Numerical study on mixing and stratification in the Ebb-Dominant Johor Estuary

Abstract

Hasan, G.M.J.; van Maren, D.S., and Hin Fatt, C., 2013. Numerical study on mixing and stratification in the ebb-dominant Johor Estuary. A three-dimensional hydrodynamic model is used to investigate intratidal spring-neap variations of turbulent mixing and stratification in the Strait of Singapore and its adjacent Johor estuary area. The waters in the Johor estuary are ebb dominant because of interaction of the O1-K1-M2 tidal constituents. In most estuaries mixing rates during the flood are larger than during the ebb because of a flood-dominant tidal asymmetry. The Johor estuary is an example where tidal asymmetry supports stronger mixing during ebb tides, whereas similar to other estuaries, tidal straining promotes stable stratification during the ebb. Therefore an analysis of intratidal variation in stratification reveals the relative importance of both mechanisms. Vertical profiles of salinity, flow velocity, and eddy diffusivity show a marked asymmetry between flood and ebb tides. Small changes in the tidal currents substantially influence the eddy diffusivity, energy dissipation rate, and build up of stratification, which is explained using the nondimensional Richardson number. The estuary is found completely mixed during flood tide and slightly stratified during ebb tide, suggesting tidal straining (generating ebb stratification) is more important for the intratidal variation in mixing and stratification than tidal asymmetry (flood stratification). © Coastal Education & Research Foundation 2013.