Author(s): Masahiro Hashiba; Yasuhiro Yoshikawa; Hiroshi Yokoyama
Linked Author(s): Hiroshi Yokoyama
Keywords: No keywords
Abstract: This study aimed to analyze field data on the behavior of river ice and hydraulic phenomena during river ice breakup collected using non-contact acoustic devices of SWIP (Shallow Water Ice Profiler), ADCP (Acoustic Doppler Current Profiler) and Echo-Sounder. Firstly, we conducted an experiment with a large water tank (height 2.44m, capacity 10.65m3) in order to check the accuracy of these acoustic devices. To simulate the large water tank into the ice-covered river, 1) we set the ice block which was 0.15m thickness on the surface and 2) we set the snow which was adjusted low density (0.375g/cm3) and high density (0.482g/cm3) under the ice block as a pseudo frazil ice. We measured between top of the device and bottom of the ice in the tank at an interval of 0.2 m from bottom to pseudo ice using an auto elevating the acoustic device set upward. We compared with direct measured length and each device measured length. In the experimental results, regardless of the type of acoustic device, direct measured length and device measured length were almost same and standard deviations were from 0.03 to 0.04 m. Also, regardless type of these devices, it was showed that measured border of ice was the bottom of ice sheet or frazil ice regardless density. Secondary, in the field study, we observed the behavior of river ice and hydraulic phenomena seen in the Teshio River using SWIP and ADCP. It was found that the rising of water levels during ice breakup tended to lag behind the maximum flow rate because of ice accumulation as well as ice jams formed in the upstream part of the river. A phenomenon was observed in which ice fragments and frazil that were formed upstream and flowed downstream moved under river ice. It was found that the Froude number under icecovered conditions remains at about 0.1, and that the coefficient of roughness tended to decrease because of changes in river ice thickness. Based on analysis of the field data collected, we proposed the possibility that ice-transport capacity could be described using a dimensionless flow strength formula.
Year: 2018