Last class we were discuss about

Irrigation methods
1. Surface irrigation and sub-surface
2. Gravity and pressurized
 Flood , Basin, Border and Furrow
 Drip or trickle and sprinkler
In this class we will discuss about
Water conveyance and control structures
 Irrigation canal network
 Layout of canal network
 Design of alluvial and non alluvial canals
 Methods of water measurement
 Diversion head work, cross drainage works and control structures(Reading
Assignment)
 Chapter -5
Water conveyance and control
structures.
 Irrigation Canal Networks

 Any type of irrigation scheme whether direct or storage irrigation

scheme require a network of irrigation canals of different sizes and
capacities.

 The entire network of the irrigation channels is called the canal system.

 A canal system consists of :

 Primary distribution system/ main canals
 Secondary distribution system/ secondary canals
 Tertiary distribution system/ tertiary canals
 Field channels.
 Distribution system for canal irrigation

I. Primary distribution system:

 Conveyance of water from the source to the branch canals
 feeding two or more branch canals
 Runs through the irrigation season with varying supply.
II. Secondary distribution system:
 Consists of large number of distributaries with varying discharge
 They are fed by the main canals.
II. Tertiary distribution system:
 Water flowing into the water course or it branches, from an outlet of
distributaries is allocated to varies field channels by this system.
 Tertiary distribution system is mostly controlled by farmers/cultivators.
IV. Field channels:
 taken from the outlets of the distributaries channels by the cultivators to
supply water to their own lands.
A complete canal system in large scale schemes
Distribution system for canal irrigation
Irrigation Canal Networks
 Layout of Canal Networks

A canal irrigation shall convey water from the head work to command
areas through the best route.

Layout of canal network mainly include:

 Alignment of canals
 Distribution systems
 Layout of Canal Networks
General Canal Layout criteria:
 Canals should be laid in such a way that there is minimum loss of
command area.

 As much as possible, canals are aligned on ridges and drains are aligned
in depressions. Why?

 The alignment which require heavy filling should be avoided.

 As much as possible the canal should run through the heart of the
command area to keep the cost of the distribution system to minimum.

 Canal structures has to be simple and manageable.

 Layout of Canal Networks

General Canal Layout criteria:

 The canal alignment should avoid inhabited areas, religious places,
valuable property, and other important monuments.

 As much as possible curves in the canal should be avoided. If not possible,

the curve must be with large radii.

 The canal should be aligned in such a way that its crossings with the road,
rail way line and drainage line should be at straight line.
 Layout of Canal Networks

General Layout criteria for field canals:

Field canals are the smallest and the last canals of the distribution system, they
supply water directly to the crop.
The following points must be considered while aligning field canals.
 The canals should be aligned along the boundaries of the agricultural field.
 The canals should be aligned across contours so that furrows or basins will
be aligned along contours.
 Field canals must be capable of supplying enough water to the tail end of
the field with sufficient head.
 Field canals must be as few as possible to minimize the losses of water
and cost of the project..
 Layout of Canal Networks

Types of Alignment of canals:

 Irrigation canals can be aligned in any of the following three ways:
i. Watershed canal
ii. Contour canal
iii. Side-slope canal.
 Layout of Canal Networks
i. Watershed canal
• The dividing ridge line between the catchment areas of the two streams (drains)
is called the water divide ,or the ridge.
• Thus, between two major streams, there is main watershed(ridge line), which
divides the drainage area of two streams,
• The canal which is aligned along any natural watershed divide (ridgeline) is called
a watershed canal, or a ridge canal.
• Aligning a canal (main canal or branch canal or distributaries) on the ridge,
ensures gravity irrigation on both sides of the canal.
 In doing so, attempts should be made that the main canal mounts the ridge in as
small length as possible from the point of off take.

 The canal should run straight even when watershed makes sharp loop.
 Layout of Canal Networks

E.g. Level at head work =1420m

Required canal slope =1/3000,
Distance to bring water from A to B = 15km
 Layout of Canal Networks

ii. Contour canal:

 In cases where virtually impossible to take the canal on the top of such a
higher ridge line, contour canals are usually constructed.

 Contour channels follow a contour, except for giving the required

longitudinal slope to the canal.

 As the drainage flow is always at right angles to the ground contours, such
a channel would definitely have to cross natural drains and streams,
necessitating construction of cross-drainage structures.
Layout of Canal Networks
 Layout of Canal Networks

iii. Side slope canal:

 A side slope canal is that which is aligned at right angles to the contours.

 Due to nature of the ground, canals may be aligned at right angles to the
contours. i.e. parallel to the drains or rivers.

 Since such canal runs parallel to the natural drainage channels, thus,
avoiding the construction of cross-drainage structures.
Layout of Canal Networks
 Design of Canals

 The entire system of canals must be designed properly for realistic

value of peak discharge that must passes through them, so as to
provide sufficient irrigation water to the command areas.

 Inputs required for Design:

 Land suitability map
 Topographic map of the area; General and detail
 Irrigation water duty
 Hydro-metrological data
 Soil characteristics of the area
 Design of Alluvial and Non-Alluvial Canals

Additional Factors Affecting Canal Design:

 Construction cost
 Safety constructions
 Hydraulic operational characteristics
 Water management needs
 Maintenance requirements
 Environmental conservation
 Need of emergency spill structures
 Cross-channel surface drainage needs
 Secondary uses (clothes washing, swimming, others)
 Aesthetics
 Design of Canals

Steps for Design:

 After an area generally suitable for irrigation identified the
exact area that would receive irrigation water would be
determined.

 After suitable area for irrigation is determined, the irrigation

need for this area will be calculated.

 The irrigation water demand in liter/sec/ha(duty) for the

recommended crop can be obtained from CROPWAT
(Agronomist or Agronomy Department )
 Design of Canals

Steps for Design:

 Total water requirement for the command area including
distribution, application and conveyance efficiency will be
calculated to fix total amount of discharge that should be diverted
(received) from the source.
 In the process of doing so topographic survey of the suitable
command area will be surveyed and the highest possible level of
the command area will be fixed.
 After fixing the maximum possible level of the command area that
should receive irrigation water, longitudinal slopes and permissible
velocity for the canal type and soil formation will be chosen.
 The conveyance canal section will be fixed.
 Then come to the irrigation system layout (distribution net work).
 Types of Canals

Generally, two types of canals according to surface of canals

Mobile Boundary canals
 Alluvial canals
 Design method: Empirical methods ( Lacey’s and
Kennedy’s Theories); Tractive force Approach.
Rigid Boundary canals
 Non-Alluvial canals
 Lined canals
 Design method: Uniform flow equation (Manning’s,
Chezy’s equations)
 Types of Canals

Alluvial canals:
 The soil which is formed by transportation and of silt through the agency
of water, over a course of time, is called alluvial soil.
 The canals when excavated through such soils, are called alluvial canals
and direct irrigation is generally preferred in such areas.

Non-alluvial canals:
 Mountainous regions may go on disintegrating over a period of time,
resulting in the formation of rocky plain area, called non-alluvial area.
 Rivers passing through such areas, have no tendency to shift their
course.
 Canals passing through such areas are called non-alluvial canals and
storage type of irrigation is recommended.
 Design of Alluvial Canals

 The problem in the design of alluvial canals is scouring during high

velocity of flow and silting and eventual breaching of canals during low
velocity of flow.
 Alluvial canals are fairly accurately designed by The Kennedy’s
Theory or Lacey’s Theory.
Kennedy Theory:
 This is based on the concept of Non-silting and Non-scouring channel.
 The basis for designing of non-silting, non-scouring canal is that,
whatever silt has entered the channel at its head is kept in
suspension, so that it does not settle down and deposit at any point of
the channel and not to scour.
 He defined the critical velocity(Vo) in a channel as the mean velocity
(across the section) which will just keep the channel free from silting
or scouring, and related it to the depth of flow by the equation.
 Design of Alluvial Canals

Vo = 0.55*m*y^0.64 ………………………(1)

Where:
Vo=critical velocity in the channel
y = water depth in the channel in m
m = critical velocity ratio (introduced to account the soil type)

Table 1. Recommended value of m

 Design of Alluvial Canals

Design Procedure:
 Determine the critical velocity Vo by equation (1) assuming a trial
depth.
 And then determine area by dividing discharge by velocity.
 Determine channel dimensions.
 Compute the actual mean velocity (V) that will prevail in the canal of
this cross-section, by using Kutters’s , Manning’s or Chez’s formula.

 Finally if the two velocities Vo and V work out to be the same, then the
assumed depth is all right, otherwise change it and repeat the
procedure, till V and Vo equal.
 Design of Alluvial Canals

Recommended Canal Section:

 The canal section shall be trapezoidal, having the following internal
side slopes -
 Canals in cutting - 1:1
 Canals in filling - 1.5:1

 Free board above the water surface up to the top of the bank shall be
provided as follows –
 0.3m Up to 1 m3/s
 0.5m 1 to 10 m3/s
 0.75m 10 to 30 m3/s
 Design of Alluvial Canals

Recommended value of n for unlined channels:

 Design of Alluvial Canals

Radii of curvature:
The recommended radii of curvature for canals in its curved reaches shall
usually have the minimum values given in Table below.

Table: Canal Discharge and Radii of Curvature Parameters

Discharge [m3 / s] Radius, Min. [m]
80 and above 1,500
Less than 80 1000
Less than 30 600
Less than 15 300
Less than 3 150
Less than 0.3 90
 Design of Alluvial Canals

Example:
Design an irrigation main channel to carry 50 cumecs of discharge. The
channel is to be laid at a slope of I in 4000. The critical velocity ratio for the
soil is 1.1. Use Kutter’s rugosity coefficient as 0.023.

Given:
Q = 50 cumecs, S=1/4000; m = 1.1 n=0.023

Solution:
 using equation (1), Vo = 0.55*m*y^0.64
 Assuming a depth equal to 2 m,
Vo = 0.55*1.1*(2)^0.64 = 0.605*1.558 = 0.942m/s
A=Q/Vo=50/0.942=53.1m^2
 Design of Alluvial Canals

 Assuming side slopes as 0.5:1(0.5H:1V)

A=y(b + y*0.5)
53.1 = 2(b+1)
 Therefore,
b = 25.55 m
P = b+2*{1+0.25}^0.5*y
P = b + 2(5^0.5)/2*y = 25.55+(5^0.5)*2 = 30.03
R = A/P = 53.1/30.03 = 1.77m
 But, from equation (2),
 Design of Alluvial Canals

1.016 m/s >0.942 or V>Vo Scouring prevails

 In order to increase the critical velocity (Vo), we have to increase the
depth. So increase the depth.
 Let y = 3m depth:
Vo = 0.605*(3)^0.64 = 0.605*2.02 =1.22m/sec
A = 50/1022 = 40.8 m^2
40.8 = 3*(b+0.5*3)
 Or ,
13.6 -1.5 = b = 12.1m

P = 12.1 + 2*(5^0.5)/2*3 = 12.1 + 6.72 = 18.82

R = A/P =40.8/18.82 =2.17: therefore R^0.5 = 1.47
 Design of Alluvial Canals

 Using Critical velocity equation, Vo = 1.22m/s

 Using Kutter’s equation, V= 1.16m/s

 Since, 1.16 m/s >1.22 or V<Vo Silting prevails

 In order to decrease the critical velocity (Vo), we have to decrease the

depth. So decrease the depth.

 If we Use 2.7m, V (= 1.148 m/s) ≈Vo (= 1.147m/s).

 Design of Alluvial Canals

 Using Critical velocity equation, Vo = 1.22m/s

 Using Kutter’s equation, V= 1.16m/s

 Since, 1.16 m/s >1.22 or V<Vo Silting prevails

 In order to decrease the critical velocity (Vo), we have to decrease the

depth. So decrease the depth.

 If we Use 2.7m, V (= 1.148 m/s) ≈Vo (= 1.147m/s).

 Design of Alluvial Canals

Lacey’s Theory:
 He stated that alluvial channel can be designed under an assumed
state of true regime.
 An alluvial channel is in a state of true regime if the following
conditions are satisfied.
 Discharge is constant
 Flow is uniform
 Silt charge is constant
 Silt grade is constant

 Under such assumption, he developed empirical equations that will

enable one to design alluvial channels.
 Design of Alluvial Canals
Design Procedures:
1. Calculate the velocity from
V=[Q*f2/140]1/6 m/sec
Where, f is silt factor, given by f=1.76√d in which d is the average
particle size in mm
2. Compute Hydraulic mean depth (R)
R=2.5(V2/f)
Where, V is in m/sec and R is in m
3. Compute the area of the canal section, A=Q/V
4. Compute wetted perimeter,
P=4.75√Q
Where, Q is in m3/sec and P is in m
 Finally the bed slope S is determined by
S=[f5/3/3340Q1/6]
 Design of Unlined Canals

The criteria for design of unlined canals using uniform flow equations are:

 the design discharge should flow at non-erosive velocity. i.e. the

velocity should not exceed the maximum permissible value.

 side slopes should be flat enough not to be cave in when

saturated

 longitudinal slope should not be excess

Design of Unlined Canals
 Design of Unlined Canals
Table 2. Maximum permissible velocity for earthen canals

Table 3. Recommended Bed width – depth ratio for

trapezoidal channel
 Design of Unlined Canals

 Example: Compute a trapezoidal channel with the following

information:
 Type of channel: earthen channel
 Carrying Capacity, Q = 400ft3/sec
 Longitudinal slope, S = 0.0016
 Manning’s n = 0.025
 Side slope, z:1 = 2:1
 Maximum permissible velocity, V = 4.5 ft/sec

1.486 2 / 3 1/ 2
Use : V R S
n
 Design of Unlined Canals

Solution:
 Steps:
1) From V = (1.486/n )(R2/3S1/2), R = 2.60ft

2) From Q = AV, A = 88.8ft2

3) From R = A/P, P = 34.2ft

4) From relation A= (b+zd)d and P = B+2d (1+z2), b= 18.7ft

5) Therefore, d= 3.46 ft
 Method of Water Measurement
Structures that used to measure water flow:

Weirs
Flumes
 Weirs
A weir is an overflow structure installed perpendicular
to open channel flow
• Has a unique depth of water at an upstream
measuring point for each discharge
• If the water springs clear of downstream face,
acts as sharp-crested weir
• A long, raised channel control crest is a broad-
crested weir
 Weirs

Usually named for the shape of the overflow

opening
 Rectangular
 Triangular
Lowest elevation on overflow is zero reference
elevation for measuring h
 Weirs

Rectangular weirs can be either contracted or

suppressed
Suppressed weirs use side of flow channel
for weir ends
 No side contraction occurs
 Often used in divide boxes

Canal overshot gates can act as weirs

Weirs
 Weirs

Cipolletti Weir
 Weirs

Maximum downstream elevation should be at

least 0.2 ft below crest
Head measurement should be greater than 0.2 ft
for optimal elevation
Head is measured upstream 4 X maximum head
on crest
Approach must be kept free of sediment
deposits
 Weirs

Given: Standard Contracted Rectangular

Weir
L = 2 feet
h = 0.40 feet

Find: Q, in cfs

Solution: Refer to Table A7-2 in BoR Water

Measurement Manual, 3rd edition
Weirs
Diversion Head works
Diversion Head works - structures which are constructed
across a river in order to divert water towards the off-taking
canal .

The various purposes of diversion head works:

 Raise the water level in the river so that sufficient
quantity of water can be supplied.
 Regulate the supply of water into the canal.
 Control the entry of silt into the canal.
 Store some water for a short period of time.
 Reduce the water level fluctuations in the river.
 Location and Site Selection

Location of diversion head work:

 Generally located in the boulder or alluvial stage of a
river.
 On alluvial stage is generally preferred unless command of
fertile land proposed for irrigation is lost.

Site selection criteria for diversion head work:

 Narrow, straight and well-defined channel.
 Confined between stable banks not submerged by the
highest flood.
 Local construction materials like sand, stone, etc. are
available in the vicinity.
 The site should be accessible.
 Types of Diversion Head works

Types of Diversion Head Works:

 Temporary diversion head works
• Consists of bund constructed across a river.
• These bunds may be required to be constructed every
year after flood as they may be damaged by the
floods.

 Permanent diversion head works

• Consists of a permanent structure such as weir or
barrage.
 Types of Diversion Head works

Permanent head works:

Weir: The major part of the entire ponding of water is achieved
by raised crest and a smaller part or nil part of it is achieved
by the shutter.

Barrage: The major part of pounding achieved by gates and

smaller or nil part of it is done by raised crest
 Types of Diversion Head works
pond
Crest Level = pond level level Shutter
P2=0 P2 Crest
Level
P=P1 P
P1

P1 >> P2
a) Without shutter b) With shutter

Weir
pond pond
level level Shutter
Shutter
P =P2 P2
P Crest
Level
P1
P1=0
P1 << P2
a) Without crest b) With crest

Barrage
 INTRODUCTIONS OF CROSS DRAINAGE STRUCTURES
Cross drainage works
are structural elements
Required for conveying the canals across natural
drainage
Should be considered at planning and design stage of
Irrigation Systems, special when canal layout is planned
Drainage feature encountered by irrigation canals within
the command area of the project
small and shallow depressions
Large rivers.
 Definition
In an irrigation project, when the network of main canals,
branch canals, distributaries, etc. are provided, then these
canals may have to cross the natural drainages like rivers,
streams etc at different points within the command area of the
project.
The crossing of the canals with such obstacle cannot be
avoided. So, suitable structures must be constructed at the
crossing point for the easy flow of water of the canal and
drainage in the respective directions.
These structures are known as cross-drainage works
 Necessity of Cross-drainage works:
 For proper running the irrigation system.

 For the smooth running of the canal with its design

discharge the cross drainage works are required.

 To maintain their natural direction of flow.

possible solution for conveying an irrigation
canal across a natural channel is by providing a
water conveying structure which may:
 Carry the canal over the natural stream;
 Carry the canal beneath the natural stream; or
Carry the canal at the same level of the natural
stream.
It is not generally possible to construct cross-drainage
structures for each of the small streams.
Measures to reduces cost,
 Some of the small drainage courses are, therefore,
diverted into one big channel larger streams and river,
 Changing the alignment of the canal so that it
crosses below the junction of two streams.
 where the cost of diversion becomes costlier than
providing a separate cross-drainage work, individual
structures to cross the canal across the stream is
provided.
1. STRUCTURES TO CARRY CANAL WATER OVER A
NATURAL STREAM

When canal bed level is higher than stream high flood level.
 AQUEDUCT –

Aqueduct –
The aqueduct is just like a bridge where a canal
is taken over the deck supported by piers
Generally, the canal is in the shape of a
rectangular trough which is constructed with
reinforced cement concrete.
Sometimes, the trough may be of trapezoidal
section.
Trough type Aqueduct
Barrel Type Aqueduct
 SIPHON AQUEDUCT

canal whose bed level is below but full supply level is

above the stream high flood level.

•The necessary headway between the canal bed level and the
drainage HFL can be increased by shifting the crossing to the
downstream of drainage.
•
 SIPHON AQUEDUCT
Required when
 In case the HFL of the natural stream goes above the
canal bed level (CBL)
 or the barrel roof level (BRL), then the flow in the
natural watercourse would be pressured and the
sections are modified to form which is known as siphon
aqueducts
Siphon aqueduct
The siphon aqueduct, the bed of the drainage is depressed
below the bottom level of the canal trough by providing
sloping apron on both sides of the crossing.
Siphon aqueduct cont..
 STRUCTURES TO CARRY CANAL WATER AT THE
SAME LEVEL OF THE NATURAL STREAM

Canal with full supply level almost matching the

high flood level of the natural stream
 LEVEL CROSSING Cont,,
The level crossing is an arrangement provided to regulate
the flow of water through the drainage and the canal when
they cross each other approximately at the same bed levl
Crest Wall: It is provided across the drainage just at the
upstream side of the crossing point. The top level of the crest
wall is kept at the full supply level of the canal.
Drainage Regulator: It is provided across the drainage just
at the downstream side of the crossing point. The regulator
consists of adjustable shutters at different tiers.
Canal Regulator: It is provided across the canal just at the
downstream side of the crossing point. This regulator also
consists of adjustable shutters at different tiers.
LEVEL CROSSING
 LEVEL CROSSING Cont,,

The plan layout of a level crossing with two sets of

regulators, one across the drain and the other across
the canal, is shown in Fig above.
Normally, the canal regulator regulates its flow with
the drain regulator kept closed.
Whenever the flash floods occur, the canal gates are
closed and drainage gates opened to let the flood flow
pass.
 INLET AND OUTLET
In the crossing of small drainage with small channel no
hydraulic structure is constructed.
Simple openings are provided for the flow of water in
their respective directions. This arrangement is known
as inlet and outlet.
A structure in which the water of the stream is allowed
to flow into the canal from one side and allowed to
leave from the other, known as a level crossing ,
In this system, an inlet is provided in the channel bank
simply by open cut and the drainage water is allowed
to join the channel
At the points of inlet and outlet, the bed and banks of
the drainage are protected by stone pitching.
STRUCTURES TO CARRY CANAL WATER BENEATH THE
NATURAL STREAM; (DRAINAGE)
The hydraulic structure in which the drainage is passing over
the irrigation canal is known as super passage.
This structure is suitable when the bed level of drainage is
above the flood surface level of the canal.
The water of the canal passes clearly below the drainage
A super passage is similar to an aqueduct, except in this case
the drain is over the canal.
The FSL of the canal is lower than the underside of the trough
carrying drainage water.
Thus, the canal water runs under the gravity.
Reverse of an aqueduct-
super-passage
 Siphon super-passage.

Else, when the canal passes below the trough as

a pressure flow, then it is termed as a Siphon
super-passage
The bed of the canal is depressed below the
bottom level of the drainage trough by providing
sloping apron on both sides of the crossing
When canal bed level is much lower, but the FSL
of canal is higher than the bed level of drainage,
a canal siphon is preferred.
 CANAL SIPHON OR INVERTED SIPHON

Inverted siphons are pipelines or box culverts

which carry canal water beneath a river bed or
across a depression or valley or across roads
and railways.
 Inverted siphons

Where a small canal crosses a large drainage

channel, it is usually more economical to carry
the canal water under the channel in an inverted
siphon than to carry the drainage water under
the canal through a culvert.
A siphon is a closed conduit designed to run full
and under inverted siphons with internal
pressure.
 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
Ditch crossing structure for farm road frequently
are necessary for access to the fields
Most common Culvert materials ,
 . Corrugated metal, smooth metal or concrete
Pipe Culverts
The factors which affect the selection of suitable
type of cross drainage works are:
Relative bed levels and water levels of canal and
drainage
Size of the canal and drainage.
When the bed level of the canal is much above the
HFL of the drainage, an aqueduct is the obvious
choice.
When the bed level of the drain is well above FSL of
canal, super passage is provided.
The necessary headway between the canal bed level and
the drainage HFL can be increased by shifting the
crossing to the downstream of drainage. If, however, it is
not possible to change the canal alignment, a siphon
aqueduct may be provided
When canal bed level is much lower, but the FSL of canal
is higher than the bed level of drainage, a canal siphon is
preferred.
When the drainage and canal cross each other practically
at same level, a level crossing may be preferred.
CONTROL STRUCTURES
Drops, or falls, and chutes are control structures required at
suitable intervals in canals or channels which must have a more
gentle slope than that of the adjacent land, so as to reduce the
water level downstream, and reduce the velocity of flow.
They also provide for the safe dissipation of surplus energy.
Generally such a control structure is called a drop, or a fall, when
the lowering of the water level is accomplished over a short
distance.
When the water is conveyed over long distances at slopes which
are still steep enough to maintain high velocities (shooting flow),
the structure generally used is a chute.
Chutes may also be used on sloping land where a single drop, or
a series of drops (i. e.cascades), would be more expensive or
otherwise undesirable.
•A drop (or fall) structure is a regulating structure which
lowers the water level along its course
 The slope of a canal is usually milder than the terrain
slope as a result of which the canal in a cutting at its
headwork’s will soon outstrip the ground surface.
In order to avoid excessive infilling the bed level of the
downstream canal is lowered, the two reaches being
connected by a suitable drop structure
The drop is located so that the fillings and cuttings of
the canal are equalized as much as possible.
Wherever possible, the drop structure may also be
combined with a regulator or other structure.
In the case of main canals, branch canals or
sub-branch canals, which do not directly
irrigate any area, the site of a drop is
determined in consideration of the cost of
canal construction, including balancing cut and
fill and the cost of the structure itself.
In the case of distributing canals, the falls are
located so as to serve the commanded area
without having to build the canal banks too
high.
The possibility of combining a drop with an intake,
cross regulator, measuring device, bridge or some
other canal structure must be given due
consideration, as such combinations often result in
economy and better regulation.
Drops are usually provided with a low crest wall,
hump or check gate upstream to prevent shooting
flow in the upstream approach section
The location of an off take from the canal also influences the
fall site, with off takes located upstream of the fall structure.
Drops are usually provided with a low crest wall and are
subdivided into the following types:
I. the vertical drop,
II. the inclined drop and
III. The piped drop.
The choice between vertical and inclined drops is governed
mainly by the difference in water level to be controlled by the
structure, in other words, the energy to be dissipated