ce2301 irrigation engineering ln - fatima michael college of engineering...

IRRIGATION ENGINEERING

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: <0.002 mm

– Textural triangle: USDA Textural Classes

– Coarse vs. Fine, Light vs. Heavy

– Affects water movement and storage

• Structure

– Definition: how soil particles are grouped or arranged

– Affects root penetration and water intake and movement

Water in Soils

• Soil water content θm = Mw

Ms

– Mass water content (θm)

– θm = 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 = (θv A L) / A = θv 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

– 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, Kennedy’s and Lacey’s 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, Bligh’s Creep

theory, Lane’s weighted theory and Khosla’s 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.

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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.


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.


Balancing Reservoirs

A balancing reservoir is a small reservoir constructed d/s of

the main reservoir for holding water released from the

main reservoir.


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..


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.

ce2301 irrigation engineering ln - fatima michael college of engineering...

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