GEOLOGICAL AND GEOTECHNICAL INVESTIGATIONS FOR PUMPED STORAGE HYDROPOWER PROJECTS IN PENINSULAR INDIA : KEY ISSUES

There has been a tremendous spurt and enthusiasm amongst the hydro power community in the development of pumped storage hydropower projects (PSHPs) in the post covid times. It would not be wrong to say that the PSHPs have now taken significant position in planning for power development in India.

To understand geological implications is it necessary to appreciate how the PSHPs are different from conventional hydro. They consist of an upper reservoir at a higher elevation and a lower reservoir below typically with 150-500 m head. The two reservoirs are connected by a water conducted system having surface or underground power houses. During the off-peak hours when there is surplus or low-cost power available in the system through thermal or solar sources the water from the lower reservoir is pumped upwards whilst during peak hours the power station runs in the generation made.

Geologically, the PSHPs are more challenging than conventional hydro because in this case the upper reservoir has be placed on an elevated plateau that is hard to find together with space for lower reservoir also that too in hospitable rocks. The upper dams instead being across the rivers in hydro projects are more of circular or irregular hexagonal or may be broadly rectangular shaped depending on topography. The lower dams may be across the river or small stream or even isolated just like upper reservoir. Certain other conditions have to met to make them attractive.

Where the Himalaya was considered more disturbed, recent experiences have shown that the peninsular India also has geological difficulties as well. The sites have to be carefully chosen and systematic investigations performed particularly for upper dams planned on a plateau or flat topped mountain. The power houses are typically large in the range 750-2000 MW with requirements of deep excavation for surface power houses or large multiple underground caverns or openings. Besides there are multiple large diameter pressure shafts that may be vertical inclined or even surface penstocks. The paper encompasses key issues in investigation and geological evaluation.