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ADAMA SCIENCE AND TECHNOLOGY UNIVERSITY

SCHOOL OF CIVIL ENGINEERING AND ARCHITECTURE
DEPARTMENT OF CIVIL ENGINEERING

HYDRAULIC STRUCTURE ASSIGNMENT I

NAME: GUTA TESFAYE

ID No: Ugr/22741/13
Section: 2

SUBMITTED To Mr. BEHAILU

SUMISSION DATE JAN 2 2025
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CHAPTER 5

5. Canal
structures

Canal structures are required for the control and measurement of the water flow. An open canal,
channel, or ditch, is an open waterway whose purpose is to carry water from one place to another.
Channels and canals refer to main waterways supplying water to one or more farms.
The flow of irrigation water in the canals must always be under control. For this purpose, canal
structures are required. They help regulate the flow and deliver the correct amount of water to the
different branches of the system and onward to the irrigated fields.
There are four main types of structures: erosion control structures, distribution control structures,
crossing structures and water measurement structures.
i. Erosion control structures
a. Canal erosion
Canal bottom slope and water velocity are closely related. Water flowing in steep canals can
reach very high velocities. Soil particles along the bottom and banks of an earthen canal are then
lifted, carried away by the water flow, and deposited downstream where they may block the
canal and silt up structures. The canal is said to be under erosion; the banks might eventually
collapse.
b. Drop structures and chutes
Drop structures or chutes are required to reduce the bottom slope of canals lying on steeply
sloping land in order to avoid high velocity of the flow and risk of erosion. These structures
permit the canal to be constructed as a series of relatively flat sections, each at a different
elevation.

Drop structures take the water abruptly from a higher section of the canal to a lower one. In a
chute, the water does not drop freely but is carried through a steep, lined canal section. Chutes
are used where there are big differences in the elevation of the canal
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ii. Distribution control structures

Distribution control structures are required for easy and accurate water distribution within the
irrigation system and on the farm.
a) Division boxes
Division boxes are used to divide or direct the flow of water between two or more canals or
ditches. Water enters the box through an opening on one side and flows out through openings on
the other sides. These openings are equipped with gates

b) Turnouts
Turnouts are constructed in the bank of a canal. They divert part of the water from the canal to a
smaller one. Turnouts can be concrete structures
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c) Checks
To divert water from the field ditch to the field, it is often necessary to raise the water level in the
ditch. Checks are structures placed across the ditch to block it temporarily and to raise the
upstream water level. Checks can be permanent structures.

iii. Crossing structures

It is often necessary to carry irrigation water across roads, hillsides and natural depressions.
Crossing structures, such as flumes, culverts and inverted siphons, are then required.
A. Flumes
Flumes are used to carry irrigation water across gullies, ravines or other natural depressions.
They are open canals made of wood (bamboo), metal or concrete which often need to be
supported by pillars.
B. Culverts
Culverts are used to carry the water across roads. The structure consists of masonry or concrete
headwalls at the inlet and outlet connected by a buried pipeline

C. Inverted siphons
When water has to be carried across a road which is at the same level as or below the canal
bottom, an inverted siphon is used instead of a culvert. The structure consists of an inlet and
outlet connected by a pipeline . Inverted siphons are also used to carry water across wide
depressions.
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iv. Water measurement structures

The principal objective of measuring irrigation water is to permit efficient distribution and
application. By measuring the flow of water, a farmer knows how much water is applied during
each irrigation. In irrigation schemes where water costs are charged to the farmer, water
measurement provides a basis for estimating water charges.
The most commonly used water measuring structures are weirs and flumes. In these structures,
the water depth is read on a scale which is part of the structure. Using this reading, the flow-rate
is then computed from standard formulas or obtained from standard tables prepared specially for
the structure.
a. Weirs
In its simplest form, a weir consists of a wall of timber, metal or concrete with an opening with
fixed dimensions cut in its edge .The opening, called a notch, may be rectangular, trapezoidal or
triangular.

b. Parshall flumes
The Parshall flume consists of a metal or concrete channel structure with three main sections:
✓ a converging section at the upstream end, leading to
✓ a constricted or throat section and
✓ a diverging section at the downstream end.

Depending on the flow condition (free flow or submerged flow), the water depth readings are
taken on one scale only (the upstream one) or on both scales simultaneously.
c. Cut-throat flume
The cut-throat flume is similar to the Parshall flume, but has no throat section, only converging
and diverging sections . Unlike the Parshall flume, the cut-throat flume has a flat bottom.
Because it is easier to construct and install, the cut-throat flume is often preferred to the Parshall
flume.
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5.1 Division Box

A division box is a vital hydraulic structure that splits the flow of water from a single source into
multiple channels, playing a crucial role in irrigation and water management.

5.1.1 Significance and Relevance

1. Efficient Water Distribution:
✓ Ensures equitable water supply to various users, enhancing agricultural productivity.
✓ Allows flexible flow adjustments based on seasonal needs.
2. Enhanced Monitoring and Management:
✓ Equipped with flow measurement devices for continuous monitoring.
✓ Provides data for informed decision-making on water allocation.
3. Environmental Protection:
✓ Reduces water wastage, essential in water-scarce regions.
✓ Incorporates sediment traps to maintain water quality and protect ecosystems.

5.1.2 Relevance to Canal Structures

1. Integration:
✓ Seamlessly connects with canal systems, ensuring efficient water flow.
✓ Structural design considers hydraulic gradients and sediment transport.
2. Operational Efficiency:
✓ Adjustable gates enable real-time flow regulation.
✓ Maintenance features ensure long-term operational viability.

5.1.3 Practical Applications

Agricultural Irrigation: Used in large-scale farms for tailored water distribution, improving
crop yields.
Urban Water Management: Manages stormwater runoff in cities, mitigating flooding
and enhancing water quality.
Environmental Conservation: Supports wetland restoration projects by controlling water flow
into sensitive ecosystems.
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5.2 canal drops

Canal falls(drops), also known as weirs or barrages, play a vital role in hydraulic engineering by
regulating the flow of water in canals and rivers. These engineered structures are designed to
control water levels, facilitate irrigation, and prevent erosion, making them essential components
of water management systems worldwide. Canal falls come in various forms and are built to suit
specific purposes, from diverting water for agricultural needs to generating hydropower.
When the field's slope abruptly becomes steeper, regulating the canal bed slope becomes
challenging and necessitates extensive earthwork in the filling process. To manage this situation
efficiently, falls are constructed to prevent excessive earthwork when the land slope remains
relatively consistent and exceeds the designated canal bed slope.

5.2.1 Location of Canal Falls

The location of a canal fall is contingent upon key determinants, including:
✓ The natural topography of the canal's surroundings.
✓ The economic considerations related to excavation and filling.
These factors collectively influence the strategic placement of the canal fall. A thorough
understanding of the topographical context aids in selecting the most suitable type of fall and
optimizing its performance and cost-effectiveness.

5.2.2 Types of Canal Falls

The various types of Canal Falls are:
a. Ogee Fall: The ogee fall incorporates a combination of both convex and concave curves.
This design ensures a smooth transition of water flow and minimizes adverse effects. It is
typically recommended for canals unless a sudden change in natural terrain to a steeper slope
occurs, in which case stone pitching is added both upstream and downstream to manage the
transition effectively.
b. Rapids Fall: The rapid fall features a long sloping glacis and is constructed when the natural
ground surface is relatively flat and extensive. A bed of rubble masonry is used, finished with a
cement mortar mixture. Curtain walls are provided upstream and downstream to maintain the
slope of the bed, although it's worth noting that rapid falls can be more expensive to construct.
c. Stepped Fall: Stepped fall involves vertical steps at gradual breaks and is an adaptation of the
rapid fall design. It is suitable for canals where the upstream is significantly higher than the
downstream, connecting these two levels with vertical steps or drops to control water flow
effectively
d. Well-type Fall: Well-type falls, also known as siphon drop falls, incorporate an inlet well
with a pipe at its base upstream. This pipe conveys water to a downstream well or reservoir,
with the choice between the two depending on discharge capacity.
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5.2.3 Advantages and Disadvantage of Canal Fall

The advantages of Canal Falls are:

✓ Controls water flow and minimizes erosion.

✓ Facilitates energy dissipation.
✓ Enables water level regulation.
The shortcomings of Canal Falls are:
✓ Construction cost.
✓ Maintenance and repair expenses.
✓ Potential for sediment accumulation.

5.3 Chute
Chute (open channel or trough) spillway is a spillway whose discharge is conveyed from the
upper reach of the channel or a reservoir to the downstream channel level through an open
channel placed along a dam, abutment (supporting wall), or through a saddle. Chute structures
are useful for gully head control and they could be used for drops up to 5 to 6 m. Chute spillways
are constructed at the gully head to convey the discharge from upstream area of gully into the
gully through a concrete or masonry open channel, when drop height exceeds the economic limit
of drop structures. Chute spillway has more advantage than a drop spillway, when a large runoff
volume is required to be discharged from the area. Flow in a chute spillway is at super-critical
velocities.
5.3.1 Components of Chute Spillway
The chute spillway consists of the following three design components :
• Inlet or Entrance Channel: The most common type of inlets used in chute spillways are
the straight inlet, box type inlet and sometimes side channel inlet also. The box type inlet
is generally used in a situation when straight type inlet is not sufficient to carry the runoff
at the desired drop.
• Channel Section or Conduit: In chute spillway, the rectangular type conduits are mostly
common. The side walls of conduit confine the flow rate and discharge distribution. The
top edge of side walls is constructed in such a way that it may be flushed with the
embankment slope. The vertical curve section is continued through the channel in such a
manner so that it conveys and guides the discharge to the lower elevation without erosion.
• Outlet: The outlet dissipates the energy of the flowing water and provides non-erosive
velocity downstream. Straight apron type outlets are most commonly used in small gully
control structures.
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5.3.2 Applicability
➢ Chute spillways are used whenever a channel is to be constructed down a steep slope.
➢ They are preferred over drop spillways when the drop exceeds the economic limits of the
latter.
➢ It is superior to a drop inlet spillway when large discharges are required to be conveyed.
When there is no opportunity to provide temporary storage, the chute spillway with its
inherent high capacity is preferred over the drop inlet spillway.
➢ Chute spillways are frequently used in combination with earth dams to drop water farther
than is feasible with drop structures. The capacity of a chute spillway is not reduced due to
sedimentation at the outlet.
➢ However, sometimes there is a danger that rodents may undermine the structure and in poorly
drained locations seepage may endanger the foundations.

5.4 Siphon And aqueducts

Siphons and aqueducts are critical hydraulic structures designed to transport water over varying
terrains, often used in irrigation and municipal water supply systems. They play essential roles in
effective water management and distribution.
1. Siphons
• Functionality: Siphons utilize atmospheric pressure and gravity to move water from
higher to lower elevations, often crossing valleys or obstacles without the need for
pumps.
• Cost-Effectiveness: Siphons eliminate the need for expensive pumping stations, reducing
operational costs.
• Environmental Compatibility: They can be designed to minimize ecological disruption,
preserving surrounding habitats.
2. Aqueducts
• Functionality: Aqueducts are large structures that convey water over long distances,
using gravity and elevation changes. They can be open channels or enclosed conduits,
often elevated on arches or bridges.
• Infrastructure Development: Aqueducts enable the transfer of water from remote
sources to areas with high demand, crucial for urban and agricultural needs.
• Historical Significance: Historically, aqueducts have played a vital role in the
development of civilizations, showcasing engineering prowess and ensuring water supply.
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5.4.1 Practical Applications

1. Agricultural Irrigation
❖ Water Distribution: Siphons and aqueducts are integral in distributing water from main
sources to agricultural fields, ensuring efficient and reliable irrigation practices.
❖ Increased Crop Yields: By facilitating timely water delivery, these structures contribute
to enhanced agricultural productivity.
2. Urban Water Supply
• Municipal Systems: Cities utilize aqueducts to transport water from distant sources to
urban centers, ensuring a stable supply for residential and industrial use.
• Flood Mitigation: Siphons can manage excess runoff, preventing flooding in urban areas
by directing water to designated drainage systems.
3. Environmental Conservation
• Sustainable Practices: Both structures can be designed to minimize environmental
impact, aiding in conservation efforts by maintaining natural watercourses and habitats.
• Ecosystem Management: Controlled water flow via aqueducts and siphons supports the
health of local ecosystems, ensuring biodiversity is preserved.