EXPERIMENTS ON THE INSTABILITY OF A RIVER MOUTH IN A POCKET BEACH

Abstract

It is commonly observed that, in pocket beaches, river mouths are located at either end of beaches adjacent to one of the headlands. Izumi et. al. presented a linear stability theory to explain the instability of river mouths in pocket beaches. The theory shows that river mouths cannot stay stably in the central region of beaches but can stay only within regions near either end of beaches when the capability of longshore sediment transport is not sufficient compared with the load of river sediment supply. In this study, a series of experiments are performed to study the instability of river mouths with the use of a simplified physical model. It is found that river mouths are always unstable at the center of beaches even without the shielding effect of headlands on the wave energy; thus, the shielding effect is not essential for the instability. Contrary to the theoretical results, river mouths are unstable at the beach center even if sediment supply is not sufficiently large.