By Stuart Haszeldine OBE FRSE C.Geol. Professor of Geology, University of Edinburgh (https://www.research.ed.ac.uk/en/persons/stuart-haszeldine)

The geological foundations of Glen Earrach proposal are very poorly known, this has been surveyed only briefly in 1983, finding multiple types of complex faults, which are likely of very different ages, including up to the present day. That’s not a surprise as Loch Ness follows the UK’s largest fault, which has an exceptionally complex history. But at this site, no detailed updates have been published, and published geophysical survey plans appear too widely spaced to detect all faults and will need a lot more detail. A warning comes from Glen Doe, across the other side of Loch Ness, where under surveying failed to discover a steep fault, which collapsed when hydro water flows started. The project was closed for several years with extra costs of multiple millions of pounds.

By contrast, the project near Fort Augustus at Coire Glas has spent several years surveying faults, drilling and coring a dedicated site borehole and an exploratory tunnel. Mapping the surface geology metre by metre – includes discovery of previously unknown soft clay fill at depth, reminiscent of the Glen Doe fault failure. Constructing dams to emplace a water body above these faults also has a risk of increasing the groundwater head pressure, which can force flow of water downwards along fault lines. And in some dam constructions, the additional pressures from the weight of dam and water can trigger small earth tremors. Planners need to know that all these diverse site investigations have been completed and present minimal hazard to the project and its environment.

Individual hydro storage projects may seem straightforward. But no single project has been asked to assess the effects of cumulative development. Because all the developments are trading in the UK electricity market, they will tend to all behave synchronously. When the price of power is low, they will store water uphill. When the price of power is high, they will all discharge to turn turbines and make money. That means the ecosystem effects around the loch will be cumulative – changes of water level, scour at outflows into the loch, temperature changes of water into the loch. Have these effects been calculated and simulated all together, to understand how the unusual Loch Ness ecosystem will be forced to respond? From the southern inflow to the northern outflow, entry and exits into and out of the Lock system will be affected. And road travellers touring Scotland can observe the beach tidelines from metres of water level change, rather than the impression of undeveloped wilderness.