From the beginning of the feasibility study work of UTKHEP, Rolwaling tributary has been proposed to enhance the discharge of Upper Tamakoshi by diverting the dry season flow of Rolwaling stream into the intake pond of Tamakoshi River. The diversion of Rolwaling Khola has performed at desk study level and estimated from the previous study that the Rolwaling khola will add about 15% flow in the dry season
The scheme would involve a diversion dam, intake and transfer tunnel from Rolwaling Khola to the UTK HEP intake pond at Lamabagar. The water from Rolwaling Khola will mix with the water from Tamakoshi itself before being conveyed to the power station. As UTK HEP receives sufficient water from Tamakoshi river for full production in the monsoon season, the additional water from Rolwaling Khola will be transferred in the dry season and in the transition periods between dry and wet seasons only. Diversion of Rolwaling Khola will play vital role to enhance the dry season energy production from Upper Tamakoshi Hydropower Project which might be higher value than wet season energy.
The installed capacity of UTK HEP is 456 MW, and the average annual energy production is estimated to be 2281 GWh excluding Rolwaling contribution. The design discharge is 66m3/s. In stage 2, the water from Rolwaling Khola will also be diverted via a transfer tunnel through the mountain between Rolwaling Khola and Tamakoshi River. Thus, the annual energy production will be 2448 GWh with increased discharge .
Rolwaling khola at proposed Intake site viewing upstream (Photo: Subarna Shrestha)