Possibility of early warning for large-scale landslides using hydrological and sediment transport observations in mountain rivers

Abstract

Early-warning systems for sediment disasters are important tools for disaster risk reduction, achieving sustainable development, and ensuring livelihoods. In 2005, the Japanese government initiated a new nationwide early warning system for landslide disasters. The main methodology of the system involves setting a criterion for the occurrence of debris flows and slope failures based on several rainfall indices. However, these rainfall thresholds did not always work well and could not ensure early evacuation. We considered that the early detection of small-scale sediment movement, likes sediment discharge from streams, could be used effectively in early warning systems for large-scale landslides; however, the difficulties in directly monitoring traction processes, such as bedload and mass movements, has been widely recognized. Here, we propose a new observation method for monitoring bedload transport in mountain rivers using an acoustic method: the use of hydrophones, as proposed by Mizuyama et alii (1996). Moreover, we demonstrate the applicability of this method to clarify bedload dynamics in Japanese mountain rivers. Then, we argue that our new method offers the possibility of improvements in early warning systems of largescale landslides using real-time monitoring systems for bedloads in mountain rivers.