Frazil ice concerns for channels, pump-lines, penstocks, siphons, and tunnels in mountainous regions

This paper discusses frazil ice concerns associated with water-conveyance systems located in mountainous regions. Such systems commonly comprise open-water channels (or reservoirs) linked to pressurized conduits (pump-lines, penstocks, siphons, and tunnels) that pass water down, up, over, or through steep terrain. The discussion addresses fundamental aspects of frazil formation and behavior in flows undergoing substantial pressure changes. An important consideration for such flows is that increased pressure depresses the freezing temperature of water. As flow pressure subsequently decreases (e.g., on passing through a turbine, or rising up a pump-line), water may become supercooled and prone to form frazil. The melting of ice entering a pressurized conduit (e.g., a penstock) can cool water flowing through the conduit. Such cooling may occur even when there is no heat loss through the conduit's wall. It is well known that water-conveyance systems in cold regions are prone to significant frazil-blockage problems at entrance trash-racks. Less well known, however, are that some pressurized conduits also are at risk of accumulating frazil within themselves, and others may disgorge bolus accumulations of frazil, possibly mixed with other ice, that then create blockage problems at a downstream section. Several case-studies are used to illustrate situations where frazil has posed problems for penstocks, siphons, and tunnels in mountainous regions.