Final Report on Alternative Studies

7/29/2019 Final Report on Alternative Studies

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Yamne-I Hydro Electric Project

Report on Project Alternative Studies 1

Table of Contents

1. INTRODUCTION .................................................................................................................................................. 2

2. NEED FOR THE ALTERNATIVE STUDY.................................................................................................... 2

3. HYDROLOGY OF THE PROJECT .................................................................................................................... 3

3.1. Design Flood ..................................................................................................................................................... 3

4. ALTERNATIVE STUDIES FOR PROJECT LAYOUT ................................................................................ 3

4.1. Project Layout Alternative - I ................................................................................................................... 4

4.2. Project Layout Alternative - II .................................................................................................................. 7

4.3. Project Layout Alternative - III ................................................................................................................ 9

4.4. Conclusions andRecommendation for Project Layout .............................................................. 11

5. ALTERNATIVE STUDIES FOR OPTIMIZATION OF FRL ................................................................. 12

5.1. De-Silting Arrangement ........................................................................................................................... 13

5.2. Concrete Gravity Dam ............................................................................................................................... 12

5.3. Power Potential Study .............................................................................................................................. 15

5.4. Cost Benefit at each FRL ....................................................................................................................... 15

5.5. Conclusions and Recommendation .................................................................................................... 16

6. CONCLUSIONS ................................................................................................................................................... 16


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1. INTRODUCTIONThe Yamne - I HEP is being proposed as a Run of the River scheme across the River

Yamne, which is a left bank tributary of Siang River in Arunachal Pradesh. The

Project site is located in the upper most reaches of Yamne Basin.

The Government of Arunachal Pradesh has signed a Memorandum of Agreement

(MoA) for development of Yamne stage I project in between El. 800.0 m to El.

600.0 m with M/s Abir Construction Pvt. Ltd. (Presently known as Abir

Infrastructure Pvt. Ltd.)

As per MoA conditions SPV in name of M/s KU Yamne Energy Ventures Pvt. Ltd. was

formed which later changed name to M/s SS Yamne Energy Ventures Pvt. Ltd. for

implementation of project.

The dam site of Yamne I HEP is located downstream of the confluence of Yamne

and Yaming River. The tailrace outfall of Yamne I HEP has been proposed to be

located more than 2.0 km upstream of Yamne II submergence to have a2km free

flowing stretch of the river. The provided free stretch is such that it meets the MoEF

criteria of free flow stretch of river between two hydroelectric projects.

In this Report, the details of various alternative studies which are carried out to

finalize the project layout, optimization of FRL and selection of Diversion structure

are discussed.

2. NEED FOR THE ALTERNATIVE STUDYThe Yamne I HEP has been envisaged as Run of the River scheme and comprises of

a diversion structure, underground water conductor system, Surge Shaft and

Powerhouse. The maximum available gross head which can be harnessed in

technical and environmental sustainable manner is about 190.0m and the probable

installed capacity of the project would be about 120 150 MW.

The purpose of alternative studies is to arrive at a most cost effective and techno-

economically optimum layout which is most environment friendly. It is important to

note that cost of any hydro project is dependent upon its respective components

and to arrive at the most optimum project layout, assessment of respective costs

and energy benefits associated with any particular layout is of utmost importance.


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This report also aims at studying various possible options of project layout, their

respective costs and energy benefits.

3. APPROACH OF ALTERNATIVE STUDIESIn order to develop the most optimum layout two stage studies were conducted.

Stage I: Alternatives having same FRL but water conductor system on different

banks and surface / underground powerhouse options.

Stage II: After selecting the most optimum layout of water conductor system and

powerhouse, alternative studies for selecting the most optimum FRL for Yamne I

HEP.

4. HYDROLOGY OF THE PROJECTThe Project hydrology is one of the prime parameter for planning of hydro projects.

The 10-daily water availability data of 1978 79 to 2008-09 was submitted to CEA

/ CWC on 22.02.2012 and the same has been approved vide letter no

2/ARP/34/CEA/10-PAC/1399-1401, dated 9th March 2012. The approved 10-daily

discharge series for Yamne I HEP has been considered for power potential studies

of the alternative studies.

4.1. Design FloodIn the alternative studies, concrete gravity dam has been considered as a diversion

structure for the project. Probable Maximum Flood (PMF) has been considered as

design flood for the proposed diversion structures per the recommendations made

in IS 11223-1995. The PMF for Yamne I HEP has been estimated as 5783 cumecs

and the same flood intensity has been considered in the alternative studies for the

design of Spillway.

5. ALTERNATIVE STUDIES FOR PROJECT LAYOUT (STAGE I)The alternative study for Project Layout has been carried out to select the most

Techno-Economical layout for Yamne I HEP. After the preliminary evaluation of

many layouts the following three layouts have been considered for detailed study.

The details of these layouts are tabulated in Table 1.


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Table 1 Details of Project Layout Alternative Studies

Study No: Description

Project

Layout

Alternative-I

The Layout comprises of a Concrete Gravity Dam with the FRL at

El.740.0 m, Water Conductor System with surge shaft on the right bank

of Yamne River and Surface Powerhouse located about 1.0km

downstream of SipungNala Confluence. The average River bed level at

Powerhouse location is about El.550.0m. (Refer Drawing No. Yamne I

/ Alt studies / 001).

Project

Layout

Alternative-II


El.740.0 m, Water Conductor System with surge shaft on the Left Bank

of Yamne River and Surface Powerhouse located about 400.0m

upstream of Sipung Nala Confluence. The average River bed level at

Powerhouse location is about El.565.0m. (Refer Drawing No. Yamne I

/ Alt studies / 002).

Project

Layout

Alternative-

III


El.740.0 m, Water Conductor System with surge shaft on the Left Bank

of Yamne River and an underground Powerhouse located about 1.30

km downstream of Sipung Nala Confluence. The average River bed

level at Powerhouse location is about El.550.0 m. (Refer Drawing No.Yamne I / Alt studies / 003).

The ground levels considered in this study are worked out based on the Survey of

India Topo sheets. The Power Potential Studies for the above three alternatives

have been given inAnnexure1

5.1. Project Layout Alternative - IThe details of the major project components considered in the Project Layout

Alternative I are shown below in Table 2,

Table 2 Details of Project Layout Alternative - I

Project

ComponentDescription

Diversion

StructureThe Concrete Gravity Dam with Sluice Spillway and Stilling basin


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arrangement has been considered as diversion structure. The FRL of

the Project is considered at El. 740.00 m. The dam axis is located about

800.0m downstream of Yamne and Yaming River confluence. The

average River Bed Level at Dam site is about El.690.0m. The height of

the dam above average River Bed level is about 53.0m.

Water

Conductor

System

A Fore bay type Power Intake structure located on right bank of Yamne

River which will feed the design discharge to the HRT of 6.50m

diameter and 12.60km long. A surge shaft also been provided to take

care of the hydraulic transients expected during plant operations.

From the surge shaft the design discharge is conveyed through a

pressure shaft of 5.0 m diameter and 956.0 m length to the surface

Powerhouse. Four numbers of construction adits have been proposedat suitable intervals along the HRT to facilitate its construction.

Surface

Powerhouse

The surface Powerhouse is located on the right bank of Yamne River at

1.0km downstream of Sipung Nala. The tail water level is considered at

El.550.0m.

Heads &

Installed

Capacity

FRL of the Project - El. 740.0 m

MDDL of the Project - El. 735.0 m

TWL of the Project - El. 550.0 m

Head Loss in WCS - 14.58 m

Gross Head - 190 m

Rated Head - 173.75 m

Design Discharge - 98.84 cumecs

Installed Capacity - 155 MW

Annual Energy - 682.41 MU

Levelised Tariff - 6.95 INR/Unit

The primary project cost has been estimated based on the preliminary drawings

and rational assumptions. The completed cost of Project layout Alternative I has

been worked out to be INR 2218 Crores and the detailed breakup of the cost


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estimation is placed atAnnexure II. The Merits and Demerits with the Project

Layout Alternative I has been pointed out below.

Merits with Project Layout Alternative I:

1. The main advantage of this alternative is that the highest possible gross head of190.0m can be harnessed.

2. The Powerhouse site on located on a large natural terrace.3. No Local disturbance and hindrance.4. No agricultural land comes into land requirement of the project.

Demerits with Project Layout Alternative I:

1. The Complete water conductor system is traversing on the right bank of YamneRiver where no access roads are available. Thus field investigation shall require

at least one extra year and during the construction stage also one more year for

construction would be required in comparison to the left bank water conductor

system. Thus the Alternative I layout would require two more years in the

total execution period as compared to the other alternatives planned on the left

bank of Yamne River.

2. These studies are carried out based on Topo sheet of Survey of India in whichthe level difference between the powerhouse locations has a level difference of

15.0 m and the same has been considered for this study. However, during the

Site Visit on 20thJune 2012, fly leveling was carried out along the river with a

total station between the Powerhouse locations of upstream and downstream of

Sipung Nala. From the survey it has been observed that the total level difference

between these locations is about 8.0m and an additional tunnel length of about

1.0 km is required to harness this head. The additional tunnel length of 1.0 km

would result in about a meter of head loss and hence additional net head of 7.0m

could be utilized if the powerhouse is located downstream of Sipung Nala. Thus

it may not be an economically feasible option to have a Powerhouse location on

downstream of Sipung Nala by extending the HRT by about 1.0 km for

harnessing 7.0 m of additional net head.


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3. About 25 km of hill roads which includes two permanent bridges have to beconstructed at dam site and Powerhouse site for crossing the River during the

construction & operation stage. Construction of roads / bridges on steeper right

bank will induce slope stability problems.

4. The temporary River diversion tunnel has to be planned on the left bank ofYamne River as the WCS of the projects placed on the right bank. At the dam

site, a large slide zone is located about 300.0 m downstream of dam axis and

hence the construction of diversion tunnel would be complex and require heavy

rock support system. In this alternative, the temporary river diversion

arrangement will be costliest.

5.2. Project Layout Alternative - IIThe details of the project components considered in the Project Layout Alternative

II is tabulated in Table 3 below,

Table 3 Details of Project Layout Alternative - II

Project

ComponentDescription

DiversionStructure

The Concrete Gravity Dam with Sluice Spillway and Stilling basin


the Project is considered at El. 740.0 m. The dam axis is located about800.0 m downstream of Yamne and Yaming River confluence. The

average River Bed Level at Dam site is about El.690.0 m. The height of

the dam above average River Bed level is about 53.0 m.

Water

Conductor

System

A Fore bay type Power Intake structure located on left bank of Yamne

River which will feed the design discharge to the HRT of 6.50 m

diameter and 11.20 km long. A surge shaft also been provided to take


From the surge shaft the design discharge conveyed through a

pressure shaft of 718.0 m long and 5.0 m diameter up to the surface

Powerhouse. Four numbers of construction adits have been proposed

at suitable intervals along the HRT to facilitate its construction

activities.


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Surface

Powerhouse

The surface Powerhouse is located on the left bank of Yamne River at

400.0 m upstream of Sipung Nala. The tail water level is considered at

El.565.0 m.

Heads &

Installed

Capacity





Gross Head - 175 m






The primary project cost has been estimated based on the preliminary drawings

and rational assumptions. The completed cost of Project layout Alternative II is

worked out to be INR 1747 Crores and the detailed breakup of the cost estimation

is placed at Annexure II. The Merits and Demerits with the Project Layout

Alternative II has been pointed out in successive paragraphs.

Merits with Project Layout Alternative II:

i. The entire project layout is well connected with the existing motorable road onthe left bank.

ii. The Left bank terrain is comparatively flatter than the right bank which willprovide adequate space for muck disposal sites and other infrastructure

facilities.

iii. The temporary diversion arrangement could be planned on the right bank of theRiver.

iv. The length of the HRT is shorter about 500.0m and will save constructionperiod.


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v. The Powerhouse site is located on a large natural terrace and the geologicallybetter site for back slopes.

Demerits with Project Layout Alternative II:

i. The maximum possible head could not be harnessed.ii. Local disturbance and hindrance are expected.

5.3. Project Layout Alternative - IIIThe details of the project components considered in the Project Layout Alternative

III is tabulated in Table 4 below,

Table 4 Details of Project Layout Alternative - III

Project

Component

Description

Diversion

Structure

The Concrete Gravity Dam with Sluice Spillway and Stilling basin


the project is at El. 740.0 m. The average River Bed Level at Dam site is

about El.690.0 m. The height of the dam above average River Bed level

is about 53.0 m.

Water

Conductor

System

A Fore bay type Power Intake structure located on left bank of Yamne

River which will feed the design discharge to the HRT of 6.50 m

diameter and 13.51 km long. A surge shaft also been provided to take


From the surge shaft the design discharge conveyed through a

pressure shaft of 5.0m diameter and 809.0 m to the surface

Powerhouse. Four numbers of construction adits have been proposed

at suitable intervals along the HRT to facilitate its construction

activities.

Underground

Powerhouse

The Underground Powerhouse is located on the left bank of Yamne

River at 1.30 km downstream of Sipung Nala. The tail water level is

considered at El.550.0 m.

Heads &

Installed

Capacity




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Gross Head - 190 m






The project cost has been estimated based on the preliminary drawings and

rational assumptions. The completed cost of Project layout Alternative III is

worked out to be INR 2100 Crores and the detailed breakup of the cost estimation

is placed atAnnexure II. The Merits and Demerits with the Project Layout

Alternative III has been pointed out in successive paragraphs.

Merits with Project Layout Alternative III:

i. The entire project layout is well connected with the existing motorable road andthe highest possible head of 190.0m can also be harnessed.

ii. The Left bank terrain is comparatively flatter than the right bank which willprovide adequate space for muck disposal sites and other infrastructure

facilities.

iii. The temporary diversion arrangement could be planned on the right bank of theRiver which would be comparatively cheaper than the left bank.

Demerits with Project Layout Alternative III:

i. The length of the HRT is significantly longer than the other alternatives and italso requires crossing Sipung Nala to harness the maximum head which will

require costly precautionary arrangements during construction.

ii. The cost of HRT to harness the additional net head of 7.0m could not be justifiedwith the project cost.

iii. The proposed underground Powerhouse location needs to be explored with adrift and will required one more year for the investigation works.


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iv. The tailrace tunnels, construction and access tunnels also make theUnderground Powerhouse complex become costlier than the Surface

Powerhouse options.

5.4. Conclusions and Recommendation for Project LayoutFrom the above detailed alternative studies on Project Layout the following points

may be noted,

1. The Layout on right bank (Alternative I) of Yamne River will require two moreextra years as compared to other alternative layouts in which the WCS on the

left bank and the Cost-Benefit also higher than the other two alternatives.

2. The Alternative II has a significant advantage of being Simple Layout and theEnergy benefits are quite better than other two alternatives and it has a main

advantage of being well connected to the existing road, so that accessibility

would not be a problem during construction phase of the project.

3. The Alternative III has a similar trend of cost to benefits of Alternative I andit well connected with the existing road. The main disadvantage of the

Alternative III is that it has to cross the Sipon Nala and which may cause

seepage and stability problems during construction and operation stage of the

project.

The summary of the Cost-Benefit of project layout alternative studies are presented

below in Table 5.

Table 5 Summary of Cost-Benefit of Project Layout Alternative Study

Study

No

Installed

Capacity,

MW

Annual

Energy,

MU

Total

Project

Cost (Cr.)

Cost per MW

Levelised

Tariff

(INR/Unit)

Alt - I 155 682.41 2218 14.31 6.95

Alt - II 140 622.20 1747 12.48 6.00

Alt - III 155 678.48 2100 13.55 6.61

From the above table, it can be seen that the Alternative II is the better proposal

than other two in the both technical and economical considerations. Thus it is

suggested that the Alternative II shall be considered for the Project Layout for

Yamne I HEP and the same shall be considered for further optimization studies.

The Diversion structure is one of the vital structures in Alternative II and hence it


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is also recommended to carry out comprehensive studies for optimization of FRL of

the project.

6. ALTERNATIVE STUDIES FOR OPTIMIZATION OF FRL (STAGE II)Based on the above alternative study for Project layout, the layout of Alternative IIhas been considered suitable for Yamne I HEP and the same considered for

optimization of FRL of the project.

The optimum FRL of the project is the reservoir level at which the cost of energy

generation would be minimum. In this study, Six FRLs have been considered for

optimizations which are ranging from El. 715.0m to El. 740.0m.

The de-silting arrangements and the concrete gravity dam are the two important

structures which influence the cost of the project at different FRLs, so cost of these

structures are estimated at different FRL alternative study, while the cost of

remainig project components are considered same with different FRL alternative

studies.

6.1. Concrete Gravity DamDuring the site visit on 20th July 2012, various possibilities of Dam site location for

Lower FRL have been assessed and a location at 100 m downstream of Yamne

confluence is considered for technical assessment and the following points are

evaluated,

1. The river section is narrow and hence the cost of diversion structure will beminimum and it has an adequate space for de-silting basin arrangement.

2. The main concern with this location is that the life of the reservoir will beless as the dam site is located just downstream of confluence and the

reservoir area is not adequate enough to hold the sediment load on higher

reaches.

3. It also been noticed during the visit that the Yamne river carries lots ofsediment load during monsoon season which necessitates for de-silting

arrangement for the project.


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Hence the earlier proposed location (i.e. 800 m downstream of Confluence) of dam

site is considered preferable for locating the diversion structure for Yamne HEP and

the same is considered in this study.

The Concrete Gravity Dam with Stilling Basin arrangement is considered as

diversion structure in all FRL studies. The foundation of the dam has been

considered 30.0m below the average River bed level (i.e. El. 660.0 m). In all the

study a free board of 2.0 m has been provided above the FRL.

The features of Concrete Dam considered with different FRLs are tabulated below

in Table 6.

Table 6 Details of Concrete Gravity Dam at various FRLs

FRL Crest Levelof Spillway

Number ofGates

Size of

Spillway Gates(W X H) m

Length ofDam at Top

El. 740.0m El. 705.0 m 4 8.35 X 12.0 238.35 m

El. 735.0m El. 705.0m 4 9.15 X 12.0 220.36 m

El. 730.0m El. 705.0m 4 10.3 X 12.0 197.36 m

El. 725.0m El. 705.0m 4 12.0 X 12.0 171.09 m

El. 720.0m El. 705.0m 5 12.10 X 15.0 152.55 m

El. 715.0m El. 700.0 m 5 12.20 X 15.0 127.96 m

The detailed hydraulic calculations for design of spillways and energy dissipation

arrangements and corresponding engineering drawings are placed atAnnexure

III andAnnexure IV respectively.

6.2. De-Silting ArrangementAs different FRLs have been considered in this study, the requirement of De-Silting

chamber has been justified for each FRL and the cost of De-Silting arrangement also

been included in the project cost.

The requirement of De-Silting arrangement has been evaluated based on the level

difference between invert of HRT and Spillway crest level and the gross storage

capacity of the Reservoir.


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The De-Silting arrangement may not be required, if adequate level difference is

provided between spillway crest and intake and the reservoir would act as natural

De-Silting basin, if the gross storage capacity is good enough to settle the suspended

particles in the River water.

Based on the experience and provisions made in similar projects, the following

limits have been considered in this study for eliminating the de-silting

arrangements in the water conductor system of the project,

With the above criteria for De-Silting arrangement, the details of each FRL study has

been tabulated below in Table 7,

Table 7 Limits to Eliminate De-silting Arrangements

Description

Limit to avoid De-Silting

Arrangement

Level Difference between Spillway Crest

and Inver level of HRT> 15.0 m

Length of the Reservoir > 4000 m

Table 8 Details of Elevations and Reservoir Capacity

FRL (m) El. 740.0 El. 735.0 El. 730.0 El. 725.0 El. 720.0 El. 715.0

MDDL (m) El. 735.00 El. 730.00 El. 725.00 El. 720.00 El. 715.00 El. 713.00

Submergenceabove Overt (m)

3.25 3.25 3.25 3.25 3.25 3.25

Overt Level

of HRT (m)El. 731.75 El. 726.75 El.721.75 El.716.75 El.711.75 El.706.75

Centre Line

of Intake (m)El. 728.50 El. 723.50 El. 718.50 El. 713.50 El. 708.50 El. 703.50

Invert level

of HRT (m)El. 725.25 El. 720.25 El. 715.25 El. 710.25 El. 705.25 El. 700.25

Spillway Crest (m) El. 705.00 El. 705.00 El. 705.00 El. 705.00 El. 705.00 El. 700.00

River bed

Elevation (m)El. 690.00 El. 690.00 El. 690.00 El. 690.00 El. 690.00 El. 690.00

Level Diff between

Spillway Crest &Invert of HRT (m)

20.25 15.25 10.25 5.25 0.25 0.25

Gross Storage

at FRL (MCM)55.72 45.25 35.57 26.58 18.16 10.54

Length of

Reservoir

(m)

Yamne 4337.12 4043.02 3750.0 3472.44 3190.50 2847.36

Yaming 4166.88 4037.08 3904.04 3775.92 3650.39 3151.37

De-Silting

RequirementNo No Yes Yes Yes Yes


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From the above table it can be seen that the length of reservoir is greater than 4.0

km at FRL 740.0m and 735.0m which is substantial and at these FRLs the De-silting

arrangement have not been considered.

6.3. Power Potential StudyThe Power Potential Studies have been carried out at each FRL and the summary is

shown in Table 9 below and the detailed computations of each study are placed at

Annexure V.

Table 9 - Summary of Power Potential Study at Different FRL

FRL MDDL

Head

loss,

m

Rated

Head, m

Installed

Capacity,

MW

Annual

Energy,

MU

Annual

Load

Factor

Lean

Season

Factor

Design

Discharge,

cumecs

740 735 14.20 159.132 140 622.20 50.7% 13.9% 90.52

735 730 14.08 154.256 135 602.10 50.9% 14.0% 93.38

730 725 15.04 148.289 135 585.73 49.5% 13.5% 97.14

725 720 14.94 143.395 130 565.73 49.7% 13.5% 92.72

720 715 14.82 138.511 125 545.76 49.8% 13.6% 99.99

715 713 14.47 134.859 120 529.28 50.4% 13.8% 94.48

6.4. Cost Benefit at each FRLThe costs of the Project at each FRL have been estimated and it compared with the

energy benefits to conclude the most optimum FRL of Yamne I HEP. The summary

of the Cost-Benefit at each FRL is shown below in Table 10.

Table 10 - The Summary of Cost Benefit at Different FRL

FRL

Installed

Capacity,MW

Annual

Energy,MU

Total

ProjectCost (Cr.)

Levelised

Tariff (INR /Unit)

740 140 622.20 1747 6.00

735 135 602.10 1662 5.90

730 135 585.73 1794 6.54

725 130 565.73 1678 6.34

720 125 545.76 1613 6.32

715 120 529.28 1552 6.27

The details of Project cost at each FRL have been placed atAnnexure VI.


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6.5. Conclusions and RecommendationFrom the study of FRL optimization, the following observations could be made,

1. The De-Silting arrangement is required when the FRL kept below El. 735.0mand will significantly increase the project cost.

2. From Table 10, it can be seen that the project cost variation between the FRLsof El. 740.0 m and El. 735.0 m is -4.90%, but the energy loss will be 3.23% and

the same way the variation in Project cost and energy loss between the FRLs El.

740.0m and El. 730.0 would be +2.65% (increased due to de-Silting

Arrangement) and5.86% respectively. Hence the Project cost to benefit ratio is

better at FRL El. 735.0m and it shall be considered as FRL of Yamne I HEP and

it can also be seen that the levelised tariff is minimum at FRL 735.0m. Thus the

FRl 735.0m shall be considered most economical than other FRLs.

7. CONCLUSIONSFrom this alternative study the following conclusions are derived,

The project layout shall be planned on the left bank of Yamne River as the studies

showing the Alternative II as the most preferable option from techno-economic

angle in both technical and economical directions.

The FRL of the project shall be considered at El. 735.0m as it gives the best tariff

compared to other options.

This alternative study report is submitted to M/s SS Yamne Energy Ventures Pvt.

Ltd for their review and approval, so that the preparation of PFR for Yamne I HEP

with new parameters evaluated from this study shall be commenced.

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Final Report on Alternative Studies

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