Panel of Experts (Hydrologist/Sediment Expert)

Asian Development Bank (ADB)

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Objective and Purpose of the Assignment
A. Background  
1. Tanahu Hydropower Limited (THL) was established as a Subsidiary Company of Nepal Electricity 
Authority (NEA) in the year 2012 to develop Tanahu Hydropower Project. The storage type project of 
installed capacity 140 MW, which is under construction, is co-financed by the Asian Development Bank 
(ADB), the Japan International Cooperation Agency (JICA) and the European Investment Bank (EIB). 
2. Tanahu Hydropower Limited (THL) has identified the Lower Seti (Tanahu) Hydropower Project in the 
downstream reaches of the Seti River. Following the Desk Study of the Project, THL has also acquired the 
Survey License of Generation from the Ministry of Energy in the year 2018. Subsequently, THL has engaged 
the JV of WAPCOS Limited, India and Nippon Koei Co., Japan, herein referred to be the "Consultant", for 
Detail Engineering Design and Preparation of Bidding Documents in May 2019 under Grand 0361-NEP (Project 
Preparatory Facility  for Energy) of Asian Development Bank. 
3. Lower Seti (Tanahu) Hydropower Project lies in Tanahu district of Western Development Region (WDR) of 
Nepal between longitudes of 84⁰17’30”E and 84⁰28’42”E and between 27⁰47’30”N to 27⁰55’00”N. The project 
lies in the Seti River of the Middle Hilly Region which constitutes a broad complex of hills and 
valleys. The dam site is located at Nalabun Dharampani, Kota VDC at about 19 km upstream of confluence 
of Seti and Trishuli River, while the powerhouse site is located at Gaighat, Kota VDC on the right bank 
of the Seti river approximately 2 km downstream from the confluence of Seti and Trishuli Rivers. The 
elevation of the intake site is about 255 m above the mean sea level (amsl) and that of the powerhouse 
site is about 200 masl. 
4. Lower Seti (Tanahu) Hydroelectric Project has been conceived as a Peaking Run-of-River (PROR) type 
scheme with the installed capacity of 104 MW. The major civil components of the project are as follows: 
(i) LSHPP has Catchment area (at intake site) 2849 Km2. Its Mean Annual Discharge is189.66 m3/s and 
Design Discharge of 145.34 m3/s with Probability of Exceedance of 40 %. 
(ii) Headworks consisting of a gated dam and a side intake at the right bank of River. The crest length 
of the dam is 200 m with four radial gates in order to pass the design maximum flood (1 in 10,000) of 
7779 m3/s. The height of dam including foundation is 45 m. There will be two numbers of intakes of size 
8 m x 12 m each. 
(iii) A two chambered underground desilting basin of size 180.5 x 16.5 m x 20.5 m to trap silt/sand 
particles larger than 0.2 mm.  
(iv) Water conveyance system consisting of Inverted D-shaped headrace tunnel of 8 m diameter with total 
length of 5.5 km. 
(v) A surge shaft of 18 m diameter and 55.26 m height at the end of headrace tunnel.  
(vi) A vertical drop shaft of 80 m height and 7.2 m in diameter.  
(vii) A steel penstock of diameter 6.5 m and length 100 m including bifurcation. The thickness of 
penstock pipe is estimated to be 20 mm.  
(viii) A surface type of powerhouse of size 60 m x 24 m x 43 m.  
(ix) A tailrace canal of length 250 m to discharge the water from the turbines back to Trishuli River. 
The electro-mechanical equipment consist of two turbine units of Francis Turbines (Rated Power of 53,300 
kW each) each coupled with a synchronous generator (Rated Power of 61.2 MVA).The energy generated from 
the project will be injected to the Damauli- Bharatpur Transmission line to be constructed by Tanahu 
Hydropower Limited with the switching arrangements.
5. As per agreement with the ADB, THL is required to engage an Independent Panel of Experts (POE) to 
review detail design of the project, currently being prepared by the Consultant.  The Panel (POE) shall 
work closely recognizing the importance of technical, economic, environmental and social considerations 
throughout the review of the project.  The POE will therefore draw from the technical expertise and 
knowledge of the Panel members as required on issues of engineering design of hydropower components with 
engineering geology and rock mechanics, tunneling and hydrological and sedimentation aspect.   
6. The POE- Hydrologist/Sediment Expert will be appointed by THL to undertake periodic, comprehensive 
and independent reviews of the hydrological and sediment analysis/study of the project. The objectives 
of the reviews are to provide advice and guidance to THL and Consultant to ensure i) appropriate & 
sufficient study/analysis of hydrology i.e. mean monthly flow, flow duration curve, flood analysis; ii) 
study and analysis of sedimentation aspect including impact and measures for sediments considering 
sediment flushing of Tanahu Hydropower Project; and iii) analyzing and method for minimization of 
adverse impacts on the physical and social environment from engineering perspective.  
7. The Panel of Experts (POE) will comprise three distinguished experts in their field, namely the 
Hydropower/Civil Engineer (a Team Leader), Hydrologist/Sediment Expert and Geotechnical Engineer/ 
Geologist. The Hydrologist/Sediment Expert shall act in co-ordination with Hydropower/Civil Engineer. 
The other two experts will be appointed separately but the Panel will be required to meet concurrently 
and work together when on the assignment, with the exception of special meetings which may be convened 
to review particular technical aspects.   
8. The panel members will try to meet/operate concurrently as often as possible, so that there can be 
cross referencing and a more effective use of resources. Also, that they will primarily be responsible 
for reviewing the work of others and undertaking verification and inquiry, rather than developing 
original analysis.  

Scope of Work
B. Scope of Work  
9. The primary responsibility of the POE is to provide an independent review of the detail design and 
other reports submitted by the Consultant. In addition, the scope of the Panel also covers compliance 
checking as per ADB’s safeguard policy statement. The Panel will be expected, in addition to any other 
items which they deem pertinent, to: 
a. Review the overall layout, design criteria and parameters (Design Basis Memorandum, DBM), project 
optimization, specifications and design of the project structures, including river diversion structures, 
dam, spillway, energy dissipater, outlets, intake, desilting basin, tunnels, surge tank, pressure shaft, 
hydraulic elements of the powerhouse and tailrace (Draft Detail Engineering Design Report); 
b. Review of all hydrological and sediment data, hydrology and sedimentation studies including all 
numerical modelling related to reservoir sedimentation in consideration of flushing operation of Tanahu 
Hydropower Project; 
 c. Evaluate the impact of the expected sediments on the choice of intake structures and desilting 
d. Review and if necessary upgrade the seismic hazard assessments and required inputs for seismic design 
parameters for design of the major structures; 
e. Review potential landslide areas along the river in the upstream of the dam, etc. and required 
remedial measures including survey and monitoring; f. Evaluate all design parameters (DBM) at and along 
the extent of the project structures;  
g. Review the proposed instrumentation to monitor the performance of the dam. Review of quality and 
sufficiency of the geological investigations and the interpretation thereof; correctness of the 
geological and hydrological models of the region, reservoir area and dam site; engineering implications 
with respect to foundation design, stability of natural and excavated slopes; and support of surface and 
underground excavations; 
h. Carry out a critical review of the structural adequacy of all structures and nongeotechnical 
construction materials; 
 i. Review the overall risk management. Provide guidance on the risk register and the geotechnical 
baseline report.  
j. Provide recommendations in consultation with other POE members and project stakeholders, on any 
specific environment, health and safety issues which might arise during project implementation. 
10. The tenure of the POE will span until the end of the design phase (excluding interface phase). 
However, it is a good practice that the same POE will be maintained during construction supervision up 
to the commissioning of HPP and initial operational period of one year. 

Detailed Tasks and/or Expected Output
C.  Meetings, Schedules and Output/Reporting Requirements 
11. The Hydropower/Civil Engineer will be nominated as the Chair of the panel. The chair will coordinate 
with other panelists to ensure the delivery of the expected outputs from the POE and to provide balance 
to its reviews and recommendations. The Chair will coordinate the activities and communications of the 
Panel, call and chair its meetings, and liaise as appropriate with THL and the Consultant, inviting as 
deemed necessary relevant experts for each meeting.  
12. The POE will convene at regular intervals to review the status of detail design of project. The 
frequency of meetings and their timing will be adjusted to conform to the schedule of detail design of 
project in progress. At each meeting, the scheduled dates for the next meeting and tentative timing for 
the subsequent meeting and field visit will normally be fixed to enable POE members to arrange their 
individual schedules. Extraordinary meetings of the POE may be called on critical situations, and the 
services of individual members may be solicited between meetings as considered necessary or desirable by 
THL with copies of the required inputs being sent to other POE members. The initial meeting will include 
an extensive field visit. Field visits to the project area coinciding with subsequent meetings will be 
arranged at the POE’s request. Panel members will be supplied with complete set of documents and will be 
briefed in Kathmandu by THL and the Consultant before the initial field visit. The Panel would normally 
visit the wider project area, location of all project components, and affected communities upstream and 
13. The Hydropower/Civil Engineer as the Chairman will prepare and submit written proceedings of the 
meetings and field visits (regular or extraordinary), including observations and recommendations, by 
receiving inputs from each member of the POE, within two weeks of the meetings, and in case of emergency 
will prepare technical memoranda or aide memoires during the meetings. A preliminary report will be 
prepared before the adjournment of each meeting and signed by all member of the POE before departure 
from Kathmandu. Copies of all proceedings being submitted to THL shall be subjected to review by the 

Minimum Qualification Requirements
D. Organization, Membership and Qualifications  
14. The Hydrologist/Sediment Expert shall have minimum of Master’s degree or equivalent in 
hydropower/water resources/ hydrology/ sedimentation and must have 25 years of professional experience. 
The expert will review long term hydrological series developed and adopted for energy generation, design 
flood peaks of different return period, assess probability of occurrence of 'GLOF' in the project 
catchment and its impact on design flood if any. The expert will also review the available flow/sediment 
data of hydrological stations, rainfall data of stations in the catchment and other available hydro-
meteorological data.  
The expert will review the hydrological study reports carried out the Consultant including but not 
limited to the following: 
a. Analysis of the long-term hydrological series including flow duration curve used for power 
generation; b. The criteria and methods by which the data were used to estimate Maximum Probable Flood, 
Design Flood, reservoir inflow and flows to be diverted during project construction, and the need to use 
other methods to improve accuracy of results; c. Review on Dam Break analysis in view of GLOF and PMF;  
d. Review of Numerical/Physical Model Test reports prepared by the Consultant; e. Assessment of peaking 
energy; f. Review on Sediment study/analysis, in consideration of sediment load during flushing of 
Tanahu Hydropower project; g. Low flow hydrology, availability of water for flow releases; and h. Review 
of analysis of GLOF study carried out by the Consultant. 
15. The Hydrologist/Sediment Expert shall have previous similar experiences of working in the Panel of 
16. The Hydrologist/Sediment Expert must be fluent in verbal and written English.