hydrology & irrigation -...

Hydrology & Irrigation

For

Civil Engineering

By

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Syllabus

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Syllabus for Hydrology & Irrigation Hydrology: Hydrologic Cycle, Precipitation, Evaporation, Evapo-Transpiration, Watershed,

Infiltration, Unit Hydrographs, Hydrograph Analysis, Flood Estimation and Routing, Reservoir

Capacity, Reservoir and Channel Routing, Surface Run-off Models, Ground Water Hydrology - Steady

State Well Hydraulics and Aquifers; Application of Darcy’s Law.

Irrigation: Duty, Delta, Estimation of Evapo-Transpiration; Crop Water Requirements; Design of

Lined and Unlined Canals, Head Works, Gravity Dams and Spillways; Design of Weirs on Permeable

Foundation; Types of Irrigation Systems, Irrigation Methods; Water Logging and Drainage; Canal

Regulatory Works, Cross-Drainage Structures, Outlets and Escapes

Analysis of GATE Papers

Year Percentage of Marks Overall Percentage

2015 5.00

2.10%

2014 2.00

2013 2.00

2012 -

2011 -

2010 4.00

2009 3.00

2008 8.00

2007 4.00

2006 2.00

Contents

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Contents

Chapter Page No.

# 1. Open Channel Flow 1 – 15

Introduction 1 Types of Channel 1 – 9

Pressure Distribution 10 – 14

Hydraulic Jump 14 – 15

#2. Irrigation 16 – 22 Introduction 16 – 17

Flow Irrigation 17 – 21

Assignment 22

Answer Keys & Explanations 22

#3. Water Requirements of Crops 23 – 27 Definition 23 – 24

Duty at Various Places 24 – 26

Optimum Utilization of Irrigation Water 26 – 27

#4. Soil Moisture Irrigation Relationship 28 – 34 Introduction 28 Field Capacity 28 – 29

Solved Examples 30 – 34

#5. Sediment Transport and Design of Irrigation Channels 35 – 69 Sediment Transport 35 – 37

Mechanics of Sediment Transport 37 – 40

Water Logging Control 40 – 41

Tube Wells 41 – 43 Design of Channels 43 – 47

Kennedy’s Regime Theory 47 – 48 Lindley’s Regime Theory 48 – 51

Design of Irrigation Channel by Lacey’s Regime Theory 51 – 54 Causes of Failure of Weir or Barrage on Permeable Foundation 54 – 55

Bligh’s Creep Theory for Seepage Flow 55 – 56 Lane’s Weighted Creep Theory 57 Khosla’s Theory and Concept of Flow Nets 57 – 67 Exit Gradient 67 Assignment 68


Contents

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#6. Hydrology 70 – 127 Introduction 70

Hydrologic Cycle 71 – 72 Water Budget Equation 72 – 73 World Water Quantities 74

Precipitation 74 – 77

Measurement of Precipitation 77 – 79

Preparation of Data 80 – 84

Frequency of Point Rainfall 84 – 85

Evaporation 85 – 90

Variation of AET/PET 90 – 94

Measurement of Infiltration 94 – 97 Stage Discharge Relationships 97 – 99 Measurement of Velocity 99 – 102 Hydrograph and Runoff 102 – 106 Base Flow Separation 106 – 111 S–Curve Technique 111 – 113 Floods Estimation 113 – 116

Well Hydraulics 116 – 117

Saturation Formation 117 – 118 Well Hydraulics Introduction 119 – 121 Steady Flow in Open Well 121 – 122 Assignment 123 – 126

Answer Keys & Explanations 126 – 127

Module Test 128 – 131 Test Questions 128 – 130


Reference Books 132

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"In order to succeed you must fail so that

you know what not to do the next time."

…Anthony J. D'Angelo

Open Channel Flow

Learning Objectives After reading this chapter, you will know:

1. Types of Channel

2. General Types of Flow in Open Channels

3. Geometrical Parameters of an Open Channel Flow

4. Pressure Distribution

5. Hydraulic Jump

Introduction An open channel is a sloped liquid flow passage having solid boundaries with the top surface open

to gaseous atmosphere. The top surface of the channel, called free surface which is the surface of

contact between the flowing liquid and the overlying gas, its subjected to constant pressure

throughout its length and breadth. In the pipe, flow occurs due to pressure gradient, but for open

channel flow, it happens mostly for gravity

The cross-section section for pipe flow is mostly circular but for open channel flow the cross-section

can be of any geometry

Types of Channel 1. Open and Closed Channels: Open channels are also called uncovered channels have no cover at

the top and it is completely open to atmosphere. Close channel are called covered channels,

have cover or roof at the top. In other words the closed channel is a closed passage which does

not run full, so that the liquid has free surface in contact with air. Air occupies the space

between the liquid surface and the top cover.

2. Natural and Artificial Channels

3. Prismatic and Non-Prismatic Channels: A channel having the same flow cross-section

throughout its length and having a constant bottom flow is called prismatic channel

4. Exponential and Non-Exponential Channels: Depending on the type of cross-section of the

channel, it is classified as exponential and non-exponential channels. In case of an exponential

channel, the cross-section area is prescribed by the equation A Ky , where A is the sectional

area, y is the depth of flow, k and n are the experimental constant. The examples of exponential

channels are rectangular, triangular and parabolic channels. For non-exponential channels,

examples are trapezoidal and circular channel.

CH

AP

TE

R

1

Open Channel Flow


General Types of Flow in Open Channels

1. Steady and Unsteady Flow

If the flow characteristic of an open channel do not change with time, then it is steady flow and

if it is changing with flow, then it is unsteady flow

For ste y low N

t

For unste y low N

t

2. Uniform and Non-Uniform Flow

When the flow characteristics does not change with space, then it is uniform flow or else it is

non-uniform flow. N

s Uni orm low

N

s or non uni orm low

The non-uniform flow is further classified into two types

(i) RVF- Rapidly Varied Flow

(ii) GVF- Gradually Varied Flow

RVF: It is defined as that flow in which the depth of flow changes abruptly over a small length of

a channel.

3. Laminar and Turbulent Flow

Reynol s num er R VD

L h r teristi Length

D h r teristi Dimension

For n open h nnel D is the hy r uli r ius R whi h is e ine s Wette re

Wette perimeters

R A

P

R L min r Flow

R Tr nsition l Flow

R Turnulent Flow

4. Subcritical, Critical and Super Critical Flow

F (Foru e No) V

√ D Where V is the velo ity o low g ue to gr vity

D is the hydraulic depth.

y

T

Area A

Open Channel Flow


D A

T

Froude no is the ratio of inertia force and gravity force

F Interti For e

Gr vity For e

I F Sub critical flow/Tranquil flow/ Steaming flow

I F Then it is critical flow

I F Super critical flow/Rapid flow/Shooting flow

Geometrical Parameters of an Open Channel Flow

1. Depth of Flow (y): It is the vertical distance b/w the lowest point in the channel section and the

ree liqui sur e it is enote y ‘y .

2. Depth of Flow Section (d): It is the actual depth of the channel measured normal to the direction

o low. It is enote s ‘

3. Top Width (T): It is the width of the channel at the free surface open to the atmosphere it is

enote y ‘T .

4. Hydraulic Depth (D): A T⁄

The hy r uli epth or i erent se tion re

(i) Re t ngul r (y)

(ii) Tri ngul r (y

)

(iii) Tr pezoi l ( y)y

my

(iv) P r oli y

(v) ir ul r r

( sin

sin )

5. Wetted Area:

(A) For Rectangular y

(B) For Triangular my

(C) For Parabolic

(D) For Trapezoidal ( my)y

(E) Circular

( sin )

Free Liquid Surface

Channel Bottom

y d

l

h

Open Channel Flow


6. Wetted Perimeter: The length of the channel boundary which comes in contact with the flowing

liquid is called wetted perimeter and it is denoted by P .

(a) Rectangular y

(b) Circular r

(c) P r oli

(d) Trin gul r y √m

(e) Tr pezoi l y √m

7. Hydraulic Radius:

8. Bed Slope of Channel: The inclination of the channel bed with the horizontal is the bed slope of

channel it is denoted by so for a uniform flow, since the bed slope and liquid surface slope are

same, then it is denoted by S. S sin

where, h is the vertical disp and this relation is

valid for when is very small where , sin t n

9. Section Factor: Section factor for critical flow is the product of wetted area and the square root

of hydraulic depth. It is denoted by A√D A(

)

A T

( ) Re t ngul r y .

( ) Tri ngul r my .

√

( ) P r oli T ( y

) .

( ) Tr pezoi l [( my)y] .

( my) .

(e) ir ul r

√sin *r

( sin )+

.

For Discharge Equation for Uniform Flow in Open Channel

1. The Chezy equation, V = √RS C hezy s onst nt

R A

P

To find out the value of c,

(a) Kutter s Formul

.

H( .

)

√

Where n roughness o e i ient

( ) .

. (

√ )

zin Formul

m . For smooth sur e

. For rough sur e

( ) R

n M nning s Formul

Open Channel Flow


2. M nning s Equ tion V n⁄ R S here the value of

n = 0.1 for smooth surface

= 0.04 for rough surface

Channel of most efficient cross-section An open channel of given slope, roughness and area if

flow is said to be hydraulically efficient or most economic section, when it carries the maximum

discharge.

For hezy s equ tion or given slope n roughness velocity is maximum when hydraulic

radius is minimum. Further for a given area hydraulic radius is maximum when wetted

perimeter is minimum.

Rectangular Channel

For Rectangular channel

y R y

Trapezoidal Channel

y (√ m m)

y √ m

Circular Channel

R . D here D i

Example: Find the bed slope in channels of the following sections having top width 5 m and

uniform depth 2 m. Take the discharge value as 0.03 m se n hezy s onst nt s .

Find out for

1. Rectangular channel

2. Triangular

3. Trapezoidal channel with side slope 1H:3V

Q . m

se T m m

Solution:

(i) Rectangular

V √RS R A

P

.

√

S

y

y

y

b

m 1

y

b

Open Channel Flow


(ii) Triangular

R A

P

m y

y √m

A

Ty

P PS QS

(iii) Trapezoidal

Example: The cross-section of a navigation channel is shown in figure determine the discharge

through the channel if the depth of flow in 12 m the channel has a slope of 1 in 2000 and

the hezy s onst nt is .

Solution:

y m

S

V √RS

D E

m

m

H

m m

A

m m m

G

I J

F

m

(b+2 my)=T

b

y

m y m y

P Q T

S

y

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