
5.10cm height is arranged in front of every outlet in order to assure continuous and sufficient
supply of water into the field. The discharge of the offtake would be controlled by wooden/steel
gates.

43
Water is diverted from the tertiary canal into furrows by means of siphons placed over the side of
the ditch or canal bank and be allowed to flow downstream along the furrow. The water level in the
canal must be raised to a sufficient height above the level of the furrows by using a piece of wood,
check plates, or canvas filled with sand. This creates a head difference between the water level in
the field ditch and the furrow, which is necessary for the water flow. The water is gradually
absorbed into the soil and spreads laterally to wet the area between the furrows. With furrow
irrigation, water is mainly lost by deep percolation at the head end of furrow and runoff at the tail
end.

Furrow design is an iterative process that should consider the shape of the furrow, the spacing
between furrows, with the furrow length determined, amongst other factors, by the stream size to
apply and its application time, the soil type and the slope.

Concerning the design of weir that includes the design of stilling basin, the geology of the weir site
as well as the catchment of the project dictate the type of weir to be ogee. That is to say, alluvial
deposits from the size of boulders up to small sized gravel around the riverbed is one of the factors.
Furthermore, big boulders are coming from upstream mountainous area that need smooth passage
from upstream to downstream. In this regard, ogee weir is the best option and that is why ogee weir
is selected and designed.

Average river bed slope around the weir site, Iav = Hav/L = (2 x 195.525m2)/94 = 4.16m/94m =
0.04425 = 4.425%. The water level is obtained from stage ~ discharge curve. After preparing stage
~ discharge curve (i.e., plotting discharge versus depth), the tail water depth (depth of water during
the expected maximum flow) is estimated as 0.90m. For stage ~ discharge curve, the discharge was
calculated by using Manning equation, Q = (A/n)*(R2/3 I 1/2
). Thus, high flood level of the river
(HFL) before construction of weir structure is; HFL = 1861.30m + 0.90m = 1862.20m

Expected maximum flow for Jalele catchments is estimated by Rational Method Qp = 0.00216
CIA0.73 = 0.00216 * 0.63 * 96mm * (1700ha)0.73 = 29.8 m3/s ≈ 30m3/sec, based on field data
observation, i.e., land slope classification, coverage of the area, and value of runoff coefficient, C.

The crest length of the ogee weir is decided to be 16.00m from both observation and experience
point of views.

Ogee weir crest level was determined from average elevation of the highest field in the command
area. The highest field elevation in the command area is 1860.70m. Total head loss is the
44
summation of head loss across head regulator, along main canal, at turnout, at entrance and exit.
The value of total head loss = 1.50m; is from
✓ Water depth required = 0.31m.
✓ Head loss across head regulator = 0.15m.
✓ Head loss along the main canal =0.807m.
✓ Head loss at turnout = 0.05m.
✓ Entrance, friction and exit loss = 0.0803m.
✓ Free board = 0.10m.

Since average river bed elevation = 1861.30m and total head loss = 1.50m, ogee weir crest level
which is the summation of highest field in the command and total head loss is equal to 1862.20 =
1860.70 + 1.50. Thus, ogee weir crest height was determined by taking the difference between ogee
crest level and average river bed level (i.e., h = 1862.20 - 1861.30 = 0.90m).

The equation of ogee-shaped weirs as per the Water Ways Experiment Station is expressed as:
X*n = K0Hdn-1Y,
Where:
X and Y are co-ordinates of the crest profile with the origin at the highest point of the crest,
Hd is the design head excluding the head due to the velocity of approach and,
K0 and n are parameters depending on the slope of the upstream face.
For Jalele ogee weir, the upstream face has a slope of 3 Vertical to 2 Horizontal (3V:2H). This
implies that
K0 = 1.939
n = 1.810.
After substitution, we get the following formula for Jalele weir crest geometry;
Y = -X1.810/1.5937
The shape of the weir is determined by assigning different values to co-ordinate X and calculating
the corresponding co-ordinate, Y.

Y = -X1.810/1.5937
Serial Nr. X Y = -X1.810/1.5937
1 0.000 0.000
2 0.250 -0.051
3 0.500 -0.179
4 0.750 -0.372

45
 5 1.000 -0.627
6 1.225 -0.905

Since the toe of the weir should be connected to the base by a circular curve, the radius of the base
bucket R0 = 1.528m. The center of gravity of the ogee geometry, (X, Y) = (0.451, -0.550)

The stability of the ogee weir structure was analyzed from sliding, overturning and overstress point
of view under both static and dynamic conditions. The outcomes show that the ogee weir is safe
against sliding, overturning and overstress.

The bed level of stilling basin is determined by trial-and-error method. The hydraulic jump, d1 is
computed by the principle of conservation of energy and the value is equal to 0.278.

d1 2.593 – 0.17918/d12 Remark

0.27 0.135
0.278 0.274 Almost equal (OK)
0.28 0.307

By using Froud Number, Fr = v1/√(gd1) = 6.744/√ (9.81*0.278) = 4.084.

d2 = (d1/2) √[(1+8Fr2) – 1] =1.473m.

If the water surface of the jump is 0.20m higher than the downstream water level,
EL = WL3 + 0.20 = 1862.20 + 0.20 = 1862.40.
1862.40 – 1.473 = 1860.972 > 1860.500.
The sequent depth, d2 is greater than the tail water depth by 0.573m. Hence, it is decided to depress
the floor level to an elevation of 1860.727.
Length of basin, L = 5(d2 – d1)
= 5(1.473 – 0.278)
= 5.975m. ≈ 6.0m.

Scour depth, exit gradient and thickness of the floor under static and dynamic cases

Scour depth
The depth of scour was calculated from Lacey’s Formula as:
R = 1.35[q2/f]1/3,

46
 Where R = Depth of scour below the highest flood in meter.
q = highest flood discharge of the river in m3/sec per meter length of the point of
consideration.
f = silt factor = 1.
R = 1.35[(1.875)2/ 1]1/3 = 2.05m.
✓ Upstream scour depth = 1.25R = 2.566m. ≈ 2.57m.
✓ Downstream scour depth = 1.5R = 3.075m ≈ 3.08m.

Exit Gradient
The factor of safety for exit gradient for soil types of our case (as of the geologic information of the
weir axis) is selected to be 1/5.
The general formula adopted for exit gradient is
EG = (H/d) *1/(π√ λ)

A graph based on Khosla’s theory is placed to indicate the correction between the floor length, b
and cut off depth, d i.e.,

d and 1/(л√ λ) to determine exit gradient.

λ = (1+√ 1+ d2 )/2 , d = b/d
for b = 9.24 and d = 1.00m.

d = 9.24/1.00 = 9.24
For d = 9.24 from the graph, 1/(л√ λ) = 0.146
Hmax – is for the static case and equal to 0.90m.

EG = 0.90/1.00*1/(л√ λ)
=0.90*0.146
=0.1314 < 0.20 ------------------- safe.

Thickness of the floor

For the downstream apron, the thickness to be determined depends on whether a static or dynamic
case is being considered.

47
1. Static case:
Head on the structure
= 1862.200-1861.300
= 0.90m

2. Dynamic case:
Head on the structure
= Upstream TEL – Downstream TEL
= 1863.093 – 1862.282
= 0.81m
The Maximum static head that is 0.090m was used for designing purposes.

Weighted creep length

According to Lane’s method, weighted creep ratio is recommended in the form,
L > CH
where L: percolation distance (m.)
H: maximum head, = 0.90
C: Lane’s creep ratio = 3.20
L > 3.20x0.90
L > 2.880
L= Σlv+1/3lh ≥ CH
Lc = (1.00+-.50+1.08+1.10) + (0.50+0.70+1.00+6)1/3
= 3.68+2.733
= 6.41
Weighted creep ratio =Lc/head on the structure
= 6.41/0.90 = 7.72

48
 Static case (Hmax = 0.90)
Point Weight creep length Hmax [1-LA/LC] (TWL-WLA) t(Safety factor/rm-1)
Case H V L
A 2.20 2.58 3.31 0.435 0.200 0.635
B 4.20 2.58 3.98 0.341 0.200 0.541
C - 2.58 4.65 0.247 0.200 0.447
Dynamic case (Hmax = 0.81)
Point Weight creep length Hmax [1-LA/LC] (TWL-WLA) t(Safety factor/rm-1)
Case H V L
A 2.30 2.58 3.31 0.392 0.598 0.989
B - 2.58 - 0.306 - 0.306
C - 2.58 - 0.222 - 0.222

Checking the thickness at each point shows satisfactory results. The results are
Point A 1.00 > 0.989--------------- Ok (Dynamic case)
Point B 0.55 > 0.540--------------- Ok (Static case)
Point C 0.45 > 0.447 --------------- Ok (Static case)
Finally, furrow surface irrigation and ogee weir are successfully design for Jalele project. The
project is small scale irrigation.

49
6. CONCLUSION AND RECOMMENDATIONS

To be effective and bear fruit land use, land management, soil and water resources conservation
should be implemented in the project vicinity.

Liming (from locally available material like wood ashes) application is recommended to increase
the availability of phosphorus and nitrogen, to furnish calcium and magnesium for plant nutrition,
to improve soil properties like bulk density, infiltration capacity and percolation.

Green manuring and application of other organic matters is suggested to improve soil fertility,
infiltration capacity, permeability and available water holding capacity of the soil

Where irregular rock outcrops and surface stones are encountered on canal route it should be lined
as it is difficult for excavation and create the loss of irrigation water through seepage.

To protect command area from erosion as the topography is sloppy; terracing, ridge cultivation,
planting fruits and crops around ridges is recommended.

Jalele river flows on sloppy land especially on its upstream catchment area. During rainy season the
river transports boulders and big stones that have big enough to affect the weir structure. Ogee weir
was recommended and the design was done by considering this recommendation.

Right and left side of the river is gently sloping, so it can be easily eroded; for this reason, any
possible care should be given to protect the area from erosion.

Where there is sandy clay on the canal route (for example after crossing Leku river) attention
should be given on its designing for sliding may be the problem.

Ogee weir was designed by using Waterways Experimental Station Standard having 2H:3V up
stream face. The downstream profile was done by the equation xn = KHdn-1y where (x, y) are the
coordinates of the points on the crest profile with the origin at the highest point of the crest, called
the apex. Hd is the design head including the velocity head, K and n are constants depending upon
the slope of the upstream face. Ogee weir of 0.90m above river bed was placed on 16m width of the

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river section. Ogee weir of 2H:3V up stream face was recommended as the river flood water are full
of boulders and big stones.

A main canal of length 3550m was designed. On main canal there are closed and box conduit, box
canal, trapezoidal lined canal, and trapezoidal earthen canal. The hydraulic parameters of the main,
secondary and tertiary canals are designed by using Manning’s Equation.

Where the topography of the area dictates, drop and chute were provided to be compatible with
elevations of the area. Drops were provided to convey water from a higher to a lower elevation and
to dissipate excess energy resulting from this drop. A canal along this same terrain would ordinarily
be steep enough to cause severe erosion in earth canals or disruptive flow in hard surface lined
canals. The water must therefore be conveyed with a drop structure designed to safely dissipate the
excess energy. Chutes designed were used to convey water from a higher elevation to a lower
elevation. Chutes are similar to drops except that they carry the water over longer distances, over
flatter slopes, and through greater changes in grades.

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7. REFERENCES

Awulachew SB, Yilma A, Loulseged D, Loiskandl W, Ayana M, Alamirew T, (2007). Water Resources
and Irrigation Development in Ethiopia. Colombo, Sri Lanka: International Water Management
Institute. pp. 78

Awulachew SB, Merry J, Kamara AB, van Koppen B, Penning de Vries F, Boelee E, Makombe G
(2005). Experiences and opportunities for promoting small-scale/micro irrigation and rainwater
harvesting for food security in Ethiopia. Colombo, Sri Lanka: International Water Management Institute
(IWMI). pp. 91

Bacha D, Regasa N, Ayalneh B, Abonesh T (2011). Impact of Small-Scale Irrigation on Household

Poverty: Empirical Evidence from the Ambo District In Ethiopia. Irrigation and Drainage. 60: 1–10.

Bassett, D. L. et al. 1980. Hydraulics of surface irrigation. In: Jensen, M.E. (ed). Design and Operation
of Farm Irrigation Systems. ASAE Monograph 3. St Joseph, MI, 447-498 pp.

Belay M, Woldeamlak B (2013). Traditional Irrigation and Water Management Practices in Highland,
Ethiopia: Case Study in Dangila Woreda. Irrigation and Drainage. 62: 435– 448.

FAO. 1988. Irrigation methods. Irrigation water management training manual No. 5. By Brouwer, C.,
Prins, K., Kay, M. and Heibloem, M. Rome, Italy.

FAO. 1989. Guidelines for designing and evaluating surface irrigation systems. FAO Irrigation and
Drainage Paper No. 45. By W.R. Walker. Rome. Italy. 137 p.

FAO (2001). Irrigation Manual: Planning, Development Monitoring and Evaluation of Irrigated
Agriculture with Farmer Participation. 3:8.

FAO (2002). Irrigation Manual: Planning, Development Monitoring and Evaluation of Irrigated
Agriculture with Farmer Participation. 2:7.

Hagos F, Makombe G, Namara RE, Awulachew SB (2009). Importance of irrigated agriculture to the
Ethiopian economy: Capturing the direct net benefits of irrigation. Colombo, Sri Lanka: International
Water Management Institute. 37p. (IWMI Research Report 128).

52
Jensen, M.E. 1983. Design and operation of farm irrigation systems. American Society of Agricultural
Engineers, U.S.A.

Kay, M. 1986. Surface irrigation - systems and practice. Cranfield Press, Bedford, U.K.

Makombe G, Kelemework D, Ared, D (2007). A comparative analysis of rainfed and irrigated

agricultural production in Ethiopia. Irrigation and Drainage Syst. 21: 35-44.

Makombe G, Namara R, Hagos F, Awulachew SB, Ayana M, Bossio D (2011). A comparative analysis
of the technical efficiency of rain-fed and smallholder irrigation in Ethiopia. Colombo, Sri Lanka:
International Water Management Institute. pp. 37

Michael, A.M. 1994 (reprint from 1978). Irrigation theory and practice. Vikas Publishing House Pvt
Ltd.

MoA (2011a). Natural Resources Management Directorates. Small-Scale Irrigation Situation Analysis
and Capacity Needs Assessment, Addis Ababa, Ethiopia.

MoA (2011b) Natural Resources Sector, Small-Scale Irrigation Capacity Building Strategy for Ethiopia,
Addis Ababa, Ethiopia.

Skogerboe, G.V., Hyatt, M.L., Anderson, R.K., and Eggleston, K.O. 1967. Design and calibration of
submerged open channel flow measurement structures: Part 3, Cutthroat flumes. Report WG31-4, Utah
Water Research Laboratory, Utah State University, Logan, Utah.

Skogerboe, G.V., Somoray, V.T., and Walker, W.R. 1971. Check-drop-energy dissipator structures in
irrigation systems. Water Management Technical Report No. 9, Water Management Research Project,
Colorado State University, Fort Collins, Colorado.

Walker, W.R. 1978. Identification and initial evaluation of irrigation return flow models. Report EPA-
600/2-78-144, Robert S. Kerr Environmental Research Laboratory, US Environmental Protection
Agency, Ada, Oklahoma.

Walker, W.R. and Skogerboe, G.V. 1987. Surface Irrigation: Theory and Practice. Prentice-Hall,
Englewood Cliffs, New Jersey.

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