Determination of spatially varying Van der Burgh's coefficient from estuarine parameter to describe salt transport in an estuary

Abstract. The estuarine parameter v is widely accepted as describing the relative contribution of the tide-driven and density-driven mixing mechanism of salt transport in estuaries. Van der Burgh's coefficient K is another parameter that also determines the relative strength of two mechanisms. However, a single value of K, which has been considered in previous studies, can not represent the spatial variation of these mechanisms in an estuary. In this study, the spatially varying K has been determined from the v value calculated using intensively observed longitudinal salinity transects of the Sumjin River Estuary with exponential shape. The spatially varying K describes the spatial variation of these mechanisms reasonably well and is independent of the river discharge downstream of the estuary where the strong tides cause well mixed conditions. However, K values increase upstream and are found to depend on the freshwater discharge, with suppressing vertical mixing. The K value has been scaled on the basis of the v value and ranges between 0 and 1. If K < 0.3, the up-estuary salt transport is entirely dominated by tide-driven mixing near the mouth. If 0.3 < K < 0.8, both tide-driven and density-driven mixing contribute to transporting salt in the central regimes. If K > 0.8, the salt transport is almost entirely by density-driven circulation in the upper most regimes. In addition, another K-based dispersion equation has been solved by using this spatially varying K. The spatially varying K demonstrates density-driven circulation more prominently at the location of strong salinity gradient compared with a single K value.