RIASSUNTO
We developed a multipurpose freezing simulation model that can be used as a tool to provide an evaluation of proposed countermeasures to port freezing during winter and examined its application to a field site. This freezing simulation consists of 3 sub models: Seawater flow field calculation; phase changes in ice or snow; and movement of ice floes. The phase changes in ice and snow are able to take into consideration a variety of meteorological conditions and stages of melting. We confirmed from comparisons between observed and calculated results that this simulation method could roughly reproduce freezing tendencies and characteristics.
INTRODUCTION
Harbor freezing, a phenomenon in which water in harbors freezes during winter, causes considerable economic damage to ports, harbors and fishing ports in Hokkaido, in northern Japan, due to the inability to fish and anchor, the damage to ships, and other problems. We are engaged in developing a multipurpose numerical simulation model of port sea freezing as a tool to provide a relative evaluation of proposed countermeasures against freezing for Otsu Fishing Port, which suffers serious damage from freezing nearly every year. The port is an excavated-type fishing port facing the Pacific Ocean in eastern Hokkaido, at the southwest corner of the Tokachi River estuary(Figs. 1 and 2). Fig. 2 shows the sea freezing that occurred at Otsu Fishing Port in 2000. One of the main factors behind the freezing of this fishing port is the relativelylow air and seawater temperature in winter. It has also been pointed out that it is difficult to remove frazil crystals and pancake ice because the port is excavated and tidal exchange (or heat exchange) with the open sea is unlikely to occur (Kodama et al., 2003). The freezing period in Otsu Fishing Port occurs from late December through early March.