Author(s): Hashiba M; Yoshikawa Y; Yokoyama H; Haga S
Linked Author(s):
Keywords:
Abstract: In order to study the occurrence and release of anchor ice, we conducted continuous observations for about a week in three different actual rivers (the Yubetsu River, Nayoro River, and Bebetsu River). These rivers were the depth of about 0.3-0.4 m, and the Froude number was at Fr> 0.2; shear stress in anchor ice was 0.08 on average. The observation system has the following equipment installed into the water. 1) Time-lapse camera with LED light on the riverbed. 2) Precision water thermometer (resolution ±0.001degree). 3) The precision thermometer was embedded in the stone on the riverbed. 4) Underwater illuminance. Anchor ice occurred from the gaps between the stones and spread for the whole of the river bed. It was shown that the water temperature and riverbed stone temperature of the river bed decreased simultaneously with the disappearance of solar radiation. 1) Occurrence; In Yubetsu River, the anchor ice occurred from 6:00 P. M. to 11:00 A. M. before noon, where the temperature dropped to around -20 degrees. The anchor ice occurred when the water temperature was supercooling, but the stone temperature on the riverbed was almost over 0 degrees. In the Nayoro river, it occurred from 6:00 P. M. to 9:00 A. M. in the morning, where the temperature dropped to around -10 degrees. The anchor ice occurred at the timing of both supercooling of the water temperature, and the riverbed stone temperature dropped below freezing. 2) Releasing; The peaks of solar radiation, water temperature, and stone temperature increased, the anchor ice released to delay by 3-4 hours after the riverbed stone temperature rose. Although the illuminance and riverbed stone temperature are directly and indirectly related to the occurrence and release of anchor ice, it can be assumed the water temperature is the largest factor.
Year: 2020