Funding Agency: Upper Tamakoshi Hydropower Limited
Client: Upper Tamakoshi Hydropower Limited
Date: February 2015 – September 2016

The optimization study of UTKHEP performed in the Detailed Feasibility Study (DFS) concluded that the Project will be developed in two stages: (a) Stage 1 corresponding to normal turbine water flow of 44m3 /s (309 MW), and (b) the Stage 2 adding 22m3/s, totaling turbine water flow of 66m2/s (456 MW).

Stage 1 would utilize all water in Tamakoshi River at Lamabagar in the dry season for energy production having installed capacity of 309 MW.

Stage 2 comprises two components:

Increasing the plant capacity to a total of 456 MW corresponding to 66m3/s design discharge: and
Utilizing the dry season water flow of Rolwaling Khola for energy production in UTKHEP by constructing a diversion tunnel from Rolwaling Khola upto UTKHEP reservoir.

However, as per the outcome of the Detailed Engineering Design of UTKHEP, UTKHPL had decided to include component (i) into Stage 1 with total generating capacity of 456 MW in a single stage and leaving only component (ii) into Stage 2, i.e., inclusion of Rolwaling water into UTKHEP reservoir.

Thus, Stage 2 will comprise only following work:

Diversion of Rolwaling Khola
Construction of headworks at Rolwaling Khola
Construction of diversion tunnel from Rolwaling to UTKHEP Intake reservoir including adit tunnel

UTKHPL has envisaged two alternative layouts of the Intake and Diversion Tunnel, which are described as below:

Alternative 1: It is studied preliminarily during the Detailed Feasibility Study (DFS). Intake is planned at an elevation approximately 2010 masl(meters above sea level). 6 km long free flow diversion tunnel (x- sectional area 14 m2 and slope 1:300) and about 150 m long adit tunnel at lower Lamabagar are proposed.

Alternative 2: It will be integrated with proposed Upper Tamakoshi ‘A’ (UTA), located upstream of UTKHEP, by further extension of the Rolwaling diversion tunnel towards upstream in later stage. Since tentative intake of UTA is proposed at elevation 2180 masl, intake of Rolwaling diversion is considered as approximately at elevation 2190 masl. About 5.5 km long low pressure/ free- flow tunnel about 1 km long adit tunnel at lower Lamabagar are proposed.

Overall Services provided:

TMS in association with Lahmeyer International is responsible for the following tasks:

A. Review of previous studies and EIA reports of UTKHEP.

B. Conduct topographical surveys at Rolwaling intake locations, adit tunnels portal and outlet areas for different alternatives.

C. Hydrological Studies of both Tamakoshi River and Rolwaling Khola.

D. Preliminary geological and geotechnical studies and prepare a schedule of field investigation works to be carried out by the contractor,

E. Carry out optimization of layouts and recommend the best alternative for further designs based on the comparisons of costs, benefits and other important aspects of the different alternatives,

F. For the recommended alternative

Carry out the detailed design of hydraulic structures, viz., weir, intake, settling basin(if required), diversion tunnel, outlet structure, trash racks, gates, stop logs, etc ;
Prepare Engineer’s Cost Estimate and Bills of Quantities (BoQ);
Construction plan and Schedules;
Financial Analysis; and
Prepare Bidding Documents.

G. Supplementary EIA study of the recommended alternative of Rolwaling

H. Reconnaissance study of Upper Tamakoshi ‘A’ (UTA) HEP.

I. Detailed Topographic survey.

J. Prepare engineering geological maps of the intake and outlet areas and along the diversion tunnel alignment.

Detailed Engineering Design & Preparation of Bidding Documents of Rolwaling Diversion