Temporal changes in the ebb-tidal delta bathymetry of Imagire-guchi inlet in Japan.

This study focused on the morphologic changes in an ebb-tidal delta of Imagire-guchi inlet, Japan, at several temporal scales and the characteristics. The bathymetric information of the inlet was collected from multiple small fishing vessels. The position and depth of the vessel during operation were acquired with a GNSS antenna and fish finder, respectively, and these spatial data were logged with timestamps. The inlet bathymetry was consequently prepared to evaluate changes in the inlet morphology and delta-front volume. An assessment of the bathymetry monitoring data from 2008 to 2016 showed several reversals of the trends and various rates of accretion or erosion in the terminal lobe. The rate of the terminal progradation ranged from 7 to 30 m/y, and the rate of retrogradation ranged from 3 to 100 m/y over the eight years. The trend of progradation reversed in correspondence to three characteristic typhoons. The morphologic impact appeared in the terminal lobe and topset bed. The inlet channel also responded to typhoons with an expansion of shallows. The volume of delta-front sediment was annually evaluated, and the annual changes were compared with the equilibrium. [ABSTRACT FROM AUTHOR]