Refinement of DPR Project Layout

BLUE ENERGY PVT. LTD.
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Super Trishuli Hydropower Project

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(100 MW)
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Refinement of DPR Project Layout
April 2017
Power Division
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Super Trishuli Hydropower Project (100 MW)
TABLE OF CONTENTS
PAGE NO.
1 INTRODUCTION ........................................................................................................... 1
2 BRIEF DETAILS OF PROJECT AS PER DPR ............................................................ 3
3 SURVEY AND INVESTIGATIONS................................................................................ 4
3.1 Topographic Survey ............................................................................................. 4
3.2 Geotechnical Investigations ................................................................................. 4
4 GEOLOGY AND SEISMICITY ...................................................................................... 6
4.1 Barrage Site ......................................................................................................... 6
4.2 Trash Rack Structure ........................................................................................... 6
4.3 Power Intake and Power house complex ............................................................. 7
4.4 Seismicity ............................................................................................................. 7
5 HYDROLOGY ............................................................................................................... 8
5.1 Trishuli River Flows .............................................................................................. 8
5.2 Riparian Release.................................................................................................. 8
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5.3 Design Flood ........................................................................................................ 9
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5.4 Sedimentation aspects ......................................................................................... 9

5.5 Tail water levels ................................................................................................... 9
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6 REFINEMENT IN PROJECT LAYOUT ....................................................................... 11

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6.1 Overall Layout .................................................................................................... 11

6.2 Barrage and fish ladder ...................................................................................... 12
6.3 Tail race outlet.................................................................................................... 15
6.3.1 Discussions ............................................................................................ 19
6.4 Trash rack and Intake Layout............................................................................. 20
6.5 Powerhouse ....................................................................................................... 22
6.6 Mechanical designs............................................................................................ 24
6.7 Electrical equipment’s and Power Evacuation ................................................... 26
7 PLANT OPERATING HEADS..................................................................................... 27
7.1 Full Reservoir Level ........................................................................................... 27
7.2 Minimum Draw Down Level ............................................................................... 27
7.3 Tail Water Levels ............................................................................................... 27
7.4 Head Range ....................................................................................................... 28
8 PLANT OPERATION AND ENERGY GENERATION ................................................ 29
8.1 Run-of-River Mode ............................................................................................. 29
8.2 Peaking mode .................................................................................................... 29
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8.3 Energy generation .............................................................................................. 30

8.4 River flow regulation and protection measures .................................................. 30
8.4.1 Run-of-river mode .................................................................................. 30
8.4.2 Peaking mode ........................................................................................ 31
8.5 Sedimentation aspects ....................................................................................... 31
9 PROJECT COST......................................................................................................... 33
10 SUMMARY AND CONCLUSION ................................................................................ 34
ANNEXURES:
Annexure-1: Salient Features
Annexure-2: Annual Energy Generation for Average Monthly Flows (Run-of-River
Operation)
Annexure-3: Annual Energy Generation for average monthly flows (Diurnal Peaking
Operation)
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PLATES
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Plate-1: Geological Plan of Barrage and Powerhouse Area

Plate-2: Project Layout – Plan & Section (Sheet 1 of 2)
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Plate-3: Project Layout – Plan & Section (Sheet 2 of 2)

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Plate-4: Barrage Plan & Sections (Sheet 1 of 4)

Plate-8: Fish Ladder Plan & Sections (Sheet 1 of 2)
Plate-9: Fish Ladder Plan & Sections (Sheet 2 of 2)
Plate-10: Embankment Sections
Plate-11: Intake and Silt Flushing Plan and Sections
Plate-12: Powerhouse – Plan at El 268.5m
Plate-13: Powerhouse – Section A-A
Plate-14: Powerhouse – Section B-B
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LIST OF TABLES AND FIGURES

PAGE NO.
TABLES:
Table-1: Long term mean monthly flows (m3/s) ................................................................. 8

Table-2: Impact of analysis on the Tail Water Levels ........................................................ 9
Table-3: Plant Operation during Peaking Mode .............................................................. 29
Table-4: Energy Generation (95% availability) ................................................................ 30
Table-5: Comparison of Project Cost .............................................................................. 33
FIGURES:
Figure-1: Tail Rating Curve in Trishuli River.................................................................... 10

Figure-2: Project layout comparison with DPR layout ..................................................... 12
Figure-3: Barrage layout comparison with DPR layout ................................................... 14
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Figure-4: Tailrace layout comparison with DPR layout ................................................... 16
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Figure-5: Water Surface Profiles in Tailrace channel ...................................................... 18

Figure-6: Tail rating curve at outlet sill............................................................................. 19
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Figure-7: Intake layout comparison with DPR layout ...................................................... 21

Figure-8: Power house layout comparison with DPR layout ........................................... 23
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1 INTRODUCTION
Super Trishuli Hydropower Project is located in Chitwan, Gorkha and Dhading districts in the
Central Development Region of Nepal. The project is located on Trishuli River, which is a
major tributary of Narayani River, and is conceived as a run-of-the-river scheme with diurnal
pondage. The proposed installed capacity of the project is estimated as 100MW
(2X33.33MW + 1X33.34MW). Development rights of the project have been assigned by the
Department of Electricity development, Ministry of Energy, Nepal to Blue Energy Private Ltd.
(BEPL) who is developing the project on Build-Own-Operate-Transfer (BOOT) basis. BEPL
has appointed SNC-Lavalin Engineering India Pvt. Ltd. (SLEI) to provide engineering
services for preparation of detailed project report (DPR) and tender documents for the
project.
The project is a low head dam-toe type development basically designed for power trade with
India and adopted the design discharge corresponding to dependability of Q29%. The
characteristic nature of low head dam-toe development, the adoption of higher design
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discharge from conventional NEA criteria of Q40% proves to be economically more beneficial.
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The detailed project report (DPR) was prepared and submitted in February 2015. In each
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subsequent stage of project development, that is tender engineering, model studies and
detailed engineering, the project designs are refined and improved upon. DPR level designs
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are reviewed and further detailed/refined to tender level designs and for physical model
studies. These studies were carried during September 2015 to February 2016. The physical
model studies are in progress and undertaken by Infraplan Engineering Services Pvt. Ltd.,
Pune, India. The results of model studies will also be incorporated in project designs,
subsequently.
This report provides the details of the improvements performed during tender engineering
and list out all the changes with respect to DPR layout. The report is arranged in following
sections:
a) Brief Details of Project as DPR - It provides a short description of main project

parameters as per DPR
b) Survey & Investigations - This section provides information on survey and

investigations results used for tender designs.
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c) Geology and Seismicity – This section provides a brief summary of the project
geology. For complete information, the chapter 4 & 5 of DPR and investigation
reports should be consulted.
d) Hydrology – This section provides a brief summary of the project hydrology. For
complete information, the chapter 6 of DPR should be consulted.
e) Refinement in project layout – This section provides the details of refinements

undertaken during tender designs
f) Plant operating heads – This section provides the range of operating heads.
g) Plant operation and energy generation – This section describes the plant capability to
operate in run-of-river or peaking generation mode, annual energy generation,
regulation of river flows and sedimentation aspects.
h) Project cost – This section provides the revised project cost estimates due to
changes in the layout and compares it with cost as estimated in DPR.
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i) Summary and conclusion – This section summarizes the report and highlight the
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conclusions, provides the revised project salient features.
j) Annexures – This section consists of annexures to the report.

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k) Plates – This section consists of important layout drawings.

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2 BRIEF DETAILS OF PROJECT AS PER DPR
The proposed scheme consists of barrage (founded on rock) as a diversion structure. The
intake and the powerhouse are accommodated on the right side of the barrage. The scheme
will be located close to Chumlingtar village, about 3km downstream of Phisling Bazar. The
main project data are as follows:
• River & Basin : Trishuli River, Narayani Basin
• Catchment area upto Intake : 11659 km2
• 1 in 50 years flood Discharge : 6979 m3/s
• 1 in 500 years flood Discharge : 9882 m3/s
• Full Reservoir Level (FRL) : 275.0 m a.s.l.
• Minimum draw down level : 267.0 m a.s.l.

(MDDL)
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• Barrage (On Impervious : 33m height from deepest foundation level
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foundation)
• Barrage width between : 97.0m

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abutment
• : 5 Nos. Radial Gates; 14.0m x 22.8m

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Barrage gate type, (W x H)
• Temporary river diversion for : During phase 1 & 2, left 3-spillway bays will be
construction isolated, during phase 3 & 4 remaining 2-spillway
bays and powerhouse will be isolated and
constructed
• No. of Trash rack bays : 18 nos.
• Trash rack size (W x H) : 10 nos. panel of 4.28m x 2.2m
• Intake Gate Size (W x H) : 6 nos., 5.5m x 14.8m
• Powerhouse : Surface, Right bank
• Machine Hall (W x H x L) : 21.0m x 47.45m x 63.30m
• Number & Turbine Type : 3 nos., Bulb Type
• Installed Capacity : 3 x 33.5 MW
• Project Cost (Oct 2014) & : 13354.7 Million NRs, Four Years
Construction period
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3 SURVEY AND INVESTIGATIONS
The survey and investigation works were carried out in stages during DPR studies. All
survey and investigation data are compiled and examined.
3.1 Topographic Survey
Detailed topographic survey was carried through Sai Om Engineering Consultancy

Pvt. Ltd., Kathmandu by BEPL. The head works and powerhouse sites lie between
Darechok V.D.C. ward No.2, Khani Khola/Chumlingtar at left bank of Chitwan
district/Narayani zone as well as Tanglichok V.D.C. ward No. 9, Gordi at right bank of
Gorkha district/Gandaki zone. The co-ordinates/elevations for the survey work were obtained
from the Geodetic Survey Branch and the Topographical Survey Branch of Survey
Department of Nepal.
The project encompasses area from 84° 34’ 00" to 84° 41’ 06" East longitude and
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from 27° 48’ 41” to 27° 52’ 56" North latitude. All the data necessary to determine
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the locations, coordinates and elevations were obtained by direct measurements in the field
using total station having a least count of 1”. Detailed topographic survey had been carried
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out covering all permanent works of the project. A total of 48.544 Ha of area were covered in
the ground survey. Control survey was carried out and sufficient numbers of permanent
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survey stations have been established near the main project components by constructing
concrete pillars. About 12 numbers of river cross-sections near tail race outlet had been
bathymetrically surveyed using boat.
3.2 Geotechnical Investigations
Geological investigations including mapping, sub-surface exploration required for planning

and design of the project were carried out. Detailed surface geological mapping was carried
out by SLEI. The sub surface investigations/explorations comprising of electrical resistivity,
drilling was carried out to assess thickness of overburden and nature of foundation strata.
Electrical resistivity tomography (ERT), drilling and construction material testing was carried
out by I.C.G.S. (Pvt.) Ltd, Kathmandu.
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Altogether four electrical resistivity tomography lines namely ERT-1, ERT-2, ERT-3 and
ERT-4 have been undertaken. Among them two profiles (ERT 1 & ERT 2) had been carried
out on right bank covering the barrage body and powerhouse area. The other two profiles
were carried out on left abutment covering the Barrage body. These four profile lines
aggregate to total length of 600 meter.
Seventeen (17) drillholes have been done in the entire project area aggregating 499.5m of
length. Out of them, six drillholes were drilled along barrage axis – three each on left and
right abutments. Besides, three boreholes were drilled at powerhouse location covering the
entire area of powerhouse; two drillholes were located at downstream of Barrage axis and
two at upstream of dam axis a river channels; one borehole is located at tailrace channel
and the other two were located on the left abutment. In addition four exploratory pits
covering the project components like headworks and powerhouse complex area were also
done to assess the overburden materials. During drilling campaign, in-situ permeability test
in each drillholes were carried out to assess the permeable nature and fracturing condition of
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rock mass.
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The geological and geotechnical data gathered during DPR has been examined and plotted.
The rock contours in Barrage and Powerhouse areas are developed as shown in Plate-1.
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4 GEOLOGY AND SEISMICITY
The diversion site is located near village Chumlingtar. Trishuli River flows nearly in a straight
course towards west through moderately wide asymmetrical valley. In general, the river
course is more or less straight for a length of about 800m extending from upstream to
downstream of the proposed axis. Average elevation of the riverbed at the site is about
253m and the width of the river channel around 110m. The river bed comprises river borne
material consisting of rounded to sub rounded boulders, pebbles and gravels of phyllite,
quartzite with silty sand matrix; the permeability of overburden, in general, varies between
2.967x10-3 & 9.87x10-3 cm/sec that is considered as moderately high.
4.1 Barrage Site
The results of sub-surface explorations indicate that the site is suitable for about 33m high
barrage as diversion structure and could be founded on bedrock. The drilling along the
diversion axis indicates that bedrock comprising of quartzite/phyllitic quartzite at the centre of
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the river channel is available at a depth of about 5.70m and it is about 8.25m towards right
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abutment. The thickness of overburden towards left abutment is about 3.4m. In general both
the abutments are covered by fluvial terrace deposits. The left abutment rises moderately
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and is occupied by thick terrace deposits above El 265m. On the other hand the right
abutment rises gently from river bed upto El 280m i.e. near to road level and is covered by
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fluvial deposits. Isolated bedrock exposures are observed above that. The exposed bedrock
includes phyllite, sericite phyllite with quartz veins and phyllitic quartzite. Bedrock is slightly
to moderately weathered. The nature of bedrock as assessed from the drilling is poor to fair.
The permeability value in bedrock is in the range of 2 to 5 Lugeon.
4.2 Trash Rack Structure
Trash rack structure is proposed to be installed in front of intake to arrest entry of the
unwanted floating debris and to convey clean water to powerhouse. The structure is aligned
with barrage axis, by 110o. The drilling data indicates depth of bedrock in the area varies
from about 7.0m to nearly 10.0m and depth of overburden increases towards downstream
reach. The overburden in river bed comprises river borne material consisting of rounded to
sub rounded boulders, pebbles and gravels of phyllite, quartzite with silty sandy matrix.
The bedrock encountered in the exploratory drill holes is slightly weathered, fractured, and
medium to fine grained, grey to greenish gray, bluish grey moderately strong to strong
phyllitic quartzite.
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The permeability in bedrock varies from 2 to 5 lugeon. The structure may be founded on
bedrock by removing the overburden of about 10m thick going down to El 244.20m or
slightly below that level.
4.3 Power Intake and Power house complex
Surface powerhouse of Super Trishuli Hydropower Project is envisaged on the right bank of
the river as dam toe powerhouse like arrangement. Average elevation of the riverbed at the
site is about 253m and the width of the river channel around 120m. The riverbed of the wide
valley at proposed site is covered by large boulders, gravels, pebbles of quartzite, gneiss
and phyllite admixed with silty and sandy matrix. As per the layout conceived, the surface
powerhouse has been proposed on the partly on the right river channel and partly on right
bank terrace T0 immediately downstream of the barrage axis. This terrace is wide and
adequate space is available for locating the surface powerhouse. The gradient on right bank
of the river is gentle and no slope stability problem is expected. A right bank tributary,
Shikhar Khola joins the river Trishuli about 100m downstream of the proposed powerhouse
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area. Shikhar Khola has incised a narrow valley on the right bank terraces.
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The geological logs of drill holes indicate that the thickness of the overburden around
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powerhouse area varies between 6.0m and 8.0m and overburden material comprises
sub-rounded to rounded boulders, pebbles and gravels of quartzite, gneiss, quartzitic phyllite
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with silty & sand matrix. The bedrock comprises slightly weathered, highly jointed to
fractured, medium to fine grained, grey, greenish grey, weak to strong phyllitic quartzite. It is
also observed that the rock mass in this area is always in saturated condition. The bedrock
appears to be of fair quality as evident from core recovery and RQD in general.
4.4 Seismicity
The Super Trishuli Hydropower Project is located in Lesser Himalaya between MCT and
MBT. Keeping the seismo-tectonic setup of the region in view, the project area has been
assigned to Zone-IV in the vicinity of Zone-V as per Map of India Showing Seismic Zones
(IS:1893-2002 (Part-1). So, for preliminary design purpose as per codal provision for zone
IV, the seismic parameters are adopted. The site specific study to determine the seismic
coefficients for final designs is under progress.
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5 HYDROLOGY
The project is located on Trishuli River, which originates in Higher Himalayas in the Tibet
Autonomous Region of China. It flows in a south-south westerly course and joins Narayani at
Devighat. Narayani eventually flows into India and joins the Ganges.
5.1 Trishuli River Flows
The long term flows at intake is estimated using observed flows at Betrawati and Arughat
measuring stations from period 1977-78 to 2005-06 (29 years). These measuring stations
are located upstream of Intake site in its catchment. The Betrawati is located on River
Trishuli and Arughat is located on Budhi Gandaki (upstream major tributary of Trishuli River).
The flows are derived on the basis of catchment area proportion; no significant variation in
rainfall can be established for these catchment areas. The flow values reproduced in
Table-1 represents the gross discharge available at intake for power generation.
Table-1: Long term mean monthly flows (m3/s)

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Year Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May
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Average 553.1 1444.1 1458.5 938.0 452.6 295.6 172.1 120.8 108.3 120.5 190.7 457.5
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As evident from the flows, Trishuli River shows a definite seasonal flow pattern similar to that
observed in Himalayan Rivers. The dry period for the river lasts from December to April,
during this period most of the contribution to flows is from groundwater and snowmelt. The
wet period lasts from June to September; during this period high flows occur in the river due
to the effect of the monsoon and increased snowmelt. The monsoon season lasts from June
to September and non-monsoon from October to May. The hydrological year is considered
from June to May (of the following calendar year).
5.2 Riparian Release
The riparian release will be environmental flow released for sustenance of ecosystem in
downstream reach of diversion structure. In DPR, the riparian release of 10.62m3/s is
considered for the power potential studies.
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5.3 Design Flood
Magnitude of flood for the project has been assessed using Probabilistic and
Hydro-meteorological approaches, which gives similar values. The 500-year return period
flood is chosen as design flood for the project site and has been estimated as 9882m3/s. The
25-year return period flood is chosen as design flood for construction activities and has been
estimated as 1410m3/s for period Oct to May and 6112m3/s for remaining period.
5.4 Sedimentation aspects
The sedimentation aspects have been elaborated under section 8.5.
5.5 Tail water levels
The tail rating curves downstream of barrage or at tail race outlet are important input for
barrage design and for determination of available head for generation. During DPR stage
studies, the Tail Water Level (TWL) was determined using the slope-area method. As part of
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tender engineering, the tail water levels are evaluated in more detail using latest
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bathymetrically surveyed river cross-sections and available data from gauge & discharge
(G&D) measuring site. The back water analysis is performed using HEC-RAS, which is more
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appropriate than the slope-area method as it considers the impact of individual river cross
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sections while performing the computations. The impact of analysis on the tail water levels
are as follows in Table-2.
Table-2: Impact of analysis on the Tail Water Levels
River Tail water levels (Elm)

Remarks
Flows DPR designs Tender designs
Average monsoon flows to determine the
1204 m3/s El 260.5 El 257.0
rated head
6980 m3/s El 264.2 El 265.5 1 in 50 yr flood to design stilling basin
1 in 500 yr flood to design spillways &
9882 m3/s El 266.5 El 268.0
operating platforms
The tail rating curve in the river just downstream of barrage end sill and in front of tailrace
outlet so developed using HEC-RAS is given in Figure-1.
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Figure-1: Tail Rating Curve in Trishuli River

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6 REFINEMENT IN PROJECT LAYOUT
As part of tender engineering process, the DPR designs are reviewed by an independent
team and possible refinements are performed as follows.
6.1 Overall Layout
Careful examination of the project structures holistically reveals possible refinements in the
layout. It is observed that bedrock on left abutment is not available down to about 43m depth
as evident from drill hole DH-9. This non-availability of bedrock indicates requirement of a
long training wall to extend the length of the seepage path around the Barrage, in DPR this
requirement was fulfilled by the fish ladder proposed on the left bank.
It is proposed to relocate the fish ladder on the right side of the barrage, i.e. between the
barrage and the powerhouse. This arrangement will be better appreciated by environmental
specialists as the fish normally prefer water currents (attracting flow). Since the powerhouse
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will operate almost on a continuous basis (except maybe during very lean periods when the
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operation would be diurnal), the fish will be attracted more towards the right bank. The intake
entry to the leftmost turbine unit is also improved; the space so created is used to
accommodate the fish ladder.
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After finalizing the above changes, the overall barrage-fish ladder–powerhouse complex is
adjusted to fit best within the available space. It is observed from the rock contours
developed from results of the drill holes that about 50m upstream from DPR axis the bed
rock will be available in shallow depth. Since, it is always recommended to abut a barrage on
the rock wherever possible. At this location, two small non-overflow blocks needs to be
added on the left bank to ensure that the barrage abuts against the rock. The same concrete
blocks will be used to create the storage space for stoplogs and access to barrage
foundation galleries. The proposed arrangement also helps to dispense with the 105m long
and 28m high left training wall, which would have involved quite a bit of extra excavation and
concreting.
Keeping the above apprehension on geological interpretation, it is proposed that barrage

axis should be shifted some 50m upstream from the DPR location, where bedrock would be
available at shallow depth. The proposed arrangement will reduce the cost and will
significantly mitigate the risk of seepage. The tail race of powerhouse will also be located
away from the adverse influence of right bank nallah.
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The upstream shift of barrage axis has only marginal impact (about 2%) on the reservoir
storage, which is inconsequential. The comparison between DPR layout and proposed
Tender layout is shown as in Figure-2. The revised project layout plan and section is shown
in Plate 2 and 3.
AXIS (TENDER)
Penstock AXIS (DPR)

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DPR LAYOUT
TENDER LAYOUT
ROCK CONTOURS
Figure-2: Project layout comparison with DPR layout
6.2 Barrage and fish ladder
In DPR, concrete gated barrage with five (5) bays of each opening size
14m (W) x 22.8m (H), proposed to be founded on bed rock. The total width of gated barrage
across the river is 97m. The crest level of the barrage structure corresponds to the general
river bed level of El 252.5m. The maximum reservoir level will be at El 275.0m, the bridge
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deck slab has been proposed at El 277.0m having freeboard of 2m. A 42m long stilling basin
is proposed for energy dissipation, with downstream cistern level depressed to El 249.50m.
As a process of tender engineering, the following changes/refinements are performed:
• With revised, tail water levels (Table-2) design of spillways, piers, training walls,
stilling basins are performed.
• Two technically feasible options of spillway arrangement that is one with breast wall
(pressure flow) and other one with free flow spillway are studied. As compared to free
flow option, the total width of barrage in case of breast wall option is increasing by
about 10%. Even though, height of the gate is reduced from 22.5 to 13.2m for breast
wall option, but one additional gate has to be provided to pass the design flood. More
excavation and concrete works is required to be done, thus this arrangement will be
more costly. Thus, free flow option as proposed in DPR remains favorable.
• The width of each spillway bay can be slightly reduced from 14m to 13.2m, the
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cistern level of stilling basin reduced from El 249.50 to El 248.50m. The overall length
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of spillway section reduced from 87m to 79.1m. This would, of course, be further
verified through testing on the physical model.
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• The top of barrage as El 277.0m is checked by performing freeboard calculation in

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accordance with IS:6512, and found to be sufficient.
• Another proposed change pertains to the width of the piers, particularly the end piers
and the double pier. While the width of all the intermediate single piers has been
retained as 5m as proposed in the DPR, width of the end piers is proposed to be
increased from 3m to 4m and that of the double pier from 5m to 8m.. This change is
mainly proposed keeping in view the heightened seismic activity and to have a
design which is more likely to be adopted during detailed engineering.
• The anchorage of radial gates is revised to pre-stressed anchorage arrangement.

This system is especially advantageous in the case of large sized gates where very
high loads are required to be transferred to the piers.
• With all above refinements, the total width of spillway remains same as proposed in
DPR i.e 97.0m.
• The arrangement of construction joints, divide walls are reviewed and checked with
the respect to the stability, constructability and temporary river diversion point of
view.
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• The foundation galleries, stoplog storage bay, lift shaft, equipment shaft, stair case
arrangements to access foundation galleries are planned.
• The foundation arrangement with respect to the availability of bed rock for each
barrage block and its interface with the foundation of power house bays, forebay
intake are studied and planned.
• The layout of the fish ladder has been designed and entrance has been positioned at
the right bank of the river where current is highest. The outlets at two different levels
i.e at FRL and MDDL have been planned. It is designed for minimum 1.5m3/s, drop of
height per pool has been kept within range of 0.3 to 0.4m and velocity through slot
less than 2m/s
• The right bank 95 m long concrete closure wall is revised with 52m long clay core
rockfill embankment (refer Plate-2).
The comparison of proposed layout plan with DPR layout is shown in Figure-3.
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Figure-3: Barrage layout comparison with DPR layout
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The following configuration of barrage is proposed. The layout plans and sections are shown
in Plate-4 to Plate-10.
• Number of Spillway bays : 5
• Number of non-overflow bays : 2
• Width of each bay : 13.2m
• Height of each bay : 22.5m
• Spillway crest level : El 252.5m
• Thickness of twin piers : 4m
• Thickness of intermediate/end piers : 5m
• Length of Stilling Basin : 35m
• Cistern level of stilling basin : 248.5m
• End Sill level : El 252.0m

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• Number of fish pools : 66
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• Slot opening of Fish ladder : 0.4m

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• Width of Fish Ladder : 2.5m

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• Length of each pool : 4.2m
6.3 Tail race outlet
The proposed refinements in tail race outlet are discussed before intake and powerhouse
arrangement because its refinement had resulted in change of rated head and
corresponding designs discharge. Thus, results of changes in intake and powerhouse will
then be better understood.
The surface powerhouse has been planned on the right bank of the Trishuli River adjacent to
barrage structure. As per arrangement proposed in DPR, a 70m long tail race channel will
discharge water back into Trishuli River, just downstream of barrage end sill. Initial width of
tailrace channel was proposed as 46.6m, which widens to 70m at tail race outlet sill by
flaring right flank wall by an angle of 38.38o.
The best hydraulic performance in a discharge channel is obtained when the confining
sidewalls are parallel and the distribution of flow across the channel is maintained uniformly.
With gradual expansion of tailrace allows recovery of velocity head, resulting in less head
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loss at the exit. The rate of divergence of the sidewalls must be limited or else the flow will
not spread to occupy the entire width of the channel uniformly and will result in undesirable
flow conditions at the terminal structure. The angular variation of the flow boundaries for
acceptable transition should not exceed, as given by equation1 tanα = 1/(3F), where F is
Froude’s number. The Froude’s number at the outlet sill will be 1 for most of the time, thus
flare angle should be limited to 18.4º. The layout of tailrace is improved by providing uniform
flare of both flank walls of tailrace as shown in Figure-4.
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DPR LAYOUT
Figure-4: Tailrace layout comparison with DPR layout
In DPR, tail race outlet sill has been kept at about 2m above the river bed to avoid entrance
of bed load into the tail race, which is desirable. The tail race channel will have reverse slope
of 1 in 4 to meet outlet sill at El 254.0m and further meets the river bed curvilinearly at
1
Reference –Design of small dams, USBR
161026-40ER-0008-PA 16
El 252.0m with downward slope as shown in Plate-3. It is apparent that control section will
be located at outlet sill location, except during high floods. The flow will leave the tailrace
outlet sill at critical depth, till the river water level exceeds during floods results in reduction
of generation head. The rated head is so chosen, where most of the energy is generated.
The maximum energy will be generated during monsoon, thus it is desirable that turbines
should operate at best efficiency during most of time in monsoon season.
In DPR, the average river water level during monsoon was considered at El 260.5m.
The reservoir shall operate at FRL (El 275.0m). Thus, the rated head of 14.1m after
accounting for head losses was chosen in DPR.
The river flow corresponding to El 260.5m is estimated as 3000m3/s from tail rating curve so
developed using HEC-RAS as shown in Figure-1. It is observed from flow series, that most
of time river inflows remain far less than 3000m3/s. Thus, average monsoon tail water level
can be reduced from considered level of El 260.5m. As per inflow series, the average
monsoon flows are 1204m3/s and corresponding river water level shall be El 257.0m as
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shown in Figure-1. Thus, for rated condition average river water during monsoon can be
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considered at El 257.0m.
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The tailrace channel is also modelled in HEC-RAS, to evaluate the following-

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• Location of Control section in tail race channel
• To determine the head and discharge in tail race to generate 100.0 MW with river
water level at El 257.0m (average monsoon river water level), which will corresponds
to rated condition.
• Water and total energy levels in tailrace corresponding to river water level at
El 257.0m.
• To study the impact on tailrace conditions with change in river water levels.
• To develop the rating curve at tailrace outlet sill.
• To determine the tailrace water levels for powerhouse designs
• The manning’s coefficient of 0.015 is adopted in the studies and results are shown in
Figure-5.
161026-40ER-0008-PA 17
Figure-5: Water Surface Profiles in Tailrace channel

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The results have been plotted in Figure-5, following is inferred:
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• It has been determined that control section in tail race channel will be located at the
outlet sill.
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• Flow profile (PF1) represents the rated condition, with river water level at El 257.0m.
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It has been observed that tailrace outflow of 724.9m3/s can maintain a critical depth
at the outlet sill as shown in Figure-5. The corresponding energy level at sill will be
El 257.77m. Thus, the average net head available for generation during monsoon
shall be (275-257.77-0.7=16.53m), which can be considered as rated head.
• Flow profile (PF2) represents a condition with tail race flows of 724.9m3/s and
barrage gates are closed. The downstream river water level will be El 255.9m.
• It has been observed that rise in river water levels from El 255.9m till El 257.77m, will
have negligible impact on the flow conditions in the tailrace. Thus, as river water
levels tends to be more than 257.77m, results in reduction of net head and
corresponding turbine output.
The tail rating curve at the tailrace outlet sill is given Figure-6. The same will be verified from
physical model studies.
161026-40ER-0008-PA 18
Tail Rating Curve ‐ Tailrace Outlet
266.00
(264)
264.00
262.00
Tail Race
260.00
River
El.m
(257.77)
258.00
(5585)
256.00
(1616)
254.00 (724.9)
252.00
0 1000 2000 3000 4000 5000 6000
River Flows (m3/s)
Figure-6: Tail rating curve at outlet sill

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6.3.1 Discussions
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During low river flows, the tailrace water levels and corresponding net head shall be
governed by the turbined flows. During high river flows, river water levels shall be higher
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which results in reduction of net head from the rated conditions. As shown in Figure-6, the
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river flows upto 1616m3/s, will have negligible impact on the tailrace conditions. Thus, upto
release of 891m3/s (1616-725) from barrage, the turbines can be operated at rated condition.
The rated condition to generate 100.5 MW shall corresponds to 16.53m of head and turbined
flow of 724.9m3/s. The turbines can be operated upto minimum head of 10.75m (65% of
rated head). With reservoir level at El 275.0m, the river flow corresponding to ~El. 264.0m
(El. 275-10.75m), will be about 5585m3/s. Thus, plant can remain in operation upto river
flows of 5585m3/s. During non-monsoon season, the plant will be operated in
peaking/ run-of-river mode and net head shall be governed by the turbined flows.
As a result, it is proposed to change rated head from 14.1m (as proposed in DPR) to
16.53m, thus reducing the design discharge from 850m3/s to 725m3/s. The reduction in
design discharge would be considered more conducive from environmental point of view
also. It has been checked that with these parameters the project will generate more annual
energy as compared with DPR, as elaborated in section 8.3. The refinement in tailrace
layout is shown in Plate 2 and 3.
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6.4 Trash rack and Intake Layout
In DPR, the intake arrangement for feeding water to each turbine is located on the right side
abutment of the diversion structure and leads to Power House. The trash rack structure has
been provided at an angle of 100º to the barrage axis and sill level has been provided at
El 255.0m to prevent extraneous materials into powerhouse. Any debris collected near the
foot of the intake wall will be occasionally flushed out by opening the right side gate of the
barrage. In all there are 18 bays of 4.0m each with 1.5m thick piers, which keep flow velocity
<1.5m/s corresponding to design discharge of 850m3/s. A 8.0m wide operational platform for
trash rack cleaning machine has been provided at the top of trash rack structure at
El 277.0m. The platform will be approachable from the top of the barrage which is at the
same level.
Intake was designed to convey the design discharge of 850m3/s and has 3 bays of 13.0m
each with 5.52m thick intermediate piers and 3.0m thick end piers. The invert level of the
main intake was kept at El 241.7m to have sufficient submergence depth below MDDL to
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void possibility of vortices formation. The MDDL of El 267.0m was judiciously decided, to
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have storage for 850m3/s so that plant can be operated in diurnal peaking mode. Gates have
been provided at upstream end to serve as the isolation device for turbine during shutdown
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and maintenance. For maintenance of gates, stop log grooves have been provided just
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upstream of the gate grooves.
• With revised design discharge of 725m3/s, design of trash rack and intake structure is
undertaken and submitted.
• The intake entry to left most turbine is improved, the space so created is used to
• Angle of trach rack structure revised to 110o, to reduce the length of right wall of
intake pool and wing wall.
• The intake well as provided in DPR, is optimized and provided with a more functional
design which will facilitate collection and disposal of pebbles and shingles that would
pass through the trashrack.
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• The pebbles/shingle would be flushed through the silt flushing duct into the barrage
stilling basin downstream of the barrage. The bonnet type gates will be housed in
chamber, accessed from turbine floor of power house.
• In the process, the height of intake guide wall reduced from 37.3m (as proposed in
DPR) to 26m.
• The bell-mouth entry of intake is also optimized by accommodating the bell-mouth in

total length of 20.3m compared to 24.3m proposed in DPR.
The comparison with DPR layout is shown in Figure-7. The layout drawings of Intake are
shown in Plate-11.
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Figure-7: Intake layout comparison with DPR layout
The revised intake dimensions are summarized below:
As per DPR Revised
Design Parameters
Design Discharge 850m3/s 725m3/s
FRL El. 275.0m El. 275.0m
MDDL El. 267.0m El. 269.0m
161026-40ER-0008-PA 21
Trash Rack Structure
No. of bays 18 nos. 14 nos.
Trash rack size 10 nos. panel of 4m x 2m 10 nos. panel of 4m x 2m
Sill level of Trash rack El. 255.0m El. 255.0m
Clear Opening between trash bars 150mm 150mm
Total Nos. of unit 180 140
Flow through velocity <1.5m/s <1.5m/s
Intake
No. of bays 3 nos. 3 nos.
Sill elevation of Intake Gates El. 241.7m El. 242.5m
Number of openings 6 nos. 6 nos.

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Opening Size (WxH) 5.5m X 14.8m 5m x 13m
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6.5 Powerhouse
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In DPR, surface powerhouse of size 21m (W) x 47.65m (H) x 86.31m (L) (including service
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bay of 23m) is planned on the right bank will have three (3) hydraulic turbine-driven
generating units of 33.50 MW capacity each, with total installed capacity of 100.5 MW. To its
downstream, there will an auxiliary block of size 10.3m (W) x 28.85m (H) x 86.31m (L).
The transformers will be placed above draft tubes at deck level of El 268.0m. The service
bay level had also been kept at El 268.0m, about 1.5m above maximum anticipated flood
level of El 266.5m. The powerhouse house size was designed to house horizontal bulb type
generating units having rated head of 14.1m and unit discharge of 283m3/s.
• Nepal Electricity Authority has given clearance for 100MW.
• The powerhouse size is revised corresponding to revised rated head of 16.53m and
unit discharge of 242m3/s.
• The layout of service bay, transformer bay and floor levels are revised corresponding
to revised maximum anticipated flood level of El 268.0m.
161026-40ER-0008-PA 22
• The adequacy of arrangement of beam and columns in service bay, machine hall and
auxiliary bay areas are checked by performing structural analysis. The arrangement
of beam and columns in auxiliary bay and transformer bay area are revised.
• The arrangement of upstream wall is revised to meet the electro-mechanical

requirements.
• In the process, more space above draft tube duct and below transformers deck will
be available at turbine floor.
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Figure-8: Power house layout comparison with DPR layout
The comparison with DPR layout is shown in Figure-8. The powerhouse layout is shown in
Plate-12 to 14. The changes in powerhouse layout are summarized below:
161026-40ER-0008-PA 23
As per DPR Revised
Design Parameters
Design Discharge 850 m3/s 725 m3/s
Net head 14.1m 16.53m
Maximum anticipated flood level El 266.5m El 268.0m
Power house-Dimensions
Overall (WxHxL) 21m x 47.65m x 86.31m 20m x 46.85m x 83.25m
Service bay (WxHxL) 21m x 20.35m x 23m 20m x 19.85m x 23m
Machine hall (WxHxL) 21m x 47.65m x 63.3m 20m x 46.85m x 60.25m
Auxiliary bay (WxHxL) 10.3m x 28.85m x 86.31m 10.3m x 29.85m x 83.25m
Powerhouse – Floor Levels

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Unit Centre Line El 249.1m El 249.0m
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Turbine Floor El 258.0m El 258.5m
Service bay El 268.0m El 268.5m

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Transformers deck El 268.0m El 268.5m

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GIS Floor El 272.5m El 272.5m
Control room El 268.0m El 268.5m
Crane rail El 280.5m El 280.5m
6.6 Mechanical designs
The surface power house shall house three (3) horizontal bulb type turbines directly coupled
to the synchronous generator housed inside the bulb located in water path. Intake gates
shall serve as the isolation device for turbine during maintenance.
The basis mechanical designs, specifications, necessary equipment layouts and mechanical
system schematics are complete and submitted. The major turbine parameters are as
follows:
161026-40ER-0008-PA 24
As per DPR Revised
Technical Data
Installed capacity 3 X 33.5 MW 2X33.33MW +

1X33.34MW
Full reservoir level El 275.0m El 275.0m
Minimum drawdown level El 267.0m El 269.0m
Minimum TWL (all units shutdown) El 254.0m El 254.0m
Minimum TWL (one unit at 10% discharge) El 254.8m El 254.39m
Minimum TWL (one unit at 50% discharge) El 255.5m El 255.14m
Normal TWL (all units at rated head) El 257.83 El 257.77m
Maximum TWL during high flood El 266.5m El 268.0m
Turbine no/Type Three/ Horizontal Bulb Three/ Horizontal Bulb
Rated output 35.26 MW 34.2 MW

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Turbine rated speed 93.75 rpm 107.14 rpm
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Turbine runner center line El 249.1m El 249.1m
Total rated discharge 850m3/s 724.9m3/s

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Rated discharge per unit 283m3/s 241.63m3/s

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Rated head 14.1m 16.53m
Operating heads 14.1m - 8.77m 20.56 – 10.74m
Major Dimensions
Turbine Runner Diameter 6.20 m 5.6m
Bulb Turbine Inlet Cross Section (W x H) 13.00m x 14.80m 12.00m x 13.00m
Diameter of Bulb housing the Generator 7.00m 6.50m
Draft tube cone outlet diameter 9.60m 8.8m
Distance of Draft tube outlet from Runner 30.60m 30.6m

C.L.
Crane Capacity 160 / 32 MT 160 / 32 MT
Crane Lift (from service bay) 12.50m 12.00 m
161026-40ER-0008-PA 25
6.7 Electrical equipment’s and Power Evacuation
The surface power house shall house three (3) horizontal bulb type turbines directly coupled
to the synchronous generator housed inside the bulb located in water path. Intake gates
shall serve as the isolation device for turbine during maintenance.
The generated voltage of 11kV will be stepped up to 220kV through step-up transformers.
The transformers are located on the downstream side of the power house on draft tube
deck. HV side of the transformers will be connected to 220kV GIS through GIB.
It is envisaged in DPR that total power will be evacuated through one 220kV double circuit
27 km dedicated line to the New Bharatpur substation (substation was under construction by
NEA), which has a path to export energy to Indian grid. As a recent development, NEA is
planning to construct substation at Markichowk and interlinked it with New Bharatpur
substation. Marichowk substation shall be near to the project site. ITECO Nepal (p) Ltd
performed the desk study of different possible transmission route alignment from
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Supertrishuli substation to Marichowk substation and recommended a 19 km route for
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survey license. BEPL had initiated the detailed project report/ EIA studies for the
recommended route.
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The interconnection between GIS and switchyard shall be through transmission line
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conductor. The outgoing lines shall be provided with Lightning arresters, CVTs and Wave
traps.
The high voltage equipment to be placed in the outdoor switchyard will be designed for a
minimum 40 kA rms rated short circuit current.
The switchyard and its surrounding area will have their respective grounding system.
The earthing grid will be designed and constructed for operating voltages and short-circuit
capacities corresponding to short-circuit and earth-fault current levels.
The basis electrical designs, specifications, necessary equipment layouts and single line
diagrams are complete and submitted.
161026-40ER-0008-PA 26
7 PLANT OPERATING HEADS
7.1 Full Reservoir Level
Full reservoir level (FRL) for the project is fixed at El 275m, limited by the lowest settlement
levels at Phisling Bazar.
7.2 Minimum Draw Down Level
In DPR, minimum draw down level (MDDL) was chosen at El 267. In Tender designs, it is
judiciously selected at El 269m, to have an adequate submergence of intake to prevent the
vortices entering into the water passage to turbines. The sill level of trash rack structure has
been provided at El 255m, to prevent the bed load materials entering into the water passage
and also limiting the flow velocity through trash racks below 1.5m/s. This aspect will be
verified from the ongoing physical model studies.
The live storage available between FRL and MDDL is 3.16MCM, which can be used as
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diurnal storage during peaking operation.
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7.3 Tail Water Levels

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The intake and powerhouse are accommodated on the right side of barrage. The river flows
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will either pass through barrage spillways or through generation units housed in power
house or from both when river inflows are more than design discharge.
In DPR, tail race outlet sill has been kept at El 254m, about 2m above the river bed to avoid
entrance of bed load into the tail race, which is desirable. The control section in tail race
channel will be located at outlet sill location, except during floods. The tail rating curve at the
tailrace outlet sill is given Figure-6.
It is evident from Figure-6, that during low river flows, the water levels in river remain below
tail race water levels. During high river flows, river water levels shall be higher which results
in reduction of net head from the rated conditions.
161026-40ER-0008-PA 27
7.4 Head Range
It is a low head, dam-toe type development and considering the large variations in the
operating head and discharge, most suitable choice will horizontal bulb (Kaplan) type
turbine. The rated head is so chosen, where most of the energy is generated. The maximum
energy will be generated during monsoon, thus it is desirable that turbines should operate at
best efficiency during most of time in monsoon season.
The average monsoon flows are 1204m3/s (Table-1) and corresponding river water level
shall be El 257.0m. After accounting for head losses, the net head of 16.53m shall be
available for generation and is considered as rated head. The design/rated discharge shall
be 724.9 m3/s to generate 100.0 MW, will have the dependability corresponding to Q29%.
It has been observed from tail rating curve that river flows upto 1616m3/s, will have negligible
impact on the tailrace conditions as shown in Figure-6. Thus, upto release of ~891m3/s
(1616-725) from barrage, the turbines can be operated at rated condition.
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The turbines will be operated upto minimum head of 10.75m (65% of rated head). With
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reservoir level at El 275.0m, the river flow corresponding to ~El. 264.0m (El. 275-10.75m),
will be about 5585m3/s. Thus, plant can remain in operation upto river flows of 5585m3/s.
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8 PLANT OPERATION AND ENERGY GENERATION
8.1 Run-of-River Mode
The normal operating pattern of plant will be run-of-type operation or as base load station
throughout the year at a load depending upon the river inflows available for power
generation. The individual units shall be required to be operated for any load between 40%
to 110% of rated capacity depending on water availability, generating unit availability and
transmission network capacity. The plant will be operated mostly at FRL (El 275m). With
available inflows and operating heads as discussed above, the energy and power generation
is given in Annexure-2.
8.2 Peaking mode
The availability of live storage can provide flexibility in energy production during a day to
cater the peak demand in the system. Particularly during non-monsoon season, when river
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inflows are less than design discharge, the off peak period will be utilized to fill the available
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storage in the reservoir and during peak hours plant will be operated utilizing the flows from
stored volume. Thus, energy will be injected into the system during its peak demand.
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During non-monsoon season, the plant will operate during peak hours between El 275 (FRL)
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and El 269 (MDDL) as given in Table-3. The weighted output corresponding to weighted
reservoir level of El 273 will be 84.85MW. Due to limitation of live storage, the plant will be
operated in two blocks of 12 hrs each. The energy and power generation is given in
Annexure-3. During monsoon season, generally river flows will be more than design
discharge, thus plant will operate at FRL (El 275).
Table-3: Plant Operation during Peaking Mode

Reservoir Operation Tail Turbined Gross
Losses Net Head Output
Level water level Flow Head
(Elm) (Elm) (m3/s) (m) (m) (m) (MW)
275 (FRL) 257.77 724.9 17.23 0.7 16.53 100.5
273 (Weighted) 257.63 685.2 15.37 0.6 14.77 84.9
269 (MDDL) 257.31 596.4 11.69 0.5 11.19 56.0
161026-40ER-0008-PA 29
8.3 Energy generation
Normally, plant will operate in run-of-river mode but will have flexibility in energy production
during a day to cater the peak demand in the system. The comparison of two mode
operation is as below-
The annual energy generation will be more if plant operates in run-of-river mode as given
below in Table-4:
Table-4: Energy Generation (95% availability)
Run-of-river Peaking Peaking (DPR)
Installed capacity (MW) 100.0 (3X33.5) 100.0 (3X33.5) 100.5 (3X33.5)

Not accounted as
Riparian release operation is run-of- 10.62m3/s 10.62 m3/s
river
Annual Energy 471.2 GWh 429.8 GWh 406.7 GWh
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8.4 River flow regulation and protection measures
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8.4.1 Run-of-river mode

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• The reservoir level will be mostly maintained at FRL (El 275m) except during flushing
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operation.
• During non-monsoon when river inflows are low, barrage gates will remain close and
flow will pass through the Individual units, which shall be operated for any load
between 40% to 110% of rated capacity depending on river inflows.
• During monsoon when river flows are high, upto 724.5m3/s will pass through the
individual units and remaining shall be released through barrage gates.
• The operation of plant will be run-of-river; riparian release is not accounted in energy
calculations.
• The regime of river downstream of diversion structure will remain mostly unaffected.
• The scouring and protection measures in form of concrete blocks and loose stones in
wire crates are foreseen for barrage and tailrace structure.
161026-40ER-0008-PA 30
8.4.2 Peaking mode
• During monsoon, reservoir level will be mostly maintained at FRL (El 275m) except
during flushing operation. During non-monsoon, reservoir level will vary between FRL
(El 275m) and MDDL (El 269m).
• During monsoon when river flows are high, upto 724.5m3/s will pass through the
individual units and remaining shall be released through barrage gates. The average
river flows during monsoon is about 1204m3/s.
• During non-monsoon, plant can operate in two blocks in a day and barrage gates will
be mostly closed. During reservoir filling operation plant will be closed, which will vary
from 9.2 hrs to 1.5 hrs during each block. During this period, riparian flow of
10.62m3/s will be released downstream and accounted in energy calculations. The
plant will be in operation from 2.8 to 10.5 hrs during each block. The flows released
downstream will vary from 724.9m3/s to 596.4m3/s as per Table-3. The average river
inflow during non-monsoon is about 207m3/s.
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• During peaking operation, the flows downstream will be regulated but flows shall
remain confined with in river banks/water marks. Thus, no special protection
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measures for river banks are foreseen.

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• The scouring and protection measures for barrage and tail race structure will remain
same as required for run-of-river operation.
8.5 Sedimentation aspects
Super Trishuli is a low head scheme, envisaged to have low speed horizontal bulb type
Turbines. The sediment sampling and analysis at headworks was carried out by Hydro Lab
Pvt. Ltd., Nepal during monsoon season of year 2010. The results of observations are as
follows:
• About 87% of collected samples contain concentration of suspended sediments in

range of 1000 to 5000 ppm.
• At the start of July, concentration was measured as 3000ppm and during end of
September it was 500ppm.
• From particle size distribution curve of suspended sediments, the d75 size
corresponds to about 0.15mm and d90 size to about 0.3mm.
161026-40ER-0008-PA 31
• About 68% of suspended sediments are hard minerals (Mohs hardness scale value
above 5). The concentration of quartz mineral varies from 49% to 67%.
The height of barrage from river bed is about 24.5m, which results in a 5km long
reservoir. The flow velocities at the start of the reservoir will be more and reduces
progressively towards the barrage as flow depth increases. The sedimentation and
flushing aspect of reservoir is under study using physical and mathematical
modeling, basic philosophy is discussed as below-
Monsoon season (Peaking & Run-of-river operation)
• The plant will mostly operate at FRL (El 275), the average velocities (flows as per
Table-1) at the tip of the reservoir will varies from 4.4m/s to 2.9m/s which gradually
reduces to about 0.4m/s to 0.2m/s near intake. The substantial deposition of bedload
material will happen in the initial reach of reservoir and finer material will remain
suspended. It is expected that sediment mound will start at the reservoir tip and will
be progressive towards the barrage, which will be occasionally flushed off by
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drawdown flushing of the reservoir by opening barrage gates.
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• The average velocities in intake pool at FRL corresponding to design discharge of

724.9 m3/s will be about 0.5m/s. With such low velocities in intake pool, it expected
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that bed load material may not enter into the water passage. To prevent extraneous
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material passing turbines, trash rack and pebble traps are foreseen in the
arrangement. The flow velocities and length of intake pool in not sufficient to induce
settlement of finer sediments, which will remain suspended and will pass through the
turbines.
• The impact of sediments on turbines is expected to be less because of low head and
speed. Suitable measures will be under taken by equipment supplier by providing
protective coating of underwater parts.
Non-monsoon season (Peaking & run-of-river operation)
• It is expected that river will carry less sediments during non-monsoon, thus impact of
sediments during non-monsoon season is expected to be negligible during both
mode of operations.
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9 PROJECT COST
The project cost is updated, by revising the bill of quantities based on tender drawings, all
other cost parameters has been kept same as in DPR. The comparison of cost is as follows:
Table-5: Comparison of Project Cost
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161026-40ER-0008-PA 33
10 SUMMARY AND CONCLUSION
• It is proposed to shift barrage axis marginally upstream from DPR axis as the bed
rock on the left bank will be available in shallow depth. This will help to abut the
barrage on the rock with the provision of two small non-overflow blocks, which will be
used to create the storage space for stoplogs and access to barrage foundation
galleries. The proposed arrangement also helps to dispense with the 105m long and
28m high left training wall, which would have involved quite a bit of extra excavation
and concreting. The tail race of powerhouse will also be located away from the
adverse influence of right bank nallah.
• It is proposed to relocate the fish ladder on the right side of the barrage, i.e. between
the barrage and the powerhouse. Since the powerhouse will operate almost on a
continuous basis (except maybe during very lean periods when the operation would
be diurnal), the fish will be attracted more towards the right bank. The intake entry to
the leftmost turbine unit is also improved; the space so created is used to
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• Tailrace rating curves have been developed using the bathymetric data and by
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carrying out a numerical analysis using HEC-RAS software. The average river water
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level in monsoon season was estimated as El 260.5m during DPR studies. In the
present studies this level is computed as El 257m. As a result, the rated head has
been revised from 14.1m (as proposed in DPR) to 16.85m, thus reducing the design
discharge from 850m3/s to 721m3/s.
• With above changes, the refinements of all project structures are performed. The
revised salient features are shown in Annexure 1.
• Impacts due to changes in project layout, on plant operation and energy estimates,
project cost are evaluated and results are favorable.
161026-40ER-0008-PA 34
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ANNEXURE-1
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Salient Features
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161026-40ER-0008-PA 1
Refinement of DPR Project Layout Annexure-1
SALIENT FEATURES
• Project Location
o Country : Nepal
o District, Zone : Chitwan (Narayani) Gorkha (Gandaki)

Dhading (Bagmati)
o Development Region : Centre Development Region
o Geographical Location
- Rivers : Trishuli
- Type of Project : Run-of-River
- Nearest Town : Kurintar, Phisling Bazar
- Latitude : 27°51’38.45’’ N
- Longitude : 84°38’38.31’’ E
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• Accessibility
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o Kathmandu to Project Site : 100 km
o Nearest International : Kathmandu

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(Nepal) Airport
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• Hydrology
o River Basin : Narayani
o Catchment area : 11659 km2
o Rainfed Area : 7609 km2
o Snowfed Area : 4050 km2

(Assuming permanent snow
line above El. 4500m)
o Maximum Discharge : 2052.2 m3/s

(Average Monthly)
o Minimum discharge : 84.34 m3/s

(Average Monthly)
o 1 in 50 years flood Discharge : 6979 m3/s
o 1 in 500 years/ SPF flood : 9882 m3/s

Discharge
161026-40ER-0008-PA Page 1 of 5
Description As per DPR As per Tender

Designs Designs
• Reservoir
o Full Reservoir Level (F.R.L.) : 275.0 m a.s.l. 275.0 m a.s.l.
o Minimum Draw-down Level : 267.0m a.s.l. 269.0 m a.s.l.

(M.D.D.L.)
o Gross Storage at FRL : 6.08 mm³ 5.91 mm3
o Live storage : 3.99 mm³ 3.16 mm3
o Length of submergence : 5055 m 5000 m
o Area under submergence at : 63.7 Ha 62.67 Ha

FRL
• River Diversion
o Diversion Arrangement : Stage-1: Coffer dam Stage-1: Coffer dam

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to isolate area for 3- to isolate area for 3-
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spillway bays on left spillway bays on left

side side
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Stage-2: Upstream Stage-2: Upstream

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and downstream and downstream

cofferdam in cofferdam in
continuation to divide continuation to divide
wall of isolate wall of isolate
2-spillway bays and 2-spillway bays and
Powerhouse area Powerhouse area
o Diversion Discharge (one in : 1410 m3/s 1410 m3/s

25 Year Non-monsoon)
o Diversion Discharge (one in : 6112 m3/s 6112 m3/s

25 Year monsoon)
• Barrage
(On Impervious foundation)
o Top of Barrage : 277.0 m a.s.l. 277.0 m a.s.l.
o Barrage width between : 97.0m 97.0m

abutment
161026-40ER-0008-PA Page 2 of 5

Designs Designs
o Barrage Sill Elevation at : 252.5m a.s.l. 252.5m a.s.l.
Barrage Axis
o Gate Type and Size (W x H) : 5 Nos. Radial Gates; 5 Nos. Radial Gates;
14.0m x 22.8m 13.2m x 22.8m
o Hoist Type and Capacity : Twin Hydraulic Hoist Twin Hydraulic Hoist
(2x175 T) (2x175 T)
o Stop log Type and Size (W x : Vertical lift slide type Vertical lift slide type
H) (8units 14.0m x (8 units 13.2m x
2.85m) 2.85m)
• Trash Rack Structure
o No. of Trash rack bays : 18 nos. 14 nos.
o Trash rack size : 10 Nos. panel of 4.28 10 Nos. panel of 4m x

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x 2.2 2m
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o Sill level of Trash rack : 255m 255m
o Clear Opening between : 150 mm 150 mm

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trash bars
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o Total Nos. of unit : 180 140
• Intake
o Sill elevation of Intake Gates : 241.70m a.s.l. 243m a.s.l.
o Design Discharge Q29 : 849.79 m3/s 724.9 m3/s
o Intake Emergency Gate : Vertical lift fixed Vertical lift fixed wheel
wheel type type
o Intake Gate Size (WxH) : 6 Nos. 5.5m x 14.8m 6 Nos. 5m x 13m
o Intake Stoplogs : Slide type Slide type
o Intake Stoplogs overall Size : 5.5m x 14.8m 5m x 13m

(WxH)
• Surface Powerhouse
• Machine Hall Dimensions : 21.0m x 47.45 m x 20m x 46.35m x

(W x H x L) 63.30 60.25m
161026-40ER-0008-PA Page 3 of 5

Designs Designs
o Turbine Type : Bulb Type Bulb Type
o Number of Units : 3 3
o Elevation of Turbine Runner : 249.10 m a.s.l. 249.50 m a.s.l.
Center Line
o Rated Discharge per Unit : 283.26 m3/s 241.67 m3/s
o Turbine Speed : 93.75 rpm 107.14 rpm
o Operating heads : 14.1 – 8.77m 20.15-10.74 m
o Rated Head : 14.1m 16.53 m
o Installed Capacity (MW) : 100.5 (3 x 33.5 MW) 100.5 (3 x 33.5 MW)
o EOT Crane capacity : 1 Nos. 160/ 32 MT 1 Nos. 160/ 32 MT

(Powerhouse)
• Draft Tube Gates

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o Type of Gate : Vertical lift fixed Vertical lift fixed wheel

wheel Type Type
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o Gate Size (W x H) : 3 Nos. 9.6m x 9.4m 3 Nos. 9.6m x 8.6m
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Generator
o Number of phases : Three Three
o Type : Bulb Type Hydro Bulb Type Hydro

Generator Generator
o Number : 3 3
o Nominal speed : 93.75 rpm 107.14 rpm
o Generator Voltage / : 11 kV / 50Hz 11 kV / 50Hz

Frequency
o Power Load Factor (CosØ) : 0.9 0.9
• Step Up Transformer
o Voltage Ratio : 11kV/ 220kV 11kV/ 220kV
o Rating : 41MVA 41MVA
161026-40ER-0008-PA Page 4 of 5

Designs Designs
• Tailrace Channel
o Width at sill : 70m 58m
o Outlet sill elevation : 254.0 m.a.s.l 254.0 m.a.s.l
• Switchyard
o Type : GIS GIS
o Interface : Switchyard Switchyard
o Area (L x W) : 49m x 26m 49m x 26m
• Construction Period
o Construction Period : 4 (Four) years 4 (Four) years

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161026-40ER-0008-PA Page 5 of 5
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ANNEXURE-2
Annual Energy Generation for Average Monthly
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Flows (Run-of-River Operation)

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161026-40ER-0008-PA 2
ANNUAL ENERGY GENERATION FOR AVERAGE MONTHLY FLOWS (RUN-OF-RIVER OPERATION)
FRL(El m) = 275.0
Installed Capacity (MW) = 100
Combined Efficiency = 85.50%
Rated Head (m) = 16.53
Design Discharge (m 3/s) = 721.2
Riparian Flow (m3/s) = Not required (Dam Toe development with run of river operation) 0.00
Run-of-river operation with design discharge as Q29%-724.9m 3/s 95% Plant Availability
River Inflow
Month No. of Days
(m3/s) Turbined Flow Head Loss Tail Water Level Net Head Power Energy Power Energy
(m3/s) (m) (Elm) (m) (MW) (MU) (MW) (MU)
Monsoon Period
Jun 30 706.6 706.6 0.6 257.71 16.69 98.92 71.22 95.00 68.40
Jul 31 1425.1 722.9 0.7 257.86 16.44 99.68 74.16 95.00 70.68
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Aug 31 1596.1 718.1 0.7 258.08 16.22 97.69 72.68 95.00 70.68
Sep 30 1087.0 721.2 0.7 257.76 16.54 100.0 72.03 95.00 68.40
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Oct 31 467.9 467.9 0.3 256.82 17.88 70.18 52.22 70.18 52.22
Nov 30 237.4 237.4 0.1 255.79 19.11 38.04 27.39 38.04 27.39
Non Monsoon Period
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Dec 31 155.8 155.8 0.1 255.35 19.55 25.54 19.00 25.54 19.00
Jan 31 121.1 121.1 0.1 255.14 19.76 20.07 14.93 20.07 14.93
Feb
Mar
Apr
May
28
31
30
31
106.2
113.3
160.0
297.3
106.2
113.3
160.0
297.3
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0.1
0.1
0.2
255.05
255.10
255.38
256.08
19.85
19.80
19.52
18.72
17.69
18.82
26.20
46.68
11.89
14.01
18.87
34.73
17.69
18.82
26.20
46.68
11.89
14.01
18.87
34.73
Annual Gross Energy, MU = 483.13 471.18
Dry Period Wet Period

Annual (MU)
(MU) (MU)
Total energy with 100% plant availablity = 483.1 113.4 369.7
Total energy with 95% plant availablity = 471.2 113.4 357.8
Note - Dry period energy (from Dec to May)
161026-40ER-0008-PA Page 1 of 1
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ANNEXURE-3
Annual Energy Generation for Average Monthly
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Flows (Diurnal Peaking Operation)

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161026-40ER-0008-PA 3
Super Trishuli Hydropower Project (100.5 MW)
Refinement of DPR Project Layout Annexure 3
ANNUAL ENERGY GENERATION FOR AVERAGE MONTHLY FLOWS (DIURNAL PEAKING OPERATION)
FRL(El m) = 275.0
MDDL(El m) = 273.0
Tail Race Outlet crest level (El m) = 254.0
Installed Capacity (MW) = 100.00
Combined Efficiency = 85.50%
Rated Head (m) = 16.53
Design Discharge (m3/s) = 721.3
Diurnal Peaking operation with design discharge as Q29% - 721.3m3/s
Blocks of operation in 24hrs, Peaking time -4 hrs per block, Available volume between FRL & MDDL - 3.16Mm3
For each block of operation - 12hrs 24 hrs Monthly Generation Monthly Generation (95% Avail.)
River Weighted
No. of Diverted Tail Time to Total Total Off Off-
Mo-nth Inflow Riparian Weighted Head Net Power Peak Off-Peak Total Peak Total
Days 3 Available Flow for Water fill Peak Off-Peak Peak Peaking Peaking
(m /s) Flow 3 reservoir Loss Head during Energy Energy Energy Energy Energy
3 flow (m /s) generation Level Reservoir time (hr) time (hr) time time Energy
(m /s) 3 level (Elm) (m) (m) Peak (MU) (MU) (MU) (MU) (MU)
(m /s) (Elm) (hr) (Hrs) (Hrs) (MU)
(MW)
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Monsoon Period
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Jun 30 706.6 10.6 706.6 706.6 275.0 257.67 0.60 16.73 0.00 99.16 4.00 7.76 8.00 15.51 23.80 47.59 71.39 22.80 45.60 68.40
Jul 31 1425.1 10.6 1414.5 719.3 275.0 257.86 0.70 16.44 0.00 99.18 4.00 7.97 8.00 15.93 24.60 49.19 73.79 23.56 47.12 70.68
Aug 31 1596.1 10.6 1585.5 714.5 275.0 258.08 0.70 16.22 0.00 97.20 4.00 7.89 8.00 15.77 24.11 48.21 72.32 23.56 47.12 70.68
Sep 30 1087.0 10.6 1076.4 721.3 275.0 257.77 0.70 16.53 0.00 100.00 4.00 8.00 8.00 16.00 24.00 48.00 72.00 22.80 45.60 68.40
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Oct 31 467.9 10.6 457.3 457.3 275.0 257.62 0.60 16.78 0.00 64.36 4.00 3.61 8.00 7.22 23.80 24.09 47.89 23.56 24.33 47.89
Nov 30 237.4 10.6 226.8 226.8 275.0 257.62 0.60 16.78 0.00 95.99 3.77 0.00 7.55 0.00 21.73 1.25 22.98 21.50 1.48 22.98
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Non-Monsoon Period 142.04 218.33 360.37 137.78 211.24 349.03
Dec 31 155.8 10.6 145.2 145.2 273.0 257.62 0.60 14.78 6.04 84.55 1.63 0.92 3.27 1.84 8.56 4.83 13.39 8.56 4.83 13.39
Jan 31 121.1 10.6 110.5 110.5 273.0 257.62 0.60 14.78 7.94 84.55 1.53 0.41 3.07 0.82 8.04 2.15 10.19 8.04 2.15 10.19
Feb 28 106.2 10.6 95.6 95.6 273.0 257.62 0.60 14.78 9.17 84.55 1.50 0.19 2.99 0.37 7.08 0.89 7.97 7.08 0.89 7.97
Mar 31 113.3 10.6 102.7 102.7 273.0 257.62 0.60 14.78 8.54 84.55 1.51 0.29 3.03 0.59 7.93 1.54 9.47 7.93 1.54 9.47
Apr 30 160.0 10.6 149.4 149.4 273.0 257.62 0.60 14.78 5.87 84.55 1.65 0.98 3.29 1.97 8.35 4.98 13.33 8.35 4.98 13.33
May 31 297.3 10.6 286.7 286.7 273.0 257.62 0.60 14.78 3.06 84.55 2.22 2.83 4.44 5.65 11.63 14.81 26.44 11.63 14.81 26.44
Annual Gross Energy, MU = 51.59 29.20 80.79 51.59 29.20 80.79
Dry Energy (Dec- Wet Energy (Jun-

Annual May) (MU) Nov) (MU)
(MU)
Non- Non-
Peak Peak
Peak Peak
Total energy with 100% plant availablity = 441.2 51.6 29.2 142.0 218.3
Total energy with 95% plant availablity = 429.8 51.6 29.2 137.8 211.2
161026-40ER-0008-PA Page 1 of 1
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PLATES
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161026-40ER-0008-PA
PLATE -1
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SNC LAVALIN
Engineering India BLUE ENERGY PRIVATE LTD
SUPER TRISHULI
HYDROPOWER PROJECT (75MW)
PLATE - 2
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NOTES:
PLATE - 3
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TENDER STAGE DRAWING
NOTES:
PLATE - 4
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PLATE - 5
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PLATE - 6
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PLATE - 7
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PLATE - 8
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PLATE - 9
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PLATE - 12
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PLATE - 13
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PLATE - 14
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SECTION B-B

Refinement of DPR Project Layout - 13.4.16

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BLUE ENERGY PVT. LTD.

Super Trishuli Hydropower Project

5.4 Sedimentation aspects ......................................................................................... 9

6 REFINEMENT IN PROJECT LAYOUT ....................................................................... 11

6.1 Overall Layout .................................................................................................... 11

8.3 Energy generation .............................................................................................. 30

Plate-1: Geological Plan of Barrage and Powerhouse Area

Plate-3: Project Layout – Plan & Section (Sheet 2 of 2)

Plate-4: Barrage Plan & Sections (Sheet 1 of 4)

LIST OF TABLES AND FIGURES

Table-1: Long term mean monthly flows (m3/s) ................................................................. 8

Figure-1: Tail Rating Curve in Trishuli River.................................................................... 10

Figure-5: Water Surface Profiles in Tailrace channel ...................................................... 18

Figure-7: Intake layout comparison with DPR layout ...................................................... 21

a) Brief Details of Project as DPR - It provides a short description of main project

b) Survey & Investigations - This section provides information on survey and

e) Refinement in project layout – This section provides the details of refinements

conclusions, provides the revised project salient features.

j) Annexures – This section consists of annexures to the report.

k) Plates – This section consists of important layout drawings.

2 BRIEF DETAILS OF PROJECT AS PER DPR

• River & Basin : Trishuli River, Narayani Basin

• Catchment area upto Intake : 11659 km2

• 1 in 50 years flood Discharge : 6979 m3/s

• 1 in 500 years flood Discharge : 9882 m3/s

• Full Reservoir Level (FRL) : 275.0 m a.s.l.

• Minimum draw down level : 267.0 m a.s.l.

• Barrage width between : 97.0m

• : 5 Nos. Radial Gates; 14.0m x 22.8m

Barrage gate type, (W x H)

• No. of Trash rack bays : 18 nos.

• Trash rack size (W x H) : 10 nos. panel of 4.28m x 2.2m

• Intake Gate Size (W x H) : 6 nos., 5.5m x 14.8m

• Powerhouse : Surface, Right bank

• Machine Hall (W x H x L) : 21.0m x 47.45m x 63.30m

• Number & Turbine Type : 3 nos., Bulb Type

• Installed Capacity : 3 x 33.5 MW

3 SURVEY AND INVESTIGATIONS

3.1 Topographic Survey

Detailed topographic survey was carried through Sai Om Engineering Consultancy

3.2 Geotechnical Investigations

Geological investigations including mapping, sub-surface exploration required for planning

4 GEOLOGY AND SEISMICITY

4.1 Barrage Site

4.2 Trash Rack Structure

4.3 Power Intake and Power house complex

5.1 Trishuli River Flows

Table-1: Long term mean monthly flows (m3/s)

5.2 Riparian Release

5.3 Design Flood

5.4 Sedimentation aspects

The sedimentation aspects have been elaborated under section 8.5.

5.5 Tail water levels

Table-2: Impact of analysis on the Tail Water Levels

River Tail water levels (Elm)

Figure-1: Tail Rating Curve in Trishuli River

6 REFINEMENT IN PROJECT LAYOUT