Abstract
the water circulating quantity in Sapporo city which centers the Toyohira river almost there was no change in closely 10 years. The water resource of the Toyohira river is circulating with separated three ways in Sapporo city. eutrophication was advancing in barato river. As measure of eutrophication, water conveyance into the barato river that water took from the toyohira river and through into the sousei river was done by 2007. The water circulating quantity increased 100m3/day with water conveyance, circulating ratio of central route increased from 32% to 39%. BOD density decreased 1mg/L with the effect of the dilution and the extrusion by water conveyance. and it was found that from the sousei river confluence point the effect appears in the upstream and downstream.
