This research field intends to explicit the causal factors inducing erosion phenomena (e.g. landslides, collapse and debris flow, etc.) and changes to devastated lands occurring in Japan and overseas, caused by sediment related disasters and acute environmental changes in mountainous area. These factors are investigated through field survey, experimental methods and remote sensing techniques, etc. For this purpose, in this research field we educate and research on theory and techniques for conservation of natural phenomena (e.g.sediment and hydraulic phenomena), through the understanding of their reciprocal relationship, and the comprehension of processes related to devastation and restoration of natural environment.