Earthen Channel Design_1

Channel Plan Forms/PatternChannel Plan Forms/Pattern

• Straight ChannelStraight Channel– Water moves parallel to the channel banksWater moves parallel to the channel banks– Sinuosity varies from 1 – 1.05Sinuosity varies from 1 – 1.05

• Meandering ChannelMeandering Channel– Follow the sinuous pathFollow the sinuous path

• Braided ChannelBraided Channel– Channels flows in more than one sub-channels, Channels flows in more than one sub-channels,

because the natural topography does not because the natural topography does not match the hydraulics conditions of a river. match the hydraulics conditions of a river.

SinuositySinuosity

• The meander ratio or sinuosity index is the ratio of The meander ratio or sinuosity index is the ratio of actual length along a meandering river (Lm) to the actual length along a meandering river (Lm) to the straight distance S between the end points (AB). straight distance S between the end points (AB).

• It is an indication of quantification of meandering. It is an indication of quantification of meandering.

• For a straight river course this ratio is equal to unity. For a straight river course this ratio is equal to unity. A ratio varying from 1 to 1.5 defines the river course A ratio varying from 1 to 1.5 defines the river course as sinuous and from 1.5 to 4 as meandering. as sinuous and from 1.5 to 4 as meandering.

Geometric features of Geometric features of meandermeander

Meander Belt

Straight ChannelStraight Channel

Meandering ChannelMeandering Channel

Braided ChannelBraided Channel

Earthen Channel Earthen Channel DesignDesign

IntroductionIntroduction

• The efficiency of the canal design has a bearing on its The efficiency of the canal design has a bearing on its workingworking

• The canal efficiency suffers from silting and scouring The canal efficiency suffers from silting and scouring of the canal due to faulty design necessitating heavy of the canal due to faulty design necessitating heavy maintenance and at time even remodeling if the maintenance and at time even remodeling if the original design is past redemption.original design is past redemption.

• The other worse problems whose origin lies in faulty The other worse problems whose origin lies in faulty design are; weed growth infection, heavy seepage design are; weed growth infection, heavy seepage losses entitling development of water-logging losses entitling development of water-logging alongside the canal.alongside the canal.

IntroductionIntroduction• Canal design practices also depend on the conditions, Canal design practices also depend on the conditions,

particularly the soil formation, sediment transport particularly the soil formation, sediment transport characteristics, operational needs and desired standards characteristics, operational needs and desired standards of maintenanceof maintenance

• Usually irrigation canals are constructed in alluvial soils Usually irrigation canals are constructed in alluvial soils and the supplies are essentially from river and carry silt.and the supplies are essentially from river and carry silt.

• The sediment passed on into the off-taking channel of low The sediment passed on into the off-taking channel of low velocity, deposits in the canal bed resulting in silting up velocity, deposits in the canal bed resulting in silting up and consequently causing loss of discharge carrying and consequently causing loss of discharge carrying capacity necessitating frequent silt clearing.capacity necessitating frequent silt clearing.

• On the other hand a high velocity in channel cause On the other hand a high velocity in channel cause erosion/scouring thereby lowering Full Supply Level erosion/scouring thereby lowering Full Supply Level resulting in loss of command. resulting in loss of command.

Types of Canal SectionsTypes of Canal Sections

• There are two types of canals sectionsThere are two types of canals sections

– Unlined channels, Unlined channels, most of our main irrigation canals are most of our main irrigation canals are unlined/earthen canals which cause seepage and result in unlined/earthen canals which cause seepage and result in losses and raising in the W/T of the adjoining area.losses and raising in the W/T of the adjoining area.

– Lined channels, Lined channels, lined with RC, PCC, Bricks, Stones etc, to lined with RC, PCC, Bricks, Stones etc, to minimize the seepage losses and increase the efficiency of minimize the seepage losses and increase the efficiency of the system.the system.

• Recently irrigation canals are built with liningRecently irrigation canals are built with lining

Factors affecting the Factors affecting the Design of CanalsDesign of Canals

• Main factors:Main factors:– Water discharge, QWater discharge, Q– Sediment Discharge, QsSediment Discharge, Qs– Sediment size, dSediment size, d– Slope of canalSlope of canal– Bed width, depth and velocityBed width, depth and velocity

Factors affecting the Factors affecting the Design of CanalsDesign of Canals

• Secondary factors:Secondary factors:– Acceleration due to gravity, gAcceleration due to gravity, g– Shear stressShear stress– ViscosityViscosity– TemperatureTemperature– Sediment density etc.Sediment density etc.

Design of irrigation Design of irrigation canalscanals• It is the process to obtain a cross-section, slope and It is the process to obtain a cross-section, slope and

geometry of channel/canal which should not have geometry of channel/canal which should not have objectionable siltation and scouring.objectionable siltation and scouring.

– Determining (1) depth, (2) bed width, (3) side slope Determining (1) depth, (2) bed width, (3) side slope and (4) longitudinal slope of the channel so as to and (4) longitudinal slope of the channel so as to produce a non-silting and non-scouring velocity for produce a non-silting and non-scouring velocity for

the given discharge and sediment loadthe given discharge and sediment load..

Approaches used for Approaches used for Design of Earthen CanalsDesign of Earthen Canals

• EmpiricalEmpirical

• Semi empiricalSemi empirical

• RationalRational

Empirical ApproachesEmpirical Approaches

Empirical Approaches (Regime Theories):Empirical Approaches (Regime Theories):

• These methods are based on those canals which were These methods are based on those canals which were working reasonably well and they were not having any working reasonably well and they were not having any objectionable silting and scouring and having stable cross-objectionable silting and scouring and having stable cross-sections. These channels were fulfilling the requirements sections. These channels were fulfilling the requirements to carry designed water and silt discharge.to carry designed water and silt discharge.

• These theories are not dimensionally homogenous and do These theories are not dimensionally homogenous and do not follow any laws or theories. not follow any laws or theories.

Concept of Channel in Concept of Channel in Regime Regime

• Channel in Regime (Stable Channel)Channel in Regime (Stable Channel)– Lindley (1919):Lindley (1919): When an artificial channel is When an artificial channel is

constructed in alluvium to carry silty water, its bed constructed in alluvium to carry silty water, its bed and banks would silt or scour until the depth, slope and banks would silt or scour until the depth, slope and width attain a state of balance, to which he and width attain a state of balance, to which he designated as channel in regime.designated as channel in regime.

– Lane (1953) defined stable channel asLane (1953) defined stable channel as• Which carries waterWhich carries water

• The banks and bed of which are not scoured The banks and bed of which are not scoured objectionably by moving water and objectionably by moving water and

• In which objectionable deposit of sediment do not In which objectionable deposit of sediment do not occur.occur.

Design of Earthen Design of Earthen ChannelChannelKennedy Regime Theory (1895):Kennedy Regime Theory (1895): • Executive Engineer UBDC.Executive Engineer UBDC.• Published his work in 1895.Published his work in 1895.• He did pioneering research work for obtaining a He did pioneering research work for obtaining a

stable non-silting, non-scouring irrigation canal stable non-silting, non-scouring irrigation canal system. On the basis of observation made at 20 system. On the basis of observation made at 20 different site of Upper Bari Doab Canal system in different site of Upper Bari Doab Canal system in Punjab, Kennedy concluded that:Punjab, Kennedy concluded that:– The flowing water is to counteract friction against The flowing water is to counteract friction against

the bed of channel resulting in generation of the bed of channel resulting in generation of vertical eddies rising up gently to the water vertical eddies rising up gently to the water surface. surface.

– A velocity sufficient to generate these eddies keeps A velocity sufficient to generate these eddies keeps the sediment in suspension thereby avoiding silting the sediment in suspension thereby avoiding silting up of channel (Non silting Non Scouring velocity)up of channel (Non silting Non Scouring velocity)

Kennedy Regime Kennedy Regime TheoryTheory

– Safe velocity against erosion for canals in Punjab Safe velocity against erosion for canals in Punjab soil is 1m/s corresponding to depth of not more soil is 1m/s corresponding to depth of not more than 3 m.than 3 m.

– The amount of silt held in suspension is The amount of silt held in suspension is proportional to the upward acting force of vertical proportional to the upward acting force of vertical eddies and varies as bed width and some power eddies and varies as bed width and some power of the velocity of the flow in the channel. of the velocity of the flow in the channel.

– A A regime channelregime channel is one which neither silts nor is one which neither silts nor scours.scours.

– The The Manning’s roughness coefficient (n) is Manning’s roughness coefficient (n) is 0.02250.0225 for all irrigation channels for all irrigation channels

Kennedy Regime Kennedy Regime TheoryTheory• Kennedy presented the following Kennedy presented the following

relationship based on his research:relationship based on his research:

VVcc = 0.55 D = 0.55 D0.64 0.64 (S.I.) (S.I.)

VVcc = 0.84 D = 0.84 D0.640.64 (FPS)(FPS)

• When the same formula was applied in Sindh and When the same formula was applied in Sindh and punjab canals other than UBDC, then the constant punjab canals other than UBDC, then the constant 0.84 was not found to be correct. Therefore a 0.84 was not found to be correct. Therefore a general formula was proposed as:general formula was proposed as:

VVcc = mKD = mKDNN

WhereWhere• Vc = Critical velocity i.e. non silting and non scouring velocityVc = Critical velocity i.e. non silting and non scouring velocity

• m = Constant which depends on the nature and the charge m = Constant which depends on the nature and the charge (Parts/million) of the silt. It has a greater value for coarser silt (Parts/million) of the silt. It has a greater value for coarser silt (value varies 1.1 – 1.2 for canals having coarser sediment than (value varies 1.1 – 1.2 for canals having coarser sediment than UBDC and 0.8 – 0.9 for finer sediments)UBDC and 0.8 – 0.9 for finer sediments)

• m= critical velocity ratio = V/Vc, V is the velocity of channel m= critical velocity ratio = V/Vc, V is the velocity of channel being designed. being designed.

• N = Constant, and its value is 0.64N = Constant, and its value is 0.64

• K = 0.84 (FPS) and 0.55 (SI)K = 0.84 (FPS) and 0.55 (SI)

Kennedy Regime TheoryKennedy Regime Theory

Drawbacks and Limitations of Kennedy's Theory:Drawbacks and Limitations of Kennedy's Theory:• Kennedy did not give any method of measurement of Kennedy did not give any method of measurement of

CVR (m).CVR (m).

• Kennedy's equation of non-silting and non-scouring Kennedy's equation of non-silting and non-scouring velocity Vc is only the function of depth Dvelocity Vc is only the function of depth D. . Shape, Shape, channel width, roughness of bed, side slope and channel width, roughness of bed, side slope and longitudinal slope are not at all considered in assessing longitudinal slope are not at all considered in assessing this velocity.this velocity.

• Assumption of first approximate depth to initiate the trial Assumption of first approximate depth to initiate the trial and error method is difficult. Some approximate method and error method is difficult. Some approximate method depending on designed discharge should have been depending on designed discharge should have been predicted to save computational time.predicted to save computational time.

• His regime velocity did not consider the sediment load as His regime velocity did not consider the sediment load as a variable.a variable.



Steps involved for the design of Earthen Canals:Steps involved for the design of Earthen Canals:• Assume a suitable depthAssume a suitable depth• Find out Vc using Kennedy,s approachFind out Vc using Kennedy,s approach

VVcc = 0.55 D = 0.55 D0.64 0.64

• Calcualte Area of cross-section, A = Q/VcCalcualte Area of cross-section, A = Q/Vc

• Calculate R (Hydraulic radius) and B (bottom width) Calculate R (Hydraulic radius) and B (bottom width) assuming any reasonable side slope value (1V:1H, assuming any reasonable side slope value (1V:1H, 1V:2H, 1V:1.5H etc)1V:2H, 1V:1.5H etc)

• Calculate velocity using chezy’s formulaCalculate velocity using chezy’s formula

V C RS

• Find Chezy’s C by Kutter’s Formula (S.I. Units):Find Chezy’s C by Kutter’s Formula (S.I. Units):

• n = Kutter’s Coefficient, 0.0225 (UBDC)n = Kutter’s Coefficient, 0.0225 (UBDC)

0.00155 123

0.001551 23

S nn

S R


• Kutter’s Formula in FPS Units:Kutter’s Formula in FPS Units:

• n = Kutter’s Coefficient, 0.0225 (UBDC)n = Kutter’s Coefficient, 0.0225 (UBDC)

• Compare Vc with V and keep on trailing till Vc = VCompare Vc with V and keep on trailing till Vc = V

0.00155 1.81141.65

0.001551 41.65

S nn

S R



Example problem:Example problem:

• Design the canal using Kennedy’s method for the Design the canal using Kennedy’s method for the following data:following data:– Q = 80 m3/secQ = 80 m3/sec– S = 1:5500S = 1:5500

• Solution:Solution:

Example ProblemExample Problem

Q = 80 m3/secS = 1:5500 = 0.00018 m/mm = 1

Assume D = 2.5 m

V = 0.55 D0.64 = 0.989 m/sec

A = 80.918 m2

Side Slope = 1V:1.5H

n = 0.0225

D

B

1

1.5

1.803

Example ProblemExample Problem

A = B D+ 1.5D2

B = 28.617 m P = 32.223 m R = A/ P = 2.511 m

Using Kutter’s Formula in S.I. Units

C = 52.479

V = C√RS = 1.121 m/sec

Keep on trailing till Vc = V

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Earthen Channel Design_1