Lingza - Ministry of Power

CHAPTER-IV
26
Preliminary Feasibility Report
Lingza HE Project (3 x 40 MW)
TOPOGRAPHIC AND GEOTECHNICAL ASPECTS
4.1 INTRODUCTION
Central Electricity Authority proposed construction of Lingza hydroelectric scheme on
Ringpi Chu near Ishana in order to generate hydroelectricity from its water potential. The
scheme envisaged construction of a diversion structure upstream of Ishana, a water
conductor system in the left bank of Ringpi Chhu and a powerhouse downstream of
confluence of Ringpi Chu and Rangyong Chu. The scheme was expected to generate
approximately 160 MW of power. The task of preparation of pre-feasibility report was
assigned to NHPC. As per the MOU, GSI reports and site visits of experts would form
major in puts for topographic and geotechnical aspects. The present appraisal is based on
study of topographic sheet 78 A/6 and reconnaissance traverse that was undertaken by
mid October.
A study of the area was undertaken and a few modifications were made in layout of the
project, because of Panan scheme, which has been proposed in the downstream. Now, a
diversion structure shall be constructed approximately 700m upstream of Ishana, a 4 km
long water conductor system in the right hill and an underground powerhouse upstream
of confluence of Ringpi and Rangyong Chhu. The tail water shall be discharged above
the FRL of Panan Scheme. The geological report from GSI has been received and placed
as annexure 4.1.
4.2 REGIONAL TOPOGRAPHIC AND GEOTECHNICAL FEATURES
River Teesta in Sikkim is a major river originating from Zemeu glaciers and generally
flows in north-south direction, at a steeper gradient. The river is joined by several
tributaries major amongst them being Yumthang Chu, Zemu Chu, Talung Chu, Dik Chu
and Rangpo Chu, apart from others join the river. The river valleys in this region are u-
shaped while, as the tributaries had developed deep gorges, which are bound by steep