As a general rule, the more evenly the water flows into run-of-river power plants, the more electricity they can produce. Especially in the case of small and medium levels of high water, the new regulations would make better use of the additional water present. “If the weather model predicts heavy rain, the smart weir system would release a little more water into the Limmat ahead of time. Then, when the predicted rain arrives, the lake would have more of a buffer and could continue to release water evenly into the Limmat despite the heavy rainfall,” Boes explains. This would prevent the turbines from being overloaded by too much water. Of course, water managers would still have to comply with high-water regulations as well as ecological and other requirements.
Similar adaptations would also be possible on other rivers on the Swiss Plateau downstream of Alpine lakes. Boes and his team have calculated that electricity production from run-of-river power plants could be increased by around 100 gigawatt hours per year if weir systems were managed more intelligently. This would be enough to meet the annual electricity needs of around 25,000 four-person households.
Protecting turbines more effectively against sediment
The fine silt that rivers carry is the natural enemy of every hydropower turbine. It acts like sandpaper, causing turbines to wear out over time and generate significantly less electricity. Although this problem has been known for a long time, it has still not been fully resolved. While many power plants feature what are known as sand traps, these often fail to remove enough of the tiny particles from the water.
To increase the sand traps’ effectiveness, and thus protect the turbines and avoid production losses, Boes and his team investigated which types of trap are particularly effective: “Long traps with a gentle bottom gradient, which make the water flow as slowly as possible, work best. They let the particles settle more easily to the floor,” Boes says. These findings have already been used to improve the sand trap at the Susasca hydropower plant in Graubünden. However, longer traps also require more building materials and take up more space, making them expensive. As a result, decisions on which structural adaptations make economic and technical sense will differ from power plant to power plant.
Boulder bypasses for reservoirs
Weather-related erosion causes stones, gravel and other sediments to enter reservoirs via their water intake and reduce their storage volume. This problem, known as sedimentation, could reduce the storage capacity of Swiss reservoirs by around 7 percent by 2050. Today, small and medium-sized reservoirs use bypass tunnels as a structural measure against sedimentation. These tunnels guide stones, gravel and silt past the dam wall during floods. However, since floodwaters carry a great deal of sediment, the floor of the bypass tunnel is sometimes subject to pronounced wear.
Boes and his team have repeatedly looked into this problem in recent years. For example, the researchers investigated which materials are best suited to lining the floor of such tunnels. After countless tests, they came to the conclusion that high-strength granite is best able to withstand the heavy wear and tear in particularly harsh conditions. Based on this realisation, several bypass tunnels around the world have since been lined with granite.
