A PROPOSED PRACTICAL SNOWMELT CALCULATION METHOD FOR ASSESSING THE RISK OF LANDSLIDE DISASTERS

本研究の目的は，融雪に伴う土砂災害危険度評価を行うことであり，合わせてそのための実用的な融雪量推定法を提案するものである．近年，日本の至る所で大雨に伴う土砂災害が発生しているが，北海道のような積雪地域では，融雪を誘因とする土砂災害も頻発している．本研究では，積雪重量計による観測データに基づき積雪密度の設定に改良を加えた雪面低下法の他に，熱収支法，デグリーアワー法の３つの手法を用いて融雪量の推定を行った．また，それらによって土壌雨量指数を推算し，スネーク曲線で土砂災害発生危険度を評価できるかを検証した．この結果，土砂災害発生危険度の評価において熱収支法の優位性を確認するとともに，実際の道路管理等の観点からの雪面低下法の改良について提案した．This study aims to conduct risk assessments for snowmelt-related landslide disasters and to propose a practical snowmelt estimation method that accurately assesses the landslide disaster risk. In recent years, landslide disasters have occurred during heavy rainfall events in many areas in Japan. In snowy areas such as Hokkaido, landslide disasters caused by snowmelt have frequently occurred. In this study, snowmelt was estimated by using three methods. One was a snow surface lowering measurement method, which was improved in its setting of snow cover density based on data gathered by using snow weight meters. Another was a heat balance method and the third was a degree-hour method. We estimated the soil water index by using the above three methods and examined whether it was possible to use snake curves to assess the risk of landslide occurrence. The examination clarified that landslide disaster risk can be assessed by using the snow surface lowering measurement method, which has been used in actual road management, when the snow cover density is set by using the method proposed in this study. As a result, we confirmed the superiority of the heat balance method in evaluating the risk of landslide disasters, and proposed improvement of the snow surface lowering method from the viewpoint of actual road management