maiwa khola

Maiwa Khola Small Hydropower Project (Package - 2) DoED

Feasibility Study Executive Summary ES- 1 METCON

Salient Features of the Project LOCATION District: Taplejung VDCs: Dhungesanghu, Thinlabu, Change,

Santhakra, Khamlun and Phunlin.

Latitude: 270-21-0 To 270-2237

(3026000 - 3029000 N)

Longitude: 870-33-58 To 870-37-

37 (556000E - 562000E)

PURPOSE Hydropower Generation

HYDROLOGY Catchment Area 173.4 km2 Average Annual Flow 17.2 m3/s

Design Flow 8.07 m3/s

(45% exceedence)

Flood Flow 461.00 m3/s

(with 100 yrs return period)

HEADWORKS a) Diversion weir Type Nongated overflow concrete gravity Crest elevation 815 Masl

High flood level 819.5 Masl

Crest length 30m

Maximum height 7m

Design flow 461 m3/s

Geology Alluvial Deposit

(Boulders, gravels, sand)



INTAKE STRUCTURE Design flow 9.28m3/s Intake bays 2 Nos

Size of each bay 4m x 1.7m

Intake water level 815 Masl

Intake sill level 813.30 Masl

Intake length 20m (variable)

Intake velocity 0.68m/s

Geology Alluvial Deposit

HEADRACE CANAL-1 Design flow 9.28 m3/s Section Rectangular, covered

concrete lined

Size 3mx1.7m

Gradient 1:1000

Length 81m

Geology Alluvial and colluvial Deposit

DESILTING BASIN Design flow 9.28m3/s Type Single chamber with -

continuous flushing

Section Rectangular (upper-half) and

inclined at 450 (lower half)

concrete lined

Size 11m x 4.5m

Length 90m (including transitions)

Silt particle size larger than 0.20mm

Settling velocity 0.024 m/s

Mean flow velocity 0.27 m/s

Geology Alluvial and colluvial deposit



HEADRACE CANAL-2 Design flow 8.07m3/s

Section Rectangular, covered,

concrete lined

Size 2.5mx1.85m

Gradient 1:1000

Geology Alluvial and colluvial deposit

HEAD RACE TUNNEL Design flow 8.07m3 Section D-Shaped

Size 2.5mx2.5m

Gradient 1:1000

Length 4,150m

Geology Chlorite micha schist and

schistose phyllites, with or

without garnet

FOREBAY Water level 810.52 Masl Section Rectangular, concrete lined

Size 10mx2.5m

Length 58m

Geology Exposed bedrock

represented by Chlorite

sericite schistose phyllites

PENSTOCK Design flow 8.07m3/s

Diameter 1.90m

Length 700m

Thickness 20mm

Geology Colluvial deposit



POWERHOUSE AND TAILRACE Type Surface

Size Length=23.4m

Width=11m

Height=17.40m

Turbine axis at elevation 610 Masl Installed capacity 13.5Mw

Number of generating units 2

Tailrace water level 609.62 Masl Gross Head 200.90m

Tailrace canal Rectangular,

Section covered, concrete lined

Size 2.5 m x 1.86 m

Gradient 1: 1000

Length 65m

Geology Alluvial and colluviial deposits

GENERATING EQUIPMENTS

Turbines Type Vertical shaft, Francis

Number 2

Capacity Each with output 7.15 Mw

and synchronous speed 750

rpm.

Generators Type A/c synchronous brushless

excitation system

Number 2

Capacity Each with output 6.8Mw

synchronous speed 750 rpm

and generating voltage 11Kv

Power Transformer Type outdoor, oil immersed

Number 2

Rated Output Each with 8,000 KVA

Rated voltage 11Kv/132 KV



TRANSMISSION LINE Length 7Km Transmission Voltage 132KV

ENERGY GENERATION Average Annual Energy 78.11 Gwh Dry season 14.03 Gwh

Wet season 64.08 Gwh

PROJECT COST Estimated cost Rs. 1,89,61,20,000. (excluding Tax & duties

at 2009 price level)

ECONOMIC INDICATORS Nett Present Value (NPV) IN (000) Rs. 67,99.55Benefit-Cost Ratio (B/C) 1.40

Economic Internal Rate of Return (EIRR) 13.97%

FINANCIAL INDICATORS Nett Present Value (NPV) in (000) Rs. 40,30,61

Benefit-Cost Ratio (B/C) 1.31

Financial Internal Rate of Return (FIRR) 13.7 %



1. INTRODUCTION

1.1 Project Background

It is estimated that Nepal is endowed with the total hydropower potential of 83,000 Mw.

About 50% of the potential is considered as technically and economically feasible

potential. Presently, a little over 1 % of this potential has been harnessed. A large

section of national population is still away from the hydropower reach. The average per

capita consumption of electricity in the country is one of the lowest in the world. The

Government of Nepal intends to develop the potential in an economically efficient and

sustainable manner to meet the growing power demand in the country. In line with the

Hydropower Development Policy, 2001 and Water Resources Strategy, 2002, the

Government of Nepal wishes to maximize the private sector involvement in the

development of hydropower projects. Compared to large and medium scale hydropower

projects, the significant advantages of small hydropower plants are lower capital

investment, proximity to regional load centres, use of local materials and technology and

shorter construction period. Under the grant assistance from the Norwegian

Government, Department of Electricity Development (DoED) has been engaging the

competent local consultants in conducting the Feasibility Study and Environmental

Impact Assessment (EIA) of small hydropower projects for a couple of years. The

proposed assignment for undertaking Feasibility Study and EIA of Maiwa Khola Small

Hydropower Project is one such undertaking.

Based on the Technical and Financial proposals to carry out the Feasibility study and

Environmental Impact Assessment (EIA) of Maiwa Khola Small Hydropower Project as

submitted by Metcon Group Private Ltd. on 11 January 2007, DoED through its letter

dated 31st May 2007, invited the consultants for initiating the necessary procedure to

enter into a contract.

On June 27, 2007 discussions were held between DoED and Consultants regarding the

finalization of contract based on request for proposal, technical proposal and financial

proposal, description of services, reporting requirements, key personnel & sub-

consultants, breakdown of contract price in local currency and working schedule &

manning schedule. DoED & Consultants had initialed the final draft of the contract and

agreed that the initialed documents were subject to approval from respective authorities

prior to signing of the contract.



On August 5, 2007, Department of Electricity Development (DoED) and Metcon Group

Private Ltd (METCON Consultants) entered into a contract for undertaking a Feasibility

Study and Environmental Impact Assessment (EIA) of Maiwa Khola Small Hydropower

Project in Taplejung district of Eastern Development Region of Nepal.

The consultants initiated this study in August 2007 immediately after signing the

contract. Inception Report was approved by DoED in February 2008. Scoping and ToR

documents for carrying out. EIA were submitted to DoED in October 2008. In the

meantime GON announced a change in Environmental Regulation 2054 during

presentation of Budget for FY 2008/2009. Subsequently amendments were made in

Environmental Regulation 2054 and consultants were instructed by DOED letter dated

2065-5-19 to carry out Initial Environmental Examination (IEE) instead of Environmental

Impact Assessment (EIA) of the project, as stipulated in the referred contract earlier.

1.2 Previous Studies

Maiwa Khola Small Hydropower Project was identified and studied at reconnaissance

level during the works The Study of Small Hydropower Project of 5-10Mw capacity

previously done by the consultants ITECHO Nepal (P) Ltd. for DoED. Information about

the location, geology, hydrology, layout, energy generation, access and transmission line

of the project as identified and studied earlier were provided in Appendix - A of the

above referred contract.

1.3 Objective and Scope of Work

The main objective of the consultants services is to carryout and complete the Feasibility

Study including Initial Environmental Examination (IEE) Study of Maiwa Khola Small

Hydropower Project.

The specific objectives, as outlined in the TOR of the contract, are as follows:

To produce a bankable feasibility study report that will analyse and document all important aspects required for the formal approval of the project by DoED and

government authorities of Nepal;

To serve as a main document for inviting participation in the implementation of the



project by the private investors;

To complete the Feasibility Study Report by incorporating all relevant baseline investigations, assessments and plans, drawings and cost estimates regarding

technical, economic, financial and environmental aspects; and

To conduct IEE as an integral part of the Feasibility study in line with the existing environmental legislations of the country.

2. DESCRIPTION OF PROJECT AREA 2.1 Location

The project is located on Maiwa Khola a tributary of of Tamor river in Santhakra,

Thinlabu, Dhungesangu and Change VDCs of Taplejung district of Mechi Zone in the

Eastern Development Region of Nepal within 270-21-0 - 270-22-37- Latitude

(3026000 N - 3029000 N) and 870-33-58- 870- 37-37 E Longitude (556000 E - 562000

E). The overall project location and project area location are shown in Fig No ES-2.1

and ES-2.2 respectively.

2.2 Physical Features

The Maiwa khola basin is bordered by Jaljale Himal at an elevation of 4540 m amsl,

Dhupi and Sumba danda in the North, Milke, Menchhyam dada in south and East and

Giddhe and Milke dada in the west. The basic basin characteristics of Maiwa and Tamor

were assessed using the Arc View GIS tools based on the digital elevation model (DEM)

data derived from contour map published by Survey Department of Nepal Government.

The total length of the Maiwa khola from its origin to the confluence with Tamor River

near Dobhan at an elevation of about 653 m amsl is about 24 km. It has seven main

tributaries namely Lechuwa, Nenwa, Kanuwa, Yandeli, jaiwa, Hguwa and Hina. The

largest among these tributaries is Yandeli khola joining the Maiwa at an elevation of

about 960 Masl near Tenthap village located about 2 km upstream of the headworks site

of the project. The average gradient of the Maiwa khola from origin to the confluence is

about 14 %. The average gradient of the Maiwa khola for a stretch of about 7.5 km



between its confluence with Yandeli and Tamor is mild and about 3.4%. The average

slope of the Maiwa khola for the upper part of the catchment above the confluence of

Yandeli Khola is steep and varies from 8.5% to 17%. The side slope of the Maiwa

catchment above the intake varies from 2% to 57% with an average of 26.4%. The

average gradient of Tamor River in between Dobhan and powerhouse site at Tupurke

site is about 1.5%.

2.3 Accessibility

Presently the project site does not have access to existing about 250 km long Mechi

Rajmarga connecting Taplejung district headquarters with East - West Highway at

Chaarali in Jhapa district of Mechi zone in the Eastern Development Region via Phidim

and Ilam bazaar the headquarters of Paanchthar and Ilam districts respectively.

According to the Terms of Reference of the contract for the present study, the

consultants, have investigated, surveyed designed and proposed to construct a 10.95

km long district level graveled access road with a 60m long bridge over Tamor river at

approximately 700 m upstream of the powerhouse site. This access road will connect

the powerhouse site of the project with Banande a nearest roadhead on above

mentioned rajmarga. Further, it is proposed that the headworks and forebay sites of the

project will be accessible by a graveled motorable road to be diverted towards Dobhan

from the access road at the right bank of the bridge over Tamor river at Chainage no 10

+ 240. The length of this project road will be about 7 m.

Imported construction materials and construction machines, plants, tools and electro-

mechanical equipments for the powerhouse will be transported to the project site by

inland transport form the nearest seaport, Kolkotta, India. The entry point from above

seaport to Nepal will be Kakarbhitta in Jhapa district. From this entry point onwards to

the project site the transportation of all kind of construction materials except for the

materials like sand, gravel and stones available locally machines, plants, tools and all

kinds of equipments will be done Via the Mechi Rajmarga (250m) running between

Taplejung and Chharali at East - West Highway Via Phidim and Ilam bazaar the

headquarters of Paanchthar and Ilam districts respectively and the project access road

(10.5km) proposed to be constructed prior to the commencement of main civil works of



the project. About 140 km of above mentioned Rajmarga between Chharali and Phidim

is blacktopped while the remaining portion of about 110 km between Phidim and

Taplejung is just graveled. Presently the latter portion is in poor condition. However, the

concerned government department has plan to rehabilate and improve this portion

before blacktopping it in the near department has plan to rehabilate and improve this

portion before blacktopping it in the near future.

There is a fair weather airport at Sukhetar which is situated at about 3 km and 9 km

southeast of district headquarters Taplejung bazaar and project site respectively.

3. PROJECT ALTERNATIVE LAYOUTS AND RECOMMENDED PROJECT LAYOUT

Possible alternative layouts and recommended project layout were described at length in

the Revised Inception Report dated January 2008. A brief account of the mentioned

report is presented below:

3.1. Study of Possible Alternative Layouts of the Project

According to above mentioned report, altogether three possible alternative layouts-

Alternative A, B and C of the project were identified and studied using then available

topographical maps of 1:50,000 scale, aerial photographs, general information about

the environmental conditions of the project area and findings of review of available

hydrological, geological and other relevant data/information. For the comparison

purposes, all three alternative layouts were prepared in 1:50,000 scale topographical

maps and parameters of layout components and structures were determined using a

design flow of 65% probability exceedence.

The benefit-cost analysis made for the alternative layouts revealed that Alternative B

layout was more favorable than the other two Alternatives A and C. Hence, it was

selected for further phase of study. The comparison of these alternative layouts along

with the salient features, as provided in the Revised Inception Report, is referred to in

Table No. ES-3.1



Further, a benefit-cost analysis was made to determine the tentative optimum capacity of

the above selected Alternative B layout of the project. For this, a range of capacities

were considered using the flow ranging from 65% to 37% probability of exceedence. As

a result of this analysis the Alternative B layout of the project with a tentative installed

capacity of 12.74 Mw corresponding a flow of 7.8m3/s equaling to a flow of 40%

probability exceedence was found optimum as it provided the highest benefit-cost ratio

1.48. Hence, it was recommended that the Alternative B layout of the project with an

installed capacity of 12.74 Mw be taken up for further phase of study comprising of

various field investigations and design works as specified by ToR of the contract. The

results of this analysis, as provided in the Revised Inception Report, are referred to in

Table No. ES-3.2

3.2. Presentation of Recommended Layout

The recommended layout of project with tentative installed capacity of 12.74 Mw

envisages the construction of headworks comprising of a diversion weir, intake structure,

desilting basin and canals connecting intake to desilting basin to headrace tunnel,

forebay, penstock, powerhouse and tailrace. This conceptual layout of the project as

mentioned above was adopted for further studies including the field investigations,

optimization and feasibility level design. The tentative salient features of the layout as

worked out during the inception phase of study subject to revision and modification, as

required, during the further course of designing are as follow:

Gross Head 200m Design Discharge 7.8m3/s with 40% of probability of

exceedence

Installed Capacity 12.74Mw Headrace Tunnel Length 4,600m, D-Shaped

2.5mx2.5m), Non pressure tunnel

Penstock Length 560m, Diameter 1.82m Annual Gross Energy 70.89Gwh Preliminary Cost in (000)/NRs 1,31,43,00 Preliminary Annual Cost in (000)/NRs 19, 71, 00 Preliminary Annual Benefit in (000)/NRs 29, 14, 00 B/C ratio 1.48


Table No. ES-3.1: Salient Features of Alternatives A, B and C. S.N Description Alternative A Alternative B Alternative C with Audit 1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

Catchment Area at intake (km2)

Location of diversion weir site

Latitude

Longitude

Location of Power house site

Latitude

Longitude

Gross head (m)

65% exceedence flow (m3/s)

Power generation (Kw)

Annual gross energy (Gwh)

Type/Size of waterway

Waterway length (m)

Penstock pipe diameter/length (m)

Access Road (Km)

Project Road (Km)

Transmission Line (Km)

Preliminary cost in thousand NRS

Annual cost in thousand NRS

Annual benefit in thousand NRS

Cost per Kw (NRS/kw)

Energy cost (NRS/Kwh)

Benefit-cost ratio (B/C)

186.5

270-22-20

870-35-7

270-21-0

870-37-30

160

3.2

4,175

31.81

Non pressure tunnel/2.5m*2.5m

4,200

1.3/430

15

7

20

78,57,00

11,79,000

13,07,00

1,88,000

3.71

1.11

182

270-22-14

870-34-40

270-21-0

870-37-30

200

3.12

5,100

38.95


4,600

1.3/560

15

9

20

90,27,00

13,54,000

16,01,00

1,77,000

3.48

1.18

174

270-22-24

870-33-44

270-21-0

870-37-30

300

2.98

7,340

56.45


6,000

1.3/860

15

12

20

1,33,44,00

20,02,00

23,20,00

1,82,000

3.50

1.16

Feasibility Study Executive Summary ES-12 METCON

Maiwa Khola Small Hydropower Project (Package-2) DOED

Feasibility Study - Executive Summary ES-13 METCON

Table No. ES-3.2: Comparison of cost for different plant capacities corresponding to the flow with probability of exceedence ranging from 65% to 40% at gross head 200m (Alternative B)

Amount in Thousand NRS S.N Description Flow(65%)=

3.12m3/s Flow(50%)=4.4m3/s

Flow(45%)=5.9m3/S

Flow(43%) =6.4m3/s

Flow(40%)=7.8m3/s

Flow (37%)=9.75m3/s

1. Civil Works P=5.10MW P =7.11MW P=9.34MW

P=10.44MW P=12.74MW P=15.94MW

a. Diversion weir and intake structures

3,50,00 3,70,00 3,90,00 4,00,00 4,20,00 4,50,00

b. Desilting Basin 1,00,00 1,00,00 1,75,00 2,00,00 2,20,00 2,50,00 c. Water ways 34,50,00 34,50,00 34,50,00 34,50,00 34,50,00 40,48,00 d. Forebay & Penstock civil works 2,00,00

2,50,00

3,00,00

3,30,00

4,00,00 4,80,00

e. Power house & tailrace 3,10,00

3,80,00

4,40,00

4,60,00

5,50,00 6,60,00

Sub Total 1 44,10,00 45,50,00 47,55,00 48,40,00 50,40,00 58,88,002. Hydraulic steel structure (gate,

trashrack valves etc) 1,50,00 1,80,00 2,10,00 2,20,00 2,45,00 2,76,00

3. Electro-mechanical Equipments turbines, generators, transformers, etc)

14,79,00 20,62,00

27,87,00 29,23,00 35,67,00 43,04,00

4. Penstock pipe 7,01,00 7,01,00 10,19,00 10,62,00 13,06,00 15,77,00 5. Project Road 6,30,00 6,30,00 6,30,00 6,30,00 6,30,00 6,30,00 Sub Total 2 29,60,00 35,73,00 46,46,00 48,35,00 57,48,00 67,87,00

A Total Estimated Cost 73,70,00 81,23,00

94,01,00 96,75,00 1,07,88,00 1,26,75,00

B Site installation and general facilities @ 3% of A

2,21,00

2,44,00

2,82,00 2,90,00 3,24,00

3,80,00

C Contingencies: Civil works 15% Electro-Mechanical works (10%)

6,62,00 1,48,00

6,83,00 2,06,00

7,13,00 2,79,00

7,26,00 2,92,00

7,56,00 3,57,00

8,83,00 4,30,00

D Engineering, Administration and Construction Management @ 6% of A

4,42,00 4,88,00 5,64,00 5,80,00 6,48,00 7,60,00

E Environmental cost @ 2.5% of A 1,84,00 2,03,00 2,35,00 2,42,00 2,70,00 3,17,00

Grand Total 90,27,00 99,74,00 1,14,74,00 1,18,05,00 1,31,43,00 1,54,45,00 Annual cost (NRS) 13,54,00 14,92,00 17,21,00 17,71,00 19,71,00 23,17,00 Installed capacity (KW) 5,100 7,110 9,610 10,440 12,740 15,940 Annual Energy (Gwhr) 38.95 49.30 59.32 62.41 70.89

81.33

Energy cost (NRS/Kwhr) 3.48

3.03 2.90

2.84 2.78 2.85

Cost/KW (NRS/KW)

1,77,000 1,40,000 1,19,000 1,13,000 1,03,00 97,000

Annual Benefit (NRS) 16,01,00 20,26,00 24,38,00 25,65,00

29,14,00 33,43,00

Benefit/Cost Ratio (B/C) 1.18 1.36 1.42 1.45 1.48 1.44



4. FIELD INVESTIGATION AND SURVEY

In accordance with the ToR of the contract, the following field investigation and survey

works were carried out for the project alternative recommended by the Inception Report

approved by DoED on February 27, 2008. Most of these works, except for core drilling

and construction material survey, were conducted during March 2008- December 2008

with the completion of geophysical survey by 2D electrical resistivity survey. The field

investigation and survey works regarding core drilling and construction material,

however, could be conducted only during January- April 2009 as the East-West Highway

remained nonoperational during August- December 2008 due to Koshi flood of August

17, 2008 which had washed away the portion of highway at east bank upstream of the

koshi barrage. The field report on the field investigation and survey works excluding core

drilling and construction material was submitted to DoED on May 12, 2009. The report

on core drilling, construction material survey and related tests of geological/geotechnical

investigation, however, was submitted to DoED only on August 7, 2009. The summary

of these field investigation and survey works is briefly presented below:

.

4.1. Topographic Survey and Mapping

At the outset of the feasibility study the only map covering the project area was to a

scale of 1:50,000 and aerial photographs of similar scale taken in September 1996,

which was deemed to be inadequate. The main concern, therefore, was to prepare

suitable maps at the earliest possible. A survey team headed by a Senior Surveyor was

dispatched to the project site on March 14, 2008. The survey team was mandated to

undertake ground survey works for the preparation of topographical maps of proposed

headworks area, forebay area, penstock line, powerhouse site, and tailrace;

topographical strip survey for the headrace tunnel corridor; take cross sections of Maiwa

Khola and Tamor River at different locations; fix alignment of 2D electrical resistivity

survey lines; locations of drill holes and survey alignment of the access road. The field

survey except for location of drill holes was concluded in June, 2008. The location of drill

holes was done by separate survey team during January, 2009.



The entire field data were evaluated immediately in the field. The plotting as well as

mapping work was completed using AutoCad land development software programmes.

The details are presented in Appendix A-1 Topographical Survey and Mapping of Part

III of the Final Report.

4.2. Hydrological, Meteorological and Sediment Data Collection

Maiwa Khola is an ungauged river and hence no time series data on hydrology are

available. A gauging station near Dobhan just about 100m downstream of the existing

suspension bridge over Maiwa Khola connecting Dobhan bazaar and Mahadevtar

situated at its right and left bank respectively was established by the Consultants in

September 2007. A gauge reader was assigned to take daily record of water level and

sediment samples three times a week. Since then data regarding water level and

sediment were collected regularly. The hydrological data required for determination of

long term mean monthly flow, dependable flow and design flow, etc. are generated using

the available data of hydrological stations No. 690 and 684 on Tamor River at Mulghat

and Majhitar respectively obtained from DHM.

The rainfall and temperature data for Taplejung bazaar covering the period 1975-2006

and 1992-2006 respectively and rainfall data for meteorological stations at Dobhan for

1975-2006 were collected from the Department of Hydrology and Meteorology.

According to rainfall data of Dobhan meteorological station for the period 1975-2006, the

average annual rainfall in the project area is about 1674 mm. Based on the information

from Taplejung meteorological station for the period 1992-2006, the average minimum

and maximum temperature in the project area is about 40c and 250c occurring in the

month of January and August respectively of the year. The details are presented in

Appendix A-2 Hydrological & Sedimentation Investigations and Studies of Part III of the

Final Report.

4.3. Geological and Geotechnical Investigations and Mapping

The geological and geotechnical site investigations and mapping works, excluding core



drilling and construction material survey and testing were concluded in December, 2008.

A proposal was made on vertical core drilling programme for the approval from DoED in

August, 2008. In accordance with the terms of reference, the consent of DoED for drill

depth, number of drill holes, drilling sites etc. was taken before commencing the drilling

work. Although the process for mobilization of core drilling team was planned in due

time, the team has to be denied in mobilization for the time being due to the

transportation problem caused by breaching of eastern embankment of Kosi River.

However, the drilling team was able to mobilize in January, 2009. The core drilling

works were completed in April 2009.

4.3.1 Geophysical Survey

Geophysical exploration using 2D electrical resistivity survey was performed before

commencing the core drilling work in accordance with the approved Revised Inception

Report.

The geophysical team was assembled and dispatched to the project site on March 14,

2008 along with topographic survey team. A Consultants team visited the project site

during March 18-27, 2008 and altogether 18 profile lines totaling more than 3,000 m in

length at different locations were proposed for carrying out the 2D electrical resistivity

survey. The survey lines were finalized after considering the importance of the structures

for various components of the project and their location was based mainly on the

topographic condition and preliminary geological assessments.

The field survey was completed at the end of June, 2008. The details are given in a field

report on 2D electrical resistivity survey submitted to DoED on August 21, 2008.

4.3.2 Engineering Geological Mapping

The mapping team was mandated to undertake fieldwork for the preparation of

engineering geological maps of proposed headworks area, forebay area, penstock line,

powerhouse site, and tailrace at the scale of 1:1,000 and head race tunnel corridor at



1:10,000 scales.

Geotechnical field investigations such as joint measurement survey, compressive

strength determination by Schmidt Hammer and seismic studies were performed in

accordance with the terms of reference. The fieldwork was completed during November

and December, 2008. The detailed description is provided in Appendix A-3 Geology and

Geotechnical Studies of Part III of the Final Report.

4.3.3 Core Drilling

Altogether five drill holes were drilled at different locations of the project area. Two drill

holes DH-1 and DH-2 were drilled at powerhouse area to depth of 30 m each. Bed rock

was intersected at 13.90 m & 11.90 m respectively. Similarly DH-3 at forebay, DH-4 at

desilting basin and DH-5 was drilled at inlet portal of the proposed headrace tunnel.

General description of the drill holes are presented in Table No. ES-4. The geological

logs, DCPT values and permeability tests of all holes are shown in Appendices of the

Report on Core Drilling, Construction Material Survey and Related Tests of

Geological/Goetechincal Investigation dated July 2009.

The Lugeon tests were performed in DH-3 at forebay only and the same tests could

not be performed in the holes like DH-1, DH-2, DH-4 and DH-5 successfully since

the bedrock intersected in all the holes are soft, friable, poor quality with open joints

and highly foliated. However, field permeability tests were performed in rest of the

holes.



Table No. ES-4: General Description of Drill Holes

4.3.4 Construction Material Survey and Testing

Construction material such as coarse and fine aggregates and cohesive material

required for construction purpose of the project was assessed at different locations of

the project area. Most of the deposits are pocket type small to medium size located

along left and right bank of Maiwa Khola and right bank of Tamor River. The

cohesive material is available at Sakphara Tole located at about 300 m uphill from

the proposed desilting basin. The coarse and fine aggregate are available in alluvium

deposit of the above described area, which content grey, medium to coarse grained

sand with gravels, cobbles and boulders of quartzite, gneiss, phyllite and schist. The

average thickness of such material is about 3.0m. The investigation of the

construction material was done by excavating five test pits. The test pits were

logged, documented and sampled by a professional Geologist at the site separately

for separate pits. The samples were transported to Geotechnical laboratory of EMES

Pvt. Ltd. where most of the samples were assessed and tested as per the given

standard and procedure to determine the prescribed parameters. Some of tests

Drill Hole No

Inclination Location Drill hole

depth m

Bedrock intersected

depth m

DH-1 Vertical Powerhouse

30

13.90

DH-2 Vertical Powerhouse 30 11.90

DH-3 Vertical Forebay 30 8.00

DH-4 Vertical Desilting basin 20 16.95

DH-5 Vertical Inlet Portal 30 10.00



facility is not available in house laboratory, which were tested in other private and

Government Institution laboratories of the country. Evaluation of such material was

done quantitatively and qualitatively based on field data and laboratory results. The

quantity of the explored material is sufficient and the nature and quality of the

material is suitable with necessary treatment for implementing the project.

The detailed description of core drilling and construction material survey and related

tests is presented in the Report on Core Drilling, Construction Material Survey and

Related Tests of Geological/Geotechnical Investigation dated July 2009.

5. BASIC STUDIES

The basic studies that were conducted in the course of preparation of Feasibility report

are briefly summarized below:

5.1 Hydrological Studies

As per TOR of the contract, the hydrological studies of the project mainly focus on the

interpretation and analyses of collected relevant primary and secondary data information

as described in section 4 above applying the standard and appropriate methodologies

and procedures to determine such important hydrological parameters as long term mean

monthly flows, flood flows, dry season flows, construction flood flows, flow duration

pattern, and stage discharge relationship etc required for completing the feasibility

design of the project. The detailed description of the hydrological studies is presented in

Appendix A-2 Hydrological & Sedimentation Investigations and Studies of the PART III

of the Final Report.

5.1.1 Catchment Characteristics

The Maiwa khola basin is bordered by Jaljale Himal at an elevation of 4540 m amsl,

Dhupi and Sumba danda in the North, Milke, Menchhyam dada in south and East and

Giddhe and Milke dada in the west. The basic basin characteristics of Maiwa and Tamor



were assessed using the Arc View GIS tools based on the digital elevation model (DEM)

data derived from contour map published by Survey Department of Nepal Government.

The total length of the Maiwa khola from its origin to the confluence with Tamor River

near Dobhan at an elevation of about 653 m amsl is about 24 km. It has seven main

tributaries namely Lechuwa, Nenwa, Kanuwa, Yandeli, jaiwa, Hguwa and Hina. The

largest among these tributaries is Yandeli khola joining the Maiwa at an elevation of

about 960 m amsl near Tenthap village located about 2 km upstream of the headworks

site of the project. The average gradient of the Maiwa khola from origin to the

confluence is about 14 %. The average gradient of the Maiwa khola for a stretch of

about 7.5 km between its confluence with Yandeli and Tamor is mild and about 3.4%.

The average slope of the Maiwa khola for the upper part of the catchment above the

confluence of Yandeli Khola is steep and varies from 8.5% to 17%. The side slope of the

Maiwa catchment above the intake varies from 2% to 57% with an average of 26.4%.

The average gradient of Tamor River in between Dobhan and powerhouse site at

Tupurke is about 1.5%. The catchment area of the Maiwa Khola is shown in Figure

No.ES-5.1

5.1.2 The Climate

Lungthung, Taplethok, Taplejung and Dobhan are the precipitation station in the the

Tamor River basin. The closest station to the project site is Dobhan. The mean annual

basin precipitation for the Maiwa Khola basin is about 1674 mm. The monsoon rains

contribute more than 70% of the total annual precipitation. The monsoon, i.e. the wet

season, starts from May to September.

Taplejung Climatic Station with index number of 1405 is the nearest climatic stations

having relatively long (1992-2006) records of temperature data series from the study

basin. The maximum temperature at the station varies from 24.1 0C to 26.1 0C in the

month of July while the minimum temperature varies from 2.7 0C to 5.2 0C in the month

of January.



The temperature varies from place to place depending upon the altitude. The lapse rate

of 6.5 0C/km rise of altitude can be used to find the temperature of a particular place with

reference to the observed temperature at the climatic station. Since the altitude of the

study basin varies from 840 m to 4480 m, the climatic temperature varies from tundra to

temperate and tropical based on the altitude. The relative humidity may be as high as

95% during the wet season and as low as 41% during the dry season.

Figure ES- 5.1 : Maiwa Khola Catchment

5.1.3 Reference Hydrology

The Maiwa Khola is Catchment doesnot have any hydrometric station so no time series hydrological is available. However, Tamor river has two hydrometric stations with station no.684 and 690 at Majihitar and Mulghat respectively. These stations have been



established and are in operation by the Department of Hydrology and Meteorology (DHM). The monthly and yearly stream flow data of these stations have been collected from DHM. Mulghat station (690) has published the data from 1965 to 2006 only. The flow data from 1965 to 2006 of Majhitar station have been generated based on the flow records of Mulghat station using the regression equation established by using the flow data of these both stations for the common period from 1976 to 2006. The long term flow data of both these stations for the period from 1965 to 2006 have been used as the reference for determining the longterm hydrological parameters of Maiwa Khola.

5.1.4 Long Term Hydrology

The careful review of the respective hypometric data showed that the catchment characteristics in between the Mulghat and Majhitar station sites were similar to the catchment characteristic of the Maiwa Khola catchment. The nature of hypsometric curves drawn for the mentioned catchments was found similar and the catchment area values for the mean elevation were found highly correlated Hence, it was recommended to generate the long term flow of Maiwa Khola by Catchment Area Ratio method (CAR) by dividing the difference of flow by the difference of catchment area between Mulghat and Majhitar and multiplying by the catchment area of Maiwa Khola as shown below: ( ) MaiwaAAA QQMaiwaQat 684690 684690 = Where

A 690 = 5894 km2

A 684 = 4390 km2

A Maiwa = 173.4 km2

The flow values thus completed were compared with the flow values determined by other methods such as Middle Irrigation Project (MIP) and regional methods like WECS-DHM and DHM 2004 as well as the relatively very short period observed flow values at gauging station on Maiwa Khola near Dobhan bazaar. From this comparative analysis, the flow values obtained from using the CAR method were found more reliable and hence it was recommended to adopt the same for the



present study. The long term mean monthly and yearly flow of Maiwa Khola at intake site are shown in Table No ES-5.1, as obtained by using different method as mentioned above.

Table No. ES-5.1: Estimated long term mean monthly & yearly flow (m3/s) at intake site

Month

Based on Difference between Majhitar and Mulghat

WECS-DHM

DHM 2004

MIP Observed in 2008

Based on Tamor -Majhitar only

Based on Tamor -Mulghat only

Recommended

Jan 2.5 2.2 4.0 7.3 3.6 2.1 2.0 2.5

Feb 2.0 1.9 3.4 5.5 3.1 1.8 1.6 2.0

Mar 1.9 1.7 2.5 3.6 3.0 1.8 1.6 1.9

Apr 3.2 1.7 2.4 2.8 3.9 2.8 2.4 3.2

May 8.4 2.3 3.2 7.9 5.3 5.4 5.4 8.4

Jun 24.7 7.6 12.6 18.2 11.2 13.5 14.5 24.7

July 48.3 23.3 30.7 44.0 54.6 26.8 28.0 48.3

Aug 54.6 28.0 44.8 75.8 78.4 30.9 30.6 54.6

Sep 37.5 21.4 30.9 50.1 45.4 18.8 21.7 37.5

Oct 16.5 9.5 14.6 24.3 29.3 8.9 10.3 16.5

Nov 6.7 4.0 6.9 12.4 11.0 4.2 4.6 6.7

Dec 3.4 2.6 4.8 9.4 5.4 2.7 2.8 3.4

Yearly 17.2 8.8 13.5 21.9 21.4 10.2 10.3 17.2

5.1.5 Flow Duration Analysis

The generated mean daily flow data of Maiwa Khola intake site for the period from 1965 to 2006 were used for the flow duration analysis. These flow data were generated using CAR method, as explained above.



The results of analysis are presented in the Table No. ES-5.2. The flow duration curve prepared on these results is depicted in Fig No. ES-5.4.

Table No. ES-5.2: Estimated available flow (m3/s) at intake site for different Probability of Exceedence (% of year).

Probability of Exceedence (% of year) Flow (m3/s)

5 63.13 10 47.61

15 38.71

20 32.26

25 26.17

30 20.26

35 14.65

40 10.84 45 8.07 50 6.26 55 5.13

60 4.31

65 3.62

70 3.12

75 2.64

80 2.27

85 1.96

90 1.63

95 1.21

100 1.12

Maiwa Kh

Feasibility S

F

5.1.6 D

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The detailed description along with the results of these analyses is given in Appendix A-

2 in Hydrological & Sedimentation Investigation and Studies of Part III of the Final

Report.

Considering the location, type and size of the project structures like headworks and

powerhouse and tailrace, the design flood of 461m3/s with a return period of 100 years

was adopted for the design of headworks and the same for powerhouse site was taken

as 3570m3/s with a return period 1000 years taking into consideration the possibility of

the Glacier Lake Outbrust Flood (GLOF) in Tamor river.

5.1.7 Construction flood The Diversion flood estimation was carried out by frequency analysis on the generated

annual maximum monthly flow data of intake site for the dry season of the year. The

standard distributions methods like GEV and LPIII and LN were applied for the analysis.

A dry season flood of18.9 m3/s with a return period of 10 Years during the period of

November through April is considered reasonable for the diversion during construction of

the project.

5.1.8 Development of Rating Curve

The rating curves at the intake and powerhouse sites have been developed with the aid

of HEC-RAS, which is a computer program developed at the Hydrologic Engineering

Center (HEC) by US Army Corp of Engineers. The cross-sections taken during field

survey were used to study the water surface profiles by the HEC-RAS Model.

As the river reach is steep with huge gravels and boulders in the river and thick bushy

vegetations at the banks, Mannings roughness coefficients of 0.05 for channel section

and 0.06 for flood plain section were taken for the hydraulic HEC-RAS analysis. The

mixed flow simulation was done for the chances of having both sub and super critical

flow in the river reaches. The Normal depth flow boundary conditions were adopted in

the modeling. The rating curves for intake and powerhouse site are shown in Figure No.

ES-5.5 and ES-5.6 respectively.



Figure No. ES-5.5: Rating Curve at the Intake Site.

Figure No. ES-5.6: Rating Curve at the Powerhouse Site

812

813

814

815

816

817

818

819

820

0 200 400 600 800 1000 1200

Discharge (m3/s)

Wat

er L

evel

(m)

596

598

600

602

604

606

608

610

612

614

0 1000 2000 3000 4000 5000 6000 7000

Discharge (m3/s)

Wat

er L

evel

(m)



5.1.9 Riparian Release

The Hydrological analysis shows that the minimum mean monthly flow at the intake site

of the project is 1.9m3/s. This minimum flow generally occurs in the month of March. It is

estimated that 10% of this minimum flow that is 0.19m3/s will be released downstream of

the headworks of the project.

5.2 Sedimentation Studies

The sedimentation studies of the project consist of review of collected primary and

secondary sediment data analyses. Evaluation of such data and information is to

determine the sediment yield to be used for feasibility design of the project. The details

of the studies are presented in Appendix A-2 Hydrological & Sediment logical

Investigation and Studies of Part III of the Final Report.

5.2.1 Estimate of sediment Yield

The sediment yields at the intake site were estimated based on the observed sediment

concentration data and compared with the values from Himalayan Technique and other

Regional methods. Since the sediment sample is surface grasp sample and taken from

only one vertical section, certain correction factors were applied in sediment yield

estimation based on experience gained in past studies. The estimated sediment yields

were compared with the similar studies in neighboring basins and the regional specific

sediment yield. The estimated total sediment yield from the observed sediment yield was

found to be 557.0 tonnes/year yielding specific sediment yield 10.92 t/km2/yr only which

is very small compared to the regional specific yield of 7695 t/km2/yr for Tamor river

basin. The sediment yield calculated from Himalyan Sediment yield Technique was

found to be about 0.771 million tons per year at the intake site. This carresponds to a

mean annual concentration of about 1422 parts per million by weight (ppm ~ mg/l) at the

intake site using the mean annual discharge of 17.2 m3/s.



5.2.2 Sources of Sediment

Main sources of sediment in river are the soil erosion from the watershed. The human

activities like tilling of land for cultivation, construction of infrastructures like road,

buildings, felling down of trees for fire wood activates the soil erosion. Intense rainfalls

on steep bare land bring a lot of sediment in river with flowing water during monsoon

season. The soil erosion can be divided in to three categories as surface (sheet

erosion), Rills erosion and gulley erosions in high steep slope. Besides the artificial

reasons natural land slide, mass failure and debris flow are also major sources of the

sediment in Nepalese river. The GLOF can also be one of the major sources of sediment

for power house sites but it is not for the intake site as there was no glacier lake in the

Maiwa Khola study basin. About 60 % of the study basin is covered with forest; there are

little chances to have severe sheet and rill soil erosions since the surface of the

watershed are covered all over the year and prevents from direct striking with raindrop.

Due to high gradient of river and banks in some stretches, gulley soil erosions are

possible sources of sediment in Maiwa basin. The agriculture lands are the major

sources of fine sediment in Maiwa khola.

6. PROJECT OPTIMIZATION

Appendix A-4 Optimization Studies of Part III of the Final Report describes in detail the

studies made for the optimization of the project in terms of its installed capacity. The

project, as also described in Section 3 - Alternatives Layouts And Recommended

Layout of the Final Report is a run of - river type project consisting of headworks,

headrace tunnel, forebay, penstock, powerhouse and tailrace. The general approach

adopted for the project optimization is as follows:

Consider the project development options. Prepare general layout and identify the project components for each of the options

considered for the project development.



For each of the option carryout the design of the principal structures of the project components and determine their main features.

For each of the option asses the dry season and wet season energy generation and estimate benefits to be accrued.

Prepare cost estimate for the options considered. Carryout the economic valuation for each of the options by making the benefit cost

analysis based on the present value of benefit and cost.

Finally choose the option providing the maximum benefit /cost (B/C) ratio, Net Present Value (NPV) and Economic Internal Rate of Return (EIRR).

6.1 Project Development Options and Their Economic Evaluation Consultants have made a study to find out the optimum capacity of Maiwa Khola Small

Hydropower project based on the conceptual layout of the project developed with due

consideration of project location, its accessibility from the nearest existing roadhead and

topographical hydrological, meteorological and sedimentation as well as general

engineering geological and geotechnical and environmental conditions of the project

site.

Altogether seven options for the development of the project have been considered.

These options have been specified as option 1,2,3,4,5,6 and 7 with various project

capacities corresponding to design flow of 65%, 60%,55%,50%, 45%, 40% and 35%

probability of exceedence. According to hydrological studies these flows are as follows:

65% = 3.62 m3/s; 60% = 4.31 m3/s; 55% = 5.13 m3/s; 50% = 6.26 m3/s; 45% = 8.07 m3/s;

40% = 10.84 m3/s and 35% = 14.65 m3/s. After preparing the general layout, design and

cost estimate for each of these options, the economic evaluation of each of the options

was made using the following basic economic parameters.

Discount rate 10%. Cost and benefit are based on 2009 price level. Project cost is disburded in 5 years. Replacement cost of E/M equipments is considered in 25th year of operation.



Annual benefits start from 6th year. Project economic life is 50 years. Annual Operation and Maintenance cost is 1.5% of total project cost and starts from

the 6 years.

Energy generation outage is taken as 5%, both in dry and wet season. Discount rate is taken as 10%. Energy benefits are assessed as:

- Dry season energy sale @ Rs. 7 per Kwh.

- Wet season energy sale @ Rs. 4 per Kwh.

The main design features of the project components of considered options are shown in Table

No.ES-6.1.



Table No.ES-6.1:The main design features of the project components of different options considered for Optimization Study

S.No Project Option 1 Option 2 Option 3 Option 4 Option 5 Option 6 Option 7 Components Q65%=3.62m3/s Q60%=4.31m3/s Q55%=5.13m3/s Q50%=6.26m3/s Q45%=8.07m3/s Q40%=10.84m3/s Q35%=14.65m3/s

1. Intake Structure

Discharge=1.15Q% Discharge=4.16m3/s Discharge=4.96m3/s Discharge=5.90m3/s Discharge=7.20m3/s Discharge=9.28m3/s Discharge=12.47m3/s Discharge=16.85m3/s 2nos.4x0.75m 2nos.4x0.90m 2nos.4x1.10m 2nos.4x1.30m 2nos.4x1.7m 3nos.4x1.5m 3nos.4x2m Velocity = 0.69m/s Velocity = 0.69m/s Velocity = 0.67m/s Velocity = 0.69m/s Velocity = 0.68m/s Velocity = 0.69m/s Velocity = 0.7m/s

2. Headrace Cannal-1 Discharge=4.16m3/s Discharge=4.16m3/s Discharge=4.16m3/s Discharge=4.16m3/s Discharge=4.16m3/s Discharge=4.16m3/s Discharge=4.16m3/s (From intake to gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 desilting basins) roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 Rectangular Rectangular Rectangular Rectangular Rectangular Rectangular Rectangular size: 3x0.95m size: 3x1.08m size: 3x1.2m size: 3x1.40m size: 3x1.7m size: 3x2.15m size: 3x2.75m

3. Desilting Basin Discharge=4.16m3/s Discharge=4.96m3/s Discharge=5.90m3/s Discharge=7.2m3/s Discharge=9.28m3/s Discharge=12.47m3/s Discharge=16.85m3/s Velocity=0.27m/s Velocity=0.25m/s Velocity=0.27m/s Velocity=2.7m/s Velocity=0.27m/s Velocity=0.29m/s Velocity=0.294m/s size: 46x7x2.25m size: 46x9x2.75m size: 54x9x3m size: 60x9x3.5m size: 70x11x4m size: 90x12x4.5m size: 108x13x5.5m (LxBxH) (LxBxH) (LxBxH) (LxBxH) (LxBxH) (LxBxH) (LxBxH) Area=13.5m2 Area=19.50m2 Area=21.75m2 Area=26.25m2 Area=34.75m2 Area=42.38m2 Area=57.25m2

4. Headrace Canal-2 Discharge=3.62m3/s Discharge=4.31m3/s Discharge=5.13m3/s Discharge=6.26m3/s Discharge=8.07m3/s Discharge=10.84m3/s Discharge=14.65m3/s (From desilting gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 basin out let to roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 roughness=0.015 Headrace tunnel Rectangular Rectangular Rectangular Rectangular Rectangular Rectangular Rectangular inlet portal) size: 2.5x1.01m size: 2.5x1.15m size: 2.5x1.32m size: 2.5x1.52m size: 2.5x0.85m size: 3x1.93m size: 3x2.43m

5. Headrace Tunnel Discharge=3.62m3/s Discharge=4.31m3/s Discharge=5.13m3/s Discharge=6.26m3/s Discharge=8.07m3/s Discharge=10.84m3/s Discharge=14.65m3/s

D-Shaped (2.5x2.5m)

D-Shaped (2.5x2.5m)

D-Shaped (2.5x2.5m)

D-Shaped (2.5x2.5m)

D-Shaped (2.5x2.5m) D-Shaped (3x3m) D-Shaped (3x3.5m)

gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1000 gradient 1/1200 gradient 1/1500 Velocity=1.43m/s Velocity=1.5m/s Velocity=1.03m/s Velocity=1.23m/s Velocity=1.61m/s Velocity=1.74m/s Velocity=1.75m/s

6. Forebay volume 650m3 780m3 925m3 1130m3 1460m3 1960m3 2640m3

7. Penstock length/ 700/1.2m 700/1.4m 700/1.4m 700/1.6m 700/1.8m 700/2.2m 700/2.4m optimum diameter 8. Powerhouse 5.92 6.72 8.31 10.17 13.14 17.22 23.92

Capacity(Mw)



Table No ES-6.2: Summary of Economic Indicators obtained from Benefit-Cost Analysis

Options Capacity MW Total Committed Energy Generation GWH

Cost in 000 NRs

Average Benefit in 000 NRS

Benefit Cost Ratio

B/C

Economic Rate of Return

(EIRR %)

Net Present Value in

(000 NRs) Wet Season Dry Season

1

2

3

4

5

6

7

5.92

6.72

8.31

10.17

13.14

17.72

23.92

42.48

46.47

54.21

63.29

76.11

92.37

114.00

13.59

13.66

13.66

13.69

13.70

13.71

13.71

28.89

32.81

40.55

49.60

62.41

78.66

100.29

1,38,77,50

1,45,12,16

1,52,28,81

1,63,08,17

1,82,07,19

2,25,19,28

2,72,32,96

21,06,61

22,68,41

25,77,94

29,42,29

34,55,21

41,06,21

49,71,74

1.21

1.32

1.34

1.43

1.50

1.44

1.44

12.13

12.44

13.41

14.23

14.90

14.35

14.36

23,81,07

25,81,60

42,61,17

57,16,31

74,98,84

81,04,89

98,23,49


Feasibility Study Executive Summary METCON

E-34

6.2 Recommendation for the Optimum Installed Capacity

According to the economic evaluation of various options, it is revealed that option 5 is

the optimum option. This option with a capacity of 13.14 MW, if considered for project

development, provides maximum B/C, and EIRR compared to other options. As shown

in Table No ES-6.2, the benefit cost ratio (B/C) and Economic Internal Rate of Return

(EIRR) for this option is 1.50 and 14.90% respectively Hence it is recommended that the

installed capacity of the Maiwa Khola Small Hydropower Project be adopted as 13.14

MW corresponding to a design flow of 8.07m3/s with a 45% probability of exceedence.

7. PROJECT DESCRIPTION AND DESIGN

Maiwa Khola Small Hydropower Project, as proposed in the present study, is a high

head run-of-river type project with an installed capacity of 13.5Mw.

The project is located in Dhungesangu and Change VDCs of Taplejung district of

Eastern Development region of the Country. According to general layout and design,

the project comprises of a 30m long and 7m high concrete diversion weir, with an

undersluice structure, side intake capable of diverting a design discharge of 8.07m3/s,

170m long covered headrace canal-1 connecting intake to desilting basin, 90m long and

10m wide single chamber desilting basin, 60m long headrace canal-2 connecting

desilting basin with the inlet portal of 2.5x2.5m inverted D Shaped and 4,150m long

headrace tunnel, forebay, 700m long penstock pipe with diameter 1.9m, powerhouse

accommodating 2units of electromechanical equipments each with a capacity of 6.75

Mw and tailrace.

The general plan of the project in the existing toposheet of the project area is shown in

DWG No. ES-1. The general layout of the project with its components based on its

design is depicited in DWG No. C-1. The salient features of the projects have already

been presented in the very beginning of this report. A very brief description of the project

components, however, is summarized below. All drawings referred to in the description

are given in Part III Appendix A-7 Maps and Drawings of the Part II, Volume 1 Main

Report.



E-35

7.1 Description of Project Components

7.1.1 Headworks

A design of headworks of the project is prepared using the topographical maps

developed in a scale of 1:1,000 with 1m countour interval and results of study and

analysis of hydrology, meteorology and sedimentation and geology of the project area.

A special care has been taken to prevent these structures from sedimentation to the

extent possible while preparing their respective design in terms of their layout and

hydraulic as well as structural functioning. According to general layout of Headworks as

shown in DWG No. 2, the headworks consists of diversion weir, intake structure,

headrace canal-1, desilting basin and headrace canal-2. The basic design features of

these structures are briefly described below:

a) Diversion weir

It is proposed to construct a nongated concrete weir across Maiwa Khola near Mahabun

village situated at about 5.5Km upstream of Maiwa Khola confluence with Tamor river

near Dobhan bazaar. The weir is designed to pass the flood discharge of 461m3/s with a

return period of 100 years. The length of the weir including a undersluice structure at

the left bank of the river is 30m, of which, 22m is provided for the nongated weir with its

crest fixed at an elevation of 815 Masl and rest 8m is provided to accommodate two

bays (each of 3m width) of undersluice structure along with two separation peirs. The

crest of underluice structure is fixed at elevation of 812 Masl. Each bay of the

undersluice structure is provided with stoplogs and a vertical gate to be operated by

hoist installed at an elevation of 825 Masl. The width and height of gate is 3.30x3.30m.

The gates will be opened during wet season to flush down the bed load likely to be

deposited upstream of undersluice structure and will be remained closed during lean

season to facilitate the diversion of river discharge to intake structure closely located at

upstream of undresluice structure. Such operation of gates at undersluice structure

prevent the intake structure from siltation. In order to have subcritical flow conditions at

the downstream portion of weir it has been designed as a stilling basin to eliminate the

supercritical flow due to formation of hydraulic jump during the design flood passing over



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the weir. The length of stilling basin is 28m and it is made up of structural concrete

placed at an elevation of 809 Masl that is 2m below the top of the down stream

protection apron provided in the form of 1 to 1.5m thick riprap to protect the river channel

from scouring. The riprap is placed at elevation of 811 Masl. As the weir is founded on

the moderately permeable alluvial deposit, a 15m long upstream concrete apron and 2m

deep cutoff wall up to elevation of 808 Masl is provided at the upstream face of the weir.

This will help to increase the seepage length and subsequently reduce the uplift

pressure on the foundation level of the weir enhancing its stability.

The plan and sections of diversion of weir including intake and under sluice structure are

shown in Dwg. No 3, C-4 and C-5 respectively.

b) Intake Structure

The intake structure is located at the right bank of the weir immediately at the upstream

of the undrsluice structure and is connected to a rectangular covered headrace canal-1

designed to convey the flow from intake to desilting basin.

Intake is designed for a flow equivalent to 1.15 times the design flow required for power

generation considering that 15% of this flow is required for flushing operation of desilting

basin. The elevation of entrance sill of the intake is placed below the crest elevation of

the diversion weir. For a design flow of 8.07m3/s corresponding to 45% probability of

exceedance a flow of 9.28m3/s is adopted for the design of intake and elevation of

entrance sill is fixed 813.30 Masl that is 1.7m below the crest level of the weir. Two bays

of intake structures each with a width of 4m and depth of 1.7m will divert a flow of

9.28m3/s with a velocity of 0.68 m/s. The intake structure is designed as a rigid

reinforced concrete structure and is connected to covered headrace canal-1 by its side

walls designed as retaining walls. Each bay of the intake is provided with stoplogs and

trash racks. The size of the trash racks for each bay is 4m wide and 2.15m high. A

gravel trap immediately behind the trashrack is provided to remove the gravels entering

the trash rack by flushing them down to downstream of the undersluice structure. A

vertical intake gate is provided at the beginning point of covered headrace canal-1 to

regulate the flow to the canal and to facilitate the inspection and maintenance of canal

structure.



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c) Headrace Canal-1

The flow from the intake is conveyed to desilting basin through a rectangular shaped

covered canal. The canal runs through the right bank of river. For discharge of 9.28m3/s

the net size of canal is 3m wide, 1.70m high and has a gradient of 1:1000 and velocity

1.81 m/s. The canal is covered and designed as a reinforced concrete box. The top of

the box right from beginning to end is kept at elevation of 816.00 Masl.

d) Desilting Basin

It is located on a raised flat terrace on the right bank of river approximately at 90m

downstream of the diversion weir. The design discharge of desilting basin is same that of

headrace canal-1. 15% of design discharge is used to flush accumulated silt down to

the river. The basin is designed to remove the silt particles larger than 0.2 mm in size.

For the design discharge of 9.28m3/s the size of a single chamber desilting basin has

been calculated as 70m long 11m wide and 4m deep. These calculations are made

based on the assumption that the settling velocity is 0.021m/s and mean velocity of flow

in the basin is 0.27m/s. Flushing operation is supposed to be continuous, specially in the

monsoon season. Desilting basin is connected with headrace canal-1 and headrace

canal-2 by a 10m long transition structure at each end. The inlet transition structure is

provided with a gate to shutdown the desilting basin for its repair and maintenance. The

upper half of the cross section of the basin is rectangular while the lower half is inclined

at an angle of 450 towards the centre through which the sediment will roll down to two

flushing galleries running along its length at a gradient of 1:70. Near the outlet transition,

these galleries will be equipped with the gates. By opening these gates the silt will be

flushed down to river through a flushing channel. The river side face of desilting basin is

protected by gabions and backfilling required to maintain the top level of desilting basin

at an elevation of 816.00 Masl. Hill side face of the desilting basin requires excavation

over its top level to locate the road to intake and diversioin weir sites.

e) Headrace Canal-2

The silt free flow from desilting basin is conveyed to inlet portal of the headrace tunnel



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by a rectangular canal. The design discharge for this canal is 8.07 m3/s. The nett size of

the canal is 2.5m wide and 1.85m deep. The velocity is 1.61 m/s. The major portion of

canal is proposed to be constructed as covered reinforced concrete box with its top at

elevation of 816Masl. The gradient of canal is 1:1000.

7.1.2 Headrace Tunnel

The water from the headrace canal 2 to forebay is conveyed by a headrace tunnel

passing through the right bank of Maiwa Khola. It is designed to carry a flow of 8.07m3/s.

The hydraulic calculation show that an inverted D-Shaped, non pressure and completely

concrete lined tunnel of 2.5mx2.5m dimension with a gradient 1:1000 is appropriate to

convey the design flow 8.07m3/s to be used for power generation. The velocity of flow in

the tunnel is 1.75m/s for these flows.

The plan and longitudinal profile showing the support system as depicted in Dwg. No. C-

14 and C-15.

7.1.3 Forebay

A 58 m long 10 m wide and 2.5 m deep forebay accommodating a volume required for

the storage of 3 minutes design flow of 8.07 m3/s is designed and located at north corner

of Bajhogara village at the foot of an exposed rocky slope near the foot trail on the way

from Dobhan bazaar to Bajhogara village. A 5 m long and 4m wide penstock intake

structure is located at the western end of the forebay. Penstock inlet structure is

provided with sloplogs and trashrack. The normal water level at forebay is estimated as

810.52Masl after considering the headlosses in the headrace tunnel and the top level as

812.02 Masl considering a free board of 1.50 m. As there is no place for locating a

structure for the overflow of the design flow incase of sudden closure of the powerhouse,

it is proposed that the same will have to be located near the inlet portal of headrace

tunnel at an elevation of 812.00 Masl. Structurally, the forebay is designed as a

reinforced concrete structure having 0.5m thick bottom slab and 0.30m to 0.5m thick

side walls. The plan and cross sections of the forebay are shown in Dwg No. C-16 and

C-17.



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7.1.4 Penstock Pipe

A 700m long steel penstock pipe with a diameter of 1.9m and thickness of 20mm

conveys the flow from forebay to Powerhouse equipped with two units of Francis

turbines. The first 118m length of penstock pipe is aligned in southeast direction through

the flat terrace while the rest of its length aligned in eastwest direction with a horizontal

bend of about 500-0-30at the location of anchor block 2. It is bifurcated at an elevation

of 610 Masl near an anchor block behind the power house to feed the turbine. The

diameter of each pipe after bifurcation is 1.35m. The entire length of penstock pipe has

one horizontal bend and 7 including one at the location of horizontal bend vertical bends.

At all these places the penstock pipe has been provided by anchor blocks and the

expansion joints. Besides the anchor blocks the penstock pipe has been supported by

intermediate saddle supports to be located at every 6m length of pipe. The plan and

longitudinal profile of penstock pipe is shown in Dwg No. C-18 and C-19.

7.1.5 Powerhouse and Tailrace

The powerhouse and Tailrace of the project are located on the right bank of Tamor river

near a place locally known as Tupurke.

The surface powerhouse is designed to house the generating mechanical and electrical

equipments comprising of turbines with penstock inlet valves, spiral cases, draft tubes,

overhead crane and governers, and generators with excitation and power control and

protection equipments etc. The dimensions of the powerhouse has been determined

considering the space requirement for installation, operation and maintenance of the

mentioned generating mechanical and electrical equipments. According to adopted

design, it is envisaged that two sets of the said equipments each with a capacity of 6.75

Mw will be installed operated and maintained in the powerhouse. The dimensions, of

power house as determined by the design are as follows.

Length of powerhouse 23.4m (including service bay and control room)

Width of powerhouse 11.00m

Height of powerhouse 17.40 (from the draft tube foundation level to roof level of

powerhouse)



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The turbine axis has been fixed at an elevation 610Masl taking into account the Tailrace

water level of 609.62 and assumed characteristics of turbines to avoid the cavitation.

The bottom level of draft tube is at 606.6 Masl. The flow from turbine is discharged to a

tailrace canal through the draft tube. The each outlet of the draft tube is provided with

stoplogs to be operated from outside the generator floor. The generator floor is at

613.50Masl and has been provided with the space for service bay and store and

common room. An overhead crane with a capacity of 16 tonne has been installed at a

level of 618.50 Masl. The water from the draft tube is released to a covered box type

tailrace canal which discharges the same to Tamor river. The length of this canal is 65m.

For design flow of 8.07m3/s the cross section of this canal is fixed as rectangle with width

2.50m and height 1.86 at a gradient of 1:1000. The plan and sections of the power

house are shown in Dwg. No. C-22 and C-25.

7.1.6 Hydraulic Steel Structure The hydraulic steel structure of the project mainly consist of stoplogs (at intake,

undersluice, forebay), trashracks (at intake and forebay), and vertical gates (at

undersluice, intake, desilting basin and power house. The details are given in Part II,

Volume-1 of the Final Report.

7.1.7 Mechanical Equipments

The mechanical equipments are mainly 2 nos of vertical shaft hydraulic turbines

completely equipped with governors and other turbines auxiliary equipments and

accessories, 2 nos of inlet values and an overhead gantry crane.

The main parameters of the turbines are as follows:

Numbers of Turbines - 2 Types of Turbines - Francis Rated Head - 199.07 m Rated discharge per unit - 4.04 m3/s Rated efficiency - 91%



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Turbine output per unit - 7.15 MW Shaft Configuration - Vertical Shaft Rotation - Anti clockwise Turbine specific Speed - 96 Synchronous Speed - 750 rpm Runner Diameter - 0.87 m Spiral case inlet diameter - 0.87 m Static Head - 0.383 m

7.1.8 Electrical Equipments

Two units of 3 phase synchronous A/C generators with brush less excitation system are

to be coupled directly with the vertical shaft Francis turbines. The capacity of each unit of

the generators is 6.8 MW at its rated power factor 0.85 lagging. Each unit of the

generators is connected to the 11 KV bus through a circuit breaker and associated

control and protection devices as shown in single line electrical diagram depicted in

Dwg. No.E-1. The main features of the generators are as follows:

Numbers of generators - 2

Rated capacity of generator - 2 x 8 MVA

Power Factor - 0.85

Cooling System - Air cooling

Synchronous speed - 750 rpm

Frequency - 50 Hz

Generating Voltage - 11 KV

Number of Phases - 3

Excitation system - Brushless

7.1.9 Switchyard and Transmission Line

7.1.9.1 Switch Yard

A 11 KV / 132 KV outdoor switchyard is planned to be located on a flat terrace on the



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western corner of the powerhouse. The size of the switchyard is estimated to be 40 m

wide and 60 m long. Two 11KV / 132 KV, 3 phase step-up power transformers each with

8200 KVA ratings are to be located in the switchyard. The other switchyard equipments

and accessories are 132 KV SF6 breakers, current transformers (CT), Potential

transformer (PT), 132 KV metering and protection panels, disconnecting switches,

PLCC, gantry, busbar, ACSR conductors, insulators, control and power cables etc.

Numbers of power transformers - 2

Type - Outdoor, oil immersed

Rated Power Output - 2 x 8000 KVA

Rated Voltage - 11 KV / 132 KV

Rated Frequency - 50 Hz

Type of Cooling - ONAN

7.1.9.2 Transmission line It is proposed that power generated from the project (13.5 MW) will be fed into the

National Grid at Banande - the likely future point of connection not only for this project

but also for a number of other projects currently being studied in its close vicinity by a

7Km long 132 KV transmission line.

8. ASSESSMENT OF PROJECT OUTPUT AND RELATED BENEFITS 8.1 Basis for Assessment

The input data and assumptions used as the basis for the assessment of project outputs

and related benefits are as follows.

a) Assessment of Project output

The long generated term average monthly flow of Maiwa Khola. Downstream release flow 0.19m3/S



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Firm discharge (90% exceedence) 1.63m3/S Design discharge (45% exceedence) 8.07m3/S Design nett head 190.07 m Installed capacity 13.5 MW Number of Units 2 Efficiency of turbines 91% Efficiency of generator 95% Efficiency of transformers 99%

b) Assessment of Project benefit.

Average plant outage 5% Selling price for energy Rs. 7/KWh for dry season

(as per the existing NEA power Rs. 4/KWh for wet season

Purchase rate for the plant upto 25MW

Capacity)

8.2 Power and Energy computations

With the given input parameters and assumption the calculations for the monthly power

and energy generation have been carried out the total annual average energy

generation is estimated as 82.23 GWh of which 14.77 GWh is generated during dry and

67.46 GWh in wet season respectively. The maximum power generation is 13.5 MW.

8.3 Computation of Project Benefit

As described above the annual benefit are the revenues likely to be accrued from the

sale of the annual energy generation of the project. Considering the scheduled and

forced outage of the plant as 5%, the average annual energy generation is 78.11 GWh

of which 14.03 GWh is in dry season and 64.08 GWh is in the wet season as shown in

Table No. ES-8.2. The average revenues / benefits to be accrued from the sale of the

average annual generated energy is Rs. 35,45,30,00 of which Rs 9,82,10,000 for the

sale of dry season energy (14.03 GWh) at Rs. 7/KWh and Rs. 25,63,20,000 for the sale

of wet season energy (64.08GWh) at Rs 4/KWh respectively.



Table No. ES-8.1 Calculation of Power & Energy Generation Assumption and input parameters Forebay intake Level 810.52m Tailwater level 609.62m Generator Efficiency 95.00% Turbine Efficeincy 91.00% Transformer efficiency 99.00% Overall efficiency 85.59% Gross head,m 200.90m

Design flow, (Q) m3/s 8.07 Probability exceedence, %45%

Dry season outage 5% Wet season outage 5% Penstock detail Length of penstock 700 m Friction coeficient 0.0120 For steel penstock Penstock Diameter 1.9m Head loss 0.028 1Q2

Month

Mean D/S Irrigation Available Diverted Operating Design Headloss Nett Head Generation

Dry season Wet season

Monthly release release flow flow days flow Penstock (H) capacity energy energy flow 8.4xQxH

(m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m3/s) (m) (m) (kw) (kwh) (kwh) Jan 2.5 0.19 0.00 2.31 2.31 31 2.31 0.15 200.75 3,895.35 2,753.233 Feb 2 0.19 0.00 1.81 1.81 28 1.81 0.09 200.81 3,053.12 1,949,112 Mar 1.9 0.19 0.00 1.71 1.71 31 1.71 0.08 200.82 2,884.58 2,038,882 Apr 3.2 0.19 0.00 3.01 3.01 30 3.01 0.25 200.65 5,073.23 3,470,089 May 8.4 0.19 0.00 8.21 8.07 31 8.07 1.83 199.07 13,494.56 9,537,955 Jun 24.7 0.19 0.00 24.51 8.07 30 8.07 1.83 199.07 13,494.56 9,230,279 Jul 48.3 0.19 0.00 48.11 8.07 31 8.07 1.83 199.07 13,494.56 9,537,955 Aug 54.6 0.19 0.00 54.41 8.07 31 8.07 1.83 199.07 13,494.56 9,537,955 Sep 37.5 0.19 0.00 37.31 8.07 30 8.07 1.83 199.07 13,494.56 9,230,279 Oct 16.5 0.19 0.00 16.31 8.07 31 8.07 1.83 199.07 13,494.56 9,537,955 Nov 6.7 0.19 0.00 6.51 6.51 30 6.51 1.19 199.71 10,920.94 7,469,923 Dec 3.4 0.19 0.00 3.21 3.21 31 3.21 0.29 200.61 5,409.25 3,823,258 Maximum Power Generatio

maiwa khola

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