This study evaluates the flood reduction functions of five forested basins of the Yoshino river system covered with Japanese cedar and Japanese cypress. The functions are compared with that of the Meya dam basin covered with beech forest. The distributed runoff model is used, to eliminate the storage effect of the river channel that causes overestimation of the function. The functions of these basins are evaluated by the index of flood reduction function that considers resistance property of surface runoff and storage depth under the ground surface estimated by the model.
The indexes of flood reduction function evaluation of the forested basin of the Yoshino river system are higher than that of the Meya dam basin. The difference between basins appears in the equivalent roughness coefficient of surface runoff in the runoff model.