Vattenfall Inc.

In Sweden, many dams are undergoing upgrades to comply with the revised dam safety guidelines, which mandate higher spillway discharge capacities. As part of an ongoing project, a piano key weir (PKW) is proposed to replace an embankment dam and simultaneously increase the facility's discharge capacity. The PKW configuration was evaluated in a 2 m wide flume at two geometric scales (1:35 and 1:12) to assess potential scale effects. The former comprises eight units, while the latter includes three, with all components produced using 3D printing. Results indicated that the 1:35 model exhibits a slightly lower discharge capacity, likely due to scale effects. To further investigate, a 1:35 scale floor model was constructed using CNC milling to replicate the river bathymetry, the existing spillway with three tainter gates, and the proposed PKW consisting of 24.5 units. When scaled to prototype discharge levels, this model demonstrated a somewhat lower capacity than both flume models due to real approach conditions, though the differences between them were minor. In addition, the CNC milling technique yielded greater manufacturing accuracy compared to 3D printing. The findings offer insights for future PKW designs and scale model testing in similar applications.

During extreme flood events, floating trees (driftwood) can pose serious risks to the safety and operation of dams. In upgrading an existing dam, a piano key weir (PKW) was introduced to replace the aging embankment dam and to increase the discharge capacity of its gated spillway. This upgrade necessitated a detailed understanding of driftwood behavior at both discharge structures, which differ significantly in design and operating conditions. To investigate this, hydraulic model tests were conducted using small, freshly cut trees-some with branches and roots-to simulate natural trees moving towards the dam. The results indicated that tree accumulation at the gated spillway or PKW depended on flow discharge, crosssectional position in the reservoir and water levels. Blockage of the gates-or simultaneous blockage of both the gates and the PKW-caused a greater rise in reservoir water level than blockage of the PKW alone. However, the rise was still limited. This study highlights the combined use of the PKW and the gated spillway as cost-effective, as they complement each other in managing driftwood and mitigating water-level rise.

As an effective flood control structure, the piano key weir (PKW) typically features a rectangular planform for its overhangs. However, this design offers room for improvement. To enhance hydraulic efficiency, two modified PKW layouts are proposed. In the first, the floor of each key was lowered with a semicircular cross-section, forming an elliptical planform and crest. In the second, the floor was lowered with an isosceles triangular prism, creating an equilateral triangular overhang. Both modified PKW models, manufactured by 3D printing, were tested in a large-scale experimental setup. Compared to the reference weir, the elliptical-overhang PKW increased the developed crest length by similar to 36% and enhanced discharge by 30-53% across the tested flow range. The triangular-overhang PKW extended the crest length by similar to 23%, resulting in a 16-20% increase in discharge. The modified inlet key crest, whether elliptical or triangular, extended further downstream, promoting jet break-up, air entrainment at low to medium-high flows, and improved energy dissipation. The elliptical or triangular overhang facade, combined with a lowered inlet key floor, reduced entrance energy losses, improving inflow conditions. The lowered floor also accommodates additional water volume, enhancing flow motion toward the crest. For the outlet key, the lower floor facilitates outflow and mitigates local submergence at high floods. These modifications offer more effective PKW designs, which is particularly beneficial when reservoir water level increases must be controlled during floods or when spillway construction space is limited-contributing to improved dam safety and cost efficiency.

ABSTRACT Cold‐climate wind power represents a major subset of onshore global capacity, with approximately one third of existing installations located in regions prone to low temperatures and icing. The main technical challenge in cold‐climate conditions is ice accretion on turbine blades, which degrades aerodynamic performance and causes production losses, while ice falling from turbines poses a significant safety risk. These issues have driven the development of specialized technological solutions, including ice detection and mitigation systems and detailed forecasting models. In parallel, specific policy approaches have also been developed to address increased icing risks. This review focuses on wind turbine blade icing and related issues for onshore wind. It presents state‐of‐the‐art technical solutions for icing‐related challenges, as well as approaches for icing modeling and forecasting of icing conditions. In addition, relevant policies from different countries are reviewed. Production losses due to icing are highly variable, influenced by ice thickness, shape, and post‐icing wind conditions. Accurate estimation and forecasting of these losses require advanced tools, ranging from SCADA‐based analyses to machine learning methods and mesoscale weather prediction models. Ice detection technologies are being developed based on both direct and indirect measurement principles. Efforts to validate and certify these systems for operational use, such as automatically stopping and starting turbines, are ongoing. Icing mitigation includes both active technologies, such as blade heating systems, and passive approaches, such as icephobic coatings. Uncertainty quantification has become central to project financing and planning, with standards emerging to guide risk assessment. Policy and regulatory responses vary internationally: some regions, like Québec, mandate cold‐climate certifications and real‐time operational data reporting, while others focus on risk assessments and safety zones. Regulatory approaches remain somewhat fragmented and guided by local priorities. Further harmonization is needed to address critical safety issues such as ice throw. This article is categorized under: Sustainable Energy > Wind Energy Policy and Economics > Governance and Regulation