Model studies report_25-3-15_opt.pdf

Design Consultant EPC Contractor

NTPC HYDRO LIMITED

Lata Tapovan Hydroelectric Project, Uttrakhand

A Report on Model Studies of Lata Tapovan HEP

Document no (As per L&T): O1201-DD-BAR-3052Document no (As per NTPC): 5601-002 (R)-PVC-U-352

March 2015

Lata Tapovan HEP

A Report Model Studies of Lata Tapovan HEP 2/9

March 2015 July 2010

A Report on Model Studies of Lata Tapovan

HEP

Document no (As per L&T): O1201-DD-BAR-3052

Document no (As per NTPC): 5601-002 (R)-PVC-U-352

R0 21-03-2015 Om Jangid Amar Pal Singh

Revision

Date of

submission to

NTPC

Prepared Checked and

approved Remark

Design Consultant EPC Contractor

Lata Tapovan HEP



Table of Contents Page

1 Introduction ....................................................................................................................... 4

2 The Model ......................................................................................................................... 5

3 Observation ....................................................................................................................... 6

3.1 Barrage .............................................................................................................................. 6

3.1.1 Adequacy of Waterway ..................................................................................................... 6

3.1.2 Hydrostatic Pressures ........................................................................................................ 7

3.1.3 Approach flow conditions ................................................................................................. 7

3.1.4 Adequacy of u/s and d/s approach length: ......................................................................... 8

3.1.5 Water surface profile at u/s and d/s of barrage. ................................................................. 8

3.1.6 Energy dissipation arrangement. ....................................................................................... 8

3.2 Intake ................................................................................................................................. 8

3.2.1 Intake capacity ................................................................................................................... 9

Annexure:1: T.M. No.84 RR (H3-05) dated Oct-2013

Annexure-2: RR No. 85 RR (H3-06) dated March 2015

Annexure-3: A note on hydraulic studies of Intake

Lata Tapovan HEP



1 Introduction

As reviewed under technical specifications of the contract between client NTPC & L&T

(Contractor) hydro model studies were referred by L&T to IRI Roorkee in 12th

Sept

2012. The design including layout, Plans & section of river, barrage, intake and

desilting arrangement were prepared by L&T and supplied to the research organisation

for carrying out model studies.

Initially the TOR submitted to NTPC was based on scope of model studies as per scope

of tender documents. Some additional scope of work is introduced in the TOR as

requested by NTPC and it was conveyed to NTPC that financial and time implication

and increase in scope shall be dealt as per provisions of contact.

The following parameters of different structure were desired by NTPC to be studied by

IRI as below.

a) Barrage:

Model of barrage with under sluice shall be run for the flood discharge of

300,500, 1000 & 2000 cumec with water level at FRL (EL 2103m) & under free

flow condition and observation of afflux.

Variation of velocity profile, water level profile, coefficient of discharge of flow

under all discharges given above.

Sediment deposition pattern upstream of barrage & flushing capacity.

Sequence of gate operation and its effect on flow & silt flushing pattern.

Suitable measures for even distribution of flow among all bays of barrage shall

be suggested. Model shall be re-run by incorporating such measures.

Suggestions for improvement in energy dissipation at downstream of barrage.

Lata Tapovan HEP



b) Intake

Hydraulic profile of intake shall be finalized.

Check for adequacy of water seal at HRT Intake & formation of vortex.

2 The Model

A geometrically similar comprehensive model of river Dhauliganga was constructed to

a scale of 1:30 (discharge scale 1:4929.5). A river reach from 900 m upstream to 450 m

downstream of proposed barrage axis was represented in the model in cement concrete.

The discharge fed into the model was measured over a sharp crested weir provided in

the upstream of the model with the help of pointer gauge having least count of 0.01 cm.

A v-notch arrangement was made in the downstream of power intake to measure the

discharge passing through it. The velocities were observed using well calibrated mini-

current meter and the water levels were observed with the model scale. The layout plan

of the comprehensive model is shown in Drawing - 2. The view of the model is shown

in Photograph-1 & 2 of Annexure-1.

Observations in the model are converted in to prototype with the following ratio.

Sr No Model Prototype

1 Length Dimensions like depth, scour levels Model value x 30

2 Discharge Model value x 30 2.5

3 Velocity Model value x √30

4 Pressure Model value x 30

The performance of the structures were tested under the following two conditions.

1. Layout plans and section of barrage complex as shown in plates1&2 (a) & (b).

Lata Tapovan HEP



2. The above with the following modifications.

a) Smoothening of protruding rock ledge 180 m upstream of the barrage axis on left

bank.

b) Provision of a small bucket downstream of the floor of the barrage which add no

conventional system of energy dissipaters.

3 Observation

3.1 Barrage

3.1.1 Adequacy of Waterway

To examine the adequacy of waterway of barrage, the control structure having 10

barrage bays & 2 under sluice bays of 11.0 m each with its crest at El. 2090.0 m &

2088.0 m respectively, separated by 3.5 m thick pier and two intakes with its crest at El.

2095.0 m along with power intake, two chambers of desilting basin and 133.0 m long

HRT was incorporated in the model as per Drawing - 6 and as shown in Photograph -3

& 4. The model was run under free flow (i.e. gate operation) and steady state condition

at different discharges varying from 200 cumec to the maximum discharge of 2000

cumec with maintaining their corresponding tail water levels at 360 m downstream of

barrage axis as per tail rating curve

It is seen that the design discharge of 2000 cumec passed through the spillway at

average water level of El. 2093.83 m against the supplied FRL as El. 2103.0 m

indicated that the discharging capacity of barrage is more than its design discharge of

2000 cumec. The model was also run with closing of gates of barrage from left side

These observations indicate that after closing 9 gates of barrage, the reservoir level was

recorded at about FRL (El. 2103.0 m). Thus, the 4 barrage bays from left side are

surplus as per model observations.

These observations can be seen in table 1, 2&3 of T.M.No. 84 (Annexure-1).

Lata Tapovan HEP



3.1.2 Hydrostatic Pressures

Hydrostatic pressures under free flow condition without energy dissipation arrangement

were observed along the left & right abutment, pier and divide wall of the floor at 2000

cumec, 1000 cumec, 500 cumec and 300 cumec river discharges. Observed pressures

were found mostly positive but at 25.0 m d/s in left of divide wall the negative pressure

was 0.45m. Hydrostatic pressures were also observed under gated condition maintaining

FRL at El. 2103.00m at different equally gate openings of 0.3m, 0.5m, 1.0m, 2.0m.

Observed pressures were found mostly positive but at some locations they were

negative within 10% of the corresponding heads. Reference of Table 4 & 5 of

Annexure-1 may be made to study of theses pressures.

3.1.3 Approach flow conditions

The approach flow conditions to the barrage were also observed by observing the

velocity distribution across each bay at the axis at 50% & 100% of SPF in free flow and

twelve bays operative conditions keeping the intake desander closed. It is seen from

these observations that approaching flow conditions to the barrage are quite non

uniform at various discharges. It is also seen from these observations that flow was

oblique from bay no. 5 to 1 and it was attacking at pier no. 4 to 1. A variation of 2.8m in

water levels at pier no. 4 (El.2094.8 m) and bay no. 4 (El.2092.0 m) was observed at

2000 cumec discharge under free flow condition. These observations indicate that the

concentration of flow in river upstream of barrage was along right bank while a back

flow zone still persisted from barrage to about 120 m upstream along left bank at all the

discharges under consideration.

The observations of IRI can be seen in Table VI & photograph no. 5 & 8 of their

T.M.No. 84 report (Annexure-1).

Lata Tapovan HEP



3.1.4 Adequacy of upstream and downstream approach length:

Velocity observations indicate that the concentration of flow in river upstream of

barrage was along right bank while a back flow zone still persisted from barrage to

about 120 m upstream along left abutment at all discharges in gated conditions also at

FRL. IRI observation can be seen in drawing 10 to 14 of T.M.No. 84 report (Annexure-

1).

3.1.5 Water surface profile at upstream and downstream of barrage.

The observed water surface profile were normal as shown in table 7, 8 & 9 and plotted

in Fig 15 to 18 and photo 9 to 12 (Annexure-1).

3.1.6 Energy dissipation arrangement.

Since the barrage is in mountainous reach and would have supercritical flow, therefore

no conventional energy dissipation arrangement were provided by EDRC. However

scour observations are only qualitative & is not expected at site.

To ameliorate the flow and scour condition, L&T provided an alternate Layout of

barrage (with smoothening of protruding rockledge on left bank). L&T also provided

improvement in energy dissipation arrangement by including a bucket structure after

downstream of apron. These modifications are shown in plates 3 (a) and 3 (b).

The observations of flow conditions etc are shown in March 2015 report (Annexure-2)

of IRI in Table 1 to 7 of IRI has given information.

3.2 Intake

The following studies were required to be conducted by IRI.

Hydraulic profile of intake shall be finalized.

Check for adequacy of water seal at HRT Intake & formation of vortex.

Lata Tapovan HEP



The studies carried out by IRI are contains in these report T.M.No. 84 (Annexure-1).

3.2.1 Intake capacity

To examine the adequacy of intakes and power intake, the tests were observed in

ponding condition at full reservoir level (El. 2103.0 m) and maximum draw down level

(El. 2099.5 m) at 0.3m to 2.0m equal gate opening on the model.

The observed discharges were as follows.

Gate

Opening

(in m)

Observed discharge at FRL

in cumec

Observed discharge at MDDL in

cumec

With two

chambers

With one

chamber

With two

chambers

With one chamber

0.3 79.6 59.9 69.3 54.0

0.5 80.8 58.9 71.0 55.0

1.0 84.5 65.5 80.8 61.9

2.0 90.8 70.4 84.5 66.1

The design discharge of HRT is 68.9 cumec. These tests indicate that at FRL and

MDDL the discharge carrying capacity of HRT is adequate.

A note on results of intake hydraulics is appended in Annexure-3

Annexure-1:

T.M. No. 84 RR (H3-05)

IRRIGATION RESEARCH INSTITUTE

ROORKEE – 247 667 (UTTARAKHAND) (AN ISO 9001:2008 CERTIFIED ORGANIZATION)

Website : www.iriroorkee.com

(FOR OFFICIAL USE ONLY)

ROORKEE OCTOBER, 2013

Model Studies for Barrage-Intake of Lata Tapovan

Hydroelectric Project across river Dhauliganga

in Distt. Chamoli (Uttarakhand)

mRrjk[k.M ljdkj

IRRIGATION RESEARCH INSTITUTEROORKEE-247 667 (UTTARAKHAND)

(AN ISO 9001:2008 CERTIFIED ORGANIZATION)

Technical Memorandum

No. 84-RR (H3-05)

CHIEF ENGINEER & DIRECTOR : A.K.DINKAR PH : 01332-257501

FAX : 01332-262487

SUPERINTENDING ENGINEER : N.K.SHARMA PH : 01332-257505

FAX : 01332-262487

TITLE OF THE REPORT : Month of issue :10/2013

Model Studies for Barrage-Intake of Lata No. of Pages : 55

Tapovan Hydroelectric Project across river No. of Tables : 11

Dhauliganga in Distt. Chamoli (Uttarakhand) No. of Photographs : 16

No. of Drawings : 19

PROJECT SPONSORING AUTHORITY :Sponsor’s Reference:

DGM –Hydro Design, L&T Ltd,Faridabad vide his letter no. L& T/ FBD-EDRC/Lata, dated 18.02.2012

DGM- Hydro Design,

Larsen & Toubro Ltd.

Faridabad (Haryana) CODE : 3342

RESEARCH PERSONNEL :

N.K.Sharma Research Officer

Ram Swaroop Asstt. Research Officer

Vijay Kumar Tiwari Scientific Assistant

Pushkar Singh Rawat Scientific Assistant

Prem Ballave Bhatt Model Assistant

SYNOPSIS:

The Model studies were conducted for barrage-intake of Lata Tapovan hydroelectric project

proposed to be constructed across river Dhauliganga in Distt. Chamoli (Uttarakhand) on a

geometrically similar model built to the scale 1:30. Observations of the hydraulic test results

indicated that the proposed clear water way of 132.0 m with barrage crest at El. 2090.0 m &

undersluice crest at El. 2088.0 m was found to be adequate to pass the design discharge of 2000

cumec at El. 2093.83 m with all bays fully opened, while only eight bays are sufficient to pass the

2000 cumec discharge at El. 2096.5 m. The design discharge of HRT is 68.9 cumec. At FRL and

MDDL the discharge carrying capacity of HRT is adequate. But the discharge carrying capacity of

intakes at FRL is adequate, while at MDDL it is 87 % and 90 % of design discharge 79.25 cumec

with two chambers at 0.3m and 0.5m gate opening respectively.

KEY WORD : Water way, Discharging Capacity, Velocity, Rating Curve etc.

SUBJECT : Barrage-Intake

PROJECT : Barrage of Lata Tapovan Hydroelectric Project, Distt. Chamoli (U.K.)

Approved by Recommended by Submitted by

(N.K.Sharma) ( N.K.Sharma) (Ram Swaroop)

Superintending Engineer Research Officer Asstt. Res. Officer

Model Studies for Barrage – Intake of Lata Tapovan, H.E.Project across river Dhauliganga in Distt. Chamoli (Uttarakhand)

I.R.I.Roorkee (An ISO 9001:2008 certified organization) T.M.No. 84 R R (H3 – 05) October, 2013

1

CONTENTS

PARA NO. TITLES PAGE NO.

_ LIST OF TABLES 2

_ LIST OF PHOTOGRAPHS 2

_ LIST OF DRAWINGS 3

1 INTRODUCTION 5

2 THE PROBLEM 5

3 THE DATA 6

4 THE MODEL 7

5 MODEL INVESTIGATIONS 7

6 DISCUSSION OF RESULTS AND

CONCLUSIONS 13



2

(A) LIST OF TABLES

Table-1 Observed reservoir levels for rating curve of barrage under free flow

condition.

Table-2 Observed reservoir levels with closing barrage bays at 2000 cumec

discharge under free flow condition (barrage bays closed from left side).

Table-3 Observed river discharge for rating curve of barrage for FRL and

MDDL.

Table-4 Observed pressures along abutments, pier and divide wall at 2000

cumec river discharge under free flow condition.

Table-5 Observed pressures along abutments, pier and divide wall at 0.30m

gate openings at FRL (El. 2103.0m).

Table-6 Observed velocities and discharge distribution across the barrage and

undersluice bays at 1000 cumec and 2000 cumec discharge under free

flow condition.

Table-7 Observed average water levels in the upstream and downstream of

barrage at different discharges under free flow condition.


barrage at different gate openings at FRL (El. 2103.0m).


barrage at different gate openings at MDDL (El. 2099.5m).

Table-10 Observed residual velocities in the downstream of barrage at 2000

cumec discharge under free flow condition.

Table-11 Observed velocities and discharge distribution across the barrage and

undersluice bays at 2000 cumec discharge (without 4 left bays) under

free flow condition.

(B) LIST OF PHOTOGRAPHS Photograph-1 Model view as seen from upstream.

Photograph-2 Model view as seen from downstream.

Photograph-3 A view of barrage and intake as seen from upstream.

Photograph-4 A view of barrage and intake as seen from downstream.

Photograph-5 Flow condition at 300 cumec discharge under free flow.




Photograph-9 Flow condition at 0.3m gate opening at FRL (El. 2103.0m).




3



Photograph-13 Flow condition at 2000 cumec discharge under free flow as

seen from downstream.

Photograph-14 A view of scoured bed profile in downstream of barrage after

running 2000 cumec discharge under free flow condition.

Photograph-15 Flow condition at 2000 cumec discharge (without 4 left bays)

under free flow as seen from upstream.

Photograph-16 Flow condition at 2000 cumec discharge (without 4 left bays)

under free flow as seen from downstream.

(C) LIST OF DRAWINGS Drg. -1 Index map of Lata Tapovan H.E.Project.

Drg. -2 Layout details of the comprehensive model.

Drg. -3 Theoretical and observed Gauge – Discharge (G-Q) curve for

proving of model.

Drg. -4 Surface flow lines observed at 1000 cumec river discharge under

existing condition.

Drg. -5 Surface flow lines observed at 2000 cumec river discharge under

existing condition.

Drg. -6 Layout plan of barrage.

Drg. -7 Discharge rating curve of the barrage under free flow condition.

Drg. -8 Discharge rating curve of the barrage under gated condition.

Drg. -9 Locations of piezometric points.

Drg. -10 Observed velocity pattern in upstream and downstream of barrage

at 300 cumec discharge under free flow condition.




At 1000 cumec discharge under free flow condition.




at 0.3m,0.5m,1.0m and 2.0m equal gate openings at FRL.

Drg. -15 Water surface profile under free flow condition at 300 and 500

cumec discharge.

Drg. -16 Water surface profile under free flow condition at 1000 and 2000

cumec discharge.

Drg. -17 Water surface profile under gated condition at 0.3m, 0.5m, 1.0m

and 2.0m equal gate openings at FRL (EL. 2103.0m).



4

Drg. -18 Water surface profile under gated condition at 0.3m, 0.5m, 1.0m

and 2.0m equal gate openings at MDDL (EL. 2099.5m).

Drg. -19 Scour pattern in the downstream of apron after running of model




5

REPORT



6

1.0 INTRODUCTION

Lata – Tapovan Hydro Electric Project is proposed to be constructed across

river Dhauliganga near Lata village in Joshimath Tehsil, District Chamoli in

Uttarakhand. The project site is located at a distance of about 250 km from

Rishikesh. The power house is situated near Tapovan village. River

Dhauliganga is an important tributary of holy river Ganga. The project will be

executed by Larsen & Toubro Ltd. and envisages the construction of 18.0 m

high barrage to divert 79.25 cumec river discharge for power generation and a

required discharge for sediment flushing, through a water conductor system

comprising an intake, desilting chamber, HRT intake, 7.315 km. long head race

tunnel, a surge shaft, a pressure shaft, a surface power house with installation

of 3 units of 57 MW each and a tail race channel, utilizing a gross head of

277.65 m available between barrage and tail race exit point. The barrage has

been designed for 2000 cumec discharge with full reservoir level (FRL) as

2103.0 m and maximum draw down level (MDDL) as 2099.5 m. The index map

of Lata - Tapovan H.E. Project is shown in Drg. - 1.

2.0 THE PROBLEM

Model studies for barrage and desilting basin of Lata – Tapovan H.E. Project

were referred to IRI Roorkee by DGM – Hydro Design, L&T Ltd, Faridabad vide

his letter no. L&T / FBD – EDRC / Lata, dated 18.02.2012. The scopes of

studies are as follows:

2.1 For barrage model

(a) Discharge carrying capacity of spillways.

(b) Adequacy of energy dissipation arrangement.

(c) Sediment flushing capacity of spillways

(d) Checking the adequacy of upstream and downstream apron length.

(e) Checking scour depth in the downstream of barrage.

2.2 For desanding basin model

(a) Efficiency of desanding basin for the removal of 0.20 mm particles as per

gradation curve.



7

(b) Overall efficiency of desanding basin.

(c) Checking the adequacy of upstream slope and transitions.

(d) Trap efficiency of desanding basin.

(e) Optimization of holes given in the slab.

(f) Flushing capacity of trench.

(g) Checking the adequacy of intakes.

This report deals only with model studies regarding barrage model and

studies have been done for point ‘a’ to ‘e’ except point ‘c’.

2.3 Hydraulic model studies of barrage

Model studies will be carried out to confirm the adequacy of barrage to pass

the design flood corresponding to full reservoir level (FRL). The discharge rating

curve will be provided as per model observation. Hydraulic design of control

structure and arrangements for training the flow will be finalized on the hydraulic

model. Water surface profile for different range of discharges will be observed

and reported. All the above mentioned observations will be taken at full

reservoir level (El. 2103.0 m) for partial as well as full gate openings and also

different gate openings. Energy dissipation arrangements will be studied.

2.4 Hydraulic model studies of desanding basin

Model studies will be carried out for general performance and efficient

functioning of desilting arrangement for the removal of sediment particles of

0.20 mm size and to supply 68.9 cumec sediment free discharge to the head

race tunnel (HRT) for power generation. The desilting arrangement system will

be tested for different sediment concentration in lieu with the model scale.

Model studies for desilting chamber will be carried out on a separate model.

3.0 THE DATA

Following data was supplied by sponsor in various steps.

1. The contour plan of river from 900 m u/s to 450 m d/s of barrage axis.

2. X-sections of the river in above reach, at an interval of 30 m having

3. spot levels at 10 m distance on separate sheets.

3. Detailed drawings of barrage-intake.

4. Detailed drawings of power intake.



8

5. Detailed drawings of silt flushing tunnel.

6. Detailed drawings of desanding basin.

7. Detailed plan and sections of HRT.

8. Plan and sections of desanding basin.

9. Size of holes in slabs of silt flushing tunnel.

10. Silt gradation curves of suspended load of the river.

11. Tail rating curves at barrage axis and 135 m d/s of barrage axis.

12. Sediment size 0.2 mm and above was desired to be removed by silt

flushing tunnel of desanding basin.

13. Manning‟s value of “n” for river bed and banks must be taken 0.035.

4.0 THE MODEL

A geometrically similar comprehensive model of river Dhauliganga was

constructed to a scale of 1:30 (discharge scale 1:4929.5). A river reach from

900 m upstream to 450 m downstream of proposed barrage axis was

represented in the model in cement concrete.

The discharge fed into the model was measured over a sharp crested weir

provided in the upstream of the model with the help of pointer gauge having

least count of 0.01 cm. A v-notch arrangement was made in the downstream of

power intake to measure the discharge passing through it. The velocities were

observed using well calibrated mini-current meter and the water levels were

observed with the model scale. The layout plan of the comprehensive model is

shown in Drg. - 2. The view of the model is shown in Photograph-1 & 2.

5.0 MODEL INVESTIGATIONS

5.1 Proving of model

To examine the general flow condition of river, the model was run without

barrage - intake at different discharges varying from 200 cumec to maximum

design discharge of 2000 cumec and corresponding tail water levels were

maintained at 360 m downstream of barrage axis as per tail rating curve

computed from the cross sections supplied by the sponsor. The visual

behaviour of the river was seen and it was noted that due to the bends in



9

upstream river reach the concentration of flow was either on left side or on right

side of river throughout the represented reach in the model on almost all the

discharges. Heavy turbulence and super elevation was also seen in flow. The

water levels at various discharges at different river cross sections i.e. 750m

u/s,300m u/s,150m u/s, barrage axis, 120m d/s and 240m d/s were observed

and are plotted in Drg. - 3 with corresponding theoretical Gauge – Discharge

(G-Q) curve, developed and computed from the cross sections given by the

sponsor, with the help of Manning‟s equation taking the value of „n‟=0.035 and

slope=1/64 (as intimated by sponsor) & average slope of each cross section

(90m u/s to 90m d/s).These observations indicate that the differences between

observed and computed water levels are within ± 0.3 m with average slope of

each cross section (90m u/s to 90m d/s). The differences are within the specific

limit as given in IS 14955:2001 “Guidelines for Hydraulic Model Studies of

Dams and Weirs”. Hence, the model has been taken as proved.

The G-Q curve at barrage axis as computed by I.R.I Drg. -3 and give a

maximum water level of El. 2089.85 m for design discharge of 2000 cumec,

while the observed average water level was found El. 2089.60 m, which is in

order. The surface flow lines were also observed at 1000 cumec and 2000

cumec river discharge and are plotted in Drg.-4 & 5 respectively.

These observations indicate that the concentration of flow in river channel

upstream of barrage axis was on right side while on left side persisted from 330

m upstream of barrage axis to about 660 m upstream at above discharges. In

the downstream of barrage axis the concentration of flow was again on right

side.

5.2 Adequacy of waterway and rating curves of barrage

5.2.1 To examine the adequacy of waterway of barrage, the control structure having

10 barrage bays & 2 undersluice bays of 11.0 m each with its crest at El. 2090.0

m & 2088.0 m respectively, separated by 3.5 m thick pier and two intakes with

its crest at El. 2095.0 m along with power intake, two chambers of desanding

basin and 133.0 m long HRT was incorporated in the model as per Drg. - 6 and

as shown in Photograph -3 & 4. The model was run under free flow (i.e.



10

without gate operation) and steady state condition at different discharges

varying from 200 cumec to the maximum discharge of 2000 cumec with

maintaining their corresponding tail water levels at 360 m downstream of

barrage axis as per tail rating curve and corresponding water levels at about

30m upstream of barrage axis were observed. These observed water levels

corresponding to different discharges are given in Table-1 and plotted in Drg.-7

to develop the discharge rating curve of the barrage under free flow condition.

It is seen that the design discharge of 2000 cumec passed through the spillway

at average water level of El. 2093.83 m against the supplied FRL as El. 2103.0

m indicated that the discharging capacity of barrage is more than its design

discharge of 2000 cumec.

The model was also run with closing of gates of barrage from left side and

reservoir levels were observed. The observed reservoir levels are given in

Table-2. These observations indicate that after closing 9 gates of barrage, the

reservoir level was recorded at about FRL (El. 2103.0 m). Thus, the 4 barrage

bays from left side are surplus as per model observations.

The discharge rating curve under ponding condition at full reservoir level (El.

2103.0 m) and maximum draw down level (El. 2099.5 m) at 0.3m, 0.5m,

1.0m,1.5m and 2.0m equal gate opening were also observed on the model.

Discharges passing through barrage under steady state conditions were

observed for different and equal gate openings maintaining the full reservoir

level in twelve bays operative conditions. The observed discharges passing

through barrage and corresponding gate openings at the desired reservoir level

(FRL) & (MDDL) are given in Table-3 and corresponding discharge rating

curves under gated condition are plotted in Drg. - 8.

5.2.2 Hydrostatic Pressures

5.2.2.1 Hydrostatic pressures under free flow condition without energy dissipation

arrangement were observed along the left & right abutment, pier and divide wall

of the floor at 2000 cumec, 1000 cumec, 500 cumec and 300 cumec river

discharges. Observed pressures were found mostly positive but at 25.0 m d/s

in left of divide wall the negative pressure was 0.45m. The locations of



11

piezometric points is shown in Drg.-9. Observed hydrostatic pressures along

the left & right abutment, pier and divide wall at 2000 cumec discharge are

given in Table-4.

5.2.2.2 Hydrostatic pressures were also observed under gated condition maintaining

FRL at El. 2103.00m at different equally gate openings of 0.3m, 0.5m, 1.0m,

2.0m. Observed pressures were found mostly positive but at some locations

they were negative within 10% of the corresponding heads. To overcome the

effects of these negative pressures sufficient grade of concrete has to be used.

Observed hydrostatic pressures along the left & right abutment, pier and divide

wall at 0.30m gate opening at FRL are given in Table-5.

5.3 Adequacy of intakes and power intake

To examine the adequacy of intakes and power intake, the tests were observed

in ponding condition at full reservoir level (El. 2103.0 m) and maximum draw

down level (El. 2099.5 m) at 0.3m to 2.0m equal gate opening on the model.

The observed discharges were as follows.

Gate Opening

(in m)

Observed discharge at

FRL in cumec

Observed discharge at

MDDL in cumec

With two

chambers

With one

chamber

With two

chambers

With one

chamber

0.3 79.6 59.9 69.3 54.0

0.5 80.8 58.9 71.0 55.0

1.0 84.5 65.5 80.8 61.9

2.0 90.8 70.4 84.5 66.1

The design discharge of HRT is 68.9 cumec. These tests indicate that at FRL

and MDDL the discharge carrying capacity of HRT is adequate. But the

discharge carrying capacity of intakes at FRL is adequate, while at MDDL it is

87 % and 90 % of required discharge 79.25 cumec with two chambers at 0.3m

and 0.5m gate opening respectively.

5.4 Approach flow conditions to the barrage structure and discharge



12

distribution in bays

Since the river valley in the upstream of the barrage structure has some bends,

the approach flow conditions to the barrage were also observed by observing

the velocity distribution across each bay at the axis at 50% & 100% of SPF in

free flow and twelve bays operative conditions keeping the intake desander

closed. The observed velocities and discharge distribution in barrage &

undersluice bays are given in Table-6. It is seen from these observations that

approaching flow conditions to the barrage are quite non uniform at various

discharges. It is also seen from these observations that flow was oblique from

bay no. 5 to 1 and it was attacking at pier no. 4 to 1. A variation of 2.8m in water

levels at pier no. 4 (El.2094.8 m) and bay no. 4 (El.2092.0 m) was observed at

2000 cumec discharge under free flow condition. These observations indicate

that the concentration of flow in river upstream of barrage was along right bank

while a back flow zone still persisted from barrage to about 120 m upstream

along left bank at all the discharges under consideration. In the downstream of

barrage the concentration of flow was on right side. The different views of

running model from upstream and downstream are shown in Photograph – 5

to 8.

5.5 Adequacy of upstream and downstream apron length

The velocity pattern in the upstream and downstream floor of barrage were

observed at 300 cumec, 500 cumec,1000 cumec and 2000 cumec as desired

by sponsor, in free flow conditions are shown in Drg.-10 to 13. These

observations indicate that the concentration of flow in river upstream of barrage

was along right bank while a back flow zone still persisted from barrage to

about 120 m upstream along left abutment at all discharges in gated conditions

also at FRL as shown in Drg.-14. These observations indicate that the length

of upstream and downstream apron is adequate.

5.6 Water surface profile at upstream and downstream of barrage spillway

Water surface profile under free flow condition at different discharges was

observed on the model with all gates fully opened. The observed water surface



13

profiles at 300 cumec, 500 cumec,1000 cumec and 2000 cumec are given in

Table-7 and are plotted in Drg.-15 & 16. Water surface profile was also

observed with ponding condition at full reservoir level El.2103.0 m and

maximum draw down level El. 2099.5 m maintained in the upstream with the

help of spillway and undersluice gates with equal gate openings of 0.30m,

0.50m, 1.0m and 2.0m. These water surface profiles are tabulated in Table-8 &

9 and are plotted in Drg.-17 & 18. The different views of running model from

upstream and downstream are shown in Photograph - 9 to 12.

5.7 Energy dissipation and residual velocities in the downstream of barrage

structure

A 173.0m long (1.50mx1.50mx1.00m) thick PCC blocks in 12.0m width and

1.0m thick boulder in wire crated in 5.0m width over 0.5m thick filter has been

provided to safeguard of barrage structure and dissipate the kinetic energy of

flow passing over the spillway and its bed at 2086.50 m is proposed just

downstream of barrage structure to cater the residual energy escaping from

under sluice/ spillway to reduce the energy. The hydraulic performance of the

proposal for skiing action and against energy dissipation with respect to residual

velocities in its downstream was observed at river discharge of 2000 cumec

(design discharge of barrage spillway). As desired by the sponsor, residual

velocities at different sections downstream of the barrage structure were also

observed at 2000 cumec discharge. A view of downstream of the barrage

structure is shown in Photograph-13. The residual velocities observed at 0.6

depth in the river section at various distances downstream of the Barrage

structure are given in Table-10. Accordingly, the energy dissipation

arrangement should be provided.

5.8 Scour depth below the barrage

To study the scour depth below the barrage the river bed in downstream of

barrage was laid in loose shingle of 4 to 15 mm size. A profile from barrage toe

to 17 m downstream (as per the given details) underneath the mobile bed

material was also constructed in model in cement concrete . The model was run

with SPF 2000 cumec river discharge under free flow condition for a duration



14

of 4 hour 23 minutes (taking Tr=Lr/√Dr for 24 hours of prototype).

Where,

Tr = ratio of Time scale

Lr = ratio of Length scale

Dr = ratio of Depth scale

A maximum scour of the order of 5.0m at 32.0m downstream of barrage toe

along right bank was observed at design discharge of 2000 cumec. The scour

pattern in the downstream of apron after running of model was observed and is

plotted in Drg.- 19. The view of scoured bed profile is shown in Photograph-14.

5.9 Proposal for even discharge distribution in barrage bays

(without left four bays)

To improve the flow condition and even discharge distribution in barrage bays a

proposal was incorporated in the model. In proposal the left abutment was

constructed along 4 no. pier in a straight length of 120m and a smooth curve

merged to upstream hill rock. The proposal was tested at 2000 cumec

discharge under free flow condition. It was observed that flow was uniform and

flow conditions were better as shown in Photograph-15 in respect of earlier

study as described in para 5.4. The average observed reservoir level was El.

2096.5m. The discharge distribution was even in barrage bays as given in

Table-11. It may be helpful to increase the discharging capacity of intake at

MDDL (El.2099.5m) with 0.3m and 0.5m gate opening. The apron length was

60.5m. It was also observed that the jump formation was at 90.0m downstream

of barrage axis as shown in Photograph-16. So the apron length is inadequate.

6.0 DISCUSSION OF RESULTS AND CONCLUSIONS

The hydraulic tests conducted on comprehensive model of barrage-intake of

Lata Tapovan H.E.Project revealed that:-

6.1 From table-1, it can be seen that the proposed waterway of barrage 110.0 m

with its crest El. 2090.0 m and waterway of undersluice of 22.0 m with its crest

El. 2088.0 m is found adequate to pass its design discharge of 2000 cumec at



15

reservoir El. 2093.83 m in all twelve bays operative condition against El. 2103.0

m (FRL) as intimated by sponsor.

6.2 From table-2, it can be observed that without 4 barrage bays from left side the

flow was uniform and in permissible limits.

6.3 A non uniform and oblique flow across the barrage structure was observed

under free flow condition.

6.4 From table-6, it is seen that all the barrage bays have non uniform discharge

distribution under free flow condition.

6.5 A maximum velocity of the order of 6.69 m/sec at 2000 cumec discharge at

upstream apron was observed. Accordingly, the protection measures should be

provided.

6.6 A maximum scour of the order of 5.0m along right bank at 32.0m downstream

of barrage toe at 2000 cumec discharge was observed.

6.7 From para 5.3, it was observed that at FRL and MDDL the discharge carrying

capacity of HRT is adequate. But the discharge carrying capacity of intakes at

FRL is adequate, while at MDDL it is 87 % and 90 % of design discharge 79.25

cumec with two chambers at 0.3m and 0.5m gate opening respectively.

6.8 According to the observed residual velocities in the downstream of barrage

structure (table-10), the energy dissipation arrangement should be provided.

6.9 From table-11, it can be observed that the discharge distribution was even in

barrage bays and it may be helpful to increase the discharge carrying capacity

of intakes at MDDL (El.2099.5m) with 0.3m and 0.5m gate opening.



16

TABLES



17

Table-1

Observed reservoir levels for rating curve of barrage in free flow condition. - All twelve bays operative - Intake desander closed

Sl. No.

Discharge in cumec

Average reservoir level (m) at 30m u/s

Remark

1 200 2090.90 In model reach from 900m u/s to 450m d/s the flow was almost in the right side of river except 660m u/s to 330m u/s of barrage axis.

2 300 2091.33 ------------------do---------------------

3 500 2092.00 ------------------do---------------------

4 1000 2093.13 ------------------do---------------------

5 1500 2093.67 ------------------do---------------------

6 2000 2093.83 ------------------do---------------------

(Vijay Kumar Tiwari) (Ram Swaroop)

Scientific Assistant Asstt. Research Officer-3



18

Table-2

Observed reservoir levels with barrage bays at 2000 cumec river discharge (bays closed from left side)

- Intake desander closed

Sl.No.

Bays closed

from left side

Average reservoir level (m)

Remark

barrage undersluice

1 One 2094.10 2095.67 FRL= El. 2103.0 m

2 Two 2094.27 2095.87 MDDL= El. 2099.5 m

3 Three 2094.87 2096.13

4 Four 2095.00 2096.33

5 Five 2095.20 2097.07

6 Six 2097.57 2097.76

7 Seven 2099.50 2099.47

8 Eight 2100.43 2102.20

9 Nine 2103.00 2102.53

(Vijay Kumar Tiwari) (Ram Swaroop) Scientific Assistant Asstt. Research Officer-3



19

Table-3

Observed river discharge for rating curve of barrage at FRL and MDDL.

- Under gated condition - All twelve bays equally opened - Intake desander closed

Sl. No.

Equal gate opening (m)

River discharge in cumec at FRL (El. 2103.0 m)

River discharge in cumec at MDDL (El. 2099.5 m)

1 0.30 300 260

2 0.50 500 450

3 1.00 1000 900

4 1.50 1500 1350

5 2.00 2000 1790




20

Table-4

Observed pressures along abutments, pier and divide wall at 2000 cumec river discharge under free flow condition. - Intake desander closed

Sl. No. Location Height=0.0m Height=3.0m

El. (m.) Proto (m.)

El. (m.) Proto (m.)

1 Left abutment 21.0 m. u/s

2088.0 6.00 - -

2 4.0 m. u/s 2090.0 2.16 2093.0 0.75

3 Barrage axis 2090.0 1.80 - -

4 35.0 m. d/s 2087.586 1.62 - -

5 55.0 m. d/s 2086.5 1.20 - -

6 75.0 m. d/s 2086.5 2.16 - -

7 Pier no.5 at 17.0 m. u/s(L)

2088.0 4.35 - -

8 Pier no.5 at 17.0 m. u/s(R)

2088.0 7.14 - -

9 Divide wall 89.5 m. front

2088.0 2.70 - -

10 88.0 m. u/s(L) 2088.0 4.80 - -

11 88.0 m. u/s(R) 2088.0 0.42 - -

12 47.0 m. u/s(L) 2088.0 3.45 - -

13 47.0 m. u/s(R) 2088.0 6.60 - -

14 20.0 m. u/s(L) 2088.0 7.35 - -

15 20.0 m. u/s(R) 2088.0 5.85 - -

16 4.0 m. u/s (L) 2088.0 7.80 2091.0 1.50

17 4.0 m. u/s (R) 2088.0 8.25 2091.0 3.60

18 25.0 m. d/s(L) 2088.276 (-) 0.45 - -

19 25.0 m. d/s(R) 2086.538 2.40 - -

20 Right abutment 4.0 m. u/s

2088.0 5.25 2091.0 2.70

21 Barrage axis 2088.0 4.50 2091.0 1.35

22 25.0 m. d/s 2086.538 2.34 2089.538 -

23 40.0 m. d/s 2086.50 2.55 - -

24 55.0 m. d/s 2086.50 2.40 - -




21

Table-5

Observed pressures along abutments, pier and divide wall at 0.30m gate opening at FRL (El. 2103.0m). - All twelve bays opened equally - Intake desander closed

Sl. No.

Location Height=0.0m Height=3.0m

El. (m.) Proto (m.) El. (m.) Proto (m.)

1 Left abutment 21.0 m. u/s

2088.0 15.21 - -

2 4.0 m. u/s 2090.0 12.60 2093.0 10.35

3 Barrage Axis 2090.0 (-) 1.29 - -

4 35.0 m. d/s 2087.586 0.45 - -

5 55.0 m. d/s 2086.5 1.65 - -

6 75.0 m. d/s 2086.5 1.65 - -

7 Pier no.5 at 17.0 m. u/s(L)

2088.0 15.00 - -

8 Pier no.5 at 17.0 m. u/s(R)

2088.0 15.00 - -

9 Divide wall 89.5 m. front

2088.0 5.94 - -

10 88.0 m. u/s(L) 2088.0 13.50 - -

11 88.0 m. u/s(R) 2088.0 0.18 - -

12 47.0 m. u/s(L) 2088.0 2.10 - -

13 47.0 m. u/s(R) 2088.0 15.00 - -

14 20.0 m. u/s(L) 2088.0 15.00 - -

15 20.0 m. u/s(R) 2088.0 15.00 - -

16 4.0 m. u/s (L) 2088.0 14.85 2091.0 12.40

17 4.0 m. u/s (R) 2088.0 14.46 2091.0 12.52

18 25.0 m. d/s(L) 2088.276 (-) 1.50 - -

19 25.0 m. d/s(R) 2086.538 (-) 1.35 - -

20 Right abutment 4.0 m. u/s

2088.0 14.40 2091.0 11.70

21 Barrage axis 2088.0 (-) 1.50 2091.0 0.75

22 25.0 m. d/s 2086.538 1.50 2089.538 -

23 40.0 m. d/s 2086.50 2.55 - -

24 55.0 m. d/s 2086.50 0.30 - -




22

Table-6

Observed velocities and discharge distribution in the bays of barrage at 1000 cumec and 2000 cumec discharge under free flow condition. - All twelve bays operative - Intake desander closed

Sl. No.

Bay No. L-R

Observed velocities in m/sec. and discharge distribution in the bays of barrage

1000 cumec discharge 2000 cumec discharge

L C R Av. vel.

% L C R Av. vel.

%

1 1

3.1

8

2.7

1

1.7

7

2.5

5

5.4

7

3.2

8

3.5

6

2.5

2

3.1

2

5.8

5

2 2

2.4

3

2.7

1

1.3

9

2.1

8

4.6

7

3.8

4

2.9

9

2.1

4

2.9

9

4.8

0

3 3

3.2

8

3.1

8

1.5

8

2.6

8

5.0

2

4.0

3

3.7

5

2.0

5

3.2

8

4.3

9

4 4

2.9

0

2.9

9

1.6

7

2.5

2

4.3

7

3.2

8

3.5

6

1.9

6

2.9

3

3.9

2

5 5

3.1

8

2.9

9

1.7

7

2.5

6

7.1

0

4.9

7

2.9

9

2.3

3

3.4

3

6.4

3

6 6

2.6

2

2.8

0

2.9

0

2.7

7

8.1

6

4.4

1

4.4

1

2.2

4

3.6

8

8.8

7

7 7

2.9

0

2.8

0

2.7

1

2.8

0

9.0

0

4.0

3

4.0

3

2.7

1

3.5

9

7.6

9

8 8

2.1

4

2.9

9

2.6

2

2.5

8

6.9

1

3.2

8

4.0

3

3.6

5

3.6

5

7.8

2

9 9

1.3

9

2.3

3

2.6

2

2.1

2

3.4

1

3.8

4

3.2

8

2.7

1

3.2

8

7.0

3

10 10

1.4

8

2.0

5

2.1

4

1.8

9

2.0

3

2.8

0

2.9

9

3.1

8

2.9

9

5.6

1

11 1

5.0

7

5.0

7

4.7

9

4.9

8

24

.02

5.9

2

6.5

8

6.7

7

6.4

3

18

.94

12 2

4.2

2

4.4

1

3.4

7

4.0

4

19

.48

6.7

7

6.4

8

5.7

3

6.3

3

18

.65




23

Table-7

Observed average water levels in the upstream and downstream of barrage at different discharges under free flow condition. - Intake desander closed

Sl.No.

Observed average water levels in the upstream and downstream of barrage El. (m)

Discharge in cumec

Location 300 500 1000 2000

1 750 m u/s 2100.40 2100.53 2101.83 2102.30

2 600 m u/s 2098.67 2098.57 2098.77 2099.87

3 450 m u/s 2095.23 2095.67 2096.67 2097.20

4 300 m u/s 2094.10 2094.20 2094.87 2096.27

5 150 m u/s 2091.40 2092.20 2093.13 2094.00

6 60 m u/s 2091.20 2092.03 2093.00 2093.73

7 30 m u/s 2091.20 2091.93 2093.13 2093.83

8 Barrage axis 2091.20 2092.00 2093.23 2094.00

9 15 m d/s 2089.20 2089.43 2089.67 2089.87

10 30 m d/s 2088.13 2088.27 2088.50 2088.83

11 45 m d/s 2087.13 2087.50 2087.73 2088.50

12 60 m d/s 2087.20 2087.33 2087.53 2087.93

13 75 m d/s 2087.33 2087.87 2088.33 2088.67

14 90 m d/s 2088.00 2088.50 2089.13 2089.87

15 105 m d/s 2088.00 2088.50 2089.00 2089.67

16 120 m d/s 2887.50 2088.00 2088.60 2089.33





24

Table-8 Observed average water levels in the upstream and downstream of barrage at different gate opening at FRL (El. 2103.0m). - All twelve bays opened equally - Intake desander closed

Sl.No.


Gate opening in (m) / Discharge in cumec

Location 0.3m/300 0.5m/500 1.0m/1000 2.0m/2000

1 750 m u/s 2101.93 2102.63 2103.27 2103.47

2 600 m u/s 2102.00 2102.33 2103.13 2103.23

3 450 m u/s 2101.97 2102.37 2103.40 2103.43

4 300 m u/s 2102.00 2103.00 2103.00 2103.00

5 150 m u/s 2102.47 2103.00 2103.00 2103.00

6 60 m u/s 2103.00 2103.00 2103.00 2103.00

7 30 m u/s 2102.90 2103.00 2103.00 2103.00

8 Barrage axis 2103.00 2103.00 2103.00 2103.00

9 15 m d/s 2089.20 2089.27 2089.40 2089.73

10 30 m d/s 2088.15 2088.20 2088.33 2088.97

11 45 m d/s 2087.13 2087.80 2087.73 2088.50

12 60 m d/s 2087.13 2087.33 2087.50 2087.87

13 75 m d/s 2087.33 2087.63 2088.53 2088.67

14 90 m d/s 2088.07 2088.67 2089.13 2089.67

15 105 m d/s 2088.00 2088.53 2089.00 2089.53

16 120 m d/s 2087.23 2088.00 2089.00 2089.33




25

Table-9

Observed average water levels in the upstream and downstream of barrage at various gate openings at MDDL (El. 2099.5m). - All twelve bays opened equally - Intake desander closed

Sl.No.


Gate opening in (m) / Discharge in cumec

Location 0.3m/260 0.5m/450 1.0m/900 2.0m/1790

1 750 m u/s 2100.40 2100.90 2101.83 2103.33

2 600 m u/s 2099.77 2099.87 2099.30 2099.60

3 450 m u/s 2099.67 2099.70 2099.63 2100.13

4 300 m u/s 2099.47 2099.53 2099.40 2099.47

5 150 m u/s 2099.53 2099.57 2099.27 2099.53

6 60 m u/s 2099.53 2099.50 2099.57 2099.60

7 30 m u/s 2099.53 2099.50 2099.50 2099.50

8 Barrage axis 2099.50 2099.50 2099.50 2099.50

9 15 m d/s 2089.15 2089.20 2089.60 2089.73

10 30 m d/s 2088.13 2088.33 2088.50 2088.67

11 45 m d/s 2087.33 2087.50 2087.67 2088.03

12 60 m d/s 2087.03 2087.10 2087.07 2087.47

13 75 m d/s 2087.50 2087.83 2088.00 2088.40

14 90 m d/s 2088.00 2088.13 2089.00 2089.73

15 105 m d/s 2087.50 2087.83 2089.00 2089.23

16 120 m d/s 2087.00 2087.50 2088.83 2089.07




26

Table-10 Observed residual velocities in the downstream of barrage at 2000 cumec discharge under free flow condition. - Intake desander closed

Sl.No.

Observed velocities in the downstream of barrage structure (m/sec.)

Distance from left abutment

Location 0.0m (L)

30m 60m 90m 120m 150m 173m (R)

1 Just d/s of barrage structure

1.53 1.63 3.01 5.30 12.84 13.73 16.31

2 15.0m d/s 3.71 3.81 5.00 5.00 4.30 3.51 6.98

3 30.0m d/s - 3.11 3.91 2.92 2.22 4.50 4.30

4 45.0m d/s - 1.92 2.72 2.62 3.11 3.41 5.00

5 60.0m d/s - 2.02 2.92 3.41 4.01 4.20 5.20




27

Table-11 Observed velocities and discharge distribution in the bays of barrage at 2000 cumec discharge under free flow condition. - Four bays closed - Eight bays operative - Intake desander closed

Sl. No.

Bay No. L-R

Observed velocities m/sec. and discharge distribution in the bays of barrage

2000 cumec discharge

Left Centre Right Average velocity

% Discharge

1 5 2.52 2.52 3.01 2.68 9.46

2 6 2.32 2.82 3.31 2.82 9.95

3 7 2.52 3.11 3.71 3.11 10.98

4 8 2.62 3.01 3.71 3.11 10.98

5 9 3.11 2.62 2.92 2.88 10.16

6 10 4.01 2.52 1.72 2.75 9.71

7 1-U.S 4.30 4.40 4.20 4.30 19.84

8 2-U.S. 3.71 4.20 4.40 4.10 18.92




28

PHOTOGRAPHS



29

Photograph-1: Model view as seen from upstream under existing condition.

Photograph-2: Model view as seen from downstream under existing condition.



30

Photograph-3: A view of barrage and intake as seen from upstream.

Photograph-4: A view of barrage and intake as seen from downstream.



31

Photograph-5: Flow condition at 300 cumec discharge under free flow as seen from u/s.




32

Photograph-7: Flow condition at 1000 cumec discharge under free flow as seen from d/s.




33

Photograph-9: Flow condition at 0.3m gate opening as seen from upstream at FRL

(El. 2103.0m).



34

Photograph-10: Flow condition at 0.5m gate opening as seen from downstream at FRL

(El. 2103.0m).


(El. 2103.0m).



35


(El. 2103.0m).

Phatograph-13: Flow condition at 2000 cumec discharge under free flow as seen from

downstream.



36

Phatograph-14: A view of scoured bed profile in downstream of barrage after running

2000 cumec discharge under free flow condition.

Photograph-15: Flow condition at 2000 cumec discharge (without 4 left bays) under free

flow as seen from upstream.



37

Photograph-16: Flow condition at 2000 cumec discharge (without 4 left bays) under free

flow as seen from downstream.



38

DRAWINGS

Annexure-2:

Further model studies for Barrage–Intake of Lata Tapovan, H.E.Project across river Dhauliganga in Distt. Chamoli

(Uttarakhand)

______________________________________________________________________________________________________

I.R.I. Roorkee Research Report No. 85 RR (H3-06) March, 2015

1

CONTENTS

PARA NO. TITLES PAGE NO.

_ LIST OF TABLES 2

_ LIST OF PHOTOGRAPHS 2

_ LIST OF DRAWINGS 3

1 INTRODUCTION 5

2 THE PROBLEM 5

3 MODEL INVESTIGATIONS 6

4 DISCUSSION OF RESULTS AND

CONCLUSIONS 8


(Uttarakhand)

______________________________________________________________________________________________________


2

(A) LIST OF TABLES

Table-1 Observed velocities and discharge distribution across the barrage and Under-sluice bays at 1000 cumec and 2000 cumec discharge under free flow condition(Proposal-2). Table-2 Observed velocities and scour in bed, d/s of barrage at 1200 cumec and 2000 cumec discharge under gated condition. Table-3 Observed velocities and scour in bed, d/s of barrage at 2000 cumec discharge under free flow condition. Table-4 Observed velocities and discharge distribution across the barrage and Under-sluice bays at 1000 cumec and 2000 cumec discharge under free flow condition. Table-5 Observed velocities and scour in bed, d/s of barrage at 2000 cumec discharge under gated and free flow condition (Proposal-3). Table-6 Observed reservoir levels with closing barrage bays at 2000 cumec discharge under free flow condition (barrage bays closed from left side). Table-7 Observed velocities and scour in bed, d/s of barrage at 2000 cumec discharge under gated and free flow condition (Proposal-4).

(B) LIST OF PHOTOGRAPHS

Photograph-1 View of cutting rock ledge in left bank at 180m u/s of barrage and

upstream floor, blocks, gabion protection. (Proposal-2)

Photograph-2 View of downstream floor, blocks and gabion protection. (Proposal-2)

Photograph-3 Flow conditions in upstream of barrage maintaining FRL at 2000 cumec

discharge.

Photograph-4 Flow conditions in downstream of barrage in free flow condition at 1000

cumec discharge.

Photograph-5 Flow conditions in upstream of barrage in free flow condition at 2000

cumec discharge.

Photograph-6 View of upstream floor, blocks, gabion protection. (Proposal-3)

Photograph-7 View of downstream floor, blocks, pit and gabion protection.(Proposal-3)

Photograph-8 Flow conditions in upstream of barrage maintaining FRL at 2000 cumec

discharge.

Photograph-9 Flow conditions in downstream of barrage maintaining FRL at 2000

cumec discharge.


(Uttarakhand)

______________________________________________________________________________________________________


3

Photograph-10 Flow conditions in downstream of barrage maintaining FRL at 2000 cumec discharge. (Proposal-4) Photograph-11 Flow conditions in downstream of barrage in free flow condition at 1000 cumec discharge. Photograph-12 Flow conditions in downstream of barrage in free flow condition at

2000 cumec discharge. (C) LIST OF DRAWINGS

Drawing-1 Sketch of cutting rock ledge in left bank at 180m u/s of barrage in stages.

(Proposal-2)

Drawing-2 Plan of barrage with upstream floor, blocks, gabion protection and

downstream floor, blocks, pit and gabion protection. (Proposal-3)

Drawing-3 L-section of barrage and under-sluice bays. (Proposal-3)

Drawing-4 L-section of barrage and under-sluice bays. (Proposal-4)


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REPORT


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1.0 INTRODUCTION

Lata – Tapovan Hydro Electric Project is proposed to be constructed across

river Dhauliganga near Lata village in Joshimath Tehsil, District Chamoli in

Uttarakhand. The project site is located at a distance of about 250 km from

Rishikesh. The power house is situated near Tapovan village. River

Dhauliganga is an important tributary of holy river Ganga. The project will be

executed by Larsen & Toubro Ltd. and envisages the construction of 18.0 m

high barrage to divert 79.25 cumec river discharge for power generation and a

required discharge for sediment flushing, through a water conductor system

comprising an intake, desilting chamber, HRT intake, 7.315 km. long head race

tunnel, a surge shaft, a pressure shaft, a surface power house with installation

of 3 units of 57 MW each and a tail race channel. A gross head of 277.65 m is

available between barrage and tail race exit point. The barrage has been

designed for 2000 cumec discharge with full reservoir level (FRL) at El. 2103.0

m and maximum draw down level (MDDL) at El. 2099.5 m.

2.0 THE PROBLEM

Model studies for barrage-intake of Lata – Tapovan H.E. Project was referred to

IRI Roorkee by DGM – Hydro Design, L&T Ltd, Faridabad vide his letter no.

L&T / FBD – EDRC / Lata, dated 18.02.2012. The scope of studies are as

follows:

2.1 For barrage model

(a) Discharge carrying capacity of spillways.

(b) Adequacy of energy dissipation arrangement.

(c) Sediment flushing capacity of spillways.

(d) Checking the adequacy of upstream and downstream apron length.

(e) Checking scour depth in the downstream of barrage.

2.2 Hydraulic model studies of barrage

T.M. No. 84RR(H3-05), October 2013 was issued with model studies regarding barrage model and studies have been done for point ‘a’ to ‘e’ except aforesaid point ‘c’ of para 2.1.


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3.0 MODEL INVESTIGATIONS

3.1 In continuation, sponsor desired by his letter dated 10.01.2014 to run the model as per following modifications to study the impact on flow due to non-uniform flow distribution in barrage bays (Proposal-2).

1. Change in upstream bed of river from concrete bed to representative mobile bed at 380m u/s from barrage axis.

2. To study the possibility to minimize the non-uniformity of flow in barrage

bays by smoothening the protruding rock ledge at about 180m u/s on the left

bank of barrage. (Drg.-1)

3. To reduce the length of upstream raft and divide wall from barrage axis-

57.5m (39.5m from start of pier upstream).

4. True representation of upstream and downstream concrete C/C blocks and gabion protection as per following details.

(a) U/S side- C/C blocks – 5m, Gabion protection – 8m.

(b) D/S side- C/C blocks – 8m, Gabion protection – 8m.

3.2 Incorporating above modifications (Photograph-1 & 2), the model was run at

500 cumec, 1000 cumec & design discharge of 2000 cumec and corresponding

tail water levels were maintained at 360 m downstream of barrage axis as per

tail rating curve computed from the cross sections supplied by the sponsor. The

visual behaviour of the river was seen in free flow condition and it was observed

that due to the bends in upstream river reach, the concentration of flow was

either on left side or on right side of river throughout the represented reach in

the model on almost all the discharges. The discharge distribution in the bays of

barrage was found to be improved as compared with that found in earlier study

as shown in Table-1. The model was operated, maintaining FRL at 1200 cumec

& design discharge of 2000 cumec. The observed velocities and scour in bed,

d/s of barrage structure were almost same as found in earlier study. The results

are tabulated in Table-2 & 3. The pictorial views of flow conditions are shown in

(Photograph-3 to 5).

3.3 Having witnessed the above observations on dated 23.02.2014, the sponsor

proposed to conduct the model study with the following modifications in the


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7

barrage for energy dissipation arrangement and efficient hydraulics vide their

letter dated 12.11.2014 (Proposal-3).

1. Change in upstream floor length of barrage to 7.0m as per approved

drawing by NTPC. (Drg.-2 & 3)

2. To meet the velocity of flow after the barrage in same range as in virgin conditions, a pit has been introduced as shown in drawing at El. 2085.0m.

3. Introduction of downstream pier wall in each alternate bay as shown in drawing.

4. Barrage pier thickness at upstream and in downstream may be kept same shall be 2.0m.

The model was reconstructed as per aforesaid modifications (Photograph-6 &

7) and was run by maintaining FRL at the discharges 1000 cumec & 2000

cumec. It was also run in free flow conditions. The discharge distribution in the

bays of barrage during aforesaid conditions was found to be improved as

compared to those found in earlier study as shown in Table-4. The velocities

and scour in bed, downstream of barrage structure were also observed and

have been tabulated in Table-5. The pictorial view of flow conditions are shown

in (Photograph-8 & 9).

The reservoir levels were observed by closing the gates of barrage from gate no. 1 to 9 successively and the results are tabulated in Table-6.

3.4 Keeping in view the said observations, the sponsor proposed the following

modifications in the energy dissipation arrangement vide his letter dated

17.12.2014 (Proposal-4).

1. Floor: Under-sluice spillway slope to be modified from 35.5m upstream of

the key-end in a slope of 1V:48.7H and barrage spillway slope to be

modified from 10.5m upstream of the key-end in a slope of 1V:14.43H as per

drawing attached (Drg.-4). With the above modification, end of the floor (key

end) will have Elevation of 2085.772m asl.

2. Downstream Pit: Downstream Pit may further be deepen to 1m (2084.0m)

with side slope of 1V:2H same as earlier. Bottom width of the pit may be revised

to 5m compared to earlier 4m.


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The model was accordingly reshaped and was run maintaining the reported

FRL (El. 2103.0m) at the discharge of 1000 cumec & 2000 cumec. It was also

run at free flow conditions. The velocities and scour in bed, d/s of barrage

structure were also observed. The results are tabulated in Table-7. The pictorial

views of flow conditions are shown in (Photograph-10 to 12).

4.0 DISCUSSION OF RESULTS AND CONCLUSIONS

The hydraulic tests conducted on comprehensive model of barrage-intake of

Lata Tapovan H.E.Project revealed that:-

4.1 Smoothening the protruding rock ledge at about 180m u/s on the left bank of

Barrage as proposed in stage-I (Drg.-1), helps in uniform distribution of

discharge in the bays under free flow condition as shown in Table-1 & 4.

4.2 The observed velocities in the downstream of barrage have reduced in

proposal-4 as compared to those found in proposal-3. The maximum scour in

bed was recorded as 4.5m which is lesser than that found in latter. Thus the

proposed energy dissipation arrangement is working well.

4.3 The flow conditions in downstream of barrage also seems to be more

streamlined in the said conditions.

4.4 Therefore proposal-4 seems to be best one among all the proposals as per

model observations.

4.5 The waterway of barrage is sufficient to pass the design discharge of 2000

cumec in free flow condition (Table-6).


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TABLES


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Table-1 Observed velocities and discharge distribution in the bays of barrage at 1000 cumec and 2000 cumec discharge under free flow condition. - All twelve bays operative - Intake desander closed - Cutting of left bank rock ledge at 180m u/s of barrage axis as per Stage-I (Proposal-2) - Length of upstream raft and divide wall from barrage axis- 57.5m

Sl. No.

Bay No. L-R


1000 cumec discharge 2000 cumec discharge

L C R Av. vel.

% L C R Av. vel.

%

1 1

2.2

2

1.5

3

0.6

3

1.4

6

3.9

6

2.9

2

2.2

2

1.9

2

2.3

5

5.1

9

2 2

2.7

2

2.0

2

1.1

3

1.9

6

5.3

1

4.0

1

2.7

2

2.1

2

2.9

5

6.5

2

3 3

3.3

1

2.6

2

1.4

3

2.4

5

6.6

4

4.4

0

3.2

1

2.2

2

3.2

8

7.2

4

4 4

3.8

1

2.5

2

1.4

3

2.5

9

7.0

2

4.2

0

3.3

1

2.5

3

3.3

5

7.3

2

5 5

3.3

1

2.5

2

1.7

2

2.5

2

8.1

9

3.9

1

3.3

1

2.4

2

3.2

2

7.9

7

6 6

1.3

3

1.4

3

1.8

2

1.5

3

4.9

7

3.0

1

2.8

2

2.5

2

2.7

8

6.9

1

7 7

1.6

3

1.4

3

1.6

3

1.5

6

5.2

0

2.9

2

2.5

2

2.4

2

2.6

2

6.5

1

8 8

1.6

3

1.7

2

1.4

3

1.5

9

5.1

7

2.5

2

2.5

2

2.5

2

2.5

2

6.2

6

9 9

1.1

3

2.2

2

3.1

1

2.1

5

6.9

9

2.5

2

3.5

1

3.6

1

3.2

1

7.9

7

10 10

0.8

3

2.6

2

3.7

1

2.3

9

7.7

7

1.3

3

4.3

0

5.2

0

3.6

1

8.9

7

11 1

4.5

0

3.8

1

4.0

1

4.1

1

20

.05

4.9

0

4.3

0

4.0

1

4.4

0

14

.57

12 2

1.4

3

5.4

9

4.6

0

3.8

4

18

.73

3.4

1

5.6

9

4.1

1

4.4

0

14

.57



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Table-2

Observed velocities and scour in bed, d/s of barrage at 1200 cumec discharge under gated condition maintaining FRL 2103.0m. - All gates equally opened - Intake desander closed - Cutting of left bank rock ledge at 180m u/s of barrage axis as per Stage-I - Length of upstream raft and divide wall from barrage axis- 57.5m

Sl.No.

Observed velocities in the downstream of barrage axis (m/sec.)

Location from barrage axis and d/s of bay no.

Location Bay-2 Bay-5 Bay-8 Bay-11 Bay-12

1 Just d/s of gate

18.99 14.82 14.03 20.57 19.19

2 30.0m d/s 19.28 18.89 18.99 14.92 19.88

3 60.0m d/s 5.79 5.59 11.05 18.59 9.07

4 75.0m d/s 3.61 3.51 3.21 8.07 6.29

Scoured bed and scour depth

Bay-1 Bay-3 Bay-5 Bay-7 Bay-9 Bay-12

1 2084.1 2084.8 2084.4 2083.8 2082.4 2083.2

2 2.4m 1.7m 2.1m 2.7m 4.1m 3.3m

2000 cumec discharge

Sl.No.




1 Just d/s of gate

16.61 16.90 17.50 16.80 17.40

2 30.0m d/s 17.80 17.80 19.19 17.50 18.39

3 60.0m d/s 11.65 9.26 12.14 15.12 14.72

4 75.0m d/s 3.31 4.20 7.48 7.08 8.87



1 2084.0 2085.1 2084.2 2083.0 2083.0 2082.0

2 2.5m 1.4m 2.3m 3.5m 3.5m 4.5m




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Table-3

Observed velocities and scour in bed, d/s of barrage at 2000 cumec discharge under free flow condition. - Intake desander closed - Cutting of left bank rock ledge at 180m u/s of barrage axis as per Stage-I - Length of upstream raft and divide wall from barrage axis- 57.5m

Sl.No.




1 Just d/s of gate

5.40 5.99 5.79 6.59 6.09

2 30.0m d/s 13.33 13.63 13.73 13.93 8.77

3 60.0m d/s 8.57 10.36 15.53 12.54 12.74

4 75.0m d/s 2.22 2.62 4.40 5.69 5.10



1 2085.9 2084.5 2084.5 2084.0 2084.2 2080.0

2 0.6m 2.0m 2.0m 2.5m 2.3m 6.5m




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Table-4

Observed velocities and discharge distribution in the bays of barrage at 1000 cumec and 2000 cumec discharge under free flow condition. - All twelve bays operative, Intake desander closed - Cutting of left bank rock ledge at 180m u/s of barrage axis as per Stage-I - Length of upstream raft and divide wall from barrage axis- 7.0m (Proposal-3)

Sl. No.

Bay No. L-R


1000 cumec discharge 2000 cumec discharge Depth

(m) Vel.

(m/sec) Discharge (m

3/sec)

% Depth (m)

Vel. (m/sec)

Discharge (m

3/sec)

%

1 1 2.5 1.78 49.04 4.91 3.5 2.37 91.25 4.42

2 2 2.5 2.10 57.75 5.78 3.5 2.88 110.88 5.37

3 3 2.5 1.99 54.73 5.48 3.5 3.29 126.67 6.14

4 4 2.5 2.20 60.50 6.05 3.5 3.49 134.37 6.51

5 5 2.5 2.31 63.53 6.36 3.5 4.00 154.00 7.46

6 6 2.5 2.31 63.53 6.36 3.5 4.11 158.24 7.67

7 7 2.5 2.52 69.30 6.94 3.5 3.90 150.15 7.28

8 8 2.5 3.14 86.35 8.64 3.5 3.29 126.67 6.14

9 9 2.5 3.14 86.35 8.64 3.5 3.49 134.37 6.51

10 10 2.5 3.25 89.38 8.94 3.5 4.21 162.09 7.86

11 1 3.5 3.98 153.23 15.33 4.5 7.37 364.82 17.68

12 2 3.5 4.30 165.55 16.57 4.5 7.07 349.97 16.96

Total 999.24 100.00 2063.48 100.00



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Table-5

Observed velocities and scour in bed, d/s of barrage at 2000 cumec discharge under gated condition maintaining FRL 2103.0m. - All gates equally opened - Intake desander closed - Cutting of left bank rock ledge at 180m u/s of barrage axis as per Stage-I - Length of upstream raft and divide wall from barrage axis- 7.0m - Barrage pier thickness at u/s and d/s is kept 2.0m - Energy dissipation pit in d/s of barrage structure kept at El. 2085.0m (P-3)

Sl.No.


Location from barrage axis (maintaining TWL)

Location Left Centre Right

1 90.0m d/s 6.15 9.41 7.37

2 180.0m d/s 5.84 6.96 3.16

After maintaining TWL 1.0m higher

1 90.0m d/s 7.27 5.94 11.25

2 180.0m d/s 5.64 5.64 5.64

2000 cumec discharge in free flow condition

Sl.No.


Location from barrage axis and d/s of bay no. Location Bay-

1 Bay-

2 Bay-

3 Bay-

4 Bay-

5 Bay-

6

Bay-7

Bay-8

Bay-9

Bay-10

Bay-11

Bay-12

1 60.0m d/s 15.4 15.7 16.1 16.4 15.4 16.3 16.2 15.4

2 90.0m d/s 5.54 7.78 13.1

3 180.0m

d/s

6.45 5.84 6.05

Scoured bed and scour depth (Scoured bed is above El. 2000.00m)

1 Scoured

bed

82.8 82.4 82.8 82.4 81.5 82.8 81.7 82.2 81.0 81.3 82.0 80.4

2 Scour

depth

(m)

3.2 3.6 3.2 3.6 4.5 3.2 4.3 3.8 5.0 4.7 4.0 5.6



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Table-6

Observed reservoir levels with barrage bays at 2000 cumec river discharge (bays closed from left side)

- Intake desander closed

Sl.No.

Bays closed

from left side

Average reservoir level (m) at 30m u/s of barrage axis

Remark

1 - 2094.03

2 One 2094.20

FRL= El. 2103.0 m

3 Two 2094.30

4 Three 2094.73 MDDL= El. 2099.5 m

5 Four 2095.07

6 Five 2096.20

7 Six 2097.20

8 Seven 2098.93

9 Eight 2100.23

10 Nine 2103.00



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Table-7

Observed velocities and scour in bed, d/s of barrage at 1000 & 2000 cumec discharge under gated condition maintaining FRL 2103.0m. - All gates equally opened - Intake desander closed - Cutting of left bank rock ledge at 180m u/s of barrage axis as per Stage-I - Length of upstream raft and divide wall from barrage axis- 7.0m - Barrage pier thickness at u/s and d/s is kept 2.0m - Energy dissipation pit in d/s of barrage structure kept at El. 2084.0m (Proposal-4)

Sl.No.


Location from barrage axis (maintaining TWL) at 1000 cumec

Location Left Centre Right

1 60.0m d/s 15.13 14.52 15.64

2 90.0m d/s 5.43 6.76 7.68

3 180.0m d/s 2.88 4.21 4.41

At 2000 cumec

1 60.0m d/s 14.52 14.52 15.54

2 90.0m d/s 6.15 5.43 6.15

3 180.0m d/s 6.15 6.35 4.21

2000 cumec discharge in free flow condition

Sl.No.


Location from barrage axis and d/s of bay no. Location Bay-

1 Bay-

2 Bay-

3 Bay-

4 Bay-

5 Bay-

6

Bay-7

Bay-8

Bay-9

Bay-10

Bay-11

Bay-12

1 60.0m d/s 14.1 15.3 13.9 14.6 12.4 12.2 12.1 12.3 12.1 12.0 13.3 12.1

2 90.0m d/s 5.43 6.56 7.88

3 180.0m

d/s

5.02 5.43 5.74

Scoured bed and scour depth (Scoured bed is above El. 2000.00m)

1 Scoured

bed

83.2 82.8 84.2 83.1 83.0 83.2 82.0 82.4 82.5 82.8 83.5 81.5

2 Scour

depth

(m)

2.8 3.2 1.8 2.9 3.0 2.8 4.0 3.6 3.5 3.2 2.5 4.5



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PHOTOGRAPHS

Further model studies for Barrage–Intake of Lata Tapovan, H.E.Project across river Dhauliganga in Distt. Chamoli (Uttarakhand)______________________________________________________________________________________________________

I.R.I. Roorkee Research Report No. 85 RR (H3-06) March, 2015 18

Photograph-1 View of cutting rock ledge in left bank at 180m u/s of barrage and upstream floor, blocks, gabion protection. (Proposal-2)

Photograph-2 View of downstream floor, blocks and gabion protection. (Proposal-2)


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Photograph-3 Flow conditions in upstream of barrage maintaining FRL at 2000 cumec discharge.

Photograph-4 Flow conditions in downstream of barrage in free flow condition at 1000 cumec discharge.


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Photograph-5 Flow conditions in upstream of barrage in free flow condition at 2000 cumec discharge.

Photograph-6 View of upstream floor, blocks, gabion protection. (Proposal-3)


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Photograph-7 View of downstream floor, pier, blocks, pit and gabion protection. (Proposal-3)

Photograph-8 Flow conditions in upstream of barrage maintaining FRL at 2000 cumec discharge.


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Photograph-9 Flow conditions in downstream of barrage maintaining FRL at 2000 cumec discharge.

Photograph-10 Flow conditions in downstream of barrage maintaining FRL at 2000 cumec discharge. (Proposal-4)


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Photograph-11 Flow conditions in downstream of barrage in free flow condition at 1000 cumec discharge.

Photograph-12 Flow conditions in downstream of barrage in free flow condition at

2000 cumec discharge.


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DRAWINGS

Model studies report_25-3-15_opt.pdf

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