Narrow Results

The economy and life in Vietnam is associated with the existence and development of large river deltas, i.e. the Mekong Delta and the Red River Delta. The latter is located in the northern part of Vietnam and apart from thousands of square kilometers of the area, it includes more than 165 km of coastline as well. In this area, the seashore and the adjacent densely populated, low-lying regions are often subject to intense impacts from the river (floods) and the sea (typhoons, changes in sea level, currents, etc.) and therefore undergo substantial and dynamic changes and destructions.

In the current study, one of the coastal segments that are most vulnerable to destruction in Vietnam is analyzed. A synthetic analysis of the available information was carried out first and then the modeling of wave climate, currents and sediment movement patterns in the nearshore zone was done. The formulation of a phenomenological model of sediment budget, adequate for the amount of available information, allowed for assessment of the existing sediment fluxes and their relations to morphodynamic processes taking place in the studied area.

In this paper, an adapted methodology to evaluate coastal erosion vulnerability, which provides a basis for decision-making concerning risk management strategies, is described. The vulnerability evaluation was based on weighted indicators and assessed the vulnerability under different climate change scenarios. To generate the vulnerability index, dynamic processes, geo-indicators, and social and morphological parameters associated with modeled scenarios of sea level rise and predicted wave height changes were integrated. The study area included the sandy beaches in Pernambuco, NE Brazil, and was used to describe the practical application of this approach. Because the occupation of large sectors of the coastline was low, the vulnerability was concentrated in urbanized areas. The high-vulnerability sections of the coast were those with high population densities, high-rise buildings, induced coastal squeeze and hard engineering structures. The low-vulnerability beaches generally had low urbanization rates and well-conserved, resilient coastlines. Under future scenarios, the vulnerability of this coastal region will increase with sea level rise and wave height changes.

Beaches provide protection to residents living near the ocean by acting as a buffer against the high winds and waves of powerful storms or rough seas. It also helps the government to increase revenue and the development of infrastructure. Because beaches are very accessible to humans, it is very important to go through the demerits that are causing changes in the beaches and what steps can be taken to prevent the beaches from evolving. There are several studies indicating that there is an increase in the wave heights and wave periods along the Indian coasts, with maximum wave heights increasing by more than 30% in some of the locations. It is also found that at most of the locations along the east coast, wave periods are expected to increase by almost 20% whereas along the west coast, they are expected to increase by around 10% [Chowdhury et al. [2019] “Wave climate projections along the Indian coast,” Int. J. Climatol.https://doi.org/10.1002/joc.6096.]. This will alter the distribution of wave energy at the shoreline, swash-aligned beaches and additionally the design of coastal structures. It is particularly important to evaluate the wave characteristics and sediment transport which leads to erosion and/or siltation problems along the Indian coasts. In this paper, an extensive review on wave hydrodynamics, sediment transport and coastal erosion is compiled along the Indian coasts.

A coastal land area of approximately five km2 around the Pondok Bali beach in Subang, Indonesia, has been lost to the sea for the past decade. Before this land loss, there were several fish ponds with mangrove trees. The local people have suffered from the relative sea level rise, as they have had to abandon their houses because of the frequent inundations. To understand the status and causes of this coastal problem, the perception and adaptation strategies of the people, and potential countermeasures, we performed interview surveys in the associated villages and local governments. By using a sea chart of 1965 and satellite images, we calculated the cumulative volume change of deposition and erosion around the Cipunagara River mouth areas, where Pondok Bali is situated. Further, we conducted field measurements of turbidity and velocity, as well as bathymetry in the Cipunagara River to estimate the sediment supply. From the interviews, we found that a decrease in sediment discharge is a major cause of the erosion around Pondok Bali, which is due to the change of the river channel in 1965, when a floodway was constructed. At the present river mouth, a huge river delta has been formed owing to the sediment supply from the river. We also found that the local villages and governments have been considering countermeasures for reducing land erosion and promoting sustainable land use in the Pondok Bali areas, such as a plan for creating a new branch off from the main channel of the river to the Pondok Bali areas. However, further discussion on the new branch route is required among the associated villages because the effect of the new branch on Pondok Bali is unknown. From the field survey in the river, we calculated the sediment flux and estimated the total sediment supply to the river mouth, and this information is used for assessing the feasibility of the plan.

Monitoring shoreline change is one of essential tasks for appropriate design of coastal management and protection strategies. As one of remote sensing technologies, synthetic aperture radar, SAR can be a promising option because SAR is affected neither by cloud coverage nor by sun illumination. In this study, various kind of parameters, such as the grain size of bed materials, incident angles and wave height, were analyzed and it was found that the grain size is one of the most important factors for the shoreline monitoring skills using SAR.

Time variations of coastal bathymetry and sand grain size were investigated at the north Kashimanada Coast, a 40km long section of coast located between Oarai Port and Kashima Port, Japan. From the change of coastline position obtained from aerial photographs and bathymetrical surveys, it was found that the beaches located just next to Oarai Port and Kashima Port had been depositional and the areas next to those depositional beaches had been heavily eroded. Grain size distributions at the shoreline showed a tendency that grain size became coarser in the eroded areas and the areas were expanding. From analyses of the bathymetrical surveys, it was found that in almost 2/3 of the coast, offshore longshore sandbars diminished from 1984 to 2004, and it can be considered that the sediment movement caused by the headland system might be responsible for the extinction of the offshore sandbars.

The general increase of human activities, including the exploitation of the hydraulic and sediment resources of rivers, has caused extensive coastal erosion throughout the world, especially during the last 150 years or so. The true costs and impacts of this erosion have not been reflected in the price of providing commodities such as sand and gravel. These impacts and their estimated costs are presented using information from the states of Washington, Oregon, and California on the Pacific Coast of the United States of America.

The coastal erosion causes and their relative importance are site specific, changing from place to place. In the Portuguese Northwest coast, namely between Douro River and Nazaré, coastal erosion is mainly due to sediment supply reduction from Douro River. The present study analyzed the anthropogenic impacts on the river, identifying the type and time history of Human actions, the flow changes and the impact on the sediment transport along the years. Numerical formulations of sediment transport estimation allow defining the relative importance of the different interventions on the Douro River and its basin. The major importance of the dams constructed in the Douro River basin led to laboratory works on a hydraulic flume, evidencing the sediment transport reduction related with the lower flow velocities caused by the reservoirs of the dams on the upstream side.