Ce702 Irrigation Engineering

CE702 IRRIGATION ENGINEERINGCourse Instructor - Prof. Quamrul Hassan

Moisture extraction at different

depths in root zone

RECAPS

Topics to be covered

Water Requirement of Crops

NIR, FIR, GIR

Duty, Delta

Type of crops, crop season

Irrigation System and Types

Methods of Irrigation

Water application efficiencies

Planning and Layout of Canal SystemsProf. Quamrul Hassan, JMI 3

Water Requirement of Crops

• Water Requirement of Crop

• The total quantity and the way in which a crop requires water, from time it is sown to the time it is

harvested, is known as water requirements of crop.

• Crop period- The time period from sowing to harvesting

Base Period - The time period from first watering of a crop at time of sowing to last watering before

harvesting.

• Generally ⇨ Crop period > Base period; Practically, Crop period ≈ Base period

• Crop Seasons ⇨ Rabi (1st October – 31st March), example- wheat, barley, gram, mustard, linseed etc

⇨ Kharif (1st April – 30th September), example- Rice, bajra, jowar, cotton, tobacco etc

⇨ Sugarcane extends over both seasons

• Classification of Crops ⇨ Cereals, Pulses, Oilseeds, Millets, Fibre Crops, Fodder crops, vegetables, fruit

crops, Plantation crops, Spices, Narcotics (broadly 11 types)

Prof. Quamrul Hassan, JMI 4

Duty and Delta

Duty of water (D) ⇨ water supplied @1 cumec for B days matures D hectares of land.

Delta (∆) ⇨ It is the depth in cm to which water supplied to a crop during its growth

would stand on the irrigated area, if the total quantity were to stand above the surface

without percolation or evaporation.

Volume of water supplied to a crop during B days @ 1cumec = 24 ×3600×B×1 = 86400B m3

∆ (𝑚) =86400𝐵

𝐷×104 ⇨ ∆ 𝑚 =8.64𝐵

𝐷or, ∆ 𝑐𝑚 =

864𝐵

𝐷

∆ for certain crops Duty (D) for certain crops

Sugarcane 120 cm 730 ha/cumec

Rice 120 cm 775 ha/cumec

Wheat 30 cm 1800 ha/cumecProf. Quamrul Hassan, JMI 5

NIR, FIR, GIR

NIR = Cu + Losses – Rainfall

NIR = Cu – (Rainfall – Losses) = Cu – Effective Rainfall

FIR = NIR/Field Irrigation Efficiency = NIR/ηa

GIR = FIR/ Conveyance Efficiency = FIR/ηc

Paleo Irrigation : Irrigation before sowing

Kor watering : First watering which is given to a crop, when the crop is few

cm high, is called Kor watering

Kor period : period of kor watering Prof. Quamrul Hassan, JMI 6

Irrigation System

Gravity Irrigation ⇨ (a) Direct Irrigation (Diversion irrigation)

(b) Indirect Irrigation (Storage Irrigation, Tank Irrigation)

Lift Irrigation ⇨ (a) Lift Canal Irrigation

(b) Well Irrigation

(c) Tube well Irrigation

Comparison between ⇨ Lift Irrigation vs canal irrigation

Well Irrigation vs Canal IrrigationProf. Quamrul Hassan, JMI 7


Surface Irrigation

Flooding ⇨ Wild or Free Flooding

Border Flooding

Check Flooding

Contour Laterals

Basin Flooding

Furrow Irrigation ⇨ Shallow Furrow

Deep Furrow

Overhead Irrigation

⇨ Sprinkler

⇨ Perforated Pipes

⇨ Drone Irrigation

Drip Irrigation ⇨



Surface Irrigation

Wild or Free Flooding ⇨ primitive, low cost, low

efficiency, non uniform distribution of water,

excessive soil erosion

Border Flooding ⇨ Field divided into narrow strips by low parallel ridges (levees) on the sides,

⇨ 10-20 m, length 100 to 400 m, slope 1 to 5 m per 1000m,

⇨ Low maintenance cost, better utilization of water

⇨ Requires levelling and grading of land

Check Flooding - water is controlled by

surrounding area, Size 3 by 3 m to 30 by 30 m

Contour Laterals – best suited to steeper terrain,

The field is cut by relatively dense network of

contour lateral (spacing 15 to 50m)

Basin Flooding ⇨ It is essentially a check method

of flooding adopted for irrigation of orchards.

---------

Furrow Irrigation ⇨ Furrows are small

channels having a continuous and almost

uniform slope in the direction of flow.

⇨ length 10 to 500 m (desirable 100-200m)

⇨ Wetting half to one fifth of the field surface ⇨

⇨ Shallow Furrow (10 cm deep, spaced 40-75

cm apart)

⇨Deep Furrow (15-30 cm deep, spaced 1-2m Prof. Quamrul Hassan, JMI 9


Overhead Irrigation ⇨

Sprinkler ⇨ simulates natural rainfall at a

rate less than infiltration rate

⇨ suited to undulating land

⇨ No Land levelling

⇨fertilizer is applied through

sprinkler

⇨ Not recommended for crops

having high water requirements

Perforated Pipes ⇨

Drone Irrigation ⇨

Drip Irrigation

⇨ water is supplied in the form of

drops directly to the plant through

drip nozzles






Planning and Layout of Canal System• Command Area (CA) ⇨It is the area over which the

water of the channel would flow by gravity.

• Gross Command Area (GCA) ⇨Total area over

which the water of a canal system can flow by

gravity.

• Culturable Command Area (CCA) ⇨ The culturable

area includes all lands on which cultivation is

possible.

GCA =CCA + unculturable area

• Note ⇨ Area statistics by map 1:15000

• Intensity of Irrigation ⇨ area to irrigated under

different crops /CCA (expressed in %)

• Time Factor ⇨ Ratio of no. of days the canal has

actually run to the number of days of irrigation

period.Prof. Quamrul Hassan, JMI 13

Planning and Layout of Canal System

Note

⇨ Generally monthly water requirement studies are

conducted and the channel capacity is increased by 20-25%

to cater for peak demand in the month.

Outlet discharge factor (m3/s) = 864B/∆

(where B in days, and ∆ in cm)


Irrigation Efficiencies

• Losses ⇨ Efficiencies

(i) losses in main canal and branches ≈ 15-20 %

(ii) Losses in major and minor distributaries ≈ 6-8 %

(iii) Losses in field channels ≈ 20-22 %

(iv) Losses due to irregular distribution, deep percolation and surface

evaporation during application of water ≈ 25-27 %

(v) Utilisation by crops in the form of evapotranspiration ≈ 28-29 %Prof. Quamrul Hassan, JMI 15


Wr = Irrigation water released (supplied) at the diversion point

Wd = Irrigation water delivered at the outlets to the fields

We = Irrigation water evapotranspired by the crop

Ws = water stored in the root zone during irrigation

Ww = water needed in the root zone prior to irrigation

Wu = water beneficially used including leaching water

D = Mean depth of water stored during irrigation

d = average of the absolute values of deviations

from the mean (i.e. D)Prof. Quamrul Hassan, JMI 16


(i) Irrigation Efficiency or Project efficiency,

𝜼𝒊 =𝑾𝒆

𝑾𝒓× 𝟏𝟎𝟎

(ii) Water Conveyance efficiency 𝜼𝒄 =𝑾𝒅

𝑾𝒓× 𝟏𝟎𝟎

(iii) Water Application efficiency or Field Application efficiency

𝜼𝒂 =𝑾𝒆

𝑾𝒅× 𝟏𝟎𝟎

(iv) Water Storage Efficiency 𝜼𝒔 =𝑾𝒔

𝑾𝒘× 𝟏𝟎𝟎

(v) Water Use Efficiency 𝜼𝒖 =𝑾𝒖

𝑾𝒅× 𝟏𝟎𝟎

(vi) Water Distribution Efficiency, 𝜼𝒊 = (𝟏 −𝒅

𝑫) × 𝟏𝟎𝟎Prof. Quamrul Hassan, JMI 17

Examples 2.13


Examples 2.13 (Solution)


Examples#1 • Compute evapotranspiration (consumptive use) by Hargreaves method for wheat crop at Roorkee.

Also Compute NIR, FIR, GIR

Period Ep observed or

computed (cm)

Effective

Rainfall, Re (cm)

Remarks

November 5-30 7.22 0.31 Pre-sowing irrigation 7.5 cm

December 1-31 5.82 1.32 Paleo irrigation of 7.5 cm is essential

before sowing

January 1-31 6.03 0.33 Growing period of plant assumed

from 5th Nov to 30st March

February 1-28 16.30 3.77 No irrigation beyond 15th March

March 1-30 17.36 1.92


Examples#1Solution• Compute evapotranspiration (consumptive use) by Hargreaves method for wheat crop at

Roorkee. Also Compute NIR, FIR, GIR

• Assuming ηa = 0.70 ηc = 0.75

Period Mid

point

% of

growing

season

(GS)

K=

Et /Ep

from

Table

Ep

(cm)

Et = KEp

(cm)

Re

(cm)

NIR

(cm)

FIR=

NIR/ηa

(cm)

GIR=

NIR/ηc

(cm)

7.50 10.71 14.28

November 5-30 13 8.9 0.12 7.22 0.86 0.31 0.55 0.78 1.04

December 1-31 42 28.7 0.36 5.82 2.09 1.32 0.77 1.1 1.46

January 1-31 73 50.0 0.65 6.03 3.91 0.33 3.58 5.11 6.81

February 1-28 103 72.5 0.88 16.30 9.06 3.77 5.29 7.56 10.08

March 1-30 132 92.9 0.70 17.36 12.15 1.92 10.23 14.61 19.48

Total 146 days Total 27.92 39.87 53.16


Examples#2 • The CCA of a watercourse is 1200 ha. Intensities for sugarcane and wheat crops are respectively

20% and 40%. The duties for the crops at the head of water course are 730 ha/cumec and 1800

ha/cumec respectively. Find

(a) the discharge required at the head of watercourse

(b) Determine the design discharge at the outlet, assuming a time factor equal to 0.8


Examples#2 (Solution)• The CCA of a watercourse is 1200 ha. Intensities for sugarcane and wheat crops are respectively

20% and 40%. The duties for the crops are at the head are of water course are 730 ha/cumec and

1800 ha/cumec respectively. Find

(a) the discharge required at the head of watercourse

(b) Determine the design discharge at the outlet, assuming a time factor equal to 0.8

Solution:

Given ⇨ CCA = 1200 ha; II for sugarcane = 20%; II for wheat = 40%

Therefore, Area to be irrigated under sugarcane = IIsugar× CCA = 0.20 × 1200 = 240 ha

Area to be irrigated under wheat = Iiwheat × CCA = 0.40 × 1200 = 480 ha

Discharge required for sugarcane = Area/Duty = 240/730 = 0.329 cumec

Discharge required for wheat = Area/Duty = 480/1800 = 0.271cumec

(a) Discharge at the head of watercourse = 0.329+0.271 = 0.60 cumec

(b) Design Discharge = 0.60/Time factor = 0.60/0.8 = 0.75 cumecProf. Quamrul Hassan, JMI 23

Examples#3 The CCA for a distributary is 15000 ha. The II for Rabi (wheat) is 40% and for kharf (rice) 15%. If

the total water requirement of the two crops are 37.5 cm and 120 cm and time periods of growth

are 160 days and 140 days respectively.

(a) Determine the outlet discharge from average demand considerations.

(b) Also determine the peak demand discharge, assuming that the kor water depth for two crops

are 13.5 cm and 19 cm and their kor periods are 4 weeks and 2 weeks respectively.

Solution:

Crop II

(%)

∆

(cm)

B

(days)

Average

D= 864B/∆

(ha/cumec)

Area under

irrigation =

II×CCA

Outlet discharge

= Area /D

(cumec)

Rabi 40 37.5 160 3686 6000 ha 1.63

Kharif 15 120 140 1008 2250 ha 2.48

Kor watering

Rabi 40 13.5 28 1792 6000 3.35

Kharif 15 19 14 636 2250 3.93


Examples#4• A stream of 130 litres/second was diverted to a canal and 100 litres/second were delivered to

the field. An area of 1.6 ha was irrigated in 8 hours. The effective depth of root zone was 1.7

m. The runoff loss in the field was 420 cum. The depth of water penetration varied linearly

from1.7 m at the head end of the field to 1.1 m at the tail end. Available moisture holding

capacity of the soil is 20 cm per metre depth of soil. It is required to determine the water

conveyance efficiency, water application efficiency, water storage efficiency and water

distribution efficiency. Irrigation was started at a moisture extraction level of 50% of the

available moisture.


Examples#4 (Solution)Solution:

Wr = Irrigation water released (supplied) at the diversion point = 130 litre /second

Wd = Irrigation water delivered at the outlets to the fields = 100 litres/second

Water delivered to the field = 100 ×8 ×3600 ×10-3 =2880 cum,

runoff loss = 420 cum (given)

We = Irrigation water evapotranspired by the crop

= water delivered to the field – runoff loss = 2880 – 420 = 2460 cum

(i) 𝜼𝒄 =𝑾𝒅

𝑾𝒓× 𝟏𝟎𝟎 =

𝟏𝟎𝟎

𝟏𝟑𝟎× 𝟏𝟎𝟎 = 𝟕𝟔. 𝟗%

(ii) 𝜼𝒂 =𝑾𝒆

𝑾𝒅× 𝟏𝟎𝟎 =

𝟐𝟒𝟔𝟎

𝟐𝟖𝟖𝟎× 𝟏𝟎𝟎 = 𝟖𝟓. 𝟒%


Examples#4 (Solution)Moisture holding capacity of soil = 20 cm per metre depth of soil

Moisture holding capacity of soil in root zone = 20 cm per metre depth × 1.7m

= 34 cm

Moisture already available = 50% = 0.50 × 34 cm = 17 cm

Water needed in the root zone = 0.17 × 1.6 ×104 = 2720 cum

iii. 𝛈𝐬 =𝐖𝐬

𝐖𝐰× 𝟏𝟎𝟎 =

𝟐𝟖𝟖𝟎−𝟒𝟐𝟎

𝟐𝟕𝟐𝟎× 𝟏𝟎𝟎 =

𝟐𝟒𝟔𝟎

𝟐𝟕𝟐𝟎× 𝟏𝟎𝟎 = 𝟖𝟓. 𝟒%

(iv) Water Distribution Efficiency, 𝜼𝒊 = 𝟏 −𝒅

𝑫× 𝟏𝟎𝟎 = 𝟏 −

𝟎.𝟑

𝟏.𝟒× 𝟏𝟎𝟎 =78.6%

D = (1.7+1.1)/2 = 1.4 m

d = Mean of [abs( 1.7-1.4) + abs(1.1-1.4)] = 0.5 (0.3+0.3) = 0.3Prof. Quamrul Hassan, JMI 27

Summary of UNIT-I

Text Books

1. Irrigation, Water Resources and Power Engineering by P.N. Modi, Standard Book

House, Delhi

2. Irrigation Engineering and Hydraulic Structures by S.K. Garg, Khanna Publishers,

Latest edition

References :-

1. Irrigation and Water Resources Engineering by G.L. Asawa, New Age International

Publishers

2. Theory and Design of Irrigation Structures by By Varshney and Gupta, Vol. I and II,



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Ce702 Irrigation Engineering