ch. v ramaiah (1).pptx

8/10/2019 Ch. V Ramaiah (1).pptx

http://slidepdf.com/reader/full/ch-v-ramaiah-1pptx 1/119

The cross regulator is provided to effect equitable distribution of

supplies amongst the distributary and parent canal, to raise water

level when supply in the parent canal is low, to release surplus

water from canal, in conjunction with escapes, or to provide means

for cutting off supplies to the downstream side for repairs etc.

The criteria for the Hydraulic Design of cross regulators for canals

is as per I.S. code: 7114 – 1973 (reprint December, 1979).



The driving head is the difference between the water levels on U/S

and D/S side of the regulator. This is provided to allow the passage

of required discharge on D/S through the regulator at full supply

level.

Depending upon the driving head (fully utilizing the driving head)

the regular width may be flumed up to a maximum of 50% of thecanal width to economize the cost of the structure.



Q = C Bt H3/2

Where Q = D/S full supply discharge in m3 /sec

C = Co-efficient of discharge

Bt = Clear water way in metres.

H = Head over crest i.e. Full supply level on the U/S + head

due to velocity of approach – crest level.

The value of ‘C’ is determined using Malikpur graph (a graph drawn

between drowning ratio and co-efficient of discharge based on

experiments).



Crest level is calculated as per CWC, Manual i.e, Crest level = U/sTEL – head over crest (H)

The height of crest above up stream bed level should not be more

than 0.4 H. Glacis profile is calculated as per CWC manual with 2:1slopes to negotiate the levels and smooth curves at the junctions.

The radius of curvature to be adopted is H/2 on up steam and ‘H’ on downstream as specified therein.



D/s floor of the regulator is depressed to form a cistern to dissipateenergy. Since the U/s and D/s C.B.Ls and F.S.Ls are almost the

same in the NSP Canals and distributaries, the energy dissipation

arrangement is quite simple. To dissipate energy at low flows

through regulator the cistern with water cushion with a minimum

length and deflector wall at the end of the cistern are provided. Onmain system the hydraulic jump calculations are to be done for

different opening conditions i.e., ¼, ½, ¾ and full supply. Further if

there are more than one vent, these calculations have to be made

for different conditions of vents opening. The height and length of jump in each case is to be found. Based on these calculations the

depth and length of cistern will be fixed. Refer I.S:4997 –1968 or

Small Dams by USBR.



When there is no water on D/s of the regulator and water at FSL

on U/s, the exit gradient is to be calculated and the thickness of

floor has to be designed for the uplift pressures at various

sections. The formula for exist gradient is:

GE = 1 x H

(π √ λ) d

Where: λ = 1 + 1 + α2

2



α = b d

H = difference between crest level and downstream bed level in m

b = length of impervious floor in md = depth of downstream curtain wall in m

Scour depths are to be calculated at the U/s and D/s transition ends

and the curtain walls to be taken up to 1.5 times the scour depth.



Piers to be designed considering hoist loads, load due to water

thrust on gates, wind pressure and water currents. Whenever a

road bridge is provided the live load moments, tractive force and

braking force etc., are to be considered while checking the

stability.

Abutments to be designed with super imposed loads, live loadmoments, tractive force and braking force and the earth pressure

behind them.



Conventional Wings and returns to be designed for the earthpressures with T.V.A. procedure considering Ф as 32 degrees and

δ as 16 degrees.

U/s and D/s canal bed and sides are to be protected with C.C.

lining in M 15 grade concrete with profile walls at the end. Thethickness of lining is normally the same as for the remaining

length of the canal in the reach.



It is in VRCC M 20 grade, designed for its self weight plus forcestransmitted through the screw rod or the hoist and crowd load of

400 kg/ sqm.

Either sliding type or fixed wheel type gates are provided depending

on the size of opening. Electrically or manually operated hoistarrangement is to be made to operate the gates.



FIG.16



The canal fall or drop is required to be provided, whenever, the

natural slope of the country is steeper than the bed slope of the

canal and the difference in levels is adjusted by constructing a fall

or drop. Drops become necessary in the case of distributaries,

which are generally aligned along the ridge for commanding the

area on either side. There are two main types of falls.

In this type of fall, the nappe impinges clear into the water cushionbelow. The dissipation of energy is effected by the turbulant

diffusion as the high velocity jet enters the deep pool of water

downstream.



This type utilizes the principal of standing wave for dissipation of

energy. This type of fall can be divided into following threeclasses.

(a) Straight glacis with baffle platform and baffle wall.

(b) Straight glacis without baffle platform and baffle wall.

(c) Modified glacis type.The falls are further divided into:

(a) Flumed or unflumed falls and

(b) Meter or non – meter falls.

As per the Central Water Commission’s Manual on falls, thefollowing table indicates the type of falls to be selected for thegiven discharge and height of drop.



The Design Circular No. 35/1807 dated 2.2.1978 of CE., N.S.L.C.stipulated the type of drop to be adopted for different discharges andheights of drops.

Design Procedure:

(1) Clear width of throat (Bt): The fluming of Canal should not exceedthe limits given below subject to the condition that over all width of

throat is not more than Bed width of channel on the downstreamside.

Height of drop Percentage of fluming

1) Up to 1.0 m 66%

2) Over 1.0 m to 3.0 m 75%

3) Above 3.0 m 85%



2) Crest Level: The Crest level is fixed by working out ‘D’ using formulaeQ - = C. Bt. D 3/2

Where Q = discharge in cumec

C = co-efficient of discharge depending on the drowning ratio. Up to 70%

fluming

C = 1.84 can be adopted and above that, it is to be read from Malikpur

graph

Bt = Throat width in ‘m’. D = Depth of crest below U/S TEL in ‘m’

After calculating value of D from the formula, crest level is fixed with the

equation:Crest level = U/S TEL – D



3) Length of Crest: 2/3x D.

4) Height of Crest: Should not be greater than 0.4 D, above theupstream canal bed level.

5) D/S Glacis: In the case of baffle type glacis drops, glacis slope is to

be 2/3: 1 joined tangentially to the crest on the U/S side and baffleplatform on the downstream side with radius equal to ‘D’. In the

case of straight glacis provide glacis slope of 2:1 with radius of

curvature as D at the junction with the crest at the upstream end

and pavement at the downstream end.

6) U/S Glacis: Glacis slope is to be ½: 1 joined tangentially to the crest

with a radius equal to D/2.



7) Protection:

(i) Length of U/S protection: 3 times F.S.D. or as per the standard fixed

by the project authority. The protection is in CC M 15 grade with

profile walls at the end.(ii) Length of D/S protection: 4 (d + h) where d = d/s F.S.D. and h

= difference in F.S.Ls or as per the standard fixed by the project

authority. The protection is in CC M 15 grade with profile walls at

the end.8) Glacis fall without baffle:

(i) The hydraulic jump is calculated to be the most efficient means of

dissipating the energy. To ensure formation of the hydraulic jump,it is necessary that the depth of tail water flowing at sub –critical

velocity in the canal downstream should bear the following relation

to hypercritical depth of flow at the toe of glacis:



dx = -d2 + √ 2v2² d2 + d22

g 4

Where v2 = velocity of water at the formation of jumpd2 = hyper critical depth at formation of jump

dx = sub – critical depth in canal on downstream side

The values of d2 and dx are calculated from the following formulas

dx

for unflumed falls = 0.985 q0.52 x Hx

0.21

For flumed falls d1x = Hx - HL + dx (unflumed)

Where = Hx

HL

K 0.152

Hx = calculated drop in mHL = actual drop in m

K = fluming ratio (D/S bed width / throat width).

d2 = 0.183 q0.89 x Hx- 0.35



d2 = 0.183 (q) 0.89 x Hx -0.35 dc = Critical depth

dc = q2 1/3

g

q = discharge per meter width.

R.L. of Baffle wall = R.L. of Baffle Platform + Hb.

(iii) Thickness of Baffle wall = 2/3 x Hb

(iv) Length of Baffle Platform Lb = 5.25 (Hb)

The baffle platform should join the toe of glacis with a radius equal to D

and the baffle wall with a radius R = 2/3 Hb



v) Cistern:

(a) Depth of cistern: D/S FSD/10 subject to a min of 15 cm for

distributaries and minors and 30 cm for main canals and branches.

(b) R.L. of the cistern = D/S bed level – depth of cistern

(c) Length of cistern = 5 times down stream F.S.D. (d) R.L. of the deflector wall = D/S CBL + D/S F.S.D/ 10

10) Friction blocks and glacis blocks:

(i) Glacis fall with baffle

(a) If the height of drop is less than 2.0 meters, friction blocks and

glacis blocks are not required. If the height of drop is more than 2.0

m, two rows of friction blocks staggered in plan are to be provided.



Size of friction blocks:

Height (h) = 0.262 dx,

Length (L) = h

Top width (W) = 2h / 3

Distance between two rows = h.

The downstream edge of downstream row of friction blocks shall be

provided at a distance of one third length of cistern from the end of the

cistern floor.

b) Glacis blocks: Single row of glacis blocks of same size as friction

blocks is to be provided at the toe of the glacis.

(ii) Glacis fall without baffle



Four rows of friction blocks staggered in plan are to be provided in thecase of flumed falls. The upstream edge of first row of blocks may be ata distance of 5 times the height of blocks from the toe of glacis.

Size of friction blocks:Height (h) = D/S FSD

8

Height (L) = 3h

Height (W) = 2h

3

Distance between rows = 2h

3

11) Deflector wall:

In glacis falls, a deflector wall of height equal to one tenth of thedownstream FSD is provided at the downstream end of the cistern.The minimum height should be 15 cm.



12) Curtain wall:

i) Depth of U/S curtain wall = U/S FSD subject to minimum of 0.50 m

3

ii) Depth of D/S curtain wall = D/S FSD subject to minimum of 0.50 m

2These should be checked with scour depth formulae with suitablefactor of safety. Downstream cut off can be increased suitably toreduce the thickness of floor.

13 (i) Exit gradient and uplift pressure:H = difference between crest level and D/S CBL

d depth of D/S curtain wall

b = length of impervious floord depth of D/S curtain wall



Find out the corresponding value of φ E from graph i.e, from plate 17

CWC manual on falls.

ii) Thickness of floor: The uplift pressures at toe of glacis, at the end of

baffle and at the end of cistern are worked out by interpolation forfixing the thickness of floor.

Thickness of floor at toe glacis:

% age of pressure @ toe of glacis

= φ E at D/s + (φ E1 − φ E D/s) X L/b b = total length of impervious floor.

L = Length of floor up to toe of glacis from D/S end.

Thickness of floor at the toe of glacis

= %age of pressure @ toe of glacis x H100 x (ρ − 1)

Where ρ is specific gravity of CC i.e., 2.4



Similar method is to be adopted for calculating thickness of floor at the

end of the baffle, at the end of cistern etc.

FIG.17



FIG.18



Vertical drop:

Design procedure:

1) a) Throat width Bt = B.W. of canal (If canal bed width on upstream and

downstream are different, lower of the two).b) Crest Level:

Crest level is obtained by working out value of D (depth of crest below

upstream TEL) from the following formula.

Q = C x Bt D 1/6 x D 3/2

Lt

Where Bt = Throat width in m

C = Coefficient of discharge usually taken as 1.835

Lt = Length of crest in mD = Depth of crest below upstream TEL in m

U/S T.E.L = U/S FSL + Velocity head

R.L. of crest = U/S TEL – D



5) U/S and D/S Protections:

i) Length of U/s protection= 1 ½ times the U/S FSD or as per standard

fixed by the Project authority.

ii) Length of D/s protection = 3 times the D/S FSD or as per standard

fixed by the Project authority.

6) Exit Gradient & Uplift pressures

a) Exit gradient:

H = R.L. of crest – D/S CBL.

d = depth of D/S curtain wall off = FSD/ 2 or as per the requirement

to bring the exit gradient within the limit.

b = Length of impervious Floor = Foundation offsets + width of dropwall + length of cistern + width of curtain wall.



For drops in silty or clayey soils the followingmodifications may be adopted (Design CircularNo. 35/1807 dated 2.2.1978 of C.E., N.S.L.Canals).

(a) For drops of 1.5 m and above, for alldischarges, wings and returns may be

provided.(b) For drops less than 1.5 m height and discharge

above 1 cumec, wings and returns may beprovided.

Following are the recommendations of the ExpertCommittees on design of drops on distributarysystem.



(a) For drops with height of less than or equal to0.60 m and discharge of less than 50 cusec,unflumed core wall type drops may be

provided.(b) For drops with height more than 0.60 m and

discharge between 50 and 100 cusec, unflumedvertical drops with wings and returns may beprovided.

(c) For drops with discharges more than 100 cusec,straight flumed drops may be provided. Wherefluming ratio as per codel provision could notbe adopted for drops of height less than 0.60 m,unflumed vertical or unflumed core wall typedrop may be provided.



TABLE No. I

DETAILS OF COMPONENTS OF VERTICAL

TYPE DROPS WITH

D i s

c h a

r g e

Q ( c u

m )

H e i

g h t

o f

d r o p D

e p t h

o f

c i s t

e r n

b e l

o w

D / S

B . L ( x )

L e n

g t h

o f

c r e

s t ( L t . )

T h r

o a t

w i d

t h ( B t . ) D

e p t h

o f

c r e

s t b e l

o w

U / S

T . E . L ( D

) H e i

g h t

o f

c r e

s t a b o

v e

U / S

B . L ( D 1 )

B o t

t o m w i d

t h o f

d r o p

w a l

l ( L W )

L e n

g t h

o f

a p r

o n

( L a )

W i

d t h

o f

a p r

o n

( W a )

T h i

c k n

e s s o

f a p r

o n

( t a )

1.5 to

1.0

0.8

1.0

1.2

1.5

0.15

0.17

0.19

0.22

0.8 0.3

0.8 0.3

B e d w i d t h

o n U / S o r D / S w h i c h e v e r i s l e s

s

A s p e r f o r m u l a e

A s p e r f o r m u l a e

0.80

0.80

0.90

1.10

3.4

3.8

4.2

4.7

B e d w i d t h o n D / S

0.60

0.65

0.65

0.70

1.0 to

0.5

0.6

0.8

1.0

1.2

1.5

0.12

0.14

0.16

0.18

0.21

0.6 0.6

0.8 0.8

0.8

0.60

0.70

0.80

0.90

1.10

2.7

3.1

3.5

3.8

4 .3

0.60

0.60

0.60

0.65

0.70

0.5 to

0.1

0.6

0.8

1.0

1.21.5

0.10

0.12

0.14

0.150.17

0.6 0.6

0.6 0.8

0.8

0.60

0.70

0.80

0.901.00

2.4

2.8

3.2

3.54.0

0.60

0.60

0.60

0.650.70

0.1 and

below

0.6

0.8

1.0

1.2

1.5

0.07

0.08

0.09

0.10

0.12

0.6 0.6

0.6 0.6

0.8

0.60

0.60

0.70

0.80

1.00

2.0

2.3

2.6

2.8

3.2

0.60

0.60

0.60

0.60

0.70



FIG.19



TABLE No. II

Table showing discharges and depth of crest

below U/S T.E.L. for vertical type drops withrectangular opening and free fall.

Discharge Q = 1.835 Bt (D/ Lt)1/6 D3/2 in cumec

or D = {(Q/ Bt) x (Lt1/6/ 1.835)}3/5 in meters

Discharge per Meter run

of crest wall i.e., Q/Bt

Depth of crest (D) below U/S T.E.L. in

meters for length of crest Lt

Cumec 0.6 m 0.8 m

0.10 0.166 0.172

0.15 0.212 0.218

0.20 0.252 0.259

0.25 0.288 0.296

0.30 0.321 0.331

0.35 0.352 0.362

0.40 0.383 0.393

0.45 0.409 0.422

0.50 0.436 0.449

0.55 0.462 0.475

0.60 0.437 0.501

0.65 0.511 0.526

0.70 0.534 0.549

0.75 0.556 0.573

0.80 0.578 0.595



or D = {(Q/ Bt) x (Lt1/6/ 1.835)}3/5 in meter where Bt

= Width of crest = Canal Bed width in meters

Lt = Length of crest along axis of canal in metersNotch type drop: (Trapezoidal/ Rectangular)

As per Irrigation manual by W.M Ellis.

Design procedure:

1) For half discharge, find out F.S.D. Usually it is 0.7F.S.D.

2) Calculations of no. of notches:

No. of notches = Bed width

1.5 x FSD



Vide – Emperical rule No.4 page No. 229 of„Irrigation practice & Engineering‟ by Etcheverry)

Find discharge per notch i.e., = QNo. of notches.

Silt level of drop = U/S CBL

3) For free fall notches:Case I:

For free notch, the equation used for finding outnotch dimensions is

Q = 2.96 C d3/2 (L + 0.4 d n)

Where : Q = discharge in cumec



C = The coefficient of discharge of notch = 0.70

d = depth of water in metres over sill of the not

L = width of the horizontal sill of the notch in „m‟. n = 2 tan α, where α is the angle made by each ofthe sides of the notch with the vertical.

If „n‟ is Zero, then it becomes a rectangular notch. Case II: For submerged notch:

Q= 2.96 C√ d-E E +d L + 3 E2 + (d-E) E +0.4 (d-E)2 n 2

4



Where E = the submersion depth of tail waterover the sill of the notch.

Q, C, d, L, n are the same as in the case – I.

Find L and n by using the above equations (freefall or submerged) for full supply discharge andhalf supply discharge conditions.

Substitute the values of L and n to get top widthof notch in the equation = L + nd.

4) Length of drop wall between abutments:

Length of drop wall between the abutments

should not be less than 7/8th of the canal bedwidth on up stream. However in practice, thelength of drop wall is provided equal toupstream bed width.



(5) Width of notch pier at FSL should not be lessthan half of upstream F.S.D. „d‟

Top width of notch is generally 0.75 d, wherenotch is free and d where notch is submerged.

6) Water cushion:

The depth „x‟ of the water cushion is worked outfrom the following equation

X + d1 = 0.91 dc √ h

Where d1 = D/S F.S.D

dc = Depth of water over the crest.

h = height of drop (difference in FSLs).



7) Length of cistern:

Length of the horizontal floor of the cushion = 2

dc + 2 √ dc h subject to a minimum of1.2 + 2√dc h. It is to be designed on the basis of up liftpressures and exit gradient if the soil is pervious.

8) Thickness of cistern floor = 0.55√ dc + h. Thisshould be designed on the basis of uplift

pressure and exit gradient, of the soil ispervious.



9) Drop wall:

i) Top width of drop wall at sill level

(0.5d + 0.15) to (0.5d + 0.3)ii) Bottom width of drop wall = H + dc+x

√ ρ

Where H = vertical height of the sill from theapron, dc = depth of water over the crestand x = depth of water cushion

10) Protection works:

i) Length of the U/S revetment = 3dc subject tomin of 3 meters



ii) Length of the D/S revetment = 4 (d + h) subjectto min of 6 meters or as per standard fixed by

the Project Authority(11) Scour depth calculations:

Scour depth = 1.34 q2 1/3 metres

f

q = discharge/ meter width

f = lacey‟s silt factor. (12) Check for uplift on floor: As per Khosla‟s

Theory.



Trapezoidal notch core wall drops :( CE NSLCCircular No. DW.150/ 3845 – S, 3-9-1980)

Various components of the notch type drop withcore wall for different ranges of discharges i.e., 1.5cumec to 1 cumec, 1 cumec to 0.5 cumec, 0.5 cumecto 0.1 cumec, 0.1 cumec and below and for various

heights of drops i.e., 0.6 m, 0.8 m, 1.0 m, 1.2 m and1.5 m with clear over fall are given in table I and II.The same may be adopted for drops ondistributaries' having discharge of 1.5 cumec and

less.For drops in silty or clayey soils the followingmodifications may be adopted.

i) F d f 1 5 d b f ll



i). For drops of 1.5 m and above, for alldischarges, wings and returns may beprovided.

(ii). For drops less than 1.5 m height anddischarge above 1 cumec, wings and returnsmay be provided.

TABLE No. I (A)

DETAILS OF COMPONENTS OF NOTCHTYPE DROPS WITH CORE WALL (FREEFALL) FOR DISCHARGES LESS THAN 1.5CUMEC AND HEIGHT OF DROP LESSTHAN 1.5 m



D / S D i s c h a r g e i n

C u m

H e i g h t o f d r o p h

i n m

N o . o f n o t c h e s

Details of each notch

X c u s h i o n

T h i c k n e s s o f e n d

p i e r

T o p o f d r o p w a l l

L t

B o t t o m w i d t h o f

d r o p w a l l

L e n g t h o f d r o p

c o r e w a l l

L e n g t h o f a p r o n

( L a )

T h i c k n e s s o f

a p r o n ( t a )

L L + nd

1 2 3 4 5 6 7 8 9 10 11 12

1.5 to 1.0 1.0 1.2 1.5 1 1 1

R e

f e r T a

b l e I I

( A )

R e

f e r T a

b l e I I

( A )

-

-

0.09

0.6

0.6

0.6

0.6

0.6

0.6

1.3

1.4

1.6

3.6

3.8

4.0

0.70

0.75

0.75

1.0 to 0.50.8 1.0 1.2

1.5

1 1 1

1

-

-

-

0.08

0.60

0.60

0.60

0.60

0.60

0.60

0.60

0.60

1.2

1.2

1.4

1.6

3.2

3.4

3.6

3.8

0.65

0.70

0.70

0.75

0.5 to 0.10.6 0.8 1.0

1.2 1.5

1 1 1

1 1

-

-

-

-

0.06

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.5

0.8

1.0

1.2

1.2

1.4

2.4

2.6

2.8

2.9

3.1

0.60

0.60

0.65

0.70

0.75

0.1 and below0.6 0.8 1.0

1.2 1.5

1 1 1

1 1

-

-

-

-

0.04

0.45

0.45

0.45

0.45

0.45

0.45

0.45

0.45

0.45

0.45

0.7

0.8

0.9

1.0

1.3

1.6

1.7

1.8

1.9

2.1

0.60

0.60

0.60

0.65

0.70



Q/ d3/2

Width of Notch at

sill level ‘m’

Width of notch at

F.S.L ‘m’

2.2 0.546 1.844

2.1 0.521 1.760

2.0 0.496 1.676

1.9 0.471 1.592

1.8 0.446 1.508

1.7 0.422 1.425

1.6 0.397 1.341

1.5 0.372 1.257

1.4 0.347 1.173

1.3 0.322 1.090

1.2 0.298 1.006

1.1 0.273 0.922

1.0 0.248 0.838

0.9 0.223 0.754

0.8 0.198 0.671

0.7 0.174 0.587

0.6 0.149 0.503

0.5 0.124 0.419

0.4 0.099 0.333



Notch type drop with core wall:

In core wall type, the drop wall is combined with

a straight wall, which is extended into the bankswith proper keying. There are no wings & returnson the U/S and D/S sides. But CC apron and sideprotection with CC lining (better if double the

normal thickness provided) is provided.i) Formulae adopted for working out the

rectangular notch

Q = 1.708 [ L – 0.1 nd] d3/2

Where n = no. of notches

L l th f th d ll i t



L = length of the drop wall in metres

d = depth of water in meters over the crest of drop

ii) Formulae adopted for trapezoidal notch is sameas discussed in the previous case.

iii) Length of apron, thickness of apron and watercushion – same as discussed in the previous

case (trapezoidal notch). The drops can be combined with bridges

wherever possible. In such cases the clearance

between sill of drop to deck may be provided asbelow:



N = h1 (hs + 0.3 m) from civil engineering handbook volume II by „LELIAWSKY‟.



OFF TAKE SLUICE:

Off takes are provided on the conveyance system to

irrigate the ayacut localized under branch ordistributary. As per World Bank norms, the waterdistribution system is broadly classified as:

i) Supply system or conveyance system.

ii) Distributary System.1) Supply system or conveyance system:

Main canal, branch canals and majors carrying adischarge above 5.66 cumec (200 cusecs) areconsidered as supply system. They will runcontinuously. The distributaries taking off fromthese have gated structures if the carrying capacityis 5.66 cumec (200 cusec) and above.

2) Di t ib t t



2) Distributary system:

The distributaries have capacity less than 5.66cumec (200 cusecs). These will run either full or

closed. The water will be distributedproportionally through modules (APM or OFM).No gated structures will be there on thedistributary system.

In the first reach of distributary, a standing waveflume which is used as a measuring device, isprovided.

Gated off – takes:

These may be either: i) Rectangular/ square vents covered with R.C.C

slab or

ii) Pipes

R l



Rectangular vents:

(1) Sill level: The sill of O.T is kept either at or

above the CBL of parent canal depending onthe ratio of discharges in distributary andparent canal.

% of O.T. discharge to parent

canal discharge

Height of sill of sluice above the CBL of parent canal

when FSD in the parent canal is:

Above 2.14 m 2.14 to 1.22 m Below 1.22 m

15% and above 0.075 - -

10% to 15% 0.15 0.075

5% to 10% 0.30 0.15 0.075 m

2% to 5% 0.30 0.30 0.15 m

2% and less 0.30 0.30 0.30 m

(2) Driving head:



(2) Driving head: (3) The driving head at O.T. is arrived at normally

considering half supply discharge in the parentcanal when the full supply discharge flows intothe distributary channel.

Driving head = Supply level in parent canal forhalf supply discharge FSL in distributary

The FSL of off take channel is generally fixed at 15cm below the half supply level of parent canal forthe channels taking off from main canal andbranch canal and 7.5 cm for channels taking offfrom the distributaries. However vent way is

designed with minimum driving head of 7.5 cm(3”) for pipes. The level difference between the silllevel and C.B.L. of parent canal is negotiated byproving suitable longitudinal slope.

(3) Vent way:



(3) Vent way:

(4) The vent way for square or rectangular/circular vents is calculated by the formulae.

Q = Cd. A. √ 2g H = 2.746 A√ H

Where Q= Discharge of off take sluice in

cumec Cd = 0.62 for square or rectangular openings

A= Area in sqm

H= Driving head in m.

The vent way for circular openings with C = 0.75 is calculated by the formula:

Q = 3.322 . A√ H



(5) R C C slab under earth bank:



(5) R.C.C. slab under earth bank:

It is designed for weight of earth over it inaddition to its self weight. Live load is also tobe taken into consideration for the slab underinspection path.

(6) Transitions: The U/S and D/S transitions are providedwith 1 in 3 and 1 in 5 splay respectively as per

practice.



Off t k ith h i



Off – takes with hume pipes:

(1)The minimum diameter for off takes from

main/ branch canal and distributaries is asfollows:

Min φ of pipe

Main/ Branch

canalDistributary

0.90m

i) 14.15 to 2.83cumec

discharges –

0.23m φ

ii)2.83 cumec and

less – 0.15m φ



i) For pipe sluices of 6” (150 mm) dia and below



i) For pipe sluices of 6 (150 mm) dia and belowand vents of

equivalent area with F.S.D of parent canal notexceeding No control

4ft (1.22 m). and O.T discharge 1.5 c/s and less

(ii) For pipe sluices of diameters above 6” andupto and including 12”(300 mm) with F.S.D ofparent canal not Stem shutter exceeding 4ft(1.22 m).

iii)For all sluices where the FSD in the parentcanal Screw is more than 4ft (1.22 m) and forsluices of larger ventways. gearing shutter

SEMI MODULAR OUTLETS



SEMI MODULAR OUTLETS The Expert Committee (Core Committee) suggested toprovide Semi modular outlets (ungated ) for the

outlets with discharge of 0.5 cumec and less, taking offfrom channels having discharge less than 25 cusec(about 0.7 cumec)

Definition of semi modular outlets (flexible

modules) The outlets whose discharge is independent of thewater level of the outlet channel but depends on thewater level of the distributary so long as minimumworking head required for their working is available.The discharge through such an outlet will therefore,increase with the rise in the distributary water surfacelevel and vice versa. The common examples of thistype of modules are

1 Open Flume Module (O F M)



1. Open Flume Module (O.F.M)

2. Adjustable Orifice Semi module (A.O.S.M)/Adjustable Proportional Module (A.P.M)

3. Pipe Semi - module -free fall pipe outlet (P.S.M)

1) Open flume module:

It is weir type outlet with a constricted throat andan expanded flume on D/S side. Due toconstriction, super critical velocity is ensured inthe throat and thereby allowing formation of jumpin the expanding flume. The formation of

Hydraulic jump makes the outlet dischargeindependent of water level in the outlet channel,thus making it a semi - module.

(2) Adj t bl O ifi S i M d l (A O S M)



(2) Adjustable Orifice Semi - Module (A.O.S.M):

An adjustable orifice semi - module consists of an

Orifice provided with gradually expanding flumeon the d/s side of the orifice. The flow through theorifice is super critical, resulting in the formation ofhydraulic jump in the expanded flume portion. The

formation of jump makes the discharge independentof water level in the out let channel.

3) Adjustable Proportional Module (A.P.M):

This type is the most commonly used outlet in thisclass. In this, the CI roof block is fixed to the checkplates by blots, which can be removed and depth ofoutlet adjusted after masonry around is dismantled

(4) Pipe Semi - Module (P.S.M):



( ) p ( )

Pipe outlet discharging freely into atmosphere isthe simplest and the oldest type of flexible outlet.

The discharge through such an outlet will dependonly upon the water level of the distributary andwill be independent of water level in the outletchannel so long as the pipe is discharging freely.This can be provided where sufficient leveldifference between distributary and outlet channelis available.]

The suitability of the type of the semi module

outlet is determined based on the ratio of parentcanal discharge (Q) to the discharge of the out let(q) and the throat width (Bt) as detailed below.

i) for (Q/q ) < or = 20 and B t ≥ 6 cm Open



i) for (Q/q ) < or 20 and B t ≥ 6 cm OpenFlume Module( OFM)

ii) for (Q/q ) < or = 20 and B t < 6 cmAdjustable Proportional module ( APM )

iii) for (Q/q ) > 20

If the above requirements do not suit the sitecondition, provide pipe semi module (wherepossible) with diaphragm of required diameterinserted at the first joint. The minimum diametreof pipe used will be 150 mm.

The above conditions are further explained as



The above conditions are further explained asbelow

Arrive at the ratio of parent channel / out letchannel.If it is < or = 20, select OFM. Calculate the Bt( throat width ), using weir formula.

If Bt is > 6 cm it is ok.Otherwise select A.P.M.

Work out the Bt using the sluice formulasetting the crest of outlet at less than 0.80 D

from FSL of Parent Channel and adjusting theheight of outlet opening.

If Bt = or > 6 it is ok

Otherwise go for pipe semi module (PSM), if it



Otherwise go for pipe semi module (PSM), if itis possible to do so. Check for proportionally

Open flume module

Discharge through the out let (q) in cumec isgiven by the formula:



Adjustable Orifice Semi Module (A.O.S.M) or



Adjustable Orifice Semi Module (A.O.S.M) orAdjustable Proportional Module (APM)

Discharge through outlet in cumec.

Q = 4.03 Bt Y Hs1/2

Y =Height of opening in metres.

Bt =Throat width (minimum 0.06 m )

G =Depth of water in parent canal over the



G Depth of water in parent canal over thecrest in metres

Hs = Depth to under side of the roof blockbelow FSL of parent canal.

Hs = G – Y , Hs ≤ 0.80 D

y > (2/3 ) G

Setting of crest, G = 0.750 x D , where D = Fullsupply depth in the parent canal

Setting of crest shall not be below D/S B.L.

Minimum modular head Hm = 0.75 Hs formodularity between full supply and anyfraction of full supply.

Crest level ≈ U/S FSL- 0 75 D



Crest level U/S FSL 0.75 D

Length of throat = width of roof

block + GU/S slope of glacis = curve withradius 2G.

U/s approach wings = one curved and

the other straight, top at FSL + 0.15 m

D/S expansion = 1 in 10 to meetbed width of outlet channel

Pipe semi module



Pipe semi module

Design criteria

The discharge through pipe semi module isgiven by

Q =Cd . A (2g hc )1/2

Where Cd = 0.62 for free pipe out let

hc =head on U/S above the centre of pipe

hc should be more than 1.5 times the dia of thepipe proposed.

The above formulae can be reduced to

Q =0.62 x √ (2x 9.81 ) A √ (hcnt)

=2.746 A hc 1/2

For free fall condition set the F S L of OT



For free fall condition set the F.S.L of OTChannel below the pipe sill level keeping inview the command under the pipe sluice .It is asimplest type and the users will appreciate.

Throttling the vent way of existing pipe outlets: (From design guidelines for structured

irrigation network to suit to RWSS).When the existing diametre of pipe is morethan required then, to reduce the size of thepipe a sleeve pipe is introduced whose

diametre is worked out by equating operatinghead to the headloss.

h = Ki (Vs2/ 2g) + (Vs – Vp )2 / 2g + f x (Lp/ Dp) x



i ( s / g) ( s p ) / g ( p/ p)(Vp

2/ 2g) + Ko(Vp2/ 2g)

Where, Ki = 1, Loss coefficient at inletLp = Length of pipe

Ko = 1, Loss coefficient at exit

Dp = Diametre of pipe

f = Friction loss coefficient = 0.02

Vs = Velocity in sleeve pipe

Vp = Velocity in the pipe

Substituting the values in the equation find out theVs, then the area of sleeve pipe As Findout the dia of sleeve pipe Ds = (4 As/ 3.14)0.5. Thelength of sleeve pipe shall be 5 Ds

FIG.24



FIG.24

FLOW MEASUREMENT STRUCTURES



FLOW MEASUREMENT STRUCTURES

GENERAL

Provision of "measuring structures/devices"shall conform to the following guide linesgiven by Sri R.K. Malhotra, World BankConsultant.

A measuring structure is to be provided downstreamof every off-take of major from the main canal/ branchcanal, distributory from a major, minor from thedistributory and sub-minor from the minor etc.

Measuring structure is also to be provided at off-takeof branch canal from the main canal and also in themain canals.

Types of measuring structures shall be broadly:



yp g y"Standing Wave Flumes” in concrete (SWF) andParshall Flumes & Cut Throat Flumes (CTF) in fiber

glass reinforced plastic material with their hold-faststo be embedded in concrete structures. Standing WaveFlumes may be provided in the main & branchcanals; Cut Throat Flumes /Parshall Flumes in themajors/distributaries, while Cut Throat Flumes maybe provided in the minors/sub-minors. The Parshalland Cut Throat Flumes in fiber glass reinforced plastic(FRP) material shall have engraved gauge markings incentimeters as well as in liter/second.

Division Boxes shall be constructed in concrete.Likewise, turn-outs shall be constructed in concrete.

STANDING WAVE FLUME



STANDING WAVE FLUME

Standing wave flume is a critical depth flume.

The discharge through this is independent ofwater level on downstream and varies withwater levels on upstream. The hydraulicbehavior is same as that of a broad crested

weir. Since only one gauge reading is requiredto be taken for measuring the discharge anddue to ease of construction, standing waveflumes are recommended as a flow measuring

device. The following are the three types of flumes

proposed for adoption



FIG.40



(1) Discharge

Discharge through standing wave flume ( Q )in cumec is given by

Q = 2 2 g . Cf Bt . H3/2



Q g f t

3√ 3

= 1.705 . C f . Bt . H 3/2

Where B t = Throat width in „m‟ H = Height of specific energy over the crest in„m‟. = Depth of flow over the crest on upstream (d1)+ head due to velocity of approach (v)

= d1 - Z + v 2 /15.2

Where Z = Height of hump over U/S canalbed level

Cf = Coefficient of friction

For Q Value of Cf



0.3 to 1.5 cumec 0.980.5 to 15 cumec 0.99

above 15 cumec 1.00Modular Limit value of submergence ratio ofH2/H1 at which the real discharge deviates by 1 %of Q calculated by discharge equation. It should bebetween 0.7 to 0.95

With straight transition from throat width todownstream bed width in a length of 4 H

Modular Limit H2 /H1 = 0.8 to 0.85Minimum modular head = 0.15 H to 0.2 H

2) Height of hump :



The height of hump is the difference between the

u/s canal bed level and the sill level of the flume.Height of hump, for proportionality between fullsupply and any fraction of full supply between thechannel and weir is given by the equations.

1m 1/x 11

m 2/3 -1

(i) Z = d1 – D1 = d1 m1/x 1- For channels running

with fluctuating discharge



From the discharges Q,Q',Q'',Q''', etc , for the flow ofdepths of d1 d'1 d''1 d'''1 etc respectively the value of x



depths of d1,d 1, d 1,d 1, etc respectively, the value of xin the equation is estimated by least square method byconsidering 4 sets of d and corresponding Q.

∑ log Q . Log d - (∑ log Q ) ( ∑ log d) Where M =No. of sets = 4x = M

∑ ( log d )2 - ( ∑ log d )2 M

Figure 2 gives the height of hump required forvarious values of x and fluctuations. In case ofchannels which run either full or closed, a flumewhich gives proportionality at full supply discharge

is desirable. In the case of channels, in whichdischarge varies considerably, bulk proportionality ispreferable. Figure 3 gives the heights of hump for bulkproportionally.

(3) Head loss:



The head loss consists of the following losses:

(i) Approach transition,

(ii) Exit transition,(iii) Friction in structure, and

(iv) Hydraulic jump

The loss in approach and exit transitions dependson the amount of fluming and its gradualness. Thefriction loss is usually very small. The loss inhydraulic jump is given by the equation:

HL = (d2 – d1)2

4 d1 d2

Where d1 = depth of flow before jump

d2 = depth of flow after jump

(4) Approach transition



( ) pp

The radius of side walls of the bell mouthentrance should be 3.6 H 1.5 metres. If „H‟ is lessthan 0.30m, the radius may be 2H from thethroat. The curvature (formed from the throat)should continue till it subtends an angle of 600,

from where, it should be continued tangentiallyto meet the side of the channel upstream.

The bed convergence should begin on the samecross section as the side convergence. The radius

of curvature of hump in the bed should be:rh = L1

2 + Z2

2 Z

Where rh = radius of curvature of hump



L1 = length between the junction of side wallwith the bed of upstream channel andupstream end of the throat measured along theaxis.

Z = height of hump above u/s bed level.

FIG.42



(7) Gauge (Stilling) well



( ) g ( g)

The stilling well should be so located as to

measure the water upstream of the sill, wherethere is no curvature of flow. This could beensured by locating the stilling well intake pipeat a distance of 4 Hmax upstream of the bell

mouth entrance. Hmax is the maximum value ofupstream head over the sill (including velocityhead).



Design criteria



The standing wave flume fall is essentially a broadcrested weir and IS: 6062 - 1971 "Method ofmeasurement of flow of open channels usingstanding wave flume fall" and "Manual on canalfalls" by Central Water Commission are followedfor the design of standing wave flume fall . Thedesign calculations are similar to that of standingwave flume. The main difference between the twois in the energy dissipation arrangements. In thecase of normal standing wave flume, head loss isconsiderably low and does not require any specialenergy dissipation arrangements. In the case ofstanding wave flume combined with fall or drop,energy dissipation arrangements are provided asper the requirements for the falls.

(1) Discharge



Discharge through standing wave flume ( Q )in cumec is given by the equation given in sub-para (1) of para 6.1.1, similar to that for standingwave flume without fall.

In case, piers are provided in the flume, the

discharge is given by the formaula:Q = 2 2 g . Cf (Bo – mb – 2Cc m H) H1.5

3 √ 3

Where Q = discharge in cumec Cf = Coefficient of friction having the following

values:

0.97 for Q = 0.05 to 0.30 cumec



0.98 for Q = 0.30 to 1.50 cumec

0.99 for Q = 1.50 to 15.0 cumec1.00 for Q = 15.0 cumec and above

Bo = Overall throat width including piers

m = no. of piers

b = thickness of each pier

Cc= coefficient of contraction having values of0.045 for piers with round nose and 0.04 for

piers with pointed nose.H = head over sill including velocity head givenby equation



(4) Inlet transition:



The radius (R) of the side walls of bell mouth

entrance should be 3.6 H 1.5. The curvature shouldcontinue till it subtends an angle of 600, from whereit shall be continued tangentially to meet the side ofthe channel. However when the curved walls meet

the sides of channel when it subtends an angle of600, it is not necessary to continue the walls further.The length of inlet transition (L1) may be found outknowing B1 , B2 and the radius of bell mouthentrance R using the relation:

L1 = 2 R - B1 – B 0 B1 – B0

√ 2 2

Where B1 = upstream bed width of channel



B0 = overall throat width

The radius of curvature of hump (rh) in the bedis given by the following equation.

(rh) = L12 + Z 2

2 Z

When the total head above the standing wavefall (SWF) sill becomes considerable, say 1.2 m,the height of hump „Z‟ becomes insignificant as

compared to „L1‟ so that the radius becomeslarge and the U/S end of the throat may be joined by a straight line to the channel bedU/S.

5) Design of Glacis :



The glacis should have a slope of 2:1 connectedwith the throat upstream by a curve of radius2H and with the cistern downstream by a curveof radius H. The side walls should be straightover glacis portion. With steeper glacis slope of

2:1 and greater loss of head, proper expansionshould be provided. For controlling the issuingflow, parallel sides should be extended downto the toe of glacis followed by hyperbolic

expansion in the cistern using equation:By B0 B3 L

L B3 - ( B 3 - B o ) y



4 d3 for shingle bed

L 5 d f d th b d



L = 5 d3 for good earthen bed

6 d3 for sandy bed

If the channel is lined with CC, length of cisternmay be taken as 4 d3.

In order to stabilize the flow, bed of cistern

should be made steeper in the center by 25%compared to the sides.

(7) Control blocks

Two rows of control blocks, staggered in planshould be provided downstream of the toe ofthe glacis in the cistern. The size of the blocksshould be as follows:

Height (h) = 1/6 depth of water in mid cistern



Length (l) = 1.5 to 3 h

Width (w) = 2/3 hClear distance between blocks = l

Clear distance between rows = w

The first row of blocks should be at 3 to 5 timesthe height of the blocks from the toe of glacis.

8) Deflector

A deflector should be provided at thedownstream end of the cistern.

Size of deflector:



Height (h) = 1/12 depth of water in mid cistern

Width (w) = hGap in the deflector = h

Internal of gaps = 4h

Short walls of same height should be placed closeto the upstream of gaps.

(9) Gauge well

RECTANGULAR THROAT FLUME:



The discharge in a open channel may bemeasured by means of a flume. Consistingessentially of contractions in the sides and / orbottom of the channel forming throat. When the

dimensions are such that critical flow occurs inthe downstream, (in other words it is freeflowing) discharge can be determined from thesingle upstream depth measurement. This device

is called “Critical Depth Measuring Flume ".Thisstructure may be adopted for measuring smallerdischarges less than 1 cumec.

Design criteria:



(a) Rectangular throat with hump

(b) Let 'Y' be the depth of flow and velocity be"V" m/sec in the normal section. Then totalenergy

head is equal to depth of flow and due to

velocity of approach i.eE = Y + V2 / 2g

Take the value of 2 g equal to 19.2

In Rectangular section , critical depth (Yc ) isequal to two thirds the Total Energy

head ,i.e Yc = 2/3 E

The throat width is worked out by dischargeti hi h i i f ll



equation , which is given as follows :-

Q = 2/3 √ 2/3 x g . Cf

. b . H1.5 = 1.705 C f

bH1.5

where C f = co-efficient of friction = 0.97

b= throat width

H = Yc = depth of flow at critical section

Length of the crest is equal to 2H.

ch. v ramaiah (1).pptx

Documents