Abstract
Flood concetration time equations are derived from fractal theory for urban rivers and sewer network. To know the effect of urbanization on flood controll, flood observation had been started in Tama New Town for the past fourteen years and its data were analyzed hydrologically. The major results are as follows; on the process of urbanization, concentration time has been shortened since impervious area, river improvement and sewer network increased in a watershed. However, the peak runoff coefficient only increased with impervious area and sewer network. These mechanism can be explained very clearly by the concentration time equations expressed by fractal.
