Irrogation Scheme -Thoery Part

8/8/2019 Irrogation Scheme -Thoery Part

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DESIGN OF IRRIGATIONCANAL SCHEME RASHID KAMRAN

BSCE-01103108

Section (B)

2014

Civil Engineering Department

The University of Lahore


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CHAPTER: 1

: Introduction:

1.1Irrigation:Irrigation is the man-made supply of water to the land to encourage vegetation. It is a substitute for

inadequate or erratic rainfall and is extremely essential for arid regions where there are no rivers and also

in humid regions to improve crop output. In Pakistan, 75% of the agricultural land is under irrigation.

Three major water sources in Pakistan are rain water, ground water and rivers.

1.2 Irrigation System:

A land area, together with the network of canals and other hydraulic-engineering and operating

structures that ensure its irrigation.

In addition to the land, systems for regular irrigation include a main water-intake unit, which

draws water from a source (river, reservoir, canal, or well) and protects the system from debris,

slush, and trash; an irrigation network; a runoff network; a collector-drainage network, which

lowers the level of groundwater and carries water and salts away from the territory being

irrigated; hydraulic-engineering structures, which regulate water intake (regulator sluices, water-

lifting structures, and so on) and its distribution over the area being irrigated; operating

structures, such as roads and devices for observing the condition of the land being irrigated; and

wooded strips.

Irrigation systems may have gravity-flow water intake, in which the water enters the canals from

the source under natural flow, or systems with mechanical water-lifting, in which the water is

supplied by a pumping station.

1.3 Irrigation System of Pakistan:

Pakistan is basically a dry country with the River Indus and its tributaries being the main source

of water supply. Dams both large and small and barrages have been built on the Indus and its

tributaries. Large dams such as Tarbela Dam and Mangla Dam are multipurpose projects which


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not only store water, irrigate lands but also generate hydro-electricity. Small dams like Khanpur

Dam, Rawal Dam and Hub Dam supply water for agriculture, industrial and domestic purpose

and act as a reservoir as well. A hilly terrain is required to build a dam. Barrages on the other

hand are built on flat surfaces they also supply water for irrigation purpose and industrial and

domestic use. Some barrages are Sukkur Barrage, Guddu Barrage, Kotri Barrage, and Chashma

Barrage.

Canals are taken out from rivers, dams and barrages. Pakistan has one of the largest canal

irrigation systems in the world. The Inundation canals are taken from rivers and they receive

water only when the water level in the rivers is high such as during floods. The perennial canals

are taken from dams and barrages and supply water to the fields throughout the year. In Pakistan

there are 3 large dams, 85 small dams, 19 barrages, 12 inter link canals, 45 canals and 0.7 million

tube wells to meet the commercial, domestic and irrigational needs of the country.

1.4 Sources of Irrigation Water:

Sources of irrigation water can be groundwater extracted from springs or by using wells, surface

water withdrawn from rivers, lakes or reservoirs or non-conventional sources like treated

wastewater, desalinated water or drainage water.

A special form of irrigation using surface water is spate irrigation, also called floodwater

harvesting. In case of flood (spate) water is a diverted to normally dry river bed (wadis) using a

network of dams, gates and channels and spread over large areas. The moisture stored in the soil

will be used thereafter to grow crops. Spate irrigation areas are in particular located in semi-arid

or arid, mountainous regions.

1.5 Types of Irrigation

There are various types of irrigation techniques differ in how the water obtained from the source

is distributed within the field. Which are;

Surface irrigation

In surface irrigation systems, water moves over and across the land by simple gravity flow in

order to wet it and to infiltrate into the soil. Surface irrigation can be subdivided into furrow,

border strip or basin irrigation. It is often called flood irrigation when the irrigation results in

flooding or near flooding of the cultivated land.


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Localized irrigation

Localized irrigation is a system where water is distributed under low pressure through a piped

network, in a pre-determined pattern, and applied as a small discharge to each plant or adjacent

to it. Drip irrigation, spray or micro-sprinkler irrigation and bubbler irrigation belong to this

category of irrigation methods.

a. Drip Irrigation

Drip irrigation, also known as trickle irrigation, functions as its name suggests. In this system

waterfalls drop by drop just at the position of roots. Water is delivered at or near the root zone of

plants, drop by drop. This method can be the most water-efficient method of irrigation,if

managed properly, since evaporation and runoff are minimized.

b. Sprinkler Irrigation

In sprinkler or overhead irrigation, water is piped to one or more central locations within the

field and distributed by overhead high-pressure sprinklers or guns. A system utilizing sprinklers,

sprays, or guns mounted overhead on permanently installed risers is often referred to as a solid-

set irrigation system. Higher pressure sprinklers that rotate are called rotors and are driven by a

ball drive, gear drive, or impact mechanism. Rotors can be designed to rotate in a full or partial

circle.

1.6 Benefits of Irrigation:

1.6.1 Major benefits:

Major benefits of irrigation include:

i. Increased agricultural production

Increased crop productivity

Expansion in crop areas

Increase in cropping intensity

Increase in crop diversification

ii. Increased commercial fish production (in-land fisheries)

iii. Increased benefits of water use in industrial, commercial and residential sectors — from raw

water provided through irrigation infrastructure or from groundwater


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iv. Increased environmental benefits of water for in-stream flows, disposal of waste, wildlife,

flora and fauna; increased farm forestry and vegetation in irrigated areas.

v. Increased health benefits — improved sanitation due to better access to water.

vi. Other direct positive impacts

Increased benefits from flood control

Increased benefits from water use for rural domestic and livestock purposes

Increased groundwater recharge; reduction in opportunity costs of water uses

Increased recreation from water bodies, sightseeing, fishing

1.6.2 Secondary benefits of Irrigation

i. Increased employment in agriculture due to increased cropping intensity, increased crop area

and output from irrigation

ii. Increased employment outside agriculture from increased crop output in related industries

such as input industry (backward linkages) and output processing industries (forward

linkages)

iii. Positive impact on poverty reduction through increased productivity and increased

employment opportunities

iv. Increased food security at national, regional and local levels

v. Lower food prices for consumers, due to productivity gains and increased overall food

supplies

vi. Improved nutrition, improved calorie intake and improved health

1.7 Planning and Design of Surface Irrigation System:

Following two steps are taken for planning and design surface irrigation system.

1.7.1 Identification of Area:

First of all find out GCA,CCA and NCCA after that boundary is developed.CCA is divided intosmaller blocks called chakbandi.In CCA its not necessary to supply water to whole area it is the

smallest unit which is focus as well as irrigation system is concerned each portion of CCA has its

own management system.


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i. Alignment of Irrigation System

This portion is divided into two parts

a) Alignment of canal

b) Alignment of water course

a) Alignment of canal:

For best possible alignment canal should run along the ridge line and valley i.e. at higher

elevation compare to the whole area. The reason is that water can flow under gravity we prepare

that area where cut and fill in balanced position.

Then by contour map we mark possible allignment for canal then economic analysis is done

considering different parameters i.e. water is under gravity, drainage works. Canal should not

pass near the areas which are already irrigated by other means. Main branch canal should not

irrigate a land directly. Length of canal should be minimum no curvature should be provided.

b) Alignment of water course:

Field channel also called water course or khaal. They should economically irrigate the area with

minimum losses. Minimum length irrigate by water course is called tertiary level of distribution

of water each and every water course is aligned within a chak.Chaks are further divided into

smaller boxes called square. Water course is aligned within each square in the outlet command

area. A water course should irrigate both sides of square this is done to avoid adsorption losses.

1.7.2 Identification of Crops:

i. To decide cropping pattern of areas

ii. To decide about the cropping intensity or cultivation intensity

iii. Crop water requirement

i.

Cropping Pattern of Areas:

It is defined as different kinds of crops which are being cultivated over a particular area it‘s

basically used to decide which type of crop you are cultivated. If you don‘t know which type of

crop should be cultivated then crop pattern is done there are several steps to decide the cropping

pattern.


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Climate of the area

Soil characteristics

Hydrology( rain fall pattern)

Water allowance

Now experts are trying to know about ―croppingpatternoptimization‖ keeping in mind the

available and the crop water demand.

ii- Cropping Intensity

It is the percentage of area over which particular crop is cultivatedw.r.t total CCA.

iii- Crop Water Requirement

The total quantity of water, a crop requires at different intervals of time from pre-sowing to harvesting is

called the crop water requirement of that crop. Different crops will have different water requirements

dependingon climate, type of soil, method of cultivation, useful rainfall, etc. Crop water

requirement is defined as the depth of water needed to meet thewater loss through

evapotranspiration of a disease free crop growing in large fields under non restricting soil

conditions including soilwater and fertility and achieving full production potential under

growingconditions.

a) Methods to findCrop Water Requirement

Direct method/field method

Empirical method

Pan evaporation method

b) Factor Affecting Water Requirement of Crop

1. Texture and structure of the soil and its moisture storage capacity

2. Position of ground water table

3. Slope of the ground

4. Drainage conditions

5. Climate condition like rainfall, temperature, wind movement and relative humidity

6. The system of irrigation adopted

7. Intensity of irrigation


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8. Type and amount of manure supplied to fields

1.8 Crop Season:

There are two crop season in Pakistan

i.

Rabi season

ii. Kharif season

Rabi season

Rabi crops are sowing during autumn and harvested in spring

Kharif season

Kharif crops are sowing in monsoon period and harvested in autumn.

1.9 Important Definitions:

Water Requirement

It is the water required by a crop to mature it from the time of sowing to the time of harvesting.

The water requirement of a particular crop doesnot remain uniform in different areas.It varies

according to variation in climate,rainfall and type of soil. Water requirement of a particular crop

in a particular region cannot be considered applicable for all areas.

Optimum use of water:

The quantity of water supplied to a particular crop during is growth period,which results in the

maximum yield of the crop is known as optimum water requirement.

Cultivable Command Area (CCA):

The area which can be irrigated from a scheme and is fit for cultivation.

CCA =GCA-NCCA

Normally CCA is 75-80% of GCA.


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Gross Irrigated Area:

It is the area enclosed between the imaginary boundaryline up to which any irrigation channel

capable of supplying water for irrigation purpose.

Base Period:

It is the time normally in days for which a crop occupies a field to attain its full maturity.

This time is counted from the day when irrigation water us first issued to the field for

preparing it for sowing the crop, to the last watering before crop is harvested.

Crop Period:

The time period between sowing and harvesting is called Crop Period.The time between first

watering to a crop at its sowing to its last watering before harvesting is called Base Period.

Delta:

The total depth of water required by a crop from sowing to maturity iscalled its delta.

Duty of Water

The duty of water is the relationship between the volume of water andarea under crop matured.

Total volume = Discharge × Base period

Water Allowance:

Water allowance is defined as antonymous of duty and is expressed in cusec/1000 acres or

in cumecs/100 ha. At outlet head, distributary head or main canal head as the case may be. Water

allowance is fixed on canal basis but some time water allowance is also fixed on region basis,

taking into account all the variable factors for cropping pattern on that canal or region.


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CHAPTER: 2

: Methodology of Irrigation System:

2.1

design of irrigation System:

i. Decide the cropping pattern of the area

ii. Based on the given cropping pattern, estimate the crop water requirement

iii. Estimate the design discharge

iv. Estimate outlet command area and number of outlets

Cropping area = total CCA* cropping intensity

Volume of water = cropping area* delta

Design discharge for Rabi:

Qr = Vr*43560/Rabi period

Discharge of kharif:

Qr = Vk*43560/kharif period

Water Allowance

W.A = Qd*1000/ CCA

Outlet Command Area

Qoutlet = W.A *CCA/ 1000

Minimum Number of outlet

Min no. = CCA/CCA of outlet

Qs = 30%of Q outlet

Qt = Q outlet + Qs

2.2

Plantation of Irrigation Scheme:

Plantation of irrigation scheme on graph includes:

i. plantation of contour map on a large sheet

ii. Show the alignment of the canal


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iii. Divide the CCA into outlet CCA

iv. Marks designation of outlet

v. Write area allocated to each outlet

vi. Mark canal reaches

vii. Mark the running distance for the canal

2.3

Discharge or Capacity Statement for all canal scheme;

iii. A canal reach is the distance b/w AB, CD and so on

iv. A discharge in each reach can be found out

v. To make the discharge statement it is start with tail reach for any canal

vi. Discharge statement for the canal should be made first

2.4 Design of outlet, canal Reaches and Water Course:

i. Design of Outlet

We use open flume outlet

Q=C*W*H3/2

Where

C = 3

W = 0.5 ‗

H = head 0f water over crest

ii.

Design of Canal in Reaches

First find wetted perimeter of canal

Find side slope of the canal

Find hydraulic radius R

Find equation b/w B & D and determine the relation between them

Pw =2.667 Q

S=f 5/3

/1844Q f= 1.76 d

R= A/P

V = (1.436*R 3/4

* S1/2

)/n

R= A/P A = BD+ZD

2

Z horizontal slop2/3

iii. Design of Water Course

Design based on the manning‘s formula

Q = (1.49*R 2/3

*S1/2

)/n


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CHAPTER: 3

: Calculation of Irrigation Scheme Design:

For Rabi Season

Crop

Crop

Period

(days)

Cropping

intensity

(%)

Delta

(in)

Cropped

area

(acr)

Volume

of

water

(act-ft)

Wheat 130 40 15 4120 5150

Gram 110 35 12 3605 3605

Oilsead 150 25 18 2575 3862.5

12617.5

For kharif Season

Crop

Crop

Period

(days)

Cropping

intensity

(%)

Delta

(in)

Cropped

area

(acr)

Volume

of

water

(act-ft)

wheat 120 30 15 3090 3862.5

Gram 155 28 12 2884 2884

Oilsead 185 42 18 4326 6489

13235.5

3.1 Proposed Cropping Pattern:

Design discharge for Rabi:

Q = (12617.5*43560)/183*24*3600

Q = 34.59ft3/s

Discharge for kharif:

Q= (13235.5*43560)/183*24*3600

Q =36.46 ft3/s


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Water Allowance:

W.A= (36.46*1000)/4960

W.A 7.35 cuses/1000 acs

Outlet Command Area:

Let Q outlet = 3 cuses

Q = (W.A * CCA)/1000

3 = (7.35*CCA)/1000

CCA outlet =410 acr

Minimum number of Outlets:

# = (CCA)/CCA of outlet

Min # outlet = (4960)/410 = 12

3.2 Discharge at Each Outlet:

Q outlet = 30 % of Q

Qt =Qoutlet + Qs

Sr#RD of

outlets

Side Designation G.C.A N.C.C.A C.C.A Q outQ

seepage(30%)

Qtotal

Ft acres acres acres ft3/sec ft3/sec ft3/sec

1 0+000 L L1 300 0 300 2.1 0.63 2.73

2 1+000 L L2 300 0 300 2.1 0.63 2.73

3 2+500 L L3 450 0 450 3.15 0.945 4.095

4 3+400 L L4 400 0 400 2.8 0.84 3.64

5 0+000 R R1 495 0 495 3.465 1.0395 4.5045

6 1+000 R R2 495 0 495 3.465 1.0395 4.5045

7 2+500 R R3 495 0 495 3.465 1.0395 4.5045

8 3+900 R R4 495 0 495 3.465 1.0395 4.5045

9 4+900 R R5 400 0 400 2.8 0.84 3.64

10 0+700 L ML1L1 300 0 300 2.1 0.63 2.73

11 1+900 L ML1L2 400 0 400 2.8 0.84 3.64

12 1+900 R ML1R1 430 0 430 3.01 0.903 3.913

Total Qtotal 45.36


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3.3 Discharge Statement

Sr#Canal

Reach

Lengt

h of

canal

reach

outlet/mi

nor

designatio

n

RD of

outlet

in

reach

es

QoutletQseepage(

30 %)

Q in

reach

Qtotal

in

reach

L R Total

ftft3/s

ec

ft3/s

ec

ft3/s

ecft3/sec ft3/sec ft3/sec

1 LM 700 ML2 4.17 3.98 8.15 2.445 10.595 10.595

2 KL 500 ML1 4+900 4.42 3.64 8.06 2.418 10.478 21.073

3 JK 900 L6 3+400 3.64 3.39 7.03 2.109 9.139 30.212

4 IJ 1500 R5 2+500 4.095 3.37 7.465 2.2395 9.704539.916

5

5 HI 1500 R4 2+500 5.224.504

5

9.724

52.91735

12.641

85

52.558

35

6 GH 900 R3 4.46 3.99 8.45 2.535 10.98563.543

35

7 FG 1200 R2 1+900 3.64 3.63 7.27 2.181 9.45172.994

35

8 EF 1200 R1 1+900 3.98 3.913 7.893 2.367910.260

9

83.255

25

9 DE 700 L5 0+700 2.73 3.07 5.8 1.74 7.5490.795

25

10 CD 1000 L4 1+000 04.504

5

4.504

51.35135

5.8558

5

96.651

1

11 BC L3 1+000 2.73 0 2.73 0.819 3.549

100.20

01

12 AB L2 0+000 3.414.504

5

7.914

52.37435

10.288

85

110.48

9

L1 0+000 2.73 0 2.73 0.819 3.549114.03

8

3.4 Design of Outlet

We use open flume outlet

q = C*W*H3/2

For L1

C= 3

W = 0.5

q = 2.73


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2.73 = 3*0.5*H3/2

H = 1.49 ft

Sr # RD/ designation Qt H

1 L1 2.73 1.493647

2 L2 2.73 1.493647

3 L3 4.095 1.959878

4 L4 3.64 1.81116

5 R1 4.5045 2.089114

6 R2 4.5045 2.089114

7 R3 4.5045 2.089114

8 R4 4.5045 2.089114

9 R5 3.64 1.81116

10 ML1L1 2.73 1.49364711 ML1L2 3.64 1.81116

12 ML1R1 3.913 1.90108

3.5 Design of Canal Reaches:

For reach start:

Pw = 2.667 Qt

Pw = 2.667(110.45)1/2

=28.028 ft

f = 1.76 d

=1.76 *(0.22)1/2

= 0.825

S = f 5/3

/(1844Q1/6

)

= (0.825)5/3

/ (1844*(110.45)0.6

)

=0.000179

Hydraulic Radius

V= (1.346*R 3/4

* S1/2

)/n

V= (1.346*R 3/4

*0.0001791/2

)/(0.214) =0.096R 3/4

………………….(1)

V= 1.1547(fS)1/2

=1.1547(0.9216S) = 1.094S1/2

………………………….(2)

Comparing (1) & (2)


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R = [0.01667/S1/2

]4

R =2.42 ft

To develop a quadratic equation Between B and D

R=A/P

A= BD+ZD2

67.83=BD+1.5D2

………………………………….. (3)

P=B +2 (slope) D

P = B +3.6D

28.03=B +3.6D…………………………………….. (4)

B=28.03-3.6D put in (3)

67.83=28.02D-3.6D2+ 1.5D

2

Simplified the above equation gives

2.1D2 -28.02D +67.83=0

Solve the above equation and get

D= 12.22 and 3.17 select D= 3.317ft

Then B= 7.16ft

Let B/D = 2.158

D = 28.03/(2.158+1.5) =3.317ft

B = xD

=2.158 *3.317 = 7.17ft

For rest of the reaches, fix B/D as 2.158


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Sr#Canal

Reach

Breach

DischargeS R P A D B

1 LM 0 0 0 0 0 18.6

2 KL 19.59 0.000239 1.358223 11.8043 16.03286978 2.3 10.32

3 JK 21.07 0.000236 1.391667 12.24208 17.03690761 2.294 10.3416

4 IJ 30.212 0.000223 1.569681 14.65928 23.01040319 2.383 10.0212

5 HI 39.91 0.000212 1.722633 16.8486 29.02396265 2.507 9.5748

6 GH 52.55 0.000203 1.888438 19.33345 36.51003038 2.534 9.4776

7 FG 63.54 0.000197 2.012099 21.25919 42.7755812 2.769 8.6316

8 EF 72.99 0.000192 2.10747 22.7853 48.01934047 2.862 8.2968

9 DE 83.25 0.000188 2.202114 24.33409 53.58645206 2.956 7.9584

10 CD 96.65 0.000183 2.314669 26.21947 60.6894072 3.068 7.5552

11 BC 100.2 0.000182 2.342725 26.69666 62.54293031 3.098 7.4472

12 AB 110.45 0.000179 2.420187 28.02889 67.83514477 3.177 7.1628

3.6 Design of Water Course:

Sr # Outlet Designation Outlet Discharge D B

1 L1 2.73 0 0

2 L2 2.73 2.3 10.32

3 L3 4.095 2.294 10.34164 L4 3.64 2.383 10.0212

5 R1 4.5045 2.507 9.5748

6 R2 4.5045 2.534 9.4776

7 R3 4.5045 2.769 8.6316

8 R4 4.5045 2.862 8.2968

9 R5 3.64 2.956 7.9584

10 ML1L1 2.73 3.068 7.5552

11 ML1L2 3.64 3.098 7.4472

12 ML1R1 3.913 3.177 7.1628


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3.7 Design of Vertical Drop

Design a 1.5m fall for a canal having a discharge of 12 cumes with the following data

u/s bed level = 103.0m

side slopes of canal = 1:1 D/s bed level = 101.5m

F.S.L U/S = 104.5m

Bed width at U/S and D/S = 10m

C =7.5

Solution:

Length of crest

Same as d/s bed width =10m

Crest level

Q= 1.84*L*(H)3/2

*(H/B)1/6

12= 1.84*10*H3/2 *

(H/0.8)1/6

H= 0.76m

Shape of Crest

B=0.55(d)0.5

d= 103.77 – 101.5 = 2.27m

B = 0.55(2.27)05

B =0.825 >0.8 okThickness at base = (h+d)/S

= (0.755 - 0.025) + 2.27 /2

= 1.5m

Design of Cistern

Depth = x = 0.25(H.H)2/3

= 0.25*(0.76*1.5)2/3

= 0.3 m

Length = 5(H.H)0.5

= 5.5m

Length of Impervious Floor

According to Bligh‘s theory

h/l≤1/c

h=head causing seepage

h=CL-D/S Bed Level

h=103.77-101.5=2.27m


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Minimum creep length=say

Minimum length of impervious floor

L=h*c

L=2.27*7.5 Minimum length of D/S floor

=17.025m =2 (water depth+1.2) + H f

=say 17.1m =2(1.5+1.2)+1.5= 6.9m= say 7m

CHAPTER: 4

:Results and Recommendation:

4.1 Result

GCA=6000 acres

CCA=4960 acres

Main canal=1

Total outlets=12 outlets

Q max=54.242 ft3/sec

For Canal Reaches

Pw=28.08 ft

X=2.158

D=3.317 ft

B=7.16 ft

4.2 Recommendations

Improving irrigation system performance is now perceived as a more pressing need than

developing new irrigated areas, after large budgetary allocations have gone for decades into

expanding irrigated acreage. The irrigation system represents a significant engineering

achievement and provide water to the fields that account for 90 percent of agriculture production.


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Water measurement is a basic requirement for improving the operation of any irrigation

system. In fact, developing and updating the discharge rating for each essential flow

control structure in a system should be standard operating procedure.

Proper communication facilities are one of the more cost-effective measure for improving

the performance of an irrigation system.

Canal design should be such that there should be least siltation if siltation occurs clear the

slit at the spring and improve the lining in the main canal, gates to control water delivery

should be properly installed.

The most important component, however, is organized in an effective manner, frames

will demand equitable water distribution.

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