In-situ ice strength distribution of anchor ice dams

Abstract

Ice runs and ice jams can cause significant damage to infrastructure and other human interests. Accurate modelling and prediction of these events rely on data and assumptions about river ice properties. This paper seeks to address the lack of data on ice strength distributions and associated properties in small, steep rivers and to obtain a better understanding of those. To this end, an ice data collection campaign was carried out in the Sokna river in central Norway during the 2020–2021 winter field season. The following types of data were collected for anchor ice dams and level ice sections: Borehole Jack (BHJ) in-situ ice strength, ice thickness, ice density, thin section imagery and associated depth measurements. A total of 27 ice cores and 68 thin sections were successfully collected and processed. Furthermore, a survey was carried out recording GPS coordinates of anchor ice dams in the river. Meteorological and hydrological data was also collated, and large boulder location data was obtained through the analysis of aerial photography. Ice strength distributions and trends on how ice strength varies in small, steep rivers were obtained from these data. A binomial generalized linear model for predicting ice dam locations was developed using field measurements and aerial photography data. This model describes how river width, slope and to a lesser degree large boulder density affect ice dam location. Sinuosity was shown to have no effect on ice dam location. This work highlights the significant variation in microstructure and large-scale structure of ice in small, steep rivers.