Pumped storage projects involve major civil engineering works costing tens of millions of pounds but are nevertheless an efficient way of storing energy and economically a better method of meeting peak loads than building bigger generating stations. Because they require special environments, reservoirs for pumped storage raise difficult problems in engineering geology.
Such schemes operate with maximum efficiency with heads of the order of 1000 ft and relatively short hydraulic systems. There is no need for natural catchment at the upper reservoir, since water is pumped, but for the same reason the engineering geologist must ensure that minimum leakage will occur. As high-level, small corrie/cwm basins are likely to be used, the upper reservoir site may need to be topographically and geologically suitable for the high dam required to gain capacity.
The limitations of very brief starting time and high output impose severe limits on the lengths of tunnels, etc. and on the position of the power station in the system. The geologist, therefore, has not the same freedom to suggest geologically better tunnel routes and power station sites, and has to give an opinion whether the rocks present are suitable for large tunnels and underground power station chambers.
At the lower reservoir site, unless there is a considerable natural inflow, leakage must again be reduced to a minimum. Moreover, as the lower reservoir is often in developed areas, very careful account must be taken of possible alterations to the water table and of the results of large and frequent