Examination of hydrological indices related to landslide occurrences over a wide area in Hokuriku Region

Abstract

Assessment of landslide potential over a wide area is a crucial issue for mitigation of landslide disasters especially in the Hokuriku Region (Niigata, Toyama and Ishikawa Prefecture) , central Japan, where a large number of landslides are induced not only by intensive rainfall but also by snow melting. Hydrological data on dam inflow was analyzed in order to predict the occurrence of landslides induced by hydrological phenomena such as change of subsurface water flow and increase of groundwater pressure. Several hydrological indices to be analyzed their statistical characteristics were formulated on the basis of the hydrological observation results including dam inflow discharge from 13 selected dams on which few artificial influences are found. The relationship between those hydrological indices and landslide occurrences was examined using data set on landslides in the Hokuriku Region during 5 years. As a result the peak daily water head at the dam preceding the landslide occurrences were selected as the appropriate index for prediction of landslide occurrences because it shows the highest probability of detection (POD) and the lowest error rate with the least expected days exceeding the critical value. The selected index shows the value about 70% as the POD with 15 days exceeding the critical value per year on average. The index is useful as prediction criteria and applicable for initiating site patrolling and inspection.