Small-scale Plumes From a Semi-enclosed Basin: Yin-Yang Bay


Sea-level elevation, offshore-current data and a sequence of color plume photographs were employed as a basis for numerical simulation of the unsteady behavior of small-scale plumes from Lien-Tong Stream which flows into Yin-Yang Bay located on the northeast coast of Taiwan. We first discuss how alongshore tides are affected by the irregular structure of the bottom topography and coastline in the studied area. Subsequently, tide-plume interaction is examined. The importance of tides on plumes can be estimated by a dimensionless tidal-excursion number, P=W/L, where W is the width of the source outlet and L is the tidal-excursion length. Most of the existing numerical models treat the case when P is larger. In that case tidal effect is minor. In the present study P is O(1) or smaller; tidal advection becomes extremely important.
It is demonstrated numerically that the alongshore tides produce re­ circulation eddies inside the bay during both flood and ebb periods. The recirculation eddies induce plume movements inside the bay that are out of phase with the tidal currents over the shelf. Entering the coastal ocean, the plume water is advected by alongshore tides. The advection is rather asym­metric with respect to the axis of the bay due to the Earth's rotation. For the right-bound (ebb) tidal current, the plume tends to follow the Kelvin wave characteristic and hugs the coast. This tendency is absent during the left­ bound ( ood) tidal current. Scale analysis suggests that the advection by the ambient tidal current enhances this asymmetry.

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