CLARIFICATION OF A RIVER ICE JAM PHENOMENON IN THE TOKORO RIVER IN MARCH 2018

Abstract

 This study aimed to clarify the situation of a river ice jam occurred on the Tokoro river in Hokkaido. We carried out water level observation, video and aerial photography, and also visually monitored the river ice area. The phenomenon of ice jam became clear by this observation. The water level rapidly increased to 3.1 m in 2 hours due to the ice jam phenomenon. River ice size is large near ice jam occurrence point. And this size is small at an upstream point more distant than an ice jam occurrence point. River ice velocity before and after the occurrence of the ice jam was calculated by PIV analysis. The speed of river ice flow before and after the ice jam was determined by CCTV cameras. The maximum velocity of the river ice is 3.5 m/s. As the flow rate increases, more water flows downstream with the ice, which clogs the river channel where it tends to accumulate, blocking the flow and causing the water level to rise.