canal alignment and h ps

CANAL ALIGNMENT AND HYDRAULIC PARTICULARS,CM&CD WORKS.

BY B.Lakshmanarao,B.Tech, M.B.A.,F.I.E,

CHIEF ENGINEER , I&CADCentral Designs Organisation & NSRS Srisailam Project

HYDERABAD.

09-12-2011

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NAC, HYDERABAD

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INTRODUCTION TO CANAL ALIGNMENT &

HYDRAULIC PARTICULARS

IRRIGATIONThe process of supplementing the supplies of rain water on the area to be cultivated at the season to the extent required for the successful cultivation of the Crop.

Process of Irrigation comprises of a) Source of Water b) Carrier System to transport water from the source to the place of cultivable lands.

Efficiency of Irrigation mainly depends upon the1) Effective functioning of the Carrier System & 2) Efficient Controlling.

The distribution system which conveys water from the head works to the land to be irrigated is called CANAL SYSTEM.

The canal system is a vital element for the success of an IRRIGATION PROJECT.09-12-2011 NAC, HYDERABAD

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CARRIER SYSTEM

CANALS CANAL STRUCTURE

Main Branch Major Minor Field Cross Drainage Works

Cross Masonry Works

Contour Canal for Main Canals

Side Slope Canal

Ridge Canal for Branch, Dist

& Field Channels

09-12-2011 NAC, HYDERABAD

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CANALSCANALS

MAIN CANALMAIN CANAL BRANCH CANALBRANCH CANAL MAJOR MAJOR DISTRIBUTORYDISTRIBUTORY

MINOR MINOR DISTRIBUTORYDISTRIBUTORY

FIELD CHANNELFIELD CHANNEL

TAKES OFF DIRECTLY FROM THE U/S SIDE OF

WEIR HEAD WORKS OR DAM

OFF TAKE FROM MAIN CANAL

Q > 14.15 Cumecs(500 c/s )

OFF TAKE FROM MAIN / BRANCH

CANALQ = 14.15 to

0.028 Cumecs( 500 to 1 c/s )

OFF TAKE TAKING OFF FROM A

MAJOR DISTRIBUTORYSERVING > 40.47

Hectares(100 Acres)

PIPE OFF TAKE SERVING LESS

THAN 40.47 Hectares of Ayacut

(100 Acres)


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CANALS which carry water play a very significant role in the branch of Irrigation since these canals carry Water to the fields starting from Main canal to Branches and Distributaries and then to Field Channels .

They can be Lined or Unlined depending upon the availability of water and the importance of works besides economy.

CANAL ALIGNMENT: a) covering the entire / maximum area to be irrigatedb) with shortest possible length c) its cost including the cost of CM & CD works should be minimum.d) shorter length of canal ensures less loss of head due to friction and smaller loss of discharge due to seepage and evaporation, so that additional areas can be brought under cultivation.

Certain decisions consistent with economy and safety have to be taken while aligning a canal.


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CANAL STRUCTURES

CROSS DRAINAGE WORKS CROSS MASONRY WORKS

CROSS DRAINAGE WORKS

AQUEDUCT/UT/VIADUCT SP LEVEL CROSSING INLET & OUTLETSYPHON

DRAINAGE SYPHON CANAL SYPHON

CROSS MASONRY WORKS

REGULATION & CONTROL WORKS COMMUNICATION WORKS

Head Regulator Drops Measuring Devices OT SluicesEscapesCross Regulator Bridges, Roads & Railways

Foot Bridges for Men & Cattle

CROSS DRAINAGE WORKS

To Pass Irrigation Canal Over the Drainage by means of Aqueduct/ UT/

Viaduct / Syphon Aqueduct

To Pass Drain through Irrigation Canal By means of Inlet & Outlet/ Level

Crossing

To Pass Drain Over the Irrigation Canal By means of SP/ Canal Syphon


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Irrigation canals are generally aligned with reference to the contours of the country in one of the following ways:

Contour canals

Ridge canals

Side slope canals.


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CLASSIFICATION OF CANALS:

1. Contour Canal:-- a)Canal aligned nearly parallel to the contours of the countryb)include all culturable area of the valley on one side of the canal.c) To enable the water to flow by gravity, some surface slope is given . d)in highly undulated tracks, deep cutting across the ridges and high embankments across the valleys are inevitable in order to reduce the unnecessary length of the channel in long detours and sharp curves in the alignment

2. Ridge Canal ( water shed canal):a)aligned along a water shed b) runs for most of its length on a water shed . c) a larger area can be brought under cultivation.d) Also no drainage can intersect a water shed and hence necessitates no CD work across the canal.


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3. Side Slope Canal:

a) aligned roughly at right angles to the Contours

b) neither on the water shed nor in the valley. c)it has very steep bed slope d)not preferred in general


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BROAD PRINCIPLES CONSIDERED FOR THE CANAL ALIGNMENT

The alignment of canals will have to be such that it would result in the greatest saving of both capital and maintenance costs and also in the loss of head and transmission losses. In an undulating country a straight alignment of canal for any length may not be possible as it would involve heavy filling and cutting resulting in both heavy capital and maintenance investments. The economically shortest route is to be kept in view which can be attained strictly following the falling contour line where balanced filling and excavation is feasible. An irrigation canal must run on a water shed or ridge and where that is not possible it should run as near a ridge as possible so that the canal will be able to command on both sides. The alignment of an irrigation canal should be central in its command as far as possible and the length of the off-take canal should be minimum. The drainage line should not be blocked as the canal itself may get damaged and result in flooding and water logging of the surrounding areas.


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In addition to the above, practical points also be considered while fixing the alignment of canals.

Proper location of cross drainage works is most important. The crossing should be located at places where the water way is sufficient and the foundations are good and the material of construction is available nearby.

The alignment of canal should avoid difficult country, i.e. one having ridges, rocky sandy and alkaline strata and also religious centers such as mosques, temples and burial grounds.

When a canal passes near a village or an important town, it should pass on the lower side even at additional cost .In case it passes on the higher side of the town it should be at a considerable distance and may be lined as the seepage from canal may create difficulties.


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To minimize silting problem, the canal shall be so aligned as to avoid level crossings with drainages.

Hydraulics of channels is very much a complicated subject since it involves several elements such as 1) Discharge 2) Velocity 3) Area of water way 4) Wetted Perimeter 5)Side Slopes 6) Surface fall 7) Rugosity coefficient 8) Silt factor

9) Quantity of sediment 10) Size of silt particles transported etc.which are inter dependent.

Usually the design procedure is to compute Discharge from the known ayacut. As such this is a basic factor and all other variants are designed to suit this.


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MODIFIED PENMAN METHOD:

Often the existing systems are being designed on an arbitrary assumption of duty on average basis.

The duty required from Project to Project varies depending on several parameters.

Thus adopting a single duty as a means of estimating the Irrigation water requirement resulted in an improper estimation.

MODIFIED PENMAN METHOD gives a reasonable assessment of the crop water requirement, duly taking into consideration, the various climatic factors, the duration of crop, the stage of growth of crop etc,.


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DESIGN OF CANAL SECTION

THE BASIC KNOWN FACTOR IS REQUIRED DISCHARGE ‘Q’

FOR THIS ‘Q’ , b/d RATIO IS TO BE FOUND OUT FROM C.W.Cs RECOMMENDATIONS

LONGITUDINAL SLOPE MAY BE DETERMINED EITHER BY LACEY’S CURVES FOR VALUE OF ‘f’ OR AS REQUIRED BY THE TOPOGRAPHY OF THE COUNTRY

AS A FIRST APPROXIMATION, ASSUME d = 0.73Q1/3

THEN ADOPT A SECTION WHICH SATISFIES b/d RATIO AS PER C.W.C


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Allowable Velocities :-

In no case, the velocity should not be too low to allow weed growth or deposit of water borne material.


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2g) BERMS:- A berm is a narrow strip of land on eitherside of the canal between upper edge of the cut & toe of the bank..

In Irrigation Dept. of Kerala State, Codal norms are not being recommended / followed for uniform adoption where land is very costly & scarce. The Engineer-in - charge may decide upon the width of Berm.


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2h) DOWELS:- Dowels are short projections provided on canal bank usually on water edge of the bank to prevent cutting up of bank slopes due to rain.

They provide additional safety so far Free board is concerned & also give greater safety in driving.

IS: 10430- 2000 recommended Dowels on one or both the banks.

CDO recommended on both banks on water edge.


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2f) FREE BOARD:- The free board shall be measured from the FSL to the Top of lining / TBL. The height of dowel portion should not be used for purposes of free board.

For Lined Canal : >10 Cumecs 0. 75 m (as per IS 10430-2000) 3 to 10 0.60

1 to 3 0.50

For Unlined Canal : >10 Cumecs 0. 75 m (as per IS 7112-1973) < 10 Cumecs 0.50


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2b) CRITICAL VELOCITY RATIO:-

Non silting & non scouring velocity is known as Critical Velocity Ratio (V/Vo)

Here Vo = 0.39 x d0.55 for Godavari Fine SiltVo = 0.53 x d0.52 for Krishna Fine Silt

This criteria is required to be considered when there is appreciable bed & suspended load.

This is not required for canals taking off from Reservoirs & tanks ,as they carry almost no sediment.

In case of lined canal, question of scouring does not arise.Hence V/Vo recommended is > Unity.


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2e) SIDE SLOPES:- Steeper side slope makes the canal C/s narrow and deep leading to smaller water surface width with an increased Unit Discharge there by leading to reduced evaporation or percolation loses.

Previously it is in vogue to consider 1/2 :1 or 1:1 for Design &1:1or 11/2:1 for execution.

Now both are being adopted as same.The side slopes to be adopted depend upon the nature of the soil in which the

channel is to be excavated, depth of cutting & height of embankment.


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Design Design


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THANK YOU

09-12-2011 49NAC, HYDERABAD

canal alignment and h ps

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