02. main sentences - review report on existing studies - hasang hpp project 130225.pdf

February 2013

CONSULTING SERVICES UP TO PPA CONCLUSION FOR

HASANG HYDROPOWER PLANT PROJECT

REVIEW REPORT ON EXISTING STUDIES

ConsultingServicesuptoPPAConclusionforHasangHydropowerPlantProject

Nippon Koei Co., Ltd. i| Page

LOCATION MAP

HHaassaanngg PPjjtt SSiittee


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EXECUTIVE SUMMARY

1. INTRODUCTION

This Report has been prepared in accordance with the Agreement for Consulting Services up to PPA

Conclusion for Hasang Hydropower Plant Project (hereinafter referred to as “Project”) between PT.

Binsar Natorang Energi (hereinafter referred to as “BNE”) and Nippon Koei Co., Ltd. (hereinafter

referred to as “NK”) signed on December 27, 2012.

2. HYDROLOGY

The probable 100-year flood discharge at the weir site in the Feasibility Study (=539 m3/sec) is

underestimated. It is recommended that the Creager’s coefficient at the Hasang weir site shall be 20

at minimum. By applying the coefficient of 20, the 100-year flood discharge at the Hasang weir site

shall be around 1,000 m3/sec at minimum.

Runoff coefficient at the Project under the Average Scenario is as large as 0.67 assuming that mean

annual basin rainfall is 2,500 mm. From hydrological points of view, the Average Scenario with mean

annual runoff depth of 1,681 mm seems to be overestimated. This might cause risk of overestimation

of expected annual energy production. In this respect, it is recommended that the Moderate Scenario

having the mean annual runoff depth of 1,574 mm shall be applied to estimation of annual energy

production of the Project.

3. GEOLOGY

From the geomorphologic and geological viewpoints, it is suggested to; i) adjust the axis of the intake

weir, ii) adjust the location of the de-sander and connecting waterway route, iii) chick and monitor the

possibility of the landslides, iv) add the work adit for construction of the headrace tunnel, v) adjust

alignment of the penstock route, vi) adjust the location of headrace tunnel inlet, vii) provide surface

drains at the cut & cover section, and viii) to make gentler the excavated slope gradients.

4. POWER GENERATION

The project layout proposed in the Feasibility Study is not optimal with the respect of the penstock

length. With this penstock length, the fly wheel effect of the generators (GD2) is required to be

increased to an un-practicable or un-economical level to ensure the stability of penstock and to avoid

excessive pressure rise. Preliminary comparison of the alternatives indicates that the most

recommendable option is to provide newly a surge tank between the head pond and the powerhouse.

The surge tank will be of an exposed cylinder which stands on a ridge above the powerhouse.

Preliminary examination indicates that the tank’s diameter will be about 10m and exposed height

about the ground yard will be about 65m. The tank will be of steel, or pre-stressed concrete instead.


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With taking account of the hydrological duration, the river maintenance flow (or duty flow) and the

loss above, the saleable mean annual energy of the Project for checking the project feasibility would

be:

Comparison of Annual Energy

Description Unit Base Case Low Case Reg No. 38

1. Hydrology Series - Average Moderate Moderate

2. River maintenance flow m3/s 1.0 1.0 6.7

3. Installed Capacity GW 42.45 42.45 42.45

4. Theoretical Mean Annual Energy GWh 288.3 260.5 190.7

5. Availability % 98.5 98.5 98.5

6. Available Maximum Annual Energy GWh 284.0 256.7 187.9

7. Station Loss (2% of 6.) GWh 5.7 5.1 3.8

8. Spillage Loss GWh 2.8 2.6 1.9

9. Saleable Mean Annual Energy GWh 275.5 249.0 182.3

10. Plant Factor % 74.1 67.0 49.0

‘Base Case’ and ‘Low Case’ correspond to Annex 17.3 and 17.4 of the Feasibility Study, respectively.

‘Reg. No. 38’ corresponds to the case when the Government Regulation No.38, 2011 is strictly applied to ‘Low Case’.

Source: based on energy simulation in Feasibility Study and Review Team

5. DESIGN ISSUES

Design issues which may cause substantial impact to the project cost are seen in the following table.

Design Issues which may substantially cause Impact to Project Cost

No. Item Description 1 Access Road Re-route In F/S, the existing road will be widened and paved in the

same route to construct the access road. However, several sections of them are very steep in longitudinal gradient and too small horizontal radius. Construction of new road by re-route or improvement of vertical alignment for these sections will be necessary.

Pavement width Typical width of pavement is 6.0 m in the Feasibility Study. It can be reduced to 4.5 m. For passing vehicle each other, preparation of a passing bay every 500 m interval is recommendable.

2 Intake Weir and Power Intake Location change The ridge in the left bank in which the intake is located is

rather thin. After excavation of abutment of the intake weir and the intake, the remaining sound rock become be very thin. As the countermeasure, change of layout of the weir axis is recommended.

Removal of boulders There are many big boulders at the intake weir site. Almost of all of them are derived from the construction works of the hydropower station in upstream. These boulders shall be removed to downstream prior to start of the construction works as much as possible.

Debris barrier In order to prevent entering boulders in front of the power


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intake. It is recommended to construct some debris barrier structure in upstream of the intake weir.

Increase of 100-yr flood Due to the underestimate of 100-year flood discharge, design flood water levels in the above shall be updated and dimensions of the intake weir shall be increased.

Protective measures for piping Additional protective measures for piping such as deepening the cut-off trench or provision of upstream concrete slab shall be required.

3 Intake Channel and De-sander Protective measures for landslide Protective measures such as removal of upper part of

landslide mass shall be required.. Foundation treatment According to core logs near the de-sander, foundation is of

more than 50 in SPT, however actual location of the channel and de-sander is more river side. Some special treatment of the foundation such as replacement of concrete with poor soil will be required.

Deletion of stoplog and additional gates

The stoplog in front of gate at the inlet is not necessary always because this gate is opened in normal condition and maintenance/repair will be done easily. In the contrary, a gate will be necessary at the end of the de-sander, otherwise, water come into the sand trap basin from downstream during flushing operation and flushing will be not done effectively.

Steel lining of flushing channel Flushing channel under the de-sander is recommended to be constructed with embedded steel liner which is act as form work because this structure is small and complicated.

4 Headrace Tunnel Tunnelling in soft materials The followings shall be noted as the risk factors for

tunneling; i) intercalation of Palaeo-soil and soft materials, ii) thin earth cover and iii) ground water level.

Permeability in tuff layer If the Tuff layer shows high permeability, careful grouting surrounding rock and or membrane behind concrete lining is recommendable.

Work adit Work adit shall be provided to ensure the construction schedule against the possible delay due to geological risks and other reasons.

5 Headrace Channel incl. Cut & Cover

Cutting slope to gentle Excavation slopes of the cut and cover section and of the Headrace Channel are too steep. For the former, 1 to 0.5 or more gentle slope is recommendable, even it is temporary. For the latter, 1 to 1.0 more gentle slope is recommendable if no protective measure.

Crossing structures Design of crossing structures such as pipe culvert and bridge should be made. Especially, size of pipe culvert should be decided carefully taking flood water into consideration.

6 Head Pond and Spillway Slope protection Protective measure such as shot-crete or sodding against

erosion on the excavated slope is required. Extension of access road Access Road shall be extended to gate and raking operation

yard. Guide wall of spillway Guide wall of the spillway at the beginning shall be higher. Spillway section type Application criteria of standard section of Type -2, 3, 4 and

5 are not clear. Type-3 should be applied at the end portion only.

7 Penstock New provision of surge tank A surge tank shall be provided to ensure stability of the

penstock and to prevent excessive pressure rise of the


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penstock. Slope protection Geology around penstock site is composed on top soil and

weathered tuff and erodible by water. All excavated surface shall be protected by wet rubble masonry/shotcrete/sodding.

8 Powerhouse & Swichyard Increase of 100-yr flood Probable flood of 100-year shall be revised to 1,000 m3/s,

then the elevation of the powerhouse yard shall be set to ensure safety against this flood.

Location of draft gate Location of the draft gate can be shifted to upstream to minimize the powerhouse structure.

Top elevation of tailrace wall and erection bay access

Elevation of the erection bay of P/H and the end of Access Road are set at EL. 351.75. On the other hand, the upstream end of the tailrace wall is set at EL. 355.00. Flood water will flow into the Powerhouse through the erection bay. A guide wall along the Access Road is required.

Enlargement of powerhouse There seems no sufficient space for removal of the rotor and shaft assembly from the generator. In case horizontal-shaft turbine is used for this project, the space between the units shall be widened by at least 2 m and the space between Unit 3 and the powerhouse side wall by at least 2 m. Size of the control room and the switchgear room seems not enough.

Enlargement of switchyard in case of double pi T/L

If double-pi connection is employed, two more transmission line bays become necessary.

Addition of switchgear equip. in case of double pi T/L

If double-pi connection is employed, two more transmission line bays become necessary.

9 Transmission Line Double Pi T/L It is conceived that the selected option in the Feasibility

Study to provide the new Kampung Pajak substation and the Project is connected to there is technically the best solution. Single-pi connection has problem in reliability of transmission, and thus not recommendable. Meanwhile Double-pi connection requires necessity of 4 circuits, and the price of transmission line becomes high.

Source: NK

6. CONSTRUCTION PLAN AND SCHEDULE

The critical path of the construction schedule runs through the early site establishment of access road

to the tunnel portals, the timely commencement of tunnel excavation followed by lining and finishing

and connection to the cut & cover section, water filing and commissioning.

The schedule of tunnel works without additional work adit will be hardly kept and possibly delayed

by 2-3 months due to geological risks and other reasons. Meanwhile, an additional work adit can be

constructed easily and does not require high cost from the topography. If the work adit is prepared,

delay by geological risk and other reasons can be mitigated.

7. COST ESTIMATE

Impacts to the direct cost due to review result of design in compliance with NK’s recommendations

are roughly estimated. Total project cost to which the above cost impacts are incorporated is as below.


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Summary of Project Cost

Item Amount (mil. US$)

Direct Cost Civil Works 46.53 Hydro-mechanical Works (incl. Penstock) 10.46 Electro-mechanical Works 25.95 Transmission Line 15.53

Total Direct Cost 98.47 Indirect Cost Client Administration 4.92 Engineering 4.92 Land Acquisition and EIA Cost 4.26 Technical Management Services 2.84 Insurance 4.92 Taxes (VAT on all local items) 11.17

Total Indirect Cost 33.03 Total Project Cost (without IDC) 131.50

Total Project Cost (with IDC) 154.67

Source: NK based on Feasibility Study

8. PROJECT FEASIBILITY

The possible cost increase may affect the project profitability; the return on equity (ROE) may go

down by 3% from the FS Base Case. If one considers the possible energy decrease, ROE further may

go down by 2 %. As a whole, there is a concern that ROE might nose down to the level the investors

can hardly accept, as demonstrated below.

Analysis Cases Cost w/o IDC Energy Tariff ROE

FS Base Case 110.0 USDm 275.5 GWh USc7.5/kWh 14.4%*

Cost Up 131.5 USDm 275.5 GWh USc7.5/kWh 11.2%

Cost Up & Energy Less 131.5 USDm 249.0 GWh USc7.5/kWh 9.4% * FS has computed ROE (return on equity) to be 14.92% for the base case with USc7.5/kWh tariff, while the

Review Work does 14.4% under the same assumptions.

In order to compensate such possible profitability decrease, the investors should examine higher tariff

for energy sales, assuming 15.0% of the required ROE:



Cost Up & Energy Less 131.5 USDm 249.0 GWh USc10.03/kWh 15.0%


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9. CONCLUSION AND RECOMMENDATION

As a result of review on the existing studies of the Project, this Report concludes that;

- It is recommended that the Moderate Scenario shall be applied instead. Based on this, the

salable annual mean energy of the Project will be 249.0 GWh, which is of about 10% decrease

compared to 275.5 GWh in the Feasibility Study.

- The project cost without IDC will be 131.5 US$m which is about 20% increase compared to

110.0 US$m in the Feasibility Study.

- The possible energy decrease and cost increase above may cause profitability decrease. To

compensate this, higher tariff should be examined.

This Report recommends the following actions to be conducted.

- The observed daily flow records at the Pulao Dogom station from 2000 to date shall be analyzed

for prediction of monthly energy generation through in-depth review and scrutiny of the flow

data.

- Detailed survey shall be conducted to confirm possibility of landslide f at the de-sander site and

the powerhouse site.

- Additional topographic survey and geological investigation shall be conducted along the newly

proposed penstock alignment and at the surge tank area.

- Comparative study shall be conducted to confirm the optimal selection of type and number of

the units of turbine-generator.


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CONSULTING SERVICES

UP TO PPA CONCLUSION

FOR HASANG HYDROPOWER PLANT PROJECT

REVIEW REPORT ON EXISTING STUDIES

Table of Contents

Page

LOCATION MAP

EXECUTIVE SUMMARY

1 INTRODUCTION ............................................................................................. 1

1.1 General.................................................................................................................. 1

1.2 Background ........................................................................................................... 1

1.3 Objectives of Task-1 in Services .......................................................................... 3

1.4 Scope of Task-1 in Services .................................................................................. 3

2 HYDROLOGY ................................................................................................... 5

2.1 General.................................................................................................................. 5

2.2 Design Flood Discharges ...................................................................................... 5

2.3 Inflow.................................................................................................................... 10

3 GEOLOGY.......................................................................................................... 17

3.1 Geologic Components and their General Features ............................................... 17

3.2 Headworks ............................................................................................................ 20

3.3 Desander ............................................................................................................... 24

3.4 Inlet of Headrace Tunnel ...................................................................................... 27

3.5 Tunnel Section of Waterway ................................................................................. 28

3.6 Outlet of Headrace Tunnel and Cut & Cover Section of Waterway ..................... 34

3.7 Head Pond............................................................................................................. 35

3.8 Penstock ................................................................................................................ 35

3.9 Powerhouse ........................................................................................................... 37

3.10 Suggestions and Recommendations ..................................................................... 40

4 POWER GENERATION ................................................................................... 41

4.1 General ................................................................................................................. 41

4.2 Project Layout ...................................................................................................... 41

4.3 Power Generation ................................................................................................. 45


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5 DESIGN ISSUES: ACCESS ROAD ................................................................ 47

5.1 General.................................................................................................................. 47

5.2 Access Road ......................................................................................................... 47

6 DESIGN ISSUES: CIVIL WORKS ................................................................. 48

6.1 General.................................................................................................................. 48

6.2 Intake Weir and Power Intake ............................................................................... 48

6.3 Intake Channel and De-sander .............................................................................. 53

6.4 Headrace Tunnel ................................................................................................... 55

6.5 Headrace Channel ................................................................................................. 56

6.6 Head Pond and Spillway....................................................................................... 57

6.7 Penstock ................................................................................................................ 60

6.8 Powerhouse and Switchyard ................................................................................. 60

7 DESIGN ISSUES: HYDRO-MECHANICAL WORKS ................................ 62

7.1 General.................................................................................................................. 62

7.2 Penstock ................................................................................................................ 62

7.3 Hydro-mechanical Equipment .............................................................................. 62

8 DESIGN ISSUES: ELECTRO-MECHANICAL WORKS ............................ 64

8.1 General.................................................................................................................. 64

8.2 Mechanical Equipment ......................................................................................... 64

8.3 Electrical Equipment ............................................................................................ 64

9 DESIGN ISSUES: TRANSMISSION LINE ................................................... 66

9.1 General.................................................................................................................. 66

9.2 Transmission Line ................................................................................................ 66

10 CONSTRUCTION PLAN AND SCHEDULE ................................................. 67

10.1 General.................................................................................................................. 67

10.2 Construction Plan ................................................................................................. 67

10.3 Construction Schedule .......................................................................................... 70

11 COST ESTIMATE ............................................................................................. 73

11.1 General.................................................................................................................. 73

11.2 Bill of Quantities .................................................................................................. 73

11.3 Unit Prices ............................................................................................................ 74

11.4 Impact to Cost Estimate due to Design Review ................................................... 76

12 PROJECT FEASIBILITY ................................................................................ 78

12.1 Financial Analysis ................................................................................................ 78

12.2 Possible Effects from Cost and Energy Change ................................................... 79

13 CONCLUSION AND RECOMMENDATION ............................................... 80


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ANNEX

COMMENTS ON TECHNICAL PROPOSAL BY POSCO ENGINEERING

List of Tables

Table 1.2.1 Chronicle ................................................................................................... 1

Table 1.2.2 Most Recent Studies .................................................................................. 2

Table 1.2.3 Salient Features ......................................................................................... 2

Table 1.4.1 Scope of Task-1 in Services ....................................................................... 3

Table 1.4.2 Documents for Review .............................................................................. 4

Table 2.2.1 Estimated Probable Flood Discharge at Pulao Dogom Station ................. 6

Table 2.2.2 Estimated Probable Flood Discharges at Hasang Weir Site (F/S) ............. 6

Table 2.2.3 Estimated Probable Flood Discharges at Hasang Weir Site (Pre-F/S) ...... 7

Table 2.3.1 Comparison of Runoff Depth of Annual Mean Discharges

at Hasang Weir Site ................................................................................. 11

Table 2.3.2 Plausible Range of Runoff Estimated from Water Balance ..................... 12

Table 2.3.3 Comparison of Runoff Coefficient at Hasang Weir Site ......................... 14

Table 3.5.1 Geologic Description of Core Sample of Drilling PB-T1 ....................... 31

Table 3.6.1 Summary of Laboratory Tests at Cut & Cover Site ................................. 34

Table 4.1.1 Two Scenarios for Energy Simulation ..................................................... 41

Table 4.2.1 Alternatives for Penstock Stability .......................................................... 43

Table 4.3.1 Mean Annual Energy ............................................................................... 46

Table 5.1.1 Main Access Roads to be Upgraded and/or Newly Built ........................ 47

Table 6.1.1 Main Civil Structures of the Project ........................................................ 48

Table 11.1.1 Summary of Project Cost in Feasibility Study ........................................ 73

Table 11.3.1 Main Unit Rates for Civil Works in Feasibility Study ............................ 74

Table 11.4.1 Impact to Cost Estimate due to Design Review ...................................... 76

Table 11.4.2 Summary of Project Cost ......................................................................... 77

Table 12.2.1 Updated Financial Stream with Higher Tariff ......................................... 79

List of Figures

Figure 1.2.1 Layout Alternatives in Previous Studies .................................................... 2

Figure 2.2.1 100-year Floods in Sumatra ...................................................................... 7

Figure 2.2.2 Chart of Creager’s Number ....................................................................... 8

Figure 2.2.3 20-year Floods in Sumatra ......................................................................... 9

Figure 2.2.4 2-year Floods in Sumatra ........................................................................... 9

Figure 2.3.1 Plausible Range of Mean Annual Runoff Depth at Hasang Weir Site ..... 13

Figure 2.3.2 Isohyetal Map of Mean Annual Rainfall in Sumatra Island .................... 13


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Figure 2.3.3 Relationship between Runoff Coefficient and Mean Annual Basin

Rainfall in Various River Basins in Sumatra Island ................................ 14

Figure 2.3.4 Relationship between Runoff Coefficient and Mean Annual Runoff

in Various River Basins in Sumatra Island .............................................. 15

Figure 3.1.1 Project Area on Geological Map ............................................................. 17

Figure 3.1.2 Schematic Geologic Section .................................................................... 18

Figure 3.1.3 Estimated Distribution of Aeolian Deposit and Pyroclassic Flow .......... 19

Figure 3.1.4 Estimated Distribution of Tapanuli Group .............................................. 19

Figure 3.2.1 Location of Recent Sediments and Change of Water Course .................. 20

Figure 3.2.2 Location of Resent Sediments and Change of Water Course .................. 21

Figure 3.2.3 Locations of Drill Holes and Test Pits in Headworks Site ...................... 22

Figure 3.2.4 Geological Section of Headworks Site .................................................... 22

Figure 3.2.5 Section of Weir and Assumed Depth of Foundation Rocks .................... 23

Figure 3.2.6 Possible Leakage Path on Permeability Tests .......................................... 24

Figure 3.3.1 Locations of Drill Holes and Test Pits in Desander Site ......................... 25

Figure 3.4.1 Different Depth to Assumed Rock Line among Drawings at Inlet Site .. 27

Figure 3.5.1 Plan of Headrace Tunnel ......................................................................... 28

Figure 3.5.2 Section of Headrace Tunnel ..................................................................... 28

Figure 3.5.3 Geological Section of Headrace Tunnel .................................................. 30

Figure 3.5.4 Catchment Area of Headrace Tunnel ....................................................... 32

Figure 3.5.5 Foreseeable Groundwater Condition ....................................................... 33

Figure 3.5.6 Possible Locations of Work Adits and Access Roads .............................. 33

Figure 3.8.1 Estimated Distribution of Tapanuli Group .............................................. 36

Figure 3.9.1 Possible Landslide Features just upstream of Powerhouse Site .............. 39

Figure 4.2.1 Layout of Alt. 1-1 .................................................................................... 44

Figure 4.2.2 Layout of Alt. 1-2 .................................................................................... 44

Figure 6.2.1 Proposed Layout ...................................................................................... 49

Figure 6.2.2 Debris Barrier Structure........................................................................... 50

Figure 6.2.3 Contraction Joint of Overflow Weir ........................................................ 52

Figure 6.2.4 Curtain Grout Line and Study of Piping .................................................. 53

Figure 6.2.5 Curtain Grout Line .................................................................................. 53

Figure 6.3.1 Location of Geological Investigation ...................................................... 54

Figure 6.3.2 Comments on De-sander ......................................................................... 55

Figure 6.4.1 Concrete Lining of Headrace Tunnel ...................................................... 56

Figure 6.5.1 Excavation Slope and Embankment ........................................................ 57

Figure 6.5.2 Cross Drain and Bridge ........................................................................... 57

Figure 6.6.1 Head Pond Gate Operation Yard ............................................................. 58

Figure 6.6.2 Comments on Head Pond ........................................................................ 59

Figure 6.6.3 Embankment and Cross Drain of Spillway ............................................. 59


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Figure 6.6.4 Typical Section of Spillway ..................................................................... 59

Figure 6.8.1 Powerhouse layout ................................................................................... 61

Figure 6.8.2 Coffering of Powerhouse ......................................................................... 61

Figure 10.1.1 Construction Master Schedule in Feasibility Study ................................ 67

Figure 10.2.1 Site Installation Works ............................................................................. 68

Figure 10.2.2 Coffering of Intake Weir .......................................................................... 69

Figure 10.2.3 Access to Headrace Tunnel...................................................................... 69

Figure 10.3.1 Work Adit ................................................................................................ 71

Figure 10.3.2 Construction Schedule of Headrace Tunnel without Work Adit ............. 71

Figure 10.3.3 Construction Schedule o Headrace Tunnel with Work Adit .................... 72

List of Photos

Photo 3.2.1 Upstream View of Headworks Site ......................................................... 21

Photo 3.2.2 Downstream View of Headworks Site ..................................................... 21

Photo 3.2.3 Outcrop on Thin Ridge of Left Abutment ............................................... 23

Photo 3.3.1 Sediment Trap Facility Site ..................................................................... 26

Photo 3.5.1 Condition of Water course on Lowest Portion on Headrace Tunnel ....... 29

Photo 3.5.2 Upper Layer of “Tuff” ............................................................................. 29

Photo 3.5.3 Ignimbrite ................................................................................................ 30

Photo 3.5.4 Lower Layer of “Tuff” ............................................................................. 30

Photo 3.8.1 Gully Erosion after Excavation of Access Road to Powerhouse ............. 37

Photo 3.8.2 Gully Erosion after Excavation of Access Road to Powerhouse ............. 37

Photo 3.9.1 Outcrops of Moderately Hard Ignimbrite at Powerhouse Site ................ 38

Photo 6.2.1 Situation at Intake Weir and Power Intake .............................................. 49

Photo 6.2.2 Construction Works in Upstream ............................................................. 50


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1. INTRODUCTION

1.1 General

This Report has been prepared in accordance with the Agreement for Consulting Services up to PPA

Conclusion for Hasang Hydropower Plant Project (hereinafter referred to as “Project”) between PT.

Binsar Natorang Energi (hereinafter referred to as “BNE”) and Nippon Koei Co., Ltd. (hereinafter

referred to as “NK”) signed on December 27, 2012.

The Report presents background and objective of the Services, and the review results of the existing

studies for the Project including the issues such as general hydrology and geology, hydropower

planning and design/specifications, cost estimation, facility renewal planning, operation planning,

saleable power, construction time schedule and contractual systems.

1.2 Background

BNE was established by PT. Titan Multi Power and LG International Corp. as the Special Purpose

Company for an Independent Power Producer of the Project. The Project is a run-of-river hydropower

along the left bank of the Kualu river, running south-east of the Lake Toba down to the Malakka Strait.

Location map of the Project is attached in the opening page of this Report.

Promotion of the Project by BNE started in 2010 and following progress has been so far made.

Table 1.2.1 Chronilcle

Event Month Year

Environmental Impact Assessment (EIA) approval was obtained from Toba Samosir Regency.

March 2010

Concession Right was obtained from Toba Samoir Regency. July Pre-feasibility Study was completed. April

2011

Forestry License is obtained from North Sumatra Province. September Enlisted in PLN RUPTL 2012-2021.

December Enlisted in PLN Fast Track Program Phase-2. CDM sub-project was registered by UNFCC. Direct Appointment Approval was obtained from Ministry of Energy and Mineral Resources.

March 2012

Feasibility Study was completed. April Direct Appointment Approval was obtained from PLN. May MOU for Consulting Services was concluded with NK. September IPP Prequalification was passed by PLN. October Agreement for Consulting Services was concluded with NK December

Source: Agreement for Consulting Services up to PPA Conclusion for the Project

The Project was first identified in the hydropower potential studies in Indonesia by NK in 1983 and

1999. After that, several alternative studies were conducted. The most recent studies are the

Feasibility Study by Poyry Energy Ltd. in 2012 the Pre-Feasibility Study by PT. Wahana Adya in

2011.



Table 1.2.2 Most Recent Studies

Study Outline

Feasibility Study in 2012 by Poyry Energy Ltd.

The feasibility study was prepared on the basis of the alternative L2-1 which was selected in the pre-feasibility study.

Pre-Feasibility Study in 2011 by PT. Wahana Adya

7 alternative layouts were examined, and as the result the alternative L2-1 (free surface tunnel + power channel + shorter penstock + surface type powerhouse) was selected as the most promising layout.

Source: Feasibility Study

The Project was optimized in the Feasibility Study as a straightforward run-of-river type development

of 42.45MW installed capacity. The Feasibility Study reassessed the seven (7) alternatives which had

been studied in the Pre-Feasibility Study, then concluded that the alternative L2-1 was the most

attractive for development, of which layout is seen in the following figure.


Figure 1.2.1 Layout Alternatives in Previous Studies

Salient features of the Project proposed in the Feasibility Study are summarized in the following table.

Table 1.2.3 Salient Features

Description Salient Features

Project Name Hasang Hydro Power Plant (HPP) Project

Project Scheme IPP (Independent Power Producer to PLN)

Location Aek Kualu-River Area, Nassau subdistrict, Toba Samosir Regency, North Sumatera, Republic of Indonesia

Type Run-of-River

Catchment Area 501 km2

Mean Annual Flow 26.7 m3/s

Maximum Plant Discharge 27.5 m3/s

Net Head 189.27 m

Installed Capacity 3 x 14.150MW = 42.450 MW

Annual Energy Output 275.53 GWh

Project Cost US$ 129.4 mil.




The Consulting Services up to PPA Conclusion for the Project of which the Agreement was

concluded between BNE and NK on December 27, 2012 (hereinafter referred to as “Services”) consist

of the following tasks:

- Task-1: Review of the Existing Studies

- Task-2: Review of and Advice on the Request for Proposal (RfP) from PLN

- Task-3: Assistance in IPP Proposal Preparation in Response to RfP

- Task-4: Assistance in Response to Technical Clarifications from PLN

- Task-5: Advice on Tariff Negotiations

- Task-6: Advice on PPA Negotiations in Technical Aspects (excluding the legal advice in PPA

negotiation)

1.3 Objectives of Task-1 in Services

The objectives of Task-1 in the Services are;

- to review the existing studies, relevant data and information thereon in order to have clear and

objective understanding of the development plan of the Project, and

- to recommend the tariff components A, B, C, D and E based on the main financial indicators

analyzed.

1.4 Scope of Task-1 in Services

The scope of Task-1 in the Services includes the followings.

Table 1.4.1 Scope of Task‐1 in Services

Scope Description

(1) Review the exiting studies

(a) General hydrology and geology

River conditions might not meet the business requirements, e.g., droughts or floods. Geological conditions might demand extra costs to develop the project facilities. The Consultant will appraise the natural conditions and perceive the grade of the potential risks.

(b) Hydropower planning and design/specifications thereof

Facility layouts and specifications are directly linked to the financial viability of the project. The Consultant will examine if the project has been optimized in terms of hydropower generation.

(c) Cost estimation in construction and non-construction

The Consultant will verify that the capital expenditures are pertinently estimated from the proper price quotations.

(d) Facility renewal planning and cost thereof

Hydro turbines and generators need renewal in the future. The Consultant will verify that the renewal cost as part of the capital expenditures is pertinently estimated.

(e) Operation planning and costs thereof

The Consultant will verify that the operating expenditures are pertinently estimated.

(f) Generation cost The Consultant will carefully estimate the unit generation cost by incorporating effects of the scheduled outage for the maintenance activities and the forced outage due to droughts in dry seasons.



(g) Core construction time schedule

Optimistic estimation of the construction years may jeopardize the overall investment plan; delay in construction would increase the capital expenditures and reduce the project revenue. The Consultant will examine if the construction time schedule is pertinently built.

(h) Contractural systems, lotting and contractor candidates

The capital expenditures may enormously differ depending on the risks allocated to the contractor. The Consultant will examine if the project risks are nicely distributed/assigned.

(2) Recommend the tariff components

To be discussed in Task-3

Source: Agreement for the Services

The existing studies which were provided by BNE to NK for the review in Task-1 are the Feasibility

Study Report in 2012 and the Pre-Feasibility Study Report in 2011 for the Project. The Structures of

the respective reports provided are as seen in the following table.

Table 1.4.2 Documents for Review

Title Report Structure Feasibility Study Report in 2012 by Poyry Energy Ltd.

Vol. 1 Executive Summary Vol. 2 Main Report Vol. 3 Drawings Vol. 4 ESIA Vol. 5 Annex

Pre-Feasibility Study Report in 2011 by PT. Wahana Adya

Vol. 2 Main Report Vol. 3 Drawings

Pre-F/S Report for 150kV T/L in 2012 by Wiratman & Associates

Vol. 1 Executive Summary Vol. 2 Main Report Vol. 3 Attachment Vol. 4 Drawings

Source: BNE

NK conducted the desktop review on the documents above, and performed a site reconnaissance

survey on 17th and 18th January 2013 at the Project site to confirm the actual conditions especially of

geology. NK reported the interim results of their review to BNE in the progress meetings held in

biweekly basis then compiled those comments in the relevant chapters in this Report.

Besides the above, NK received form BNE the electronic files of Technical Proposal on the Project

prepared by LG International and POSCO Engineering. NK’s Comments on this document is

presented in Annex of this Report.



2. HYDROLOGY

2.1 General

Hydrological study in the Feasibility Study Report (in Chapter 6 Meteorology, Hydrology and

Sedimentation, Volume 2 Main Report) has been well carried out in detail despite very limited

availability of long-term hydrological data in the Kualu River basin where the Hasang HPP Project is

located. Major outcomes of hydrological study which might affect the project cost and energy

generation were carefully reviewed based on experiences of various hydrological analyses in past

hydropower and water resources development projects in Indonesia. Highlighted are as follows:

- Estimation of design flood discharges at the Hasang weir site

- Estimation of Inflow at the Hasang weir site

2.2 Design Flood Discharges

2.2.1 Probable 100-year Flood Discharge

Feasibility Study

The design flood discharges (probable flood discharges) at the the Hasang weir site was estimated

based on flood frequency analysis using the observed flow records at the Pulao Dogom water level

gauging station. The Pulao Dogom station is located approximately 100 km downstream from the

weir site. The catchment areas are 1,141 km2 at the Pulao Dogom station and 501 km2

at the weir site.

The flow records at the Pulao Dogom station are available for 11 years from 2000 to 2010. Because

staff gauge reading was conducted three times per day, continuous hourly flow records including

flood peaks are not available for flood frequency analysis for estimating probable flood discharges.

Due to this, continuous hourly flow series were estimated applying interpolation technique to the

observed flow data and then used for flood frequency analysis in the Feasibility Study in 2012.

Flood frequency analysis is usually carried out based on the annual maximum flood peak discharges.

In the Feasibility Study, however, partial series was applied instead of selecting annual maximum

flood peak discharge series due to the consideration that the observation period is only 11 years and

seems rather short for frequency analysis. Totally the partial series of 47 flood peaks exceeding 350

m3/sec were selected. It is however acceptable from hydrological view point that the probable

flood discharges with larger recurrence interval such as 100-year and 200-year flood discharges

estimated from the partial series tend to become smaller than those from the annual maximum

series. This is readily understandable from the stochastic viewpoint that the recorded maximum flood

peak of 650 m3/sec at the Pulao Dogom station (which is interpolated from plotted maximum flood

peaks in Figure 6-25 in the Feasibility Study Report) is assumed in the recorded maximum flood peak

in the period of 47 years for frequency analysis, although this peak was the recorded maximum in the

period of 11 years.



In the Feasibility Study Report, the estimated probable flood peaks at the Pulao Dogom station is

given as follows (see Table 6-7 in the Feasibility Study Report):

Table 2.2.1 Estimated Probable Flood Discharges at Pulao Dogom Station

Return Interval (year)

Probable Flood Discharge (m3/sec)

10 674 25 728 30 739 50 769 100 810 200 851


Finally probable flood discharges at the Hasang weir site are estimated using the well-known

Creager’s equation for flood regionalization as listed below (see Table 6-8 in the Feasibility Study

Report).

Table 2.2.2 Estimated Probable Flood Discharges at Hasang Weir Site (F/S)



Creager’s Coefficient

10 449 11.59 25 484 12.52 30 492 12.71 50 512 13.22 100 539 13.93 200 566 14.63


As shown above, the 100-year flood at the weir site which was used as the design flood discharge for

hydraulic design of civil structures is estimated to be 539 m3/sec.

Figure below shows the relationship between 100-year flood discharges in Sumatra Island applied in

various hydropower development projects and catchment areas thereof. Besides, the Creager’s curves

with coefficients of 20 and 30 as well as the 100-year flood discharge at the Hasang weir site are also

plotted for reference.



Source: Potted Floods from Hydro Inventory Study, July 1997, PT.PLN

Figure 2.2.1 100‐year Floods in Sumatra

The Creager’s curve is commonly applied to assist in quick estimation of probable flood peak

discharges and evaluation of estimated probable flood discharges through comparison of the same

probable flood discharges applied in other schemes. Along this line, in the Hydro Inventory Study in

1997 recommended to apply Creager’s coefficient of 30 for Sumatera Island for preliminary study of

hydropower development schemes from the conservative aspect.

As is apparent from the figure above, the 100-year flood discharge at the Hasang weir site seems

slightly small compare to other 100-year flood discharges applied in various hydropower schemes.

The Creager’s coefficient at the Hasang weir site is as small as 13.93 as shown in the table above.

It is recommended that the Creager’s coefficient at the Hasang weir site shall be 20 at minimum. By

applying the coefficient of 20, the 100-year flood discharge at the Hasang weir site shall be around

1,000 m3/sec at minimum.

Pre-Feasibility Study

After review of the Feasibility Study Report, the Pre-Feasibility Study Report becomes available. A

different approach from the Feasibility Study was made for estimation of probable flood discharges.

Probable flood discharges were estimated by applying the Nakayasu unit hydrograph method by use

of probable basin rainfalls as summarized below.

Table 2.2.3 Estimated Probable Flood Discharges at Hasang Weir Site (Pre‐F/S)



5 913.97 10 1,025.79 25 1,167.07 50 1,271.88 100 1,375.92 200 1,479.58

Source: Pre-Feasibility Study



As shown above, the 100-year flood discharge at the Hasang weir site was proposed to be 1,372.92

m3/sec in the Pre-Feasibility Study Report. Besides, the estimated 100-year flood discharge was

evaluated by Creager’s coefficient as shown below. It is noted that plotted probable flood discharges

are of specific discharges expressed by the unit of m3/sec/km2.

Source: Pre-Feasibility Study

Figure 2.2.2 Chart of Creager’s Number

The estimated 100-year flood discharge at the Hasang weir site is plotted close to on the Creager’s

curve with coefficient of 30. It was concluded in the Pre-Feasibility Study that the estimated 100-year

flood discharge is applicable to feasibility design.

Conclusion

From the review result above, it is concluded that the probable 100-year flood discharge at the weir

site in the Feasibility Study (=539 m3/sec) is underestimated. It is recommended that the Creager’s

coefficient at the Hasang weir site shall be 20 at minimum. By applying the coefficient of 20, the 100-

year flood discharge at the Hasang weir site shall be around 1,000 m3/sec at minimum.


The construction of weir structure is proposed to implement in two phases as follows (see Sub-section

12.3.1.3 in the Feasibility Study Report):

- Phase 1: Construction of the structures at the left bank

- Phase 2: Completion of the weir structure

In the Feasibility Study, the construction pits for Phase 1 is proposed to be safe against a 25-year

flood. Thus both upstream and downstream cofferdams will be constructed (see Sub-section 12.3.4).



The designed 25-year flood discharge of 484 m3/sec at the weir site s also evaluated in terms of the

Creager’s curve. Figure below is the plots of design 20-year flood discharges in various hydropower

schemes. It is assumed the no significant difference is expected between 20-year flood discharges and

25-year flood discharge at Hasang weir site, since no 25-year flood discharges are available.

As seen in the figure, it appears that the design 25-year flood discharge is plotted on the Creager’s

curve with coefficient of 10, which is judged as a little underestimated for 20-year floods in Sumatra

Island.

Source: Potted Floods from Hydro Inventory Study, July 1997, PT.PLN



As described in the above, the Feasibility Study assumed a 25-year flood as the design flood for the

river diversion of the intake weir. However, this is too conservative for construction of the intake

weir of concrete type. For this type of construction, 2-to 5-year floods are considered to be sufficient.

Source:

Potted Floods from Hydro Inventory Study, July 1997, PT.PLN


Return Period = 2 year

10

100

1,000

10,000

10 100 1,000 10,000 100,000

Catchment Area (km2)

Flo

od P

eak

Dis

char

ge (

m3/

s)

2

C=10

Masagn-2 2



Figure above is the plots of design 2-year flood discharges in various hydropower schemes. As seen

C=10 is the upper envelope curve of 2-year floods in Sumatra Island.

The above indicates that the designed flood discharge for the river diversion of 484 m3/sec at the weir

site proposed in the Feasibility Study, of which Creager’s coefficient is about 10, is still applicable,

but should be regarded as the probable 2- to 5-year flood discharge, not of 25-year.

2.3 Inflow

2.3.1 Inflow Duration Curves at Hasang Weir Site

Inflow data at the Hasang weir site is available only in the form of flow duration curve. No daily

inflow data is given in the Feasibility Study Report. In the Feasibility Study Report, the inflow at the

Hasang weir site was defined by the duration curve. This flow duration curve is used for energy

generation simulations together with optimization of development scheme.

Flow duration curve is essentially required to determine an optimum development scale for run-of-

river type scheme. Flow duration curve at the Hasang weir site is developed by different two

approaches. The following duration curves have been derived in the Feasibility Study Report (see

Section 6.5):

- Moderate scenario: The duration curve at the weir site is estimated based on the duration curve

derived from the Pulao Dogom station in the period of 2000-2006 (2002 and 2005 excluded) to

down-scaled to match the annual mean discharge of 25 m3/sec, which is derived from water

balance analysis results ranging from 17 m3/sec to 30 m3/sec as a realistic value.

- Optimistic scenario: The duration curve deprived from the observed river discharges from

December 2010 to November 2011 at the Hasang weir site is assumed to be representative

for long-term runoff conditions. Annual mean discharge is computed to be 28.5 m3/sec. It is

said that the year 2011 was a hydrological wet year, although annual rainfall data was not

collected during the feasibility study.

Considering hydrological conditions under both scenarios, an additional scenario was proposed as the

Average of both scenarios (named Average scenario). This scenario is to compute flow duration curve

by means of an arithmetical average of both flow duration curves. The computed annual mean

discharge in the Average scenario is 26.7 m3/sec. The average flow duration curve was used for

purpose of optimization and forms the basis for the base case of the economic and financial

analyses. The moderate duration curve was used as a conservative scenario for the sensitivity analysis

(see Sub-section 10.2.1 in the Feasibility Study Report).

The annual runoff depth is computed by dividing the accumulated annual runoff volume by the

drainage area. The annual runoff depth is computed by the following equation:

Rd (mm) = Md (m3/sec) x 60 (sec) x 60 (min) x 24 (hour) x 365 (day) / (Ca (km2) x 103)

where, Rd: Annual runoff depth



Md: Annual mean discharge

Ca: Catchment area of Hasang weir site (= 501 km2)

The runoff depth three scenarios are compared as summarized below.

Table 2.3.1 Comparison of Runoff Depth of Annual Mean Discharges at Hasang Weir Site

Moderate Scenario Optimistic Scenario Average Scenario 25 m3/sec 28.5 m3/sec 26.7 m3/sec 1,574 mm 1,794 mm 1,681 mm


As indicated above, the flow duration curve under the Optimistic scenario is only deprived from the

observed flow data at the Hasang weir site from December 2010 to November 2011. Monthly rainfall

records in 2010 and 2011 at both Bor-Bor and Silaen stations were collected. No records are available

at the remaining two stations of Bukit Likma and Maranti (see Sub-section 6.4.1). Annual basin

rainfall from December 2010 to November 2011is estimated by arithmetical mean of two stations of

Bor-Bor (2,253 mm) and Silaen (1,960 mm). The estimated annual basin rainfall is 2,107 mm.

Annual rainfall loss and runoff coefficient are computed to be 313 mm (= 2,107 – 1,794) and

0.85 (= 1,794 / 2,107). From the hydrological viewpoints, it can be said that the estimated annual

rainfall loss is apparently very small and the runoff coefficient is very large, comparing to

empirical ranges of such values reflected by hydro-meteorological characteristics in Indonesia.

As for both the Moderate and Average scenarios, annual basin mean rainfall at the Hasang weir

site is unknown because of difficulty for estimation thereof.

Under such being the case, annual water balance analysis was carried out in the feasibility study in

order to estimate plausible range of mean annual runoff depth at the Hasang weir site as described

below. This approach is reasonable from the viewpoints of hydrological analysis.

2.3.2 Water Balance Analysis

As described in Sub-section 6.4.3 in the Feasibility Study Report, simple annual water balance

formula was introduced as follows:

R = P – AET

where, R: Mean annual runoff depth at weir site (mm)

P: Mean annual basin rainfall at weir site (mm)

AET: Mean annual rainfall loss (basin actual evapotranspiration) (mm)

As indicated above, the difference between the mean annual rainfall and mean annual runoff depth is

so-called an evapotranspiration loss or annual rainfall loss.

As mentioned in Sub-section 6.4.3.1, the mean annual basin rainfall at the weir site was estimated by

GIS analysis based on the data collected for 6 gauging stations in the Hasang catchment and its

vicinity. The estimated mean annual basin rainfall was 2,150 mm. In addition the mean annual basin

rainfall with vertical precipitation gradient was estimated to be 2,130 mm. Detailed methodology for

both estimations is not mentioned in the Feasibility Study Report.



Furthermore, the estimated mean annual basin rainfall with vertical precipitation gradient was

increased by 1.25 applying as the gauge correction factor considering that most rainfall gauges are

“under-catching” due to the windfield close to the measurement device. The upper range of mean

annual basin rainfall was thus estimated to be 2,663 mm (= 2,130 x 1.25), although the rainfall

amount of 2,130 mm was assumed to be the lower range.

As for AET in the above, AET was assumed to be a linear function of potential evapotranspiration

PET as shown below. The factor “f” varies in the order of 0.7 to 0.9.

AET = f x PET

As described in Sub-section 6.4.3.2 in the Feasibility Study Report, PET was estimated to be 1,162

mm. Therefore the range of AET was estimated from 813 mm (= 1,162 x 0.7) to 1,046 mm (= 1,162 x

0.9).

The results of water balance analysis were summarized in Table 6-6 in the Feasibility Study Report as

quoted below.

Table 2.3.2 Plausible Range of Runoff Estimated from Water Balance


Based on the above, plausible ranges of the mean annual runoff depth as well as mean annual basin

rainfall at the Hasang weir site are illustrated below.



Source: based on Feasibility Study

Figure 2.3.1 Plausible Range of Mean Annual Runoff Depth at Hasang Weir Site

As indicated above, the feasibility study concluded that the mean annual basin mean rainfall varies

from 2,130 mm to 2,663 mm and the mean annual runoff depth is in the range between 1,084 mm and

1,850 mm. The average of mean annual basin rainfall is estimated to be 2,397 mm by means of

arithmetical mean of upper and lower mean basin rainfalls.

On the other hand, the figure focused below is an isohyetal map of mean annual rainfall in Sumatra

that is prepared by BMG. The catchment area of the Hasang weir site is illustrated on the map. As

seen in this map, the mean annual basin rainfall at the Hasang weir site is around 2,500 mm.

Source: BMG

Figure 2.3.2 Isohyetal Map of Mean Annual Rainfall in Sumatra Island



The table below shows the comparison of runoff coefficients at the Hasang weir site for three

scenarios assuming that the mean annual basin rainfall at the site is 2,500 mm. Runoff coefficient

becomes 0.67 under the Average Scenario.

Table 2.3.3 Comparison of Runoff Coefficient at Hasang Weir Site

Scenario Moderate Scenario Optimistic Scenario Average Scenario Mean Runoff 25 m3/sec 28.5 m3/sec 26.7 m3/sec Runoff Depth 1,574 mm 1,794 mm 1,681 mm Basin Runoff 2,500 mm 2,500 mm 2,500 mm

Runoff Coefficient 0.63 0.72 0.67

Source: based on Feasibility Study

2.3.3 Comparison of Runoff Coefficients of Various River Basins in Sumatera Island

Runoff coefficients of 16 river basins in Sumatera are available in the report of Project for Master

Plan Study of Hydropower Development in Indonesia in 2011. Runoff coefficients are compared with

mean annual basin rainfalls and mean annual runoff depths respectively as illustrated in two figures

below.

Source: based on Project for Master Plan Study of Hydropower Development in Indonesia, 2011, JICA

Figure 2.3.3 Relationship between Runoff Coefficient and Mean Annual Basin Rainfall in Various

River Basins in Sumatra Island

As shown above, runoff coefficients become large exceeding 0.6 in the river basins where mean

annual rainfalls are larger than 3,000 mm. As for the river basins same as the Kualu River basin at the

Hasang HPP Project with mean annual basin rainfall from 2,130 mm to 2,660 mm, runoff coefficient

varies from 0.45 to 0.6.



Source: based on Project for Master Plan Study of Hydropower Development in Indonesia, 2011, JICA

Figure 2.3.4 Relationship between Runoff Coefficient and Mean Annual Runoff Depth in Various

River Basins in Sumatra Island

Together with the above, runoff coefficients in river basins in Sumatera are evaluated in terms of

mean annual runoff depth. As shown above, runoff coefficient is in the range from 0.45 to 0.6 for the

river basins same as the Kualu River basin at the Hasang HPP Project with mean annual runoff depth

from 1,084 mm to 1,850 mm.

Runoff coefficient at the Hasang HPP Project under the Average Scenario is as large as 0.67 assuming

that mean annual basin rainfall is 2,500 mm. From hydrological points of view, the Average Scenario

with mean annual runoff depth of 1,681 mm seems to be overestimated. This might cause risk of

overestimation of expected annual energy production. In this respect, it is recommended that the

Moderate Scenario having the mean annual runoff depth of 1,574 mm shall be applied to

estimation of annual energy production of the Project.

2.3.4 Necessity of Long-term Monthly Inflow

As mentioned in Section 2.3.1in the above, inflow data at the Hasang weir site is available only in the

form of duration curve. No long-term monthly mean inflow data were estimated in both Pre-feasibility

and Feasibility Studies. From the hydrological point of view, inflow duration curve at the Hasang weir

site fluctuates year by year according to the fluctuation of annual rainfalls in the upstream basin

thereof. As a result, the expected annual energy generation inevitably fluctuates year by year, highly

depending on the fluctuation of inflows. Thus there is a risk of reduction of energy output due to

occurrence of hydrological drought year. In this sense, it is very important to estimate likely variation



of annual and monthly energy generation outputs in advance based on the long-term series of monthly

inflows.

Furthermore, in Section 8.3 “Planned Energy Supply and Planned Discharge” of Article 8 in the

Model PPA, it is mentioned that “At least three months prior to the Scheduled Commercial Operation

Date, SELLER shall submit PLN its desired Planned Energy Supply and Planned Discharge for the

first Contract Year”. This means SELLER should predict monthly energy generation for coming

three months. In this respect, the estimated likely variation of monthly energy production could be

very informative.

Considering the availability of flow data, the observed daily flow records at the Pulao Dogom station

from 2000 to date would be usable for prediction of monthly energy generation through in-depth

review and scrutiny of the flow data.



3. GEOLOGY

3.1 Geologic Components and their General Features

According to a published geological map “Geological Map of Pematang Siantar Quadrangle”, the

following geologic units are distributed on and around the project area.

- Alluvium (Qh)

- Toba Tuff Unit (Qvt)

- Peutu Formation, Parapat Member (Tmppt)

- Tapanuli Group Undifferentiated (Put)

Although different locations of the project areas are shown in existing reports (see Figure 3.1.1), the

bedrock of the project area seems to be Toba Tuff Unit (Qvt) and Tapanuli Group Undifferentiated

(Put).

Source: overwriting on page 7-4, Pre-FS report, March 2011

Figure 3.1.1 Project Area on Geological Map

Most of project area is underlain by the Toba Tuff Unit (Qvt); “Rhyodacic crystal-vitric ash flow

(pyroclastic flow) and air-fall (aeolian deposit) of late Pleistocene”. The Unit is roughly divided into

“Aeolian deposit VOLCANIC ASH” and “Pyroclastic flow IGNIMBRITE” as shown in existing

reports (see Figure 3.1.2).

Page 7-5, Volume 2,

Pre-FS report,

Page 95, FS report,

Switch Yard,

Attachment 7-1,

Pre-FS report

Conceivable project area



Source: overwriting on page 7-10, a part of Fig.7.5, Pre-FS report

Figure 3.1.2 Schematic Geologic Section

The distribution of the “Aeolian deposit” seems to be limited in the area of the tunnel outlet and cut-

fill section of waterway. The aeolian deposit looks originally soft and further softened due to

weathering, and N values of most of shallow sections are N=10 or less.

The “Pyroclastic flow” seems to be distributed on the foundations of major structures, except for the

tunnel outlet and cut-fill section of waterway. The pyroclastic flow is originally slightly to

moderately welded and consolidated (20 MPa to 40 MPa) with sparsely joints, while softened at

shallow portions due to weathering (5 MPa to 20 MPa). Cooling joints generally develop in highly

welded tuff, but cooling joints in tuff is sparse (30 cm to 1 m interval) in the project area, since the

degree of welding is not so high. Highly to completely portion of the pyroclastic flow is soft, like

residual soil, and there is no distinct difference in its view and property from the weathered portions

of the aeolian deposit.

Although strategic relation is not clear, the “Aeolian deposit” is distributed on high elevation. The

distribution area of the Aeolian deposit and pyroclastic flow along the downstream section of the

headrace tunnel is estimated as shown in Figure 3.1.3.



Source: overwriting on a part of Drawing HS-003-002, FS report

Figure 3.1.3 Estimated Distribution of Aeolian Deposit and Pyroclastic Flow

Another geological unit of clay stone to silt stone, which seems to be “Tapanuli Group

Undifferentiated (Put)” of Paleozoic, is distributed on the foundation of the head pond. The clay

stone to silt stone was found at Drill hole W-1 as shown in Figure 3.1.4. The Tapanuli Group seems

to be distributed on steep mountains, surrounding the project area, as well as downstream areas where

conceivable quarry site is located. The rock is hard and assumed unconfined compression strength is

40 MPa in an intact portion, while the rock pieces show flaky nature.


Figure 3.1.4 Estimated Distribution of Tapanuli Group

The above-mentioned bedrock is covered with unconsolidated sediments; Alluvium (Qh). The

unconsolidated sediments are roughly divided into talus deposits and recent river deposit. The talus

Aeolian deposit of Toba Tuff Unit

Pyroclastic flow of Toba Tuff Unit

Tapanuli Group

Aeolian deposit

Pyroclastic flow



deposits are mainly distributed on gentle slopes, and the deposits generally consist of poorly sorted

clay to silt with weathered rock fragments. The recent river deposits are distributed along river course

where river gradient is not so steep, and the deposits generally consist of silt to sand with rather fresh

rock fragments.

3.2 Headworks

3.2.1 Geomorphology and Sediments

Excavated materials are dumped into river at the Hasang 1 site, and a big volume of the excavated

materials are accumulated on gentle portion of the Kualu River. The accumulation of the excavated

materials causes the following change of condition of the river course.

- On the upstream section of the weir, boulder- to cobble-size excavated materials are

accumulated on the left side of the river course, and the water flow on the meandering section is

blocked as shown in Figure 3.2.1 and Photo 3.2.1. Although it is difficult to forecast the feature

change of water course, there is possibility that no water will flow to the intake gate of the

present design, if accumulation of the sediments continues on the left side of the upstream

section. A possible solution is to change to be straight along the thin ridge on the left abutment

as shown in Figure 3.2.2. Cost increase for excavation of the thin ridge seems not to be much,

since the ridge should be excavated for the new alignment of waterway route.

- On the downstream section the weir, boulder- to cobble-size excavated materials are

accumulated on the previous river course, and rive water course is changed to the left side,

resulting in erosion of the left bank, where paddy field was located as shown in Figure 3.2.1 and

Photo 3.2.2. Due to the erosion of the left bank on the downstream of the weir, alignment of the

waterway and desander will be shifted to the mountain side as shown in Figure 3.2.2.

Source: overwriting on a part of Drawing HS-01-002, FS report)

Figure 3.2.1 Location of Recent Sediments and Change of Water Course

Weir axis

No water flow

Photo 2.1

Waterway route

Recent

S di t

Change of water course with erosion of

paddyPhoto 2.2

Recent



Photo 3.2.1 Upstream view of Headworks Site (see Figure 3.2.1 for location)

Photo 3.2.2 Downstream View of Headworks Site (see Figure 3.2.1 for location)


Figure 3.2.2 Location of recent sediments and change of water course

Weir axis

Waterway

Alternative waterway route

Alternative weir axis

Recent

Sediments

Recent

Sediments



3.2.2 Engineering Geology

Based on the result of site reconnaissance and existing data (such as drill logs of BH-D1, BH-D2, BH-

D3, and BH-D6; see Figure 3.2.3 for the locations), no serious problem is foreseen on foundation

geology of the weir and intake structures. Points on engineering geology, including an issue on thick

river deposit, are summarized as follows.

Source: a part of Drawing HS-03-001, FS report

Figure 3.2.3 Locations of Drill Holes and Test Pits in Headworks Site

- Concrete structures of the weir and intake will be emplaced on slightly weathered pyroclastic

flow (Ignimbrite) for the most of the weir foundation as it shown in FS report (see Figure 3.2.4).

Soft materials on shallow depth, such as top soil, talus deposits, and completely to highly

weathered Ignimbrite, will be removed from the foundation of concrete. Moderately weathered

Ignimbrite will lie on some parts of the foundation, and it seems that the partial appearance of

moderately weathered rocks is not a big problem in terms of strength of the foundation. Since

continuous outcrops of highly to moderately weathered Ignimbrite are seen beside the river as

shown in Photo 3.2.3, suitable foundation of the weir and intake structures will be distributed at

shallow portions on the both abutment.


Figure 3.2.4 Geological Section of Headworks Site

A foreseeable rock line (worse case)H:V=3:1



Photo 3.2.3 Outcrop on Thin Ridge of Left abutment

- At dill hole BH-D6, recent river deposits is distributed up to 12 m deep (EL.543.246 m).

Although assumed rock line is shown around EL.548.00 on the design drawing HS-11-003,

there is possibility that recent river deposits are distributed deeper portion (e.g. 5 m deeper than

the assumed rock line) as shown in Figure 3.2.5. The actual rock line might be much deeper as

shown in Figure 3.2.4. It is better to emplace concrete onto the rock foundation at the cut-off

portion of the weir structure mainly for the preventing. If the foundation rocks lie on deeper

portion, the excavation to the foundation rocks will be difficult due to seepage water. In such

case, another issue that increases of excavation volume and concrete volume will be arisen, and

another measure for preventing leakage should be taken, instead of deep excavation. Since

grouting in recent river deposit is considered not effective; only waste of cement, and thereby, a

watertight measure in recent river deposits by grouting is not applicable. Sheet piling may also

be not applicable, since penetration of piles in recent river deposits with many boulders is so

difficult. An applicable measure may be to extend seepage path by means of adding concrete

slab to the upstream.


Figure 3.2.5 Section of Weir and Assumed Depth of Foundation Rocks

EL.543 m

Continuous outcrop



- The recent river deposits seem to have enough bearing capacity and shear strength as foundation

of the weir structure, if the materials are dominant in sand and gravel. In case that soft clay and

silt appear on excavated weir foundation, the soft materials should be removed and replaced

with concrete.

- According to Appendix-B.3, FS report “Lugeon Test [Permeability/Packer Test], permeability

of the foundation seems to be rather high; 1×10-2 cm/sec to 1×10-4 cm/sec. Based on the rock

conditions observed on outcrops and drilling core samples, the obtained values seem to be a bit

high, which may be due to leakage during the testing as illustrated in Figure 3.2.6. Standing on

safety side, permeability coefficient of 1×10-3 cm/sec will be used for seepage analysis, if the

analysis is required.

Figure 3.2.6 Possible Leakage Path on Permeability Tests

3.3 Desander

3.3.1 Geomorphology and Erosion

As described in the previous clause 3.2 Headworks and shown in Figure 3.2.1, foundation of water

way to the sediment trap facility was eroded due to change of watercourse of the Kualu River.

Based on observation during the site reconnaissance, some parts of the sediment trap facility and

connecting waterway route in the present design are located on or just beside the new river course.

Construction of facilities and embankment onto river course should be avoided, since such works are

technically difficult and costly, and the risk of erosion of the facilities and embankment is high.

The following responses are required for proper layout of the structures.

- Topographic mapping of the affected area

- Revision of geologic map and sections, based on the new topo-map

- Design review and necessary re-arrangement or re-design of structures, based on the new

topographic and geologic information

Open-mouse test (permeability test)

Lugeon test (packer test)

Overburden

Bedrock

Test sectionWater intake to be measured

Leakage, which should not occur

Overburden

Bedrock

Test sectionWater intake to be measured

Leakage, which should not occur Packer

Casing Drilling rod

Water hose



The facilities will be shifted to mountain side in order to layout then on stable foundation. Although

the cost for excavation will increase due to the shift of facilities, it is recommendable to avoid the risk

of erosion from a viewpoint of long-term stability of the facilities.


Based on the result of site reconnaissance and existing data (such as drill logs of BH-D3 to BH-D5;

see Figure 3.3.1 for the locations), some more efforts are required on the following issues.

Source: a part of Drawing HS-03-001, FS report

Figure 3.3.1 Locations of drill holes and test pits in desander site

Stability of foundation of facilities

Although the sediment trap facility and connecting waterway are not big structures, stability (mainly

bearing capacity and shear strength) of the foundations will be checked, after final layout of the

facilities are fixed. In order to utilize geological investigation results properly, it is required to show

the simplified logs of drill holes and pits on the design drawings. There is no data of the result on

existing design drawings. Although assumed rock lines are shown in some parts of HS-13-001 to HS-

13-004, no evidence for the estimation of the line is shown in the drawings.

Protection against erosion of foundation of facilities

Although the layout of facilities will be reviewed and re-designed as mentioned in the previous clause,

the risk of erosion due to meandering of the river should be taken into account, because of the

following situations.

- Wide paddy field was washed away with recent flood

- The intensity of erosion may increase, since the river bank forms a typical undercut slope due to

the recent flood

If it is foreseen that further erosion will affect the foundation of the facilities, slope protection on the

river side of the slopes will be planned. The slope protection may be concrete wall, masonry, or

gabion fixed with stiff foundation for preventing scouring at the bottom.



Slope stability on the mountain side of the facilities

Because of the following geological and geo-morphological conditions, slopes on the mountain side

of the facilities look like landslide features and might be unstable due to the excavation of the

facilities.

- Drilling result at BH-D4 and BH-D5 indicates completely to highly weathered tuff is distributed

to a depth of 20 m or more. The upper portions of the tuff look like soil and might be re-worked

materials.

- Horseshoe-shaped lines are seen and trees look disturbed on the slopes as shown in Photo 3.3.1,

and which geomorphology is similar to what develops in landslide areas.

So far, the identified landslide feature has not been confirmed as a real landslide and it can be said as

risk at present. On the existing report, there is no description on landslides, and consequently, it is

foreseen that no check on landslides have been done yet. Landslides might exist on other locations in

project areas. If landslides really exist and activate during and after construction, certain damage to

facilities might occur. The possibility of existence of real landslides can be judged somehow in detail,

with further site investigations to be conducted, and the result will be used for clarifying the degree of

the risk and necessity of measures.

Photo 3.3.1 Sediment trap facility site

Sky

Vegetation

New scarp River

Sediment

Old scarp

Terrace

Vegetation

White tree trunk

Landslide feature White tree trunk

Sketch of the photo above

Disturbance of trees



3.4 Inlet of Headrace Tunnel

3.4.1 Geomorphology

The inlet of headrace tunnel is located on a small ridge, it is judged to be a suitable location from the

following conditions.

- Small possibility of uneven earth pressure

- Small possibility of adverse effect to the inlet, due to erosion and debris flow

In case that the location of inlet is shifted to mountain side due to the re-layout of sediment trap

facility, the new location should be in a suitable area where there is no adverse condition in terms of

uneven earth pressure and erosion/debris flow.


Investigation drilling at BH-T1 has been done in the inlet site. Although drill logs and geologic

profiles of FS report show the assumed rock line at a depth of 6.7 m at BH-T1, assumed rock line on

the design drawings (HS-13-002 and HS-14-002) is at a depth of about 2 m as shown in Figure 3.4.1.

It seems that geological data was not properly taken into consideration in design.

Figure 3.4.1 Different Depth to Assumed Rock Line among Drawings at Inlet Site

The location of the inlet portal will be shifted to mountain side from what shown in the design

drawings, in order to secure enough rock cover above the tunnel crown at the inlet.

Overwriting on a part of Drawing HS-03-001

Overwriting on a part of Drawing HS-3-002

Depth to assumed rock line is 6.7 m

Distance is about 8 m

Distance isabout 8 m

Depth to assumed rock line is about 2 m

H:V=3:1 H:V=1:1



3.5 Tunnel Section of Waterway

3.5.1 Geomorphology

The headrace tunnel route lies on undulated hilly area. According to Drawing HS-03-002 of FS report,

the height elevation on the route is about 645 m with earth cover above the tunnel of about 90 m and

the lowest elevation is about 580 m with earth cover of about 25 m, except for inlet and outlet portal

section as shown in Figures 3.5.1 and 3.5.2. A straight water course lies on the location of the lowest

elevation as shown in Figure 3.5.1 and Photo 3.5.1. This water course may form a lineament,

although air-photo observation is required for the identification of the lineament.

Issues, relating to the thickness of the earth cover and the linear water course, will be described in the

next sub-clause, together with the geological conditions.

Source: overwriting on a part of Drawing HS-03-002

Figure 3.5.1 Plan of Headrace tunnel


Figure 3.5.2 Section of Headrace tunnel

Earth cover of about 90 m

Earth cover of about 25 m

The height elevation of about 645 m The lowest elevation of about 580 m

A straight water course, along which a weak zone might be distributed



Photo 3.5.1 Condition of Water Course on Lowest Portion on Headrace Tunnel


According to a geological section in drawings HS-03-006, Headrace tunnel route is underlain by

“Tuff”, “Ignimbrite”, and “Tuff”, as shown in Figure 3.5.3.

Based on observation and photographs of drilling core samples, the upper layer of “Tuff” is soft

(originally soft aeorial deposit, further softened due to weathering), look like soil as shown in Photo

3.5.2 “Ignimbrite” is slightly welded, moderately hard, and jointed with an interval of 10 cm to 50 cm

as shown in Photo 3.5.3. The rock seems to be originated in pyroclastic flow as mentioned in clause 3.

1 and Figure 3.1.3. The lower layer of “Tuff” is also moderately hard, but a little bit softer than

“Ignimbrite”, which may be due to lower degree of welding. The lower layer of “Tuff” is originally

the same rock as “Ignimbrite”, while degree of welding is lower. Some sections of core samples of

the lower layer of “Tuff” are densely jointed, but most of horizontal joints of the core samples seem to

be created with damage during drilling as shown in Photo 3.5.4.

Source: BH-T2, 5.00 m - 10.00 m, a part of page 26, Appendix D, FS report

Photo 3.5.2 Upper Layer of “Tuff” (soft, like soil)




Photo 3.5.3 “Ignimbrite” (Moderately hard, sparsely jointed)


Photo 3.5.4 Lower Layer of “Tuff” (Moderately hard, dense joints by drilling)


Figure 3.5.3 Geological Section of Headrace Tunnel

The upper layer of “Tuff” is soft and not a good foundation of tunnel, and the present design of

downstream section of tunnel (cut and fill with concrete culvert) seems suitable.

“Ignimbrite” and the lower layer of “Tuff” is moderately hard and sparsely jointed, and no serious

problem in tunnel excavation is foreseen in terms of strength of the rocks.

Points on engineering geology to be noted are as follows.

Tuff

Tuff

Ignimbrite

Groundwater level



Intercalation of Palaeo-soil and soft materials

- On the core samples of recent drilling PB-T1, two layers of palaeosoil were found, together with

palaeo-weathered zones as shown in Table 3.5.1.

Table 3.5.1 Geologic description of core sample of drilling PB‐T1

Depth (m) Geological description Geologic Unit (tentative)

- 27.0 Slightly weathered Ignimbrite Lower section of flow unit 1

27.0 - 27.2 Palaeo-topsoil

Complete section of flow unit 2

27.2 - 28.2 Palaeo-soil

28.2 - 30.0 Highly weathered Ignimbrite

30.0 - 30.2 Moderately weathered Ignimbrite

30.2 - 47.5 Slightly weathered Ignimbrite

47.5 - 47.7 Palaeo-topsoil

Upper section of flow unit 3 47.7 - 48.2 Palaeo-soil

48.2 - 48.6 Highly weathered Ignimbrite

48.6 - 50.0 Moderately to slightly weathered Ignimbrite

- The succession of palaeo-topsoil to slightly weathered Ignimbrite is a sedimentation unit of

pyroclastic flow and successive weathering before sedimentation of the next pyroclastic flow as

shown in Table 3.5.1.

- In case that palaeo-topsoil and weathered zones have been eroded before sedimentation of the

next flow unit, no clear boundary of the units can be identified.

- Considering the above-mentioned condition, there is possibility that soft materials might be

encountered during tunnel excavation.

- Based on the condition of the soft materials in core sample of drilling PB-T1, stability of the

tunnel can be secured with applying typical section for rock class IV in Drawing HS-14-004.

- In case that much softer and thicker palaeo-soil is encountered in tunnel, steel supports might be

required to secure the tunnel stability.

Thin earth cover

- As mentioned in the previous sub-clause, earth cover at middle section of the tunnel (around

Chainage 1+750) is thin, about 25 m thick.

- Referring to the result of drilling at BH-T4, the upper-half section of the earth cover may be soft

materials, and the lower half may be highly to moderately weathered Ignimbrite.

- The tunnel stability seems to be secured by applying a proper support pattern among typical

sections shown in Drawing HS-14-004. But, serious situations might occur, if the tunnel section

is in the following adverse conditions.

- A case that a weak zone (such as a fault or sheared zone) lies along straight water course (see Figure 3.5.1)

- A case that palaeo-topsoil or other soft materials is distributed at the tunnel elevation



- A case that groundwater fills the weak zone (if the groundwater is pressurized with massive cover of the upper flow unit, situation will be much worse).

- Although possibility of worse situation with combination of the above-mentioned cases seems to

be low, it is recommendable to study about measures to cope with conceivable worse situations.

Groundwater level

- In general, abrupt flush out of groundwater into tunnel cause serious accident during tunnel

excavation.

- In case of the Headrace tunnel, possibility of abrupt flush out of groundwater is not so high,

because of the following conditions.

- Catchment area is rather small, about 1 km2, as shown in Figure 3.5.4. - Groundwater level, measured in drill holes, is not so high, as shown in Figure 3.5.3.

- There is small possibility of abrupt groundwater flushing, in case of combination of the

following conditions.

- A high permeable layer such as the layer of palaeo-soil, is distributed on the tunnel route. - Confined and high-pressure groundwater exists in the layer as shown in Figure 3.5.5. - If there is indication of the abrupt flushing, such as increase of seepage water from tunnel

face, pilot drilling may be carried out to release the confined groundwater gradually as shown in Figure 3.5.5.

Source: overwriting on a published topo-map on a scale 1:50,000

Figure 3.5.4 Catchment Area of Headrace Tunnel

1 km



Figure 3.5.5 Foreseeable Groundwater Condition

Considering risks on geological conditions and others during construction, such as trouble of

machinery, it is recommendable to consider in detail about installation of work adit as mentioned in

Clause 15.2.6.1 (page 228), FS report in order to reduce the risk of extension of construction period,

since the tunnel excavation is a critical path in construction schedule.

Possible locations of the work adits and access roads are shown in Figure 3.5.6. Inclination of the

adits will be 5% to 10%, and the half of section of adits will be constructed with open excavation. A

straight water course, along which a weak zone might be distributed, will be considered as a risk.


Figure 3.5.6 Possible Locations of Work Adits and Access Roads

A straight water course, along which a weak zone might be distributed

Possible location

: Work adit

Free groundwater

Confined groundwater

Free groundwater

Pilot drilling



3.6 Outlet of Headrace Tunnel and Cut & Cover Section of Waterway

3.6.1 Geomorphology and Engineering Geology

Original ground height elevation at the outlet of the headrace tunnel is about 590 m and this gradually

comes down along the alignment of the waterway to about 560 m.

Geological investigation, at two drilling holes at BH-T5 and BH-T6 and four test pits at TP-W1 to

TP-W4, have been done at FS stage. The investigation results revealed that the tunnel section from

Chainage 2+445 to 2+760 was underlain by soft materials as summarized in Table 3.6.1, and

accordingly, the tunnel is planned to construct by cut & cover with installation of concrete culvert.

The design is judged to be suitable, and the following points will be taken into consideration.

Table 3.6.1 Summary of Laboratory Tests at Cut & Cover Site

Hole/Pit Depth (m) Water

Content (%)

Specific gravity

Shear Strength

C (kg/cm2)

φ (degree)

BH-T5 3.50-4.00 35.26 2.63 0.33 10.69

9.50-10.00 35.52 2.52 0.18 11.00

13.50-14.00 34.41 2.58 0.33 14.22

17.50-18.00 26.29 2.56 0.33 15.72

BH-T6 5.00-5.50 24.95 2.27 0.15 7.46

11.00-11.50 36.54 2.40 0.14 6.89

13.50-14.00 24.91 2.56 0.28 10.98

17.50-18.00 31.86 2.53 0.26 7.33

TP-W1 1.50 37.38 2.59 0.25 20.37

2.00 38.53 2.54 0.37 11.09

TP-W2 1.00 33.20 2.50 0.37 22.36

2.00 40.29 2.60 0.26 14.17 TP-W3 1.50 34.37 2.55 0.37 19.62

TP-W4 1.00 36.21 2.49 0.29 16.41

2.00 38.29 2.58 0.24 15.64

Average 33.87 2.53 0.28 13.60 Maximum 40.29 2.63 0.37 22.36 Minimum 24.91 2.27 0.14 6.89

Temporary slope stability measures

According to Drawing HS-14-003, the gradient of the excavated slopes is H:V=1:5. Since the height

of the slopes is more than 30 m at the tunnel outlet, and the slopes will be exposed to rain and

weathering for about 2.5 years, slope protection measures are required to secure the slope stability.

Conceivable measures are as follows.

- To apply gentler excavated slope gradient on the upper portions of high slopes, where softer

materials are distributed.

- To install surface drain ditches on berms and natural slopes above the excavation area as well as

connecting drain between drain ditches on the berms



- To cover the slope surface with shotcrete, etc. to prevent surface erosion and surface collapse

due to the erosion

- To apply nailing with steel bars to prevent surface sliding by unifying soft portions on the slopes

- To protect the lower portions of the excavated slopes with concrete wall or masonry wall to

prevent erosion on the bottom of the slopes

The above-mentioned measures i) and ii) will be added on design drawing, and measures iii) to

v) will be adopted during construction, based on the observation of the actual condition of the

excavated slope surface.

Permanent drainage of surface water

Although most of the portion of the excavated slopes will be back filled, the backfill materials are soft

and subject to erosion and infiltration of rain water. The infiltrated water and surface water may

gather at starting point of open channel, resulting in damage or disturbance with eroded materials at

the starting portion of open channel. Surface drainage on the backfill portion will be required to

prevent such adverse effect of surface/ infiltrated water flow.

3.7 Head Pond


The head pond is positioned on a rather steep mountainside. Original ground height elevation of along

the head pond axis is about 555 m.

At the head pond site, drilling investigation was carried out at BH-W1 (Z=539.234 m.a.s.l). The

result indicates the following geological condition. 0.00 m – 3.00 m : Decomposed clay stone or talus deposit 3.00 m – 5.00 m : Highly to completely weathered clay stone 5.00 m – 12.5 m : Moderately weathered clay stone 12.5 m – 15.00 m : slightly weathered clay stone

According to Drawings HS-16-002 to HS-16-004, most of concrete structure of the Head Pond will be

emplaced on the foundation after excavation of 3 m deep or more. The foundation seems to have

enough bearing capacity of the Head Pond structure.

3.8 Penstock


The penstock is laid on a gentle downhill beneath the head pond.

The foundation of penstock, including foundation of anchor blocks will be soft materials. The soft

materials seem to be two origins; aeolian deposit and pyroclastic flow as shown in Figure 3.8.1.



The aeolian deposit is originally soft and the deposit is accordingly weathered up to deep portion. At

the drilling point BH-P1, N values of the deposit are less than 10 to a depth of 12 m.

The other section of the Penstock is underlain by pyroclastic flow. The thickness of completely

weathered zone, which shows N=10 or less, is variable; 2 m to 10 m thick.


Figure 3.8.1 Estimated Distribution of Tapanuli Group

Points on engineering geology are as follows.

Stability of foundation of anchor blocks

Foundations of some anchor blocks may be soft and require deep excavation to emplace the structures

on suitable foundation.

Stability of embankment

Embankment is planned at several areas on the foundation of the Penstock. The highest embankment

of more than 10 m high is located just downstream of the Head Pond. In order to secure the stability

of the embankment, proper management of construction is required as mentioned below.

- Top soil and loosened zone on the surface should be removed.

- Method of compaction of the embanked materials, including number of passes of compactor,

should be determined, based on the compaction test. The thickness of one layer for compaction

will be 30 cm.

- Surface protection measures should be taken in order to prevent erosion of the embankment.

Rip-rap materials will be embanked on the surface.

Aeolian deposit of Toba Tuff Unit

Pyroclastic flow of Toba Tuff Unit

Tapanuli Group



- Under drain of pipe culvert should be inclined 3% or more to prevent sedimentation in the pipe.

Screen will be installed at the inlet, so that the pipe is not plugged with big rock fragments.

In case the embankment is getting unstable, serious damage to penstock is foreseen. It is

recommendable to change alignment of the penstock, so that embankment can be minimized.

Stability of excavated slopes

Access road to the Powerhouse has been constructed, it is may be for transportation of drilling

equipment, since it is too steep to use construction purpose. Although excavation for the access road

is not so big, gully erosion is seen in several places as shown in Photos 3.8.1 and 3.8.2.

Photos 3.8.1 and 3.8.2 Gully Erosion after Excavation of Access Road to Powerhouse site

3.9 Powerhouse


The powerhouse is located at the foot of the gentle slope beneath the penstock.

Drilling investigation was carried out at BH-S1 and BH-S2. Soft materials (completely to highly

weathered Ignimbrite) are distributed to a depth of 11 m at BH-S1 and 13.2 m at BH-S2. On the

riverbed of the Kualu River, continuous outcrops of moderately hard Ignimbrite are seen as shown in

Photo 3.9.1, and same good rocks will be distributed on the foundation of the Powerhouse. It is

thereby judged that there is no serious problem in engineering geology at the Powerhouse site.



Photo 3.9.1 Outcrops of Moderately Hard Ignimbrite at Powerhouse Site

Points on engineering geology are mainly on slope stability as mentioned below.

Stability of excavated slope on soil foundation

Gradient of excavated slope behind the Powerhouse are H:V=1:5 for all permanent and temporary

slopes as shown in Drawings HS-20-001 and HS-20-002. As clarified with drilling investigation at

BH-S1 and BH-S2, soft materials of 10 m thick or more are distributed on the slope behind the

Powerhouse, slope gradient on the upper portion of permanent slopes will be much gentle to secure

the stability. It is required to consider geological investigation result for the design of excavated

slopes.

Rock slide due to platy joints (cooling joints) dipping to river side

On the outcrops on the riverbed, platy joints are seen as shown in Photo 3.9.1. The platy joints seem

to be developed during cooling of welded tuff. The joints dip to river on the slope behind the

Powerhouse, and thereby, plane slide of rock mass is foreseeable on the excavated slopes. Joint

condition and slope stability of excavated rock mass should be carefully observed, and necessary

measure such as rock bolts will be taken, when indication of instability is found.

Landslide features on the left bank of the Kualu River, just upstream of the powerhouse site

Possible landslide features are identified on the topo-map as shown in Figure 3.9.1, although no

detailed site reconnaissance has been done. In case that the landslides really exit and activated during

and after construction, big amount of materials may be moving to the downstream and might

endanger the powerhouse facilities. The water course where spillway is planned may be the boundary

of the landslide masses. Water, to be flowing along spillway, might infiltrate into ground and activate

the landslides.

Direction of platy joints



It is recommendable to carry out detailed investigation on landslide. The first step of the investigation

is site reconnaissance to clarify the evidence of the landslides. If certain evidences are found, further

investigation such as some more detailed topo-mapping and drilling investigation with laboratory test

and monitoring will be done as the second step for proper measures.


Figure 3.9.1 Possible Landslide Features just upstream of Powerhouse Site

Possible landslide features



3.10 Suggestions and Recommendations

From the geomorphologic and geological viewpoints, suggestions and recommendations are made as

follows.

a) Adjustment of axis of intake weir

Because of a big amount of recent sedimentation, river course is changed. Taking account of the thin

ridge on the left bank also, it is recommendable to consider changing the location of the intake as well

as the alignment of weir axis.

b) Adjustment of location of sediment trap facility and connecting waterway route

The recent sediments also affected downstream course of weir site, where the de-sander is planned.

Some of the area of the de-sander seems to be eroded due to the change of the river course, and there

is no enough space to layout the facility. It may be necessary to shift the de-sander to the mountain

side to meet geomorphology changed recently.

c) Landslides on the areas of de-sander and powerhouse

Possible landslide features are identified at the sites of de-sander and powerhouse. Although those

features have not been confirmed as real landslides, it is recommendable to check the possibility, in

order to minimize the risk of the landslides.

d) Addition of work adit

Several issues are arisen on engineering geology of headrace tunnel. Although the issues are not so

serious, it is possible to encounter difficulty in tunnel excavation due to combination of several issues.

Considering that the tunnel construction is the critical path in construction schedule, it is

recommendable to consider to add work adit.

e) Alignment of penstock route

Several issues are arisen on engineering geology of penstock route. In order to minimize risks

relating to penstock, it is recommendable to consider changing alignment of the penstock.

f) Others

The re-study or re-design on the following issues may be done for smooth construction works.

- To fix the location of tunnel portal, based on geological investigation results

- To install drain system of surface water on the cut & cover section of waterway

- To check excavated slope gradients, based on the geological investigation results



4. POWER GENERATION

4.1 General

In the Feasibility Study, the energy simulation was carried out based on the hydrological analysis and

the feasibility design for the following two scenarios.

Table 4.1.1 Two Scenarios for Energy Simulation

Scenario Hydrological Duration Mean Annual Energy Mean Annual Energy with Loss

Base Case Average (26.7 m3/s) 288.32 GWh 275.53GWh Conservative Case Moderate (25.0m3/s) 260.53 GWh 248.98 GWh

Source: Chapter 10.4 of Feasibility Study

Hereinafter discussed are NK’s comments on the input parameters for the energy simulation adopted

in the Feasibility Study, and possible impact to such simulation due to review result of the hydrology

as well as the project layout of the Study.

4.2 Project Layout

Before we examine the energy simulation, we need to discuss if the project layout proposed in the

Feasibility Study is optimal or not. The most critical issue is the penstock length of the Project.

4.2.1 Stability of Penstock

The penstock length proposed in the Feasibility Study is 1,669m against the design net head of

189.27m. This penstock length is too long to obtain the stability of penstock with a reasonable fly

wheel effect of the generators (GD2).

Assuming that this power plant is required to be used for frequency control and/or capable for isolated

operation, stability of penstock is checked by the following formula.

where,

Tw : Starting up time of water column (s)

L : Length of waterway (penstock) (m)

V : velocity of water (m/s)

g : Acceleration of gravity (m/s2)

H : Design head (m)

22

00274.0 22

TmTw

P

NGDTm

gH

LVTw

t



Tm : Starting up time of unit (s)

GD2 : Flywheel effect of generator (ton-m2)

= 310,000 * (Pg/N1.5)1.25 (Water Power & Dam Construction)

N : Rotational speed (rpm)

Pt : Turbine output (kW)

Pg : Generator output (MVA)

Tm = 4.41 > 2 Tw^2 = 58.46 (not OK)

Based on the present data, the stability of waterway (penstock) is not secured and large GD2 (537 t-m)

will be required. It is impossible.

If stability of waterway is not satisfied, there is high possibility to be instable in power generation

operation such as frequency will be fluctuated exceeding the required limit and power output also will

be fluctuated when demand is changed.

To overcome this issue, two (2) alternatives are conceivable:

Alt-1-1: To shift the head pond to the river side

Alt-1-1 is to shift the head pond to the river side as much as practicable topographically and the

penstock is started there. In this layout, the headrace channel will be constructed on the embankment

and the head pond will be rather high structure. The head pond might be shifted to where anchor

block P2-P3 are located then length of the penstock will be about 1,200m.

General layout of Alt-1 is seen in Figure 4.2.1. Even in this case, however, stability of the penstock is

not satisfied and requires GD2 of 278 t-m. This is still too large.

Alt-1-2: To provide a surge tank between the head pond and the powerhouse

Alt-1-2 is to locate the head tank at the same location as the present design. The pressured headrace is

started at the head pond. The pressured headrace is connected to the surge tank which is located

around at EL. 500m and the penstock is started there for about 450 m length. The pressured headrace

will be of steel. The surge tank will be of a high structure of steel or pre-stressed concrete. General

layout of Alt-2 is seen in Figure 4.2.2. Cost of the surge tank is roughly estimated at US$ 3 mil.

4.2.2 Pressure Rise

Even in case that this power plant is not required to be used for frequency control and/or isolated

operation, and thus stability of penstock is not a matter of issue, the long penstock will cause another

problem; that is, an excessive pressure rise due to the water hammer. To overcome this issue, three

(3) alternatives are conceivable.

Alt-2-1: To add GD2 so as to allow slow closing of guide vane



Alt-2-1 is to add GD2 so as to allow slow closing of the guide vane to prevent severe pressure rise. To

limit the maximum pressure rise at 35 %, the required GD2 in case of the original layout is 106 t-m,

which is judged still applicable. Cost of the additional weight of the generator is roughly estimated at

US$ 9 mil.

Alt-2-2: To adopt Pelton type turbines instead of Francis type turbines

Alt-2-2 is to adopt the Pelton type turbines, instead of the Francis type turbines. Although this type is

essentially a high head turbine, the planned discharge and the head of the Project are plotted near the

boundary, but within the application range, of the Pelton type turbines. The Pelton type turbines are

equipped with jet deflectors which allow slow closure of the needle.

Disadvantage of the Pelton type turbines is that they must be installed above the highest probable

taiwater level which may sacrifice the available head. Also the efficiency at the peak discharge is

lower than the one of the Francis type turbines. Loss of energy due to these reasons is roughly

estimated at 5.5% of the total energy. This is equivalent with additional cost of US$ 4 mil.

Alt-2-3: To adopt the pressure regulator (pressure relief valve)

Alt-2-3 is to attach pressure regulators (pressure relief valves) to the Francis type turbines to release

the excessive pressure rise induced by any rapid closing. This option, however, is not recommended

as high reliability is required for the devices. If malfunction occurs, the whole system of the Project

will be jeopardized.

Comparison of the alternatives are seen in Table 4.2.1.

Table 4.2.1 Alternatives for Penstock Issues

Alternatives Advantage Disadvantage Assessment1 Stability of Penstock

Alt.1-1 To shift the head pond to the river side

No substantial impact is caused to energy production.

Required GD2 is still too large.

×

Alt.1-2 To provide a surge tank between the head pond and the powerhouse


Cost will be increased for Surge Tank

◎

2 Pressure Rise Alt.2-1 To add GD2 so as to

allow slow closing of guide vane


Cost will be increased for larger GD2

△

Alt.2-2 To adopt Pelton type turbines instead of Francis type turbines

No substantial impact is caused to project cost.

Energy production will be decreased.

○

Alt.2-3 To adopt the pressure regulator (pressure relief valve)


In case of malfunction of Pressure Regulator, the system will be jeopardized.

×

Source: NK

Preliminary comparison of impact to project cost and energy production as well as the risk above

reveals that Alt. 1-2 is the most recommendable option.



Source: Overwriting on drawing in Feasibility Study

Figure 4.2.1 Layout of Alt. 1‐1


Figure 4.2.2 Layout of Alt. 1‐2



4.3 Power Generation

4.3.1 Hydrological Duration

As discussed earlier in chapter 2.3, it is evaluated that the Average Scenario which was adopted in the

Feasibility Study Report is rather overestimated and the Moderate Scenario is therefore recommended

to apply for estimation of the annual energy production by the Project.

4.3.2 River Maintenance Flow

A river maintenance flow (or duty flow) of 1m3/s constant over the entire year was proposed in the

ESIA and thus was taken into account for the energy simulation in the Feasibility Study.

In the past, there was no regulation in Indonesia on how much maintenance flow is required for the

hydropower plants. The latest hydropower master plan study by JICA in 2011 titled “Project for the

Master Plan Study of Hydropower Development in Indonesia” adopted a rate of the minimum flow

release at 0.2 m3/s per 100 km2 of catchment area above the intake weir. This rate was set referring to

other hydropower projects constructed or being constructed in Sumatra.

In Japan, the rates of 0.1 m3/s - 0.3 m3/s per 100km2 of the catchment area are adopted as the

guideline issued by Ministry of Land, Infrastructure, Transport and Tourism for renewal of permission

of hydropower business.

Taking account of the above as well as the catchment area of 501 km2 for the Project, it is reasonable

that the river maintenance flow was set at 1.0 m3/s in the Feasibility Study.

Meanwhile, article 25 of the government regulation No.38, 2011 regarding the River stipulates that

the river maintenance flow would be the 95% dependable river runoff. It is unclear to which extent

this regulation will be applied for run-of-river type hydropower or if any exclusion from application

exists or not. Due to that uncertainty, it is suggested that the annual energy production will be

estimated assuming the river maintenance flow for the both cases of; i) ESIA, and ii) Government

Regulation No. 38, 2011.

4.3.3 Loss

The energy loss, which is physical and/or imaginary energy not being delivered to the off-take point,

is reasonably taken into account in the Feasibility Study. The total loss assumed was 4.5% to the

theoretical maximum energy generation after deducting the river maintenance flow. It is composed of

reasonable figures; 1.5% for outage, 1% for sediment removal, and 2% for station use.

It is of paramount important for the investors to understand that the river maintenance flow would

bring about fatal damage to the Project profitability, if it is of the 95% dependable river runoff.



4.3.4 Mean Annual Energy

With taking account of the hydrological duration, the river maintenance flow (or duty flow) and the

loss above, the saleable mean annual energy of the Project for checking the project feasibility would

be:

Table 4.3.1 Comparison of Annual Energy

Description Unit Base Case Low Case Reg No. 38

1. Hydrology Series - Average Moderate Moderate

2. River maintenance flow m3/s 1.0 1.0 6.7

3. Installed Capacity GW 42.45 42.45 42.45

4. Theoretical Mean Annual Energy GWh 288.3 260.5 190.7

5. Availability % 98.5 98.5 98.5

6. Available Maximum Annual Energy GWh 284.0 256.7 187.9

7. Station Loss (2% of 6.) GWh 5.7 5.1 3.8

8. Spillage Loss GWh 2.8 2.6 1.9

9. Saleable Mean Annual Energy GWh 275.5 249.0 182.3

10. Plant Factor % 74.1 67.0 49.0

‘Base Case’ and ‘Low Case’ correspond to Annex 17.3 and 17.4 of the Feasibility Study, respectively.

‘Reg. No. 38’ corresponds to the case when the Government Regulation No.38, 2011 is strictly applied to ‘Low Case’.

Source: based on energy simulation in Feasibility Study and Review Team



5. DESIGN ISSUES: ACCESS ROAD

5.1 General

The Feasibility Study identified that a total of approximately 7 km of exiting unpaved/partly paved

road will need to be upgraded and 5 km of new permanent access roads will be newly built. Among

them, the main roads to be upgraded and/or newly built are as follows.

Table 5.1.1 Main Access Roads to be Upgraded and/or Newly Built

Route Length Existing Condition Janji to Sipultak 1.8km Mostly unpaved Sipultak to Halilogoan (Head Pond) 1.95km Unpaved Harilogoan to Dolok Barimbing 2km Unpaved Dolok Barimbig to Powerhouse 1.2km Unpaved Access to road to weir site 1.5km To be newly constructed


5.2 Access Road

The followings are commented as the result of the site reconnaissance and the desktop review.

- Access to Parsoburan from Medan through the existing road is good, betterment will not be

required. However, notice and permission of police and related organization should be made and

obtained when transportation of heavy equipment.

- According to the present design, the access road from Janji to near the head pond, the existing

road will be widened and paved in the same route. However, several sections of the existing

road are very steep in longitudinal gradient and too small horizontal radius. Thus, trailer to

transport heavy equipment cannot pass. Construction of new road by re-route or improvement of

vertical alignment for these sections will be necessary. Additional land acquisition will be

required. In addition, loading capacity of bridge and box culvert should be checked.

- The above access road is belonging to Kabupaten Road at the moment, it is recommended to be

clear responsibility of repair and maintenance during construction and after construction

(operation stage).

- New access road from the head pond to the powerhouse will be constructed in the same route of

the existing access road which was used in the investigation stage. However, this road is also too

steep, it should be re-routed.

- Application of Type-1 and Type-2 shown in HS-30-004 should be clear. Typical width of

pavement is 6.0 m. It can be reduced to 4.5 m. For passing vehicle each other, preparation of a

passing bay every 500 m interval is recommendable.



6. DESIGN ISSUES: CIVIL STRUCTURES

6.1 General

The Feasibility Study formulated the Project with the following main civil structures.

Table 6.1.1 Main Civil Structures of the Project

Main Structures Description Intake Weir A fixed overflow weir, including two sediment flushing gates at the

left bank Power Intake At the left bank, equipped with trash rack Intake Channel A free flow system for a design discharge of 25 m3/s De-sander Consisting of three surface basins and flushing facilities to remove

particles >0.3mm Headrace Tunnel 2.76 km long, concrete lining at invert and walls Headrace Channel 1.15km long open channel, U-shape, 4.0mW x 4.0mH Head Pond and Spillway NOL: EL.555.0m, design discharge of spillway at 27.5m3/s Penstock 1.67km long, 2.3m dia. Powerhouse Surface type equipped with 3 x 13.4MW Francis units, transformers

and switchyard, TWL: EL.347.9m


Hereinafter discussed are NK’s comments on the design of the civil structures adopted in the

Feasibility Study.

6.2 Intake Weir and Power Intake

6.2.1 General Layout

According to the actual site conditions observed on January 18, 2013, the left river bank in

downstream of the intake weir site in which the intake channel and de-sander are located, was eroded

and slid down. The present layout of the intake channel and the de-sander cannot be situated, and it

should be confirmed by survey.

Further, the ridge in the left bank in which the intake is located is rather thin. After excavation of

abutment of the intake weir and the intake, the remaining sound rock become be very thin.

As countermeasure for above items, change of layout of these structures including weir axis is

recommended. (refer to Figure 6.2.1)

According to the design in the feasibility study, the curved overflow weir in the center is designed as

curvature alignment. It is rather complicated for construction and water flow in flood condition will

be turbulent. More simple alignment is desirable. Change of layout is justified from this viewpoint.



Eroded left river bank (location of Intake Channel & De-sander)

Ridge of Left abutment of Intake Weir and Power Intake

Photo 6.2.1 Situation at Intake Weir and Power Intake


Figure 6.2.1 Proposed Layout

6.2.2 Impact due to Development in Upstream

There are many big boulders at the intake weir site. According to the site inspection on January 17,

2013, almost of all of them are derived from the construction works of the hydropower station in

upstream. Excavated materials of about 1.8 km long waterway (Open Channel), penstock and

powerhouse were thrown into river. (It is clear because no Spoil Bank was observed.) The excavation

works was still underway and progressed about half. The construction works of the said power station

are suspended at the moment. Construction schedule of it in future should be confirmed. When the

construction works will be resumed, it is recommended strongly to stop the spoiling of excavation

materials to river. Otherwise, the Intake Weir will be filled up the excavated materials soon.

Weir axis

Waterway

Alternative waterway route

Alternative weir axis



These boulders shall be removed to downstream prior to start of the construction works as much as

possible.

In order to prevent entering such boulders in front of the power intake. It is recommended to construct

some debris barrier structure in the upstream. (refer to Figure 6.2.2.)

Intake Weir (Only half was completed) Victoria Fall

Excavation of Headrace Channel (suspended) Excavation of Powerhouse (Additional boring is being undertaken)

Photo 6.2.2 Construction Works in Upstream

Source: Overwriting on topographic map in Feasibility Study

Figure 6.2.2 Debris Barrier Struture



6.2.3 River Diversion

25 years probable flood of 480 m3/s is applied for design flood for the river diversion. Considering

the construction period of the intake weir about 1 year and the concrete weir, 2-5 years probable flood

is enough. However, as examined in the Hydrology, the probable flood discharge is deemed to be

estimated lower side. Then, using of the present design discharge is still acceptable.

Re-layout of the intake weir may omit the dividing wall which was positioned at the boundary of the

straight and curved overflow spillways in the Feasibility Study.

6.2.4 Hydraulic Design

As mentioned in Sub-section 12.3.1.3 in the Feasibility Study Report, the 100-year flood discharge

was used as various load cases for hydraulic design of the weir structure as follows:

- Design flood: 100-year flood with all gates open

- Check flood: 100-year flood and one gate not operational (n-1 rule)

- Safety check flood: 1.5 x 100-year flood with all gates open

The design flood water levels estimated from the original 100-year flood are given in Sub-section

12.3.5.3 in the Feasibility Study Report as summarized below.

- Water Level Design Flood (HQ100, n): 560.0 m a.s.l.

- Water Level Check Flood (HQ100, n-1): 560.7 m a.s.l.

- Water Level Safety Flood (1.5 x HQ100, n): 560.9 m a.s.l.

Due to the underestimate of 100-year flood discharge, design flood water levels in the above shall be

increased to some extent. Therefore it is necessary to make hydraulic calculation design again.

According to the feasibility report (see Sub-section 12.3.5.3), the crest elevation of embankment at the

intake weir was determined at 561.5 m a.s.l. with a freeboard of 0.6 m given during the Safety Flood

(561.5 = 560.9 + 0.6). Therefore the crest elevation of embankment shall be increased applying the

same freeboard from the safety viewpoint of Hasang weir.

Besides the above, due to an increase of the 100-year flood discharge from 539 m3/sec to 1,000 m3/sec,

the following design water levels and associated hydraulic design calculation shall be carried out by

use of HEC-RAS software as applied in the feasibility design.

- Tail water levels (see Sub-section 12.3.5.1): Figure 12-7, Figure 12-8, Table 12-3

- Weir capacity (see Sub-section 12.3.5.2): Figure 12-8

- Check for un-submerged flushing conditions (see Sub-section 12.3.5.4)

- Stilling basins (see Sub-section 12.3.5.5)



Two sets of radial gate are proposed at the weir site in the feasibility study, one of which is with a flap

gate. Due to an increase of the 100-year flood discharge, maximum flood water level in time of the

increased 100-year flood would increase from the designed water level in the feasibility study.

It might cause submergence of pin structures of radial gate. It is recommended to review on selection

of gate type through hydraulic design. If risk of submergence occurs, slide gate shall be recommended

to avoid submergence from the safety viewpoint of gate operation.

6.2.5 Structural Design

Stability

Stability analysis of the fixed overflow weir was made together with stilling basin. The weir and

stilling basin structures should be separated by the contraction joint. And then, stability analysis

should be made separately. (refer to Figure 6.2.3) Location of contraction joints and details of them

for the intake weir and related structures should be clearly shown.

Up lift of the weir foundation in stability analysis is not uniform. Uplift of upstream of the grout

curtain should be full water depth.


Figure 6.2.3 Contraction Joint of Overflow Weir

Piping

Safety against piping for several sections of foundation should be checked. (refer to Figure 6.2.4)

In the left abutment, outcrop of Ignimbrite is observed and it is rather weathered and soft. In the

present design, abutment wall is designed, it is reasonable but buck-fill materials should be

impervious materials and cut-off wall maybe requested in order to align the grout curtain line up to

abutment continuously, also. The same recommendation is given in the left abutment.




Figure 6.2.4 Curtain Grout Line and Study of Piping

Others

If key cut-off is shifted upstream by about 2.0 m,

the grouting works can be done from the toe of

Weir after concrete placement and shorten the

construction period. The curtain grout maybe

omitted if further geological investigation proves

that the permeability of the foundation rock is low.


Figure 6.2.5 Curtain Grout Line

6.3 Intake Channel and De-sander

6.3.1 Consideration on Geological Aspect

The intake channel and de-sander will be constructed on Tuff, Soil Materials and Ignimbrite.

According to core logs of BH D-3, D-4 and D-5, foundation of the channel and de-sander will be

constructed on the foundation more than 50 in SPT, however actual location of the channel and de-

sander is more river side. Geological conditions at the actual site should be confirmed and some



special treatment of the foundation such as replacement of concrete with poor soil will be required.

(refer to Figure 6.3.1). Possibility of landslide is also an issue as discussed in chapter 3.3.


Figure 6.3.1 Location of Geological Investigation

6.3.2 Intake Channel

The intake channel has two curves and can be modified to more simple alignment with one curve.

6.3.3 De-sander

The de-sander has three (3) basins in the Feasibility Study, meanwhile two (2) basins de-sander is

conceivable to simplify the structures.

Structure of the inlet of the de-sander is rather complicated, simple structure is desirable.

The stoplog in front of gate at the inlet is not necessary always because this gate is opened in normal

condition and maintenance/repair will be done easily. In the contrary, a gate will be necessary at the

end of the de-sander, otherwise, water come into the sand trap basin from downstream during flushing

operation and flushing will be not done effectively.

Flushing channel under the de-sander is recommended to be constructed with embedded steel liner

which is act as form work because this structure is small and complicated.

Typical section of the Flushing Channel to the river is recommended to wider section and with energy

killer.



Location and details of the contraction joint shall be shown.


Figure 6.3.2 Comments on De‐sander

6.4 Headrace Tunnel


About 1,500 m long out of 2,445 m of the headrace tunnel will penetrate the Tuff layer below the

Ignimbrite. According to the geological investigation, this Tuff is fresh and hard, however RQD of

cores are not so high and shows high permeability having 100 Lu value or more.

After boring core observation on January 18, 2013, it was judged that difference between Ignimbrite

and Tuff layers is not significant and the Tuff layer below the Ignimbrite is sound for tunnel

excavation.

If the Tuff layer shows high permeability, careful grouting surrounding rock and or membrane behind

concrete lining is recommendable.

Meanwhile, the followings should be noted as the risk factors for tunneling as described in Chap.3.5.

- Intercalation of Palaeo-soil and soft materials

- Thin earth cover

- Groundwater level



6.4.2 Structural Details

Sequence of concrete placing, bottom slab is placed in advance and both side walls are followed, is

reasonable. However, haunches at the lower corners are difficult to construct and can be omitted.

(construction method) (refer to Figure 6.4.1)

Drilling of drain holes shall be decided carefully. Permeability of tuff layer shows high value.

Joint arranged every 12 m requires water stop.


Figure 6.4.1 Concrete Lining of Headrace Tunnel

6.5 Headrace Channel


According to the core observation of BH T-6, the Tuff layer above the Ignimbrite is very weak and

tunnel heading stand by itself is questionable. The end point of tunnel shall be decided based on the

actual conditions during construction.

Excavation slopes of the cut and cover section and of the Headrace Channel are too steep. For the

former, 1 to 0.5 or more gentle slope is recommendable, even it is temporary. For the latter, 1 to 1.0

more gentle slope is recommendable if no protective measure. (refer to Figure 6.5.1)




Figure 6.5.1 Excavation Slope and Embankment


Backfill to the original ground at the cut and cover section is not necessary. It cause bigger earth

pressure. (refer to Figure 6.5.1) As for materials, excavated site materials, mainly weathered tuff, is

not suitable. Excavated tunnel muck (ignimbrite) and/or river deposit are recommendable.

Design of crossing structures such as pipe culvert and bridge should be made. Especially, size of pipe

culvert should be decided carefully taking flood water into consideration. (refer to Figure 6.5.2)


Figure 6.5.2 Cross Drain and Bridge

6.6 Head Pond and Spillway

6.6.1 Head Pond

The followings shall be noted:

- Protective measure such as shot-crete or sodding against erosion on the excavated slope is

required.

- Width of rock trap shall be wider to 2.0m.



- Access Road shall be extended to gate and raking operation yard. (refer to Figure 6.6.1)

- Operation yard of Head Pond Release Gate shall be widen and accessible. (refer to Figure 6.6.1)

- Gravel Sluice Valve should be protected and accessible. (refer to Figure 6.6.3)


Figure 6.6.1 Head Pond Gate Operation Yard

6.6.2 Spillway

- Guide wall of the spillway at the beginning shall be higher. (refer to Figure 6.6.2)

- Longitudinal profile of spillway is not shown, should be clear.

- Application criteria of standard section of Type -2, 3, 4 and 5 are not clear. Type-3 should be

applied at the end portion only. (refer to Figure 6.6.4)

- As for embankment materials, excavated site materials, mainly weathered tuff, is not suitable.

Excavated tunnel muck (ignimbrite) and/or river deposit are recommendable.




Figure 6.6.2 Comments on Head Pond


Figure 6.6.3 Embankment and Cross Drain of Spillway


Figure 6.6.4 Typical Section of Spillway



6.7 Penstock


Geology around penstock site is composed on top soil and weathered tuff and erodible by water. All

excavated surface shall be protected by wet rubble masonry/shotcrete/sodding.


As discussed in chapter 4.2, provision of a surge tank is suggested to ensure i) stability of penstock for

frequency control and ii) avoidance of excessive pressure rise. Preliminary check indicates that the

diameter and the height of the surge tank will be about 10m and 65m, respectively. Additional survey

of topography and geology along the penstock line is required for further examination.

Followings are noted as the comments for the design in the Feasibility Study.

- Alignment of the Penstock shall be straight, especially at the end portion as much as possible.

- Arrangement of diameter (average 2.3 m) is recommended to first one-third : 2.5m, second one-

third : 2.3 m and last one-third :2.1m.

- Water Hammer (Pressure Rise) by emergency stop of turbine is not considered to design of the

Penstock. Water Hammer at the emergency closing of turbine should be calculated.

6.8 Powerhouse and Switchyard

6.8.1 Hydraulic Design

Probable flood of 100-year shall be revised to 1,000 m3/s, then the elevation of the powerhouse yard

shall be set to ensure safety against this flood.


A coffering of the powerhouse construction is difficult because of rapid river flow. Remaining of the

original ground is recommendable measure. (refer to Figure 17)

Location of the draft gate can be shifted to upstream to minimize the powerhouse structure. (refer to

Figure 16) However, if draft tube requests such length, location of draft gate cannot be shifted.

Elevation of the erection bay of P/H and the end of Access Road are set at EL. 351.75. On the other

hand, the upstream end of the tailrace wall is set at EL. 355.00. Flood water will flow into the

Powerhouse through the erection bay. A guide wall along the Access Road is required.(refer to Figure

16 & 17)

The supporting column of the overhead crane girder is about 19 m high without horizontal strut.

Detail structural analysis is needed. (refer to Figure 16)




Figure 6.8.1 Powerhouse Layout


Figure 6.8.2 Coffering of Powerhouse



7. DESIGN ISSUES: HYDRO-MECHANICAL WORKS

7.1 General

Hereinafter discussed are NK’s comments on the design of the hydro-mechanical works adopted in

the Feasibility Study.

7.2 Penstock

The length of standard erection piece should be longer as far as possible to minimize the number of

site welding joint. Unit pipe length should be decided from the available plate width in Indonesia.

The wider plate is preferable to make longer unit pipe.

The required plate thickness should be studied taking the local stress at saddle support into

consideration.

The method of supporting should be studied to lengthen the supporting span of penstock more than 12

m to minimize the number of concrete saddles. The ring girder support is advantageous compared

with the saddle support proposed in FS report.

According to the direction of vertical bend, a half block may be adopted for the anchor block.

Instead of trifurcation, a manifold type branch should be studied from the point of view of hydraulics

and alignment of the penstock.

Stainless steel plate should be adopted instead of stainless clad plate taking account of less

marketability of stainless clad plate.

Considering the construction time, the comparison study should be made between the erection using

winch and the direct unloading by the mobile crane, although an access road is required along the

penstock line in case of erection by mobile crane.

Taking account of the construction time, three sections should be considered for the erection of steel

penstock to shorten the duration of construction.

As for the upper part of penstock, the application of readymade steel pipe might be considerable, if

such pipe is available in Indonesia market with lower cost compared with the cost of ordered pipe.

7.3 Hydro-mechanical Equipment

7.3.1 Spillway Gate

The vertical lift gate type should be compared with the radial gate as the spillway gate.

Considering the dimensions of radial gate, the mechanical type hoist, namely the wire rope winch

seems to be economical and familiar for the Indonesian operator to maintain the equipment rather than

the hydraulic hoist.



The gate leaf with flap gate is complicated for operation and maintenance. The flap should be

cancelled. For the river maintenance flow, it is preferable to install the required gate of capacity with

small dimensions. Or the spillway gate will be opened partially to discharge.

The box culvert should also be studied as an alternative plan of sediment flushing.

7.3.2 Raking Equipment and Trashrack

The type of raking equipment should be selected from the characteristics of trash. The disposal of

trash raked up should be well considered for the actual operation. (Intake and inlet of penstock)

The location of trashrack should be decided to prevent the trash from depositing in the bay in front of

trashrack. (Intake)

7.3.3 Intake Gate and Stoplog

Though two intake gates are installed, it seems that one gate is enough.

The water seal of gate leaf should be studied which is suitable the upstream or downstream system.

Instead of curtain wall for intake gate, the full height gate against the high water level is considerable

with three edges upstream water seal system.

From the scale of gate leaf, the mechanical hoist such as wire rope winch or spindle type hoist is

suitable instead of hydraulic hoist.

Considering the operation of intake, stoplog for intake gate will be eliminated.

7.3.4 Penstock Inlet Gate

Though the slide type of gate is selected, the supporting type of slide or wheel should be studied for

suitable type of emergency closure. Accordingly, the hoist type should also be re-examined.

The emergency closure by self-weight should be re-examined because the dead weight of gate leaf

seems to be short for overcoming against the friction during closure.

7.3.5 Draft Tube Gate

Some temporary draft tube gates should be considered if necessary during the construction period.



8. DESIGN ISSUES: ELECTRO-MECHANICAL WORKS

8.1 General

Hereinafter discussed are NK’s comments on the design of the electro-mechanical works adopted in

the Feasibility Study.

8.2 Type of Turbine and Number of Units

Considering the penstock length of 1,669 m in the Feasibility Study, it is considerable that type of

turbine would be changed to; i) Pelton turbine, or ii) Francis turbine with a pressure regulator

(pressure relief valve) in order to decrease the momentary pressure rise in the penstock and turbine

for economical design. However, taking account of ensuring stability of the penstock for frequency

control, it is suggested to shorten the penstock length by providing a surge tank as discussed in

chapter 4.2.

Horizontal-shaft Francis type turbine was proposed in the Feasibility Study for 207 m head and 14.5

MW output. In accordance with normal design practice, vertical-shaft Francis turbine is usually

selected for these ratings. Horizontal-shaft Francis turbine will have a disadvantage for the

powerhouse layout to arrange the required additional space for removal of the rotor and shaft

assembly from the generator.

Three (3) numbers of units are proposed in the Feasibility Study. Generally speaking, less number of

the turbine - generator units would be more economical, which depends on balance of reduction of

cost and energy. It is suggested that suitable number of units shall be confirmed along with change of

the turbine type.

8.3 Equipment Layout

8.3.1 Powerhouse

Installation Space between Uits

Referring to Drawing No. HS-20-005, there seems no sufficient space for removal of the rotor and

shaft assembly from the generator.

In case horizontal-shaft turbine is used for this project, the space between the units shall be widened

by at least 2 m and the space between Unit 3 and the powerhouse side wall by at least 2 m.

Control Room

Size of the control room is 10m x 4m. Space seems not enough. At least the size shall be doubled.



Panels of only “14 Protection” and “15 Synchronisation” are shown on the drawing. However,

operator console, mimic board, programmable controller, energy meters, low voltage panels, logging

printers etc. shall be needed.

In PLN’s normal practice, SCADA is to be introduced, and sometimes independent communication

room may be needed.

Swichgear Room

Size of the switchgear room is 8m x 3.65m. Space seems not enough. Panels of only “Low voltage

distribution board” are shown on the drawing. The spaces between such Low voltage distribution

board are at present 0.9m only. This shall be doubled.

Location/space for 11kV cubicles shall be confirmed.

8.3.2 Switchyard

Size of the switchyard is 115 x 80m. The size of the switchyard is large enough. However, if

double-pi connection (4 circuits towers) mentioned in Pre-FS Report for 150kV TL, is employed, two

more transmission line bays become necessary.



9. DESIGN ISSUES: TRANSMISSION LINE

9.1 General

Comparison of different options to connect the Project with the existing transmission line system in

North Sumatra was once studied by PLN. As the result, the option to provide an interconnection point

to 150 kV transmission line at Kampung Pajak (between Aek Kanopan substation and Rantau Prapat

substation) was found to be the most suitable option for PLN. The Feasibility Study Report of the

Project (Apr., 2012) envisaged a double circuit ACSR 240 mm2 150 kV transmission line of 34.5 km

length would lead from the Project to the new Kampung Pajak substation which PLN would finance

for construction.

In the Pre-Feasibility Study for 150 kV transmission line for the Project (Sep., 2012) by BNE, the

interconnection point was again studied among the alternatives, then connecting to the existing tower,

not to the new substation, at Kampung Pajak was proposed.

9.2 Transmission Line

Connecting to Porsea, Aek Kanopan, or Rantau Prapat substations will need new transmission lines of

long distance, and apparently not feasible. It is conceived that the selected option in the Feasibility

Study to provide the new Kampung Pajak substation and the Project is connected to there is

technically the best solution, even though the construction cost of the new substation becomes

necessary. Installing circuit breakers at the connecting point of the new transmission line from the

Project to the existing line is preferable for the point of view of protection and operation.

This option was by some reasons discarded in the Pre-Feasibility Study for 150 kV transmission line,

and connection to the existing tower at Kampung Pajak by Single-pi connection or Double-pi

connection was proposed.

Single-pi connection has problem in reliability of transmission, and thus not recommendable.

Meanwhile Double-pi connection requires necessity of 4 circuits, and the price of transmission line

becomes high.

Hence, it is recommended that the comparison of construction of new Kampung Pajak substation and

Double-pi connection (4 circuits towers) are to be made again for the final decision. At present, there

may be increase of demands of rural area in Kampung Pajak.

It is noted that, if the new transmission line from the Project is connected to the existing line by a

double-pi connection without circuit breakers, every stoppage of the Hasang power plant (by fault or

maintenance) may affect the existing transmission line operation.



10. CONSTRUCTION PLAN AND SCHEDULE

10.1 General

The Feasibility Study Report of the Project describes that the overall construction period would be 36

months (including a buffer of 3 months) assuming a start of the works on 1st January 2013. The

critical path runs through the early site establishment of access road to the tunnel portals, the timely

commencement of tunnel excavation followed by lining and finishing and connection to the cut &

cover section, water filing and commissioning.


Figure 10.1.1 Construction Master Schedule in Feasibility Study

10.2 Construction Plan

Detail construction plan/method shall be prepared by the Contractor and responsibility of the

Contractor. In the Bid Documents, construction method shall be shown/suggested only outline for

evaluation and negotiation purpose. The Client has the construction plan/method in detail for some

extend.

Comments on construction of the Access Road are given in Chapter 5.

Site Facilities

- Electricity during construction cannot be supplied from PLN system because capacity of power

supply at the site is not enough, the Contractor should be prepared generator at each work site.

- On January 18, 2013, the proposed quarry site for aggregate located about 3 km far from the

Head Pond was inspected. Quality and quantity of this site are deemed to be satisfied the

requirements. Further, investigation to confirm quality, quantity and thickness of overburden by

boring is recommended.

- Spoil Bank located upstream of the Intake Weir Site is rather dangerous. If land slide/slope

failure happen on Spoil Bank, slid materials come into Intake Weir, it is better to locate

downstream of Intake Weir site.(refer to Figure 10.2.1)



- Location of Spoil bank mentioned above and Site Installation are better to change.(refer to

Figure 10.2.1)

- Site installation/storage areas are requested to Gate & Penstock and Electro-mechanical Works

as fabrication yard and temporary storage. Top of the spoil banks are available.(refer to Figure

10.2.1)


Figure 10.2.1 Site Installation Works

Intake Weir

- The construction of the dividing wall requires the coffering for foundation excavation and

concreting, although this structure might be omitted in case of change the weir location.

- The right downstream toe portion of the overflow section in the first stage river diversion and

the left downstream toe portion of the overflow section in the second stage river diversion are

overlapped with cofferdam and impossible to construct. It is recommended to construct the right

downstream toe portion of the overflow section together with the left side wall of the overflow

section and the layout of the second stage coffering shall be moved to downstream. (refer to

Figure 10.2.2)

- The cofferdam will be constructed to close to the excavation of the Intake Weir and foundation

of river deposit. Countermeasure for leakage water will be required, blanket embankment of

impervious materials in front of the cofferdam and/or construction of sump pits and pumping up

are recommendable measure.

- For transportation of Form, Re-bar and concreting, a Tower crane or Jib crane will be needed.




Figure 10.2.2 Coffering of Intake Weir

Headrace Waterway

- Details of inlet and outlet for the tunnel works should be clear. These will subject to the concrete

works of channel after completion of tunnel works. .(refer to Figure 10.2.3)


Figure 10.2.3 Access to Headrace Tunnel



Transmission Line

- When connect to the existing 150kV Transmission Line at Kampung Pajak, stop of operation of

T/L is necessary, detail discussion with PLN is recommendable.

10.3 Construction Schedule

Access Road

- Construction periods of the access road are deemed to be short taking our comment in the

Chapter 4 into consideration and detail study is recommended. The construction of the access

Road is the first activity of the project and governs the all construction works.

Intake Weir

- By shifting of Curtain Grout line in the Intake Weir mentioned in 4)-11), grouting period will be

free from the concreting works

Headrace Tunnel

- Progress rates of the tunnel works in the schedule are not same as the text. Following progress

rates of tunnel works are considered to be reasonable or rather optimistic,

Excavation with supporting : 100m/month

Invert concrete : 300 m/month or more

Sidewall concrete : 192m/month

- Based on the above rates, the schedule of tunnel works without additional work adit is shown in

Figure 10.3.2. However, no geological risk is considered. The proposed schedule will be hardly

kept and delayed by 2-3 months.

- On the other hand, an additional work adit will be constructed easily and does not require high

cost from the topography as shown in Figure 10.3.1. If the work adit is prepared, an delay by

geological risk and other reasons can be mitigated. The construction schedule with work adit is

shown in Figure 10.3.3.

Others

- Design and fabrication schedules of the Hydro and Electro-mechanical Works shall be

considered and presented.

- Schedule of the Transmission Line is not shown.




Figure 10.3.1 Work Adit


Figure 10.3.2 Construction Schedule of Headrace Tunnel without Work Adit




Figure 10.3.3 Construction Schedule of Headrace Tunnel with Work Adit



11. COST ESTIMATE

11.1 General

The cost estimate for the Project in the Feasibility Study Report was based on a price level of the first

quarter (Q1) of 2012. The costs estimated for each item were based on quantities and unit rates, or as

a mark-up on percentage basis.

The cost estimate was provided for the main components of the direct and indirect costs as follows.

Table 11.1.1 Summary of Project Cost in Feasibility Study

Item Amount (1,000 US$)

Remark

Direct Cost Civil Works 35,745 Conti: 10% (20% for tunnel) Hydro-mechanical Works (incl. Penstock) 10,411 Conti. 10% Electro-mechanical Works 24,948 Conti. 10% Transmission Line 10,350

Total Direct Cost 81,454 Indirect Cost Client Administration 4,073 5% of Direct Cost Engineering 4,073 5% of Direct Cost Land Acquisition and EIA Cost 4,260 Provided by the Client Technical Management Services 2,840 Provided by the Client Insurance 4,073 5% of Direct Cost Taxes (VAT on all local items) 9,246

Total Indirect Cost 28,564 Total Project Cost (without IDC) 110,018

Total Project Cost (with IDC) 129,398


Hereinafter discussed are NK’s comments on the bill of quantities and unit prices for the direct costs

adopted in the Feasibility Study, and impact to the cost estimate due to review result of design in

compliance with NK’s recommendations which are described in the preceding chapters.

11.2 Bill of Quantities

11.2.1 Civil Works

In the Feasibility Study, the bill of quantities are prepared for the main items only such as excavation,

embankment, concrete works and roads and pavement. Other miscellaneous items are not counted. It

is suggested that 10% will be added to the cost of the civil work to cover the costs of those

miscellaneous items.



11.2.2 Hydro-mechanical Works

Penstock

There are inconsistency in thickness and tonnage of the steel pipe among Table 12-12, Table 16-3 and

the bill of quantities in Annex 16 of the Feasibility Study. Basis for calculating the design head

(including pressure rise) and the thickness need to be clarified for justifying the tonnage.

Hydro-mechanical Equipment

In the Feasibility Study, the estimate of weight of the different type of gates was based on empirical

formulae presented in “Design of Hydraulic Gate (by Paulo C.F. Erbisti, 2004). The weight of the

moving part of the gate is given as a function of the parameters of B2hH, where B and h are the span

and the gate height respectively, and H is the head on the sill.

Although the expression are based on statistical data and thus they are not for premise estimates of

gates, they are recognized be adequate to be adopted in the feasibility study stage.

11.2.3 Electro-mechanical Works

As described in 11.4.3, the cost estimate of the electro-mechanical work was obtained on the

published diagram based on statistic data, and thus no detailed bill of quantities was prepared.

11.2.4 Transmission Line

Length of the transmission line is assumed at 34.5km in the Feasibility Study.

11.3 Unit Price

Quotations of cost estimate for respective component of the direct cost should be asked to the

contractors / manufacturers. The following opinions are based on NK’s past experiences in similar

projects in Indonesia and/or South-East Asia.

11.3.1 Civil Works

Main unit rates applied in the Feasibility Study for the cost estimate of the civil works are seen in the

following table, with NK’s assessment.

Table 11.3.1 Main Unit Prices for Civil Works in Feasibility Study

Item Unit Unit Prices in F/S Assessment Open excavation , soil US$/m3 4.5 Sufficient Open excavation , rock US$/m3 18.0 Sufficient Tunnel excavation US$/m3 65.0 Adequate Backfill US$/m3 8.0 Sufficient Structural concrete US$/m3 75.0 – 85.0 Adequate Formwork US$/m2 10.0 – 65.0 Sufficient Reinforcement steel US$/ton 1,750 Adequate

Source: based on NK’s experience



The unit prices set in the Feasibility Study seem to be sufficient or adequate.

11.3.2 Hydro-mechanical Works

A unit price of US$ 5,500 per ton steel was adopted in the Feasibility Study for the cost estimate of

the penstock. This seems to be adequate.

A unit price of US$ 12,000 per ton steel was basically adopted for the cost estimate of other hydro-

mechanical works. This seems to be sufficient.

11.3.3 Electro-mechanical Works

The cost estimate of the generating equipment in the Feasibility Study was based on the diagram

which had been presented in a publication of “International Water Power and Dam Construction (Feb.

2009)”. This diagram is often quoted in feasibility studies as this allows a close cost estimation of

E&M equipment which are accommodated in powerhouses. The compiled data in the diagrams

correspond to the E&M equipment which include turbine, governors, valves, cooling and drainage

water systems, cranes, workshops, generators, transformers, earthing systems, control equipment,

telecommunication systems and auxiliary systems.

Although the diagram are based on statistical data and thus they are not for premise estimates of E&M

equipment, they are recognized be adequate to be adopted in the feasibility study stage.

11.3.4 Transmission Line

Both the unit prices of 0.3 million US$/km adopted in the Feasibility Study and 0.349 million

US$/km adopted in the Pre-Feasibility Study for 150kV transmission line seem to be sufficient for the

single pi option. For the double pi option, it is reasonable to adopt 150% of these prices.

It is noted that those unit prices are assumed to include the cost for land acquisition also.



11.4 Impact to Cost Estimate due to Design Review

Impact to the direct cost due to review result of design in compliance with NK’s recommendations

which are described in the preceding chapters are roughly estimated and summarized as below.

Table 11.4.1 Impact to Direct Cost due to Design Review

Item Description Cost Impact (US$ m.)

Chapter in this Report

1. Miscellaneous Item of Civil Works for F/S Design 3.23 11.2.1 2. NK’s Recommendation on Design 2.1 Access Road

1) Re-route 0.20 5.2 2) Pavement width -0.30 5.2

2.2 Intake Weir and Power Intake 1) Location change 0.20 6.2.1 2) Removal of boulders 0.06 6.2.2 3) Debris barrier 0.01 6.2.2 4) Increase of 100-yr flood 0.10 6.2.4 5) Protective measures for piping 1.00 6.2.5

2.3 Intake Channel and De-sander 1) Protective measures for landslide 0.10 6.3.1 2) Foundation treatment 0.03 6.3.1 3) Deletion of stoplog and additional gates 0.05 6.3.3 4) Steel lining of flushing channel 0.03 6.3.3

2.4 Headrace Tunnel 1) Tunnelling in soft materials 0.10 6.4.1 2) Permeability in tuff layer 0.05 6.4.2 3) Work adit 0.50 10.3

2.5 Headrace Channel incl. Cut & Cover 1) Cutting slope to gentle 1.10 6.5.1 2) Crossing structures 0.50 6.5.2

2.6 Head Pond and Spillway 1) Slope protection 0.10 6.6.1 2) Extension of access road 0.20 6.6.1 3) Guide wall of spillway 0.10 6.6.2 4) Spillway section type 0.20 6.6.2

2.7 Penstock 1) New provision of surge tank 3.00 4.2.3 2) Steel penstock 0.00 4.2.3 3) Slope protection 0.10 6.7.1

2.8 Powerhouse & Swichyard 1) Increase of 100-yr flood 0.10 6.8.1 2) Location of draft gate -0.09 6.8.2 3) Top elevation of tailrace wall and erection bay access 0.02 6.8.2 4) Enlargement of powerhouse 0.10 8.3.1 5) Enlargement of switchyard in case of double pi T/L 0.04 8.3.2 6) Addition of switchgear equip. in case of double pi T/L 1.00 8.3.2

2.9 Transmission Line 1) Double Pi T/L 5.18 9.2

Sub-total 2 13.78 Total 1 & 2 17.01 Total of Direct Cost 98.47




Total project cost to which the above cost impacts are incorporated is as below.

Table 11.4.2 Summary of Project Cost

Item Amount (mil. US$)

Remark

Direct Cost Civil Works 46.53 F/S + Item 1 + 2 (except below) Hydro-mechanical Works (incl. Penstock) 10.46 F/S + Item 2.3 3) Electro-mechanical Works 25.95 F/S + Item 2.8 6) Transmission Line 15.53 F/S + Item 2.9 1)

Total Direct Cost 98.47 Indirect Cost Client Administration 4.92 5% of Direct Cost Engineering 4.92 5% of Direct Cost Land Acquisition and EIA Cost 4.26 Same as F/S Technical Management Services 2.84 Same as F/S Insurance 4.92 5% of Direct Cost Taxes (VAT on all local items) 11.17 Same assumption as F/S

Total Indirect Cost 33.03 Total Project Cost (without IDC) 131.50

Total Project Cost (with IDC) 154.67 Same assumption as F/S




12. PROJECT FEASIBILITY

12.1 Financial Analysis

Reasonable assumptions are set forth in the Financial Analysis discussed in the Feasibility Study

Report (FS, Figure 17-2: Financial analysis for the base case of Hasang HPP, Chapter 17, Volume 2).

Because it does not fully disclose breakdowns of cash inflows and cash outflows, the review work

could not perfectly trace the original computations. However, difference between the original

computation in FS and in the Review Work can be regarded as negligible small.

Notwithstanding the appreciation of the financial analysis above, the investor should pay attentions to

the following issues:

(1) Exchange rate used in FS need be updated;

Currency FS Reviewed (as of February 2013)

Indonesian Rupee (IDR): 1 USD = 8,550 IDR 9,740 IDR

EURO (EUR): 1 USD = 0.72 EUR 0.76 EUR

Japanes Yen (YEN): 1 USD = 80 JPY 93 JPY

(2) Possible cost increase need be considered;

Project Cost FS Suggestion in Review Work

Direct Cost without IDC = 110.0 USDm 131.5 USDm

(3) Possible energy decrease need be considered;

Hydrology & Energy FS Caution in Review Work

Hydrology = Average Moderate

Saleable Annual Mean = 275.5 GWh 249.0 GWh

Annual Revenue (USc7.5/kWh) = 20.7 USDm 18.7 USDm

12.2 Possible Effects from Cost and Energy Change

The possible cost increase discussed in Section 11.4 may affect the project profitability; the return on

equity (ROE) may go down by 3% from the FS Base Case. If one considers the possible energy

decrease discussed Section 4.3.4, ROE further may go down by 2 %. As a whole, there is a concern

that ROE might nose down to the level the investors can hardly accept, as demonstrated below.


FS Base Case 110.0 USDm 275.5 GWh USc7.5/kWh 14.4%*


Cost Up & Energy Less 131.5 USDm 249.0 GWh USc7.5/kWh 9.4% * FS has computed ROE (return on equity) to be 14.92% for the base case with USc7.5/kWh tariff, while the

Review Work does 14.4% under the same assumptions.



In order to compensate such possible profitability decrease, the investors should examine higher tariff

for energy sales, assuming 15.0% of the required ROE:



Cost Up & Energy Less 131.5 USDm 249.0 GWh USc10.03/kWh 15.0%

The financial stream is re-analyzed as demonstrated in Table 12.2.1. This financial stream

corresponds to both of the Cost Up case and the Cost Up & Energy Less case above with the new

average tariffs of USc 9.0625/kWh and USc 10.0266/kWh respectively.

Table 12.2.1 Updated Financial Stream with Higher Tariff

12.3 Recommendations in Financial Analysis

It is recommended that the financial analyses be updated with the latest investment plan (e.g., the

most likely loan conditions and the equity investment) based on the levelized tariff concept (Volume 2

Part 3 of RfP) to assess and confirm the profitability of the Project. It is also recommended that such

financial analysis updates include balance sheets, profit and loss statements, cash flow statements, and

estimated dividends paid out, so that more precise financial indicators and the investors’ return can be

presumed.

Year CAPEX OPEX Cost Revenue Equity DebtOutstandingLoan begin Interest Repay

OutstandingLoan end Deprec

GrossIncome

Tax Profit ROE

1 65.75 65.75 21.90 46.93 43.86 3.07 46.93 -68.82 -21.89 -

2 39.45 39.45 13.15 31.44 73.24 5.13 78.36 -44.58 -13.14 -

3 26.30 26.30 8.75 24.26 95.91 6.71 102.62 -33.01 -8.75 -

4 1.94 1.94 24.96 102.62 7.18 10.26 92.36 7.31 8.53 2.13 3.45 -

5 1.98 1.98 24.96 92.36 6.47 10.26 82.10 7.31 9.21 2.30 3.96 -

6 2.02 2.02 24.96 82.10 5.75 10.26 71.83 7.31 9.88 2.47 4.47 -

7 2.06 2.06 24.96 71.83 5.03 10.26 61.57 7.31 10.56 2.64 4.97 -

8 2.10 2.10 24.96 61.57 4.31 10.26 51.31 7.31 11.24 2.81 5.48 -13.6%

9 2.14 2.14 24.96 51.31 3.59 10.26 41.05 7.31 11.92 2.98 5.99 -8.0%

10 2.18 2.18 24.96 41.05 2.87 10.26 30.79 7.31 12.59 3.15 6.50 -3.9%

11 2.23 2.23 24.96 30.79 2.16 10.26 20.52 7.31 13.27 3.32 7.00 -0.7%

12 2.27 2.27 24.96 20.52 1.44 10.26 10.26 7.31 13.94 3.48 7.51 1.7%

13 2.32 2.32 24.96 10.26 0.72 10.26 0.00 7.31 14.61 3.65 8.01 3.7%

14 2.36 2.36 24.96 7.31 15.28 3.82 18.78 6.8%

15 2.41 2.41 24.96 7.31 15.24 3.81 18.74 8.8%

16 2.46 2.46 24.96 7.31 15.19 3.80 18.71 10.3%

17 2.51 2.51 24.96 7.31 15.14 3.78 18.67 11.3%

18 2.56 2.56 24.96 7.31 15.09 3.77 18.63 12.1%

19 6.72 2.61 9.33 16.64 6.57 0.74 0.19 7.13 12.4%

20 2.66 2.66 24.96 6.57 15.73 3.93 18.37 12.9%

21 2.72 2.72 24.96 6.57 15.68 3.92 18.33 13.3%

22 2.77 2.77 24.96 6.57 15.62 3.91 18.29 13.7%

23 2.83 2.83 24.96 6.57 15.57 3.89 18.25 13.9%

24 2.88 2.88 24.96 22.08 5.52 16.56 14.1%

25 2.94 2.94 24.96 22.02 5.51 16.52 14.3%

26 3.00 3.00 24.96 21.97 5.49 16.47 14.5%

27 3.06 3.06 24.96 21.91 5.48 16.43 14.6%

28 3.12 3.12 24.96 21.84 5.46 16.38 14.7%

29 3.18 3.18 24.96 21.78 5.45 16.34 14.8%

30 3.25 3.25 24.96 21.72 5.43 16.29 14.8%

31 3.31 3.31 24.96 21.65 5.41 16.24 14.9%

32 3.38 3.38 24.96 21.59 5.40 16.19 15.0%

33 3.45 3.45 24.96 21.52 5.38 16.14 15.0%

TTL 138.22 78.70 216.92 740.61 43.79 102.62 777.42 54.42 102.62 689.70 142.57 326.69 118.28 350.99



13. CONCLUSION AND RECOMMENDATION

As a result of review on the existing studies of the Project, this Report concludes that;

- Average Scenario, which was applied as the inflow duration curve at the Hasang weir site in the

Feasibility Study seems to be overestimated. This might cause risk of overestimation of

expected annual energy production. It is recommended that the Moderate Scenario shall be

applied instead. Based on this, the salable annual mean energy of the Project will be 249.0

GWh, which is of about 10% decrease compared to 275.5 GWh in the Feasibility Study.

- Some design considerations, which were not taken into account in the Feasibility Study, are

required to ensure technical feasibility of the Project. One of the most critical issues is

unbalance of 1,669 m long penstock against 207m head in the Feasibility Study, which may

hinder stable speed regulation, and may cause excessive pressure rise in the penstock. It is

recommended to consider a surge tank to be constructed between the head tank and the

powerhouse to overcome this issue. The other issue is type of transmission line. Single-pi

connection has problem in reliability of transmission, and thus not recommendable. It is

recommended to adopt the double-pi connection instead.

- Taking account of those and other design considerations in the Report, the project cost without

IDC will be 131.5 US$m which is about 20% increase compared to 110.0 US$m in the

Feasibility Study.

- The possible energy decrease and cost increase above may cause profitability decrease. To

compensate this, higher tariff should be examined.

This Report recommends the following actions to be conducted.

- To estimate likely variation of annual and monthly energy generation outputs, the observed

daily flow records at the Pulao Dogom station from 2000 to date shall be analyzed for prediction

of monthly energy generation through in-depth review and scrutiny of the flow data.

- To confirm possibility of landslide at the de-sander site and the powerhouse site, detailed survey

shall be conducted. The first step shall be site reconnaissance to clarify the evidence of the

landslides. If certain evidences are found, further investigation such as some more detailed

topo-mapping and drilling investigation with laboratory test and monitoring shall be conducted

as the second step for proper measures.

- To examine the optimum layout of the penstock and the surge tank, additional topographic

survey and geological investigation shall be conducted along the newly proposed penstock

alignment.

- To confirm the optimal selection of type and number of the units of turbine-generator,

comparative study shall be conducted.



ANNEX

COMMENTS ON TECHNICAL PROPOSAL BY POSCO ENGINEERING

No. POSCO’s Proposal NK’s Comment 1 100-yer frequency flood is estimated at

713m3/s. This seems to be underestimated as explained in Chap. 2.2 in this Report.

2 1-year frequency flood is used for the river diversion.

Common practices suggest to adopt 2- to 5-year frequency flood, as explained in Chap. 2.2 in this Report.

3 Locations of the intake weir and power intake are adjusted.

Acceptable as explained in Chap. 6.2.

4 Desander is composed of 2 sets of basin. Acceptable as described in Chap. 6.3 in this Report.

5 Inlet of the headrace tunnel is shifted to the mountain side.

This is acceptable as explained in Chap. 3.4 in this Report.

6 Alignment of the headrace tunnel is adjusted to shorten the cut & cover section.

This seems to be possible but need more consideration. NK did not observe the core of the additional bore hole.

7 Dimension of excavation section of the head race tunnel is reduced.

This seems to be acceptable.

8 Rock support class ratio is changed. This seems to be acceptable. 9 Work adit is not considered for tunnel

construction. Provision of the work adit is suggested as explained in Chap. 10.3. in this Report.

10 The head pond is shifted to the direction to the river.

This seems to be possible but need more consideration. Original ground lines and assumed rock lines should be put in the sections so that design adequacy can be checked.

11 Spillway of the head pond discharge the water to the direction of opposite side.

Maybe need more consideration. NK does not have sufficient knowledge on the site conditions there.

12 There is no description on penstock stability.

Check of penstock stability and required GD2 should be included.

13 There is no description on pressure rise for the penstock.

Check of the water hammer analysis with required GD2 should be included.

14 Powerhouse dimensions are the same as the Feasibility Study.

Powerhouse dimensions in the Feasibility Study are not sufficient, as explained in Chap. 8.3 in the Report.

15 Daily discharge data in the Feasibility Study was used without additional analysis.

Daily discharge in the Feasibility Study is overestimated as explained in Chap. 2.3 in this Report.

02. main sentences - review report on existing studies - hasang hpp project 130225.pdf

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