Anchor Ice Flooding in Jackson, WY

Abstract

Jackson, Wyoming, located in the Teton Mountains in northwest corner of Wyoming along Flat Creek, has experienced wintertime flooding caused by the production of frazil ice and anchor ice in Flat Creek. Anchor ice formation is common in shallow, turbulent streams but flooding caused by anchor ice in urban areas is rare in North America. Anchor ice is formed when frazil ice crystals are deposited on the channel bottom during cold periods when the flow of the creek becomes supercooled. The anchor ice builds up on the bottom of the channel and causes the water levels to rise upstream. Jackson has installed three thaw wells that pump ground water into Flat Creek. The ground water, at a reported temperature of 7.8°C, warms the flow of Flat Creek slightly and prevents supercooling for some distance downstream of each thaw well. The existing thaw wells, however, did not provide complete protection for Jackson during the winter of 2000–01, the first winter they were in operation. This report is a study of the ice-related flooding problems in Jackson. It describes the Flat Creek watershed, the winter climate of Jackson, the existing thaw wells and their performance during the winter of 2000–01. The length of Flat Creek that can be kept above 0°C and protected from anchor ice production determines the performance of the thaw wells. The performance was estimated based on a simple heat transfer model that assumed well mixed flow, a linear heat transfer relation between the water surface and the atmosphere based on temperature difference, and one-dimensional steady flow in the creek. It was found that the distance protected depends on the air temperature and, to a lesser extent, the flow rate of Flat Creek. The analysis roughly agrees with the performance of the wells during the winter of 2000–01.