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Truong, S.H.; Ye, Q., and Stive, M.J.F., 2017. Estuarine mangrove squeeze in the Mekong Delta, Vietnam. Although the protective role of mangroves for coasts has been increasingly recognized, that of estuarine mangroves is less well acknowledged. The complex root, stem, and canopy system of healthy estuarine mangroves efficiently reduces the impact of a strong, along-bank flow during high tides and high river discharge, protecting the riverbank from eroding. If a sediment source is available, a healthy mangrove forest also offers a higher potential for sedimentation to compensate for sea-level rise. Unfortunately, along the Mekong, Vietnam, estuaries, mangroves have been rapidly destroyed. In many regions, estuarine mangroves have degraded into narrow strips of <50 m. Riverbanks at those locations are eroding at a rate of 2-4 m y−1. The main reason for this 'estuarine mangrove squeeze' phenomenon is due to the increasing demand to create more space for local fish farming. Hence, squeeze is used in a broader sense than in the context of sea-level rise impact alone. The hypothesis is that there is a critical minimum width for an estuarine mangrove forest strip to maintain its ability to survive. The analysis of available data, both from literature and from satellite observations, supports the hypothesis: An average critical width for Mekong estuaries was found to be approximately 80 m. To obtain insight into the efficiency of a mangrove forest in reducing the impacts of alongshore flow, the state-of-the-art Delft3D model was applied to the data. The model showed that the penetration-length scale of the shear layer into a mangrove forest requires a certain minimum space to develop fully. It is hypothesized that the minimum width of a mangrove forest, which equals this maximum penetration-length scale, has a crucial role for the health of a mangrove system. [ABSTRACT FROM AUTHOR]

Phan, L.K.; van Thiel de Vries, J.S.M., and Stive, M.J.F., 2015. Coastal mangrove squeeze in the Mekong Delta. The role of mangrove forests in providing coastal zone stability and protection against flooding is increasingly recognized. The specific root, stem, and canopy system of mangroves is highly efficient in attenuating waves and currents. The sheltered environment created by a healthy mangrove forest offers great sedimentation potential in case a sediment source is available. However, the once-abundant mangrove forests in the Mekong coastal delta are becoming rapidly depleted. Especially along the Mekong eastern and southeastern coast, mangrove degradation and rapid coastline erosion are observed at many locations. At these locations, the mangrove forests usually consist of a narrow strip only, sometimes as narrow as 100 m. This mangrove squeeze is mainly due to the construction of sea dikes in a quest for the creation of space for cultivation and the prevention of salinity intrusion. The basic assumption behind our work is that there is a critical minimum width of a coastal mangrove forest strip to keep its ability to stay stable or, once surpassing the minimum width, to promote sedimentation. The larger the width the more efficient the attenuation of waves and currents will be, offering both a successful seedling and sedimentary environment. Our analysis of available data both from literature and from satellite observations supports our basic assumption: an average critical width of 140 m is found for the southeastern and eastern Mekong Delta coast as a minimum width to sustain a healthy mangrove forest. To further our insights into the efficiency of mangrove to attenuate wave energy as a function of their width we have applied a state-of-the-art wave propagation model that includes both short and long waves. Our results confirm earlier results from the literature that short waves are indeed attenuated very rapidly over distances shorter than the critical width, but as we show for the first time infragravity waves penetrate over much larger distances. We therefore hypothesize that the decay of long waves plays a crucial role in the health of the mangrove. [ABSTRACT FROM AUTHOR]

Mangroves play an important role in sustaining a healthy coastal environment, providing a natural habitat to various species, a stable shoreline and forestry products. However, the extent of mangroves developed along the tidal coast of the Mekong delta in southern Vietnam has faced and still faces the impact from both natural and anthropogenic drivers. Since the area of mangroves in the coastal Mekong delta is not well documented, this study aims to quantitatively document the evolution of the mangrove area over the past 48 years, i.e. between 1973 and 2020. Satellite Landsat images, along with a classification method comprising Iso Cluster and Maximum Likelihood algorithms, have been used for mapping land cover types including mangroves, aquaculture, soils, plants and water surfaces along the coastal districts of the Mekong delta. The study shows that remote sensing and GIS techniques can be applied to obtain mapping of the land cover, as well as detect and analyse spatial and temporal changes caused by e.g. coastal erosion or aquaculture expansion. The findings reveal that the total mangrove area of an estimated 185,800 ha in 1973 decreased significantly to 102,160 ha in 2020. Approximately 2150 ha/yr of the total mangrove loss over 1973–2020 was due to invasion by aquaculture, while roughly 430 ha/yr was lost due to coastal erosion. A slight increase in mangrove area occurred since 2010 as a result of the implementation of a series of projects to protect against coastal erosion and to restore mangroves by the Vietnamese government and international non-governmental and governmental organizations, although the success rates of mangrove restoration are relatively low. The survival of mangrove forests in the Mekong delta is related to the main pressure drivers: pollution, land use conversion, insufficient sediment sources, coastal erosion and coastal mangrove squeeze. Therefore, an integrated mangroves and shrimp farming model is one of the most appropriate approaches to achieve a beneficial balance between both aquaculture and mangroves. [Display omitted] • A detailed picture of long-term mangroves and other land cover types dynamics in the coastal area of the Mekong delta during 48 years is revealed. • The main threatening drivers to the survival of the mangrove in the Mekong delta include pollution, land use conversion, insufficient nutrient-enriched sediment, coastal erosion, coastal mangrove squeeze and improper mangrove restoration techniques in local regions. • The integrated mangroves and shrimp farming model is one of the most appropriate approaches to achieve a beneficial balance between both aquaculture and mangroves. • Landsat images are capable to evaluate the dynamics of mangrove and other land cover categories in the spatial and temporal scale. [ABSTRACT FROM AUTHOR]