Characteristics of the Act for Prevention of Disasters Due to Collapse of Steep Slopes seen
from its aim and roles act played in nonstructural measures against sediment disasters

Hiroshi MAKINO and Yukihiro ASAHINA

The Act for Prevention of Disasters Due to Collapse of Steep Slopes (Steep Slope Act) was established in 1969 to complement the relevant acts mainly including the Sabo Act and Landslide Prevention Act, with “life protection of the Japanese people" as the direct aim and “stabilization of people's livelihood and national land conservation" as the ultimate aim. The Act was pioneering and epoch]making in that it required that people who are reasonably expected to suffer damage due to steep slope failure, be advised to take appropriate measures against such slope failure and lists new nonstructural measures, including the designation of disaster danger areas, the establishment of a warning and evacuation system, and relocation of houses, not mentioned by conventional acts such as the Landslide Prevention Act. However, the Act did not necessarily serve its purpose as the nonstructural measures mentioned therein were not intended to apply to all of the areas expected to be damaged, it left building restrictions to the relevant ordinances, and it could not be applied to the debris flow disasters that frequently occur. In response, the notifications were issued in the early part of the 1980s to compensate for the drawbacks of the Act by reinforcing nonstructural measures against debris flow. Such improvement efforts were taken up by the Act on Promotion of Sediment Disaster Countermeasures for Sediment Disaster Prone Areas (Sediment Disaster Prevention Act) enacted in 2000. Clarifying the characteristics of the Steep Slope Act in comparison with the aims of other acts and having an overview of the roles the Act played in nonstructural measures against sediment disasters are considered to support measures against sediment disasters.