Prevention of Water Intake Blockage by Ice during Supercooling Events

Abstract

Blockage of water intakes by underwater ice formation during supercooling events is a widespread and common problem in northern regions during winter. In this context, underwater ice formation means deposition of frazil ice and growth of platelet ice. Blockage happens when underwater ice forms on the structural components of the intakes, particularly the intake trash racks, decreasing the area of the intake available for flow. This article evaluates potential solutions for preventing blockage. The solutions are collected into four broad categories: avoidance, prevention, mitigation, and remediation. Avoidance locates the intake so that it is never exposed to supercooled water. Avoidance is not possible in rivers and streams and requires depths in lakes and reservoirs that are not reachable for most intakes. Prevention stops supercooled water from entering the intake. The use of heat to warm the intake flow so that it is not supercooled is the most reliable way of preventing intake blockage by underwater ice. The formation of stable ice covers is a reliable means of preventing blockage events but cannot entirely eliminate them. Mitigation modifies the intake, or its operation, to prevent blockage. Ice adhesion to trash rack bars can be reliably prevented by maintaining the bar surface at a temperature greater than 0°C. Other approaches to mitigation including reducing intake flow, modifying the trash rack design, using coatings or alternative materials, or insulating portions of trash rack bars are not reliable for preventing blockage. Remediation actively removes underwater ice from the intake components while the intake is in operation. Mechanical or manual raking of the intake trash racks to remove deposited frazil ice can be a reliable means of preventing blockage. In addition, a strategy, management, addresses intake operation when practical measures for blockage prevention are not available. Management accommodates periodic blockages into the operation of facilities through detection, damage prevention, and quick and efficient restarts.