Incidents of Flooding of Underground Power Houses

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Hydro Power Stations in India – An Overview

Hydro Power Stations play a crucial role in the electric power grid of a nation. India has several hundred hydro power stations with cumulative hydro power installed capacity of 46,850 MW.(as on 31^st May 2023: source – https://powermin.gov.in). Power House structure is an integral and very important component of a hydro power station. Power house structure can be surface type or underground type. Underground power houses are adopted when flat topography to construct the surface power house is not available. Several power houses in Himalayas are underground type. Underground power houses have certain characteristics which make them vulnerable to flooding in case of mishap.

During last two decades, some incidents of flooding of underground power houses of commissioned and operational power plants have been reported. Flooding of power house leads to stoppage of power generation for several months which is not only the economic loss but also makes the power unavailable to the grid for prolonged duration. These incidents are in addition to incidents of flooding of underground power houses during construction stage.

In 2005, flooding of operational 1500 MW Nathpa Jhakhri underground power house in Himachal Pradesh was reported. In 2013, flooding of operational 280 MW, Dhauliganga underground power house in Uttarakhand was reported. On 9^th July 2023, Incident of flooding of 126 MW Larji underground power house in Himachal Pradesh was reported.

Following incident of Flooding of Nathpa Jhakri power station, CEA has come out with  a set of recommendations to be adopted in the design/operation of the power house. These following recommendations are the part of CEA guidelines for formulation of DPR of Hydro Electric Schemes (Appendix 4 of the August, 2022 – Revision 6.0).

Table 1

We note that the above recommendations are not exhaustive and flooding of underground power houses can still happen because of hydrological/hydraulic reasons.

For Example, In case of 2013, Dhauliganga Incident, the major reason is reported from the unusually high floods in the tailrace outlet area nallah and large boulder stacking in the tailrace pool leading to reverse flow of water from the tailrace side and resultant flooding of the power house.

In the incident of 9^th July 2023, Flooding of Larji underground power house, from the publicly available video, it seems to suggest that water has entered in the power house from the main access tunnel side.

There is a need for more holistic approach for rigorous review of operational power plants at regular intervals and apply additional safety/design measures to avoid such incidents in future.