PHPA-I awaits second-party opinion on sliding right bank

The Punatsangchhu Hydroelectric Project Authority-I (PHPA-I) is waiting for a proposal to shave the hill on the right bank of dam location at higher elevations as proposed by Norwegian Geological Institutions (NGI), an independent expert agency of Norway, in January this year.

The authority is the second party to offer an expert opinion after the slide on the right bank occurred in 2013 delaying the project.

Experts of Central Water Commission (CWC), WAPCOS, Geological Service of India (GSI), Central Soil and Material Research Station (CSMRS) and Indian Institute of Technology (IIT)-Delhi also tried to develop remedial measures for the slide.

PHPA-I implemented stabilizations measures of consolidation grouting, cable anchoring and Reinforcement Cement Concrete (RCC) micro-piling at the right bank.

In April 2017, NGI submitted an initial report based on the data WAPCO provided. The final NGI report issued after their experts visited the site was also submitted to the technical coordination committee.

NGI proposed that excavation below elevation of 1,140m should not be carried out until slopes stabilize and unstable mass above the major shear zone be removed. Also, use of long cable anchors, removal of top soil, and trimming of slope to an angle less than 35 degrees were proposed.

The Managing Director (MD) of PHPA, R.N Khazanchi, said that works were stopped from May 3 this year after NGI’s recommendations.

The MD said the WAPCOS, CWC and NGI proposals would be merged but the authority is yet to receive the final NGI proposal. “I hope the proposal would come within a fortnight or sooner,” said the MD, adding that the removal of the top soil on the hill is designed in such a way that it will not affect any private land. However, he said the road alignment may change.He mentioned that after monsoon excavation of the right bank in the portion between elevation 1,120m-1,090m, works would be resumed and completed and also the excavation of left bank and dam pit would continue. “The remedial measures will, however, not delay the commissioning of the project,” said R.N Khazanchi.

A budget of Nu 3.7bn has been allocated for the remedial measures out of a total budget of Nu 93.75bn for Puna-I. The MD said that almost Nu 3bn is spent for remedial measures on the right bank and an additional Nu 1bn would be required for remedial measures.

The chief engineer of the dam, J.S.Bajwa, said that excavation below elevation of 1,140m which was suspended on May 3 this year as per NGI and CWC’s recommendations would be resumed cautiously in 3m-deep stages at a time after monsoon this year. “It would be continued with strict monitoring of movements,” said the chief engineer.

He said for Puna-I, 10m remains to reach the left dam foundation. The maximum depth of the left dam is 115m. About 50m is left to reach the right dam foundation. The maximum depth of the right dam is 130m.

According to the R.N Khazanchi, as per experts, the timeline for Puna-I completion would be between the last quarter of 2021 and early quarter of 2022.The project has cost Nu 70.17bn as of July this year. “It would require another Nu 25-26bn to complete the project,” said the R.N Khazanchi. The MD said that 90% of the power house complex is completed so far. The Head Race Tunnel (HRT) of Puna-I was completed in June 2015.

PHEP-I with a capacity of 1,200MW has total employee strength of 874 of which 734 are nationals, 113 Indians and 81 on contract and consolidations. The dam site is 7km downstream of Wangdue Bridge and all other project components are located on the left bank of the river between 7 km-17 km downstream of the Wangdue Bridge. The project implementation started on November 11, 2008.

Dechen Dolkar from Wangduephodrang