Manual Irrigation Power Channels

8/17/2019 Manual Irrigation Power Channels

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G O V E R N M E N T O F I N D I A

C E N T R A L W A T E R C O M M IS S IO N

MANUAL ON

IR R IG A T IO N A N D P O W E R C H A N N E L S

NEW DELHI

M ARCH 1984


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M A N U A L O N

IR R IG A T IO N A N D P O W E R C H A N N E L S

Prepared by

C E N T R A L \N A T E R C O M M IS S IO N

Published by

C en tra l B oa rd o f Irrig atio n a nd P ow e r

Malcha Marg, Chanakyapuri, New Delhi-11 0021


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The economy and the well-being of the rural masses depends on

agriculture of which irrigation is the most important single input. The canal

system is a vital element for the success of an Irrigation Project. Canals are

also vital components of many run-of-the-river hydro-electric power projects.

Although India has a long and enviable record of successful design and cons-

truction of irrigation and hydro-power projects, it was felt desirable to com-

pile useful information in the form of a manual for the benefit of those

engaged in the planning, designs, construction, operation and maintenanceof canals. This manual on Irrigation and Power Channels deals, in brief, withthe planning and design of both lined and unlined canals.

Chapter I introduces the importance and advantages of irrigation and

the additional uses of canal waters.

Chapter II gives in brief the planning and investigations necessary

before detailing an irrigation scheme. The field data to be collected, prelimi-

nary and detailed surveys to be done, different types of canal alignments

generally adopted, and other features regarding the L-Section and X-Sections

are brought out.

Chapter IlIon design of unlined canals gives in brief some of theimportant farmulae used in the design of stable channels. Recommendations

of I.S.!. in their various Codes have also been mentioned with respect to pro-

vision of side slopes, inspection paths, free-board; bed width to depth ratio,

allowable velocities, berms, dowels, etc.

Chapter IV on design of lined canals describes different types of

lining in use and their suitability in different situations. I.S.I. recommendations

pertaining to various aspects of the design of lined canals have also been

included. Necessity and details of under-drainage arrangements are also

described in details.

Chapter V on power channels describes the speCial considerations to betaken into account while designing power channels.

Chapter VI gives in brief the various types of problems faced during

construction, operation and maintenance of the cana Is.

Appendix I gives some examples on design of unlined canals, while

Appendix II gives examples on design of lined canals. A number of plates have

been included to simplify the calculations and save time.


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The Manual gives the broad guidelines for planning and design of a

system. A satisfactory and successful design depends upon the individual skill

and practical experience of a Designer and should cater to the site require-

ment. I hope this Manual will be of assistance to the engineers in the field of Irrigation and Power in planning and design of canal systems.

I would like to bring on record the useful work done by Shri P.C.

Lau, Deputy Director, Shri P. Sen, former Director, and Shri R.P. Malhotra,

Director (B.C.D.-II) in preparation of this Manual. Contributions of Shri R.

Rangachari, Member (JRC): Shri K. Madhavan, Chief Engineer (Designs)

and Shri N.K. Agrawal, former Member (D&R) in the preparation of this

Manual are acknowledged.

Comments and suggestions for improvement of the Manual are welcome.

PRIT AM SINGH

Chairman

Central fVater Commission


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Chapter II

Chapter III

Appendix I

Chapter IV

Appendix II

Chapter V

Chapter VI


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S

S.R.

V

Va

W

Area of Cross-section of Channel in Square Metre

Bed Width in Metres

Coefficient of Discharge

Cubic Metres per Second

Canal Bed Level

Critical Velocity Ratio

Depth of Water in Metres

Lacey's Silt Factor

Free Board in Metres

Full Supply Level

Full Supply Depth

Ground Level

Inspection Path

Coefficient of Rugosity

Wetted Perimeter in Metres

Discharge in cumecs

Discharge in Cumecs/Meter Width

Hydraulic Mean Depth in Metre

Side Slope Ratio

Longitudinal Surface Slope of Water

Service Road

Mean Velocity in Metre/sec.

Kennedy's Critical Velocity in Metre/sec.

Water Surface Width in Metres

A

B

Cd

Cumecs

C.B.L.

C.V.R.D

f

F

F.S.L.

F.S.D.

G. L .

LP.

N

P

Qq

R


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Introduct ion

1.1 India is potentially one of the richest agricul-tural countries in the world. The total arable land inIndia is estimated to be 147 million hectares which isthe third largest in the world, rank ing behind only theU.S.S.R. with 225 million hectares and the U.S.A.with 194 million hectares. This is owing to the fact

that the proportion of arable land to total geographi-cal area is t he highest in India being 45 percentagainst 10 percent for U.S. S. R. a nd 25 percent for U.S.A.

Irrigation has been practised in India from veryearly times from wells, tanks, inundation canals and small channels. Major projects were built by t heBritish starting in the middle of the 19th Century, and the rate of development though, moderate, was steady.

1.2 Irrigation is defined as the natural or artifi-cial application of water to soil for the purpose of supplying the moisture essential or beneficial to plantgrowth.

Water is tlOrmally supplied to the plants by naturethrough the agency of rain. A second agency is throughthe flood waters of rivers which spread and inundatelarge areas during the flood season and recede back leaving the land well irrigated for cultivation of a cropduring the dry season. These natural processes areusefully supplemented by canals to maximise the

benefits to cultivators.

1.3 This manual is an attempt to cover broad guidelines, keeping in view the practices recommended by ISl in their various published Cod.es and the prac-tices adopted by reputed Agencies and Organisationslike U.S.B.R., U.S. Army Corps of Engineers, etc.,which may be of some help to the designers. The

Irrigation distribution system consists of various components like regulation structures, cross drainagestructures, bridges, lined or unlined channel sections,etc. In this manual, only the channcI part has beendealt in detail.

1.4 The source of all water used for irrigation is'precipitation', i.e., the water received on the earthfrom the atmosphere in the form of rain, snow and hail etc. The prOC~3Sof utill3ation of this water in-volves th~ construction of engineering works of appre-

ciable magnitude, and is termed 'artificial Irrigation.'Artificial Irrigation may be divided into 'lift' irrigationand 'flow'· irrigation according to whether the water islifted to the fields by some mechanical/man ual meansor flows by gravity from the source to the field.

In order to provide artificial irrigation, irrigationschemes are planned and executed utilising the avail-a?le natural source. of ~ater . The schemes mainly con-SISt of storage or diverSIon str uctures and distributionsystems. In this publication an attempt has beenmade to cover the latter, comprising open channels.

1.5 . In addi.tion to the surface water, ground water reserVOIrS provId~ ,!ery usef~l ~ources which .are beingmore and more utilised for lfflgatlOn purposes thesedays. Augmentation Tube Wells have been installed to promote conjunctive use of surface and sub-surfacewater~ to !neet. the increased demand of irrigation and to mamtalJ1 sUitable ground water conditions. Due tointroduction of high yielding crop varieties and multi-

ple cropping such conjunctive use of water has severaladvantages. Some of these are:

(1) Water loss due to see page from canals and water courses, irrigated areas, etc., is utilised again there by mitigating to some extent thewaterlogging problem.

(2) Compared to surface water, ground water isrelatively free from surface pollutants, and hasthe advantage of being less susceptible tochanges in quality, chemical composition and temperature variation.

(3) puring the period whe.n canal water supply is

madequate or not avaJlable, the farmers could draw supply from tube wells to irrigate their fields in time.

In North India, Tube Wells have been found to beso useful and advantageous that their number has

been increasing rapidly.

1.6 It is hardly necessary to emphasise the import-ance and advantages of irrigation development whenthe pressing necessity of stepping up food production


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for the growing population of the country has automa-tically brought it to the forefront. Even so, some of

tae salient advantages of development of irrigation arerecapitulated below:

(i) Protection from Famine

This is the most important function of irrigation inthis countly. Though most parts of India receiveconsiderable rainf all, it is mostly seasonal and oftenerratic. The subsistence level of the farmers beingvery low, and their surplus wealt~ even i? no~malyears practically nil, failures of raInS even 111 a smgleyear would lead to large scale distress ~nd mor~ t~anone successive failures to acute famll1e causing lm-

poverishment and starvation in the affected area, butfor the protection offered by artificial irrigation.

(ii) Improvement in Yield and Value of the Crops

The yield of practically all crops increases by arational and scientific and assured application of water . The optimum quantity of water, i.e., delta togive best results f or a certain cr o p in a certain a~eacan be d etermined experimentalIy. Any quantitylesser than or in excess of optimum red uces yield .When permanent. r egular and timely supply of ' water is assured, hybrid crops natnrally replace inferior crops to increase yield.

Almost all the lar ge irr igation systems in India are

very well planned, f inancially sound and pay revenue tothe State. Mor e important. perhaps. is the incr ease inthe wealth and pros perity of the cultivators. With theintroduction of irrigation land value a ppreciates and it is beneficial to both the land holder and the State,8S the latter can legitimately enhance the irrigationcess on such land.

(iv) Generation of H.E. Power

On projects primarily designed for irrigation, power generation can often be obtained at comparati-vely low cost by utili sing the available head.

(v) Inland Navigation

Irrigation canals can be us~d for inland navigationto mitigate the load of transport on Road System and consumption of petroleum products.

(vi) Effect of Health

In case suitable drainage f-ystem is not pr ovided for irrigated areas, the d ir ect influence of a canal irri-gation pr o ject is to increase the sub· soil water leveland water logging in lower areas and the incidence of malaria could occur in the area. The indirect effectof reducing the risk of crop failures and increasingfood production improves the nutrition of the peopleconsid erably. This leads to increased resistance todisease.

(vii) Domestic Water Supply

In large dry areas the canals are the only sourceof water for domestic purposes. The rise in sub-soilwater level in dry area could assist in meeting dem-ands of domestic water supply by pumping the ground water.

(viii) Improvement of Communications

On all important channels and upto d istributaries,an unsurfaced driving road /service r oad is provided primarily for purpose of inspection and control. Th?seroads ar e sometimes the only motorable roads avaIla-

ble into the inter ior for essential purpose in command area. This net work of canals with r oad s improve thecommunications in r emote areas of command.

(ix) Canal Plantations

Trees are planted along banks of channels, near masonry works and . in any open land available withthe canals. They add to the timber wealth of thecountry and play their part in checking soil erosionsand keeping ecological balance in the area.

(x) Industrial Water Supply

Often the requirements of the neighbouring indus-try or the Thermal Power Stations f or cooling etc.could also bl; met with from these channels.


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P la n n in g a n d

2.1 Preliminary Surveys

. When the proposal f or extending canal irrigationlOtO a new area IS taken up for consideration, the first

steps IS

to mak e a thorough reconnaissance survey of the area. During this survey all the factors which effectirrigation development must be carefully observed and notes mad e fr om judgement and from quick measure-ments which can be taken on the spot. The follov ..•ingar e the main f actors to be considered:

(i) Spring Levels in t he Area

The s pring levels in the ar ea should be ascerta ined and noted as they have an important bearing on thedesirability of canal irrigation. If the s pring ~levels ar ealread y high, it would be a factor against though notn.ccessarily decisive to the intr oduction' of canal i rriga-tlOIl f or the following r easons:

(a) The seepage from the canal system, if cons-tructed, may r aise the water-table still further by making the area prone to waterlogging.

(b) Uncertainty of Demand: In areas where thewater-table is high, irrigation demand may beslack. At the same time, such areas may bewell adopted to development of cash cropswhich cannot be grown without irrigation.

(c ) Rise of water· table may increase the incidence

of malaria in the area and the opinion of public health authorities on this point should be obtained.

(ii) Rainfall Figures in (he Ar ea

The available rainfall d ata of the area should beobtained and studied with r es pect to the percentage of years in which the rainf all deDarf s fr om the normalduring monsoon and in winter: This will give a good idea of the likelihood of irrigation demand in thearea.

(iii) Type of Soil

The type of soil should be judged by visual inspec-tion and by enquiry. Subsequently, soil surveys should pe ~arried ou t before finalisinf,?; the scheme,

Inves t iga t ions

(iv) Topography of the Area

A canal system operates essentially by gravity flowsystem. It has to be so laid out in an a rea that allthe channels run on ridges so that they may irrigate oneither side by flow. The topography of the area may be judged keeping in view the above mentioned re-quirements. If the project is considered worth further investigations contour ed maps are prepared.

(v) Crops Already SOH,'/J in the Area

The crops grown in the area should be noted and Agriculture Department should be consulted f or exist-ing and pr o posed cropping pattern and cropping cal-endar . Water requirement of each crop should befinalised consider ing the local practice, useful rainfall,and type of soil in the area. The water demand ini-tially will depend on the crops grown/ proposed and fortnightly water requirements. The intensity of irri-

gation in the area should be assessed from records toarrive at reasonable intensity of irrigation in the area.

(vi) Extent of Existing Well and Pond Irrigation in the

Area

(a) The limited resources available in the countryshould be considered and deployed suitablywhere there is maximum need and providesthe greatest benefit. If an area has an extensivesystem of irrigation from open wells and pondswhich is sufficient f or its protection againstfailure of rains. it should naturally receive alow priority f or the introduction of canalirrigation.

(b) Since it may not be possible to meet the de-mand of irrigation during low supplies/closuresfr om the sources, i.e., river /reservoir, the pcssi- bility of conjunctive use of ground water tomeet the demand of sowing, transplant ation/maturing of crops during Jaw supplies/closureshould be examined. This will, on ncrasir nreduce the capacity of channels and s~ve inconstruction cost and encourage the optimumutilisation of available water resources. Thiswill incidently keep the rise of sub-soil water level within permissible limit and give more~ime for maintenance of distribution system,


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(vii) Quality of Cultivators and their Views of IrrigaiiQn

Intelligent, hardworking cultivators would adaptthemselves to irrigated cultivation, avail of its advant-ages and make economical, efficient use of water. Thereverse would be the case if they are otherwise. Thiscan make all the difference to the success or failure of an irrigation project.

After reconnaissance, all the information gathered should be carefully analysed. If the result indicatesfeasibility of the project, more detailed surveys and

collection of data would then be carried out.

2.2 Detailed Survey

2.2.1 In settled areas the work of detailed investi-

gations is very much facilitated with the help of re-venue records and mouza maps which are available for each village. The following statistics of area for eachvillage should be obtained from revenue records-totalarea of land, cultivated area, culturable waste, area of each crop grown in the last few yeaTs, and the areairrigated under existing arrangements from ponds and wells .. This information, will be required in comput-ing gross and culturable commanded areas and indetermining the intensity of irrigation and the area to

be irrigated.

2.2.2 Crops and Crop Calendar

After examining the records of eX\stlOg cultivated areas and the crops, the proposed cropping pattern

and crop calendar should be evolved considering theexisting soil and climatic conditions in the area inconsultation with the Agricultural Department.

Water requirement of each crop should be worked out by suitable methods like Penman's formula or bycarrying out experiments considering the type of soil,temperature, rain fall in the area, etc. Net fortnightlywater requirements are then worked out consideringeffective useful rain fall for each crop and the capacityof canal assessed. on the peak demand.

2.2.3 The village settlement maps called "Shajra"maps are prepared at the time of settlement to thescale of 1:4000. These maps show the bound ary and number of each field, location of inhabited areas,

culturable and barren land, groves, tanks and a fewother distinguishing features.

These sheets are then to be completed for topographical detail not available on them butessential for planning of an irrigation scheme. Thefirst necessity is to mark out the contours after carrying out levelling in the area. The contours should

preferably be at 0.5 m intervals. In other areas sim-ilar contoured plans to a scale of 1:15000 and a contour interval of 0.50 m will be prepared abinitio b~ usualmethods of engineering survey-ch&h~ ~ud cQ:~~wass.or

plane table a s CQnyeni~llt,

2.2.4 The trial pits/augerholes at intervals of 500

m or at suitable intervals depending on the variationof soil strata along the canal alignment should betaken upto the designed bed level. The strata metwith should be brought out alongwith the L-Section of the canal. Transmission losses should be estimated as per the strata met with in various reaches to arriveat realistic figure.

The distribution system should be economical fromconsiderations of capital investment and cost of an-nual maintenance. It should provide adequate irriga-tion facilities to the areas under the command of chan-nel. The following broad principles may be considered

for the layout of distribution system.

(i) Water should be taken directly as far as possible to the area of the command, subject to pra-tical considerations of lnaximum permissibleheight of the bank filling and cutting. Thealignment of the canals will have to be thatwhich would result in the greatest saving of

both captial and maintenance l'Osts and alsoin the loss of head and transmission losses.

In an undulating country a straight align-ment of canal for any length may not be possi-

ble as it would involve heavy filling and cuttingresulting in both heavy capital and maintenanceinvestments. The economically shortest route

is to be kept in view which can be attained byan alignment (which could be arrived at bytrial and error) between:

(a) A line strictly following the falling con-tour line where balanced filling and exca-vation is feasible.

(b) A straight line from head to tail in arolling country involves heavy filling and deep cutting. In a flat country saving inloss of head throughthe straight alignmentis an important factor. The transmissionlosses assume more significance in case of unlined canals than in case of lined canals.

(ii) An irrigation channel must run on a water shed or ridge and where that is not possible itshould run as near a r idge as possible. Inridge position the canal will be able to com-mand on both sides and will avoid interferingwith natural drainage. Where the main canalsare not aligned along the ridge, branch/distributaries could be aligned along subsidiaryridges which the canal would cross during itscourse.

(iii) The alignment of an irrigation channel/canal

should p~ ~entral in its comwano all far a~


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possible and the length of the off-take canals

should be minimum.

Water should be carried in bulk as far as possible and whenever the canal bifurcates thetotal wetted perimeter increases and results

in greater losses. ,Generally, the cost ?f onecanal is not proportIOnate to the capaCity ~sthe two channels are costlier than one for theIr combined capacities. Canals with a bigger capacity can be. designed with a fla.tter slopeand will be ultImately beneficIal III a flat

country.

The drainage line should not be blocked asthe canal itself may get damaged and result Inflooding and water logging of t~e surroun.dingareas. When irrigation channel IS on t~e ndge!

water shed interference with drainage IS avoId-ed but if it is not located on ridge and it h~~ tocross various drainage lines adequate provlSlonto pass the drainage water safely across the

channel is necessary.

In addition to the above, the foll?wing practi-cal points should also be consIdered whtlefixing the alignment of canals.

Proper location of cross drainage works ismost important as the cost of C.D. Worksin a canal system is a expensive item. Thecrossing should be located at places wherethe waterway is sufficient, the catchmentis minimum, the foundations are good and the material of construction is available

nearby.

The alignment of canal sho.uld ~void difficult country, i.e., one haVIng ndges,rocky, sandy and alkaline strata and alsor eligious centres such as mosques, templesand burial grounds.

When a canal passes near a village or animportant town, it sho~l~ pass on t helower side even at addltlOnal cost. Incase it passes' on the high~r side of t~e

town it should be at a conSIderable dIS-tance and may be lined as the seepagefrom canal may create difficulties.

Irrigation channels are generally alig~ed with re-ference to the contours of the country IIIone of the

following different ways:

(i) as contour channels,

(ii) as Ridge channels, and

(iii) as side-slope channels.

A contour channel is c arried on an alignment

which conforms generally to that of the contours of the country traversed by giving, such slope along itslength as is necessary to produce the required velocityof flow. As the line of flow of surface drainage is atright angles to the ground contours such a channelcuts across th~ natural drainage lines of the countrytraversed. Such an alignment does not imply anexact conformation with the contours of the naturalground, as it is usual, when traversing undulatingcountry which displays any marked natural featuresto shorten the line by crossing ridges in deeper cuttingand valleys in higher bank than the general average.Thus in such country a contour channel would be of short~r length than the corresponding falling contour laid out along the ground surface without taking anyshort cuts.

A ridge channel is one alignment along any naturalwatershed. There will clearly be no drainage crossingsuch a line. The watershed bc:ing the highest ridge inthe doabs, water from a channel on the watershed canflow by gravity to fIelds on either side, directly or through some otber irrigation channels.

The main canal has to take-off from the river, thelowest point in the cross-section, and it must mountthe ridge Or the highest point in the area in as short adistance as possible. This is possible because the canalrequires much less bed slope than is usually availablein the country near its head reaches. It is within thisreach that all the important cross drainage works onthe canal have to be constructed. In its head reaches acanal is also generally in heavy cutting and this com-

bined with the C.D. works makes this portion of thecanal very expensive. The alignment in this reach is to be determined by studying the various alternatives,and comparing the advantages and disadvantages and the costs of each.

2.3.3 Side Slope Channels

A side stope channel is one alignment at right anglesto the contours of the country traversed and not on awatershed or valley line. ~uch a line would be parallel

to natur~l r~n-off of.dramage and thus such an align-ment aVOIds mterceptwg cross-drainage.

2.4 The main aim of these arrangements of thelayout of a distribution system is to secure in the mosteconomical way effective water distribution combined w~th adeq~ate ,:ommand of the area to be irrigated WIth as little mterference as possible with naturaldrain~ge. The above statement of ai~s at once suggestan ahgnment ~tong any watershed WIthin the irrigablearea as secunng command of all the ground upto thenext valleys on either side of the alignment without


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any interf er ence with drainage and it may be tak en asaXIomatic that the watersheds laying in any ir r igated tract should be occupied by distribution channels un-

less there are strong reasons against such an arrange-ment. Side slope channels haVe the advantage of notintercepting cross-drainage but their course mustfollow the shortest route to the nearest valley and suchchannel will be along a line of steepest possible slopeexcept in very flat areas. Only the smaller of the dis-trihutary channels should be so located. Contour channels are carried on slopes, the main watersheds of which are not commanded . Such channels with minor exceptions only irrigate on one side of them from theupper boundaries of the irrigated area.

One of the 3 ways of aligning the canal may beadopted but there may be situations in which it may be necessary to deviate the canal off the adopted

course for short reaches. For example, the watershed ·or the contour might tak e a sharp loo p between. some

points, the alignment may cut acr oss "a badi", or alar ge number of drainages may cr oss th.e a1Jgnment.In the case of water shed or contour taklllg a sharploop, by aligning the canals str a~ght consid erable l~ngthcan be saved. It will, however , Inter cept the dr alllageof the pock et of land be~ween .the wa~ersh~d and thecanal, in such reaches. ThIs dr amage Will either have

to be passed across the canal by suitable C.D. wor k or the feasibility of diversion to adjacent catchmentcould be done to avoid the C.D. work . The alignment

of canal may have to be diverted so as to bye- pa~stowns or vi'llages located on them. Number of cr oss-drainage works may b(" reduced by shifting alignmentas far as economically and technically feasible.

Curves in unlined canals shall be as gentle as possible as they lead to disturbance of flow and atendency to silt on the inside and to scour on the out-side of the curve. The curves are usually, simple cir-cular curves. At the velocities, permissible in unlined channels, the super-elevation of water surface is verysmall. The situation will be different in lined channelswhere higher vel0cities are permissible. In any reach

of a lined channel, with hy per -critical velocity, cur vesare best avoided ; in case they have got to be pr ovided ,the water surface pr ofile must be very carefully work ed out.

As per I.S.I. r ecommend ations, r adii of cur vesshould be usually 10 to 15 times the bed width sub jectto minimum given in Table 1.

Discha rge

m3{ sec

Radii Min.

m

Di scharge

m3{ sec

Radii Min.

m

80&above

Below 80 t o 30

Below 30 to 15

Below 15 to 3Below 3 to 0.3

Less than 0.3

1500

1000

600

300

150

90

280 & above

Below 280 t o 200

Below 200 t o 140

Below 140 to 70

Below 70 to 40

900

760

600

450

300

The above radii are not applicable to unlined canals located in hilly reaches and in highly per -

meable soil.

On lined canals where the above radii cannot be provid ed, pr o per super-elevation shall be

provided.

For navigation channels further modification may have to be made.


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From the headworks where water enters the maincanal to the outlet where it enters the watercoursethere are continuous losses which have to be accounted for in the designs. These losses are quite considerableroughly forming 25 to 50 percent of the water di-verted . There are losses in the water course and on thefield also, but they are taken to be c overed in theoutlet discharge factor .

The losses in the canals take place on account of two causes: (1) e vaporation and (2) seepage. Theev.aporation losses are usually a small proportion of the total losses in earthern channels and are generallyneglected. The seepage loss is influenced by the natureand porosity of the soil; the depth, turbidity and temperature of water; the age and shape of the canalsection; and the position of the ground water level.The seepage losses in unlined channels as suggested byEtcheverry and Harding are given in Table II.

Seepage LossCumecs/million

m20fwetted

Perimeter

Impervious clay loam

Medium day loam under laid with hard pan at depth of notover 0.60 to 0.90m below level

Ordinary clay loam silt soil or lavash loam

Gravelly or sandy clay loam,cemented gravel, sand and clay

Sandy loam

Loose sandy soils

Gravelly sandy soils

Porous gravelly soil

Very gravelly soil

2.70 to 3.60

3.60 to 5.20

5.20 to 6.10

7.00 to 8.80

8.80 to 10.70

10.70 to 21.30

In the case o flined canals seepage losses may beassumed as 0.60 cumec/million m2 of wetted perimeter .

A capacity and design s tatement along with com-mand statement should be drawn up for each channelto enable its L-Section to be prepared. Specimen formsfor the above statements are given in Plates 1 and 2.

For this purpose the locations of outlets and the boundaries of areas to be irrigated by each outletshould be marked on the contoured survey plan of the

area showing the alignment of the channel and itsirrigation boundary. The irrigation boundaries usuallyfollow the drainage lines between two ridges. In mark-mg the boundaries of irrigated areas, the folloWing points should be kept in vIew:

(i) The area allotted to each outlet should notrequire more than 0.09 cumecs or less than0.03 cumecs.

(ii) The length of main water course should notexceed 3 km.

(iii) Water course should not be required to crossnatural drainages.

(iv) The crossing of national highways and roadsshould be aVOIded as far as pOSsible.

The disadvantages of large sized outlets are:

(i) Cultivator s find it difficult to manage or main-tain the field channel.

(ii) Disputes arise due to greater number pf share-holders on one ou tIet.

(iii) 'Warabandi' troubles arise particularly for shareholders of small holdings.

The disadvantages of small sized outlets are:

(i) There is greater loss of water by absorption.~I: outlet With 0.015 cumecs discharge mayIrngate only If3rd the area irrigated by anoutlet of 0.03 cumecs.

(ii) The cost is comp'aratively mOre owing to thegrea ter number of outlets, V. R. Culverts an d W.C. Culverts r equired.

(iii) Low.v.elocity in water course causes silting upreq l.lIr1I1gfrequent clearance.

(il') G:eater number of outlets cause trouble in dis-tnbutJOn of water and regime of the channel.

Havin.g .marked the boundaries of the areas thatcould be.lrnga~ed by :a~h o~tlet, the next step is tofix .the. 1l1tenslty of Irngatl.on: The intensity of irri-gatIOn IS go~e~ne~ by the eXlst1l1g protection by welland pond lrf1gatl~n, types of crops sown or likelyto develop after. lr:troduction of canal irrigation

perfor.~ance of eXlstmg channels in similar areas and quantItIes of water available,

. ." Duty" of .can.al water can be defined as the arealfflgated by unIt dIscharge which in metric units wi l l


14/57

mean the number of hectares irrigated by 1 cumec for the specific number of days cal~ed the base period for the duty. Duty for a channclIs usually calculated on

the head discharge. Duty based on d Ischarge passed through the outlet and thus excluding all losses in thecanal ~system, is called the outlet discharge factor.

The commanded and uncommanded area and the

water levels required at the head of water courses or field channels and supply channels should be marked out. This is more a process of trial and error.

A good deal of judgement which can-be acquired

by practice is required in fixing the water level at thehead of water course and marking c~)lnman.de~ areaswhich will neither pitch the F.S.L. III an IrngatlOn

channel unnecessarily high in an attempt to command isolated high patches, nor lowe:: it too much at thecost of irrigation on which the whole SUCl'essof the pr o ject depends. It has to be Iemem ber ed that suchhigh patches are levelled up IIIcourse of t Ime by the

cultivator s themselves.

For determining the F.S.L. i n a distri butary

channel, the w ater levels r equir ed . at thc head of watcr

courses all along the length ~f channel s.hould be plotted on the ~-~ection. on whIch G.L. sprmg levelsand other f ield Inf ormatIOn have already been plotted.The F.S. Line should thus be so marked at the pre-determined slo pe, as to give a good aver age workmghead into the water courses. This procedu.rc .r ead tly

determines the location of falls ~m the d~str~blltarychannel as well. The F.S.Ls. d etermmed at dlstr~butar y

heads should similarly be plotted on the L~SectlOns ?f branch and main canals and then ~.S. Imes fixed IIIthe same manner as f or (1Jstnbutanes. If ~owever,the consid eration of balancmg de pth enables hIgher fullsupply to be f ixed, it may have to be done. Usually,.it is f ound sufficient to work at the command atoff tak ing channels u pto the f ust fall, f or the pur poseof fixing' F.S.Ls. in the main and b ranch canals. But,when there is a reverse slope Jl1 the country, the F.S.L.at the head should be dete!mincd after consid ering the

command fr om head to tatl.

In working out the F.S.Ls. in channels, the

following working head s ar e usually allowed:

Head over fleld

Slope in water cour se

Min. working head from major distributary to a minor

Min. wor king head at outlet

Min. working head from branch to branch or to ma jor distributary

Min. workir g head fr om main canal

0.0751 '0

1 in 5000

0.30m

0.15m

O.SOm

0.60m

A contr ol point on a r egulating bridge should be provided below the off take. A minimum working head of 0075m should be allowed at these points.

2.9 Plotting of L-Section

(a ) It is essential that an L-Section of channelshowing all salient information o bser ved in the field such as natural surface levels and sub-soil water levelsfull supply levels, canal bed levels, water surface slopes:

bed WIdths, free board, broad details of hydraulic d ataof ou.tlets, regulators, bridges, drainage cr ossings,offtaklllg channels etc. and nature of soil where thecanal is passing through b~ giving test pit or auger hole data at about 500 m inter vals be prepared . For the L-Section a longitudinal scale of about 1:10,000 to1:20,000 and vertical scale of about 1:100 are recom-mend ed. A specimen L-Section of canal is shown in

Plate No.3.

(b) While plotting L-Section d esigned d ischarge bed gradient, bed widlh, full supply d e pth should beindicated. Designed discharge sholl1d account for off take channel dischar ges and losses in canal. Water levels should be assessed af ter consid ering head lossesin various structur es, i.e., regulators, f alls, br idges,cn. wor ks etc.

The f ollowing main ty pes of str uctur es will berequired on a canal:

(ii) Regulating structures

(iii) Communication structur es/ bridges.

The r ust two types of structur es ar e mor e essentialfor the safety and maintenance of the canals and areusually provid ed on all canals ir r espective of itsca pacity. The r egulating structur es could be usef ul inequitable distribution of water in the command ar ea.Communication wor ks are necessary to pr ovide inter-communication in the command ar ea lying on either sid e.

(i) Cross Drainage Wor k s: Generally the alignmentof th~ .canals crosses the natur al drainage valleys and

provIsIOn has to. be made to. tak e the d r ains safelyacross the canal WIthout damagll1g it. The usual kind of cross dr ainage works are:

(1) Su per passage

(2) Drainage syphon

(3) Canal Syphon

(4) Level crossing

(5) Aqueduct.


15/57

PLANNING AND INVESTIGATIONS

In effect there are three ways of crossing of thedrainage water and the canal.

To pass the drainage over the irrigationchannel the bed level and the water level of the drai~ is higher than the canal. This type

is named as a super passage.

To pass the drainage into the irrigation channelso that the drainage and irrigation water mixup. This type is called a level crossing.

To pass the drainage under the canal. Thistype is called a drainage syphon or a syphonaqueduct. The full supply level, the bed level

of canal and the H FL and bed l evel of thedrainage reach for the most suitable alignmentof canal will determine the type of structures.The particular type to be adopted cculd further be determined by the magnitude of theflood discharge of the nallah and thc designdischarge of the canal.

(ii) Regulating Sauctures : These structures arerequired to maintain the level and the discharges atthe designed figur e. Some of the works may be auto-matic and some require regulation, establishment and manipUlation. The Control could be from upstreamor by downstream, i.e., "Demand Management".

(b) Cross regulator

(c) Head regulator of distributaries/minors

(d) Escapes

(e ) Outlets for water courses

(f) Silt ejectors.

Falls are provided in a canal when the fall of theterrain is more than that of the canal and the water level

becomes in excess of the level required in the canal toreduce maximum permissible velocity and earth work.

This structure dissipates the excess energy and the

filling reach is minimised.

Cross regulators are required to maintain the fullsupply level in the canal. These are provided at inter-vals across the canal and below major off-take pointsso that when the canal is running at less than fullsupply discharge water can be raised to feed the off-take canal/channel to take its authorised discharge at

design full or part supply levels.

Head regulators are provided for regulating thedischarges to feed the distributaries.

Escapes are provided for discharging the excesswater out of the canal during periods of low demand

in t he command. They are generally provided up-stream of cross regula tors near a natural valley so asto release the water from the canal and avoid floodingin the command area during flood /rainy season.

Outlets for water courses are provided from minorsand distributaries according to the demand in thlZcommand. Canals taking off f r om the head worksgenerally carry silt along with water . The silt load and size of silt requires critical examination. In casesilt is of coarse or medium coarse, this gets deposited in the canal and reduces its capacity. Ivfedium coarseand coar se silt is also harmful for fleld s i n case thisfl11ds its way to the fields through the water courses.Power channels also need to consid er the safe silt size

permitted for the turbines. Silt ejectors are provided

in the head reach so as to remove the silt to permissible limits to save the canal from silting and field s!irrigated areas from losing the fertility. Silt ejectorsare provided in power c\laJ1llels to eject the silt fromwater to save turbines from getting damaged.

(iii) Communication Works: These are mostly road bridges and are provided for all existing and futureanticipated roads to provide communications facilityin the command area. In addition to this some moreroad bridges are a lso provided so as to providecommunication facilities to towns and villages. Theseare generally provided at interval of about 6 km. Butin case of distributaries, road bridges are generally

provided at intervals of 2 to 3 km depending

on local cond itions to f acilitate the movement of material and people.


16/57

------

sL. R.D. OF AN OFF CRITICAL DIST ANCE FPOlI LOSS OF NEAD DEPTH

NO. TAKE OR PO IN T I N N .S . CRITICAL FIELD

OUTLET POINT T O

HE AD OF

OUTLET

--- _ .. _ _ . ------I 2 3 4 5 6

--1------_. _ -_ .

PLATE ~.u. I

COMMAND ST ATEMENT

OF

WATEf lLEV EL

AT HEAD OFOUTl . E T

(COLUMN3~·5. j·

61

W O R K IN G

HEADtQOLUMN $-71

. _ - - - - - - - - - - - - - - - - - _ . \I

- -------_._-------------

.Q.APA CIT Y a DESIGN STATEMENT. . Q E

."._-~

------SL. B E L O W K M . R .O.OF AN G RO SS G RO SS CU LTURAL OU TLET OULEr LOSSES TOTAL TOTAL

NO. OFF TAKE AREAlaA.1 C""''''''''''EO COMM A NDED ARE A TO Bf . IRR IGATED

OISCHARGE DISCH AR GE IN REACH l.OSSES DISCHARGE... £HA NNE L DIMENSIO NS

OR OUTLET IHECT.1 AREA AREA F ACTOR IN CU MECS _.

IG .C.A.I ICC.A.1 RABI SUGAR RI CE FULL FULL DESIGN LA CEy'S', ,

tHECT.1 IHECT.1 IHEcn B E D SlO N: BED WIDTH SU P f' LY S UP PL Y BED LEVE L D"C HA f lGt: OR n H T. OF BAN K

DEPTH LEVEL --_ ... -I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19

-- "

-_._--,

. -PL ATE NO.2: CAP ACITY & DESIGN S1' TEMENT

· - - - - - - - - - - - - · · - - - - - l

VELOGI;~--r -" -- ._- -"-

IN M lSEC. II R EMAlll(S

- 2 0 - t - - - - - - -


17/57

(')G > !"'

. . , (')

" '~ " ! n c 3:0 !" -; QlZ C r r -; »l; z Z z0

' "" ' r G > ~Z" ' '"~ < z'"

. . .. . .r

' "'0 ~3 .z.92.15 92.65 1·135

150 92·59 1.435

300 92·48 1.255

450

600

750

00

10:50

1200

1350 91.59

1500

1650 91.72

1800 91.4El 91.16

1950 91.41 9/.10 91.50

2100 91.15 91.04 91.54

2250 92.85

w-OUI

00g

'" Cl (') . . ,

!' " " (:) »(') is~

r » G > r c:

" ' " r '" '" »

' " ' " -;

' " 0"

1\

CS

SW

S

OL

1

CS-

\/ I

3 l- iEs I I/ . . - I I

7Acl

RS I4

II

8

S-

~ ES

r RX

C'l;U VRS

l>0i T iz CS-i

-" I 'T1 UI()()():I:;Ui- x~0in~in:'n~~~

al : TJ ~

I 'T1

Z()

m(J)

r

r I

(j)

()~

l> -l

Zo~Z

o'TI

: s :l>

Z


18/57

D es i g n o f Un l in e d C an a ls

The flow of water s pecially in earthern channels pr esents a complicated pro blem, which cannot besolved with mathematical precision. The unlined channel is an open channel excavated and shaped tothe requir ed cr oss-section in natural earth or fill,without s pecial treatment to the sub-grad e. Wherea channel is constructed partly or entirely in fill or innatural earth of unstable char acter istics it may

become necessar y to prevent seepage and percolation by com pacting the sub-gr ad e.

The motive f orce off lowing water in o pen channelsis entir ely d ue to the slopes of the channel. The water flows f rom higher to a lower point by. virtue of gr avity. The flowing water has to over come ther esistance in the channel caused by numer ous factorssuch as surface tension, atmos pheric pr essur e at surfaceand f riction at side and bottom of the channel. Thef rietien on the channel section cle pends on the

material formir .g the wetted perimeter " the irregularityof the wetted per imeter , var iation in the size and sha pe of the cr oss-sections, cur ves, weeds and variouskind s of gr owth, scouring, silting, sus pend ed materialand the bed load. In pr actice the r esultant of all thesef or ces is expr essed by a coefficient of r oughness deter -mined by ex periments.

3.2 Flow Characteristics of Open Channels

The dischar ge passing in an open channel IS ex- pressed by the continuity f or mula:

Q = Ax V

Q = Dischar ge in cumecs A = Cross-sectional area in sq m

V = Mea~ velocity of flow i n m/sec

The mean velocity is given by t he Chezy's formula:

V = C V R.S

R = Hydr aulic mean radius in m

8 = Sine of slope of water surface

This is a pr actical and fundamental formula f or the un!form flow of water in open channels and it isthe ?asls of all modern velocity formulae. Since co-~fficler:rt 'c' r e presents the r etarding influences variousInvestIgator s have d etermined its value on the basis of expernnents and o bser ved data. The most widelyused values of 'c' ar e given by : .

(a) Kutt er' s For mula

23 t. 0.00155 1

, --S -+ N C=--------

. 1+ (23+ _0.0~155 ) :

The values of ' N ' as r ecommend ed by I.S.I. ar egiven in Ta ble Ill.

For some conditions value of 'C' fr om Kutter'sformula ar e given in Plates 4 and 5.

(b) Manning's Formula

1V = -- f i.2/3 81 / 2

II

The Chczy's 'C' r .nJ Manning's 'n' ar e related bythe Equation:

1C =-~R1/6

n

In normal r anges of slo pes and hydr aulic meanradius the values of Manning's 'n' and Kutter's "N"generally seem to be numerically ver y close f or practi-cal purposes.

87

1+~V~


19/57


20/57

D =Depth C'f flo w i n metres

m =

Critical velocity ratio

Mr . R .G. Kennedy mad e his o bservations on t heU pper Bar i Doa b Canal system, one of the oldest in.

the Punja b. On this systeI~1 he selected a n~mber otsites on various channels which had not reqUIred anysilt clear ance for the last thirty years and were t husconsidered stable. By plotting his observations .of velocity and depth on sta ble reaches, Kennedy obtam-

ed his well known equation.

Vo = 0.55 D 00f 4

This equation is applica ble to channels. flow~ng insandy silt of the same gr ade as that w]:uch eXists onthe Upper Bari Doa b canal system on whIc.h the obser-vations wer e made. K enned y later r ecogmsed that thegrad e of silt played a par t in this rela~ionship and intr od uced another factor in the equatIOn, called byhim as "the cr itical velocity r atio" and given thesym bol ' m' . The equation was then written as

V = 0.84 111 D O ' 6 4

Sands c()ar ser than the standar d wer e assigned valuesof m f r om 1.1 to 1.2 and those finer fr om 0.9 t o 0.8.K ennedy mad e no corr elation between wate~ surfaceslope of regime chanmls and the mean. velOCity. or thever tical depth. He r elied on Kutter s equatIOn to

give slopes to the channels.

The values of Va f or dif f er ent depths are shown in

Plate No.7

The f ollowing equations were obtained by obser-

vations at other places:

V = 0.391 D O ' 55 God avar i Delta

V = 0.53 D O ' 6E K rishna Western Delta

V = 0.567 D O ' 57 Lower Chena b Canal

V =0.283 D O ' 73 Egy ptian Canals

A general f eature of these f or mulae ~as that. thevalue of 'c' was pr o por tional to the SIze of the bed mater ial.

In actual pr actice, the design can be. carried . outwith the help of Garret's d iagrams whIch p;ovlde a

hical solution of K ennedy's and Kutter s e qua-gtr a ps Garr ets diagrams are given in Plate Nos. 8 and

Ion. .' f 1 1 •9. The pr ocedur e f or theIr use IS as 0 ows .

(i ) Follow the given discharge cu.r ve till it meetsthe given ho~izontal ~lope Ime a nd mark off

their point of IDter-sectlOns.

(ii) Draw a ver tical line thr ough the point of inter section. This will inter sect several bed

width cur ves.

(ifi) Choose the point of inter section of the ver ticalline on any bed wid th and read the corres pond-ing value of water depth (D), and critical velo-city Va' on the right hand ordinate.

(iv) Calculate the actual velocity of flow (V) for the chosen bed width and the correspondingvalue of the water depth.

(v) Determine the critical velocity ratio 'm'

( :: ) taking V as calculated and Va as r ead.

(vi) If the value of VIVo is not the same as given,

r e peat the procedure with other values of the bed width till the C.V.R . approximates to the

gi ven val ue.

These d iagrams ar e d rawn for side slo pes of t:l onthe ass~lmption that irrigation channels after sometime acquire this slope due to silt d e position on the ber ms, irres pective of the initial side slo pe pr ovid ed.These cur ves are d rawn f or N =0.0225. They canalso be utilized f or any value of N with the help of amonogr am provided at the to p of the curves. Whenusing for a ny other value of N, the ver tical line dr awnat the intersection of t he discharge and slo pe line hasto be shifted, either to the left or to the r ight sid e to theextent given in t he monogram. Further procedure f or

determining bed width and depth r emains unaltered .

Lacey used Kennedy's data and substituted 'F'"Lacey's silt factor" for 'm' and found that '1' wor ked out to be square r oot of the critic81 velocity ratio

(:: ) for velocities not exceeding mor e than Im/sec

and if the hydraulic mean r adius 'R' is substituted f or 'D' the variation in ex ponent as found on the d iffer -ent canal system d isappear s. The concept of 'R' in

place of' D' by Lacey, accor ding to him, is becauseeddies which keep the silt in sus pension ar e gener ated

fr om bed and sides both normal to the surfaces of gene-r ation and not from bed only as stated by K enned y.He,therefore, assumed that hyd raulic mean rad ius (R)as variable. However, it has been obser ved that ther eis hardly any differ ence in values of R & D in wid echannels. On the basis of the above arguments Laceyderived a set of equations by plotting mean value6 of observed data.

• •. (i)

•.. (it)


21/57

A=Ar ea of the channel section in m2

V=Velocity ('·f f low in m / se c.

f=Lacey's silt factor.

Lacey's regime flow equation is

V=10.8 R 2j 3 S 1 / 3

Fr om the above equations perimeter-discharge relation:

P=4.825Y Q

.. . (iii)

(i) and ( ii ) he der ived

P is wetted per imeter in m

Q is d ischar ge in cumecs

Fr om this equation it was thus esta blished that

wetted perimeter of a channel in regime was depen-dent on the d ischarge only and was Inde pend ent of

the gr ade of silt d enoted by I' ·

Fi om these equations a number of other impor~antr elationshi ps have been o btained which are gtven

below:

f 5 / 3

S =3316Q J / ~

V=0.4382(Qj2) 1 j6

R=0.47 ( ]. y f 2

(

q 2 ) 1 / 11.35 7- .

ql/ l A=2.28 jT J 2

Silt Factor 'f'

According to Lacey, the silt f actor' f' will b~ d~- pend ent o n the aver age size of bound ary ~atenalll1the channel and its density. Its value vanes as thesquar e r oot of the mean diameter of the par ticles.

f=-1.7 6 Y n1r

m,.=aver age size o f p ar ticles in mm.

Designs based on the Lacey's equations can be

solved with the help of graphs in plates 10, 11,12and 13 r e presenting gr a phically the equations.

3.4 Selection of Method of Design

Fr om the designer's view point, the whole of Indiacan broadly be divid ed into two regions, the northernstates of I ndia comprising of the Punja b, Haryana,V.P., Bihar , West Bengal, Rajasthan and some partsof M.P. where canals d raw their supplies from riverscar rying heavily sediment laden water . These canalscarry sediment similar to that forming their bed and

bank s. On the other hand, the canals in South India

though not d evoid of sediment, carry much lesser sediment and the boundary mater ial of canal section

is dissimilar to the sediment in trans port. On the basis of above dissimilarity the f ollowing practices of design are recommended:

(i ) For channels taking off from reservoirs carry-ing silt free water and flowing through hard soils or disintegrated or fresh rock, it appearsquite desir a ble from the point of view of eco-nomy to design the channel for as high avelocity as the soil can withstand withouterosion, consistent with the slope av~ilablefrom the command point of view and econo-mies of the channel section. Too steep a slo peshould normally be avoided . Lacey's designis generally not applicable to design of suchchannels. The permissible velocity should

first be fixed and the channel section should be determined from Chezy's f ormula withKutter's value of C & N. The K ennedy or Garrets' diagr ams may be used to f acilitatedesigns and avoid calculations by trial and error method.

Different sections are possible d e pending. upon the choice of depth. The channel section

should be dee p and narr ow particular ly f or small channels lik e d istributar ies and minors.Pr actical bed width-d e pth r atios as given in para 3 5 may be used f or gener al guid ance.Departure may however, be mad e where f ound necessary to provid e shallow and wid e sectionto avoid cutting in hard soil below the ground .

The cr iter ia of balancing d epth may not bed esir able to be ad her ed to in such cases.

(ii) For the canals carrying heavily sediment lad enwater the d esign pr actice ar e mostly based onthe Lacey's and Kenned y's f ormula. Lacey'smethod of design should be used for design of new channels flowing through alluvial soils.Gr eatest car e should be exccr ciscd in selectingthe value of ' f'. The section may then bedetermined either by calculations as illustr ated in the example in Appendix-II or read fr omLacey's diagram. It should be examined tosee that the mean velocity is neither too highnor too low f or the type of the soil along thealignment of the channels. If necessary, the

value of 'I' may be corr elated to the K ennedy'sC V . R. Lacey's d esign cannot, however , beused f or silt bearing channels car r ying lowd ischarges, the limit of which is given by thestraight line on the left sid e of Plate-9 beyond which the discharge cur ves ar e discontinued.In such cases water surf ace slo pe may bework ed fr om Lacey's equations and dimensionsdetermined fr om Kutter's formula. Thismethod is also usually ad o pted f or d esign of channels with low silt f actor in cohesivesoils.


22/57

Wi) In case of existing channels requiring remodel-

. ling which have not been originally designed with Lacey's equation, it will not generally befound convenient and economical to adoptLacey's design. Lacey-cum-Kutter or Kennedy-cum-Kutter formula may be used.

3.5 Bed Width-Depth Ratio

Problem of selecting a section often arises in caseof channels or reaches of channels in which morethan one water surface slope can be adopted withoutaffecting the command. This results in more thanone section with different bed-width-depth ratios for the same discharge, value of n and critical velocityratio as may be seen from the Table IV.

TABLE IV

Q n CVR Slope Bed F.S.

(Cumecs) per width Depth

1000 m m

28317 0.0225 Lo 0.22 9.75 2.5328.317 0.0225 1.0 0.20 12.04 2.30

28.317 0.0225 1.0 0.18 16.15 1.98

28.317 0.0225 1.0 0.16 28.96 1.42

The same difficulty has been experienced in chan-nels taking off from reservoirs and carryil~g relativelysilt free water. The CVR is not the dommant factor in such cases and the channel· may be design~d for

permissible velocity which the soil can stand without

scouring.

According to Ellis the best channel section for thesame cross-section area and slope, posses. water atmaximum velocity with greatest hydrau!Jc !!1eanradius. For any trapezoidal channel of fixed se.ctlOnalarea (A), if ',' is the ratio of horizontal to vertical. of the side slopes and '8' is the length of th~ two SIdeslopes. per unit depth which equals 2 V ,- + 1 and 'M' is the ratio of bed width to depth.

.• jM", .;-Hydraulic Mean Radius (R) = 'V M'!- S v A

and it is maximum when M =S - 2,

Accordingly for a channel of side slope t : 1, for the best discharging section, the value of M works out

t o be 1.236 or say M= H·For least absorption, M works out to be .4. Ell,is also

stated that in case of all sizes of.cha.nnels m whIch t~erelationship of velocity to ?ept.h .ISgiven by Kennedy sequations, the absorption IS mmlInum for val!les of M between 1.5 and 3.2. For val~es f M varyIng from1.2 to 5 the loss due to absorptIOn IS never more than

5 per cent in excess of minimum.

The experience of the working of irrigatio~ chan-nels in alluvial soil has however, shown. the eXistenceof certain bed-width-depth ratio dependmg upon the

discharge or in other words size of channel. TheKennedy depth formula gives maximum depth thatcan be allowed in an earthen open channel. As for example, a channel situated in a soil which can stand mean scouring velocity of 1 m/sec. cannot have fullsupply depths of more than 2.56 metres as may be seenfrom Plate No.7. This however, has no relationshipwith t he shape of channel i.e. bed-width-depth ratio.Whenever therefore, there is a free choice for selectingdimensions of bed width and depth the ratios whichmay be obtained from Plate No. 14 may generally beused for guidance.

3.6 Most Efficient Cross-Section

Considering purely from the stand point of hydr-aulics of a channel, the most efficient cross sections

is the one which with a given slope and area has themaximum carrying capacity. Chezy's formula indi-cates that for a given water surface slope, the velocityand consequently, the discharging capacity of thesection is maximum when the hydraulic mean radius(R) is maximum. The lraximum R is given by thecircular section. Since channel in earth have usuallytrapezoidal section, maximum R i s given by half hexagonal described about the semi circle with itscentre at the water surface. Such a section however,requires great depths for larger discharges. 1hevelocity induced in such section may also become sogreat as to cause erosion of the sides and scour in the bed of the channel. The non-scouring mean velocitiesas recommended by various authorities includingCWPRS, Pune are given below:

(1) Very light, loose sand toaverage sandy soil. 0.3 to 0.6 mfsec.

(2) Sandy loam, black cottonsoil & similar soil. 0.6 to 0.9 m/sec.

(3) Ordinary soils. 0.6 to 0.9 m/sec.

(4) Firm loam, clay loam,alluv ial soil, soft clay and murum . 0.9 to 1.1 m/sec.

(5) Hard clay or grit. 1.0 to 1.5 m/sec.

(6) Gravel and shingle. 1.5 to 1.8 m/sec.

(7) Cemented gravel conglomite,hard pan. 1.8 to 2.4 m/sec.

(8) Soft rock . 1.4 to 2.4 m/sec.

(9) Hard rock. 2,4 to 3.7 m/sec.

(10) Very hard rock or cementconcrete. 4.5 to 7.6 m/sec.

3.7 Side Slopes

The side slopes to be adopted depend upon thenature of the soil in which the channel is to be eXCa-vated, depth of cutting and fheight of embankmentand shall be designed with the following conditions, in

alluvial soils.


23/57

(a) Sudden dr aw down conditio!ls f or inner slopes.

(b)· The canal running full with plenty of r ainfaIlf or outer slopes.

The minimum slo pes usually all owed arc given inTable V

]. Very light loose sand 1.5:1 t o 2:1 (cutting)

to aver age sandy soil. 2:1 to 3:1 (embankment)

2. Sandy loam, loamy 1:1 to 15:1 (cutting)soil and similar soils

2:1 (embankment)

3. Sandy soil or gr avel. 1: 1 to 2:1

4. Mur um, har d soil 0.75:1 to 1.5:1

etc.

5 . R ock 0.25:1 to 0.5: 1

The slopes given above are suita ble for averageheight upto 3 metres. For greater heights, it is pre-fer a ble to provide ledges 1.5 to 3 111wid e at inter-vals of 3 m instead of flattening the slo pes. Thelatter method is, however , slightly economical.

In aIluvial and sandy soils t be side slopes in cuttinggenrally assume side slo pes of t : 1 on silting up, i ncourse of time. This slo pe is ther efore, assumed in

d esigning the section f or com putation of hyd r aulicmean radius, ar ea and perimeter even though in ex-ecution actually flatter slopes are ad o pted .

In hard clays and rocky soils, however, it is n otnecessary to follow the a bove practice. The side slopeactually pr ovid ed in excavation may be taken into ac-count for working out the sec:tional area of channel.

3.8 Fr ee Boar d

Free boar d in gener al will be gover ned by consider-ation of the f ollowing aspects:

(i) Soil Char acter istics.

(ii) Size of canal and its locations.

(iii) Hydraulic gradient.(iv ) Water surface fluctuations.

(v ) Per colation.

(v i) Ser vice road r equirements.

According to U.S. Bureau of Reclamation practicesfree board may be determined by the f ormula:

F= 1 X J C.1J 1.812 \j

wher e, F= Fr ee board in metres.C= Coef f icient.

1)= Depth of water in canal in metr es.

The coefficient 'c' var ies linearly fr om 1. 5 wher ethe canal capacity is 0.7 cumecs to 2.5 f or canal of 85cumecs or mor e. However , gr eater f r ee board s and bank heights than those within these r ane:es may beused in exce ptional ci rcumstances. '"

As per I.S.I. reco'1lmend ations a minimum free board of 0.50 m for dischar ges less than 10 cumecsand 0.75 m for dischar ges gr eater tban 10 cumecs is to

be pr ovided. The f r ee board shall be measured fromthe F.S.L. to t be level of the to p of bank. The heightof dowel porti


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(c ) To recede the banks away from the direct

action of water to pr event breaches.

(d) To provide a SCO pe f or future widening of canal.

(e) To provide space for borrowing earth duringconstruction at times o f necessity and later onf or maintenance when the berms ar e formed.

(f) To br eak the f low of rain water d own the bank slope. Berms are to be provided in all cuttings,when the depth of cutting is more than 3 m.Where a canal is constructed in a d eep throughcut requiring waste banks, berms should be

provided between the canal section cut and the waste bank.

The following pr actice is recommended:(i) When the F.SL. is above G.L. but the bed

is below G.L., that is, the canal is partly in

cutting and partly in filling, ber m may bek ept at N.S.L. equal to 2D in width where,D is F.S.D.

(ii) When the F.S.L. and the C.B.L. are both

above the G.L. that is, the canal is infilling, the ber m may be kept at the F.S.L.equal to 3D in wid th.

(iii) When the F.S.L. is below G.L., that is thecanal is completely in cutting, the bermmay be k ept at the F.S.L. equal to 2D in

wid th. In em bankments, adequate berm

may be provided so as to r etain the mini-mum cover over the hydr aulic gr ad e line.

For a channel running in em bank ment. the per co-lation line thr ough the bank though actually cur ved, isassumed straight and sloping at 1:4 to 1:6 gr adientdepending upon the bank material. It is taken for or dinary loamy soil as 1:6, aver age clayey soil 1:5 and good clayey soil 1:4. A soil having hydr aulic gr ad ientflatter than 1:6 is not suita ble f or canal bank s. Whenthe height of bank is such that percolation line inter-sects the outer slope above G.L., an extra layer of earth is put to provide a minimum cover of 0.30 m.The surface of this cover is either kept par allel to thehydr aulic gr ad ient or is in hor izontal steps.

For embankments more than 5 m height, the tr ue position of saturation line shall be worked out and

stability of slope should ,be checked as in earth d ams.

Dowel is gener ally constr ucted on the inner sid e of the bank, while in those places, wher e rains are heavy,d owels are provided on both sides of the bank to pr e-vent their cutting. Water is then led out at intervalsthr ough artificial gutters. The height of the d owel isgener ally k e pt 0.5 m with side slopes 1.5:1 and top

width as 0.5 m.

Typical cr oss-section s of u nlined canal are shown

in Plate 15.

Some ty pical exam ples of design of unlined canalar e given in A ppendix-I


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Example I

Design of Channel section by Kennedy, Chczy &Ku tter formulae.

DATA

Q =30 cumecsN =0.02

S = 1 / 8000Side Slope t : 1

DESIGN

Against Q = 30 cumecs the value of bid ratio fromcurve from plate No. 12 works out

=7.5

Let the depth of chaJ1]~el = 2.15 illb =2.15x7.5 = 16.125 m = say 16.0 mArea (l6+1.08)x2.15=36.72 m2

Pw 16+4.81 = 20.81 m

A 36 .72---=-----=176 m

Pw 20.81 .

23 + ---~---+ (~~ _ l? ..?-)

(23 +()0155 ) X ~

1+--S- ".1-1\-

1=23+-0:-020· +000155 X 8000

1+(2H-.00155 x 80(iO)~-

y' 12623+50+ 12.40

1+ (23+ 1240) x 0.021:f3-

85.40-i~5-3-2- 55.8

V C V RS -----

55.8 X V 1.76 x 1/8000558x1.33

----- =0.84 m/sec.89.4

Q A X V = 36.72 0.840 =30.84 cumecs

Critical velocity =0.55 D 0.64

= 0.58 x 2.15°'64

=0.90 m/sec

9.v·R. ;;: ~:~~ =Q.9~ O,K.

Example II

Design of channel section for 30 cumecs discharge.using Lacey's formulae.

DATA

Q = 30 cumecsf = 1.0Side slopes =t: 1

DES'GN

R 0.47 X (}9:- y f 3

047 X (+)1/3= 1.46 m

Pl V or P = 4.825 V-Q= 4.825 V 30' = 26.43 m

D =Pw = = V Pw2-6.944 RPw------- --------3-:-472"--··------

=26.43 - " .1 6 9 8 :-5 4 -6.944-->::1.46>


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MEANCOEFFICIENTS n OF ROUGHNESS

MEAN:£

RAD.R RAD -R

6z METRES .009 .010 .011 .012 .013 .015 .017 .020 .025 .030 .035 .040 METRESI1J..JII. .

0 . 025 52 45 40 35 31 25 21 17 12 9 8 6 . 025I-

% . 050 63 55 48 43 39 32 27 21 16 12 10 8 · 050

:>· 1 75 66 59 53 48 40 34 27 21 16 13 II . 1a : : .

wO. 2 87 17 69 62 57 48 41 34 26 21 17 15 . 2I l .0

NO

· 4 99 88 80 72 69 57 49 41

32 26 22 19

· 4oln0%· 6 104 93 84 77 71 53 45 25 22-0: 61 36 29 · 6

• • I III 100 90 83 77 67 59 50 40 33 28 25 Iw 2 118 107 98 90 84 74 65 56 46 39 34 30 20..0 4 124 113 104 97 90 79 71 62 51 44 39 35 4..Jl/l

10 130 119 110 102 96 85 77 67 57 50 45 40 10

30 135 124 114 107 100 90 82 73 62 55 50 46 30

t . 025 55 47 41 37 33 27 22 17 13 10 8 7 · 025

t!) . 050 66 58 51 45 40 33 28 23 17 13 II 9 · 050zw -I 78 68 61 55 50 42 35 28 21 17 14 12 · 1..JII..

· 2 90 80 70 64 59 49 42 35 27 22 18 15 · 20I-

· 3 95 85 76 70 63 54 47 39 30 24 21 17 ' 3z:> · 4 99 89 80 73 67 57 50 42 32 27 22 20 · 4a::

· 6 105 94 85 78 72 62 54 45~g 36 30 25 22 · 6. , . I n I III 100 90 83 77 67 59 50 40 3 3 28 25

,ON

2 117 106 97 89 83 73 65 56 45 38 34 30 2o!:0- 4 123 III 102 95 88 78 70 61 50 43 38 34 4. .

6 125 114 105 97 91 81 72 63 53 46 40 36w 60..0 10 128 117 108 100 93 83 75 66 55 48 43 39 10..Jl/l

30 132. 121 112. 104 98 87 79 70 60 52 48 43 30

MEANCOEFFICIENTS n OF ROUGHNESS

MEAN

RAD·R RAD·R

:i METRES .009 .010 .011 .012 .013 .015 .017 .020 .025 .030 .035 .040 METRESl-t!) . 025 57 50 43 38 34 28 23 18 13 II 9 7 · 025zL L J · 050 69 59 52 47 42 34 29 23 17 13 II 9 · 050..JII .. . , 80 70 63 56 50 42 36 30 22 17 14 12 . ,0

· 2 90 80 72 65 60 50 43 35 27I- 22 18 16 ' 2Z '3 96 86 77 70 64 54 47 39 30 25 21 18 ' 3:>Q:O · 4 100 89 81 74 67 58 50 42 33 27 23 19 · 4wo0..0 .6 104 94 85 78 72 62 54 46 36 30 25 22 ' 60--z I III 100 90 83 77 67 59 50 40 33 28 25 I0-0- 2 116 106 97 90 83 7 2 64 55 45 38 33 29 2

I; II

w 4 121 III 102 94 87 77 69 60 50 42 37 33 40..0 G 124 113 104 97 90 80 71 . 62 52 45 40 36 6..JVl 10 127 115 106 99 92 82 73 64 54 47 42 38 10

30 130 119 110 102 96 86 77 68 58 51 46 42 30

'--- -


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:r.. . . .(!)

ZIJJ..J

IJ ..

o• . . .Z:: >ffio0.011')0NOOVOz0-0-

• II, .~o

_ Ilfl

------,-,- - -

COEFFICIENTS r I OF ROUmiNESS M t : : A N

.0~101.f1~li

RAD·n

5009 .010 .011 .012 .Ol~ .015 .017 .020 _ ,..025 :(j~() MEnlES

( j C C C G G C C C C C C

5 34 29 25 22 20 17 14 II 9 7 6 5 . 025

44 38 33 30 27 22 19 16 12 9 8 7 .0558 50 44 40 36 30 26 21 16 13 II 9 . 1

' 1 '2 63 56 51 46 39 34 28 21 18 1 5 13 . 2

82 72 64 58 53 45 39 33 25 21 11 \5 . 3

89 79 71 64 59 50 44 3 7 29 23 2D 17 · 4

99 88 80 72 67 57 50 42 33 28 23 20 . 6

III \ 00 90 83 77 67 59 50 40 33 28 25 I

121 109 100 92 85 74 66 57 46 38 33 29 (·5012' / 115 106 96 91 80 71 61 50 42 37' 32 2

136 124 114 1 06 99 87 78 68 56 48 42 37 :3

142 1: 10 120 III 104 93 83 73 61 52 46 41 4

149 137 12'7 119 III 1 00 90 80 61 58 51 46 6

158 145 135 127 120 108 98 8 8 75 66 59 53 10!64 151 141 133 126 114 1( ) 4 94 81 7 ' l. 64 59 1516'7 15. ' 5145 13 7 1 30 1 18 108 98 85 75 108 62 20\ 72 160 150 142 135 123 113 103 90 81 '74 68 :30

- ---

MEAN

RAO.R

r .U ::T R E

.02

.05

.1

. 2

. 3

. 4

. 6

Q

I-50

t

3

4

G

10

i~

20

?P

- . _. - . _-. 025 40 35 30 26' 24 20 '" I 13 10 8 7 5 · m m.05 52 44 39 34 31 26 22 18 13 1\ 9 7 .05

· 1 65 57 50 44 40 : >4 29 24 18 14 12 10 · 1. 2 79 69 62 56 51 43 37 3' 0 23 "': :1' 9 16 13 · 2

· 3 87 77 . 69 62 51 " · 8 42 35 27 22 18 16 ' 3

· 4 93 83 74 67 62 53 46 38 30 25 21 18 · 4. 6 10 2 90 82 74 69 59 52 43 34 28 24 21 · 6

JO I. III 100 90 83 77 67 59 50 40 33 28 25 I.0 '·5 118 10' 1 97 90 83 73 65 55 45 38 53 28 1·50

102 94 87 77 59 4· 8 35 31 20 2 ; 123 III 68 41t\I

j 129 1 17 1 08 100 93 83 74 64 53 45 40 35 3~ \

104 97 86 77 68 56 49 43 38 4- 4 133 121 1 1 '2" 6 136 1 26 117 109 102 91 8? 72 61 53 47 42 6

IQ 143 131 122 1\ 4 107 96 87 78 66 58 52 47 10

15 1 41 13 5 1 26 11 8 III. 10{) 91 82 70 62 56 51 1520 150 137 128 120 113 103 94 84 72 64 58 53 203Q 152 140 131 123 116 105 97 87 76 68 G2 57 30

--~ _.

,--- - -fJll';t lN G()EFr -!C ~ENTS i1 OF OOUGH f \lESS MEANR AD.r~ RA[).R

f JE'fRES 01)09 .010 .011 .(W l .em l .015 .Oi'f .020 .025 .030 .055 .040 METRE~

:l!:l-

.025 47 40 35 31 2 8 22 19 15 II 9 7 6 .O2~l!lz . 05 59 50 44 40 35 29 25 20 15 12 10 8 . 0 5w..J

26 16 13 II -(lL . 1 72 62 55 50 45 ?J ; 7 32 190

~4 74 66 60 54 46 39 '32 25 20 17 14 · 2

I- ' 2zo -3 91 81 73 66 60 51 44 37 28 23 19 17 -3' = '0 · 4

97 86 77 70 64

55 48 40 31 25 21 18 · 4

0 : :0wO . 6 104 · 92 83 76 70 60 53 45 35 29 25 21 ' 6':::~

i' III 100 90 83 77 67 59 50 4· · 0 33 28 25 I0 _ _

° d H , 117 105 96 8 e: B2 72 - 64 54 44 34 32 28 1'502 120 109 100 92 35 15 67 57 47 40 34 30 2

II 4 128 116 107 99 92 32 n64 53 46 40 36 4IJJ

56 49 43 39 6d . G 131 1\ 9 110 102 96 85 n 679 10 135 123 1/ 4 106 100 89 31 71 60 53 4' 7 43 10If)

15 137 126 ilG 109 102 92 83 "/4 63 55 50 46 15

--- 00 141 12: 9 120 112 106 ~5 37 78 67 59 54 50 30 ____. _" _-'==-_. _ _-= --~ ~ _ '_ " '_=_ . _ _ _ ....-c- _"_ ,- _____


28/57

HYD RA UL IC V ER Y SM OO SM OOT H

MEAN DEPTH(R) TH CEMEN BOARDS BRIOK

\IN METERS.) & - PLANED OONO. GLAZE.(BOARDS. EARTHEN

WARE PIPES.

-----

M=0.1085 M=O,29

ASHLAR EARTH C1


29/57

0 0.00

0·00 0.00

1'0 o.~?

---2'0 I (}857

3'0 1 1'110

010 I ~~~ZO i 0.25 i 0·30.122 .163 I 0.~225· .254

DEPTH FROM a TO 3.95METRES

0.3;;-' 0'40 10.45 10'50 ! 0.55 I 0·60 0'65.2DO 0.306 0 330 '353 .375! ·397 I .417

.667 ,662 ·698 ~ ~750 L'748 .761

·949 ·963 ~;;;;-I ,989)',0021"014 '027" I'

1'192 1·205 1·215 1,·226 1·237 1,·248 1·260

_ .

~

0'70 0'75 · 0'80 0'85

.437 .457 ·476 ·495

I-0514 I O~

I0·844 I'Tl3

~801'816 0·830

I1·039 1·051 1·063 1·075

~~'~1'271 1.282 1'292 1·303

I1,314 1'325

I

I[ ,

I

I' 1 _

.~~~-~18

·882 i '896 .911

1·154 ..~-- 1·158 i


30/57

SLOPE IN eM./ KM.. . . , . . . , UI • (JI (1\ 2 1 C D < DCJ)0 0 Ul 0 0 0 0 0 0

z"0.05 0

0.02 0

NN(Jl

0.03

0;04

0.05

"1J 0.07'510.20

r

~rn 0.10z 00

CJ)0.1250

:z :C D J> 0.150 f o , e:: 0G) 0.20Q m Z» z 0.025;0

0.0275;0 0rn c 0.0303: 0.75-i rr l I. . •

0

I(j)

0 0-35

- 0'.0»Q 0·45::0 0'50: t : - 0.55& 0.60

0.650;>00.75

1.00 i3·00

1.250

1.500

I

L:750 5.00I

IIII

! " -

!

I:- ~ N0 N U 1

- " j"0 0(JI 0 r .1l

i 0 (J) r, .' ! vi Ul t . . '1 0 lJ! N l)l();I

L -----------


31/57

a: ; 10 C C DC O C7l 10 l\l It' 0 ~ It' 0 It'~ 10 l\l C D It' l\l ~ I(:C\i

" " (11 I{\ 0

10

>0

(11 0) C 1 ' ci C O It' r : : : C O C O " 7 It' It' "t0 0 0 0 (; 0 0 0 0 0 0 0 0 0

I , , , I

0 0 10 00

It' It" l\l

qN . . •"

2~.OO

" " 2.e.00"" -24·0(;

22.00

20.00

19.00

18.00

17.00

16.00

15.00 ~/4.00

! / 'W:> N I 3d01S


32/57

-lI

Q

e n

C D

0Ol G O r - ..0 0 0


33/57

ooo0 ::UJa.

(/)

I-0: :«a.Z

UJa.

9(/)

J · o0.8

0·6

0-1

0·08

0·06

I "J· Z

1'3 01'4::~~

t-- ~I I III

- ~I _ - r -- _

r--- -y --- ----I--~1--", ,--- - --J..! .:9 ---U: .S. --

~--r --r --r

Manual Irrigation Power Channels

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Transcript of Manual Irrigation Power Channels