砂河川斐伊川の河床低下，低水路幅の縮小化と是正のための今後の対応

抄録

In the sandy Hii River, sediment supplies from the upper basin have been decreasing due to constructions of check dams. The sediment transport in the Hii River occurs during not only the flood but also the ordinary discharge because of small and uniform sand composing the river bed. Therefore, river bed degradation and channel widths reduction downstream from the Igaya groundsill have developed due to non-equilibrium sediment transports at the groundsill during the ordinary discharges and small scale floods. We proposed proper shapes of the groundsill and river cross-section for mitigating the river bed degradations and channel widths reductions by using the numerical simulation model for long-term bed topographic changes in the river.