Experimental study on changes of bed configuration caused by a permeable groyne of stone gabion

Abstract

The permeable groyne of stone gabion is recently proposed as countermeasures for the scouring problem and also for suitable ecosystem because it keeps the stable flow and bed conditions near the groyne tip. However it should be considered that typical flow phenomena as same as impermeable groyne such as developments of large-scale vortices still occur far downstream the groyne and the phenomena might affect on the morphology of main channel. Especially in Japanese rivers, these effects will be seen due to sudden change of discharge due to heavy rainfalls so that flow around the groynes change rapidly from submerged and flow conditions. These phenomena are one of the reasons for morphological changes at the downstream of groyne. In the present study, the characteristics of bed configuration downstream of a single permeable groyne are experimentally discussed on effects of the permeability and the scales of groyne and stone gabion as well as the flow conditions such as submerged flow over the groyne. The results show that local scour around the permeable groyne is proved to be significantly small, whereas the bed configuration of the downstream region far from the groyne largely changes forming sand waves.