Lessons from 1982 Nagasaki flood disaster

On the night of July 23, 1982, localized torrential downpours caused a natural disaster in Nagasaki. Nagayo, a suburb of the City of Nagasaki, experienced 187 mm of rainfall in one hour, the highest ever recorded. The natural disaster was twofold, involving both urban flooding due to rivers overflowing their banks and soil failures in suburban areas due to landslips and debris flows. In hilly Nagasaki, large amounts of water from the torrential downpours flowed at once into rivers and low-lying areas, causing rivers to overflow their banks while simultaneously triggering multiple soil failures. Roads were cut off by flooding or soil failures, and organized efforts were impossible in the initial stages. The disaster left 299 people dead or missing, caused losses of \315.3 billion, destroyed or seriously damaged 1,538 homes, and flooded 17,909 homes above the floorboards. As part of the reconstruction process, a disaster-resistant city scheme with consideration for the unique characteristics of Nagasaki was developed by a committee whose participants included community representatives. Main proposals under this scheme, based on the problems and lessons of the disaster are summarized in this paper