Dugar Hydro Power Limited
Dugar Hydropower Project
ALTERNATIVE STUDY REPORT
Report No. R-71.2471.00.003_R0
May 2013
smrTypewritten textANNEXURE-V A
Dugar Hydro Power Limited
Dugar Hydro Electric Project
Alternative Study Report i/77
AF-Consult Switzerland Ltd Täfernstrasse 26, CH-5405 Baden, Schweiz Phone +41 (0)56 483 12 12. Fax +41 (0)56 483 12 55. www.afconsult.com
Date Name Signature
Created 01.05.2013 Martina
Checked 07.05.2013 Markus
Approved 14.05.2013 Sai
Index of versions
No. Page(s) Date Remark Created
(Initial/Signature)
Approved
(Initial/Signature)
1 All 14.05.2013 First release FRM SSE
Project name Dugar HEP
Document title Alternative Study Report
Project number 2471
Name of department Hydropower
Document path N:\Working Designs\2471_Dugar\Engineering\Reports\Reports-Final\00
General\R_71_2471_00_003_Alternative Study Report R0.docx
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TABLE OF CONTENTS
1 INTRODUCTION ............................................................................ 9
2 PROJECT LOCATION ................................................................... 10
3 AVAILABLE DOCUMENTS/DATA ............................................... 11
4 BASIC PROJECT PARAMETER FOR ALTERNATIVES .................. 11
5 CONSIDERED ALTERNATIVES .................................................... 12
5.1 Dam axes considered in the Inception Report ...................................................................... 12
5.2 Alternative I-A.................................................................................................................................. 13
5.3 Alternative II-A ................................................................................................................................ 13
5.4 Alternative III-A ............................................................................................................................... 16
5.5 Alternative IV-A ............................................................................................................................... 19
5.6 Layout of surge shaft, pressure shaft and tunnels, powerhouse complex and
tailrace tunnels ............................................................................................................................... 21
6 EXPECTED ENERGY GENERATION ............................................. 26
6.1 Basic Considerations ...................................................................................................................... 26
6.2 Expected Energy Production for the 50% Dependable Year ............................................. 32
7 COST ESTIMATE OF THE DIFFERENT ALTERNATIVES .............. 34
7.1 General considerations ................................................................................................................. 34
7.2 Civil works (C) .................................................................................................................................. 35
7.3 Hydromechanical steel structures (HSS) ................................................................................. 37
7.4 Electromechanical equipment (EM) ......................................................................................... 37
7.5 Other cost ......................................................................................................................................... 37
7.6 Cost summary of basic alternatives .......................................................................................... 38
8 OPTIMIZATION OF BASIC ALTERNATIVES ............................... 41
8.1 Cost Saving Potential of the Basic Alternatives ..................................................................... 41
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8.2 Results of optimized alternatives .............................................................................................. 46
9 ECONOMIC EXAMINATION WITH OPTIMIZED LAYOUTS ....... 50
9.1 Developers Equity in the Project ............................................................................................... 50
9.2 Loan Component ............................................................................................................................ 51
9.3 Interest Rate on Loan Capital ..................................................................................................... 51
9.4 Repayment Period .......................................................................................................................... 51
9.5 Fixation of Tariff .............................................................................................................................. 51
10 CONCLUSION AND NEXT STEPS ................................................ 57
APPENDIX
1 DRAWINGS – BASIC LAYOUTS
2 UNIT RATES FOR CIVIL WORKS
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LIST OF FIGURES
Figure 1: Location Map of Dugar HEP ........................................................................................................ 10
Figure 2: Alternatives studied in the Inception Report .............................................................................. 13
Figure 3: Layout presenting main dam, cofferdams, diversion tunnels and power intakes of Alternative II-
A ................................................................................................................................................................. 14
Figure 4: Cross section through main dam of Alternative II-A ................................................................... 15
Figure 5: Layout presenting main dam, cofferdams, diversion tunnels and power intakes of Alternative
III-A ............................................................................................................................................................. 17
Figure 6: Cross section through main dam including auxiliary powerhouse (Alternative III-A) ................. 18
Figure 7: General layout of Alternative IV-A .............................................................................................. 20
Figure 8: General layout of powerhouse complex ..................................................................................... 22
Figure 9: Longitudinal section of powerhouse complex ............................................................................ 22
Figure 10: Layout of access for Alternative II-A ......................................................................................... 24
Figure 11: Layout of access for Alternative III-A ........................................................................................ 25
Figure 12: Layout of access for Alternative IV-A ........................................................................................ 26
Figure 13: Duration curve for all alternatives for 50% and 90% dependable year .................................... 28
Figure 14: Efficiency for different turbine types ........................................................................................ 30
Figure 15: Efficiency for Francis adopted for energy calculation ............................................................... 31
Figure 16: Definition of gate block............................................................................................................. 43
Figure 17: Construction cost for gate blocks ............................................................................................. 44
Figure 18: Capacity of spillway tunnel vs. internal tunnel diameter (length of tunnel 250 m) ................. 45
Figure 19: Capacity of spillway tunnels vs. internal tunnel diameter (length of tunnel 350 m) ................ 45
Figure 20: Levelised Tariff for all Alternatives ........................................................................................... 55
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LIST OF TABLES
Table 1: Duration curve for all alternatives for 50% and 90% dependable year ....................................... 27
Table 2: Environmental flow for Alternative II-A ....................................................................................... 29
Table 3: Environmental flow for Alternative III-A ...................................................................................... 29
Table 4: Environmental flow for Alternative VI-A ...................................................................................... 29
Table 5: Basic parameters for main plant .................................................................................................. 31
Table 6: Basic parameters for auxiliary plant ............................................................................................ 32
Table 7: Expected energy production for main and auxiliary plant .......................................................... 33
Table 8: Expected energy production for main and auxiliary plant .......................................................... 34
Table 9: Total investment costs for Alternative II-A (basic alternative) .................................................... 39
Table 10: Total investment costs for Alternative III-A (basic alternative) ................................................. 39
Table 11: Total investment costs for Alternative IV-A (basic alternative) ................................................. 40
Table 12: Summary of total investment costs for all basic alternatives .................................................... 40
Table 13: Cost comparison for different components for all alternatives ................................................ 41
Table 14: Feasibility for different concrete dam type based on findings of Inception Report ................. 42
Table 15: Update of suitability of different concrete dam types based on findings of cost comparison .. 46
Table 16: Total investment costs for Alternative II-A (optimized layout) .................................................. 47
Table 17: Total investment costs for Alternative III-A (optimized layout) ................................................. 47
Table 18: Total investment costs for Alternative IV-A (optimized layout) ................................................. 48
Table 19: Comparison of investment costs for all alternatives (optimized layout) ................................... 48
Table 20: Expected energy production for main and auxiliary plant (optimized layouts) ........................ 49
Table 21: Total investment cost for Alternative II-A (optimized layout with one HRT) ............................ 49
Table 22: Expected total investment cost for main and auxiliary plant (optimized layouts and alternative
II-A with one HRT) ...................................................................................................................................... 50
Table 23: Free Power to State Government .............................................................................................. 52
Table 24: Basic Parameters for Economic Evaluation ............................................................................... 54
Table 25: Summary of Economic Evaluation ............................................................................................. 56
© The Copyright remains with AF-Consult Switzerland Ltd.
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Abbreviations
masl Meter above sea level
AFC AF Consult Pvt. Ltd.
CEA Central Electricity Authority
COD Date of Commercial Operation
CVC Conventional Concrete
CWC Center Water Commission
DHPL Dugar Hydro Power Limited
DPR Detailed Project Report
FRL Full Reservoir Level
G&D Gauge and Discharge
GSI Geological Survey of India
HEP Hydro Electric Project
HRT Head Race tunnel
HSE Health Safety & Environment
IMD Indian Meteorological Department
IWT Indus water treaty
MAF Million Acre Feet
MDDL Minimum Draw-Down Level
PFR Pre-Feasibility Report
PMF Probable Maximum flood
PPE Personal Protective Equipments
RCC Roller Compacted Concrete
SPF Standard Project Flood
SRTM Shuttle Radar Topography Mission
TWL Tail Water Level
USGS United States Geological Survey
WBS Work Breakdown Structure
SI Units and Prefixes
- Units
Base quantity Name Symbol
Length meter m
Mass kilogram kg
Time second s
Hour h
Power watt W
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- Prefixes
Factor Name Symbol
109 Giga G
106 Mega M
103 kilo k
10-3
milli m
- Units used in the Report
Installed Capacity MW
Energy kWh / GWh
Storage 106 m
3/hm
3
Sediment volume Ham / 104 m
3
Storage Volume (Million acre feet – MAF) MAF / 1233.4818 hm3
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1 INTRODUCTION
AF Consult Switzerland Ltd. (AFC) has been contracted by Dugar Hydro Power Ltd. (DHPL)
to provide consultancy services for the preparation of Detailed Project Report (DPR) and
assistance to DHPL in obtaining concurrence of Central Electricity Authority and other
Governmental authorities as required, for Dugar Hydroelectric Project (HEP) on the Chenab
River in Chamba District of Himachal Pradesh by Consultancy Service Agreement dated 5th
November, 2012. The contract is scheduled to take 18 months and to be completed on 5th
May, 2014.
This green-field project has been awarded to the consortium “Tata Power Company Ltd.
and SN Power Holding Singapore Pte. Ltd.” (Owner) in May 2011, by Directorate of Energy -
Government of Himachal Pradesh on Build-Own-Operate-Transfer (BOOT) basis for a
period of 40 Years from Commercial Operation Date. To implement the project, the Owner
has constituted a Special Purpose Vehicle (SPV) by the name of M/s Dugar Hydro Power
Ltd. (DHPL).
The scope of works under this Consultancy Service Agreement broadly categorized in two
parts - Site Investigation Works and Engineering Desktop Studies, required for preparation
of DPR of Dugar HEP. Site Investigation Works mainly includes topographic survey,
geological and geotechnical investigations, geophysical survey, geological mapping,
seismo-tectonic evaluation, construction material survey, route survey and hydro-
meteorological investigations. The initial task of the consultant was to prepare an
Inception Report with the aim of review of available data, to describe the findings gained
during the site visits, and to highlight the required main data and elements to develop an
alternative study.
The main objective of the present report is the performance of a comprehensive
alternative study to determine the most attractive solution in a technical and particularly in
an economic sense. The study is divided into various working steps. In a first step the so-
called basic alternatives are prepared. Description of the layouts for each alternative are
presented in chapter 5, followed by the calculation of the expected energy generation
(chapter 6) and the cost estimates summarising the investment costs for each basic
alternative (chapter 7). In a second step the cost saving potential is determined for each
basic alternative, again followed by the recalculation of the expected energy generation
and an update of the cost estimates (chapter 8) for the optimized alternatives. Chapter 9
presents an economic examination of all alternatives (basic and optimized) followed by the
conclusion which summarizes the results and findings of the Alternative Study. In common
accordance with the client the final alternative for the further preparation of the power
potential study and the DPR will be selected.
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2 PROJECT LOCATION
Dugar HEP is in hilly terrains of the Higher Himalayas situated in the State of Himachal
Pradesh, India. The project is located on the Chenab River in district Chamba of Himachal
Pradesh. Presently there are 12 districts in Himachal Pradesh including that one of
Chamba, which has an estimated geographic area of 6528 km2 and is surrounded on all
sides by lofty hill ranges. The territory is wholly mountainous with altitude ranging from
600 to 6500 masl. The district has 6 Sub-Divisions which comprises 7 tehsils and 3 sub-
tehsils. Dugar HEP is located near Killar village which is under Pangi Tehsil, and is about 16
km from Pangi and about 63 km from district headquarter Chamba. The location map of
the project area is shown in Figure 1.
Figure 1: Location Map of Dugar HEP
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The “Access Availability” to the project site, as well as a description about the “Chenab
Basin” are given in the Inception Report (Nr. R-71.2471.00.001). It has to be noted that the
Dugar HEP lying on the Chenab River is governed by the “Indus Water Treaty”.
3 AVAILABLE DOCUMENTS/DATA
[1]. Pre-Feasibility Report of Dugar HEP, prepared by DHPL
[2]. Survey of India (SOI) Toposheet No. 52 C/8; Scale 1:50000
[3]. Survey of India (SOI) Toposheet No. 52H; Scale 1:250000
[4]. Topographical Survey provided by DHPL.
[5]. Hydrological data provided by DHPL.
[6]. Report on Design Storm Study for Dugar HEP by IMD Delhi
[7]. Inception Report (January 2013) by AFC
[8]. Hydrology & Sedimentation Study Report (March 2013) by AFC
4 BASIC PROJECT PARAMETER FOR ALTERNATIVES
The newly derived project parameters which are used throughout the Alternative Study are
described in the following. Additional parameters were defined within the Inception Report
and are not repeated. For further details it is referred to the Inception Report (No. R-
71.2471.00.001 R2, January 2013).
Required live storage: The minimum required live storage has been discussed during the
meeting in November 2012. A value of 15 hm3 has been determined to be considered as
necessary minimum live storage. This value enables the operation of the scheme on daily
mode as well as on partial (i.e. reduced) weekly mode.
Design floods: The design floods at Dugar site have been estimated by a flood frequency
analysis utilizing the maximum observed flood peaks at Udaipur G&D site during the period
1974 to 2008 as well as a hydro-meteorological approach. Details regarding the applied
methods as well as all calculated design floods are described in the Hydrology and
Sedimentation Study Report (No. R-71.2471.00.002 R1, March 2013). For the Alternative
Study two flood values are decisive for the determination of the general layout of the
diversion scheme, as well as of the permanent structures such as spillway and bottom
outlets. These floods are the Q25 for the river diversion works and the probable maximum
flood (PMF) for the main diversion structures. The flood value for a return period of 25
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years has been determined to be 2,517 m3/s whereas the PMF has been calculated to be
8,762 m3/s.
Environmental flows: A minimum discharge has to be released due to environmental
considerations. With the clearance of the 1st
stage of the TOR given by the Ministry of
Environment & Forest (MoEF) in December 2012 a new standard concerning the
environmental flow (ecological water release) has to be considered for the further design
works of Dugar HEP. The released discharges are based on the seasonal average flows for
the 90% dependable year. The different seasons are defined as “lean season” (months of
December to March), a “transition season” (months of April to May and October to
November) and a “monsoon season” (months of June to September).
Season Average flow of 90%
dependable year (m
3/s)
Environmental release
due to new guidelines (m
3/s)
Lean
to be calculated for
each alternative
20%
Transition 20%
Monsoon 30%
Design discharge of main plant: The design discharge has not been optimized. The applied
value remains 452 m3/s for the Alternative Study. After the final decision of the most
attractive alternative a power potential study will be carried out to start with the
optimization process of the design discharge of the main plant.
5 CONSIDERED ALTERNATIVES
5.1 Dam axes considered in the Inception Report
Four different dam sites have been taken into consideration in the Inception Report and
visited in the course of the site visit in November 2012. The site of Alternative I-A is located
at km 5+510 (starting from the upstream concession limit). Alternative II-A is situated
approximately 1.06 km downstream of the bridge of the Sach-Pass road at km 8+240 while
Alternative III-A is positioned at km 10+309. Alternative IV-A is located after the 90° bend
of the river at km 11+010.
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Figure 2: Alternatives studied in the Inception Report
In the following subchapters the alternatives of the Inception Report will be described in
more detail. The herein proposed “basic” layouts will be the basis for the first cost
estimations. However, it should be noted that all components will be reviewed within
chapter 8 for their cost saving potential.
5.2 Alternative I-A
The total storage capacity of Alternative I-A is only 5.884 hm3. Considering that a minimum
required live storage of 15 hm3 is asked for by SN Power for the operation of the plant, this
alternative has not been considered further in the Alternative Report.
5.3 Alternative II-A
The two power intakes are situated in the reservoir just upstream of the dam structure at
elevation 2,077.35 masl. (invert level). The invert level of the power intakes is defined by
the minimum draw down level, which is at elevation 2,094.35 masl., providing a minimum
cover above the intake in order to avoid air entraining.
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Figure 3: Layout presenting main dam, cofferdams, diversion tunnels and power intakes of
Alternative II-A
The reservoir is created by an approximately 102 m high dam which will be able to store a
water volume of 28.660 hm3. As a first draft the dam is designed as a concrete gravity dam.
The concrete dam section is founded on solid rock on the excavated river bed at
approximately 2,005 masl. (Assuming a depth of the alluvial deposits of 22 m). The dam
section has a vertical front while the downstream face is sloping with an inclination of
1(V):0.8(H). The crest is 8 m wide and approximately 159 m long. The dam crest is set at
elevation 2,107 masl.
To minimise leakage past the dam and uplift from the foundation, a grout curtain shall be
established close to the upstream face of the dam in combination with the provision of
drain holes at the downstream side of the curtain. The depth of the grout curtain is
assumed to be equal to 2/3 of the water head (difference between upstream and
downstream water level), while the depth of the drainage holes is assumed to be equal to
2/3 of the depth of the grout curtain length.
For concrete gravity dams an overflow spillway on the dam crest followed by a chute on
the downstream dam face, including flip bucket, and a plunge pool acting as energy
dissipater. This is a common economical solution. For Dugar HEP a gated spillway has to be
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selected due to the maximum allowable water level of 2,105 masl. which equals the Full
Reservoir Level (FRL). This consideration asks for a gated spillway arrangement. Therefore,
the present concrete gravity dam structure comprises six gated ogee crest spillway
openings with a width of 12 m. The sill elevation is set to 2,092.5 masl. With this gate
arrangement of the spillway a discharge of 6’250 m3/s during PMF can be expected. The
maximum water level rises up to 2,105 masl at the dam location. A bridge over the spillway
openings is foreseen to allow access from one bank to the other.
Figure 4: Cross section through main dam of Alternative II-A
The dam includes four bottom outlets. Two sliding gates per outlet are foreseen. The more
downstream one is the operation gate, which normally is closed, while the more upstream
one is a maintenance gate, which is used as stoplog and normally always open. The
selected opening size of the gates is 6 m by 5 m (height by width). The inlet elevation is set
to 2,036 masl. This level has been chosen to ensure the discharge of a sufficient water
volume in combination with a sufficiently low tailwater level particularly during flushing
operations, i.e. accumulations in the inlet area may require to be flushed/scoured by
periodic opening of the bottom outlet gates. The bottom outlets shall be used to discharge
approximately one third of the water in the case of a PMF. With a normal storage level at
2,105 masl., the bottom outlets have an approximate total discharge capacity of
2,840 m3/s. In addition, they shall be used to lower the reservoir level in a case of
emergency.
Two diversion tunnels of 346 m and 473 m respectively length with an inner diameter of
10.5 m are provided at the right bank. The tunnels are designed in a way that during wet
seasonal flows (Q25,monsoon) the water can be diverted through the tunnels without
overtopping of the embankment cofferdams. The resulting crest elevation of the
cofferdams are 2,059.8 masl (upstream) and 2,043.0 masl (downstream).
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An auxiliary hydropower plant is to be installed into the dam harnessing the required
environmental flow release during the lean and the transition season and partially during
the monsoon season (the rest will be flow over the overflow spillways or through the
bottom outlets). Two Francis turbines with a total design discharge of 28.0 m3/s (Pinstalled =
16.7 MW) are foreseen. The auxiliary powerhouse is located in the left side of the dam
structure next to the bottom outlets. The inlets are foreseen at elevation 2,082 masl. The
turbine setting level is set to 2,082.2 masl. Access to the auxiliary powerhouse is granted
by a vertical shaft (5 m by 4 m) connected with the erection bay by a horizontal adit,. The
shaft, which will be used for the transportation of equipment, is located downstream of
the dam crest. Access for the personnel will be foreseen by means of a stairway from the
dam crest to the erection bay of the auxiliary powerhouse.
The two headrace tunnels with a length of 2,230 m and 2,265 m to convey the water to the
surge shaft and the powerhouse both located underground on the south bank of the
Chenab River. For all alternatives the same layout is foreseen starting from the upstream
surge shaft. Details are presented in subchapter 5.6 herein.
Access to the dam and the power intakes is granted by a permanent road on the left
abutment which starts at Shukhrali bridge. The length of this road is approximately 1.7 km.
During construction a temporary road, also starting from the Shikhrali bridge enables
access to the diversion tunnels and to the dam construction site. The length of this road is
approximately 1 km.
The layout of the scheme of Alternative II-A is presented in five drawings:
SK-71.2471.2A.001 General layout (Layout Plan)
SK-71.2471.2A.002 General layout (L-section through HRT-2)
SK-71.2471.2A.003 Concrete gravity dam – Upstream View
SK-71.2471.2A.004 Concrete gravity dam - Plan
SK-71.2471.2A.005 Concrete gravity dam - Sections
5.4 Alternative III-A
The two power intakes are situated in the reservoir just upstream of the dam structure at
elevation 2,081.0 masl. The invert level of the power intakes is defined by the minimum
draw down level, which is at elevation 2,098.5 masl., providing a minimum cover above the
intake in order to avoid air entraining.
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Figure 5: Layout presenting main dam, cofferdams, diversion tunnels and power intakes of
Alternative III-A
The reservoir of Alternative III-A is created by a 114 m high dam which will be able to store
a water volume of 54.217 hm3. As for Alternative II-A, a concrete gravity dam is foreseen to
function as base solution. Any changes to the dam type in respect to possible cost savings
will be discussed within chapter 8. The concrete dam section is founded on solid rock on
the excavated river bed at approximately 1,993 masl. (assuming a maximum depth of the
alluvial deposits of 20 m). The cross section of the dam has been kept similar to the one of
Alternative II-A, i.e. vertical front of the upstream face and an inclined downstream face
(inclination 1(V):0.8(H)). The crest is 8 m wide and approximately 178 m long. The dam
crest is set at elevation 2,107 masl.
The grout curtain arrangement as well as the provision of drainage holes is analogue to
Alternative II-A, i.e. a grout curtain shall be established close to the upstream face of the
dam and drain holes at the downstream side of the curtain to control leakage past the dam
and reduce the uplift acting on the foundation. The depth of the grout curtain and
drainage holes are assumed analogue to Alternative II-A.
For Alternative III-A the same spillway layout as for Alternative II-A has been foreseen. This
implies that the gate arrangement also remains the same as presented for Alternative II-A.
Again, a bridge over the spillway openings is foreseen to allow access from one bank to the
other.
The dam also includes four bottom outlets with the same dimensions and gate
arrangement as for Alternative II-A. The inlet elevation is set based on the same
consideration as carried out and described for Alternative II-A to 2’020.5 masl. At a normal
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storage level at 2,105 masl., the bottom outlets have an approximate total discharge
capacity of 3,140 m3/s.
Two diversion tunnels of length 358m and 489 m respectively with an inner diameter of
10.5 m are provided at the right bank. The tunnels are designed in a way that during wet
seasonal flows (Q25, monsoon) the water can be diverted through the tunnels without
overtopping of the embankment cofferdams. The resulting crest elevations of the
cofferdams are 2,047.9 masl (upstream) and 2,028.5 masl (downstream).
The same arrangement for an auxiliary hydropower plant, as for alternative II-A is also to
be installed into the dam for harnessing the environmental flow release. The auxiliary
powerhouse is located on the right side next to the bottom outlets. The inlets are foreseen
at elevation 2,082 masl. Two Francis turbines with a total design discharge of 29.0 m3/s
(Pinstalled = 22.1 MW) are foreseen. The turbine setting level is set to 2,011.3 masl. The
access arrangement to the auxiliary powerhouse from the dam crest for equipment and
personal is the same as for alternative II-A.
Figure 6: Cross section through main dam including auxiliary powerhouse (Alternative III-A)
In contrast to Alternative II-A and of course due to the close-by location of the dam axis to
the powerhouse, the length of the headrace tunnel is decreased tremendously. The length
of the two headrace tunnel is 410 m and 368 m respectively.
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During the construction access to the dam construction side and the diversion tunnels will
be given by a road which takes off from the main road (Killar-Kishtwar Road) and continues
to the powerhouse construction site. From an intermediate turn around elevation 2,150
masl. The road will continue along the river in upstream direction towards the dam crest.
This part will function during the operation of the scheme as permanent access to the dam
crest. During construction this road will continue to the diversion tunnels and the dam
construction area. Additionally, the road will be developed to a temporary bridge spanning
over the Chenab River from where it will give access to the power intakes.
The layout of the scheme of Alternative III-A is presented in five drawings:
SK-71.2471.3A.001 General arrangement – Layout plan
SK-71.2471.3A.002 General arrangement – L-section
SK-71.2471.3A.003 Concrete gravity dam - Upstream view
SK-71.2471.3A.004 Concrete gravity dam - Plan
SK-71.2471.3A.005 Concrete gravity dam - Sections
5.5 Alternative IV-A
Alternative IV-A has been included in the Inception Report due to the consideration that
the units installed in the main powerhouse could be utilised for harnessing the discharge of
the environmental flow. Due to the close location of this alternative to the outlets of the
main powerhouse it is not necessary to install an auxiliary powerhouse at the dam toe.
Alternative IV-A utilizes a gross head of 96 m. Due to the general arrangement of the
scheme (i.e. intakes, dam and powerhouse within one area) the two power intakes have to
be located further away from the dam structure. The general arrangement of the scheme
is shown in Figure 7 below. The inverts level of Intake structure is at elevation 2’083.6
masl. The invert level of the power intakes is defined by the minimum draw down level,
which is at elevation 2’100.6 masl., providing a minimum cover above the intake in order
to avoid air entraining.
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Figure 7: General layout of Alternative IV-A
The reservoir is created by a 125 m high dam which will be able to store a total water
volume of 63.070 hm3. As discussed in the Inception Report the site of Alternative IV-A
does not allow the construction of a concrete arch gravity or a double curved arch dam.
Therefore the proposed concrete gravity dam has to be considered as only sole solution –
in contrast to Alternative II-A and III-A where more advanced dam types are in general
feasible.
The proposed concrete gravity dam is founded on solid rock on the excavated river bed at
approximately 1,982 masl. (assuming a depth of the alluvial deposits of 20 m). The dam
section has a vertical front while the downstream face is sloping with an inclination of
1(V):0.8(H). The crest is 8 m wide and approximately 181 m long. The dam crest is set at
elevation 2,107 masl.
The grout curtain arrangement as well as the provision of drainage holes are analogue to
Alternative II-A and III-A, i.e. a grout curtain shall be established close to the upstream face
of the dam and drain holes at the downstream side of the curtain to control leakage past
the dam and reduce the uplift acting on the foundation. . The depth of the grout curtain
and drainage holes shall be assumed analogue to the other alternatives..
For Alternative IV-A the same general gate arrangement for the spillway as foreseen for
Alternatives II-A and III-A has been anticipated. This implies that the gate dimensions as
well as the sill elevation remain the same. Again, a bridge over the spillway openings is
foreseen to allow access from one bank to the other.
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As for Alternative II-A and III-A four bottom outlets with the dimension of 6 m by 5 m
(height by width) are proposed. The inlet elevation is set based on the same consideration
as carried out and described above to 2,016 masl. The foreseen gate arrangement is the
same as for alternatives II-A and III-A. At a normal storage level at 2,105 masl., the bottom
outlets have an approximate total discharge capacity of 3,320 m3/s.
Due to the location of Alternative IV-A in the immediate vicinity of the main powerhouse
complex the required length of the diversion tunnels becomes longer than those necessary
for Alternative II-A and III-A since they are also utilised for the construction of the tailrace
channel outlets. Hence, two diversion tunnels of 510 m respectively 625 m length with an
inner diameter of 10.5 m are provided at the right bank. The tunnels are designed in a way
that during wet seasonal flows (Q25,monsoon) the water can be diverted through the tunnels
without overtopping of the cofferdams. The resulting crest elevation of the cofferdams are
2,027.6 masl. (upstream) and 2,007 masl. (downstream).
As for Alternative III-A and of course due to the close-by location of the dam axis to the
powerhouse, the length of the headrace tunnel is similar to those foreseen for Alternative
III-A. The resulting length of the two headrace tunnels is 330 m respectively 370 m. The
foreseen inner diameter of the tunnels is set to 10 m.
For this alternative most of the construction activities will be close to the dam site and the
powerhouse complex. Therefore all necessary construction sites (with one exception) can
be reached by means of access roads diverting from the main state road to Killar. The only
exception is the access to the power inlet which are located further upstream. Long and
steep roads plus an additional bridge would be necessary to reach this location. To easen
the access two ropeways have been foreseen one for the transportation of material and
equipment and one for personnel.
The layout of the scheme of Alternative IV-A is presented in five drawings:
SK-71.2471.4A.001 General arrangement – Layout plan
SK-71.2471.4A.002 General arrangement – L-section
SK-71.2471.4A.003 Concrete gravity dam - Upstream view
SK-71.2471.4A.004 Concrete gravity dam - Plan
SK-71.2471.4A.005 Concrete gravity dam – Sections
5.6 Layout of surge shaft, pressure shaft and tunnels, powerhouse complex and tailrace tunnels
The layout of the surge shaft, pressure shaft and pressure tunnel, the powerhouse
including transformer cavern and tailrace tunnels has been kept the same for all three
alternatives. The general layout is shown below.
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Figure 8: General layout of powerhouse complex
Two surge shafts are foreseen approximately 75 m upstream of the powerhouse complex.
The diameter of the shafts is presently set to 32 m for Alternative II-A and 18 m for
Alternative III-A & IV-A. However, further details of the final layout of the surge shaft will
be elaborated during the next phase after the determination of the final axis. The height of
the shaft varies for each alternative and is therefore approximately 60 to 70 m.
A pressure shaft with a depth of approximately 60 and an inner diameter of about 7.5 m
conveys the water through the horizontal pressure tunnel (length approximately 100 m,
inner diameter 7.5 m) to the turbines in the main powerhouse cavern.
Figure 9: Longitudinal section of powerhouse complex
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The dimensions of the powerhouse are set to a length of 110 m, a width of 20 and a height
of about 42 m. The main powerhouse is equipped with four Francis units with an installed
capacity of 91.3 MW (for Alternative II-A) and 92 MW (for Alternative III-A and IV-A). The
transformer cavern is located 40 m downstream of the main powerhouse cavern. The
dimensions are set to a length of 110 m, a width of 14 m and a height of 22 m.
The tailrace tunnel is about 410 m long. The inner diameter is presently set to 10 m.
A pothead yard is foreseen on the right river bank.
Temporary and permanent access to the surge shaft, pressure tunnel and shaft, and the
powerhouse complex is slightly different for all alternatives and will be described in the
following:
Alternative II-A: During construction access to the powerhouse complex is granted by
construction adit (width 4.5 m) which connects the right river abutment by means of a
bridge with the left abutment and in that respect with the portal of the adit. This
construction access has been extended to provide access to the downstream end of the
headrace tunnel. Access to the pressure tunnel is provided by an additional construction
tunnel at lower level which connects the tailrace tunnel with the pressure tunnel. Access to
the top of the surge shaft is given by means of an additional tunnel starting from the left
abutment to the middle of both surge shafts. Access from the river to this tunnel is
provided by means of vertical steel construction which includes a lift. Smaller equipment
and personnel can be moved by means of this device. This access tunnel should be used
later on for permanent use. Permanent access to the powerhouse and transformer cavern
are granted by means of another tunnel which is located further downstream. A bridge
connecting the right and left abutment will guide to the portal of this permanent access.
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Figure 10: Layout of access for Alternative II-A
Alternative III-A: The temporary and permanent access to the powerhouse and
transformer cavern as well as the connection between pressure tunnel and tailrace tunnel
is analogue to Alternative II-A. Access to the surge shaft is given by an additional tunnel
which starts in the vicinity of the power intakes. During construction this place is reached
by means of an access which has been described above. The same tunnel will used later on
for permanent access from the dam crest.
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Figure 11: Layout of access for Alternative III-A
Alternative IV-A: The temporary and permanent access to the powerhouse and
transformer cavern is analogue to Alternative II-A. The connection between the pressure
tunnel and the tailrace tunnel as provided for Alternative II-A is also given for Alternative
III-A. The main difference in respect to access between Alternative II-A and III-A is the
access to the surge shaft. During construction access to the upper part of the surge shaft is
provided by a tunnel which starts close to the power intakes at the left river bank. Access
to this place is given by means of ropeways which connect the right and left abutment. The
ropeway, one for material and equipment and one for personnel, is also used for the
access to the power intakes. The tunnel from the surge shaft to the intake will be used for
permanent access to the intake structure later on. Additionally it is foreseen to extend this
access tunnel to the dam crest, again for permanent access. Additional access roads to the
construction site are to be foreseen from the main state road to Killar. The necessary
layout of tunnels and roads is shown below.
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Figure 12: Layout of access for Alternative IV-A
6 EXPECTED ENERGY GENERATION
6.1 Basic Considerations
The following basic considerations have been taken into account for the determination of
the total energy production of the different alternatives (divided into production in the
main plant and auxiliary plant),:
i) The duration curve, as presented in the table below, for the different alternatives of 50% dependable year (1980-81) and 90% dependable year
(1993-94):
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Table 1: Duration curve for all alternatives for 50% and 90% dependable year
The duration curves of the 50% and 90% dependable years for the different
alternatives are also presented graphically in the following three figures:
Catchment Area 7667 km2 7823 km2 7840 km2
50% 90% 50% 90% 50% 90%
1980-81 1993-94 1980-81 1993-94 1980-81 1993-94
Inflow Discharges
Month Decade m3/s m3/s m3/s m3/s m3/s m3/s
June I 512.82 395.41 523.25 403.46 524.39 404.34
II 624.00 611.28 636.69 623.72 638.08 625.08
III 902.40 594.29 920.76 606.38 922.76 607.70
July I 947.93 840.39 967.22 857.49 969.32 859.35
II 988.67 843.11 1008.78 860.27 1010.98 862.13
III 823.66 585.31 840.42 597.22 842.25 598.52
Aug I 972.45 643.20 992.24 656.28 994.39 657.71
II 549.27 516.45 560.45 526.96 561.67 528.11
III 613.86 608.08 626.35 620.45 627.71 621.80
Sep I 389.97 461.97 397.90 471.37 398.77 472.39
II 275.93 319.39 281.55 325.89 282.16 326.60
III 214.31 259.59 218.67 264.87 219.15 265.45
Oct I 194.46 169.04 198.42 172.48 198.85 172.85
II 150.75 139.85 153.81 142.69 154.15 143.00
III 123.60 103.78 126.11 105.90 126.39 106.13
Nov I 108.71 99.76 110.93 101.79 111.17 102.01
II 100.15 103.39 102.19 105.50 102.41 105.73
III 93.92 96.00 95.84 97.95 96.04 98.17
Dec I 87.83 88.09 89.61 89.88 89.81 90.07
II 87.05 87.05 88.82 88.82 89.01 89.01
III 83.73 72.29 85.44 73.77 85.62 73.93
Jan I 83.93 64.73 85.64 66.05 85.83 66.20
II 80.69 62.53 82.33 63.80 82.51 63.94
III 84.44 58.52 86.16 59.71 86.35 59.84
Feb I 76.41 59.16 77.97 60.36 78.13 60.49
II 82.64 58.77 84.32 59.96 84.50 60.09
III 83.51 78.49 85.21 80.08 85.40 80.26
Mar I 78.75 57.60 80.35 58.77 80.52 58.90
II 77.97 68.37 79.55 69.76 79.73 69.91
III 84.68 82.91 86.40 84.60 86.59 84.78
Apr I 91.33 88.48 93.19 90.28 93.39 90.47
II 130.25 89.77 132.90 91.60 133.19 91.80
III 193.82 113.77 197.76 116.09 198.19 116.34
May I 394.25 149.58 402.27 152.62 403.14 152.95
II 415.78 174.10 424.24 177.64 425.16 178.03
III 525.29 251.79 535.97 256.92 537.14 257.47
Lean
Seaso
nTra
nsi
tio
n s
easo
nTra
nsi
tio
n s
easo
n
Alternative II-A Alternative III-A Alternative IV-A
Mo
nso
on
Seaso
n
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Figure 13: Duration curve for all alternatives for 50% and 90% dependable year
ii) The new guidelines concerning the environmental flow (ecological water release) as stated in the inception report. The released discharges are based on
0
200
400
600
800
1000
1200
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Dis
cha
rge
[m
3/s
]
Exceedance
DUGAR HEP
Duration Curves - Alternative II-A
50% dependable year (1980-81) 90% dependable year (1993-94)
0
200
400
600
800
1000
1200
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Dis
cha
rge
[m
3/s
]
Exceedance
DUGAR HEP
Duration Curves - Alternative III-A
50% dependable year (1980-81) 90% dependable year (1993-94)
0
200
400
600
800
1000
1200
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Dis
cha
rge
[m
3/s
]
Exceedance
DUGAR HEP
Duration Curves - Alternative IV-A
50% dependable year (1980-81) 90% dependable year (1993-94)
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the seasonal average flows of the 90% dependable year. Definition of seasons
can be found in chapter 4.
Table 2: Environmental flow for Alternative II-A
Season Average
discharge (m
3/s)
Relation of
release (m
3/s)
Environmental
flow (QEF) (m
3/s)
Lean 69.88 20% 14.0
Transition 131.61 20% 26.3
Monsoon 556.54 30% 167.0
Table 3: Environmental flow for Alternative III-A
Season Average
discharge (m
3/s)
Relation of
release (m
3/s)
Environmental
flow (QEF) (m
3/s)
Lean 71.30 20% 14.3
Transition 134.29 20% 26.9
Monsoon 567.86 30% 170.0
Table 4: Environmental flow for Alternative VI-A
Season Average
discharge (m
3/s)
Relation of
release (m
3/s)
Environmental
flow (QEF) (m
3/s)
Lean 71.45 20% 14.3
Transition 134.58 20% 26.9
Monsoon 569.1 30% 171.0
iii) To harness the environmental flow with additional turbines (auxiliary plant) will be adapted to the alternatives where the tail water level does not reach the
dam toe during normal inflow conditions. This means alternatives II-A and III-A
release the ecological water at the dam toe, while for alternative IV-A no
release at the dam toe is foreseen.
iv) The auxiliary plant is equipped with two Francis turbines with a design discharge of 14.0 m
3/s each for alternative II-A and 14.3 m
3/s each for alternative III-A.
These means that at the beginning and the end of the monsoon season when
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QIN > QEF >QD certain energy losses due to water spill at the dam will occur for
alternatives II-A and III-A.
v) No optimization of the installed capacity of the main plant has been carried out. The chosen installed capacity for the comparison of all alternatives is the one
which harnesses the same inflow water volume for the 50% dependable year.
This means the design discharge for the main plant for alternatives II-A and III-A
is fixed at 452 m3/s, while the one for alternative IV-A results 481 m
3/s
(452 m3/s + 29 m
3/s).
vi) Due to the higher discharge for ecological water release the main plant for alternatives II-A and III-A will be operated fewer days at full capacity than
foreseen in the feasibility study, i.e. the overall plant load factor for alternatives
II-A and III-A is somewhat smaller than that one for alternative IV-A.
vii) The efficiency for Francis turbines varies to a certain extent for flows differing from the design discharge. Indications for the variation in efficiency can be
found in the technical literature. For details see the following charts below.
Values according to technical literature
Figure 14: Efficiency for different turbine types
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Figure 15: Efficiency for Francis adopted for energy calculation
The basic parameters for the main plant of the different alternatives are as follows:
Table 5: Basic parameters for main plant
Alternatives
Parameter II-A III-A IV-A-1
Nominal discharge (QN) m3/s 452.0 452.0 481.0
Gross head for QN m 94.1 94.1 94.1
Head losses water
conveyance system
m 2.6 1.9 1.9
Nominal head for QN m 91.5 92.2 92.2
Machine efficiency (full
capacity)
- 0.90 0.90 0.90
Total installed capacity MW 365.2 368.0 392.0
Number of units - 4 4 4
Installed capacity per
unit
MW 91.3 92.0 98.0
The basic parameters for the auxiliary plant of the different alternatives are as follows.
Note that for alternative IV-A no auxiliary plant has been foreseen. The main turbines will
be used to release the ecological water:
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Table 6: Basic parameters for auxiliary plant
Alternatives
Parameter II-A III-A IV-A-1
Nominal discharge m3/s 14.0 14.5 ---
Average gross head m 69.43 88.21 ---
Head losses water
conveyance system
m 2.00 2.00 ---
Nominal head m 67.43 86.21 ---
Machine efficiency (full
capacity)
- 0.90 0.90 ---
Total installed capacity MW 16.7 22.1 ---
Number of units - 2 2 ---
Installed capacity per
unit
MW 8.35 11.05 ---
6.2 Expected Energy Production for the 50% Dependable Year
For comparison of the three alternatives the energy production has been determined using
the available water volumes corresponding to the 50% dependable year and the basic
parameters for main and auxiliary plants as given in the subchapter above. As already
mentioned before, alternative IV-A is without extra installation of an auxiliary plant at the
dam toe, because the environmental flow will be assured using the units housed in the
main powerhouse.
The resulting energy production with the main and the auxiliary plant for the different
alternatives are as presented in the table below:
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Table
The operating hours consider:
- The units housed in the main powerhouse are operating always at full capacity.
- In the case of Alternative IVsatisfy the requirements of the environmental water release operates always 24 hours
a day but not always at full capacity. However, the operating hours given in the table
above correspond to the equivalent hours of this unit with full capacity. A tentative
operation mode during a hydrological mean (50% dependable year) year, as used for
the determination of the energy production, is presented in the table below:
Table 7: Expected energy production for main and auxiliary plant
The operating hours consider:
The units housed in the main powerhouse are operating always at full capacity.
In the case of Alternative IV-A: The unit housed in the main powerhouse used to
satisfy the requirements of the environmental water release operates always 24 hours
a day but not always at full capacity. However, the operating hours given in the table
e correspond to the equivalent hours of this unit with full capacity. A tentative
operation mode during a hydrological mean (50% dependable year) year, as used for
the determination of the energy production, is presented in the table below:
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Expected energy production for main and auxiliary plant
The units housed in the main powerhouse are operating always at full capacity.
A: The unit housed in the main powerhouse used to
satisfy the requirements of the environmental water release operates always 24 hours
a day but not always at full capacity. However, the operating hours given in the table
e correspond to the equivalent hours of this unit with full capacity. A tentative
operation mode during a hydrological mean (50% dependable year) year, as used for
the determination of the energy production, is presented in the table below:
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Table 8: Expected energy production for main and auxiliary plant
- In the auxiliary plant the two units operates during monsoon and transition season 24 hours a day and during the lean season only one turbine is operating 24 hours a day,
i.e. the days of the lean season are considered with 12 hours at full capacity.
The overall plant load factor is determined using both plants, the main and the auxiliary
ones, operating all available turbines (4 units in the main plant and two in the auxiliary
plant) always at full capacity, i.e. it represents an equivalent and not a real plant load
factor.
7 COST ESTIMATE OF THE DIFFERENT ALTERNATIVES
7.1 General considerations
For each alternative the expected project costs for design and construction of civil “C”,
hydromechanical steel structures “HSS” and electromechanical equipment “EM” have been
determined. To calculate the total investment cost, other costs such as for, Establishment
and Tools & Plants (II), Buildings (III), Land acquisition (IV), Roads & Bridges (V) and Other
direct & indirect charges as per CEA (VI) have been added.
Cost has been worked out as per the “CEA Guidelines for Formulation of Detailed Project
Reports for Hydro Electric Schemes, Their Acceptance and Examination for Concurrence”,
April 2012 (Revision 3.0).
QIN Q24h Required Q24h > Qrelease
QD Time QD Time QD Time QD Time Qreleasem3/s m3/s h/day m3/s h/day m3/s h/day m3/s h/day m3/s m3/s
1'074.0 0.00%1'007.2 2.00% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes
986.2 5.00% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes911.3 10.00% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes662.4 15.00% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes639.6 16.51% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes586.8 20.00% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes556.2 22.82% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes532.6 25.00% 120.75 24.0 120.25 24.0 120.25 24.0 120.25 24.0 481.50 170.7 yes421.9 30.00% 96.08 24.0 96.08 24.0 113.00 20.2 113.00 20.2 192.16 170.7 yes406.1 33.42% 96.60 24.0 96.60 23.4 113.00 15.6 113.00 15.6 193.20 170.7 yes398.9 35.00% 84.53 24.0 120.25 21.2 120.25 21.2 120.25 21.2 84.53 26.9 yes231.8 40.00% 84.53 24.0 120.25 15.4 120.25 15.4 120.25 15.4 84.53 26.9 yes198.4 45.00% 84.53 24.0 120.25 11.3 120.25 11.3 120.25 11.3 84.53 26.9 yes144.7 50.00% 48.30 24.0 120.25 8.7 120.25 8.7 120.25 8.7 48.30 26.9 yes123.1 55.00% 102.64 24.0 120.25 8.2 120.25 8.2 120.25 8.2 102.64 26.9 yes102.4 60.00% 101.69 24.0 120.25 2.1 120.25 2.1 120.25 2.1 101.69 26.9 yes93.9 65.00% 89.76 24.0 120.25 0.7 120.25 0.7 120.25 0.7 89.76 26.9 yes90.3 68.85% 84.50 24.0 120.25 0.6 120.25 0.6 120.25 0.6 84.50 26.9 yes89.3 70.00% 81.83 24.0 96.08 0.5 120.25 0.5 120.25 0.5 81.83 14.3 yes86.5 75.00% 77.47 24.0 96.60 0.5 120.25 0.5 120.25 0.5 77.47 14.3 yes85.8 80.00% 72.13 24.0 120.25 0.7 120.25 0.7 120.25 0.7 72.13 14.3 yes85.4 85.00% 66.79 24.0 120.25 0.9 120.25 0.9 120.25 0.9 66.79 14.3 yes82.8 90.00% 61.44 24.0 120.25 1.3 120.25 1.3 120.25 1.3 61.44 14.3 yes80.0 95.00% 56.10 24.0 120.25 1.5 120.25 1.5 120.25 1.5 56.10 14.3 yes77.7 100.00% 50.76 24.0 120.25 1.7 120.25 1.7 120.25 1.7 50.76 14.3 yes
U1 U2 U3 U4
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7.2 Civil works (C)
The estimate of cost for civil works is based on the planning and preliminary design of
different components of works for each alternative.
A provision of 3% of the cost has been made to cover contingencies and work charged staff
in the estimates of different components of civil works. The contingencies have not been
taken on items for which a lump sum amount has been provided.
The estimates are based on the prices prevailing in April 2013, for materials, equipment,
labour etc. The considered unit prices are given in Appendix 1 and the cost for all civil items
are summarized in chapter 7.6 of this report.
7.2.1 River Diversion works
The river diversion works for the concrete gravity dam layout consist mainly of upstream
and downstream cofferdams and diversion tunnels. Hence, the civil work cost consists of
the cost for the diversion tunnels and the cofferdams.
The quantity of concrete (surface, backfill and lining), reinforcement, excavation
(underground and surface) and support works (shotcrete with wire mesh, rockbolts,
drainage holes, ribs etc.) have been estimated to calculate the cost of diversion tunnels for
each alternative. For the determination of the tunnel cost, 5 rock classes are considered
with the following distribution:
Rock class I Good rock 20%
Rock class II Fair rock 35%
Rock class III Poor rock 30%
Rock class IV Very poor rock 10%
Rock class V Extremely poor rock 5%
Quantities of cofferdam material for compacted random fill, jet grouting, filter material,
riprap etc. are considered for the cost of cofferdam for each alternative.
7.2.2 Dam
The cost of the concrete gravity dam consists of cost for surface excavation (soil and rock
excavation), different grades of concrete, reinforcement steel, support works (shotcrete,
rockbolts, drainage holes etc.) and the grout curtain (drilling and grout material).
The required quantities of excavation, concrete, reinforcement, support works, grout
curtain etc. have been computed for each alternative.
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7.2.3 Intake
The cost of the Power Intake consists of cost for surface excavation, concrete,
reinforcement steel, support works (shotcrete, rockbolt, drainage holes etc).
The quantities of excavation, concrete, reinforcement, support works have been computed
for each alternative.
7.2.4 Head Race Tunnel Quantity of concrete (surface for portal, backfill and lining), reinforcement, excavation
(underground and surface) and support works (shotcrete with wire mesh, rockbolts,
drainage holes, ribs etc.) have been estimated to calculate the cost for the Head Race
Tunnels for each alternative. For determination of the tunnel cost, 5 rock classes are
considered with the following distribution:
Rock class I Good rock 20%
Rock class II Fair rock 35%
Rock class III Poor rock 30%
Rock class IV Very poor rock 10%
Rock class V Extremely poor rock 5%
7.2.5 Surge Shaft
Cost for surge shaft is basically composed of the cost for underground rock excavation,
support works such as shotcrete with wire mesh, rockbolts, drainage holes, ribs as well as
permanent concrete lining with reinforcement.
7.2.6 Pressure Shaft/ Tunnel
The cost for the pressure shafts are determined in the same way as for the HRTs with the
only difference that in addition a steel liner is considered. A higher unit price has been
considered for the excavation of the vertical shafts than of the horizontal tunnels.
7.2.7 Adits and Access Tunnel in Powerhouse Area
The cost for Adits and Access tunnels in Powerhouse Area are determined in the same way
as done for the Headrace Tunnels.
7.2.8 Powerhouse complex
Cost for civil works for the powerhouse are determined based on the underground rock
excavation, concrete (substructure and superstructure), support works such as shotcrete
with wire mesh, rock bolts, drainage holes, ribs and reinforcement.
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The civil cost of transformer cavern is also included in the cost of Powerhouse complex.
7.2.9 Tailrace Tunnel
The cost for the tailrace tunnels is determined in the same way as the costs for the
Headrace Tunnels.
7.2.10 Switchyard
The cost of switchyard consists of cost of surface excavation (soil and rock excavation),
concrete, reinforcement steel, support works (shotcrete, rockbolt, drainage holes etc) etc.
7.3 Hydromechanical steel structures (HSS)
This head includes the cost of hydromechanical equipment comprising of gates, stoplogs,
hoists, its supporting structures and trash racks etc. The cost for these items are provided
on the dam, intake, diversion tunnel, power house, draft tube and tailrace for storage of
water, controlling discharge, generation of power and for maintenance purposes.
7.4 Electromechanical equipment (EM)
The estimated cost of Electro – mechanical equipments with 10% over load including unit &
station auxiliary systems, Electrical & Mechanical BOP equipments, Generators
transformers, GIS equipment & Pothead yard equipments is based on current price level
for similar machines.
The cost includes all taxes & duties, service taxes, insurance & transportation, erection &
commissioning of the equipment on turnkey basis.
The taxes & duties, insurance & transportation are based on prevailing rates. The erection
& commissioning charges has been considered as 8% of equipment cost.
7.5 Other cost
7.5.1 Establishment, Tools and Plants
This provision includes establishment cost during construction and cost of survey
instruments, camp equipment, office equipment and other small tools. This provision also
includes establishment for carrying out site supervision, quality control and cost control
cell. The establishment cost is evaluated as per section 16.5 of the CEA Guidelines, April
2012. Establishment cost is evaluated as percentage of the cost of the civil works. In the
present case cost of civil works (I works as per CEA format) is more than 750 Crores for all
alternatives, therefore, establishment cost is considered as 60 Crores plus 4% of the civil
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works cost exceeding 750 Crores. For tools & plants a provision of 2 Crores has been kept
as per section 16.6 of CEA guidelines. The costs of this provision for each alternative have
been given in Section 7.6 of this report.
7.5.2 Buildings
Provision has been made under this sub-head for permanent and temporary residential
buildings for various categories of staff, non-residential buildings for offices, workshops,
stores, rest houses and field hostels and other service buildings such as hospital, school
and utility services etc. The cost for buildings has been considered the same for all
alternatives.
7.5.3 Land
This covers the provision for acquisition/purchase of land for permanent works, approach
roads, camp sites, workshops, stores, offices and permanent colony for the maintenance
staff etc. The costs of land for each alternative have been given in Section 7.6 of this
report.
7.5.4 Roads and bridges
Provision has been made under this sub-head for construction of roads and bridges.
Provision has also been made for remodelling and strengthening of main highway and
bridges, including winter road treatment and snow removal to make them suitable for
transport of heavy equipment.
7.5.5 Other direct and indirect charges
This head includes expenses during pre-construction, capital cost and maintenance of
electrification, water supply, sewage disposal and drainage works, recreation, medical, fire
fighting equipment, inspection vehicles etc., cost of plantation, maintenance cost during
construction, compensatory afforestation, measures for maintaining environment and
ecological balance of the area, public health measures, treatment of catchment area etc.
7.6 Cost summary of basic alternatives
The resulting costs for each basic alternative are as presented in the following three tables
all alternatives with the same dam type – gravity dam - and the same powerhouse
complex):
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Table 9: Total investment costs for Alternative II-A (basic alternative)
Table 10: Total investment costs for Alternative III-A (basic alternative)
1 River diversion works 10'440 449 10'889 5.6%
2 Dam 39'810 4'413 106 44'329 22.8%
3 Intake 3'750 1'687 5'437 2.8%
4 Head race tunnel 35'380 35'380 18.2%
5 Surge shaft 8'280 8'280 4.3%
6 Adits to surge shaft 900 900 0.5%
7 Pressure tunnel and pressure shaft 1'190 3'431 4'621 2.4%
8 Adits and access tunnels in PH area 3'450 25 3'475 1.8%
9 Powerhouse cavern for main units 8'190 739 49'451 58'381 30.0%
10 Transformer cavern & GIS 7'358 7'358 3.8%
11 Tail race tunnel 10'240 541 10'781 5.5%
12 Pothead yard i/c connection to National Grid 700 412 1'112 0.6%
13 Auxiliary plant incorporated in the dam 220 3'555 3'776 1.9%
I Total Construction Cos: 122'330 11'506 60'883 194'719 100.0%
Rate in respect to total construction cost A [%] 62.8% 5.9% 31.3% 100.0%
II Establishment and Tools & Plants 8'830 4.5%
III Buildings 2'472 1.3%
IV Land Acquisition 3'221 1.7%
V Roads & Bridges 2'378 1.2%
VI Other direct & indirect charges as per CEA 11'073 5.7%
222'693 114.4%
S.NO. COMPONENTAlternative II-A - basic
Amount (INR in Lacs)
TOTAL INVESTMENT COSTS
C HSS RATE [%]TOTALEM
1 River diversion works 10'680 509 11'189 6.6%
2 Dam 49'130 4'528 106 53'764 31.6%
3 Intake 2'990 1'646 4'636 2.7%
4 Head race tunnel 6'410 6'410 3.8%
5 Surge shaft 3'540 3'540 2.1%
6 Adits to surge shaft 810 810 0.5%
7 Pressure tunnel and pressure shaft 1'190 3'431 4'621 2.7%
8 Adits and access tunnels in PH area 3'020 25 3'045 1.8%
9 Powerhouse cavern for main units 8'190 739 49'765 58'694 34.5%
10 Transformer cavern & GIS 7'358 7'358 4.3%
11 Tail race tunnel 10'240 541 10'781 6.3%
12 Pothead yard i/c connection to National Grid 700 412 1'112 0.7%
13 Auxiliary plant incorporated in the dam 220 4'191 4'412 2.6%
I Total Construction Cos: 96'900 11'639 61'832 170'371 100.0%
Rate in respect to total construction cost A [%] 56.9% 6.8% 36.3% 100.0%
II Establishment and Tools & Plants 7'860 4.6%
III Buildings 2'472 1.5%
IV Land Acquisition 4'751 2.8%
V Roads & Bridges 2'758 1.6%
VI Other direct & indirect charges as per CEA 10'353 6.1%
198'566 116.5%
S.NO. COMPONENTAlternative III-A - basic
Amount (INR in Lacs)
TOTAL INVESTMENT COSTS
C TOTAL RATE [%]HSS EM
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Table 11: Total investment costs for Alternative IV-A (basic alternative)
The comparison of the total investment costs of the different basic alternatives are as
illustrated in the table below:
Table 12: Summary of total investment costs for all basic alternatives
Alternative III-A leads to the lowest investment cost for the basic solution.
The following table shows the cost comparison of the different components, as river
diversion works, dams, headrace tunnels, auxiliary plant and land acquisition, which
interferes mainly on the variable cost. This is overall due to the entire arrangement of the
water conveyor system from the upstream surge shaft on, as well as the whole
underground powerhouse complex (including electromechanical equipment) are the same
for alternatives II-A and III-A, while for Alternative IV-A the installed capacity is somewhat
higher and consequently also the costs. Furthermore as already mentioned in Chapter 6.1
the environmental water release for alternative IV-A will be harnessed with the units
installed in the main plant. Therefore no auxiliary plant for this alternative is required.
1 River diversion works 13'180 509 13'689 7.9%
2 Dam 52'160 4'528 106 56'794 32.9%
3 Intake 2'890 1'605 4'495 2.6%
4 Head race tunnel 5'650 5'650 3.3%
5 Surge shaft 3'480 3'480 2.0%
6 Adits to surge shaft 1'460 1'460 0.8%
7 Pressure tunnel and pressure shaft 1'190 3'431 4'621 2.7%
8 Adits and access tunnels in PH area 3'020 25 3'045 1.8%
9 Powerhouse cavern for main units 8'190 739 51'105 60'034 34.8%
10 Transformer cavern & GIS 7'440 7'440 4.3%
11 Tail race tunnel 10'240 541 10'781 6.2%
12 Pothead yard i/c connection to National Grid 700 412 1'112 0.6%
13 Auxiliary plant incorporated in the dam 0 0.0%
I Total Construction Cos: 102'160 11'378 59'063 172'600 100.0%
Rate in respect to total construction cost A [%] 59.2% 6.6% 34.2% 100.0%
II Establishment and Tools & Plants 8'036 4.7%
III Buildings 2'472 1.4%
IV Land Acquisition 4'836 2.8%
V Roads & Bridges 2'296 1.3%
VI Other direct & indirect charges as per CEA 9'859 5.7%
200'099 115.9%
S.NO. COMPONENTAlternative IV-A - basic
Amount (INR in Lacs)
TOTAL RATE [%]
TOTAL INVESTMENT COSTS
C HSS EM
Alternative II-A Alternative III-A Alternative IV-A
base base baseI Total Construction Cost: 194'719 170'371 172'600
II - VI Total other costs 27'974 28'194 27'499
Total Investment Cost: 222'693 198'566 200'099112.2% 100.0% 100.8%
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Table 13: Cost comparison for different components for all alternatives
The above figures show that:
- The cost saving for the smaller dam in alternative II-A with respect to the more downstream alternatives and smaller cost for land acquisition do not compensate the
higher cost of the long required headrace tunnel (internal diameter of 10.0 m for basic
solutions).
- The cost saving in alternative IV-A for the not required additional auxiliary plant does not compensate the higher cost for the higher dam and the longer diversion tunnel, as
well as the higher cost due to increased capacity in the main powerhouse
Due to the above described facts the alternative III-A leads to the lowest investment cost.
8 OPTIMIZATION OF BASIC ALTERNATIVES
8.1 Cost Saving Potential of the Basic Alternatives
For the sake of comparison of the selected alternatives in a first step the same dam type
(concrete gravity dam) and the same gate arrangement (4 gated spillway openings at the
top of the dam and two bottom outlet openings), as well as an arbitrary chosen internal
diameter of the headrace tunnels with 10.0 m, have been considered for all three
alternatives. The corresponding results of the first step are presented in chapter 6 “Energy
production” and chapter 7 “Cost estimate”. The second step consists in identifying the
potential of cost saving to obtain the most optimized layout for each alternative. The
possibilities to lower the construction cost are in general:
- Changing the dam type from a gravity dam into an arch-gravity or double curved arch dam.
- Taken into account an optimized internal diameter for the headrace tunnel.
Alternative II-A Alternative III-A Alternative IV-A
base base base
1 C River diversion works 10'440 10'680 13'1802 C Dam 39'810 49'130 52'1604 C Head race tunnel 35'380 6'410 5'650
9 EM Powerhouse 49'451 49'765 51'10510 EM Transformer & GIS 7'358 7'358 7'44012 HSS Auxiliary Plant 220 220 012 EM Auxiliary Plant 3'555 4'191 0
IV Land Acquisition 3'221 4'751 4'836
TOTAL 149'437 132'505 134'370112.8% 100.0% 101.4%
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The following comment has been given in the Inception Report (No. 71.2471.00.001) about
the feasibility/suitability of different concrete dam types in respect to morphology and
geology matters:
Table 14: Feasibility for different concrete dam type based on findings of Inception Report
Alternative Gravity Arch-Gravity Double Curved Arch
II-A feasible feasible feasible
III-A feasible feasible feasible
IV-A feasible not suitable not suitable
As described in the Inception Report the non-suitability of the arch-gravity and double
curved arch dam type for alternative IV-A is due to:
- Extremely asymmetrical cross section
- Unfavourable discontinuity planes in the right abutment
Concerning the possibility for the construction of a double curved arch dam at the dam
sites of alternatives II-A and III-A the evacuation of the PMF (Probably Maximum Flood –
8’700 m3/s) has to be guaranteed and therefore the required evacuation system, as
spillway and bottom outlets have to be able to discharge the arriving flood to the
downstream side of the dam. In the case of Dugar HEP an important rule plays the fact that
the reservoir level immediately upstream of the dam cannot be raised above the maximum
normal reservoir level (FRL). The consequence of this requirement is that an ungated
evacuation systems cannot be foreseen. This implies that only gated evacuation systems
are to be installed either in the dam body or in other adjacent structures, as surface
spillways or spillways with underground evacuation tunnels.
In the following it will be highlighted if an evacuation system with less construction cost
than the possible available cost saving due to the change of the dam type from an arch-
gravity dam into a double curved arch dam can be found. Considering that the already 4
bottom outlets foreseen in the arch-gravity dam would be placed in the lower part of the
double curved arch dam, the capacity of the additional spillway system has to be the same
as for the surface spillways considered for the arch-gravity dam. The capacity has to be
equal to 6’250 m3/s.
The cost saving for a double curved arch dam with respect to the gravity dam is estimated
in the order of 55%, which leads to a cost reduction of:
- 12’000 INR Lacs for alternative II-A; and
- 14’500 INR Lacs for alternative III-A.
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In the case a surface spillway located at the projection of the dam crest, equipped with the
same 6 gates (opening width 12 m and gate height 12.5 m) as for the gravity dam solution,
would be foreseen in one or both abutments. The construction cost of the whole spillway,
including forebay, gate block and chute with flip bucket can be estimated. For definition of
gate block see the sketch below. In a first step only the cost for excavation, including
support measures plus the construction cost for the structure of the gate block are
considered.
Figure 16: Definition of gate block
Considering a pier thicknesses of 3.5 m, the total width of the gate blocks results in a
length of 118.0 m for all openings on the same abutment and 57.0 m for three openings on
each abutment. With an excavation slope of 1 horizontal to 4 vertical and considering a
berm with a width of 4 m every 12 m in height an overall excavation slope of 1 : 1.71 (H :
V) is resulting. This slope corresponds to an inclination of around 60° in respect to the
horizontal. If the natural terrain slope is also 60° or more, no intersection between
excavation slope and the natural terrain is possible. For flatter slopes the cost is a function
of the terrain slope of the abutments at the dam site. The total construction cost
(excavation, support measures and construction of gate structure) for the 38 long gate
block versus slope inclination of the abutment terrain is shown in the Figure 17 below. For
the cost calculation the following prices have been considered:
- 525 INR per m3 of surface rock excavation;
- 30% of the excavation cost for support measures;
- 1’500 INR Lacs for one spillway opening.
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As depicted in this chart the total construction cost of the whole surface spillway placed in
the abutments of the dam will never be lower than the cost saving due to dam type
changing, because to the indicated cost in the picture additional costs for the
chute, including flip bucket (excavation plus reinforced concrete structure) and the
excavation of the forebay has to be added. The excavation height is around 170 and 300 m
for alternative III-A and alternative II
started at elevation 2’260 and 2’390 masl for alternative III
respectively.
Due to the mentioned arguments before the solution with surface spillway openings in the
abutments is technically and economically not fe
as a possible evacuation system for a dam layout with a double curved arch dam.
This implies that only the solution with
invert of such tunnels could be placed more or less
structures. In the following charts the required internal diameter of the concrete lined
evacuation tunnels for different tunnel lengths (250 m and 350 m) are presented.
Figure 17: Construction cost for gate blocks
As depicted in this chart the total construction cost of the whole surface spillway placed in
the abutments of the dam will never be lower than the cost saving due to dam type
changing, because to the indicated cost in the picture additional costs for the
chute, including flip bucket (excavation plus reinforced concrete structure) and the
excavation of the forebay has to be added. The excavation height is around 170 and 300 m
A and alternative II-A respectively. This means the excavation has to be
started at elevation 2’260 and 2’390 masl for alternative III-A and alternative II
Due to the mentioned arguments before the solution with surface spillway openings in the
abutments is technically and economically not feasible and can therefore be dropped out
as a possible evacuation system for a dam layout with a double curved arch dam.
This implies that only the solution with underground evacuation tunnels
invert of such tunnels could be placed more or less at the same elevation as the intake
structures. In the following charts the required internal diameter of the concrete lined
evacuation tunnels for different tunnel lengths (250 m and 350 m) are presented.
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As depicted in this chart the total construction cost of the whole surface spillway placed in
the abutments of the dam will never be lower than the cost saving due to dam type
changing, because to the indicated cost in the picture additional costs for the spillway
chute, including flip bucket (excavation plus reinforced concrete structure) and the
excavation of the forebay has to be added. The excavation height is around 170 and 300 m
xcavation has to be
A and alternative II-A
Due to the mentioned arguments before the solution with