AN EFFECTIVE METHOD FOR RESTORING THE FORMER WATERCOURSES OF A RIVER WHERE THE WATERCOURSES ARE WELL ESTABLISHED

Abstract

In recent years, on the Satsunai River, a tributary of the Tokachi River, the area of gravel dry riverbeds has been rapidly decreasing because of the invasion by riparian forests. The watercourses have concentrated into one main watercourse and many of the branched streams have already disappeared even at locations where double-row bars had existed. In this study, onsite surveys and theoretical analysis were done to clarify the characteristics of bifurcations in watercourses with double-row bars and to determine a method of selecting the optimum excavation locations for effectively restoring already closed former watercourses. It was found to clearly identify riffles and pools in the longitudinal profile of the watercourse in the Satsunai River. Excavation at locations slightly downstream of a pool, where a riffle starts to emerge, were found to be effective.