Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


It has been widely observed in nature that longshore bar topography changes profile in the onshore-offshore direction. It is common for some bars to migrate onshore during post-storm phases and offshore during storms. Although the behavior of submarine bars has been widely reported, its mechanisms and forcings are far less clear. to determine the mechanism for bar migration or for the persistence of bar systems, a numerical model is developed, which accounts for the mass transport velocities in the bottom boundary layer induced by a family of combined long waves at surf-beat frequencies and wind waves. The present approach simulates the structures of the streaming velocities near the bed on mild and steep beaches under different wave conditions. The results from the numerical investigation show that the beach slope and the relative stength of the mass transport velocities between wind wave and infragravity wave appear to be the most important causes of the bar behavior. The influence of bars on modification of long waves is also considered. The long wave profiles on a barred topography show the trapping of antinodes toward bar crests with amplitude increased. The numerical approach is tested against field data obtained during the DUCK82 experiment. The model allows for long waves to be in broad-band frequencies, which is advantageous over existing approaches. The numerical results are consistent with observed data for bar formation, migration offshore, migration onshore, and even for bar maintenance.



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