Fluvial thermal erosion: Heat balance integral method

摘要

In periglacial regions, frozen river banks are affected by thermal and mechanical erosion. In Siberia, bank retreats of up to 40 m per year are observed. This thermal erosion occurs during a few weeks, at springtime, for high enough water temperatures and river discharges. Until now, models of thermal erosion have been based on the assumption of a constant thermal erosion rate. We have developed a more general model at variable rate, whose solution is calculated using the integral method. Results of this model are compared with experiments, carried out in a cold room. A hydraulic channel allows measurements of the thermal erosion rate of a ground ice sample subjected to a turbulent water flow. Once validated, the model is applied to the periglacial river study case. The model has contributed to better understanding of the roles of each parameter during the thermal erosion process. High water temperature, discharge and ice temperature produce major thermal erosion, whereas the ice content in the soil tends to slow down the thermal erosion process. The effects of water temperature are predominant. An acceleration phase characterized by an increase of the thermal erosion rate occurs at the beginning of the thermal erosion process. The duration of such an acceleration phase is systematically studied. A relatively long acceleration phase is related to a low ablation rate. During the flood season, when the water temperature is increased to 18 C, this acceleration phase lasts only a few minutes. However, for data typical of periglacial rivers, when the water temperature is close to the melting point, the acceleration phase can last a few days. Copyright (C) 2007 John Wiley & Sons, Ltd.