Author(s): Carrie M. Vuyovich; Kathleen D. White
Linked Author(s): Kathleen D. White
Keywords: No keywords
Abstract: Many dams across the United States are being decommissioned for stream restoration or as a result of structural deficiencies. On northern rivers, there are a number of examples of dam removal increasing the frequency and severity of damaging floods due to jams. Dam removal can change the location where breakup ice jams occur or initiate the formation of freeze-up jams. This paper presents an overview, based on recent studies, of the procedures used to evaluate the impact of dam removal on breakup ice jams. The first step is to understand breakup ice jam formation under existing conditions by reviewing the historical record of known jams. The historical ice events may provide data on the jam locations, the reach length of contributing ice, and the resultant stages and damages. In many cases, no historical record of jams prior to construction exists and the selection of post dam removal ice jam scenarios are based on an analysis of the river geomorphology, ice jam mechanics, and current data. The ice conditions then are characterized in terms of the meteorological and hydrologic data which provides an estimate of the range of parent ice thicknesses and discharges at which jams occur. Finally, the study reach is analyzed under these conditions with and without the dam in place to determine whether the dam plays a role in ice processes. In many cases, a hydraulic model is used to quantitatively estimate the stages that result from jams following dam removal. When insufficient data or project constraints do not allow for a model study, an analysis of the pre- and post-dam removal conditions is performed. The result is an estimation of the potential locations and severity of ice jams following dam removal.
Year: 2008