An IFIM Experience in the Toyogawa-River Japan

In order to evaluate a new "Normality" Preservation Flow (NPF: a kind of instream flow) configuration in the Toyogawa-river, we carried out nearly the full IFIM process, even though the analysis was limited to the summer season and the adult stage of some fish species. We employed three kinds of time series of flow in 1967 and 1979 representing three conditions: 1) a flow configuration where no dams and diversion weirs are installed, 2) the present state, and 3) addition of one large new dam, and the NPF configuration is changed according to a government Ministry proposal. The results of the analysis suggest that the proposed condition might give a fairly good increase of fish habitat for some species downstream of the dam, even though some flushing flows would be expected to occur for shorter intervals in fish spawning seasons than the current condition.