Numerical study of shoreline changes by emergency beach nourishment project at the Middle Beach of Beidaihe, China

Beach nourishment is a common coastal management strategy used to protect beach from erosion along the sandy coastlines. This method has been successfully applied to an emergency project at the West Beach of Beidaihe in the summer of 2008 and the full West Beach nourishment project in 2009-2010, which is the direct base of this study. Some basic information about the emergency engineering area at the Middle Beach is firstly described. The shoreline change of this area, including the analysis of beach width in five monitoring profiles in the bathing places of Middle Beach, is then discussed. After that a numerical model based on one-line theory is established and the numerical results agree well with the measured shorelines, which indicates that the model is appropriate and is qualified to predict the shoreline change of the Middle Beach. With the same model and parameters, long-term performance of the project is predicted, and the result shows that without follow-up nourishment and project, the bathing places can remain suitable for bathing for about 10 a. It is suggested to nourish the beach in time and carry out the beach nourishment project for the full Middle Beach in Beidaihe.     

Wave characteristic and morphologic effects on the onshore hydrodynamic response of tsunamis

While the destruction caused by a tsunami can vary significantly owing to near- and onshore controls, we have only a limited quantitative understanding of how different local parameters influence the onshore response of tsunamis. Here, a numerical model based on the non-linear shallow water equations is first shown to agree well with analytical expressions developed for periodic long waves inundating over planar slopes. More than 13,000 simulations are then conducted to examine the effects variations in the wave characteristics, bed slopes, and bottom roughness have on maximum tsunami run-up and water velocity at the still water shoreline. While deviations from periodic waves and planar slopes affect the onshore dynamics, the details of these effects depend on a combination of factors. In general, the effects differ for breaking and non-breaking waves, and are related to the relative shift of the waves along the breaking–non-breaking wave continuum. Variations that shift waves toward increased breaking, such as steeper wave fronts, tend to increase the onshore impact of non-breaking waves, but decrease the impact of already breaking waves. The onshore impact of a tsunami composed of multiple waves can be different from that of a single wave tsunami, with the largest difference occurring on long, shallow onshore topographies. These results demonstrate that the onshore response of a tsunami is complex, and that using analytical expressions derived from simplified conditions may not always be appropriate.     

A model study of influence of circulation on the pollutant transport in the Zhujiang River Estuary and adjacent coastal waters

A tracer model with random diffusion coupled to the hydrodynamic model for the Zhujiang River Estuary (Pearl River Estuary, PRE) is to examine the effect of circulations on the transport of completely conservative pollutants. It is focused on answering the following questions: (1) What role does the estuarine plume front in the winter play in affecting the pollutants transport and its distribution in the PRE? (2) What effect do the coastal currents driven by the monsoon have on the pollutants transport? The tracer experiment results show that: (1) the pollutant transport paths strongly depend on the circulation structures and plume frontal dynamics of the PRE and coastal waters; (2) during the summer when a southwesterly monsoon prevails, the pollutants from the four easterly river inlets and those from the bottom layer of offshore stations will greatly influence the water quality in Hong Kong waters, however, the pollutants released from the four westerly river-inlets will seldom affect the water quality of Hong Kong waters due to their transport away from Hong Kong; (3) during the winter when a northeasterly monsoon prevails, all pollutants released from the eight river gates will be laterally transported seaward inside the estuary and transport westward in the coastal waters along the river plume frontal zone. However, pollutants released from the surface layer of offshore stations near or east of the Dangan Channel will be carried into the coastal waters of Hong Kong by the landward component of the westward coastal current driven by the winter northeasterly monsoon. But the pollutants from the bottom layer of the offshore stations will be carried away from the offshore by the bottom flow driven by the northeasterly monsoon. This implies that only surface-released matter from offshore stations will affect the water quality of the coastal waters around Hong Kong during the winter when a northeasterly monsoon prevails.     

A model study of influence of circulation on the pollutant transport in the Zhujiang River Estuary and adjacent coastal waters

A tracer model with random diffusion coupled to the hydrodynamic model for the Zhujiang River Estuary (Pearl River Estuary, PRE) is to examine the effect of circulations on the transport of completely conservative pollutants. It is focused on answering the following questions: (1) What role does the estuarine plume front in the winter play in affecting the pollutants transport and its distribution in the PRE ? (2) What effect do the coastal currents driven by the monsoon have on the pollutants transport? The tracer experiment results show that: (1) the pollutant transport paths strongly depend on the circulation structures and plume frontal dynamics of the PRE and coastal waters; (2) during the summer when a southwesterly monsoon prevails, the pollutants from the four easterly river inlets and those from the bottom layer of offshore stations will greatly influence the water quality in Hong Kong waters, however, the pollutants released from the four westerly river-inlets will seldom affect the water quality of Hong Kong waters due to their transport away from Hong Kong; (3) during the winter when a northeasterly monsoon prevails, all pollutants released from the eight river gates will be laterally transported seaward inside the estuary and transport westward in the coastal waters along the river plume frontal zone. However, pollutants released from the surface layer of offshore stations near or east of the Dangan Channel will be carried into the coastal waters of Hong Kong by the landward component of the westward coastal current driven by the winter northeasterly monsoon. But the pollutants from the bottom layer of the offshore stations will be carried away from the offshore by the bottom flow driven by the northeasterly monsoon. This implies that only surface-released matter from offshore stations will affect the water quality of the coastal waters around Hong Kong during the winter when a northeasterly monsoon prevails.     

超强台风“威马逊”作用下红河三角洲海域水动力环境变化的数值研究

201409号超强台风"威马逊"于2014年7月从北部湾北部过境,对红河三角洲近岸海域的水动力环境产生重要影响。本文基于Delft3D建立三维潮、流、浪耦合数值模型,对红河三角洲水位、海流及波浪对台风的响应变化进行模拟。结果表明:威马逊台风期间,红河三角洲海域风速增大约6倍,风向由偏南风转为偏北风,表底层流速均受影响,其中表层变化较大,表现为北分量流速明显增大,流向变为偏南向,与风向主分量变化有关;波高增大为正常海况的9倍,时间变化与风速一致。本研究获得了从北部湾北部海域过境的台风影响下红河三角洲海域水动力环境的响应变化特征,对该海域的物质输运研究及海洋工程建设有重要意义。