| Insight
Aerial view of the city of Zurich and Lake Zurich in Switzerland
intelligently, which equates with enough additional power to meet the annual electricity needs of around 25,000 four-person households.
Sedimentation
Sedimentation can be a serious issue for Alpine reservoirs, as many were built in the second part of the last century and have been experiencing ongoing sedimentation issues for decades. Although Alpine reservoirs have an estimated mean annual sedimentation rate of 0.2% - considered to be relatively low mainly due to the geological characteristics of the catchment areas – safe and sustainable management of reservoirs used predominately for hydropower production is being threatened after decades of operation. Estimates suggest that the storage capacity of Swiss reservoirs could be reduced by around 7% by 2050. Research carried out by ETH Zurich into the effectiveness of sand traps discovered that longer traps, with a gentle bottom gradient to make the water flow as slowly as possible, work best as they let the particles settle more easily to the floor. However, longer traps also require more building materials and take up more space, making them expensive, so decisions on which structural adaptations make economic and technical sense will differ from power plant to power plant. The problem of wear and tear on the floor of sediment bypass tunnels has also been investigated. After countless tests in recent years, it was concluded that high-strength granite is best able to withstand heavy wear and tear, particularly in harsh conditions. Solis reservoir in Graubünden was used to demonstrate the effectiveness of bypass tunnels, where annual sedimentation was reduced by over 80%. However, this required adjustments to storage management. The power plant’s operators can further increase the tunnel’s effectiveness by bringing the water level in the reservoir down low enough to enable the inflowing river to transport particularly large quantities of rock and sediment and discharge them via the tunnel.
Swiss stepping stone Switzerland’s Nant de Drance pumped storage
project has recently helped Scotland in its ambition
of becoming a global leader in green energy, when Labour Shadow Secretary of State for Scotland, Ian Murray MP, recently embarked on a fact-finding mission to the scheme that was commissioned in 2022. This tour to the Nant de Drance project was able
to deliver essential lessons for the UK, particularly in the context of the country not having seen the development of new pumped storage hydro facilities since 1984. The visiting delegation which included representatives from Glen Earrach Energy, Green Highland, Alpiq, and AECOM, gleaned insights into the potential integration of similar technologies in the UK. Reflecting on the visit, Murray said: “Under Labour’s vision, Scotland is set to become a global leader in green energy. This visit to the Nant de Drance project is a stepping stone towards realising that ambition.” The 900MW Nant de Drance scheme is one of the most powerful pumped storage plants in Europe. Located 600m underground between the Emosson and Vieux Emosson reservoirs, with a storage capacity of 20M kWh it offers flexible power generation and plays a key role in stabilising the electricity grid throughout Europe, as well as safeguarding Switzerland’s power supply.
Above: Annual sedimentation was reduced by over 80% at Solis reservoir in Graubünden, demonstrating the effectiveness of bypass tunnels in Switzerland
Below: Although it is a proven technology, research is still being carried out to maintain the effectiveness of Swiss hydropower
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