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
–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
–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.
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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 weightedtheory 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 ofmetering flumes, types of canal modules and proportionality, sensitivity, flexibility.
Cross Drainage Works: Definition, classification, design principles of aqueducts, siphonaqueducts, canal siphons, super passages and inlet and outlets, selection of cross drainage works.
Bridges and Culverts: Discharge, Waterway and sour depth computations, Depth of Bridgefoundation, 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 curveand flow duration curve. Components of power plant-intakes, fore/bay, penstocks, functions andtypes 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.
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.