Importance of Irrigation

Definition the supply of water to crops and landscaping plants by artificial means

Estimates of magnitude world-wide: 544 million acres

(17% of land 1/3 of food production) Purpose

Raise a crop where nothing would grow otherwise (e.g., desert areas) Grow a more profitable crop (e.g., alfalfa vs. wheat) Increase the yield and/or quality of a given crop (e.g., fruit) Increase the aesthetic value of a landscape (e.g., turf, ornamentals)

Reasons for yield/quality increase

Reduced water stress Better germination and stands Higher plant populations More efficient use of fertilizer Improved varieties

Other Benefits of Irrigation

Leaching of salts Frost protection Plant/soil cooling Chemical application Wind erosion control Waste disposal

Types of Systems

Sprinkler pressurized irrigation through devices called sprinklers (water is

discharged into the air and hopefully infiltrates near where it lands)

used on agricultural and horticultural crops, turf, landscape plants Surface

Irrigation water flows across the field to the point of infiltration primarily used on agricultural crops and orchards

Micro (drip, trickle) frequent, slow application of irrigation water using pressurized systems used in landscape and nursery applications, and on high-value agricultural

and horticultural crops

Water Measurement

Volume Quantity of water; Water at rest Gallon, cubic foot, etc. V = A d (units: acre-inch, acre-foot, hectare-meter etc.)

Depth Rainfall measured as depth; Useful for irrigation applications as well Inch, foot, millimeter, centimeter, etc. D = V / A (units: usually inches or millimeters)

Flow Volume of water per unit time; Water in motion Gallons per minute, cubic feet per second, acre-inches per day, liters per

second, cubic meters per second etc.

Q = V / t (units must be consistent)

Soil Water Relationships

Texture Definition: relative proportions of various sizes of individual soil particles USDA classifications

Sand: 0.05 2.0 mm Silt: 0.002 - 0.05 mm Clay:

Water in Soils

Soil water content

Mass water content (m)

m = mass water content (fraction)

Mw = mass of water evaporated, g (24 hours @ 105oC)

Ms = mass of dry soil, g

Equivalent depth of water (d)

d = volume of water per unit land area = (v A L) / A = v L d = equivalent depth of water in a soil layer L = depth (thickness) of the soil layer

Soil Water Potential Description

Measure of the energy status of the soil water Important because it reflects how hard plants must work to extract water Units of measure are normally bars or atmospheres

s

wm

M

M

Soil water potentials are negative pressures (tension or suction) Water flows from a higher (less negative) potential to a lower (more

negative) potential

Irrigation Scheduling

General Approaches

Maintain soil moisture within desired limits direct measurement moisture accounting

Use plant status indicators to trigger irrigation wilting, leaf rolling, leaf color canopy-air temperature difference

Irrigate according to calendar or fixed schedule Irrigation district delivery schedule Watching the neighbors

Canals: Conveyance of water, open and closed conduits. Canals and tunnels functions

and classification of canals, canal alignment, balancing depth. design of lined canals,

design of unlined canals, critical velocity, regime canals, Kennedys and Laceys theories, advantages of lines canals, method of lining. Design of lines canals.

.

Lining of Irrigation Canals Most of the irrigation channels in Iraq are earthen channels. The

major advantage of an earth channel is its low initial cost, these suffer

from certain disadvantages, like the following:-

1- Maximum velocity limited to prevent erosion.

2- Seepage of water into the ground.

3- Possibility of vegetation growth in banks, leading to increased friction.

4-Possibility of bank failure, due to erosion.

5-More maintenance requirement.

Types of Canal Lining Types of lining are generally classified according to the materials

used for their construction. Concrete, rock masonry, brick masonry,

bentonite-earth mixtures, natural clays of low permeability, and different

mixtures of rubble, plastic, and asphaltic materials are the commonly

used materials for canal lining. The suitability of the lining material is

decided by:

A- Economy.

B- Structural stability.

C- Resistance to erosion.

E- Durability.

F- Hydraulic efficiency.

[A] Concrete Lining [B] Precast concrete lining [C] Shotcrete Lining [D] Bricks, Tiles and Stone lining [E] Asphaltic Lining [F] Earth Linings 1- Stabilized Earth Linings

Sub-grade is stabilized using either clay for granular subgrade or by

adding chemicals that compact the soil.

2- Loose Earth Blankets

Fine grained soil is laid on the sub grade and evenly spread. However,

this type of lining is subject to erosion, and requires a flatter side slopes

of canal.

3- Compacted Earth Linings

The graded soil containing about 15 percent clay is spread over the

subgrade and compacted.

4- Buried Bentonite Membranes

Bentonite is a special type of clay soil, found naturally, which swell

considerably when wetted.

5- Soil-cement Linings:

These linings are constructed using cement (15 to 20 per cent by

volume) and sandy soil (not containing more than about 35 per cent of silt

and clay particles). Cement and sandy soil can be mixed in place and

compacted at the optimum moisture content. This method of construction

is termed the dry-mixed soil-cement method.

3- Failure of Canal Lining The main causes of failure of lining are the water pressure that

developed behind the lining material due to high water table, saturation

of the embankment by canal water, sudden lowering of water levels in the

channel, and saturation of the embankment sustained by continuous

rainfall. When the water level in canal was raised and lowered the banks

suffering from instability due to erosion and seepage through the banks

may be occurs. In order to minimize the seepage, a secondary berms were

constructed along the length of bank at various locations.

Diversion head works: Weirs and Barrages, Layout of diversion head works and

components, failure of hydraulic structures on previous foundations, Blighs Creep

theory, Lanes weighted theory and Khoslas theory, concept of low net, u/s and d/s cutoffs and protection measures, design of vertical drop weir.

Canal Structures: Types of falls and their location, design principles and Trapezoidal

notch fall, siphon well drop, straight glacis fall. Canal regulation works, alignment of off

taking canal. Distributary head regulators and cross regulation and their design. Canal

escapes, types of metering flumes, types of canal modules and proportionality,

sensitivity, flexibility.

Cross Drainage Works: Definition, classification, design principles of aqueducts,

siphon aqueducts, canal siphons, super passages and inlet and outlets, selection of cross

drainage works.

Bridges and Culverts: Discharge, Waterway and sour depth computations, Depth of

Bridge foundation, spans and vertical clearance, efflux computations, pipe culverts and

box culverts.

Water Power: Classification of Hydropower plants, definitions pf terms, load, head,

power, efficiency, load factor, installed capacity, utilization factor, capacity factor, use of

mass curve and flow duration curve. Components of power plant-intakes, fore/bay,

penstocks, functions and types of sewage tanks, General arrangement of power house,

sub-structure and super-structure.

.

Design of Hydraulic Structures Design of Hydraulic Structures COURSE Contents

1. Introduction

2. Gravity Dams Site selection, Forces,

Stability analysis.

3. Diversion Works Weirs and Barrages

4. Canals Design and Canal Falls. 5. Cross Drainage Works

6. Head Regulators and Cross

regulators

IS Codes IS Code 6512: Criteria for Design of Solid Gravity

Dams

IS Code 1893: Criteria for Earthquake Resistant

Design of Structures

IS Code 7784-Cross-Drainage Works: Part 1 -

General

IS Code 7784- Cross-Drainage Works: Part 2 -

Aqueduct

IS Code 7784- Cross-Drainage Works: Part 2 Syphon Aqueduct

IS Code 7784- Cross-Drainage Works: Part 2 Canal Syphon

IS Code 7784- Cross-Drainage Works: Part 2 Superpassage

IS Code 7784- Cross-Drainage Works: Part 2 Level Crossing

CEL351: Design of

Why study Hydraulic Structures?

INTRODUCTION Development of water resources of

a region

Requires

Conception

Planning

Design

Construction

Operation

of various facilities to utilise and

control water, and

to maintain water quality.

Utilize/Need water

Domestic & Industrial uses

Irrigation

Power generation

Navigation

Other purposes

Water Resources Engineering

Utilisation of water

Control of water

Water quality management

Water is controlled and regulated

Flood control

Land drainage

Sewerage

Bridges

Not cause damage to property,

inconvenience to the

public, or loss of life

Water-quality management

Required quality of water for

different uses

Preserve Ecological balance

Contamination of

Groundwater/Surface water

Water Resources development

projects are planned

to serve various purposes

Main Purposes

Domestic & Industrial uses,

Irrigation

Power generation, Navigation,

Flood control

Secondary Purposes

Recreational, Fish and wild life,

Drainage control,

Watershed management, Sediment

control,

Salinity control, Pollution

abatement

Miscellaneous Purposes

Employment, Accelerate

development etc

Single-purpose andMulti-purpose

Water Resources projects Two Main Steps

First step How much water is available?

Knowledge of Hydrology

Precipitation average Abstraction Losses Runoff, Yield of basin

Flood Peak runoff Reservoir sizing Mass curve Second step How to utilise and control water?

Require various structure

Hydraulic Structures

Types of Hydraulic Structures

Storage

Diversion

Transportation

Regulation

Control

Main source of water is

Precipitation

Precipitation is not uniform over

space and time

Monsoon, North East, Himalaya,

W. Ghat

Store water at surplus location

during surplus

period Storage structures Reservoirs

Dam and Reservoir coexist

Dam solid barrier across river Reservoir artificial lake u/s of dam

Reservoir Dam

Reservoir Dam Spillway

RESERVOIRS RESERVOIRS Types of Reservoirs Single-purpose and Multi-purpose

Storage (or conservation) reservoirs

Flood control reservoirs

Multipurpose reservoir

Distribution reservoirs

Balancing reservoirs

Flood Control runoff exceeding safe capacity of

river is stored in the reservoir.

Stored water is

released in controlled manner

Detention Reservoirs regulated by GATES

Adv: More flexibility of operation and better control of

outflow; Discharge from various

reservoirs can be adjusted

Disadv: More expensive; Possibility of human error

Retarding Reservoirs UNGATES Adv: Less expensive; Outflow is automatic so possibility of

human error

Disadv: No flexibility of operation; Discharge from various

reservoirs may coincide heavy flood

Multipurpose Reservoirs Serve two or more purposes. In India,

most of the reservoirs

are designed as multipurpose reservoirs

to store water for

irrigation and hydropower, and also to

effect flood control

Distribution Reservoirs Small storage reservoirs to tide over the

peak demand of

water. The distribution reservoir is

helpful in permitting

the pumps to work at a uniform rate. It

stores water

during the period of lean demand and

supplies the same

during the period of high demand. As the

storage is

limited, it merely helps in distribution of

water as per

demand for a day or so and not for

storing it for a long

period. Distribution reservoirs are mainly

used for

municipal water supply but rarely used

for the supply of

water for irrigation.

RESERVOIRS RESERVOIRS Multipurpose Reservoirs Serve two or more purposes. In India,

most of the reservoirs

are designed as multipurpose reservoirs

to store water for

irrigation and hydropower, and also to

effect flood control

Distribution Reservoirs

Small storage reservoirs to tide over the

peak demand of

water. The distribution reservoir is

helpful in permitting

the pumps to work at a uniform rate. It

stores water

during the period of lean demand and

supplies the same

during the period of high demand. As the

storage is

limited, it merely helps in distribution of

water as per

demand for a day or so and not for

storing it for a long

period. Distribution reservoirs are mainly

used for

municipal water supply but rarely used

for the supply of

water for irrigation.

RESERVOIRS RESERVOIRS Balancing Reservoirs

A balancing reservoir is a small reservoir

constructed d/s of

the main reservoir for holding water

released from the

main reservoir.

RESERVOIRS RESERVOIRS Storage Capacity of Reservoirs Storage capacity of a reservoir depends

upon the topography of

the site and the height of dam.

Engineering surveys

The storage capacity and the water

spread area at different

elevations can be determined from the

contour map.

In addition to finding out the capacity of

a reservoir, the

contour map of the reservoir can also be

used to determine

the land and property which would be

submerged when the

reservoir is filled upto various elevations.

To estimate the compensation to be paid

to the owners of the

submerged property and land. The time

schedule,

according to which the areas should be

evacuated, as the

reservoir is gradually filled, can also be

drawn..

RESERVOIRS RESERVOIRS Storage Capacity of a Reservoir Both the elevation-area curve and the

elevation- storage curve on

the same paper. Abscissa - areas and

volumes - opposite

di ti

Area-Elevation Curve from contour map An

elevation-area curve is

then drawn between

the surface area as

abscissa and the

elevation as ordinate.

Elevation-Capacity

Curve: is determined

from elevation-area

curve using diff

formulae.

Storage Capacity calculation

formulae 1. Trapezoidal formula

2. Cone formula

3. Prismoidal formula

4. Storage Volume from cross-sectional

areas

Basic Terms and Definitions 1. Full reservoir level (FRL): is the

highest water level to which

the water surface will rise during normal

operating

conditions. Also called the full tank level

(FTL) or the

normal pool level (NPL).

2. Maximum water level (MWL): is the

maximum level to which

the water surface will rise when the

design flood passes over

the spillway. Also called the maximum

pool level (MPL) or

maximum flood level (MFL).

3. Minimum pool level: is the lowest level

up to which the water

is withdrawn from the reservoir under

ordinary conditions.

It corresponds to the elevation of the

lowest outlet (or

sluiceway) of the dam. However, in the

case of a reservoir for

hydroelectric power; the minimum pool

level is fixed after

considering the minimum working head

required for the

efficient working of turbines.

Basic Terms and Definitions

4. Useful storage: volume of water stored

between the full

reservoir level and the minimum pool

level. Also known as

the live storage.

5. Surcharge storage: is the volume of

water stored above the

full reservoir level upto the maximum

water level. The

surcharge storage is an uncontrolled

storage which exists

only when the river is in flood and the

flood water is passing

over the spillway. This storage is available

only for the

absorption of flood and it cannot be used

for other purposes.

6. Dead storage: volume of water held

below the minimum pool

level. The dead storage is not useful, as it

cannot be used for

any purpose under ordinary operating

conditions.

7. Bank storage: If the banks of the

reservoir are porous, some

water is temporarily stored by them when

the reservoir is

full.

8. Valley storage: The volume of water

held by the natural river

channel in its valley upto the top of its

banks before the

construction of a reservoir is called the

valley storage. May

be important in flood control reservoirs.

9. Yield from a reservoir: Yield is the

volume of water which

can be withdrawn from a reservoir in a

specified period of

time. The yield is determined from the

storage capacity of

the reservoir and the mass inflow curve.

10 Safe yield (Firm yield): is the

maximum quantity of water

which can be supplied from a reservoir in

a specified period

of time during a critical dry year. Lowest

recorded natural

flow of the river for a number of years is

taken as the

critical dry period for determining the

safe yield

11. Secondary yield: is the quantity of

water which is available

during the period of high flow in the

rivers when the yield is

more than the safe yield. It is supplied on

as and when basis

at the lower rates. The hydropower

developed from

secondary yield is sold to industries at

cheaper rates.

12. Average yield: is the arithmetic

average of the firm yield

and the secondary yield over a long

period of time.

13. Design yield: is the yield adopted in

the design of a reservoir.

Fixed after considering the urgency of the

water needs and

the amount of risk involved. The design

yield should be such

that the demands of the consumers are

reasonably met with,

and at the same time, the storage required

is not unduly

large.