ADCP observation of nearshore current and suspended load profile

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Beach erosion due to offshore-going sediment transport is a serious problem in Japan's coasts facing the Japan Sea. It has hot yet been made clear the mechanism of sediment transport offshore. The main aim of this study is to unveil the nearshore current structure in the surf zone by ADCP observation with the T-shaped Observation Pier(TOP), on the Ogata Coast, Niigata. Prefecture.From the observation, we estimated current characteristics as :(1) Velicity Profile : When the longshore currents become strong due to oblique winds and waves, intensity of the offshore currents becomes weak with undertow-like velocity profile are formed. Velocity profiles of both longshore and offshore currents are almost uniform below the wave trough level.(2) Longshore Currents : Strong and uniform longshore currents are generated in the surf zone by oblique winds and waves. Its direction well responds to changes in wind direction, ex. westerly wind excites east word longshore currents and vice versa.(3) Off-Shore Currents : Almost all current below the wave trough direct offshore in the surf zone. When wind and wave direction changed, W(westward) -> NW(shore-normal) ->N (eastward), the typical wind evolution pattern in this coast, strong offshore currents are observed in the shore-normal wind phase.(4) Wind Drag Coefficient near the surf zone : Wind drag coefficient near extremely shallow and high wave condition including wave breaking is derived by using Turbulent Dissipation Method (TDM), as shown in Fig.3. The fitting curve isCd=0.0223 exp(10/3)**(-U/15) when U(10m)> 10m/s.(5) Turbidity concentration vs Echo intensity of ADCP : under analyzing.