144107704 Canal Irrigation

CANAL IRRIGATION

Alluvial and Non-Alluvial Canal

Alluvial and Non-Alluvial Canal

• The soil which is formed by transportation and deposition of silt through the agency of water, over a course of time, is called the alluvial soil.

• The canals when excavated through such soils are called alluvial canals. Canal irrigation (direct irrigation using a weir or a barrage) is generally preferred in such areas, as compared to the storage irrigation (i.e. by using a dam).

• The soil which is formed by the disintegration of rock formation is known as non-alluvial soil. It has an uneven topography, and hard foundations are generally available. The rivers, passing through such areas, have no tendency to shift their courses, and they do not pose much problems for designing irrigation structures on them. Canals, passing through such areas are called non-alluvial Canals.

Channel LossesChannel Losses• During the Passage of water from the main Canal to

the outlet at the head of the water course, water may be lost either by evaporation from the surface or by seepage through the peripheries of the channels, So in determining the designed channel capacity, a provision for these water losses must be made.

(i) Evaporation• The water lost by evaporation is generally very small

a compared to the water lost by seepage in certain channels. Evaporation losses are generally of the order of 2 to 3 % of the total losses. They depend upon all those factors on which the evaporation depends, such as temperature, wind velocity, humidity, etc. In summer season, these losses may be more but seldom exceed 7 %.

Channel LossesChannel LossesSeepage: There may be two different condition of seepage, i.e. (i) Percolation, (ii) Absorption.(i) Percolation•In Percolation, there exists a zone of continuous saturation from the canal to the water-table and a direct flow is established. Almost all the water lost from the canal, joins the ground water reservoir.•The Losses of water depends upon the difference of top water surface level of the channel of the water table.(ii) Absorption• In Absorption, a small saturation soil zone exists around the canal section and is surrounded by zone of decreasing saturation. A certain zone just above the water table is saturated by capillarity. Thus, there exists an unsaturated soil zone between the two saturated zones.• In this case, the rate of loss is independent of seepage head (H) but depends only on the water head h plus the capillary head hc.

Seepage: There may be two different condition of seepage, i.e. (i) Percolation, (ii) Absorption.(i) Percolation•In Percolation, there exists a zone of continuous saturation from the canal to the water-table and a direct flow is established. Almost all the water lost from the canal, joins the ground water reservoir.•The Losses of water depends upon the difference of top water surface level of the channel of the water table.(ii) Absorption• In Absorption, a small saturation soil zone exists around the canal section and is surrounded by zone of decreasing saturation. A certain zone just above the water table is saturated by capillarity. Thus, there exists an unsaturated soil zone between the two saturated zones.• In this case, the rate of loss is independent of seepage head (H) but depends only on the water head h plus the capillary head hc.

Seepage LossesSeepage Losses

Canal lining to prevent seepage lossesCanal lining to prevent seepage losses

Cross-Section of an Irrigation Canal

Cross-Section of an Irrigation Canal

Side SlopesSide Slopes

• The side slopes should be such that they are stable, depending upon the type of the soil. A comparatively steeper slope can be provided in cutting rather than in filling, as the soil in the former case shall be more stable.

In cutting ------- 1H: 1V to 1.5 H: 1V In filling ------ 1.5 H: 1V to 2H: 1V

BermsBerms• Berm is the horizontal distance left at ground level

between the toe of the bank and the top edge of cutting.

• The berm is provided in such a way that the bed line and the bank line remain parallel. If s1: 1 is the slope in cutting and s2:1 in filling, then the initial berm width = (s2 – s1) d1.

Purposes of BermsPurposes of Berms

• They help the channel to attain regime conditions.

• They give additional strength to the banks and provide protection against erosion and breaches.

• They protect the banks from erosion due to wave action.

• They provide a scope for future widening of the canal.

Free BoardFree Board

• The margin between FSL and bank level is known as freeboard. The amount of freeboard depends upon the size of the channel. The generally provided values of freeboard are given in the table below:

BanksBanks

• The primary purpose of banks in to retain water. This can be used as means of communication and as inspection paths. They should be wide enough, so that a minimum cover of 0.50 m is available above the saturation line.

Service RoadsService Roads

• Service roads are provided on canals for inspection purposes, and may simultaneously serve as the means of communication in remote areas. They are provided 0.4 m to 1.0 m above FSL, depending upon the size of the channel.

Spoil Banks Spoil Banks

• When the earthwork in excavation exceeds earthworks in filling, even after providing maximum width of bank embankments, the extra earth has to be disposed of economically. To dispose of this earth by mechanical transport, etc. may become very costly, and an economical mode of its disposal may be found in the form of collecting this soil on the edge of the bank embankment itself.

Borrow Pits Borrow Pits

• When earthwork in filling exceeds the earthwork in excavation, the earth has to be brought from somewhere. The pits, which are dug for bringing earth, are known as Borrow Pits.

Irrigation ChannelsIrrigation Channels

• Alignment of Canal.• Canals are aligned on contour, ridge and along

side slope and they are named as:• (i) Contour Canal• (ii) Ridge or Watershed Canal• (iii) Side Slope Canal• In aligning irrigation canal the following

important points are to be considered:• (i) It must cover the entire area proposed to be

irrigated.• (ii) Smallest possible length of the canal for

economy, smaller head loss due to friction and smaller loss in seepage and evaporation.

• Alignment of Canal.• Canals are aligned on contour, ridge and along

side slope and they are named as:• (i) Contour Canal• (ii) Ridge or Watershed Canal• (iii) Side Slope Canal• In aligning irrigation canal the following

important points are to be considered:• (i) It must cover the entire area proposed to be

irrigated.• (ii) Smallest possible length of the canal for

economy, smaller head loss due to friction and smaller loss in seepage and evaporation.

Contour CanalContour Canal

• Canal aligned nearly parallel to the contour is called Contour Canal.

• In contour canal, culturable area lies on one side of it. Thus, contour canal can irrigate on one side. As one of the bank is on the higher side, so only a bank is required to construct on the lower side. Therefore, it is sometimes called single bank canal.

• Canal aligned nearly parallel to the contour is called Contour Canal.

• In contour canal, culturable area lies on one side of it. Thus, contour canal can irrigate on one side. As one of the bank is on the higher side, so only a bank is required to construct on the lower side. Therefore, it is sometimes called single bank canal.


• Drawbacks• Drainage enters from hilly side, so it has the

risk of breaching and silting.• It involves crossing the natural drainage and

therefore, costly Cross Drainage Works (CDWs) are required to be constructed.

• It can irrigate on one side only.• Advantages• Low Initial cost of construction as no need to

construct one of the bank.• Discharge capacity increases as rain water

from higher side is collected in the canal.

• Drawbacks• Drainage enters from hilly side, so it has the

risk of breaching and silting.• It involves crossing the natural drainage and

therefore, costly Cross Drainage Works (CDWs) are required to be constructed.

• It can irrigate on one side only.• Advantages• Low Initial cost of construction as no need to

construct one of the bank.• Discharge capacity increases as rain water

from higher side is collected in the canal.


Ridge or Watershed Canal


• The canal is aligned along a natural watershed, known as ridge. These canals usually take off from the contour canal. It irrigates on both sides. C.D can be avoided and hence it is more economical.

• Advantages• This canal can supply water on both sides and

thus a large area may be taken under cultivation.• As it flows along the highest line, it does not

require to cross natural drainage on its way. Therefore, costly Cross Drainage works (CDWs) are not at all necessary.

• It is the best irrigation canal and most economical.

• The canal is aligned along a natural watershed, known as ridge. These canals usually take off from the contour canal. It irrigates on both sides. C.D can be avoided and hence it is more economical.

• Advantages• This canal can supply water on both sides and

thus a large area may be taken under cultivation.• As it flows along the highest line, it does not

require to cross natural drainage on its way. Therefore, costly Cross Drainage works (CDWs) are not at all necessary.

• It is the best irrigation canal and most economical.



• Dis-Advantages• If watershed has number of sharp loops,

certain problems are encountered.• Aligning canal along the ridge, length

becomes more and if length are reduced aligning straight, high ground left between canal and the ridge line, cannot be irrigated. Moreover, CDWs are required to construct as drainage may flow from high land. If villages or towns are situated on ridge, canal has to leave the ridge to bypass the town and villages.

• Dis-Advantages• If watershed has number of sharp loops,

certain problems are encountered.• Aligning canal along the ridge, length

becomes more and if length are reduced aligning straight, high ground left between canal and the ridge line, cannot be irrigated. Moreover, CDWs are required to construct as drainage may flow from high land. If villages or towns are situated on ridge, canal has to leave the ridge to bypass the town and villages.



Side-Slope CanalSide-Slope Canal

• This canal is aligned roughly perpendicular to contour of the contour. Since it is perpendicular to the contour, construction of Cross Drainage Works (CDWs) does not arise. Since constructed along the falling contour, slope of this canal is steep, which is not essential for unlined canal. It irrigates only on one side just like contour canal.

• Advantages:• Construction of CDWs is not necessary• Disadvantages:• Slope of this channel is more. If it is unlined

erosion takes place. It also irrigates one side of the canal.

• This canal is aligned roughly perpendicular to contour of the contour. Since it is perpendicular to the contour, construction of Cross Drainage Works (CDWs) does not arise. Since constructed along the falling contour, slope of this canal is steep, which is not essential for unlined canal. It irrigates only on one side just like contour canal.

• Advantages:• Construction of CDWs is not necessary• Disadvantages:• Slope of this channel is more. If it is unlined

erosion takes place. It also irrigates one side of the canal.

Side-Slope CanalSide-Slope Canal

Distribution System for Canal Irrigation

Distribution System for Canal Irrigation

Canal Design TypesCanal Design Types

Design ParametersDesign Parameters

• The design considerations naturally vary according to the type of soil.

• Velocity of flow in the canal should be critical.

• Design of canals which are known as ‘Kennedy’s theory’ and ‘Lacey’s theory’ are based on the characteristics of sediment load (i.e. silt) in canal water.

Important Terms Related to Canal Design

Important Terms Related to Canal Design

• Alluvial soil • Non-alluvial soil • Silt factor • Co-efficient of Rugosity • Mean velocity • Critical velocity • Critical velocity ratio (c.v.r), m • Regime channel • Hydraulic mean depth • Full supply discharge • Economical section

• Alluvial soil • Non-alluvial soil • Silt factor • Co-efficient of Rugosity • Mean velocity • Critical velocity • Critical velocity ratio (c.v.r), m • Regime channel • Hydraulic mean depth • Full supply discharge • Economical section

Alluvial SoilAlluvial Soil

• The soil which is formed by the continuous deposition of silt is known as alluvial soil. The river carries heavy charge of silt in rainy season. When the river overflows its banks during the flood, the silt particles get deposited on the adjoining areas.

• This deposition of silt continues year after year. This type of soil is found in deltaic region of a river. This soil is permeable and soft and very fertile. The river passing through this type of soil has a tendency to change its course.

Alluvial SoilAlluvial Soil

Non-Alluvial SoilNon-Alluvial Soil

• The soil which is formed by the disintegration of rock formations is known as non-alluvial soil. It is found in the mountainous region of a river. The soil is hard and impermeable in nature. This is not fertile. The river passing through this type of soil has no tendency to change its course.

• The soil which is formed by the disintegration of rock formations is known as non-alluvial soil. It is found in the mountainous region of a river. The soil is hard and impermeable in nature. This is not fertile. The river passing through this type of soil has no tendency to change its course.

Silt FactorSilt Factor

• During the investigations works in various canals in alluvial soil, Gerald Lacey established the effect of silt on the determination of discharge and the canal section. So, Lacey introduced a factor which is known as ‘silt factor’.

• It depends on the mean particle size of silt. It is denoted by ‘f’. The silt factor is determined by the expression,

Silt FactorSilt Factor

Coefficient of Rugosity (n)


• The roughness of the canal bed affects the velocity of flow. The roughness is caused due to the ripples formed on the bed of the canal. So, a coefficient was introduced by R.G Kennedy for calculating the mean velocity of flow. This coefficient is known as coefficient of rugosity and it is denoted by ‘n’. The value of ‘n’ depends on the type of bed materials of the canal.



Mean Velocity Mean Velocity

• It is found by observations that the velocity at a depth 0.6D represents the mean velocity (V), where ‘D’ is the depth of water in the canal or river.

•

Mean VelocityMean Velocity

Critical VelocityCritical Velocity

• When the velocity of flow is such that there is no silting or scouring action in the canal bed, then that velocity is known as critical velocity. It is denoted by ‘Vo’. The value of Vo was given by Kennedy according to the following expression,

• Where, D = Depth of water

Critical Velocity Ratio (C.V.R)

Critical Velocity Ratio (C.V.R)

• The ratio of mean velocity ‘V’ to the critical velocity ‘Vo’ is known as critical velocity ratio (CVR). It is denoted by m i.e.

CVR (m) = V/Vo • When m = 1, there will be no silting or

scouring. • When m > 1, scouring will occur • When m < 1, silting will occur • So, by finding the value of m, the

condition of the canal can be predicted whether it will have silting or scouring

Regime Channel Regime Channel

• When the character of the bed and bank materials of the channel are same as that of the transported materials and when the silt charge and silt grade are constant, then the channel is said to be in its regime and the channel is called regime channel. This ideal condition is not practically possible.

Hydraulic Mean Depth/Ratio

Hydraulic Mean Depth/Ratio

• The ratio of the cross-sectional area of flow to the wetted perimeter of the channel is known as hydraulic mean depth or radius. It is generally denoted by R.

R = A/P Where, • A = Cross-sectional area • P = Wetted perimeter

Full Supply DischargeFull Supply Discharge

• The maximum capacity of the canal for which it is designed, is known as full supply discharge. The water level of the canal corresponding to the full supply discharge is known as full supply level (F.S.L).

Economical SectionEconomical Section

• If a canal section is such that the earth obtained from cutting (i.e. excavation) can be fully utilized in forming the banks, then that section is known as economical section. Again, the discharge will be maximum with minimum cross-section area. Here, no extra earth is required from borrow pit and no earth is in excess to form the spoil bank. This condition can only arise in case of partial cutting and partial banking. Sometimes, this condition is designated as balancing of cutting and banking. Here, the depth of cutting is called balancing depth.

Economical SectionEconomical Section

Unlined Canal Design on Non-alluvial Soil


• The non-alluvial soils are stable and nearly impervious. For the design of canal in this type of soil, the coefficient of rugosity plays an important role, but the other factor like silt factor has no role. Here, the velocity of flow is considered very close to critical velocity. So, the mean velocity given by Chezy’s expression or Manning’s expression is considered for the design of canal in this soil. The following formulae are adopted for the design.



Unlined Canal Design on Non-Alluvial Soil

Unlined Canal Design on Non-Alluvial Soil

Unlined Canal Design on Alluvial soil by

Kennedy’s Theory


Kennedy’s Theory• After long investigations, R.G Kennedy arrived at a theory

which states that, the silt carried by flowing water in a channel is kept in suspension by the vertical component of eddy current which is formed over the entire bed width of the channel and the suspended silt rises up gently towards the surface.

The following assumptions are made in support of his theory:

• The eddy current is developed due to the roughness of the bed.

• The quality of the suspended silt is proportional to bed width.

• It is applicable to those channels which are flowing through the bed consisting of sandy silt or same grade of silt.

• It is applicable to those channels which are flowing through the bed consisting of sandy silt or same grade of silt.


Kennedy’s Theory


Kennedy’s Theory• He established the idea of critical velocity ‘Vo’ which

will make a channel free from silting or scouring. From, long observations, he established a relation between the critical velocity and the full supply depth as follows

• The values of C and n where found out as 0.546 and 0.64 respectively, thus

• Again, the realized that the critical velocity was affected by the grade of silt. So, he introduced another factor (m) which is known as critical velocity ratio (C.V.R).

Drawbacks of Kennedy’s Theory

Drawbacks of Kennedy’s Theory

• The theory is limited to average regime channel only.

• The design of channel is based on the trial and error method.

• The value of m was fixed arbitrarily. • Silt charge and silt grade are not

considered. • There is no equation for determining the

bed slope and it depends on Kutter’s equation only.

• The ratio of ‘B’ to ‘D’ has no significance in his theory.

Design Procedure

Unlined Canal Design on Alluvial soil by Lacey’s Theory


• Lacey’s theory is based on the concept of regime condition of the channel.

• The regime condition will be satisfied if, • The channel flows uniformly in unlimited

incoherent alluvium of the same character which is transported by the channel.

• The silt grade and silt charge remains constant. • The discharge remains constant.



• In his theory, he states that the silt carried by the flowing water is kept in suspension by the vertical component of eddies. The eddies are generated at all the points on the wetted perimeter of the channel section. Again, he assumed the hydraulic mean radius R, as the variable factor and he recognized the importance of silt grade for which in introduced a factor which is known as silt factor ‘f’.

• Thus, he deduced the velocity as; • Where, V = mean velocity in m/sec, f = silt

factor, • R = hydraulic mean radius in meter



Drawbacks of Lacey’s Theory

Drawbacks of Lacey’s Theory

• The concept of true regime is theoretical and con not be achieved practically.

• The various equations are derived by considering the silt factor of which is not at all constant.

• The concentration of silt is not taken into account. • Silt grade and silt charge is not taken into account. • The equations are empirical and based on the

available data from a particular type of channel. So, it may not be true for a different type of channel.

• The characteristics of regime channel may not be same for all cases

Comparison between Kennedy’s and Lacey’s theory

Comparison between Kennedy’s and Lacey’s theory

Design of Lined Canal Design of Lined Canal

• The lined canals are not designed by the use of Lacey’s and Kennedy’s theory, because the section of the canal is rigid. Manning’s equation is used for designing. The design considerations are,

• The section should be economical (i.e. cross-sectional area should be maximum with minimum wetted perimeter).

• The velocity should be maximum so that the cross-sectional area becomes minimum.

• The capacity of lined section is not reduced by silting.

Section of Lined CanalSection of Lined Canal

• The following two lined sections are generally adopted

Circular section: • The bed is circular with its center at the full

supply level and radius equal to full supply depth ‘D’. The sides are tangential to the curve. However, the side slope is generally taken as 1:1.


Design Parameters for Circular Section


• Trapezoidal section• The horizontal bed is joined to the side

slope by a curve of radius equal to full supply depth D. The side slope is generally kept as 1:1


Design Parameters for Trapezoidal Section

Canal LiningCanal Lining

• Object of Canal Lining:• (a) To Control Seepage: • The seepage loss is the maximum loss in

unlined canals. Due to seepage. Due to seepage the duty of canal is much reduced which involves enhancement of storage capacity of a reservoir by constructing high dam. Thus, the expenditure of the project is increased. So to control the seepage loss through the bed and sides of the canal, the lining of the canal is necessary.

• Object of Canal Lining:• (a) To Control Seepage: • The seepage loss is the maximum loss in

unlined canals. Due to seepage. Due to seepage the duty of canal is much reduced which involves enhancement of storage capacity of a reservoir by constructing high dam. Thus, the expenditure of the project is increased. So to control the seepage loss through the bed and sides of the canal, the lining of the canal is necessary.



• (b) To prevent Water-Logging• Along the course of the canal, there may be

low lying areas on one side or both sides of the canal. Due to the seepage of water through the sides of the sides of the canal, these areas may get converted into marshy lands. This water-logging makes the land alkaline which is unsuitable for agricultural. This water-logging area may become the breeding place of mosquitos which are responsible for many infectious diseases.

• (b) To prevent Water-Logging• Along the course of the canal, there may be

low lying areas on one side or both sides of the canal. Due to the seepage of water through the sides of the sides of the canal, these areas may get converted into marshy lands. This water-logging makes the land alkaline which is unsuitable for agricultural. This water-logging area may become the breeding place of mosquitos which are responsible for many infectious diseases.


( c) To increase the capacity of canal. In unlined canal, the velocity of flow should be fixed such that the silting and scouring is avoided. In Practice, the velocity should always be kept below 1 m/s. Due to the low velocity, the discharge capacity of the canal becomes low. In unlined canal, if the capacity of the canal is to be increased the cross-sectional area has to be increased which involve more land width. So, the lining of the canal should be such that the velocity and the discharge of the canal are more with minimum cross-sectional area.

( c) To increase the capacity of canal. In unlined canal, the velocity of flow should be fixed such that the silting and scouring is avoided. In Practice, the velocity should always be kept below 1 m/s. Due to the low velocity, the discharge capacity of the canal becomes low. In unlined canal, if the capacity of the canal is to be increased the cross-sectional area has to be increased which involve more land width. So, the lining of the canal should be such that the velocity and the discharge of the canal are more with minimum cross-sectional area.


(d) To increase the command Area. If the lining is provided in the canals the various losses can be controlled and ultimately the command area of the project may be enhanced.

(d) To increase the command Area. If the lining is provided in the canals the various losses can be controlled and ultimately the command area of the project may be enhanced.

Canal LiningCanal Lining• (e) To Protect the Canal from the Damage by

Flood The unlined canals may be severely damaged by scouring and erosion caused due to the high velocity of flood water at the time of heavy rainfall. So, to protect the canals from the damage, the lining should be provided.

• (f) To control the growth of weeds : the growth of various types of weeds along the sides of the canals is a common problem. Again, some type of weeds are found to grow along the bed of the canals. These weeds reduce the velocity of flow and the capacity of the canals. So, the unlined canals require excessive maintenance works for clearing the weeds. If lining is provided in the canal, the growth of weeds can be stopped and velocity and the capacity of the canal may be increased.

• (e) To Protect the Canal from the Damage by Flood The unlined canals may be severely damaged by scouring and erosion caused due to the high velocity of flood water at the time of heavy rainfall. So, to protect the canals from the damage, the lining should be provided.

• (f) To control the growth of weeds : the growth of various types of weeds along the sides of the canals is a common problem. Again, some type of weeds are found to grow along the bed of the canals. These weeds reduce the velocity of flow and the capacity of the canals. So, the unlined canals require excessive maintenance works for clearing the weeds. If lining is provided in the canal, the growth of weeds can be stopped and velocity and the capacity of the canal may be increased.

Advantages and Disadvantages of Canal

Lining


Lining• Advantages:• It reduces the loss of water due to seepage and

hence the duty is enhanced.• It controls the water logging and hence the bad

effects of water logging.• It provides smooth surface and hence the

velocity of flow can be increased.• Due to the increased velocity the discharge

capacity of a canal is also increased.• Due to the increased velocity , the evaporation

loss also be reduced.• It eliminates the effect of scouring the canal

bed.

• Advantages:• It reduces the loss of water due to seepage and

hence the duty is enhanced.• It controls the water logging and hence the bad

effects of water logging.• It provides smooth surface and hence the

velocity of flow can be increased.• Due to the increased velocity the discharge

capacity of a canal is also increased.• Due to the increased velocity , the evaporation

loss also be reduced.• It eliminates the effect of scouring the canal

bed.

AdvantagesAdvantages

• The increased velocity eliminates the possibility of silting of the canal bed.

• It control the weeds along the canal side and bed.

• It reduces the requirement of land width for the canal, because smaller section of the canal can produce greater discharge.

• It prevents the sub-soil salt to come in contact with canal water.

• It reduces the maintenance cost of canals.

• The increased velocity eliminates the possibility of silting of the canal bed.

• It control the weeds along the canal side and bed.

• It reduces the requirement of land width for the canal, because smaller section of the canal can produce greater discharge.

• It prevents the sub-soil salt to come in contact with canal water.

• It reduces the maintenance cost of canals.


Lining


Lining• Disadvantages• The initial cost of canal lining is very

high. So, it makes the project very expensive with respect to the output.

• It involves much difficulties for repairing the damage section of lining.

• It takes too much time to complete the project work.

• It becomes difficult, if the outlet are required to be shifted or new outlets are required to be provided, because the dismantling of the lined section is difficult.

• Disadvantages• The initial cost of canal lining is very

high. So, it makes the project very expensive with respect to the output.

• It involves much difficulties for repairing the damage section of lining.

• It takes too much time to complete the project work.

• It becomes difficult, if the outlet are required to be shifted or new outlets are required to be provided, because the dismantling of the lined section is difficult.

• CROSS DRAINAGE WORKS

Siphon Aqueduct Siphon Aqueduct

• In a hydraulic structure where the canal is taken over the drainage, but the drainage water cannot pass clearly below the canal. It flows under siphonic action. So, it is known as siphon aqueduct. This structure is suitable when the bed level of canal is below the highest flood level.



Types of Cross Drainage Works


• Type-II Drainage Passes Over the irrigation Canal.

• Super Passage• The hydraulic structure in which the

drainage is taken over the irrigation canal is known as super passage. The structure is suitable when the bed level of drainage is above the full supply level of the canal. The water of the canal passes clearly below the drainage.

Super PassageSuper Passage

Super PassageSuper Passage

Siphon Super Passage Siphon Super Passage

• The hydraulic structure in which the drainage is taken over the irrigation canal, but the canal water passes below the drainage under siphonic action is known as siphon super passage. This structure is suitable when the bed level of drainage is below the full supply level of the canal.

Siphon Super PassageSiphon Super Passage

Siphon Super Passage Siphon Super Passage



• Type III Drainage and Canal Intersect each other at the same level.

• Level Crossings• When the bed level of canal and the stream are

approximately the same and quality of water in canal and stream is not much different, the cross drainage work constructed is called level crossing where water of canal and stream is allowed to mix. With the help of regulators both in canal and stream, water is disposed through canal and stream in required quantity. Level crossing consists of following components (i) crest wall (ii) Stream regulator (iii) Canal regulator.

Level CrossingsLevel Crossings

Level CrossingLevel Crossing



• Inlet and Outlet• When irrigation canal meets a small stream

or drain at same level, drain is allowed to enter the canal as in inlet. At some distance from this inlet point, a part of water is allowed to drain as outlet which eventually meets the original stream. Stone pitching is required at the inlet and outlet. The bed and banks between inlet and outlet are also protected by stone pitching. This type of CDW is called Inlet and Outlet.

Inlet and Outlet Inlet and Outlet

Selection of Type of Cross Drainage Work


• The following factors should be considered:• (i) Relative Bed Level• According to the relative bed levels of the canal and the

river or drainage, the type of cross drainage work are generally selected which has been discussed earlier. But some problems may come at the crossing point

• The following points should be remembered while recommending the type of work,

• (a) The crossing should be at right angle to each other,• (b) Well defined cross-section of the river or drainage

should be available.• (c) At the crossing point the drainage should be straight

for a considerable length.• (d) The width of the drainage should be narrow as far as

possible.• Considering the above points The C/s can be shifted to

the downstream or upstream.



Availability of Suitable Foundation•For the construction of cross drainage works suitable foundation is required. By boring test, if suitable foundation is not available, then the type of cross drainage work should be selected to site Condition.



Economic Consideration•The cost of construction of cross drainage works should be justified with respect to the project cost and overall benefits of the project. So, the type of works should be selected considering the economical point of view.



Discharge of the drainagePractically the discharge of the drainage is very uncertain in rainy season. So, the structure should be carefully selected so that it may not be destroyed due to unexpected heavy discharge of the river or drainage.



Construction of Problems•Different types of constructional problems may arise at the site such as sub soil water, construction materials, communication, availability of land etc. So the type of works should be selected according to the site condition.

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144107704 Canal Irrigation