EVALUATION OF GRAVEL BAR RESTORATION CONSIDERING SECULAR CHANGE AT THE GION AREA IN THE ASAHI RIVER

Abstract

 Forestation on the bars in the middle reaches of the Asahi River has fairly progressed in recent years. The forestation reduces flood flow capacity and increases the water level during flooding. As countermeasure works of the forestation, tree's trimming and removal of deposited sand were conducted at the bar of the Gion area. Although the restored gravel bar was maintained for several years, reforestation has been confirmed there. In this study, the effect of a combination of two countermeasure works as sand removal of the bar and backfilling sand of low-water channel was evaluated using annual scale flood flow analysis over the next several years. Numerical results show that the the combination of works is more effective against the reforestation.