08. Classification of Canals.pdf

Classification of Canals

1. 08. Classification of Canals
B.Sc. Civil Engineering 8
th
Semester
Muhammad Ajmal (PhD)
Lecturer
Agri. Engg. Deptt.
CE-402 Irrigation Engineering
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2. Classification of Canals
Canal
❖Itisanartificialcrosssecrtionconstructedonthegroundtocarrywatertothe
fieldeitherfromareservoir,tankorriver.
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3. Types of Canals
(BASED ON SOURCE OF SUPPLY)
Permanent or Perennial
Canal
Non-Perennial Canal
Inundation Canal
Thosecanalswhichgetcontinuoussuppliesby
permanentsourceofsupplylikeariverorreservoirare
calledaspermanentcanalsorperennialcanals.These
irrigatethefieldthroughouttheyearwithequitablerate
offlow.
Thesearethecanalswhichirrigatethefieldforonly
onepartoftheyearusuallyduringsummerseasonorat
thebeginningandendofwinterseason,calledasnon-
perennialcanals.Thesecanalstake-offfromrivers
whichdonothaveassuredsupplythroughouttheyear.
Drawsitssuppliesfromariveronlyduringthehighstagesof
theriver.Noregulatorisprovidedattheheadofsuchcanal.
Thisdrawslotofquantityofsiltwhichisreallybeneficialfor
thecrops.
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4. Types of Canals
(BASED ON FUNCTION)
•Carrieswaterfromitssourcetoagriculturalfields.Irrigation Canal
•Usedfortransportofgoods.Sometimesthesearealso
usedforirrigationpurposes.
Navigation Canal
•Used to carry water for generation of hydroelectricity.Power Canal
•Feeds two or more canals.Feeder Canal
Note: A canal can serve more than one purpose
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5. Types of Canals
(BASED ON ALIGNMENT)
Watershed Canal or Ridge Canal
Contour Canal
Side Slope Canal
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6. Watershed canal or Ridge canal
Fig. Canal Alignment
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7. Watershed canal or Ridge canal
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8. Watershed canal or Ridge canal (Contd.)
➢Thecanalwhichisalignedalonganynaturalwatershed(ridgeline)iscalleda
watershedcanal,oraridgecanal.
➢Aligningacanal(maincanalorbranchcanalordistributary)ontheridgeensures
gravityirrigationonbothsidesofthecanal.
➢Thusbetweentwomajorstreams,thereisthemainwatershed(ridgeline),which
dividesthedrainageareaofthetwostreams.
➢Sincethedrainageflowsawayfromtheridge,nodrainagecancrossacanalalignedon
theridge.Thus,acanalalignedonthewatershedsavesthecostofconstructionofcross-
drainageworks.
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9. Contour Canal
Acontourcanalisanartificially-dug
navigablecanalwhichcloselyfollowsthe
contourlineofthelandittraversesinorder
toavoidcostlyengineeringworkssuchas
boringatunnelthroughhigherground,
buildinganembankmentoverlower
ground,orconstructingacanallock(or
seriesoflocks)tochangethelevel.
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10. Contour Canal
➢Watershedcanalalongtheridgelinearenotfoundeconomicalinhillareaswherethe
riverflowsinthevalleywellbelowthewatershed.
➢Infact,theridgeline(watershed)maybehundredofmetersabovetheriver.Ittherefore
becomesvirtuallyimpossibletotakethecanalontopofsuchahigherridgeline.
➢Insuchconditions,contourcanalsareusuallyconstructed.
➢Acontourcanalirrigatesonlyononesidebecausetheareaontheothersideishigher.
➢Asthedrainageflowisalwaysatrightanglestothegroundcontour.Suchachannel
woulddefinitelyhavetocrossnaturaldrainsandstreams,necessitatingconstructionof
crossdrainagestructures.
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11. Side Slope Canal
Asideslopecanalisthatwhichisalignedat
rightanglestothecontours;i.e.alongthe
sideslopes.
Sincesuchacanalrunsparalleltothe
naturaldrainageflow,itusuallydoesnot
interceptdrainagechannels,thusavoidingthe
constructionofcross-drainagestructures.
Itisacanalwhichisalignedroughlyatright
angletocontoursofthecountrybutnoton
watershedorvalley.
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12. Types of Canals
(BASED ON DISCHARGE)
Main Canal
Branch Canal
Major Distributary
Minor Distributary
Water Course
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Source: Lecture Notes
Prof. Dr. M. R. Kabir

13. Types of Canals
(Based on lining provided or not)
•Bedandbanksmadeupofnaturalsoil.
•Watervelocitieshigherthan0.7m/sarenottolerable.
•Highseepageandconveyancewaterlosses.
•Profusegrowthofaquaticweedsretardstheflow
Unlined
Canal
•Lining of impervious material on its bed and banks to
prevent the seepage of water.
•Different types of lining used e.g. concrete, brick or
burnt clay tile, boulder, etc.
Lined
Canal
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14. AN UNLINED CANAL
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15. A LINED CANAL
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16. Types of Canals
(Based on Financial output)
•Thosecanalswhichyieldanetrevenuetothenation
afterfulldevelopmentofirrigationinthearea.
•Profusegrowthofaquaticweedsretardstheflow
Productive
canals
•Thosecanalswhichapplywatertoalowincome
communityforirrigationpurposestoprotectcommunity
fromfamine.
Protective
canals
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17. Types of Irrigation Canals
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Inirrigationcanaldesigntwoimportantfactorshastobecounted(i)quantityofsiltcarriedbycanal
and(ii)typeofboundaryofcanal.Therearethreetypesofchannelbasedonfactors.Theyare(a)
Alluvial(b)Non-alluvialand(c)RigidBoundaryorLined
(a)Alluvialchannels:arethosewhichareexcavatedinalluvialsoil,andcarrysufficientsiltinwater.
Theboundaryofsuchcanalisofsiltknownasalluvium.Thesiltcontentincanaldependonthe
velocityofflow.Athighvelocitymoresiltscouringatbottomofcanaloccurs,whileatlowvelocity
minimumsiltdepositionoccurs.Todesignachannelinsuchareaanonsiltingnorscouringvelocity
hastobeadopted.
(b)Nonalluvialchannels:Thesechannelareexcavatedinnonalluvialsoillike,rock,loamorclay.
Suchchannelsusuallyhavenosiltingproblemaswaterflowwithnonsiltingvelocity
(c)RigidBoundarychannels:Thosechannelswhichhavesidesandbottomofrigidmaterials.Lined
channelsarerigidboundarychannels.

18. Cross Section of Irrigation Canal
Thissectionispartlyincuttingandpartlyinfillingandaimsinbalancingthequantityof
earthworkinexcavationwiththatinfilling.
WhentheNSLisabovethetopofthebank,theentirecanalsectionwillhavetobein
cutting,anditshallbecalled‘canalincutting’.
Similarly,whentheNSLislowerthanthebedlevelofthecanal,theentirecanalsection
willhavetobebuiltinfilling,anditiscalled‘canalinfilling’.
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FSL= Full Supply Level
NSL=Natural Surface Level

19. Components of Cross-Section
Side slope
Berm
Freeboard
Bank
Service road
Back Bermor Counter Berm
Spoil Bank
Borrow Pit
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20. Side Slope
Thesideslopesshouldbesuchthattheyarestable,dependinguponthetypeofthesoil.
Acomparativelysteeperslopecanbeprovidedincuttingratherthaninfilling,asthesoilin
theformercaseshallbemorestable.
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Sr. No. Type of Soil Slope in CuttingSlope in Filling
1 ClayeySoil 1.5 : 1 2 : 1
2 SandySoil 3 : 1 4 : 1
3 Loamy Soil 1.5 : 1 2 : 1
4 Gravel Soil 0.75 : 1 1.25 : 1
5 Hard Rock 0.25 : 1 ----
6 Soft Rock 0.5 :1 ----

21. Berm
Bermis the horizontal distance left at ground level between the toe of the bank and the
top edge of cutting.
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Purposes of Berms
❖They give additional strength to the banks and provide protection against erosion and breaches.
❖They provide a scope for future widening of the canal.

22. Freeboard
❖The margin between FSL and bank level is known as freeboard.
❖The amount of freeboard depends upon the discharge of the channel.
❖Recommended minimum freeboard = 0.5 m
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23. Bank
The primary purpose of banks is to retain water.
This can be used as means of communication and as inspection paths.
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24. Service Road
These are provided on canals for inspection purposes, and may simultaneously serve
as the means of communication in remote areas.
Dowla: As a measure of safety in driving, dowlas with side slopes of 1.5: 1 to 2:1, are provided
along the banks.
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25. Back Bermor Counter Berm
Evenafterprovidingsufficientsectionforbankembankment,thesaturationgradientlinemay
cutthedownstreamendofthebank.
Insuchacase,thesaturationlinecanbekeptcoveredatleastby0.5mwiththehelpof
counterbermsasshowninfigurebelow.
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26. Spoil Bank
Whentheearthworkinexcavationexceedsearthworksinfilling,theextraearthhastobe
disposedofeconomically.
Economicalmodeofitsdisposalmaybecollectingthissoilontheedgeofthebank
embankmentitself.
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27. Borrow Pit
Whenearthworkinfillingexceedstheearthworkinexcavation,theearthhastobe
broughtfromsomewhere.
Thepits,whicharedugforbringingearth,areknownasborrowpits.
Ifsuchpitsareexcavatedoutsidethechannel,theyareknownasexternalborrowpits,andif
theyareexcavatedsomewherewithinthechannel,theyareknownasinternalborrowpits.
Internal borrow pits are more preferred than external one.
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Theinsideborrowpitmaybelocatedatthecenterof
canal.
Theideabehindthisisthattheborrowpitswillactas
waterpocketswherethesiltwillbedepositedand
ultimatelythecanalbedwillgetlevelledup.

28. Balancing Depth
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A canal section will be economical when earth work involved at a particular section has an
equal amount of cut and fill. Usually a canal section has a part in cutting and part in filling as
shown in fig.
If the amount of cut is equal to the amount of fill, it has to be paid for once only.
Definition
For a given C/S there is always only one depth of cutting for which the cutting and filling
will be equal. The depth is known as balancing depth.

29. If h = vertical height of top of bank
from the bed of canal.
b = bed width of the channel.
t = top width of the canal bank.
n:1 = side slope of bank in filling.
z:1 = side slope of canal in cutting.
d = full supply depth of canal.
y = depth of cutting.
Area of the cut = by + zy
2
= y(b + zy)
Area of fill = 2[(h –y)t + n(h-y)
2
]
Balancing Depth
Equating the area of cut and fill:
y(b + z y) = 2[(h –y)t + n(h-y)
2
]
b y+ zy
2
= 2th + 2nh
2
–2nhy –2ty –2nhy + 2ny
2
y
2
(2n –z) –(b + 4nh + 2t)y + 2h(t + nh) =0
From this equation the balancing depth of the canal
may be determined.
A canal is usually constructed with side slope of 1:1 in
cutting and a slope 1.5:1 in filling.
Putting n = 1.5 and z =1 in above equation.
We get;
y
2
–(b/2 + 3h + t)y + h (t + 3/2 h)=0

30. Example
Calculatethebalancingdepthforachannelsectionhavingabedwidthequalto18mandside
slopesof1:1incuttingand2:1infilling.Thebankembankmentsarekept3.0mhigherthanthe
groundlevel(bermlevel)andcrestwidthofbanksiskeptas2.0m.
Solution:Letdbethebalancingdepth,i.e.thedepthforwhichexcavationandfillingbecomes
equal.
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31. Example (Contd.)
Area of cutting = (18 + d) d m
2
Area of filling = 2(2+14)/2×3 = 48 m
2
Equating cutting and filling, we get
(18 + d) d = 48
or, d
2
+ 18d –48 = 0
or, d = 2.35 m (neglecting –vesign), Balancing depth = 2.35 m
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32. Canal Lining and its Advantages
➢Itisthetreatmentgiventothecanalbedandbankstomakethecanalsectionimpervious.
➢WaterConservation:Liningacanalresultsinreductioninwaterlosses,aswaterlossesin
unlinedirrigationcanalscanbehigh.
➢Noseepageofwaterintoadjacentlandorroads:Ifcanalbanksarehighlypermeable,the
seepageofwaterwillcauseverywetorwaterloggedconditions,orevenstandingwateron
adjacentfieldsorroads.Liningofsuchacanalcansolvethisproblem.
➢Reducedcanaldimensions:Theresistancetoflowofalinedcanalislessthanthatofan
unlinedcanal,andthustheflowvelocitywillbehigherinthelinedcanal.Therefore,withthe
highervelocity,thecanalcross-sectionforalinedcanalcanbesmallerthanthatofanunlined
canal.
➢Reducedmaintenance:Maintenancecostsforthefollowingissuesareeliminatedusinglining
ofcanals.
❖Periodicalremovalofsiltdepositedonthebedsandsidesofcanals.
❖Removalofweedsandwatercanals.
❖Minorrepairslikepluggingofcracks,unevensettlementsofbanks,etc.
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33. Types of lining
Hard Surface Lining
Cast InsituCement
Concrete Lining
Shotcreteor Plastic
Lining
Cement Concrete Tile
Lining or Brick Lining
Asphaltic Concrete
Lining
Boulder Lining
Earth Type Lining
Compacted Earth
Lining
Soil Cement Lining
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34. Cast In-situ Cement Concrete Lining

35. Shotcrete & Plastic Lining

36. Canal Lining
CONCRETE LINING

37. Canal Lining
Concrete tiles canal lining

38. Canal Lining
Brick canal lining
PREFABRICATED CHANNEL
SECTION

39. Disadvantages
Higherinitialinvestment
Repairiscostly
Shifting of outlet is costly because it involve dismantlingandrelayingof lining.
Longerconstructionperiod
Sophisticated construction equipment and labor is needed.

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