Pumped storage |


Above and below: Cruachan cavern construction


and many items of mechanical and electrical equipment have evolved in efficiency and size. When looking to make changes, it is often the case that new equipment is slotted into unaltered underground spaces (why would you) but to the detriment of safe, effective access. Each type of underground construction poses its own challenges when it comes to inspection and maintenance, although each have been addressed in every era according to the knowledge at the time. In unlined or partially lined tunnels and aqueducts careful consideration needs to be made of not only how it is dewatered but consider the effect that dewatering has on the structure, the speed at which it is sensible to dewater and the time it might take to make the tunnel invert safe for transit of people or plant. However anticipated it may be, it is slightly disconcerting to hear roof blocks falling into partially drained and draining tunnel, although perhaps our predecessors averted this surprise by avoiding maintenance altogether. Consider how water tight do you wish your structure


to be for maintenance crews, should there be an interlock and/or a double penstock – the speed, depth and volume of through flows effects methodology and can also have swift ecological impacts in the event of something being accidently discharged. Unchanged for decades, and perhaps obvious


but often overlooked is the fact that accessing a flat-bottomed structure is much easier on the feet than one on a radii, also much easier on the wheel bearings, axles and track growsers for plant that may need to access as space. Creating a concrete invert (as a minimum) makes walking a much more pleasant and safer experience; protecting this invert from hydraulic plucking by ensuring a suitable thickness and reinforcing should be considered. In case it’s not plain many of the hydro assets tunnels and aqueducts were unlined. The reality of almost all high-pressure tunnels is


Below: Cruachan lower control works


they will be completely round, fully lined in either concrete or steel – it’s important to think ahead to whether a completely round solution suits the future working environment – even though it’s usually best for the transient analysis. The roughness co-efficient carefully considered at time of newness requires an eye on long-term consistency: consider how this can


be maintained in environs where, generally, peat fibres will begin to coat the lining, creating what can only be described as the bobsleigh effect for anyone entering this space, especially as they will ordinarily be on a gradient. Sliding all-ways. Even if there is to be no intrusive maintenance activity, there will come a time when the ROV survey will ascertain that it’s time for some lining cleaning. The majority of these large schemes will be constructed over the course of many years – perhaps approaching a decade. Constructors in Scotland will face both of its Seasons: Winter, and June (Summer). Decade-long projects have time to build-in winter resilience and establish their setup, as seen in past projects. Maintenance activities will not necessarily have this luxury. Upper reservoirs will likely be above the potential snow line for all but three months of the year; any activity will be affected by horizontal snow, hail, constant rain, and low temperatures. Suddenly, come May, it’s usual to experience a month-long drought and almost overnight, you are not battling torrents – you have no water and dust rises everywhere you travel. In Summer, midges will also affect team productivity and morale. There is nothing quite like the feeling of helplessness as masses of these tiny creatures surround you. We all need to remember this from our planning desks while sheltered from the elements, where hopefully we are not being bitten. In every case maintenance underground will require light, electrical supply, water supply and air movement. What a delight it would be that these services were built into tunnels and underground spaces we need to access at some stage to perform maintenance. If these services are not built-in then laydown areas to accommodate supporting services should ideally be positioned at handy locations adjacent to portals and/ or access points, and maintained. There should be places to park and turn vehicles too. Thinking ahead with net zero in mind, it would be much preferable to see grid connections and water supply to these points too, saving on the burning of diesel in generators and in transporting potable water from sources, ordinarily, far away.


A lasting legacy


Many on the construction phase operations in the last revolution readily deployed narrow gauge railway infrastructure – some temporary and rudimentary, but many robust and potentially long lasting. The narrow gauge railway for British Aluminium Company’s Puggy Line can still be traced from near the centre of Fort William all the way to Loch Treig, for instance. Some of this route is now encompassed in Nevis Range Ski Centre, and other parts in cycle paths. Considering that this was a legacy linear asset which was largely ignored through the 20th Century, what an asset it could have been for the many visitors to Lochaber had the route been still passable along its entire length. In fact, many of the historical linear routes, tracks, trails, aqueducts, pipe races, tailraces and dams have become attractions, points of interest, places to visit and use for access. In building new, we must consider the legacy assets we leave behind for others to find, use and enjoy. Remembering that The Golden Eagle Statue which sits beside Glendoe’s Reservoir has become a destination for many visitors. Becoming a destination, as many schemes have,


20 | July 2025 | www.waterpowermagazine.com


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