Japan’s Experiences of Catastrophic Mountain Disasters in Wakayama

Abstract

Wakayama Prefecture is a part of the Kii Peninsula, one of the most typhoon- and rainfall-prone areas in Japan, while the 80 % of its land is covered by precipitous mountains. Due to its geographical and geological characteristics, Wakayama has ever suffered repeated sediment disasters, such as debris flows, slope failure, and landslides, since ancient times. To address sediment disasters, Wakayama has taken structural and nonstructural preventive measures, such as sediment control dams and designation of sediment disaster warning areas where warning and evacuation systems must be established and also certain development activities are restricted. However, Wakayama suffered significant damages from Typhoon No. 12 in 2011. The record-breaking heavy rainfall by Typhoon No. 12 caused sediment disasters and river flooding in many places around Wakayama. Consequently, this disaster resulted in the highest deaths of 56, out of the total 82 deaths in all prefectures. Out of 56 deaths, 35 people were victims of sediment disasters. This chapter focuses on sediment disasters in Wakayama from a perspective of disaster risk reduction. It examines current preventive measures against sediment disasters in Wakayama, especially its nonstructural preventive measures, such as designation of warning and special warning areas for sediment-related disasters, which plays vital roles as the land use zoning. It finally identifies issues and challenges on how to improve its current nonstructural measures, based on the lesson learned from Typhoon No. 12 in 2011.