Modelling lateral circulation during flood season at the Oujiang River Estuary, China

Abstract

Lateral flow plays a critical role in estuarine dynamics. It can influence longitudinal diffusivity, creates strong vertical mixing, transports sediment laterally and modifies along-channel momentum budget. The Oujiang River Estuary is an important river estuary at eastern China coast. This study aims to investigate the structure of lateral circulation and its driving mechanism under saline environment by a FVCOM model. The patterns of lateral flow varied significantly over tidal stages and critical cross-sections, which are influenced by the topography, tidal current and salinity variations during flood season. The results showed that no evident lateral circulation existed at upper part from the mouth for most time, except that weak circulation was developed near the mouth during neap tide with small river discharge for this macrotidal estuary. By contrast, distinct lateral circulation was generally developed at lower part of the estuary over a tidal cycle. Flow regime was balanced between bottom friction and centrifugal force at upper part, while off the mouth, lateral baroclinic pressure gradient due to the tilting of isopycnals was expected to be an important mechanism of lateral circulation during highly stratified ebb tide. The results in this paper also showed the satisfactory performance of the model, which provided a reasonable estimate of the driving forces of the lateral circulation.