A Seismic Shift – A Systems Engineer’s Perspective

I grew up near Comrie in Perthshire which was famous for earth tremors starting in the 18th century peaking in the 1830s. I worked in electronics manufacturing and am now retired live in Derby. I have an interest in science, technology and history. The Royal Society motto “Take Nobody’s Word” has been a guide when reading press releases, the newspapers and listening to the news.

A bit of background. The electricity grid has seen a rapid shift from coal to gas and now to renewables. The problem for the National Grid is that thermally generated electricity from coal, oil, gas and nuclear are what is called dispatchable generation, they can quickly be increased or decreased to match demand. Renewables are variable generation whose output depends entirely on the weather. The move to renewables has problems because we cannot control when the wind blows and the sun shines. Frequently we have more electricity than we need, and equally often not enough. For many years the grid relied on a few pumped storage hydro generation power stations. The two best known Cruachan and Dinorwig which were mainly used to cover very sudden large increases in demand, famously at the end of some football matches or soap operas.

We now have 5 times as much renewable generation than there was in 2012, and at the same time we now import 4 times as much electricity. Because renewables are subject to the rapid changes in the weather rapid responses are needed. Once gas generation is removed from the grid, it is reaching the end of its life now anyway, we will be reliant on the weather for most of our electricity. Wind droughts of days are common in summer and winter, the longest continuous one in the UK is 26 days but there was a period of 55 days of overlapping short duration wind droughts. Several solutions are proposed, batteries, hydrogen and pumped hydro amongst them. Neither batteries nor pumped hydro can support the grid for days or weeks of no wind, and will only last hours backing up what is available during a renewables drought not replacing it all and how long recharging will take is not defined, but these are different problems.

The planned and existing Pumped Storage Hydro Electricity schemes on Loch Ness piqued my curiosity a little while ago. Comrie is located on the Highland Fault was famous for earth tremors which peaked in the 1830s. Loch Ness is in the Great Glen another geological fault line which runs across Scotland south west to north east. This is a major fault with other smaller associated faults around it. There have been tremors in the area in the recent past. A 5.1 magnitude tremor in 1816, 4.0 in 1888, 4.5 in 1890, 5.0 in 1901 amongst the biggest and most recent are 3.1 magnitude near Drumnadrochit in 2025 and one of 2.5 in July 2026. So, although the fault is said to be stable it is not tremor free.

There are two major things that affect the Great Glen fault and create stress, first the North Atlantic Ridge expansion is forcing the continental shelf where Northern Europe and Britain are located eastwards; secondly the area around Fort William and Rannoch Moor are rising at about 1mm a year due to post glacial rebound, during the last ice age the area was under a kilometre of ice which covered all the mountain peaks in the area.

There are 4 operating, approved or planned Pump Storage Hydro electricity generation schemes which will use water from Loch Ness.  The volume and weight of water if all 4 schemes come into operation are not small, nor will these schemes be emergency only. The volume of water involved is so large that theoretically the surface level of Loch Ness could rise and fall by over 3 feet (1 metre).

Building the upper reservoirs will cause a permanent loss of habitat for flora and fauna in the flooded glens forcing some to leave the area completely and others to relocate to less suitable areas.

There are several reasons to be concerned about building pumped storage power stations in an area like this. Large reservoirs in areas where there are faults can force water into the cracks changing the structure and causing movement along the fault line. Moving large volumes of water, potentially twice or more times a day, will cause the land to sink and rise as the mass of water moves. This has been known to trigger tremors in other locations globally and is known as Reservoir Induced Seismicity or RIS. Excavation of huge underground chambers redistribute stresses in the surrounding rocks this can take time to stabilise. The water in the reservoir can potentially enter existing faults and cause movement by reducing friction between the rocks. Work can be undertaken to mitigate this at the head reservoir but it is not guaranteed to be 100% successful and nothing can really be done to Loch Ness itself. Tremors of between 1 and 2 and stronger on the Richter Scale are known from other schemes around the world. Much stronger tremors although claimed to be unlikely are possible.

The limit for tremors induced by fracking for gas in the UK is set at 0.5 magnitude, a political choice. A tremor of 2.5 is, due to the way the scale works, is roughly 1000 times stronger than the fracking limit. There is no limit on tremor strength for Pumped Hydro electricity generation as far as I am aware. The reason for the difference would appear, for a cynic, to be that Pumped Hydro is green renewable supporting other green renewable electricity generation. So, residents near shale gas deposits are protected from earth tremors whereas those near renewable energy are not.

That is a brief description of one potential impact of a very large Pumped Hydro developments. There is another which needs to be addressed. Due to the nature of grid operation it’s likely that the schemes will generate and recharge twice or more times a day. This will create artificial pulsing of the surface level of Loch Ness by up to 3 feet above and below the normal level for that day depending on the situation at the time. This level of change happens naturally over days or weeks. The reason for above and below normal is that when water is being pumped up to the top reservoir it is at a rate that exceeds the rate at which water enters the Loch. Once the storage has been filled the Loch will refill naturally and the flow of the River Ness will fall, whether it gets back to previously level is dependent on the conditions that day.  When the stored water is used to generate electricity the level of the Loch will rise until the flow out through the River Ness rises to drain the Loch.

Both the level of the Loch and the flow of the River Ness will be artificially pulsed every day, potentially more than once. The flora and fauna in and around the Loch and River are able to cope with the gradual natural changes which take place over weeks or months. Fish and insects spawning and laying eggs in shallow water can either strand fish, eggs or both leaving them vulnerable to predators. Aquatic birds nesting in shallow water can find that they are no longer separated from the bank again giving easy access to predators. Water plants either being swamped or dried daily. The changing flow in the River Ness will have these and other additional potential problems such as flooding, erosion of river banks and depositing and moving of silt. Insects that spend some of their life in rivers, such as Caddis Fly, can be dislodged or the river bed scoured. The oxygen level and clarity of the river water can be affected. Fish could receive triggers for spawning at the wrong time. The Loch itself will act as strong buffer to the more extreme fluctuations but there may be times when the full generation capacity of these four schemes, if they are all permitted, should be curtailed to protect the environment, but may not as power cuts are newsworthy.

When water is being moved from Loch Ness to the upper reservoirs it is done at very high flow rates, as much as thousands of litres per second, this results in debris and aquatic life being sucked up along with the water. This has to be prevented to protect the turbines doing the pumping from damage. There are two main ways of doing this, some kind of screen of mesh or net. This becomes clogged and has to be cleared regularly, some methods of clearing are more environmentally hostile than others. Small fish fry and insects will pass through this screen. Another method to prevent fish getting sucked into the intake is a bubble screen, bubbles of air form a screen which deters fish from getting too close. The bubbles of will mean gasses like oxygen, nitrogen and carbon dioxide will be dissolved into the Loch Water changing its chemical makeup. The intake and output will create local currents in the Loch which will be completely different from any natural ones in the loch. Fish will be confused by this and one known effect is fish congregating at the intake/output screen. This creates an attractive source of prey for predators. I am unfamiliar what types of predators there are in the Great Glen but imagine they include pike, otter, osprey, and heron. Where I live a couple of hours drive from the sea cormorants have been known in the area.

None of these environmental issues will be visible to the public as soon as the schemes come online but will take months and certainly years to become apparent. The sad truth is that there’s no method of storing electricity which doesn’t have negative impacts on the environment at home and abroad.

Sandy Sinclair – Systems Engineer