Impact of seasonal vertical stratification on the dispersion patterns of dredging plumes off the south coast of Korea

Abstract

Simultaneous satellite and ship-borne surveys have been conducted to investigate the dispersion patterns of dredging plumes off the south coast of Korea in two contrasting seasons (spring and autumn). The distribution of total suspended solid (TSS) derived from sequential satellite imagery showed that the dredging plumes in spring developed over longer distances along the surface current than those in autumn. In spring, the deep and strong stratified condition in the water column contributed to the increase in radius of plume dispersion along the water surface. In autumn, the shallow and vertically well-mixed (or un-stratified) condition in the water column enhanced sinking of suspended dredged materials. This difference is due to the Brunt-Vaisala frequency being higher in spring (0.0183 s(-1)) than in autumn (0.0123 s(-1)). Although the sediment-laden overflow significantly increased TSS near the surface during the dredging period, the TSS contribution to water column stratification was only 23-5.6% of the thermohaline contribution. Therefore, the seasonal variation of thermohaline density is the main factor determining the dispersion patterns of dredging plumes in the study area.