Ice growth in Duluth‐Superior Harbor

Abstract

The heat budget for ice in the Duluth‐Superior Harbor was obtained from measurements of temperatures and net radiation and from weather data. It was found that ice growth in the harbor is nearly uniform and depends mainly on the net radiation term. Some localized variations in ice thickness can be attributed to the spatial distribution in albedo and the variation of the turbulent heat flux in water. For localized areas with high turbulence and thermal pollution where the heat transport in water becomes significant, a 20–50% decrease in ice thickness is observed, depending on flow velocities and the proximity of the areas to the heated effluent sources. Outside of these localized areas there are smaller but persistent variations in ice thickness over broad regions of the harbor adjacent to the industrialized sections of Duluth and Superior. These variations can be attributed to the relative changes in the albedo due to particulate fallout. Landsat data were used for determination of the relative distribution in albedo, while the turbulent heat flux in water was obtained from temperature distribution measurements and from flow rates which were calculated from a numerical model of the harbor.