Morphology transitions at the mouth of River Tenryu

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An X-band radar was employed to observe morphological behaviors at the mouth of River Tenryu, Sizuoka, Japan, for 2.5 years from June 2007. Land area of the river channel showed a seasonal variation: it increases in the summer seasons and decreases in winter. The river mouth widens by floods and narrows at ordinary flow periods. Phase difference between water levels in the river and ocean decreases generally in summer and increases in winter. Also, a coefficient representing flow resistance in the estuary showed a similar seasonal variation. The sand bar at the river mouth migrated towards inland in 2009, and water depths of the sea bottom in front of the river mouth estimated by analyzing wave motions captured during storms became milder from 2007 to 2009, suggesting overall coastal slope decreased during the period.