Turbidity Water Occurrence in a Basin after The 2018 Hokkaido Eastern Iburi Earthquake and Consideration of a Management Method of Intake for Agriculture to Prevent an Effect of Turbidity Water Intake

Abstract

There has been concern that the increased turbidity in the Atsuma River due to large slope failures caused by the 2018 Hokkaido Eastern Iburi Earthquake may have an effect on the intake of agricultural water in the area. In this study, a series of observations was conducted to determine the condition of turbidity water at four headworks in the Atsuma River mainstream, and a management method of intake for agriculture was considered. The observation results from the non-irrigation season showed a relationship between the maximum suspended solid concentration at all four points and the slope failures area rate for each tributary basin. On the other hand, in the irrigation season, the peaks of suspended solid concentrations were delayed and abrupt increases were reduced due to the effect of residence at headworks. Therefore, the maximum suspended solid concentration gradually decreased as the water traveled through the headworks from upstream to downstream. As a disaster reduction method to prevent the intake of turbidity water or to minimize its effect, we calculated the criterion times for water intake operation, and considered a management method of intake for agriculture that could become a guideline for intake gate operation.