Tidal inlets along the central coast of Vietnam are located in a microtidal, wave-dominated coastal environment. In addition, the Vietnam coast is highly influenced by the seasonal monsoon regime, which is characterized by large northeast waves from October to March and calm southeast waves from April to September every year. Consequently, the tidal inlet entrance morphologies often suffer from a dynamic seasonal evolution due to distinct differences in the direction of wave-induced longshore sediment transport (LST) between the two monsoon seasons. The migration or closure of tidal inlets causes a lot of problems for socio-economic development in the region since these are the main reasons leading to an increase in the risk of coastal flooding and the obstruction of navigation. This paper presents a comprehensive study of the morphological evolutions of natural tidal inlets on the central coast of Vietnam using long-term remote sensing data sets and by the Delft3D numerical model. Surprisingly, the estimated LST rates from the former method are in an order of magnitude agreement with the results from the latter one for all of the areas in this study. Based on the conservation equation for sand and comprehensive data collection, a new simple empirical formula for predicting the sand spit elongation rate as a function of the sand spit width is developed. Although the breaching of sand spit might happen during an extreme flood event at some tidal inlets, the growth rate of the spit before and after the breaching is almost unchanged. These findings are very useful information for supporting the local coastal authorities to find better management solutions in terms of sustainable development.

This paper presents the long-term morphological changes of the sand spits at the Ken Inlet in Ha Tinh Province and Phan Inlet in Binh Thuan Province, Vietnam. The analysis results show that the sand spit morphology at Ken Inlet was drastically changed before the completion of the Da Bac sluice gate construction in 1992, after that the sand spit elongation rate became stable at a rate of about 68 meters per year. Meanwhile, the sand spit at Phan Inlet was breached three times during the winter months of 1990-1991, 1998-1999 and 2014-2015. Moreover, the results of remote sensing image analysis also show that after the sand spit have been breached, it continued elongating at a relatively stable rate of 170÷200 meters per year. Based on the analytical model by Kraus (1999) for predicting the sand spit elongation, the estimated long-shore sediment transport rates of Phan Inlet and Ken Inlet are 145,000 m3/year and 133,500 m3/year, respectively. These longshore sediment transport rates are a main contribution for the sand spit elongation in these study areas. Keywords: sand spits; tidal Inlet; breaching; elongation; Landsat images; Google Earth images.

Coastal erosion and accretion along the Quang Nam coast in Vietnam have been increasing in recent years, causing negative impacts on the inhabitants and local ecology. The Cua Lo estuary in Nui Thanh district has a complex hydrodynamic regime owing to its connection with two estuaries and three different tributaries. Therefore, a detailed study of the mechanisms and processes of these phenomena is crucial to understand the potential impact of a proposed 50,000-ton cargo port. In this study, the Delft3D model is employed to evaluate the morpho-dynamic changes in the area of Cua Lo under monsoon wave climate, storm, and flood conditions both before and after port and navigation channel construction. Results indicate that in the absence of the port, tidal currents and waves during monsoon storms cause significant erosion on the south bank and accretion on the north bank. Furthermore, the GenCade model is utilized to predict the future shoreline changes after the construction of two jetties. The model reveals that after 50 years of operation, the shoreline modifications will extend 449 m towards the sea, in comparison to natural conditions. However, the design of the northern jetty will ensure safe and proper operation without impacting the navigation channel. This study offers valuable insights into the morphological changes in the Cua Lo area and their potential implications, which can aid in the development of sustainable coastal management strategies for the region.

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LandsatGoogle Earth 95m/