2014 年 2 巻 1 号 p. 203-213
In this study, simple equations for calculating ice sheet thickness were developed on the basis of an ice sheet thickness simulation model that used heat flux. In an array of equations, the coefficients α and β represented the effects of both snow cover and frazil ice and the effects of river ice melting, respectively. The air temperature, the water temperature, and the effective water depth were represented by independent variables. A method for calculating the ice sheet thickness on the basis of data on the air temperature alone was established. In this method, water temperatures were calculated by using air temperatures and simple equations, and a constant value was given to the effective water depth. The ice sheet thickness in a river was successfully determined by using a non-contact measuring technique. The values measured by this technique were reproduced by the values calculated by simple equations that used the air temperature as the sole input value. The simple equation using the sole input value of air temperature for calculating the ice sheet thickness was also used for retrospectively predicting the day when river water began to freeze and the day when river ice began to break for the past nine years on an actual river. The mean absolute errors in the prediction of the day of ice formation and the day of ice breakup on the basis of calculated values were 6 days and 2 days, respectively, in comparison with the predictions based on the measured values. This suggests that the simple equation is useful for accurate prediction of the days of ice formation and ice breakup.