Frazil ice blockage of water intakes in the Great Lakes

Each winter, municipal water supply and thermal power plants drawing water from the Great Lakes face the problem of their water intakes becoming blocked by frazil ice formed in the lakes. Little is known about the manner in which frazil forms, how it is drawn down to the depths at which the intakes are located, and how to prevent frazil from fully blocking intakes. This paper presents an overview of frazil formation and intake blockage in the Great Lakes. The paper first reviews the current understanding of the processes of frazil formation and intake blockage, and it adds new insight regarding the processes. It then describes the problem by way of case-study examples of frazil blockage of two intakes in Lake Michigan. Based on the case studies, and experiences with other intakes in the Great Lakes, the paper outlines methods for monitoring and mitigating frazil blockage. Two options are recommended: monitoring rate of water level drop in the pump forebay onshore from the intake, and rate of headloss increase between the intake and the forebay. Laboratory modeling of intake blockage is then presented.