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Abstract

A field experiment was conducted to investigate the effects of the wave energy grouping and undulating on the sediment suspension in the surf zone at Taichung, Taiwan, in 1995. Instruments were deployed in line with the wave front, including one acoustic current meter, one pressure sensor, and four optical turbidity monitors were arranged in line and perpendicular to the bed. During the experiments the water depth was varied from 0.7 m to 3.6 m due to the tide level variations. The instruments were fixed to the ground to have data collected throughout the surf zone while the relative position of the station in the surf zone was varied with the tide level. Sediment suspension events associated with the group wave motions reached peak concentrations were 2-3 times larger than that associated with waves without grouping. A new approach using Hilbert transform and Intrinsic Mode Functions (IMF) analysis to explore the effect of energy grouping and undulating on sediment suspension is presented. It gives a close insight to the suspended sediment distribution and wave characteristics in the surf zone. An interesting bursting phenomenon of bed concentration was found dominating in the surf zone, which was closely related to the incident wave groups.

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