Discussion of "Ice jam release surges, ice runs, and breaking fronts: field measurements, physical descriptions, and research needs"

Abstract

The discusser would like to commend the author for presenting a thorough, interesting, and useful description of wa ter waves and ice transport generated by the release of river ice jams. The paper draws on the author’s extensive observational experience and compares it with the limited published information that is available. It is not easy to obtain a com plete “picture” of a river wave under the best of circumstances, let alone one that is complicated by a variety of ice effects. It is thus very important to maintain, and even expand, current field data acquisition activities with a view toward eventual quantification and prediction. A general comment concerning the use of the term “surge”: in hydraulics literature, it is taken to mean a wave of abrupt front (e.g., see Henderson 1966). This is a fair description for a jam-generated wave shortly after the release of the jam, where the water level may rise by a few metres within minutes. Surge is definitely a misnomer, however, when the wave has traveled for a long time and become both flatter and slower. By this time, the wave is anything but a surge. Nevertheless, the term has prevailed in river ice litera ture, where it is applied to all stages of the jam-release wave. Perhaps it is time to revise this practice by quantifying the “abruptness” of a river wave before it can be called a surge; this is a potential subject for future debate. Herein, the conventional, and not-so-rigorous, usage is adopted, for the sake of consistency with previous literature. The first paragraph under the heading “Unimpeded ice runs” discusses the concept of break-up-initiating discharge, and the related occurrence of nonsequential breakup. The discusser is in full agreement with these ideas, especially as he happens to be their originator. The author had perhaps intended to cite Beltaos (1995) and (or) Beltaos (1997) at this juncture. The comparison between the results of laboratory experiments and the author’s observations is instructive. An additional reason for the differences may be the relative short ness of laboratory flumes. For instance, the experiments of