Study of Looseness Factor for Barrages

STUDY OF LOOSENESS FACTOR FOR BARRAGES

A DISSERTATION

submitted in partial fulfilment of the requirements for the award of the degree of MAStER OF ENGINEERING in WATER RESOURCES DEVELOPMENT

NRUSINGH CHARAN MOHANTY

* yi~X h

WATER RESOURCES DEVELOPMENT TRAINING CENTRE UNIVERSITY OF ROORKEE ROORKEE-247667 (INDIA) OCTOBER, 1984 CEATIFICAT E

Certified that the dissertation entitled, I STUDY OF LOOSE.- US FACTORFOR BARRAGES' which is being submitted by Mr. Nru Singh Charan Mohanty in partial fulfilment for the award of the degree of master of Engineering ( Water Resources Development) of Univer- sity of Roorkee, as a record of student's own work carried out by him under our guidance and supervision, The matter embodied in this dissertation has not been submitted for the award of any other Degree or Diploma.

This is further to certify that he has worked for a period from 16.6.1984 to 16.10.1984 for preparing this dissertation for Master of Engineering at this University.

( AYAN S.iMA) (C.P. SINHA) Reader Professor Water Resources Development Water Resources Development Training Centre, Training Centre, University of Roorkee University of Roorkee Roorkee, U.P. (India) Roorkee, U.P. (India)

ROORKEE

DATED .- Oct. 2,) , 1984 CKNOLDGNENTBS

The author wishes to express his deep and sincere gratitude to Prof. C.P. Sinha, Professor in W.R.D.T.C., University of Roorkee-. and Sri Nayan Sarma, Reader in WRDTC, University of Roorkee for their valuable constant guidance and kind encouragement throughout the work.

The author owes his gratefulness to officers of U.P. I.R,I., Roorkee for their useful discussion and valuable suggestion on the subject,

R©OBKEE Nrusingh Charan Mohanty Trainee Officer October ,1984 S Y N 0 P S I S

Looseness factor of a barrage largely influences its hydraulic performance and, to a great extent, moulds the river behaviour near the site. In' absenceof any rational approach for its determination, the waterway of a barrage is generally decided by the designer depending on his judgement and the past experience. The opinion is divided on the value of looseness factor to be adopted in design of a diversion structure. Also the discharge parameter for Lacey's wetted perimeter formula is not well defined and this creates room for vagueness for the value of looseness factor.

The subjective approach to the problem of determining water way of a diversion structure has been mainly responsible for the undesirable shoal formations upstream of barrages which adversely affect the functioning of the works. In this dissertation an effort has been made to study the effect of looseness factor on sediment transporting capacity at barrage site, and also to evolve a rational procedure for determining waterway on the basis of existing sediment transport theories* The consideration has been made that the greatest volume of sediment should be carried past the structure. A procedure has been suggested for arriving at the desired waterway by adopting the concept of bed. generative discharge of Schaffernack along with the simplified DuBoy' s formula. A study has also been made on the inter-relation among waterway, pond level and operation from the consideration of minimising the silt deposition on the upstream. The 'studyhas indicated the desirability of adoption of a variable pond level, conforming to prevailing river water level as far as practicable with a view to preventing harmful siltation upstream of the barrage. C 0 N T E NT S

Pages

CE .TT Fl C \TL aCKNO`°1L2DG MSS IS SYXI PST S

C: { 1PTcR — .1 INTRODUCTION

Cj 1 APT =R — 2 LITERATURE RSVI E':!

CHAPTER — 3 CASE STUDY

CHAPTER — 4 DISCUSSION

CH \PT ER — 5 CONCLUSION

R-.F'-R'~1C35

FT GUl. S

CHAPTER-1 I

INTRODUCTION

1,1 GENERAL

Barrages and weirs are man made barriers constructed across rivers for diversion of a part of the river flow to the offtaking canal. The diverted water may be utilised for irrigation and/or for power generation. Waterway of a barrage wields a close influence not only over the hydraulic design of the structure but on its performance as well. The waterway is generally decided considering a suitable looseness factor, which is a ratio of the actually provided waterway to the Lacey's wetted regime perimeter. So far, there is hardly any consensus among river engineers and designers on the value of looseness factor that should be adopted in design. As a result the Looseness factor is often adopted by the designers banking upon his judgement and experience which differ widely from barrage to barrage. This is borne by the fact that looseness factor, of some of the existing barrages and weirs varies between 0.45 to 2.2. Also, the status of design discharge for waterway is left to the discretion of the designer and is practically decided on conjecture.

The subjective approach to the problem of determining the waterway has been responsible for Wanton shoal formation on the upstream of the diversion works thereby vitiating the hydraulics, functioning of'the structure. Obliquity of flow, shifting of deep channel, masking of some barrage bays, development of cross 2

flows are some of the problems which manifest in the wake of shoal formations in the upstream of a barrage. Other,attendent problems associated with shoal formations are increased in the depth of local scour, reduction in effective waterway of bas, increase in afflux, vitiating the hydraulic jump and increase in the value of downstream retrogression. In other words, a waterway which is not arrived at after well- thought-out and rational analysis, but decided on some sort of thumb rule, may lead to a com.. plete failure of the intended hydraulic functioning of the barrage as outlined above. In the light of the above, it has been felt that a study on the looseness factor i.e. waterway of a barrage is of great importance to the designers of barrages.

1.2. PR:FSEXT PRACTICES.

The present practice of design of barrage is to fix the waterway of barrages same as Lacey's wetted perimeter. Lacey's wetted perimeter is defined as 4,75/f, where 1 Q' is the design discharge considered for fixing the waterway and is normally 1 in 50 years, The practice of using Lacey's regime concept for fixing the waterway does not seem to be rational and in fact is very much arbitrary. This is because --

i) The constant of proportionality has a value in between 3.6 to 6.15. ii) Unlike a constant discharge in a canal, the discharge in a river is highly fluctuating. Hence the discharge to be considered for the purpose of fixation of waterway is of critical importance. iii) When a structure is built across a river, its regime gets disturbed. Hence, strictly speaking, it may not be reasonable to apply Lacey's regime theory for the post barrage condition.

s per some of the recent studies a criteria may be fixed for fixation of waterway by studying the cost economics of the barrage and the waterway giving the lowest cost may be adopted. In each design, the designer designs a structure with two. aims in front of him, (i) safety against failure and against failure in functioning (ii) structure should be economical, Hence, even though a structure is economical, i may fail to function satisfactorily. The purpose of the construction of the structure is not fulfilled.,

1.3. DESCRIPTION OF ANALYSIS i) The first aim of the analysis is to study to what extent a fixed fond level and the waterway affect the transporting capacity of the stream at different stages, 'Dakpathar' barrage has been adopted for this analysis, The analysis has been done by using shields modified curve for tractive stress. It has been found that available tractive stress varies inversely as the waterway, ii) The second aim of analysis is to fix a suitable waterway for .(a) minimum shoal formation in front of the weir or barrage (b) Least affect on the morphology of the barrage by construction of the structure.

For the above studies I Bed generative discharge, as proposed by Schaffernack has been considered, This bed generative discharge is the discharge carrying the highest volume of silt. 4

For this study Bhimgoda weir site has been taken into consideration, The main difficulty faced here is the non-availability of silt data. Hence silt volume has been estimated by using Du-Boys' equation. Bed generative discharge has been found out by using the procedure proposed by Schafferneick.

For a pond level corresponding to mean annual flood, silt carrying capacity of the river at post construction stage just upstream of the barrage has been estimated at bed generative discharge. From this the width needed for sediment carrying capacity at bed. generative discharge will give the required waterway of the river near barrage.

Lanes, simple theory relating discharge, slope, sediment discharge, Median diameter of the bed materials has been applied for arriving at the waterway which will have least affect on the morphology of the river has been determined.

The waterway obtained from the above two different ways of analyse are nearly equal. But it is very much different for the waterway required from the point of economy. Hence a compromise is to 'be made between the two.

With the waterway as found, from above and the available discharge during monsoon, pond level that can be maintained for keeping all gates opened has been found out. Also the part of the waterway that is to be closed for maintaining the pond level has been determined. From the analysis of silt carrying capacity it was seen that a variable pond level is a better concept as far as silt transport across the diversion work is concerned. 5

1.4. OBJECTIVE OF THE STUDY

In this study an attempt has been made to find out a suitable approach for fixing the waterway for (i) minimum shoal formation in front of the diversion structure, (ii) least effect on the regime of the river due to construction of the diversion work without considering the economy of the structure.

By conducting such a study, a hydraulically efficient waterway can be found out and knowing the economical waterway, a compromise can be made between the two and the waterway so obtained will be rational from the point of view of design,

logical determination of waterway of a barrage may lead to the following desirable situations -

1) Shoal formation invariably associated with diversion works may be contained within tolerable limits and river behaviour may remain stable.

2) The obliquity of approach flow if any may be corrected to tolerable limits. 3) The deep channel may not shift away from the head regulator. 4) The downstream bed retrogression may reduce and thereby tail water levels remain adequate for keeping the hydraulic jump within the glacis, 1.5 OUTLINE OF STUDY

As indicated earlier, the main objective of this study - - Y is to develop a rational approach for determining the waterway of a barrage taking help from the existing theories of sediment transport. The studies mentioned below have been undertaken in this dissertation. a) Variations, of critical discharge for incipient motion of different particle diameters withdifferent water way by using Schield' s approach. b) Determination of waterway with a view to transport, the greatest volume of silt load past the barrage employing the approach of Schafferack for bed generative discharge and simplified Du-Boys's equation for. sediment transporting capacity. c) Calculation of waterway with a view to cause least dis-» -turbance to the morphology of the river as per.Lane's's formula. d) Inter-relation among water way, pond level and barrage gate operation. 7

CHAPTER- 2

LITERATURE RE TIEW

2.1 GENERAL

A canal supplying water receives its supplies from a stream. To divert, the water into the canal it is required to cons- truct works across the river. These works are termed as = Head works', ' Headr-works' may be of two types --

i) Diversion work ii) Storage works Diverting water by construction of a weir or barrage comes in the first category. These are located across the river to raise the normal water level of the river to divert the required supply into the canal. The main functions(l) of a weir or barrage may be summarised as below -

a) To raise the water level in the river to the required extent for diverting the supplies into the canal and totally cut off all flow downstream of the works when the entire supply is required in the canal,

b) To regulate the intake of water into the canal and control silt entry. c) To reduce expensive cutting in the head reaches of the canal and facilitate command of the area by flow.

These weirs and barrages are normally located in the boulder or alluvial stage of the river. `bl

When the ponding up of water is mainly effected by means of gate control, the diversion work is termed as a barrage, But in case this pending is achieved partly by raised crest and then by falling shutters, it is called a weir. To define both specifically, Dr. R.S. Varshney(2) says,' If the difference between the pond level and crest level is within 1,5 m, the pond level can be maintained by means of falling shutters. However, if the differ- ences is more than 1.5 m, a gate controlled weir is necessary which is called a Barrage'.

In the design of a barrage/ weir the fixation of waterway is an important aspect as it affects considerably the design of other components of the barrage/weir and also affects economy and hydraulic efficiency,

The waterway and the discharge per metre run and the limit placed on the afflux also limits the minimum waterway. While designing a barrage for alluvial reaches, a likely figure adopted for fixing the width of the water way is the Lacey's stable perimeter, But it is to be remembered that the regime conditions are disturbed by construction of the structure and the formula is strictly not applicable. As regards to Boulder reaches, IS 6966-1973 ' Cri- teria for Design of Barrages and Weirs' (3) recommends that for deep and confined river reach with stable banks, the overall water way should be approximately equal to the actual width of the river at the design discharge'. For sites where the river is comparatively wider, as is generally met with in practice, no criterion is available for ascertaining waterway of barrages in boulder reaches. Waterway for Boulder reaches as well as alluvial reaches can also be decided by means of economical analysis.

2.2. DEFINITION OF LOOSENESS FACTOR Looseness is a comparative term meaning the ratio of the actually provided with of the structure to the Lacey's wetted perimeter. By equation it may be represented as P Looseness factor = P1

P p= Provided water way P1 = Lacey's wetted perimeter

Lacey 's regime concept (1,4) Gerald Lacey, who retired as Chief Engineer from Irriga- tion Department of U.P. in 1945 carried out a long detailed study of the problem of designing stable channels in alluvium contributed significantly towards the advance of knowledge on this subject. His conclusions were first published in 192-9-29 in the proceedings of the Institution of Civil Engineers, London, In his paper, in 1939 which was published in Technical Paper No.20, OBIP, India, his equations were slightly modified from his earlier publication.

Regime condition -,For regime conditions to be established, the essential requirements are - a) Discharge should be constant, b) the channel flowing in unlJ.rhited inchoerent alluvium, of the same character as that transported c) and the silt charge and silt grade are oonstant.in rivers, flow is a variable parameter. 10

Although the sand in river bed may be perfectly inchoerent, it is at full stage or at high flood time and at other times the .bed may be inert. In gravel and boulder rivers, the effect is more marked. It is only in floods of great magnitude, that the river is fully active and the bed material takes part in the flow. As the floods subside, the gravel and finally the sands even be_ come inert, The channel at low discharges has almost a rigid bbun- dary so far as sediment movement is concerned.

Wetted perimenter as given by Lacey -

At regime condition Lacey found that wetted perimeter varies directly as square root of 'Q', Where 'Q' is the dominant discharge. He found that the constant of proportionality as '8/3' when 'P' is in feet and dominant discharge in cubic feet per second.

Langbein has also applied statistical concepts to study the geometry of river channels. He also found that the water surface width varies as dominant discharge raised to the power 0.53. which matches with that given by Lacey. Leopold and Maddock studied the variation of water surface width, mean depth, and velocity at a particular cross section with variation in discharge, Such data collected on several American streams showed that Ws = a Qb. They found that when 'Q' is taken as mean annual flood 'b' equals '0.5'.

2.3 CONSTANT(5) OF PROPORTIONALITY OF LACE('S EQUATION FOR WETTED PERIMETER The conventional value of 4,75 (2,67 in F.P. aumits) for constant 'in Lacey's wetted perimeter equation is the least fit value for regime conditions, the actual value ranges from 3.6 to 6.15 11

(M.K.S, units). Nixon has demonstrated for rivers in England andWales that the value of constant varies from 8,87 to 2.99 depending on the frequency of discharge. The value of 4.75 corres- ponds to a frequency of 3.7 percent. It has been stressed that the regime condition as envisaged by Lacey, can occur only at one discharge, frequency of which vary for different climatic and geolo- gical regions. Since this constant has a wide range of values it is really difficult to choose the most appropriate one.

Discharge parameter in the wetted perimeter equation -

Lacey was of the opinion that, although the regime wa in rivers is rare due to greately fluctuating discharges, some degree of stability is reached at the peak of the high floods, and on this assumption flood and scour problems of the river can be solved considering the limitations of Lacey's expression and the divergence observed in many cases, Inglis introduced the concept of dominant discharge with a view to use Lacey's regime equations in case of rivers. In several streams the ratio of maximum to minimum discharge can attain values as high as 1000 or more. Flashy streams have very high value of this ratio„ Similarly, the variation of sediment load can also be very large. During low flows there may be little sediment transport, while during high flood the stream may carry high sediment loads with a wide range of sediment size. The following table shows the variation of discharge in some of the Indian rivers (4). 12

River Ratio of minimum to maximum discharge

1. Ganga at Farakha 34.6

2. Mahanadi at Naraj 108.0

3. Sutie j at Rupar 133.0

4. Ravi at Madhopur 411.0

5. Ujh at Chak Basti 2400.0

2.4 CONCEPT OF DOMINANT DISCHARGE (4,5)

Due to the above high variation in discharge throughout the year in contrast to that of canal, Inglis introduced the concept of dominant discharge. According to Inglis, there is a dominant discharge and gradient to which the channel returns annually. At this discharge equilibrium is most closely approached and the tendency to change is least. This condition may be regarded as the in- tegrated effect of all varying conditions over a long period of time. In other words, steady dominant discharge is that high pothe- tical steady discharge, which would produce the same result as the actual varying discharge. Inglish found that for North Indian rivers, dominant discharge is same as the bank full discharge and recommended that dominant discharge may be taken as 1/2 to 2/3rd of the maximum discharge. Blench defines dominant discharge as the discharge which is equalled or exceeded 50 percent of the time. Hence dominant discharge may be obtained by drawing a line at 50 percent frequency in the flow duration curve. 13

USBR defines the dominant discharge as the discharge that with carry the greatest sediment load of material coarser than 0.0625 mm with respect to time. This discharge is slightly higher than the medico discharge.

The work done in England, U.S.A., Japan, defines dominant discharge' as the bankful discharge or discharge with 1 in 2 years return period.

H.D. Sharma specifies dominant discharge as 60 to 75 percent of the observed maximum flood if the long term data is available or in l in 100 years flood. In case of incised rivers, the bankful discharge may be taken as dominant discharge. Schaffernack has introduced the term I bed generative discharge' defined as the discharge that transports the largest volume of coarse material. Fig- ure below explains his idea.

Rate of sediment QT X T (Frequency) Transport QT (c) (a) (b) Figure (a) represents discharge (Q), vrs frequency Figure(b) represents discharge (Q) vrs rate of sediment transport T Figure(c) is obtained by combining Fig,(a) and (b). 14

The concept of bed generative discharge is considerably reasonable as far as the regime condition of the river is concerned since this discharge carries maximum volume of silt load. The difference between concept of dominant discharge as given by U.S.B.R. and the bed generative discharge by Schaffernack is that in the- later case, there is no limitation for sediment size. 2.5 LIST OF LOOSENESS FACTOR AND WATERWAY OF SOME WEIRS AND BARRAGES IN INDIA (5,6). (A) Weirs

Name of weir(8) Looseness factor 1. Sulemanki 1.47 2. Islam 1.15 3. Merala 1.98 4. Khanki. 1.91 5. Trimmu 1.41

6. -Panjanand 1.56 7. Rasul 1.76. 8. Kalabagh 1.46 9. Okhla 2.00 10. Tajewala 1.25 11, Bhimgoda 1.27 12. Narora .7 2.20

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4- r 2, 6 STUDIES MADE UN THESE EXISTING BARRAGES(5 9 6) Weirs - Weir constructed during 19th century in Punjab ( now most of them are in Pakistan) and U.P. are generally sited in alluvial reaches or in transition reaches from boulder to alluvial stages. Those-were provided with waterway nearly equal to the width of the river with looseness factor varying from 1,5 in to 2.0. Heavy shoals have invariably formed in the upstream in. almost all cases. A lot of difficulties were faced in feeding the canal due to shifting of the channel caused by shaols. a) Bhimgoda weir The river Ganga at Hardwar is at boulder stage with bed materials sand, shingle and boulder of maximum size 300 mm. The average annual flood discharge of the river is about 6000 m3/sec. A maximum flood of about 16,000 m31 see passed in 1924. The provided waterway works out to be 1.27 for the maximum flood of 13,000 m3/ see. The average discharge intensity works out to be 26,5 m3/sec/m.

A study of the river cross sections at 0.4 km and 1,5 km upstream of the weir for various 1gmaxxixa dwtaixmmank years since 1939, indicates that there has been a progressive development of the island between the left and right river channels. The main island has now extended upto the weir crest in front of Bay 110.4, The top level of the shoals had risen by about 1.5 to 2.0 m as appears from 1961 cross section at 0.5 on upstream. During she second high flood of 1963, the shoals were washed off and these top levels were lowered. Since then the shoals on the right horse developed considerably and the deep channel has shifted towards the right afflux bund. The shoals have extended to the main island and have extended 20

to the weir crest in front of bay No.2. This has resulted in ex- cessive deepening of the main channel along the right afflux bund. The observations indicate that about 40 percent of the river discharge passes through the under sluices bays and deep scours have taken place along the right afflux bund. The daily gauge discharge observation at old Bhimgoda shows that a rise of about 0.5 m in the flood levels has taken place.

SardaBarrage

Sarda barrage was constructed at Banbassa on river ;ardor, The river bed at the barrage site consist of sand, shingle and boulder of maximum size upto 0.3 in The average annual flood discharge of the river is about 6500 m3/sec. A maximum flood of 16,400 m3/sec passed down the barrage in 3.924. For a maximum flood of 16,400, the looseness factor comes nearly to 1. T his flood has a return period of 1 in 50 year. The average discharge intensity works out to 27.m3/sec/m. it the maximum flood of 16,400 m3/sec. Pond level is 223.0 m against barrage crest level of 219.15 m(R.L.), The cross section at 0,5 km and the river surveys have indicated that the shoaling have occurred on the side of the Kalajala island depending on the extent of the development of the left or right channel, The total area of flow below the high flood level was slightly reduced indicating some accretion, The distance of the island from the barrage axis has, however, not appreciably charged.

The cross section at 1.2 km indicates raising in Kalajala island by about one metre without any appreciable change in width upt 1948. The L-section of both right and left channel indicates that appreciable aggradation has taken place in both of the channels. 21

DakDathar 3arrag

The barrage consisting of 25 bays of 18 m width was constructed in 1965 across river Yamuna about 2.5 km downstream of its confluence with river tons, The river bed at the barrage site consists of sand, single, boulder of maximum size of 0.,5 m diameter. The river before the construction of the barrage used to flow in two channels separated by an island. The barrage was sited downstream of the island where the river, used to flow in one channel, The average river slope prior to construction of the barrage was about 4.2 m/km. The crest of the six under sluices bays and other bays were kept at EL 449.95 in and 450.65 in respectively against the average river bed level of 449,0 m«. The barrage was designed to provide supply to a power channel from the left flank at a pond level of 454.15 in EL originally during monsoon period.

Since the construction of the barrage, very low floods have passed through it. The maximum flood which passed through the barrage in 1971 was of the order of 4000 xrm/sec. The waterway provided is for a flood of 11,600 m3/sec. Ike aakax way pxoxrdud i$ of frequency 1 in 50 years. The average discharge intensity at the design floods works out to be 22.5 m3/sec/m.

During the construction period, between 1962 and 1965, the month of the left channel got shoaled up and a channel developed across the island from about 1.0 km upstream of the barrage. Cross flow condition developed across the barrage while feeding the power channel during the first year of its running. The left bank channel was developed by constructing a few bed bars across the mouth of the right channel and operating only the undersluice bays upto a flood

of 1000 m3/sec. .' 22

The cross-section at 0.12 km indicates that 55 and 33 percent of the original flow area at the level and design flood of 11,600 m3/sec is left after the floods of 1966 and 1971 respectively, At 0,35 km upstream of the barrage, the area of flow reduced by about 50 percent after the flood of 1966. The L--section indicates that the slope of the river is gradually decreasing, By 1965 it was reduced to 3 m/km and by 1971 it was reduced to 2.5 m/km, The above facts indicate that heavy shoaly in the upstream of the barrage was taken place.

A study of daily gauges maintained at the head works during floods indicate that in order to feed the power channel during the monsoon, the pond level was very often raised to 455,50 m (corresponding to a flood discharge of 12,000 m3/sec). Due to per_ sistent low floods, maintenance of high pond level during floods, passage of low flood x through undersluices only and large propor- tion of sediment moving as bed load in the river, the shoals upstream of barrage have progressively developed,

While designing the barrage floor, a retrogression of 0.6 in and 1.2 in in the flood levels was assumed at a river discharge of 14,400 m3/sec and 700 m3/sec'respectively, The downstream floor levels were fixed on the consideration that the hydraulic jump forms at the toe of the glacix at all discharges, The downstream floors were thus laid about 3 to 4 m below the average bed level. Energy dissipators were also provided, After commissioning o.f'the barrage, it has been observed that, the stilling basin both for undersluices and the barrage bays have shoaled up by 2 to 3 m, The river gauge 23 discharge relation downstream of the barrage indicate that retrogression in water level to an extent of 0.3 m at the low floods of about 3000 m3/sec. Okhla weir This was constructed on river Yamuna at Delhi where the river is at alluvial stage. The river bed. consists of sand of average size 0.25 mm. The average river slope prior to the construction of the river was 0.5 m/km.

The average annual flood discharge or the river is 2830 rr / see where as a maximum flood of 5825 m3/sec has passed down the head works in 1924. The waterway is about 2 times that of the Lacey's wetted perimeter for a maximum flood of 5825 m3/sec which has a frequency of 1 in 60. The average discharge intensity works out to be 7.5 m3/sec/m,

At the time of construction of the weir the river used to flow normally and centrally to the weir. After commissioning of the weir, the river started meandering between the old railway bridge and the weir. The tendency became pronounced, after 1887. Gradually the meanders developed and shifted the main current to the left. As a result the left marginal bund was to be protected by spurs.

The river cross-sections upstream of the weir indicate raising and widening of the shoals. A raising of about 1.0 and 1.5 m is indicated at 0.8 km and 4.0 km respectively, The cross sectional area show that accretion occured rapidly after the 24

construction till the shoals developed to the crest level. Upto 1904, about one third of the area of flow below EL 202.5 (H.F.L.) was shoaled up at both the cross-sections. The L-section also shows trends of accretion. The upstream slope had flattened to 0,3 m/krn in 1895 and at present it is the same.

Barrage on Sutlej at Harike

Looseness factor is 0.97 corresponding to a design flood of 18.1414 m3 /sec, The barrage passed a flood of 26,912 m3/sec in 1955 after two years of its commissioning. During this high flood, the river bed was scoured between the guide bunds, Due to inadequate free board, the afflux bunds were overtopped and breached at few places. But there was no damage to the barrage. After that due to construction of Bhakra dam, no major flood has passed over this barrage. Heavy shoal ,formation has taken place.

2.7 COMPARISON OI' THE ABOVE OBSERVATIONS

In case of weirs and barrages, shoaling in varying degree in the upstream has invariably been observed. The shoaling in weirs and barrages, depends on the pond level maintained during monsoon when the river brings a lot of silt. In case of barrages, with high pond the gates can not be opened frequently to flush the shoals. This results in heavier shoaling and becomes rigid due to vegetable growth as time passes. Comparison of Dakpathar and Sarda barrage reveals an important conclusion leaving aside the fact that very low flood has passed over the barrage since its construction period, the pond level maintained is high, For Sarda the pond level maintained is 25 equal to the level corresponding to mean annual flood. So though the looseness factors in both the cases are nearly same, high pond level has caused the shoaling upstream of the weir. Barrage on Sutlej at Harike proves that if the water way can be provided for a lower flood and the barrage is designed for a.higher flood, then shoaling will be less.

2.8 EFFECT OF CONSTRUCTION OF A WEIR OR BARRAGE ON MORPHOLOGY OF A RIVER Definition

Rivers may be considered as self adjusting systems develop- ing towards a stable equilibrium between tractive and resisting forces, Any interferences on the system from outside means a disturbance of the self-adjusting process just taking place,

This stability means a stable morphology and morphology of a river comprises of the following parts -- (1) Plan (2) Longitu- dinal profile,(3) cross section. These three parts are considered as unit and note of them can be considered without looking at the 'other. For stability of equilibrium, Mayer Peter has given the following relation (7)

a. 6a . Ia b, dm + c. E where Q = discharge I ^ slope of energy gradient dm = mean grain'size of sediment C42 = bed load discharge a, b,c = Constants standing for the Meyer-Peter coefficients with the constants of water and sediment incorporated. a ,ti , E ¢ constant exponents found by Meyer Peter. 26

Now if, a. t~a .I~ < bdm . C.~E, the river is in stage of sedimentation

If a e *- IR > b.dm i C.(ZI, the river is in stage of erosion If a Q ,IH{7) ~=~) bdr t C Co, the river is stage of late at E erosion.

Now when a weir or barrage is constructed on the river, Q, all thesefactorschange. Hence thele happens change of the ongoing process. But the feed back-effect of the water extraction on the river itself and the consequence for the morphology are hardly noticed, in any case they are under estimated. However the res- ponse ( or should we say the revenge) of the river may be delayed but sooner or later it inevitably comes and then in many cases start: creating one problem after another,

On the other hand, when a diversion is put on the right place and designed properly, that means when its affect is in accordance with the self adjusting process just going on in the river, then the work of the river can be supported and stable condition can be reached even sooner than the pace of nature.

As far as the plain of the river is concerned, diversion and sections where the river shows braiding patterns should be avoided. Moderately, meandering river section is the most suitable one for the purpose, As far as longitudinal profile of a river is concerned, the outstanding locations for placing the diversion work is the section of latent erosion, The stage of sedimentation is the worst.

For general analysis, it is very useful to consider the original equation proposed by Lane (8), The equation states 27

Q.S cc Qs D50

Q = a discharge S = the channel slope QS= sediment bed material transport D50= median diameter of bed material

2.9 EFFECT OF ,BARRAGE OR WEIR ON THE MORPHOLOGY OF THE RIV.T? AND ANALYSIS OF SUKKUR BARRAGE DATA (9)

The first effect of a weir or barrage is a flattening of the water surface slope for some distance behind the weir due to ponding up of supplies, This results in reduction of sediment transporting power in that reach so that the river drops a part of the its sediment load resulting in formation of shoals and islands in the pond. Relatively clear water which passes over the weir takes up silt particles from the load to make up its deficit of silt carrying capacity, This results in retrogression downstream.

InAcase of Sukkur barrage on Indus in Sind, the barrage gates were first closed in 1932 with considerable ponding upstream, Coarser grade of silt and sand deposited far up while finer grades deposited on banks and berms nearby,lsthen the gates were opened to pass the high flood.discharge, coarser grades which had deposited far up moved a short distance down during the short time the gates were opened and deposited upstream while the finer grades moved down. This analysis of Sukkur barrage gives emphasis that the river upstream of the barrage is to be constricted to such an extent so that these remains sufficient tractive stress for moving the coarser particles towards the barrage. MW

2.10 RECENT STUDY REGARDING EFFECT OF WATERWAY ON ECONOMY OF THE BARRAGE (10,11) Alluvial reaches - Fixation of waterway on the basis of Lacey's wetted perimeter corresponding to design flood is not a sound practice. This is because the overall economy of the barrage depends upon the waterway and pond. level. Generally there remains little scope for adjusting pond level. In case, irrigation is the objective of the barrage construction, then the pond level is decided as per the command area to be provided with irrigation. Hence waterway plays an important role on the economy.

For a particular design discharge, the discharge intensity will vary with the water way with increase in discharge intensity, the afflux, head loss, and post pump depth will increase. Accord- ingly the level of stilling basin will be lowered and its length increased. But the number of gates and pier shall be reduced,

With decrease in discharge intensity the cost of floor will be reduced but that of pier and gates will be increased, On the basis of the above analysis on economy of barrages, the following facts are found for alluvial and boulder stages of rivers, Alluvial reaches - The design flood should of shorter return period and the barrage gates should be kept opened during floods. The design flood may be of 1 in 50 years frequency. Extra struc- tural safety and free board may be provided to take care of the high floods. 29

For barrages in alluvial rivers, the scour becomes the governing factor for both upstream and downstream cut offs and practically no economy is achieved by increasing the depth of downstream cutoff beyond the scour requirement.

Average discharge intensity ranging- from 22.0 to 27.0 m3/ sec gives the minimum total cost for barrages in alluvial rivers.

In the cases where river training works involved are ex- cessive, the cost of such works becomes a dominating factor and upsets the economy achieved by the other factors. Hence effort should be made to keep the' afflux as minimum as possible in such cases.

The waterway fixed on the above principles should be sub- jected to model tests before final adoption as the problem for each barrage are unique in many respects.

Boulder reaches The extent of constriction of natural waterway of rivers at barrages depends upon various parameters like design discharge, nature of river cross section, permissible afflux, river bed ma,- terial, training works and economics. The water way of a barrage in boulder reach can be varied with the values of above factors within permissible limits, So from site to site this analysis will vary since the limiting factors vary from site to site. From analysis, the value of this intensity of discharge for minimum cost of earth work, concrete, granite, surfacing has been found out. These are as follows Si. Name of River on Design flood Gate height Discharge in- No. Barrage which lo- discharge in in m tensity in cated /sec m3/sec/m for minimum cost i. Dakpathar . Yamuna 14,600 7, 5 30 2. Kosi barrage Kosi. 4500 4.5 and 32 at Ramnagar 6.8

3. Bhimgoda Ganga 13,200 10.0 and 26 barrage 6.0

After analysing the above barrages the following are the recommendations for fixing the waterway of barrage in boulder reaches,

1. The waterway of a barrage in boulder reach may be decided for l in 50 years or 1 in 100 years flood, 2. In case of narrow, deep and confined rivers with stable banks, the water way should be decided by the actual width of the river. 3. If the river is not narrow, the following criteria. may be followed for fixing the water way - a) When the gate height is more than 8.0 m,, the average discharge intensity may be as high as permitted by allowable afflux. b) When the gate height is less than 8.0 m, and the valley is sucl that at permissible afflux, discharge intensity more than 35 cup- mees/m can be allowed, the overall waterway should preferably be determined with the discharge intensity (average) of 30 to 32 cumecf m. The high flood can be passed through the water way so assigned. c) If the permissible afflux is low, it alone may govern the 31 waterway. d) The depth of downstream out off may be as large as possible, so that upstream floor length is minimum, depending upon the open excavation in boulder reach,

2.11 MO\1NIENT OF SEDIMENT IN RIVER (12)

Some definitions Mobile boundary - A mobile boundary is defined as one which comprises particles which can move under the action of flowing water, incipient motion condition - The prevailing conditions of flow at which a particular diameter of silt just starts to move is the incipient motion condition,

Critical tractive stress - The average stress on the bed of the open channel at which the sediment particles just begin to move in the crit.cal tractive stress. Tractive stress = zo = y. R.S., where

7 . unit weight of the liquid R = Hydraulic radius ( or mean depth) A/P S = Slope T Shear velocity = U = Po

Where P = Mass density of fluid.

2.12 DIFFERENT THEORIES ON MOVEMENT OF SEDIMENT

A completely theoretical solution for the incipient motion condition is not available. And hence recourse is invariable made to experimental analysis. For analysis it is assumed that there exists a certain velocity which imparts motion to the particle 32 under consideration or there is a certain force which leads to the movement of particle.

Depending on the above facts, three different approaches have been used to establish the condition for incipient motion of sediment particles comprising the bed. i) Competency - Here the size of the bed material is related to either bed velocity ( or bottom velocity) or mean velocity of flow, which just causes the particle to move, ii)Lift concept - In this case it is assumed that when the upward force due to the flow is just greater than the submerged weight of the particle, the condition of incipient motion is established. iii)Critical tractive stress approach - This approach is based on k} the idea that the tractive force exerted by the flowing water on the channel bed in the direction of flow is mainly responsible for the motion of the sediment particles. Among these approaches, critical tractive stress approach seems to be more rational and more sound than the others and is now used more often than the other two approaches (4). Expression for average shear stress -

Consider steady uniform flow in a wide rectangular channel and consider equilibrium of water prism (as shown in figure) abed. There is no acceleration of flow, the summation of all the forces acting on the direction of flow must be zero, 33

Now the forces acting on abcd are -

i) Weight of the prism W ii) Hydrostatic force iii) Boundary resistance iv) Resistance of air at interface with water( may be neglected)

Hence ;F = Fl + W. Sim -F o( wetted ,area) = 0

Where "~o = Average shear stress at the boundary Fl,F2= Hydrostatic forces W = weight of the prism F1 = F2 ( since both are functions of ddpth and depth is same) or ixm W sire = x wetted area or, T = W sin a ._o Wetted area Wetted area = (B+2D).x, where B = channel width

or, -t = W since

But W= y x v o lame = 1 x B x D x x

So o - y. B .D. x sin a (B.2D) x - y.R . Sin ~s

If 'B' is very large in comparison to D, B.2D =B So, -r = y. B.D. sin a D. .o B - Y. sin a

For sac $ to be small, sin = tan a = S

So o = S. 34

2,13 ESTIMA`llON OF TRACTIVE STRESS AND THE NATURE OF THE MATERIAL

Shield was the first to give a semitheoretical analysis for the determination of the critical tractive stress and his re- suits are most commonly used today.

Shields analysis - Considering particle size 'd' and of man density 1 Ps i in a fluid of man density 'P', the force required to move the particle Fl may be written as

g (PS-P). d3 = Al.g APs.d3

Where (PsP) ='LPs

Al = It is a coefficient depending upon the particle shape and angle of internal friction, ~F2 the fluid drag on the particle ~a = CD.A2.d2.P. 2

Where, Ud = velocity at the top of the particle CD = Drag coefficient at the Reynold's number corresponding to ud. A2 = Coefficient depending upon particle shape From the law of velocity distribution,

U u ,d u = fl C am) K Cd = f2 ()

ud u d Hence F2 = f2 ( -7x - ). 2 u2 . f2 (

Equating Fl to F2, and using ' subscript' •e' to denote critical condition,

d g "Ps d3 =p2 (----C-~_) p u2 f2 2 2 is 1 t y ) A2d

C Designating -g p--~. d as T , and u c d/y as R- and on simplification, 2A TC A f (Rc )

For particles of not very dissimilar shapes and for a

constant value of the angle of internal friction, Al and A2 are practically constant and the above equation reduces to TK = g (Rc )

For simplification of analysis a new parameter IRi ' may be assumed /3 .d where R ( GPs )1/3 ( g1 P 72/3

By the analysis of collected data by various investigators, the curve representing T to Ri has been shown in Fig.2.1.

2.14 WAYS OF MOVEMENT OF SEDIMENT PARTICLIS

When the average shear stress on the bed of an alluvial channel exceeds the critical tractive stress for she bed material, the particles on the bed may begin to move in the direction of flow as per the general hypothesis. The particles move in different 36

ways depending on (i) particle size (ii) density of fluid and sediment (ii) flow condition. The sediment particles may move by rolling or sliding and such type of sediment is called contact load. A second type of movement is by bouncing along the bed. Material transported in this way is known as saltation load. Saltation is an important mode of transport in case of noncohesive materials of relatively high fall velocities, such as sand in air or to a lesser extent gravel in water. The third mode of transport is in a state of XxxRXxixiony suspension. In this case the particles are supported by the turbulent f'luctt ations. Materials supported and transported by this way are known as suspended loads. The subcommittee on sediment terminology of the American Geophy- sical Union has defined the various loads as follows -

Contact loQd- It is the material rolled or solid along the bed in substantially continuous contact with the bed. Saltation load - It is the material bouncing along the bed or moved directly or indirectly by the impact of bouncing particles.

Suspended load - It is the material moving in suspension in.a fluid, being kept in suspension by the turbulent fluctuation.

For a particular ratio of mass densities of the sediment to the fluid, the mode of transport are now generally believed to depend on the average shear stress on bed. For relatively low shear stress, the material is transported almost entirely as contact load. Some material is transported as saltation load at 37 slightly higher shear stress, if such a type of motion can occur in significant amounts for the given value of PsjPf. with a further increase in shear, a part of the material is transported in a state of suspension.

Contact load and saltation load are known as bed load. Thus the bed load is the material transported on or near the bed load(18).

2.15 BED LOAD EQTJJ T10NS (4) 0

Many attempts have been made so far to relate the bed load transport rate to the hydraulic conditions and the sediment charac- teristics. These equations have been developed primarily with the help of laboratory data, because fiO4d measurement of bed load rate are difficult and very few in number. Even in the laboratory experiments, it is very difficult to measure bed load accurately Further the rate of bed load transport at a given section varies considerably with time, Measurements have shown that the instan- taneous rate may differ from the average rate by as much as 300- 500 percent, It is on account of these factors that bed load equations developed so far are not so reliable as a hydraulic engineer would like them to be,

The bed load equations were first developed by Du-Boys in 1879, Since then several equations have been proposed to predict bed load transport rate. Some of them are completely emperical in nature, some are obtained from dimensional considerations and others are based on semitheoretical approach. Du-Boys was the first to propose a bed load relation and the form of the equation proposed by him has been used subsequently by many investigators. Assumption 1. He assumed that the bed material moves in a series of layers parallel to load, 2. The velocity of each layer varying from a maximum at the top layer of the bed surface to zero for the lowest layer at some depth.

Derivation

Let there be t N' number of layers moving. Thickness of each layer Velocity of second layer from bottom = ~V Velocity of surface layer = (NW-1) AV (Here a linear variations of velocity has been assumed). Hence the bed load transport rate in weight per unit width per unit time, qb will be, 39

qb = S.N.h

Since the lowest layer is at I rest', the resisting force at this elevation must equal the tractive force on the bed.

So To = (ys-y f ) N.s.h. tan ~r

Where '¢' is the angle of repose of the bed material. The value of 'N' can be obtained by assuming that a single layer is moving under the critical condition. Then the above equation becomes,

Toc = (7s_1 f).ah. tan j6 or N =TO/TOc

So qB = 2 2'Oc or qB = A ()t

Where A _ 2. 2 oc

The above form of equation as proposed by Du-Boys for bed load transport bears similarity with some of the more recent equations inspite of several questionable assumptions in this model„ Straub has determined the values of 'A' for different values mf I d' and qS

Bed load equation based on dimensional consideration - 40

Shields' Equation

=l0 q. 7. S (ys yf).d

Here q = discharge per unit width of channel qB = Rate of bed load transport in weight per unit width Ps = Specific weight of solids P = Specific weight of liquid T = Average bed shear toc Critical bed shear S - Slope d = diameter of silt particle

2.16 F IPIRICAL FORMULA

The most commonly used empirical equation for bed, load transport is by Meyer- Peter and Muller. The equation is

' y f_7b ) x d = 0.047 +0.25 ( f)l/3 ( °B)2/3 s f a s

x I f )1/3. d`

Here ns d906/ 26.0 ( in metric units) da = Arithematic mean size of particles n = Manning's rougsity coefficient ( for both surface and grain roughness) Rb = Hydraulic mean depth corresponding to 'n'.

Simplified form of Du!-Boys' equation . (l3 )

_ _ O S c s ©75 . 2. BY . S2 (1- 3 ) ( F.P.S. unit) -

Where Sc = Critical slope d + 0.8 = 0.00025 ( —m y: m dm = Mean diameter of the sediment Ym Average depth B = Surface width

Qs = Volume rate of transport of silt.

Since no bed load, data is available for analysis, the above simplified equation of originally proposed equation by Du-Boys' has been used for estimating bed load. However, this formula is an over simplification of complex flow problems and in practice, it is desirable to investigate the actual relationship between the various flow parameters by extensive observations, 2.17 EFFECT OF CI1.NGE OF DEPTH, WIDTH ON SEDIMENT CARRYING CAPACITY (14)

(i) Manning' s formula C _ n B. D5l3 . S1/ 2 (a)

(ii) Constant 2 ,. dTn (A) Effect of change of depth, when 'Q' and 'B' are constant. From (a). S % D-10/3 Putting this in (b) 42 fps = constant, D2 x D 20/3

= constant x

Hence

So the change of depth of water decreases silt carrying capacity as it varies inversely as the sediment carrying capacity. In case of ponding up of water, sediment carrying capacity decreases as depth of water by so becomes more than the depth previous to ponding at the discharges corresponding to ponding up level. Effect of change of width on sediment carrying capacity, when

Q$ and I S' remains constant —

From equation (a), D = B 315

So, from equation (b),

Qs a B7°/5 Be

Hence +Q' increases as width of the river is decreased. 43

CHAPTER-3

CASE STUDY

3.1 GENERAL

Study on the effect of waterway on the efficiency of diversion works in transporting silt has been done in two parts.. In the first part the case of Dakpathar barrage has been taken up for study for analysing the effect of water way on available tractive stress (10) for silt transportation. In the second part, Bhiingoda weir site has been considered for carryingout the analysis on silt transporting capacity of a barrage and weir at the site with different water ways and thereby deciding on the one having maximum efficiency without looking into the economy aspect. 3.2 EFFECT OF WATERWAY ON TRACTIVE STRESS

In this part case studies have been made on effect of larger waterway on tractive stress available. For this, Dakpathar barrage has been considered.

Data for the above analysis has been collected from CBIP publications (5)(6).

Generally, a barrage or a weir causes heading up of water and maintains a certain pond level for feeding the canal, Nor- mally, most of the time this pond level is higher than the natural pre-construction water level of the river. Generally, the prevailing discharge at which pond level is maintained, comes to be lower than the discharge pertaining to the pond M level flow for all gates open condition. Slope varies inversely 44 as depth raised to the power 3,33(14), This results in decrease of available tractive stress for movement of sediment load and this causes settlement of sediment,

Again depth varies inversely as width raised to the power 3/5 and hence by constricting the water way, the effect of increase in depth on slope can be manipulated to certain extent.

3.3 PROCEDURE

Here the following steps have been followed for the analysis„

1) Using Shields curve (Fig. .2.i), the critical tractive

stress (TC) for incipient motion for a certain diameter of sediment has been found out, 2) For known value of pond level, average bed level, average depth (D) of water has been found out. For large water ways, av, depth of water has been assumed as the hydraulic mean depth at the section. 3) Available tractive stress () is equal to r.D,S., where

yI is the unit weight of water and 'S' is slope. For

incipient motion, ITQ I was equated to ITC 1. From this equation slope, +S+ required for incipient motion can be known. 4) Manning's rugosity coefficient 'n' may be suitably assumed for the section,. Knowing, n,D,S, and assuming a value of water way, (B),the discharge QU at which the above diameter particles will start moving can be estimated by using Manning's formula. 5) By taking different values of 'B', the limiting discharges for a certain diameter of particles has been found out and plotted in graphs,

3.4 CALCULATION OF CRITICAL TRACTIVE STRESS ' I BY USING MODI- FIED SHIELDS CURVE

Assumed data -

1) = specific weight of water = 1000 kg/m3 2) = kinematic viscosity of water = lO m/sec. 3) g = acceleration due to gravity = 9.81 rn/sec. 4) Ps = specific weight of sediment material

= 2650 kg/ma

= = 2650-1000 = 1650 kg/M3 1/3 ( S )1/3 P 2/3 t0 txgx( 5 ). d i) Taking diameter of the sediment = 0.25 mm = 0.25 x10 3m =16 o 1/3 (9.81)1/3 1

= 6960 From the modified shields curve (Fig.2.1) corresponding to 4 = 6.60, t = 0.042 0.042 x 9.81 x 160 x 0.25 x 10 0. 169 N/m2

Tc = 0.06 x 9.81 x 1650 x 20 x10 3= 19.42 N/m2 vii) Taking particle size as 30 mm = 30 x 10~3 m

1650 Ri ( x (9.81)1/3 x 30 x103 (1 -6 )2 /3 = 660 10 ' =0.06 = 0.06 x 9.81 x 1650 x 40 x10-3 = 29.13 N/m2 viii) Taking particle size = 40 mm = 40 x 10-3 m = (1650)1/3 R1 )1/3 x (9.81)1/3 .x 40 xl03 x (1 _b )2/3= 880 10 =0,o6

tic = 0.36 x 9.81 x 1650 x 40 x 10-3 = 38.84 N/m2

The above results have been tabulated vide, Table N'0.3.1 and figure No.3.1.

Table 3,1 - Sediment diameter and Corresponding Critical Tractive Stress

Si. Sediment diameter in Critical tractive stress (TC) in No. mm N/m2

1, 0.25 0.169 2. 1,00 0„695 3. 2.00 1.620 4. 4.00 4.172 5. 6,00 6.490 6. 20.00 19.42 7. 30.00 29,13 8, 40,00 38,84 46 ii) Taking diameter of sediment = 1 mm x 1 x 10'3 in

l= ( 0)1/3 x9.81x1650x1x10"3 = 26,40

= 0.036 ( corresponding to Iii as 26.40) zc = 0.169 x 9.81 x 1650 x 1 x 10-3 = 0.695 N/m2 iii)Taking diameter of sediment = 2 mm 9 = 2 x 10-3 m R- = t la0- )1/3 x (9.81)1/3 x 2 x 10 x '~.'i~ 0 (10-2/30) 2/3 52.80 tiK=0.042

I c = 0.042 x 9, 81 x 165 0 x 2 x 10'3 = 1.62.N/m2 iv) Taking particle size = 4 mm = 4 x 10 m. x Rl ( 1100 )1/'' (9.8 - )1/3 x 4 x 10-3 x ----- 3 = 105.6

= 0.054 ( from the modified shields curve for Ri as 105.6)

Tc = 0.054 x 9.81 x 1650 x 4 x 10-3 = 4.172 N/m2 -3 v) Taking particle size = 6 mm = 6 x 10 m R1 = ( 1OO ) 1/3 x (9.81)1/3 x 6 x 10-3 x 1 = 132 (10-6)2/3 VX = 0.057 ( from the modified shield curve) tic = 0.057 x 9.81 x 1650 x 6 x 10 3 = 6.49 N/m2 vi) Taking particle size = 20 mm = 20 x 103 in

1/3 x 20 x 1073 x ---- ~. 440 Rl = ( -1 30) 1/ x (9.81) (i06)2'3 zX = 0..06 ( this remains constant for value of ftx as 200) 48

3.5 CALCULATION OF AVAILABLE TRACTIVE STRESS (C 0)

1. Average bed level = 449.0 m 2. Pond level during = 454,15 m monsoon ( at the initial stage) 3. Waterway provided = 516,33 m D = Average depth = 454.15 - 449.0 = 5.15 m. 4. n = 0.042 a) Taking waterway as 516.33- m, A = B x D = 516.33 x 5.15 = 2659.10 m2 (i) Particle size = 0.25 mm I_c = 0,169 N/m2 -c = zc = 0.169 N/m2 or, -y.D.S, = 0.169 169 = 0.169 or 'S = 0,7.D 9a10 x 5.15 = 3.345 x 107° or, q _ ( n , D2/3. S1/2)

x 5.15 2/3 x (3.345 x 1o_6)1/2 x 2659.10 0.042

347 m3/sec, (ii) Particle size = 1 mm 2 T c = 0.695 N/m -o= zc= 0.695 N/m2 or, y.D.S. = 0.695 N/m2

-- .695 5 or S - 0,y.D -- = .98100 x 5.15 11.376 x 10` 49

©L D . = ( . o.67 80.5). A

5 150.67 37 0.5 x (10-5)0.5 0.0421 X x2659,10

= 704.2 m3/sec. iii)Particle size = 2 mm = 2 x l0. in Te = 1.62 N/m2 - Q = C = 1.62 N/m2 or 7,D.S. = 1.62 I /m2 or S= 1 6 = 1 6 --'-y—~ ~- = 3.206 x10 5 9810 x 5.15

Q _ I D0.67, 80.5 L '" n A

0 x 5.15 0.67 x (3.206 x10 5)0'5 x 2659,10m2

= 1074 m3 /sec, iv) Particle size = 6 mm = 6 x 103 in = 6.49N/m2 -C = zc = 6.49 N/m2 = Tells. or 8 = 5.l5 = 1.2246 x104 = 96 0.67. $0.5 A L = n D x 5.15 = l 0.67 x (1.2646 x 10 4)0'5x2659.10 0.042

= 2151.69 m3/sec. 50 b) Taking waterway B, as (0.9 x 5'16.33 = 464.70 m)

D=5.15m A = B x D = 464.70 x 5.15 = 2393.2 m2 i) Taking particle size as 0.25 mm Tc = 0.169 N/m2 - _ - = 0.169 = 7.D.S. 10 .c since, y and D are same as in the case of water way as

516.33 M. S will be same. D0.67 $0.5) x A

( n . D0,67. 50.5) x B.D.

Since n,D,S remains same except IBI.

QD at 464.7 in of waterway will be proportioned in the propor- tion of the water way'. So QL = 0.9 x 347 = 312.3 m3/sec. ii) Particle size = 1 mm QD = 0.9 x 704.2 = 633.78 m3/sec. iii) Particle size = 2 mm Qb = 0.9 x 1074 = 967 m3/sec. iv) Particle size - 6 mm QL = 0.9 x 2159.69 = 1937 m3/sec. c) Taking waterway, B, as (1.1 x 516,33 = 567.96 m) i) Particle size = 0.25 mm QL = 1.1 x 347 = 381,7 m3/sec. 51

ii) Particle size = l mm QD = 1.1 x 704.2 = 774.6 m3/sec.

iii)Particle size = 2 mm QL = 1.1 x 1074 = 1181.4 m3/sec.

iv) Particle size = 6 mm

Qi= 1.1 x 2159.69 = 2376 m3/sec.

D) Taking water way, B, as (1.2 x 516.33 = 619.60 m)

i) Particle size = 0.25 mm q~ = 1.2 x 347 = 416.4 m3/sec.

ii) Particle size = 1 mm

QL = 1.2 x 704.2 = 845.04 m3/sec.

iii)Particle size = 2 mm

QB = 1.2 x 1074 = 1288.8 m3/sec. iv) Particle size = 6 mm QL = 1.2 x 2159.69 = 2591.63 m3 /sec„

Comparison of the result -

The above results have been represented vide table No.3.2 and graph No.3.3 . Table 3.2 - Limiting discharge for different waterways and diameter of silt 51., Waterway 'L' in m3/sec for diff, d.ia, of silt (mm) (L) 0,25 1,00 2.00 6,00 1. -. .. 516.33 343.00 704.20 1074,00 2151.70 2. 464,70 1.2.31 633,81 967,00 1937 .00 3, 567.96 381.70 774.60 1181,4 2376.00 4, 619.60 416„40 845.04 1288.8 2591.60 53

Id 0 0 O N L(\ d° (Y'0 C) \O CO O'\ CX) CO N M M CO ~O 0 • \D !f1 H N H C`- d' CO N co H Lam- s-I Ul '•' d" M ►n M ON M I.f' o rn -t- (N CO CO (NO O r- CX) CO M u \ H 0 (0 O HO to cT Ise r4 G) r4 N N N N N N N r-1 H r-! H H t•-i r--4 O 0 O O CO N '0 --i r-i r•I r-1 N (NH H H H r-I H H rl r-i ri r-1 H O Q\ O' G'

Cr' • cQ ic\ U 4 H \iD 07 - \ co '0 O\\ t 0 ri H O o H r-H M N H N N N N N N N N N M M N n! N H H H Z I r i r i ri r-•i rI H r q ri A A r i A A r r •i A r i A rl r-1 H

H N '0 o c- •o ON N N a H u, ~- ~ 0 0 0 0 -d- 4 In • d- H ON d O O •4- H O\ tll ll'• I l\ M rr \ Qd H N N N C') N O H N CX) N. \O N- CO mot` L \ m N o C Ls' Cc' Sc' ul1 d- ~1 d' :t• "I t- d- O M. N N N N N N N CU N N N' c•-•1 r•••~ H ri rA ri r-! H e--! r-I

Co • D M i.c N d' -4- P- CO 0 LCN CV N- d' - - (T d". 0 r! t-I LC\ N F CV d' M \0 N H M 0' 0" LCD H d' U1 LC O IC' '0 ~r' et ~F ra H m r-J CO ri CO tip 0 c3 U N \0 M 0 o r~-H \0 CN 0 d- u" N 0 C/2 C- lam• cc-, H ri CO N r- \0 \0 N N its N- ic is to 't •=i- d- -i- 0 CX) H CO M IC' T N in \0 ri M N Cl) H M N CO O L'-^ 0 t`-• H .t H N- N '4" Cr U1 lam- 0' CC" P- ni QO - 0o ~ t`- 4- \M H CO ~0 0 '0 tt1 CO u O" sr 11 % CO H •4- CM 'O 3" C') CO "4-CO A co 1* ~r-I H H r-5-5 rte'! rr4 r~-1 Hr -1 rte! H r0-4 © CO b M 00 43

S+ St N d' ri M H O" N- N IC' M N '-.O H d' N- M O C1) H O C7 H t4' H H 0 '4- 0' i.n H d- N P-• 0" O H H'- O O H-i fA ~fl pry C H ~`- N r-! \fl O to ( C) r-i "4- t- t!1 0 0 ~O0 q ► 00 amc... cam,.• N 'o i` t - m H CO N M CO amc- c°- l~ CO N CO t .

•~ ~ ,~ °` CO I.r1 ~o c~ coo cr ,-t cv .o ~ rn N cp rn a~ rn mot- ~t- 0 r- II1 r- I Wit ' `i- N N 111 0 0 N \0 d0 d' f-t a" 1L-• tom.. I O o 0' N K 1 '4- d' .t P H tr' ~D IC' ISM M r•H r-f N M CO C). F-~ N N CV N CV CV M M K~ M K1 N N CM CV CV pr' M r- IC' M m 4 N r-f CV 0')) CO r-I N tt1 N N- CO \0 0 d- r-H M •' CC' d- r~ N ' i• ice• CC' CM h- M CX) ul H M ( ~ 0' 0 r-I e-f '.O N •4 \O '4- I ?, M 0 0 N 0 rl ri N CO cT M ~- :7 CT N N rl to CO N to u1 cd '0 '.O N N- CO cT N S d- N N M d- . M N to ' - °d- '4- •4 50 4- r I r1 H 0-i r-! N N N N N N N N N N(N N N N N N N 4 ~O 110 O o N \O H M 0 U'\ CO O H rl rn • M UU H (N h M rJ U1 '4- r H N rn M W N M 00 00 r--H 0 M M ,n N N H 0 O" r-i N N N 0 {~- U-\ N CO N N 0

U) J CT C) N IC' O M cT CV r 4 r-! ~0 P1 v) • M 10 ~O CJ 0 to CO N CO d" N M 0 N- pr ±- N ~' F N O' \0 CO CV 00 N CJ 0'. '0 tft C') tit '.p •4- N N •4- CD C) Cr.) ~t--. o0 • to to N O O CM 00 (0 C) 0\ i -.4- N H r-_ rn H 0\ I.c~ .' \ O~ H r! -i H H C3\ h 00 H r -f r'-•1 r-i H H ri N N r-i ni •,-# ('4 • 0" CX) !^-• N- t1' ic'. CON ~- M to N N ice- ç-4 ON N '.0 N- N K! (0 N .0 `~, 'f' H H CT N.- N CT ►- C- N- d d' •~ 0X3 p'1 d' 0 r-i \0 r-! '.O w ~ \10 o o ~.O~\0 w N o \~a \Ds~ o 0 o'~r'i~`~c~'-

tr. O N t[' '.O \10 '.O C-- \0 4 0' \10 N '.0 I-~ N 0 CX)0 N .0's-f '.O 0 co M ! (0 '.D U U1 4 !L. U\ i. CV '0 N N M• (0 Y1• t.. C` N - f`-M` t - tom-1 Lam-M t`` L`.. Q) (0 GO Co Cam- N N- !`w N Co l`- E. f..

Cd d H M 4- IC' '0 N- 40 O\ 0 rl N ~-t to H N M d- t!1 ~O N CO 0'H ri r-1 ri H r-! r-i r-i r-i a-1 N N 52

3.6 FIXATION OF WATERWAY FROM THE CONSIDERATION OF SEDIMENT TRANSPORT

Ideally if waterway is so fixed that whatever silt comes in the' river is disposed off past the barrage, no shoal formation will tare place in the upstream of the diversion work. Bed generative °discharge as defined by Schaffernack, which carries the maximum ..:volume of silt has been considered for analysing waterway. T'he analysis is based on the following premise -

The inflow of silt volume that used to enter the cross-section of the river at barrage site should be carried past the cross section after the construction of the barrage at bed generative discharge.

3 ..7.,., FLOW DURATION CURVE

A curve representing discharge IQ with its frequency 'F' has been drawn for the river for computation of bed generative dis- .charge.

For drawing the above curve, discharge record for a long period is necessary, From Northen Dixision, Ganga canals, flood data for one year has been collected (Table 3.3). Since the river flow contains, very little silt during the lean period, flood data from 20th June to 20th September has been considered for the above curve. -procedure - For different discharge ranges, the corresponding time period of flow has been calculated. When this is converted into percentages

it represents frequency 4AF (Table 3,4 and 3.5) .

U1 'o ~-1 N N '0 Lr 4- Ot a' a' ON 00 W Q? co Co

dr fl N M 0 O QO O N O tom- c4M '.0 N N Co H CO u1 M M N N N N H H H H r rH r-i H

~- ONO tc\ '0 0 O' a' a' H CO N 0 :-) r-1 P-

U'N u1 C' tU\ t`- N ON M CO \10 tom- d WN \0 N L 0 N C' O' tt.\ d- d- p I M M M M M ch M

CO r-1 M r-1 0'\ r 4 ON O ON UO H O CO n CT rte! O O H N N O N N r-~ r-1 r-H s-1 r-1 r-! H C N N H N 0 iV N U'1 N- 0 0 rl CO Lt1 '0 N tip a' h- Co ..~ Co O 0\ O\ ON O c~ t u'~ N N- '0 Lam- Co ri ON N N N- ' I a) '0 N CT L, O e!- N H acd N 0' ri 0 \0 •* 1.[,\ 'c}' H 1• H M -, - u u1 tf U1 111 H

a' C' N- N C3\ - CV '0 lit M N N H CO H mot' H 0 '0 OH CO r-I N 'cF d• CO r-1 N N N N N N N N N

O' d` O '.O CO O' O CO O \0 u-\ \0 \0 0\ H H H H -i ice! H ri {

N -t CO \0 cr r-i LC\ Lc\ i.s, '.0 4- d- 0 N pr H H H H H ON CO

HO - 4- O r.. in \0 '.0 '.0 N H { 1 \10 '0 \10 \0 \0 ~~0 1

O' a'l N tom•. -i' \0 \0 '.0 la N fi i.n u t8 CO 0 0 \0 N- tom- Lam- N 'O O \0 N

LC N NN `N N CO N 0K"~ M 5 5 Table 3.4 - Computation for Flow Duration Curve

Si. Discharge in Days aF F aF cF(percent) No. 1000 cusecs available (days) percent (percent) (from smoothened cur 1 Z 30 94 - 100 - - 2 40 92 2 97.8 2.1 2.4 3 50 90 2 95.7 2.1 5.0 4 60 79 11 84.0 11.7 10,5 5 > 70 70 9 74,5 9,6 16,0 6 ~ 80 45 25 47.9 26,6 -26,6 7 .,, 90 31 14 33.0 14.9 11.3 8 > 100 26 5 27.7 5.3 7.2 9 ~ 110 18 8 19.2 8.5 5.8 10 > 120 12 6 12.8 6.4 4.4 11 2140 8 4 8.5 4.3 3.4 12 1 150 6 2 6.4 2.1 3,0 13 190 3 3 3.2 3.2 2.4 14 1 300 1 2 1.1 2.1 1.8 15 > 400 0 1 1.0 1.1 0.2

Table 3.5

40 50 60 75 100 120 150 200 (1000 cusecs)

"F 2.4 5.0 10.5 26.6 7.2 4.4 3.0 2.3 percent

"F = This is the difference between the cumulative frequencies between the row and the rr above it.

Then the graph has been plotted for frequency uF as abscissa and the mid point of discharge ranges as ordinate (Fig,3.4) A flow duration curve has been plotted vide Fig.3.5. ,3 ,8. ESTIMATION OF SILT BID LOAD Since silt data are not available the same has been computed, by analytical means using simplified DuBoy's' - bed load equation.

The equation states S QS = 1. y2,B.D2.S2( 1 Sc ) dm

where, QS = bed load volume in ft3/sec.

dm = Mean diameter of silt in ' mm1 y = Unit wt. of water in lb/ft3 B = Width of river in feet 'or' waterway of the diversion works. D = Depth of river in feet S = Slope rt d. i.0.8 Sc = Critical slope = 0.00025 ( m D From the above parameters, 'B' and 'D' values have been calculated by using stage discharge curve at 1,2 km u/s of the weir site and the x-section of the river at 0.5 km u/s of the weir site after suitably adjusting the stage discharge curve for the site for which the x-section is available with a slope of 1.6 m/km. 57

3.9 CALCULATION OF MEAN DIAMETER

'dm t represents mean diameter of bed load and this will vary from discharge to discharge depending upon the available tractive stress. Here it has been assumed. that the bed material size dis-

- tribution is same as the bed sediment size distribution. Again since the bed material size distribution is not available, the bed material size distribution at'Haridwar dam site has been taken as same as that of weir site. This has been collected from U.P. I.R.-I. , Roorkee and represented vide Table 3.6.

Table 3,6 - Table showing silt size. distribution

Dia Above '80 mm 20mm to 4.75 2 to 0.425 0.075 Less than 80 mm to 20mm 4.75mm to 0.425 to to 0.02 mm 2mm mm 0.075 0.02 mm mm

Per- 18 22 6 26 27 1 - cent

For calculating mean diameter at different available shear

-stress, it has been assumed that a silt mass of above distribution remains, in motion and a fraction of it settles as per decrease in available tractive stress.

In the above distribution, particles of diameter upto 80 mm

are in motion and hence the critical diameter 'dc I is 80 mm and the za ar±tx liamatizx available shear stress is critical shear stress corresponding to the diameter of 80 mm, •

Mean dia 'dm' when d0 is 80 mm

=(50x18+12,375x22 • 3.375 x6.p1.2125x26 i 0,25x27 + 0.0475 x 1) x 100 = 12.31 mm.

Now as the available critical tractive stress decreases as such so that silt diameter upto 20 mm stops moving, the frequency of the silt particles reduces to 82 and hence the mean diameter becomes as follows -.

dm = (12.375 x 22 + 3.375 x 6 • 1.2125 x 26+0.25x 27 • 0.04.75 x 1) x-82- =4.04mm

In the similar fashion as id.I becomes 4,75 mm, 3.375 x6*1.21.25 x26.0. 5x27 • 0. dm= 4 0.92 mm

When d = 2 mm,.

d 1, 2125 x26+ _0.25 x 27 +r _0.047 x 1 m . 58 = 0,67 mm

These Idm' values has been shown in table 3.7 against each ' dc+ value.

Table 3,7 - Showing critical diameter and mean diameter - --~-- d 80 20 4.75 2

dm 12.31 4.04 0.92 0,67 (mm) 59

A graph has been drawn to represent 'dc* vrs. Edm' (,Fig.-3.6) . 3.10 CALCULATION OF PRE-CONSTRUCTION WIDTH AND DEPTH OF THE RIVER AT BA.BRAGE SITE FOR DIFFERENT DISCHARGES FROM THE AVAILABLE CROSS SECTION AND STAGE DISCHARGE CURVE

1) Stage discharge curve is available at old Bhimgoda which is about 1.2 km u/s of the weir (Fig.3.7). 2) Cross-section of the river has been given at 0.5 km u/s of the ._.. . weir ( Fig-3.8).

...3) Slope of the river bed = 1.6 m/km. 4) Crest level of the weir = 288.15 m.

_,. Crest level of the under sluices = 285.90 m,

Assumed average bed level of the river = 287,15 (which is about l m below the crest level of weir and about mean of the two crest levels). Hence the bed R.L. of the river at the site where section of the river is given = 287,15 0.50 x 1.6 = 287.95 m, .5) Stage at 0.5 km ujs of the weir 710x 1.6 = Stage at old Bhimgoda 1000 = Stage at old Bhimgoda - 1.10 m.

These have been represented vide Table 3.8, .r

Table 3.8 - Showing Depth of Water in the River and Width at Different Discharges

Discharge . Stage in Stage at Average Top width Remarks m 0,5 km u/s depth in B in m in m3 R.L. at of the m (feet) lOGO old Bhim- weir (.cusecs) ,oda

1133 290.55 289.45 1.5 680 'B' values (40) (223 0.4) are measured from 1417 290.89 289.79 1.84 687 Fig. 3 ,8 (50) (2253.4) 2125 291.15 290.05 2.10 700 (75) (2296.0 ) 2834 291.56 290.46 2.51 712 (100) (2235.36) 3400 291.89 290.79 2.64 725 (120) (2376.9) 4250 292.22 291.22 3.27 733 (150) (2404)

5667 L73 760 (200) (2493) 2267 291.16 290.06 2.11 590 (8S) (1935) 8500 293.44 292.34 4.39 773 (300) (2535) 61

3;11 CALCULATION OF SLOPE AND AVAILABLE SHEAR STRESS (ti ) AT DIFFE LENT DISCHARGES

Manning' s formula, has been used for computing slopes at different discharges. Manning's 'nti has been assumed as 0.04 which has been used by U.P. I.R.I. ( as gathered from U,P, I.R,I, research officers). /3 = 1n . Sl/2. B. D5

or S = . _ _ Q2 • n` B2. D10/3 , 2. D3.33

i) When Q = 40,000 cusecs = 1133 m3/sec

; w♦ ~D = 1.5 m 2 S _1133 x0.042 _ 1,05 x 6802 x 1.53.3 2 z o = y.D.S = 9810 x 1.5 x 1.05 x 10-3 = 1545 N/m

1 Newton = 1 kg x 9981 1000 kg = 9810 N ii) C = 50,000 cusecs = 1417 rr/sec. B = 687 m, D=1.84m

S -4 14172X0. 3.33 = 8.94 x10 = 687 x 1,84

o = y,D,S = 9810 x 8.94 x x-0`4 = 10,13 N/m2 62

75,000 cusecs = 2125 n3/sec

B = 700 rn, D = 2,10 m S- (2J25)2 1,24 x io -, 7002 x

o = = 9810 x 2.10 x 1.24 x10 3 = 25.75 I/rn2 iv) Q = 1,00,000 cusecs = 2834 np/sec, B = 712 rn, D .= 2.51 m S = (2834 )2 .18 x 10-3 7122 x 2.51 = 9810 x 2.51 x 1.18 x 10 = 29.05 IT/M2 v) = 1,20,000 cusecs = 3400 m3/sec.

B = 725, D = 2.84 m S = 40Q)2 x (0.04)2 = 1.08 x 1073 725 x . 33

T = 9810 x 2.84 x 1,08 x 10-3 = 30,09 N/rn2

vi) Q = 1,50,000 ousecs = 4250 m3/sec B = 733 mD = 3.27 rn S = 42502 x 0.04 = 1.04 x 1073 7332 x 3.273.33

= 9810 x 3.27 x 1.04 x = 33 .3 6 N/ 2

vii) Q = 2,00,000 cusecs B = 760 rn, D = 3,73 m 63

S = 56672 x_01.043•> = 1.19 x 733 x3.73 3

- o = 9810 x 3.73 x 1.19 x 10"3 = 43.54 N/m2

viii) Q = 3 , 00, 000 cusecs = 8500 m3/sec. B=773 m, D=4.39m S =85Q0xoO 4 1.40 x 10-3 7732 x 4,39 33 ©= 9810x4.39x1.40x1073

= 60.44 N/m2

Above this value of discharge, corresponding width of river is not available

For the above values of 'C o, do has been found out from Fig,3 ,1, 3.2 and + dm+ from Fig.3.6 and has been arranged in a tabular form vide table 3.9.

Table 3,9 -- Table showing discharge and mean diameter of silt

Q in m3 ti c d dm (1000 cusecs) (N/m2) mm mm 1133 (40) 15.45 15.90 3.3 1417 (50) 16,13 16.60 3,6 2125 (75) 25.75 26.40 5.4 2834 (100) 29.06 29.90 5.9 3400 (120) 30.09 31,00 6,1 4250 (150) 33.36 34.20 6.6 5667 (200 43.54 45.00 7.9 8500 f14nnti An AA cc 64

3.12 COMPUTATION OF INFLOW OF SILT - BARRAGE SITE FOR PR CONSTRUCTION CONDITION

Qs _ 0.170.5 72. B.D2.52 1 _ sc ) am i) Q = 40,000 cusecs am = 3.3 mm 4 Sc = 0.00025 C 4.92 = 2.08 x iT S - --S = 0.80

Q = x:75 x 62,432 x 2230,4 x 4.922x1.052x0, 80x10 6 3.3 = 12,89 ft3 /sec, = 0,365 M3 /sec, ii) Q = 50,000 cusecs d =3.6mm

Sc = 0.00025 ( 3 .60 s ~) = 182 x icr4 4 1 - S~ - = 0.80

Qs = 10 -x 62.43 2 x 2253 .4 x 6.042x8.942x10 8x0.80 3.6

= 33.20 ft3 /sec. = 0,374 m3 /sec, iii) Q = 75,000 cusecs am =5.4mm S c = 0.00025 ( . 48 90,~.a_) = 2.25 x 1074

1 _ = 1 _ 25 _x 10- = 0.82 s 1.24 x103

Qs = 0'1 0 x 62.43 2 x 2.296 x 1.252x io0 x6, 892x0.82 5.4 = 25.50 ft3 /sec. = 0.723 m3/sec, 65

iv) Q 1,00,000 cusecs dm =5.9mm

Sc = 0.00025 ( 2 ) = 2.04 x 10-4 S 3 _ —S = 0.83

s x 62.432 x 2335.36 x 8.232x1.182 5.90`75 x10^6 x0.83 32.02 ft3 /sec. = 0.907 m3/sec. v) Q = 1,20,000 cusecs dm =6.1mm

= 0.00025 C = 2.1 x 10`4 Sc 68123 08—) S 1 — Sc = 0.81

Qs - 0.17 x62.432 x 2378 x 9,322 x 1, o82xio6xo.81 6,10.75 = 33.33 ft3 /sec. = 0.945 m3/sec. vi) Q = 1,50,000 cusecs

d _ 6,.6 mm m Sc = 0.00025 ( 6.6 3 a--) = 1.72 x

1- sc=O,83

Qs = -- 10-.-r~5 x 62.432 x 2404 x10.73 2x1.042x10*6x 0.83 J.6 r 40 ft3 /sec. = 1,134 a3/sec. viii) Q = 3,00,000 cusecs dm 10.6 mm

Sc =000025 ( 1014-4Q8 ) = 1.98x104.

1 -~c =0.86

0.17 62.432 S 10.6 0.75 x x 2535 x14.4 `xl. 42x10+6x0.86 = 100 ft3 /sec. = 2.834 m3/sec,

The above results have been represented in tabular fora vide table 3.10 and by a curve vide Fig.3.9. Table 3.10 - Computation for Curve Showing discharge and Corres- ponding bed load

1000 cusecs `~' 3s ft /sec (cumecs) (cumecs)

40 2.4. 12.89 30.94 (1133) (0.365) 50 5.0 13.20 66.00 (1417) (0.374) 75 26.6 25.50 678.30 (2125) (0.723) 100 7.2 32.20 231.84 (2834) (0.907) 120 4.4 33 .33 146.65 (3400) (0,945) 150 3.0 40.00 120.00 (4250) (1.134) 200 2.3 63.15 145.95 (5667) (1.790) 300 1,5 100,00 150,00 (8500) (2.834) 67

A curve has been drawn vide Fig.3,10 to represent (Qsx F) against discharge, Q.

3 .13 ESTIMATION OF BED GEIERATIVE DISCHARGE

From the curve, the discharge having the highest (Qsxx?) is the bed generative. discharge as defined by Schaffernack,

From the curve bed generative discharge comes to be 80,000 cusecs. Bed generative discharge represents the discharge carrying the maximum volume of silt. Hence if the barrage or weir water-way is fixed in such a way that its silt discharging capacity should be same as silt inflow at bed generative discharge, then there will be least siltation u/s of the weir and hence less scour d/s of it,

kka XMiX RXd am ga iNXI RIZZ tat$X 3.14 CALCULATION OF SILT CARRYING CAPACITY AT DIFFER T WAT.a' .t4AYS

In the light of the above, the weir has been tried with different waterways and silt discharging capacity has been calculated for each case.

For the above case pond level has been assumed to be at a level corresponding to mean annual flood of 6000 m3/sec,

At old Bhimgoda, stage corresponding to mean annual flood 292.8 m Near the weir, stage = 292.8 - 1.2 x 1„6 = 290,86 m. Hence the pond level is 290.86 m (Pond level of the existing barrage varies from 290.2 m to 293.74i). 06

Average depth 'D = 290.86 —287.15 = 3.71 m i) When B = 250 in = 820 ft. D= 3.71 m = 12.23 ft.

S = 72 X 0 04 — = 1.64 x 10 2502x 3.713.33

= 'y.D.S. = 9810 x 3.71 x 1.64 x 103 = 60 N/m2

do = 62 mm dm = 13 mm from (Fig.3.6)

S c = 0.00025 (~ 23 ~-) = 2.82, x

S 1 — Sc =0.83

Qs 01 17 5 x 62.43 2 x 820 x 12.23 2xl 64 2x10 °x0.83

= 26.51 ft3 /sec. = 0.751 m3/sec. ii) When B = 300 in = 984 ft. D = 3.71 m = 12.23 ft. Q = 80,000 cusecs = 2267 rn3/sec.

S = = 1.14 x 10`3 3 002 x 3.713.33

= y.D.S. = 9810 x 3.71 x 1.14 x 103 = 41.71 N/m2 do = 43 mrm d.m = 7.9 mm Sc = 0, 00025 (-7 9l1 3'8 -) = 1.78 x 104

S 1- 5 - =0.84

Q S - 7 -90 '~5 x 62.432 x 984 x 12.232x 1.14 2x10_ Ox0. 84

= 22.6 ft3/sec, = 0.640 m3/see. iii) B = 350 in = 1148 ft D = 3.71 m = 12.23 ft. Q = 80,000 cusecs = 2267 m3/sec.

S -2 J2 x0042 =8.38x104 3502 x3.713.33

-c = 9810x3.71 x8.38x7.0.4 =30.66NT/m2

do = 32 mm dm =6„3 mm

Sc 6_3+o 4 = 0.00025 ( 12,23 8 ) = 1.45 x 1~ S 1- -s C -- = 0.83

0 17 x 62.43 2 x 1148x 12.23 x 8.3 82x10$x0.83 = 6 5 2

= 16.7 ft3/sec. = 0.473 rrn/sec, iv) B =400m=1312 ft,. D=3.71m=12.23 ft. Q = 80,000 cusecs = 2267 m3 /sec,

S = 2 22`72x0.04 = 6 4 Q n~ 2 •41 x a B2,D3 .3f 4002x 3.71 ' 70

= 7.D.S. = 9810 x 3 .71 x 6.41 x 10 =21.46N/m2 do = 22 mm dm = 4.5 mm

) = 1.08 x 10+4 Sc = 0.00025 ( 12.23 Sc 1 - = 0.83 0,17 QS = x 2.43 2 x 1312 x12.23 2x 6.412x108x0.83 4.5 = 14.4 ft3/sec. = 0.408 m3/sec.

The above results have been represented vide Table No.3.11

Table 3.11

B i $ in m3/sec, meter (ft3/sec)

250 0,751 (26.51)

300 0.640 (22.60) 350 0.6 t 473 (16.70) 400 0.408 (14.40)

The above results have been plotted in a curve vide Figure 3.11. The inflow of silt at bed generative discharge is 22.10 ft3/sec. (0.626 m3/sec) from Fig.3.9. From thegraph

representing 'B' vrs. silt carrying capacity (Fig.3.11) for 0.626 m3/sec, 'B' comes 2.95 m,

Hence if the width of the river is kept as 295m, then the silt brought into this section of the river by the bed generative discharge will be carried past the diversion works without silting.

3.15 STUDY FOR POND LEVEL Total width to be provided = 295 m as per above study Keeping 15 percent of the water way as the width of the under sluices portion = 44.25 in k J'idth available for barrage portion =250.75 m (assuming still pond regulation) Let us provide 14 number of spans of =210.0 m 15 in each, hence clear water way Width of each pier - 401 = 3,14 in (O.K.)

Total discharge to be passed = 80,000 cusecs, discharge through canal = 10,500 cusecs. For still pond regulation system, Discharge passing through. barrage = 69,500 cusecs. _ 19+49 1969.4m3/sec. Q = discharge/ m width

- 9.38 m3/sec. For passing this discharge over the barrage, Head over the crest = H = (9.38/1.71)0.67 = 3.13 m. Crest level of the 'weir' or ' barrage' = 290.86-3.13 = 287.73 m. 72

Hence the crest level of barrage is to be fixed at 287.73 in or below it for keeping all gates opened and the level of water at pond level when bed generative discharge is passing.

For, flood above 80,000 cusecs, there will be need to maintain pond level by heading up through gate closures at the water way considered. But below it there will be difficulty in maintaining pond level. At these discharges, either the gates are to be closed proportionately to maintain a fixed (pond level or all gates may be kept opened and pond level will be varied.

For discharges lower than 40,000 cusecs, when the flood water carries very little silt, if the gates are kept closed for maintaining pond level there should be no problem such as siltat tion. Hence in this analysis the flood discharges above 40,000 cusecs only has been considered.

3.16 ANALYSIS Let CR = Discharge in the river

If crest'level is fixed at 287.15 in ( ay. bed level) H = 290.86 - 287.15 = 3.71 m q = 12.22 m3/sec./m.

®c = Discharge in the canal Qn = Net discharge passing over the weir. Lg = That portion of the weir, which can be opened for passing the discharge 'q' for maintaining pond level. 73

Then Lg = QR ~c Qn Qn - q. --- = q = 12.22 L = clear water way = 210 m,

This analysis has been represented in tabular form as below (Table 3.12) . Table .3.12

S1. QR qc Qn L L '"F Remar No cumec cumecs cumecs (m) L x100 (1000 (1000 (1000 cosec) cusecs) cusecs)

1, 1133 297.00 836,00 68.41 32.57 2.4 (40) (10.5) (29.5)

2. 1417 297.00 1120.00 91.60 43.62 5.0 (50) (10.5) (39.5)

3. 1700 297,00 1403.0 114.78 54.66 10«5 (60) (10.5) (49.5)

4. 1984 297.00 1687,0 137.97 65.70 16.0 (7.0) (10.5) (59.5) 5. 2267 297.00 1970.0 161.6 76.74 26,6 (80) (10.5) (69.5)

• The above table has been shown vide Fig.3.12. By keeping •all the gates opened, the variable levels of water that can be maintained are computed as below

i) . QR = 40,000 cusecs Qn = 29,500 cusecs = 835.9 m3 /sec, q = 05 9 = 3.98 m3/sec/m 74

H- (1~)8 0.67• -1.76m

Level of water .= 287.15 p 1.76 = 288.91

ii) For QR = 50,000 cusecs Qn = 39,500 cusecs = 1120 m3/sec. _ 1120.00 ` 5.26 m 210 3/sec/m H = ( 1.21 )0.67 _ 2.12 m

Level of water = 287,15 + 2.12 = 289.27 m

iii) For Q = 60,000 cusecs Qn = 49,500 cusecs = 1402.66 m3/sec. 1402.66 q= 210 = 6.68 rn33 /sec./m.

6 )0,67 = 2.49 m H =

Level of water = 287.15 + 2.49 = 289.64 m iv) For Q = 80,000 cusecs Qn = 69,500 cusecs = 1969.40.m3/sec.

q = 1269 = 9.39 m3/sec/m

H = ( 19.37 )0.67 = 3 ,13 m

Level of 'water = 287.15 t 3.13 = 290.28 v) For QR = 70,000 cusecs Qn = 59,500 cusec = 1687.00 m3/sec.

q = 1687.00/210 = 8.038 m3/sec/m. 7•.

H= ( )0.67 = 2.82m

Level of water = 287.15 + 2.82 m 289.97

The above result has been arranged in a tabular form vide Table No.3.13 and shown vide Figure No.3.13.-

Table 3.1.

Si. Q in /sec. n No. Q in m3 /see '-F W.Z. that (1000 cusecs) ( corresp ond- can be main.- (1000 cusec) ing to 94 tained(with days) all gates open)

1. 1133.0 836,0 2.4 288.91 (40) (29.5)

2. 1417.0 1120.0 5.0 289.27 (50)• (39.5)

3. 1700.0 1403 .0 10.5 289.64 (60) (49.5)

4, 1984,0 1687,0 16.0 289.97 (70) (59.5)

5. 2267.0 1970.0 26.6 290.28 (80) (69.5)

3.17 EFFECT OF VARYING POND LEVEL ON THE CANAL FEEDING

Canal can be fed to the full capacity by i) By keeping a larger water way for the head regulator and then opening it proportionately when the pond level goes down. ii) By providing a moveable crest for the head regulator,

3.18 CALCULATION OF SILT DISCHARGING CAPACITY AT DIFFERENT DISCHARGE; WITH WAT]tWAY AS 295 m (FIXED P.L. CONDITION)

B = 295 m=967.6m D = 3.71 m = 12.23 ft( for pond level ) i) Q = 40,000 cusecs = 1133 .47 m3 /sec. S_ X1133,47)2 x 0.042 = 3 x lo- 2952 x 3,7i' 'E o = 9810 x 3 .71 x 3 x,10 4 = 10.92 N/m2 do = 12 mm

dm 2,7 mm Sc = 0.00025 ( 212* 38 ) =7.15 x 10 S 1 — _ 0.76 S

Qs = 0.17 x 62.432 x 967.6 x 12.232x32x20 8x0.76 2.70.75

= 3.16 ft3 /sec. = 0.09 m3 /sec. iii) Q = 50,000 cusecs = 1417 m3/sec.

= (1417)2 x CO,o4)2 4.69 x 10"4 2952 x 3 713 •33

T c = 9810 x 3.71 x 4.69 € 104 = 17.06 iN/m2 do =18nun dm =3.9mm Sc = 0.00025 ( 12 6 x 105 .23 ~8 ) = 9. S 1 - Sc = 0.80 77

Qs = 0'17 0.75 x 62.43 2 x 967.6 x 12.23 2x4.692 x 10-8 3.9 x 0.8 = 6.08 ft3/sec. = 0.172 m3/sec. iii) Q = 75,000 cusecs = 2125.25 m3/sec.

8 _ (2125. 25)2 x 0.04 2 _ 2 05 x 10`3 (295)2 x (3.71)3.33

do = 98.10x3.71 x 1.05 x103 =38.40N/m2 do = 40 mm dm = 7.5 mm ( from graph )

sc =0.00025 ( 71.23.52 ) =1.697x10"4 1 0,84

12.232 Qs = 750.10. 75 x 62.43 2 x 967,6 x x 1.052x10-6

19.60 ft3 /sec, = 0.555 m3/sec. iv) = 1,00,000 cusecs,= 2834 rn3/sec.

28342 x 0.042 1.876 x 10 2952 x 3.713.33 To = 9810 x 3.71 x 1.676 x 10-3 = 68.27 N/m2 do 70 mm dm = 11.3 mm Sc = 0.00025 ,( 12.23 ) = 2.47 x 1o 4 8 s 0.87 0.17 5 x 62.43 12.232 Qs 11.3 0.7 2 x 967.6 x x 1.8762 x106 x0.87 = 47.67 ft3 /sec. = 1.351 m3 /sec. v) Q = 1,20,000 cusecs = 3400 m3/sec.

Discharge passing over the barrage = Qn = 1,09,500 cusecs = 3102.86 m3/sec, 3102,86 q= 210 =14.77m3/sec/m

H = ( 14 : ) .67 = 4.24 m = 13 .9 ft.

D 4.24 m 13.9 feet.

2 x S = (3400) (0.04)2 1.73 x103 2952 x (4.24)3.33

T o = 7.D.S. : 9810 x 4.24 x 1.73 x 103 • = 72 N/rn2

do = 73 mm dm = 11.6 mm S c = 0.00025 x 12.4 = 2.23 x S 1 - S e = 0.87

= 0.177_ x (62.43) 2 x 967.6 x (13.9) 2 x (101 s 11,60. 75 6x0.87

= 51.34 ft3 /sec. = 1.455 m /$ec. vi) Q = 1,50,000 cusecs = 4250 m3/sec.

Discharge passing over the barrage = Qn = 1,3 9,500 cusecs = 3952.96 m3/sec. 79

(19 q _ ~21 6i ) = 18.82 m3/sec/m

ii = ( i882 ) 1. 1, 0.67 = 4,99 m = 16,36 feet

S = 42502 x 0.042 1.57 x 103 2952 x 4.993.33 10 =7.D.S. = 9810 x 4.99 x 1.57 x1073 = 76,85 N/n2

do =78mn, dm =12.2m

Sc =0.00025 ( 1T4 36 ) =1.99x S 1— Sc =0,87

Qs = 0.10 75 x 62.43 2 x 967.6 x 16.362 x 1, 572x10 6x0.87 12.2 56.40 ft3/sec. = 1.598 m3 /sec.

The inflow of silt has been taken from the previous calculations and tabulated for comparison with silt discharging capacity below vide Table No.3.14C,

3.19 CALCULATION OF SILT VOLUME PASSING OVM THE WEIR WHEN THE POND LEVEL VARIES AT LOWER DISCHARGES i) Q = 40,000 cusses = 1133.47 m3/sec. D = Level of water .- Average bed level 288.91 .- 287.15 = 1,76 in = 5.77 feet, S 1131, 72x0.042 _3 .60 x103 3.33 2952 x 1,7 6 o = 9810 x 1.76 x 3,6 x 10 3= 62 N/m2 do = 63 mm dm = 10.4 m L' f

S = 0.0025 ( 10.4i'0 ) = 4.85 x 104 c S 1 - s = 0.87 Qs = 6.170 x 62.432 x 5,772 x 867,6 x 3.62x10 6x0,87 .4 = 41.58 ft3 /sec. = 1.178 m3 /sec, ii) Q = 50,000 cusecs = 1417 m3/sec. D = Level, of water - Average bed level = 269.27 - 267.15 = 2.12 m = 6.95 feet

1477 2x0.042 = 3 x10-3 295 x 2.12

= 9810 x 2.12 x 3 x 1O 3 = 62.46 N/m2 -o do = 64 mm, dm = 10.5 mm 105+Q8) S.c = 0.00025 ( 4.06 x lCi4 , S 1 -- sc _ 3.665

Qs =. 1~ 5 x 62.432 x 6.95 2 x 967.6 x 3.02x.10 6x0.865 .5 = 41.40 ft3/sec. = 1.173 m3/sec. iii) Q = 75,000 cusecs = 2125.25 m3/sec. D = Level of water -- Average level of bed of river = 290.16 -287.15 = 3.01 m = 9.87 ft. S= (2125.25)2 x (0.04)2 _ 2.1 x 10`3 (295) 2 x (3(3.33 ti = 9810x3.01x2.1x103 _o =62.50N/m2 do =64 mm dm = 10.5 mm a

Sc = 0.0025 ( 1 80"8 )= 2.86 x 10`4 S i--9- =0864

Qs = 2L 7 x 62.43 2x9.872x967.6x2.12x10-6x0.864 10.5 = 40.82 ft3 /sec. = 1.157 m3/sec. iv) Q = 1,000,00 cusecs. Qs= 1.351 m3/sec.(same as with that in case of fixed pond level) v) Q = 1,20,000 cusecs Gds= 1.455 m3/sec. ( -do- ) vi) Q = 1,500,000 cusecs Qs = 1.598 m3 /sec ( -do - )

The above results have been plotted in Table No.3.14.

3.20 LANES APPROACH Lanes$ theory states the morphology of a river can be represented by four factors like, discharge, silt content, D50 of the bed material and the slope. Now let r = discharge D50 = Median diameter of the bed material S = Slope Qs = Silt content As per Lanes, theory Q.S. Qs D.

Assuming 'D50' remains constant ( in reality there will be very little change in

Q S or Q = K, Qss Table 3.14

Q in Frequen,» ►' in 1 Qs I in Percen- ' Qs * ' Qs ' P.L. cumecs cy 'F' s1 "2 tage of 3 4 (m) (percen.- m3/sec m3 / sec. gate open- In m3/ tage) (ft3/sec) ing(taken m3/sec see (taken from from table Fig.3.1o) 3..12) (1) (2) (3) (4) (5) (6)=(4)x(5) 7 8

1133 69 0.33 0.09 32 0.0289 1.178 288.91 (11.50) 1417 76.5 0.400 0.172 44 0, 0760 1.173 269.27 (14.00)

2125 47 0..58 0.555 72 0,400 1.157 290.15 (20.50) 2334 26 0,793 1.351 100 0.793 1.351 290.86 (28.0) 3 400 15 0.963 1.455 100 0.963 1.455 290.86 (34.0) 4250 64 1,247 1.598 100 1.247 1.598 290.86 (44.0)

Qs = Inflow of bed load

Qs = Silt transporting capacity of barrage assuming no effect 2 of gate-closure on it ( fixed pond level condition ) (considering B = 295 m) Qs = Silt transporting capacity of barrage assuming effect of gate closure to be of same percentage as that of gates closed( fixed pond level condition )

Qs = Silt transporting capacity of barrage with variable pond 4 level, Mw

Now considering pre construction stage, for bed generative discharge the values of the term Qs/S can be found out. Similarly for post construction stage for various values of bed width, this factor • can be evaluated. The bed width that gives the same value of ' Q5/s' as in the preconstructionStage, gives the bed width which will broadly maintain status quo ante as far as the morpholo r of the river is concerned at the bed generative discharge. Table 3.15 gives the different values of 'Q/' at different bed widths taken from previous calculations.

Table 3.16 - Computation for, bed width as per Lanes' Theory

Si. 'B'in r in S Q /s x10 No, meter s s n13 /sec. x1004 (ft3/sec.)

1. 250 0.751 16.40 0,0460 (26.51)

2. 300 0.640 11.40 0.0561 (22.60)

3. 350 0.473 8.38 0.0564 (16.70) 4. 400 0.408 6.41 0.0640 (14.40)

The above results have been plotted in figure 3.14. Now taking the silt carrying capacity of the river at pre- construction stage as 0.684 m3/see. from Fig.3.10 and slope nearly the same as at 75,000 cusecs,. i.e. 1.24 x 10-3 s = 0 6 3 = 0,055x104 Q 1.24x10

From the figure No.3,12 for this value of I qs/s' the value of 1 B comes to be 311 m. 3.21 DISCUSSION ON LOOSENESS I1'ACTOR

Table 3.18

Sl. Discharge Wetted pert- Actual . Looseness Remarks No. (cumecs) meter _ waterway factor Q =4.83/Q=P (m) = td/P (m) 1. 2267 229.97 295 1.28 W=actual water way obtained from above the analysis. 2. 18000 648,00 295 2.20

3. 2267 229.97 678.2 2.95 W = actual water way provided in case of the exist- 4. 18000 648.00 678.2 1.05 ing weir

Looseness factor and waterway are inseparably related to each other and as such any study made on water way of a barrage will have close bearing on looseness factor as well. From the above study, it appears that Looseness factor as a parameter proves to be of not much help in design as because status of design discharge in the formula is not uniform. It has become known from the experience of existing barrages and weirs that the selection of pond level closely influences siltation on the, upstream of the structure. Now, addPtion of ay» certain looseness factor for a barrage may not even.reasonably ensure maintenance of desirable river cross-section plan form and slope. CR•

3.22 DATA TO BE COLLECTED FOR FIXATION OF WATLR WAY BY THE METHOD PROPOSED IN THIS STUDY

For fixing the waterway of a diversion for good hydraulic functioning the following data are necessary.

l, Longitudinal section of the river for a distance of 15 km or upto back water zone at the upstream and 5 km downstream of the barrage or weir site. 2. Cross-section of the barrage at the site. Compass plan of barrage site showing block levels. 4, Bed material size distribution at the site upto the probable depth of scour. 5. Discharge data for a long period. 6. Silt volume for different discharges with silt size distribution in each case. 7. Stage discharge curve at barrage site. 8. Slope of water surface at different discharges. 9. Discharge of the off-taking canal. 10. Pond level and F.S.L. of the main canal near head regulator for supply of water to the command. CHAFT -4

DISCUSSION

From the available data, analysis has been done on two aspects of effect of looseness factor of waterway on formation of shoals upstream of a weir or barrage.

i) In the first part of analysis Dakpathar barrage has been considered. Taking different waterways, the limiting discharges at which particles of different diameter will start moving has been plotted. (Figure 3.3). From the graph it is clear that for the same diameter of silt particle, the limiting discharge increases as the waterway increases.

For example, taking 2 mm diameter of silt particle, the limiting discharge at 464.7 m of water way is 875 m3/sec where as at 516.33 m of water way, the limiting discharge is 1240 m3/sec. This also indicates indirectly that the particles which move at a discharge with a waterway, may stop moving as the waterway is increased gradually although the discharge is same.

ii) In the second part attempt has been made to find a suitable waterway so that least amount of silting will take place upstream of the barrage. Bhim oda' weir site has been taken for study.

From the available flow' and the computed silt volumes, the bed generative discharge as defined by Schafferndck has been found out. This comes to be 80,000 cusecs (2267 m3/sec).

The pond level has been assumed to be at the level corresponding to mean annual flood of 6000 m3/sec (2,00,000 cusecs). :]

From the consideration that the silt carrying capacity of the river at weir site should remain roughly same at the bed generative discharge for post barrage condition as at pre-barrage condition, the waterway comes to be 295 m. iii) From the equation as given by Lanes' for least affect,6n the morphology of the river by the weir, the waterway comes to be 311 m. The idea behind adopting bed generative discharge of 2267 cumecs for studying the morphological changes from the relationship presented by lane is based on the following :

i) In bed generative discharge, highest volume of sediment is to be carried past the barrage. ii) At bed generative discharge, the conditions of near equilibrium as envisaged in dominant discharge may take place.

Hence the waterway obtained by both the approaches is nearly the same. Taking waterway as 295m, and adopting x+.83 as the constant of proportionality in Lacey's equation, the value of 'Q' comes to be 3730m3/sec. From flow duration curve, this discharge has a frequency of 11%. iv) From the view of economical waterway, the waterway will be about 508 rn, taking intensity of discharge and design flood as 26 m3/sec/m and 13,200 m3/sec as taken by Devendra Kumar (9) for Bhimgoda barrage for gate height of 6.0 m and 10.0 m.

But with all the assumptions as it appears from this analysis that a waterway were than 300 m with pond level corresponding to mean annual flood will cause siltation upstream of the structure. On the other hand, if waterway is kept as 300 m, then it may be uneconomical. Hence a compromise is to be made between the hydraulically efficient waterway and the economical water way as per the necessity. However, a detailed study considering both economics of hydraulic efficiency will only reveal the optimum choice.

It has been seen from Table 3.15 that for lower monsoon discharges upto 283+ cumecs if the pond level can be varied, then the silt disposing capacity of the structure is greatly increased silt deposition on upstream reduced.

For example taking 1133 cumecs as the discharge, for the pond level corresponding to mean annual flood, varies between 0.33 to 0.09 m3/sec where as if pond level is varied and all gates are kept opened, then the silt carrying capacity increases to about 1.178 m3/ sec.

Hence if pond level can be varied for these low discharges during early monsoon period, waterway can be increased without affecting the silt disposing efficiency of the barrage of the weir. CH.PTEa-5

CONCLUSION

The data of Dakpathar barrage and Bhimgoda weir have been analysed by employing mainly Shields' approach, Schaffernack's concept of bed generative discharge and simplified Du-Boys' formula. The objective of the study was to develop a rational procedure for determination of waterway from the existing theories of sediment transport . to study the applicability of looseness factor in design. Also study has been made on the effect of waterway on pond level, siltation upstream of the structure and gate operation. On the basis of the above study, the following conclusions are drawn:

1. Looseness factor is not of much help in a rational determination of waterway of a barrage. Because the status of the discharge in the formula of Lacey's wetted perimeter is not uniform and well defined.

2. When waterway is increased, the increase in limiting discharge is more in the case of higher diameter of silt than that for the lower diameters.

3. In the case of alluvial rivers, the concept of ' Lacey's wetted perimeter can not be strictly applied for determination of waterway of a barrage because the regime conditions do not exist after construction. In boulder stages, Lacey's theory is not valid. GIs such looseness factor which is intimately related to iacey's regime water way can not be considered to be a reliable guide line for fixation of waterway. fl

L1.. The concept of dominant discharge lacks clear cut definition because of which he values adopted in design may have wide variations. Among the existing approaches, the concept of bed generative discharge of Schaffernack appears to be reasonably rational. In the case of Bhimgoda weir, the bed generative discharge comes to:be 2267 cumecs (80,000 cusecs) and the'corresponding water way is found to be 295 m for maximum transport of silt across the structure. This value of water way compares very closely with the value of water way of 311m obtained by applying Lane's relationship for morphology of a river.-

5. It can be seen from Table 3.15, for lower monsoon discharges upto 2834 cumecs and for a water way of 295 m the, silt discharging capacity can be greatly increased by suitably varying the pond level and silt deposition on the upstream can be mi.ninised. As such the pond level of a barrage can be varied with respect to the prevailing water level of the river as far as practicable for low monsoon floods when the chances of siltation exist. A fixed pond level quite often necessitates closure of barrage gates for heading up of water level resulting in siltation which may get hardened into semi-permanent islands.

SCOP1 FOR FTRTE B STUDY i) If exact quantity of bed load can be found with its size distribution at different discharges and at different times at the site of the barrage or weir, a more precise study 'can be made. ii) By closure of the gates, the correct percentage of silt that will pass over the barrage is not known. 'If this can be known with 91 accuracy, the quality of study can be improved. iii) The hydraulic functioning of the weir or barrage in respect of silt carrying capacity of the barrage can be tested by model study to confirm the result obtained by analytical means. iv) Effect of the diversion work on regime of the river. v) effect of location of the diversion work site on water way. By location is meant

a) State of the river at site b) Plan from of the river at rate

r+ P u ~ Jit REF-BRKNC

1. Singh, B.,' Fundamentals of Irrigation J gineering' , Publica- tion, Nem Chand- Bros., Boorkee. 2. Varshney, R.S., S.C. Gupta and R.L. Gupta,' Theory and Design of Irrigation Structures'. 3. I.s. Code 6966(1973) • i. Garde, R.J. and K.G. Rangaraju, (1978) ,' Mechanics of Sediment Transportation and Alluvial Streams', Publication, Wiley Eastern Limited, New relhi. 5. Sharma, H.D. and B.N. Asthana,' Study of Water, of bridges and Barrages', Irrigation and Power, (July 1976) , journal published by CBIP. 6. CBIP Publication No.121 (1973) , vol.I. 7. Scheuerlein., l., ' Feed-back Ii fect of Diversion on Biver ,Morphology' , Proc. of IJBR XI Congress Volume XX. 8. Rocha, J.S., ' Morphology of rivers with cascade of run-of- river reservoirs, Proc. IAH1 XT Congress, Vol. XX. 9. Joglekar D.V'., and Wadekarr,' The i'ffect of Weirs and Dams on the Regime of Rivers', Proceedings of IAEiR-IV Meeting. 10. Kumar., D. (1977) ., " Waterway of Barrages in Boulder Reaches- An analytical Study', Proc. L+6th 1 search ,9ession, CBIP ,Vol.II. 11. Sfi.ngh, D.P., ' Analytical Study of Waterways of Barrages',

an M.E. dissertation, Tri DTC, Roorkee. 12. Rangaraju, K.G. (1981), ' Flow through open channels', Publication, Tat a- xrc craw-Hill Publishing Company Ltd. 13• Rouse, H., ' jigineering Hydraulic', Publication, John Wiley and Sons. , INC., New York.

1i-. CBIP Publication 1.60 (September 1971) , ' Manual on River Behaviour, Control and Training'. ~~ ~ IArs'113 2 3 Fq.t Modified form of Shields' curve. " w

20 30 40 so so 70 so so too 110 its OIAM[TEN IN mm.- —'--'r"1►

F1G.3.1 CURVE FOR• CRITICAL TRATIVE STRESS Vrs DIAMETER OF SILT 20

0 10 20 to

DIAMETER Of LILY IN Mm

IG.3 2 CRITICAL. TRACTIVE STRESS Vrs CRITICAL DIAMETER BY . SH.IELD'S METHOD 2000

1400

2000

U z

1100

10 s

000

400

0 1 2 ) 4 5 • SILT Of A M t T E R IN 'p.m. ~----~

FIG. 3.3 CURVE FOR LIMITING DISCHARGE Vrs SILT DIAMETER too

330

Soo

330

100

0 I A f IN PERCENTAGE

FIG.3.4 CURVE FOR DISCHARGE Vrs AF 300

220

140 I, x U a too

0 0 20 40 •0 50 100 CUMULATIVE FREQUENCY (F) IN •/• ---^--

FIG.3.5 FLOW DURATION CURVE 100

•o

0 0 a e $ 10 It 14 'dm', MEAN DIAMETEIR IN inm. -

FIG, 3.6 CURVE FOR MEAN DIAMETER Vrs CRITICAL DIAMETER RIGHT Lt 294 w 2 7 - 290 J W W J 286 W U O W 282 0 200 600 too $00 c DISTANCE IN METRES ----► FIG .3,8 X —SECT EON 2-22 AT 0.5 KM . UPSTREAM

w w a 284

:232 W J w 290 0 5000 10000 15000 0 DISTANCE IN M3/ SEC -•-

FIG . 3.7 STAGE DISCHARGE CURVE AT OLD BH 9MGOOA

9 z RIGHT LEFT w t im I.I w p,Z i 0 200 600 goo goo DISTANCE (N METRES ------~r-

FIG.3,8 X -SECTION 2-2 AT 05 KM. UPSTREAM

U'w 296 W

z 294

J 292 JW U+ 2901 O 5000 10000 ]SOHO DISTANCE IN M3/ SEC ------0

FIG . 3.7 STAGE DISCHARGE CURVE AT OLD QH IMGODA 300

260

220

100

20 100 200 300 400 300 $00 700

(QgaAF)

FIG.3-9 CURVE FOR DISCHARGE Vrs (Q XLF) So o

210

!20

U, U,w 100 u 0 0 a ' 140

100

Q a IN

FIG.3 10. CURVE FOR DISCHARGE Vrs SILT CARRYING CAPACITY

0.71

042

0.91

0.14

U w

M 0.0 s x

0 0.5`

0.52

0.41

..0.44

0.40

`N' IN Mt ?$

FIG.3•11 CURVE FOR WATERWAY Vrs SILT CARRYING CAPACITY 2 0C

2200

2000

1x00 u x w 1000 s V VP G

1400

1200

1000 0 20 £0 to •0 100 ---1 IN PE110EMt L•t

FIG. 3.12 CURVE FOR DISCHARGE IN THE RIVER Vrs PORTION OF GATE OPENING FOR MAINTAING POND LEVEL 2400

2200

2000

W * 1100 U z w (p 1600 x U V. 0

1400

1200

1000 21$ 21$ 2 a 0 11 PONO L[VEL IN META[! (111)

FIG. 3,13 CURVE FOR MAINTAINABLE POND LEVEL Vrs DISCHARGE IN THE RIVER 0.07

0.06

0.05

Q.04L I 1 I 1 I I j 200 220 240 210 200 300 320 3'0 360 310 400

WATER WAY IN METRE

rQ x ip~4 FIG. 14 CURVE FOR WATER WAY Vrs L s