ANALYSIS ON RECENT FLOOD EVENTS AND TREE VEGETATION COLLAPSES IN KAKO RIVER

Abstract

Forestation on flood plains is a world-wide engineering issue in middle to downstream reaches in many rivers. This brings not only degradation of flow conveyance capacity but also irreversible changes of ecological system in rivers. In order to obtain information on tree vegetation behavior during flood events, field data of flow fields and tree vegetation collapse were collected in Kako River, where willows are heavily vegetated on the flood plain. After starting a H-ADCP flow measurement in 2009, small to medium size flood events frequently occurred, which enables us not only to verify an analytical model to reproduce flow fields in and out of vegetations but also to examine tree vegetation collapses after flooding. The analytical solutions on velocity profiles as well as flow force acting on trees were in good agreement with the H-ADCP measurements and tree damages, respectively.