Extraction of hazardous locations in march, 2018 hokkaido ice jam flood

An ice jam occurs when river ice flows downstream from an upstream reach where the river was frozen and accumulates downstream, resulting in rapid water level rises and subsequent flood disaster. Such ice-jam disasters occur in countries where temperatures get down to 0°C or below freezing. Disaster suffered by a sudden rise of water level from an ice jam occurred recently in Hokkaido, Japan. In this study, we tried to extract hazardous locations associated with the March, 2018, ice-jam occurrence by calculating the ice-jam scale (Sij) which can be calculated using hydrologic variables, river width, slope, discharge, and water level. The ice-jam scale proposed here, one can determine a possible location of ice-jam for any river even if we do not have sufficient field information. Sij was designed as a simple formula to allow fast calculation for an actual river. We did on-site inspections of the ice-jam-occurrence hazardous locations along the Bebetsu, Furebetsu, and Saru Rivers as determined by use of the scale. Our field observation confirmed, we confirmed that ice jams readily occur at sandbars, at a slope change point, on a mild slope, around a structure in the river, or in a meander section. Sij was also applied at known accident or ice-jam occurrence sites and around these locations. We were able to successfully extract ice-jam-occurrence hazardous locations using Sij.