Abstract
Filtration flow has an important role in the function of a set-back type floodway, and it depends on the composition of beach material of the berm. In this study, field experiment on the drainage from the floodway was carried out, while considering the improvement of ordinary-type Numakawa-daini floodway into the set-back type. Then, two-dimensional movable experiment was carried out to investigate the filtration flow in the sand layer. In the berm composed of sand and gravel, the intensity of the filtration flow increases with the water level behind the berm, and fine sand is transported away by filtration flow, resulting in increase in the intensity of filtration flow.
