Numerical Investigation of Hydrodynamics and Cohesive Sediment Transport in Cua Lo and Cua Hoi Estuaries, Vietnam

Viet Thanh Nguyen,Chi Zhang,Minh Tuan Vu

doi:10.3390/jmse9111258

Abstract

Two-dimensional models of large spatial domain including Cua Lo and Cua Hoi estuaries in Nghe An province, Vietnam, were established, calibrated, and verified with the observed data of tidal level, wave height, wave period, wave direction, and suspended sediment concentration. The model was then applied to investigate the hydrodynamics, cohesive sediment transport, and the morphodynamics feedbacks between two estuaries. Results reveal opposite patterns of nearshore currents affected by monsoons, which flow from the north to the south during the northeast (NE) monsoon and from the south to the north during the southeast (SE) monsoon. The spectral wave model results indicate that wave climate is the main control of the sediment transport in the study area. In the NE monsoon, sediment from Cua Lo port transported to the south generates the sand bar in the northern bank of the Cua Hoi estuary, while sediment from Cua Hoi cannot be carried to the Cua Lo estuary due to the presence of Hon Ngu Island and Lan Chau headland. As a result, the longshore sediment transport from the Cua Hoi estuary to the Cua Lo estuary is reduced and interrupted. The growth and degradation of the sand bars at the Cua Hoi estuary have a great influence on the stability of the navigation channel to Ben Thuy port as well as flood drainage of Lam River.

Highlights

An estuary is defined as the transition zone between land and sea, where the flow and transport of sediment between the river and the sea meet
The results suggested that wind-wave have a significant influence on sediment transport and river morphology with the effect accounting for nearly 95% whereas river discharge and tide play minor roles [22]
The hydrodynamic model was calibrated with observation data of water level and current, and the results showed that the root mean square error (RMSE) was only 2.21% for water level, 20.54% for current speed, and 27.18% for current direction, while mean absolute error (MAE) were 1.83% for water level, 13.60% for current speed, and 19.55% for current direction, as shown in Table 1, Figures 8 and 9

Summary

Introduction

An estuary is defined as the transition zone between land and sea, where the flow and transport of sediment between the river and the sea meet. Estuaries occur in many coastal areas around the world. They play an important role in human life such as providing space for navigation, entertainment, commerce as well as living. The estuarine environment contains complex physical processes that are controlled by both natural factors and human activities. The morphological change affects the hydrodynamic tidal regime and sediment transport leading to changes in the depth of the estuary and in the elevation/volume of inter-tidal areas. Due to the importance of estuaries as well as the complexity of processes in the estuarine, the forecast of the current regime, transport, erosion, and deposition of sediment is an interesting issue attracting many researchers

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Conclusion