Landform Conservation and Flood Control: the Issue of the Chitose Diversion Channel Project in Hokkaido, Japan

Abstract

Landform conservation is the main task of geomorphology in the 21st Century. Since landforms provide the templates for the development of wildlife habitats, landform change is likely to cause habitat loss, inducing a reduction of biodiversity. From the viewpoint of ‘geomorphic species’, specific landforms such as natural rivers, tidal flats and coral reefs are endangered species in the Japanese islands. To avoid the further destruction of natural rivers, environmentally appropriate flood control plans are necessary. The analysis of the Chitose Diversion Channel project in Hokkaido, Japan, revealed that (1) the construction of this diversion channel has caused not only environmental problems but also serious social conflicts relating to habitats within and beyond the drainage basin; (2) excavation of a deep channel changed the groundwater supply which previously supported a natural river system, and (3) selection of a very high discharge value as the target of flood control was the main reason for planning this project. From a landform conservation perspective, the method adopted in Japan is unsuitable because it does not incorporate the scientific procedure necessary for selecting the ‘best’ peak discharge corresponding to the target rainfall with a certain recurrence period. An alternative flood control plan, combining the selection of a lower peak discharge, construction of retention pools and the restoration of meandering river channels is proposed to avoid the further destruction of natural rivers.