| Abstract | In this document, high-level guidance is provided for the deployment of hydrokinetic turbines (HkTs) meant to operate in rivers during the winter. These devices are run‑of‑the‑river systems that harness the kinetic energy of flowing water to generate electricity. Their deployment in rivers that experience seasonal ice cover presents unique technical challenges. These turbines must operate reliably in cold environments where ice formation, maintenance difficulties, and accessibility issues complicate operations. HkTs can nonetheless function effectively in harsh northern climates; a successful example of such deployment is the RivGen system in Igiugig, Alaska.
River ice processes are central to understanding the risks faced by HkTs. Ice in rivers forms both at the surface and below it, each with distinct implications for turbine operation. Border ice, skim ice, and a complete ice cover are all influenced by air temperature, current velocity, and local channel morphology. As an ice cover develops and with the formation of ice jams, the ice increases flow resistance and raises upstream water levels. Below the surface, frazil and anchor ice (collectively referred to as underwater ice) form under turbulent, supercooled conditions. Frazil ice adheres to submerged objects in its active state, eventually coalescing into flocs that rise toward the surface as frazil transitions to its passive state. Anchor ice develops when these frazil crystals adhere to the bottom or grow in place. Processes occurring below the surface are difficult to observe directly, yet they are critical to turbine performance, as frazil can adhere to blades, housings, and sensors, while anchor ice can modify local hydraulics.
Understanding site‑specific ice conditions is essential. Historical records, local knowledge, and modern remote‑sensing tools such as optical and synthetic aperture radar (SAR) imagery provide insight into freeze‑up and break‑up timing, open‑water reaches, and ice jam locations. These data, complemented by field observations and hydrodynamic or data‑driven modeling, help identify suitable deployment zones and anticipate seasonal variability.
Mitigation measures focus on careful siting, operational planning, and protective design. Ice booms can be used to encourage the formation of stable surface ice covers, reducing frazil production upstream. They can also help divert ice away from HkTs as it drifts downstream. Selecting materials less conducive to ice adhesion and shielding exposed components can also help limit frazil accumulation. Platform‑mounted systems offer easier access but are more exposed to drifting surface ice, while bottom‑founded designs are less affected by surface movement but remain vulnerable to underwater ice and thick surface ice released during ice break‑up.
Because river ice behavior varies greatly from one location and year to another, implementing any mitigation strategy will require iterative testing and adaptive management. The integration of field data is a key element to inform and guide ice management practice. |
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