MODULE 4 REGULATING AND CROSS DRAINAGE WORKS.pptx

MODULE-4
REGULATING AND CROSS DRAINAGE
WORKS
Prepared By:- Chaudhari Silas
Civil Engineering Department
Pacific School of Engineering
Pacific School
of
Engineering
Gujarat
Technological
University
Semester : 7th
Subject: Irrigation Engineering
(3170609)
Civil Engineering Department

Canal Regulation Works
• Any structure or works which are constructed to regulate the
discharge, depth or velocity in a canal is known as canal regulation
work.
• It is classified:
1. Canal falls
2. Canal regulators
3. Canal escapes
4. Canal outlets and modules
5. Metering flumes

What is Canal Fall?
• Whenever the available natural ground slope is
steep than the designed bed slope of the channel,
the difference is adjusted by constructing vertical
‘falls’ or ‘drops’ in the canal bed at suitable
intervals, as shown in figure below. Such a drop in a
natural canal bed will not be stable and, therefore, in
order to retain this drop, a masonry structure is
constructed. Such a structure is called a Canal Fall
or a Canal drop.

Canal Fall
•Irrigation canals are designed for a prescribed bed slope so
that velocity becomes non silting or non scouring. But if the
ground topography is such that in order to maintain the canal
designed slope, indefinite filling from falling ground level is
to be made. This indefinite filling is avoided by constructing
a hydraulic structure in the place of sudden bed level. This
hydraulic structure is called canal fall or drop. Beyond the
canal fall, canal again maintains its designed slope.

Canal Fall
• Thus, a canal fall or drop is an irrigation structure
constructed across a canal to lower down its bed
level to maintain the designed slope when there is a
change of ground level to maintain the designed
slope when there is change of ground level. This
falling water at the fall has some surplus energy. The
fall is constructed in such a way that it can destroy
this surplus energy.

Necessity of Canal Falls
• When the slope of the ground suddenly changes to
steeper slope, the permissible bed slope can not be
maintained. It requires excessive earthwork in
filling to maintain the slope. In such a case falls are
provided to avoid excessive earth work in filling

• When the slope of the ground is more or less uniform and the
slope is greater than the permissible bed slope of canal.

• In cross-drainage works, when the difference
between bed level of canal and that of drainage is
small or when the F.S.L of the canal is above
the bed level of drainage then the canal fall is
necessary to carry the canal water below the
stream or drainage.

Types of Canal Fall
• Depending on the ground level conditions and shape of the fall the
various types of fall are:
Ogee Fall
• The ogee fall was constructed by Sir Proby Cautley on the Ganga Canal.
This type of fall has gradual convex and concave surfaces i.e. in the
ogee form. The gradual convex and concave surface is provided with an
aim to provide smooth transition and to reduce disturbance
and impact. A hydraulic jump is formed which dissipates a part of
kinetic energy. Upstream and downstream of the fall is provided by Stone
Pitching.

Types of Canal Fall
Stepped Fall
• It consists of a series of vertical drops in the form of steps. This
steps is suitable in places where sloping ground is very long
and require a long glacis to connect the higher bed level u/s
with lower bed level d/s. it is practically a modification of rapid
fall. The sloping glacis is divided into a number drops to bring
down the canal bed step by step to protect the canal bed and
sides from damage by erosion. Brick walls are provided at each
drop. The bed of the canal within the fall is protected by rubble
masonry with surface finishing by rich cement mortar.

Types of Canal Fall
Vertical Fall (Sarda Fall)
• In the simple type, canal u/s bed is on the level of
upstream curtain wall, canal u/s bed level is
below the crest of curtain wall. In both the cases,
a cistern is formed to act as water cushion. Floor is
made of concrete u/s and d/s side stone pitching
with cement grouting is provided. This type of fall
is used in Sarda Canal UP and therefore, it is also
called Sarda Fall.

Types of Canal Fall
Rapid Fall
• When the natural ground level is even and rapid,
this rapid fall is suitable. It consists of long sloping
glacis. Curtain walls are provided on both u/s and d/s
sides. Rubble masonry with cement grouting is
provided from u/s curtain wall to d/s curtain wall.
Masonry surface is finished with a rich cement
mortar.

Types of Canal Fall
Straight Glacis Fall
• It consists of a straight glacis provided with a
crest wall. For dissipation of energy of flowing
water, a water cushion is provided. Curtain
walls are provided at toe and heel. Stone
pitching is required at upstream and
downstream of the fall.

Types of Canal Fall
Trapezoidal Notch Fall
• It was designed by Reid in 1894. In this type a body or
foundation wall across the channel consisting of several
trapezoidal notches between side pier and intermediate
pier is constructed. The sill of the notches are kept at
upstream bed level of the canal. The body wall is made of
concrete. An impervious floor is provided to resist the
scouring effect of falling water. Upstream and
downstream side of the fall is protected by stone pitching
finished with cement grouting.

Types of Canal Fall
Well or Cylinder Notch Fall
• In this type, water of canal from higher level is
thrown in a well or a cylinder from where it escapes
from bottom. Energy is dissipated in the well in
turbulence. They are suitable for low discharges and
are economical also.

Types of Canal Fall
Montague Type Fall
• In the straight glacis type profile, energy
dissipation is not complete. Therefore, montague
developed this type of profile where energy
dissipation takes place. His profile is parabolic
and is given by the following equation,

Types of Canal Fall
Inglis or Baffle Fall
• Here glacis is straight and sloping, but baffle wall
provided on the downstream floor dissipate the
energy. Main body of glacis is made of concrete.
Curtain walls both at toe and heel are provided. Stone
pitching are essential both at u/s and d/s ends

Canal Escape
• It is a side channel constructed to remove surplus water from an
irrigation channel (main canal, branch canal, or distributary etc.)
into a natural drain.
The water in the irrigation channel may become surplus due to -
• Mistake
• Difficulty in regulation at the head
• Excessive rainfall in the upper reaches
• Outlets being closed by cultivators as they find the demand of
water is over.

Canal Escape
• It is the structure required to dispose of surplus or excess water from canal
from time to time. Thus, a canal escape serves as safety valve for canal
system. It provides protection to the canal from possible damage due to
excess supply which may be due to mistake in releasing water at head
regulator or heavy rainfall that makes sudden regular demand of
water. The excess supply makes the canal banks vulnerable to
failure due to overtopping or dangerous leaks.
Therefore, provision for disposing this surplus water in form of canal
escapes at suitable intervals along the canal is essential. Moreover
emptying canal for repair and maintenance and removal of sediment
deposited in the canal can also be achieved with the help of canal escapes.

Escapes are usually of the following three types.
Surplus Escape
• It is also called regulator type. In this type sill of the escape is
kept at canal bed level and the flow is controlled by a gate.
This type of escapes are preferred now-a-days as they give
better control and can be used for employing the canal for
maintenance.

Tail Escape
• A tail escape is provided at the tail end of the canal and is
useful in maintaining the required FSL in the tail reaches of
the canal and hence, they are called tail escape.

Scouring Escape
• This escape is constructed for the purpose of scouring of excess silt
deposited in the head reaches from time to time. Hence, it is called
scouring escape. Here the sill of the regulator is kept at about 0.3 m
below the canal bed level at escape site. When deposited silt to be
scoured, a higher discharge than the FSL is allowed to enter the
canal from the head works. The gate of the escape is raised so as to
produce scouring velocity which remove the deposited silt. This
type of Escape has become obsolete as silt ejector provided in the
canal can produce better efficiency.

Head Regulator
• Regulators Constructed at the off taking point are called head regulators.
When it is constructed at the head of main canal it is known as canal
head regulator. And when it is constructed at the head of distributary, it
is called distributary head regulator.
• Function:
• To controlthe entry of water either from the reservoir or from the main
canal.
• To control the entry of silt into off taking or main canal.
• To serve as a meter for measuring discharge of water.

Head Regulator
• Construction: The components of head regulator
depends upon the size of canal and location of head
regulator. It consists of one or more gated research
openings with barrels running through the bank. For
large canals head regulators are flumed to facilitate
the measurement of discharge.

Cross Regulator
• Cross Regulator
• A Regulator Constructed in the main canal or parent canal downstream of
an off take canal is called cross- regulator.
• It is generally constructed at a distance of 9 to 12 km along the main canal
and 6 to 10 km along branch canal.
• Functions:
• (i) To Control the flow of water in canal system
• (ii) To feed the off taking Canals
• (iii) To enable closing of the canal breaches on the d/s
• (iv) To provide roadway for vehicular traffic

Cross Regulator
Construction: For Cross Regulators abutments
with grooves and piers are constructed parallel to
the parent canal. The sill of regulation is kept little
higher than the u/s bed level of canal across which
it is constructed. Vertical lift gates are fitted in the
grooves. The gates can be operate from the road.

Silt Control Devices
• Scouring Sluices or Under sluices, silt pocket and silt excluders
• The above three components are employed for silt control at the head
work. Divide wall creates a silt pocket. Silt excluder consists of a number
under tunnels resting on the floor pocket. Top floor of the tunnel is at the
level of sill of the head regulator.
• Various tunnels of different lengths are made. The tunnel near the
head regulator is of same lengthof head regulator
andsuccessive tunnels towards the divide wall are short.
Velocity near the silt laden water is disposed downstream through
tunnels and under sluices.

• Silt Excluder: The silt excluder is located on the u/s of
diversion weir and in front of the head regulator. The
object is to remove silt that has entered in the stilling
basin through scouring sluices.
• Silt Ejector: Silt Ejector is located in the canal take off
from the diversion weir at 6 to 10 km in the canal reach.
It ejects the silt that has entered in the canal.

Silt Excluder

SiltControl Devices
Silt Ejector

Canal Outlet/modules
• A canal outlet or a module is a small structure built
at the head of the water course so as to connect it
with a minor or a distributary channel.
• It acts as a connecting link between the system
manager and the farmers.

Non-Modular Modules
• Non-modular modules are those through which the discharge depends
upon the head difference between the distributary and the water
course.
• Common examples are:
(i) Open sluice
(ii) Drowned pipe outlet

Types of Outlet/modules
• Non-modular modules

Semi-Modules or Flexible modules
• Due to construction, a super-critical velocity is ensured in the throat
and thereby allowing the formation of a jump in the expanding flume.
• Theformation of hydraulic jump makesthe outlet discharge
independent of the water level in water course, thus
making it a semi module. Semi-modules or flexible modules
are those through whichthe discharge is independent of
the water level of the water course but depends only upon the
water level of the distributary so long as a minimum working head is
available.
• Examples are pipe outlet, open flume type etc.

Semi-Modules or Flexible modules

Rigid Modules or Modular Outlets
• Rigid modules or modular outlets are those through which
discharge is constant and fixed within limits, irrespective of the
fluctuations of the water levels of either the distributary or of the
water course or both.
• An example is Gibb’s module:

Development of Various Types of canal Falls

Classification of Canal Falls and selection

Cross-Drainage Works
What is Cross Drainage Works?
• 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, nallahs, 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.

• Irrigational Canals while carrying water from headworks to crop field,
have to cross few natural drainage streams, nallaha, etc. To cross
those drainages safely by the canals, some suitable structures are
required to construct. Works required to construct, to cross the
drainage are called Cross Drainage Works (CDWs).
• At the meeting point of canals and drainages, bed levels may not be
same. Depending on their bed levels, different structures are
constructed and accordingly they are designated by different names.

Necessity of Cross Drainage Works
• The water-shed canals do not cross natural drainages. But in actual
orientation of the canal network, this ideal condition may not be
available and the obstacles like natural drainages may be present
across the canal. So. the cross drainage works must be provided for
running the irrigation system.
• At the crossing point, the water of the canal and the drainage get
intermixed. So, for the smooth running of the canal with its design
discharge the cross drainage works are required.
• The site condition of the crossing point may be such that without any
suitable structure, the water of the canal and drainage can not be
diverted to their natural directions. So, the Cross drainage works must
be provided to maintain their natural direction of flow.

Types of Cross Drainage Works
Type I (Irrigation canal passes over the drainage)
(a) Aqueduct
(b) Siphon Aqueduct
Type II (Drainage passes over the irrigation canal)
(a) Super passage
(b) Siphon super passage
Type III (Drainage and canal intersection each other of the same level)
(a) Level crossing
(b) Inlet and outlet

2. TYPES OF CROSS-DRAINAGES WORKS
Depending upon the relative positions of the canal and the drainage, the cross section works may
be broadly classified into 3 categories.
1. Canal over a drainage
a) Aqueduct
b) Syphon aqueduct

1. Canal Over The Drainage
a) Aqueduct
• An aqueduct is a structure in which the canal flows over the
drainage and the flow of the drainage in the barrel is open
channel flow.
• An aqueduct is provided when the canal bed level is higher
than the H.F.L. of the drainage.
b) Syphon Aqueduct
• In a syphon aqueduct also, the canal is taken over the
drainage, but the flow in the barrel of the drainage is pipe
flow.
• A syphon aqueduct is constructed when the H.EL. of the
drainage is higher than the canal bed level.

2. Canal below the drainage
a) Super passage
b) Canal syphon

2. Canal Below The Drainage
a) Super passage.
• In a super passage, the canal is taken below the
drainage and flow in the canal is open channel flow.
• A super passage is required when the canal F.S.L. is
below the drainage bed level.
b) Canal syphon
• A canal syphon (or simply a syphon) is a structure
in which the canal is taken below the drainage and
the flow in the barrel of the canal is pipe flow.
• A canal syphon is constructed when the F.S.L. of the
canal is above the drainage bed level.

3. Canal at same level as drainage.
a) Level crossing
b) Inlet
c) Inlet and Outlet

3. Canal at the same level as the drainage
a) Level crossing
• A level crossing is provided when the canal and the drainage are practically at the same level.
• A level crossing usually consists of a crest wall provided across the drainage on the upstream of the junction
with its crest level at the F.S.L. of the canal.
• The drainage water passes over the crest and enters the canal whenever the water level in the drainage rises
above the F.S.L. of the canal. There is a drainage regulator on the drainage at the d/s of the junction and a
cross-regulator on the canal at the d/s of the junction for regulating the outflows.
• The main disadvantage of a level crossing is that an operator is required to regulate the discharge.
b) Inlet
• An inlet alone is sometimes provided when the drainage is very small with a very low discharge and it does
not bring heavy silt load.
• It increases the discharge in the canal, which is absorbed in the space provided as the free board above the
F.S.L.
c) Inlet and outlets
• An inlet-outlet structure is provided when the drainage and almost at the same the canal is level, and the
discharge in the drainage is small.
• The drainage water is admitted the canal at a suitable site where into the drainage bed is at the F.S.L. of the
canal.
• The excess water discharged out the canal is through an outlet provided on the canal at some distance
downstream of the junction.

3. SELECTION OF A SUITABLE TYPE OF CROSS-DRAINAGE WORK
The following factors should be considered while selecting the most suitable type of the drainage work cross.
1) Relative levels and discharges: The relative levels and discharges of the canal and of the drainage mainly
affect type of cross-drainage work required. The following are the broad outlines:
i. If the canal bed level is sufficiently above the H.F.L. of the drainage, an aqueduct is selected.
ii. If the F.S.L. of the canal is sufficiently below the bed level of the drainage. a superpassage is provided.
iii. If the canal bed level is only slightly below the H.F.L. of the drainage, and the drainage a is small, syphon
aqueduct is provided. If necessary, the drainage bed is depressed below the canal.
iv. If the F.S.L. of the canal is slightly above the bed level of the drainage and the canal is of small size, a canal
syphon is provided.
v. If the canal bed and the drainage bed are almost at the same level, a level crossing is provided when the
discharge in the drainage is large, and an inlet-outlet structure is in the drainage is small.

2) Performance
• The structure having an open channel flow should be preferred to the structure having a pipe flow.
Therefore, an aqueduct should be preferred to a syphon aqueduct.
• Likewise, superpassage should be preferred to a canal syphon.
• In the case of a syphon aqueduct and a canal syphon, silting problems usually occur at the crossing.
• Moreover, in the case of crossing a canal syphon, there is considerable loss of command due to loss of head
in the canal.
• The performance of inlet-outlet structures is not good and should be avoided.
3) Provision of road
• A aqueduct is better than a superpassage because in the former, a road bridge can easily be provided along
with the canal trough at a small extra cost, whereas in the latter, a separate road bridge is required.

4) Size of drainage: When the drainage is of small size, a syphon aqueduct will be preferred to an aqueduct as
the latter involves high banks and long approaches. However, if the drainage is of large size, an aqueduct is
preferred.
5) Cost of earthwork: The type of cross-drainage work which does not involve a large quantity of earthwork of
the canal should be preferred.
6) Foundation: The type of cross-drainage work should be selected depending upon the foundation available
at the site of work.
7) Material of construction: Suitable types of material of construction in sufficient quantity should available
near the site for the type of cross-drainage work selected. Moreover, the soil in sufficient quantity should
be available for constructing the canal banks if the structure requires long and high canal banks.
8) Cost of construction: The cost of construction of cross-drainage work should not be excessive.
9) Overall cost: The overall cost of the canal banks and the cross-drainage work, including maintenance cost,
should be a minimum.
10) Permissible loss of head: Sometimes, the type of cross-drainage is selected considering permissible loss of
head. For example, if the head loss cannot be permitted in a canal at the site or cross-drainage, a canal
syphon is ruled out.
11) Subsoil water table: If the subsoil water table is high, the types of cross-drainage which requires excessive
excavation should be avoided, as it would involve dewatering problems.

SELECTION OF SITE OF A CROSS-DRAINAGE
1.At the site, the drainage should cross the canal alignment at right
angles. Such a site provides good flow conditions and also the cost of
the structure is usually a minimum.
2.The stream at the site should be stable and should have stable banks.
3.For economical design and construction of foundations, a firm and
strong sub-stratum should exit below the bed of the drainage at a
reasonable depth.
4.The site should be such that long and high approaches of the canal are
not required.
5.The length and height of the marginal banks and guide banks for the
drainage should be small.

6. In the case of an aqueduct, sufficient headway should be
available between the canal trough and the high flood level of the
drainage.
7. The water table at the site should not be high, because it will
create dewatering problems for laying foundations. .
8. The possibility of diverting one stream into another stream
upstream of the canal crossing should also be considered and
adopted, if found feasible and economical.
9. A cross-drainage work should be combined with a bridge, if
required. If necessary, the bridge site can be shifted to the cross-
drainage work or vice-versa.

9. As far as possible, the
site should be selected
D/s of the confluence of
two streams, thereby
avoiding the necessity
of construction of two
cross-drainage works.

TYPES OF AQUEDUCTS BASED ON CANAL CROSS-SECTION
• Depending upon the cross section of the canal over the
barrel (or culvert), the aqueducts and syphon aqueducts
are classified into the following three types:
•Type I Aqueduct
•Type II Aqueduct
•Type III Aqueduct

TYPES OF AQUEDUCTS BASED ON CANAL
CROSS-SECTION
• Type I Aqueduct
Figure – Type I Aqueduct

Type I Aqueduct
• In this type of aqueduct (or syphon aqueducts), the cross-section of the
canal is not changed. The original cross-section of the canal with
normal side slopes is thus retained. The length of the barrel through
which the drainage passes under the canal is a maximum in this type
of structures, because the width of the canal section is a maximum.
• In this type of structures, the canal wings are not required. This type is
suitable when the width of the drainage is small (say less than 25 -m).
If the section is changed, the cost of canal wings would be large in
comparison to the saving resulting from decreasing the length of
culvert.

CROSS-SECTION
• Type II Aqueduct
Figure – Type II Aqueduct

Type II Aqueduct
• In this type of aqueduct (or syphon aqueduct), the outer slopes of the
canal banks are discontinued and replaced by retaining walls. Thus the
length of the barrel is reduced; bur the cost of retaining wall is added
to the overall cost. This type of structure is suitable when the width of
the drainage is moderate (say 2.5 m to 15 m). So that the cost of
retaining walls is less in comparison to the saving resulting from
decreasing the length of barrel.

CROSS-SECTION
• Type III Aqueduct
Figure – Type III Aqueduct

Type III Aqueduct
• In this type of aqueduct (or syphon, aqueduct), the entire earth section
of the canal is discontinued and replaced by a concrete or masonry
trough over the drainage. This type of structure is generally suitable
when the width of the drainage is very large (say more than 15 m), so
that the cost of the trough and canal wing walls is less in comparison
to the saving resulting from decreasing the length of barrel. In this
type of structure, the canal can be easily flumed which further reduces
the length of the barrel.

TYPES OF AQUEDUCTS BASED ON
CANAL CROSS-SECTION
• Selection of suitable type The selection of the suitable type of canal
cross-section depends upon the width and discharge of the drainage. A
very small drainage requires a type I aqueduct, which in most cases
may be merely a pipe or a small culvert passing under the canal. On
the other hand, over a river of a large size type III aqueduct would be
the most economical. For moderate size of the drainage type II
aqueduct may be most suitable.
• However, the actual limits with regard to the size of drainage for
which one particular type of aqueduct will be the most suitable will
vary with local conditions and the cost of construction. Comparative
estimates should be prepared for finding out the most economical type
of aqueduct for a particular site.

DeterminationofMaximumFlood Discharge

Determination ofMaximum Flood Discharge
• The high flood discharge for smaller drain can be worked out by using
empirical formulas; and for large drains other methods such as
Hydrograph analysis, Rational formula, etc may be used.
• In general the methods used in the estimation of the flood flow can
be group as:
• Physical Indications of past floods
• Empirical formulae and curves
• Overland flow hydrograph and unit hydrograph

Determination of Maximum Flood Discharge
• Physical Indications of past floods- flood marks and local inquiry:
• The maximum flood discharge may be approximately estimated by enquiring from
the residents in the village situated on the banks of the river about the flood marks
that the high flood in their memory in the past may have left on the river banks.
• By noting the high water marks along the banks of the river the cross-section area
and wetted perimeter of the flow section as well as the water surface slope may be
computed and using the manning’s formulae, with suitable assumed value of the
flood discharge may be determined.

• Estimation of maximum flood discharge from rating curve: During the
period of high flood, it is almost impossible to measure the
discharge by making the use of markings of the high water marks on
the banks of the river, the elevated water level, can be
calculated. Making use of this values high water marks in meters the
value of maximum flood discharge can be calculated, by
extrapolation from the stage or rating discharge curve. The above
mentioned curve needs to be extended for the higher value of stage. It is
done by using following methods.
• Simple Judgment
• Logarithmic method
The above mentioned curve needs to be extended for the higher value of
stage, it is done by using following methods.
• (a) Simple Judgment
• (b) Logarithmic Method

• (a) Simple Judgment
The rating curve can be extended, by simple
Judgment.

SimpleJudgmentmethod

• (b) Logarithmic method:
The following equation can be used to extend the rating curve Q= K d n
Where,
Q= Discharge (Cumecs)
d= Stage in (m) K, n =
Constants
By taking logarithms of both sides, we get, Log Q=
log k + n Log d
If the available curve is plotted on a log-log paper, then it should be a
straight line.
This line can be extended to calculate the discharge at a higher
stage.

Logarithmicmethod

EmpiricalFormulas
Several empirical formula have been developed for estimating the maximum or
peak value of flood discharge. In these formulae the maximum flood discharge Q of
a river is expressed as a function of the catchment area A. Most of these formulae
may be written in a general formas:
• Q=CAn
Where, Cis coefficient and n is index, Both Cand n depend upon various factor,
such as
(i) Size ,shape and location of catchment ,
(ii) Topography of the catchment,
(iii)intensity and duration of rainfall and distribution pattern of the storm over
catchment area.

• Dicken’s formula:
Q =CA¾
Where,
Q=Maximum flood Discharge in cumec. A=
Area of Catchment in sq.Km
C=coefficient depending upon the region The
maximum value of C=35.
• Ryve’s Formula:
Q=CA2/3
Where, Q=discharge in cumec
A=Catchment Area in Sq. .Km
C=coefficient depending upon the region

Determination of Maximum Flood
Discharge
RationalMethod:
In this method it is assumed that the maximum flood flow is produced
by a certain rainfall intensity which lasts for a time equal to or greater than the period
of concentration time. When a storm continues beyond concentration time every part
of the catchment would be contributing to the runoff at outlet and therefore it
represents condition of peak runoff. The runoff corresponding to this condition is given
by:
Q =2. 78 CIc A
Where, Q =Discharge in Cumec,
catc
C=Coefficient which depends upon the characteristics of the
hment.
Ic= The critical Intensity of rainfall (cm/hr) corresponding to the time of Concentration
(tc) of the catchment for a given recurrence interval obtained from the intensity of
duration frequency curves.
A=Catchment Area in Km2

RationalMethod:

DeterminationofMaximum Flood Discharge
Inglis formula:
• Q= 124 A = 124 A½
√A+ 10.4
Where Q= discharge in cumec
A=area of catchment in Sq..Km.
Inglish formula is derived by using the data of rivers of Mahashtra, where it is
commonly used.
Ali NawabJangBahadurformula:
Q=CA( 0.993- 1/14 log A)
Where, Q= Discharge in Cumec A=area of catchment insq .km
C=Coefficient which varies from 48 to 60.

• Myer’s formula
• Q= 175 √A
• Where,
• Q= Discharge in Cumec
• A=Area of Catchment in Sq..Km.

EnvelopCurves:
• Areas having similar topographical features and climatic conditions
are grouped together. All Available data regarding discharges and
flood formulae are compiled along their respective catchment areas.
The maximum discharges are then plotted against the areas of the
drainage basins and a curve is drawn to cover or envelop the highest
plotted points, which is known as envelope curve. By using envelop
curves the maximum flood discharge may be estimated if the area of
the drainage basin is known.

Overlandflow Hydrograph andUnit Hydrograph:
• AHydrograph is a graphical plot of discharge of a natural stream
or river versus time. It shows variation of discharge with time, at a
particular point of a stream. It also shows the time distribution of total runoff at the
point of measurement. Discharge is usually expressed in cumec or hectare-metre per
day and time is expressed in hours, days or months. Discharge is plotted on Y-axis and
the corresponding time is plotted on X-axis.
• Unit Hydrograph: A unit Hydrograph is a hydrograph
representing 1 cm of runoff from a rainfall of some duration and
specific areal distribution.
• Unit Hydrograph is defined as the hydrograph of surface runoff of
a catchment area resulting from unit depth of rainfall excess or net
rainfall occurring uniformly over the basin at uniform rate for a specified duration.

DeterminationofMaximumFloodDischarge
• When a unit hydrograph is available for the
catchment under consideration, it can be applied to
the design storm to yield the design flood
hydrograph from which peak flood value can be
obtained.
• Whenever possible it is advisable to use the unit
hydrograph method to obtain the peak flood. It gives
not only the flood peak but also the complete flood
hydrograph which is essentially required in
determining effective storage of reservoir on flood
peak through flood routing.

FlumingofCanal
• The Contraction in the waterway of the canal (i.e. fluming of
canal) will reduce the length of barrels or the width of the
aqueduct. This is likely to produce economy in many cases. The
fluming of canal is generally not done when the canal section is
in earthen banks.
• The maximum fluming is generally governed by the extent that
the trough should remain subcritical, because if supercritical
velocities are generated, then the transition back to the normal
section on the downstream side of the work may involve the
possibility of the formation of a hydraulic jump, This hydraulic
jump, where not specially required and designed for, would lead
to undue loss of head and large stresses on the work. The extent
of fluming is further governed by economy and permissible loss
of head. The greater is the fluming, the greater is the length of
transition wings upstream as well as down stream. This extra
cost of transition wings is balanced by the saving obtain due to
reduction in the width of the aqueduct. Hence an economical
balance has to be worked out for any proposeddesign.

FlumingofCanal
• After deciding the normal canal section and the flumed canal section,
the transition has to be designed so as to provide a smooth change
from one stage to the other, so as to avoid sudden transitions and the
formation of eddies, etc For this reason, the u/s or approach wings
should not be steeper than 26.5 and the d/s or departure wings
should not be steeper than 18.5. Generally the normal earthen canal
is trapezoidal, while the flumed pucca canal section is rectangular. It
is also not necessary to keep the same depth in the normal and
flumed sections. Rather, it may sometimes be economical to increase
the depth and still further reduce the channel width in cases where a
channel encounters a reach of rocky terrain and has to be flumed to
curtail rock excavation. But an increase in the water depth in the
canal trough will certainly increase the uplift pressure on the roofas
well as floor of the culvert, thus requiring larger roof and floor
sections and lower foundations. Due to these reasons, no appreciable
economy may be obtained by increasing depth.

FlumingofCanal
• The following methods may be used for designing the channel
transitions:
• Mitra’s method of design of transition (when water depth remains
constant)
• Chaturvedi’s method of design of transitions(when the depth remains
constant)
• Hind’s method of design of transitions (when water depth may or may
not vary).

FlumingofCanal
• Mitras method of design Transition when water depth
remains constant:
• Shri A.C. Mitra, Chief Engineer, U.P, Irrigation Department
has proposed a hyperbolic transition for the design of
channel transitions. According to him, the channel width at
any section X-X, at a distance x from the flumed section is
given by.

FlumingofCanal
• Prof R.S Charturvedi, Head of Civil Engineering
Dept, in Roorkee University, on the basis of his own
experiments, had proposed the following equation
for the design of channel transitions when water
depth remains constant.

DesignofBank Connections
• Two sets of wings are required in aqueducts and syphon-
aqueducts. These are:
• Canal wings or Land wings
• Drainage Wings or Water Wings
• Canal Wings: These wings provide a strong connection between
masonary or concrete sides of a canal trough and earthen canal
banks. These wings are generally warped in plan so as to change
the canal section from trapezoidal to rectangular. They should be
extended upto the end of splay. These wings may be designed as
retaining walls for maximum differential earth pressure likely to
come on them with no water in the canal. The foundations of
these wings should not be left on filled earth. They should be
taken deep enough to give safe creep length.

DesignofBank Connections
• Drainage Wings or Water Wings or River Wings:
These wing walls retain and protect the earthen slopes
of the canal, guide the drainage water entering and
leaving the work, and join it to guide banks and also
provide a vertical cut-off from the water seeping from
the canal into drainage bed. The foundations of these
wings wall should be capable of withstanding the
maximum differential pressure likely to come on
them.
• The layouts of these sets of wings depend on the extent
of contraction of canal and drainage waterways, and
the general arrangement of the work.

Uplift Pressure on the Underside of the trough or the Barrel Roof
• Uplift Pressure on the Barrel Roof
• The amount of the uplift pressure exerted by the drain water on the roof of
the culvert can be evaluated by drawing the hydraulic Gradient line (H.G).
• The uplift pressure at any point under the roof of the culvert will be equal to
the vertical ordinate between hydraulic gradient line and the underside of the
canal trough at that point From the uplift diagram it is very evident that the
maximum uplift occurs at the upstream end point near the entry. The slab
thickness should be designed to withstand this maximum uplift.

Uplift Pressure on the Underside of the trough
or the Barrel Roof
The uplift pressure exerted by the drain water on the roof of the culvert

Uplift Pressure on the Underside of the trough
or the Barrel Roof
The floor of the aqueduct or siphon is subjected to uplift due to two cases:
(a) Uplift due to Water-Table: This force acts where the bottom floor is
depressed below the drainage bed, especially in syphon aqueducts.
• The maximum uplift under the worst condition would occur when there
is no water flowing in the drain and the watertable has risen up to the
drainage bed. The maximum net uplift in such case would be equal to
the difference in level between the drainage bed and the bottom of the
floor.

Uplift Pressure on the Underside of the
trough or the Barrel Roof
(b) Uplift PressureduetoSeepageofwaterfromthecanaltothedrainage.
• The maximum uplift due to this seepage occurs when the canal is running full and
there is no water in the drain. The computation of this uplift due to this seepage
occurs when the canal is running full and there is no water in the drain. The
computation of this uplift, exerted by the water seeping from the canal on the
bottom of the floor, is very complex and difficult, due to the fact that the flow takes
place in three dimensional flow net. The flow cannot be approximated to a two
dimensional flow, as there is no typical place across which the flow is practically
two dimensional. Hence, for smaller works, Beligh’s Creep theory may be used for
assessing the seepage pressure, But for larger works, the uplift pressure must be
checked by model studies.

Uplift Pressure on the Underside of the
trough or the Barrel Roof
Thefloor oftheaqueductor siphonsubjectedtouplift

MODULE 4 REGULATING AND CROSS DRAINAGE WORKS.pptx

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