MP
M.H. Phan
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1
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.
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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.
Tide is influenced due to not only mainly tide generating force but also local wind and weather patterns. The East Asian monsoons cause strong seasonal climatic variations in the Mekong Delta. A two-dimensional, barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the South China Sea with a particular interest for its characteristics along the Mekong deltaic coast under wind monsoon climate. The results reveal that wind monsoon climate could causes damped or amplified tidal amplitudes around Mekong deltaic coast approximately 2–3 cm due to the changing atmospheric pressure, the tangential stress of wind over the water surface, and wind enhanced bottom friction. The monsoon climate influences rather strongly on the M2 semidiurnal tide system in the eastern Mekong deltaic coast, meanwhile the monsoon climate controls K1 diurnal tide in the western region of Mekong delta.
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Tide is influenced due to not only mainly tide generating force but also local wind and weather patterns. The East Asian monsoons cause strong seasonal climatic variations in the Mekong Delta. A two-dimensional, barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the South China Sea with a particular interest for its characteristics along the Mekong deltaic coast under wind monsoon climate. The results reveal that wind monsoon climate could causes damped or amplified tidal amplitudes around Mekong deltaic coast approximately 2–3 cm due to the changing atmospheric pressure, the tangential stress of wind over the water surface, and wind enhanced bottom friction. The monsoon climate influences rather strongly on the M2 semidiurnal tide system in the eastern Mekong deltaic coast, meanwhile the monsoon climate controls K1 diurnal tide in the western region of Mekong delta.
Coastal retreat problems occur in many deltas over the world. Coastal features are not constant over time and are affected by sea level rise, river runoff, sediment supply, wave and tidal energy, underlying geology and climate. In addition, human activities profoundly influence the coastal processes as a result of changing natural patterns of runoff, littoral sediment supply and construction and reconstruction of engineering works.
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Coastal retreat problems occur in many deltas over the world. Coastal features are not constant over time and are affected by sea level rise, river runoff, sediment supply, wave and tidal energy, underlying geology and climate. In addition, human activities profoundly influence the coastal processes as a result of changing natural patterns of runoff, littoral sediment supply and construction and reconstruction of engineering works.
A two-dimensional, barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the South China Sea with a particular interest for its characteristics along the Mekong deltaic coast. The study indicates that tidal waves propagate from the Pacific Ocean into the South China Sea mainly through the Luzon Strait (LS), where the K 1 diurnal tide dominates due to a quarter wavelength resonance in this semi-enclosed basin, and that the incoming tidal waves from the Celebes open boundary play a more important role than those from the Andaman and Flores open boundaries. Previous studies have not explained why both adjacent seas including the South China Sea and the Gulf of Thailand are dominated by a diurnal tide, while a semidiurnal tide dominates along the eastern Mekong deltaic coast. By means of Green's law, continental shelf tidal resonance theory and standing wave theory, this study clarifies that the large amplified M 2 semidiurnal amplitude leading to a prevailing mixed semidiurnal tide is caused not only by the shoaling effect and the continental shelf oscillation resonance phenomenon but also by the position on the standing wave anti-node line. Moreover, the finding of radial tidal currents occurring along the southern Mekong estuarine coast has not been revealed in earlier studies. Based on a number of numerical, geometrically schematised experiments, we suggest that the interaction between the large amplified amplitude near the shoreline associated with the adjacent low amplitude band system, causing convex hydraulic gradients of tidal amplitude due to basin geometry as well as sloping topography, is the mechanism for developing these radial tidal current systems. The results reveal that wind monsoon climate could cause either damped or amplified tidal amplitudes around the Mekong deltaic coast of which approximately 2–3 cm is due to the changing atmospheric pressure, the tangential stress of wind over the water surface and wind enhanced bottom friction. Also, this study suggests that the tidal generating forces should be considered to achieve accurate model results depending on the geographical region of interest. Findings achieved from this study contribute to a deeper insight of tidal wave propagation from a deep ocean to a shallow flat basin similar to the South China Sea and its Mekong deltaic coast.
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A two-dimensional, barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the South China Sea with a particular interest for its characteristics along the Mekong deltaic coast. The study indicates that tidal waves propagate from the Pacific Ocean into the South China Sea mainly through the Luzon Strait (LS), where the K 1 diurnal tide dominates due to a quarter wavelength resonance in this semi-enclosed basin, and that the incoming tidal waves from the Celebes open boundary play a more important role than those from the Andaman and Flores open boundaries. Previous studies have not explained why both adjacent seas including the South China Sea and the Gulf of Thailand are dominated by a diurnal tide, while a semidiurnal tide dominates along the eastern Mekong deltaic coast. By means of Green's law, continental shelf tidal resonance theory and standing wave theory, this study clarifies that the large amplified M 2 semidiurnal amplitude leading to a prevailing mixed semidiurnal tide is caused not only by the shoaling effect and the continental shelf oscillation resonance phenomenon but also by the position on the standing wave anti-node line. Moreover, the finding of radial tidal currents occurring along the southern Mekong estuarine coast has not been revealed in earlier studies. Based on a number of numerical, geometrically schematised experiments, we suggest that the interaction between the large amplified amplitude near the shoreline associated with the adjacent low amplitude band system, causing convex hydraulic gradients of tidal amplitude due to basin geometry as well as sloping topography, is the mechanism for developing these radial tidal current systems. The results reveal that wind monsoon climate could cause either damped or amplified tidal amplitudes around the Mekong deltaic coast of which approximately 2–3 cm is due to the changing atmospheric pressure, the tangential stress of wind over the water surface and wind enhanced bottom friction. Also, this study suggests that the tidal generating forces should be considered to achieve accurate model results depending on the geographical region of interest. Findings achieved from this study contribute to a deeper insight of tidal wave propagation from a deep ocean to a shallow flat basin similar to the South China Sea and its Mekong deltaic coast.
The coastal zone of Mekong delta is suffering under intense pressures from climate change as well as human intervention. Currently, the coastline evolution of Mekong delta is a complex combination of impacts due to (1) relative sea level rise i.e. the sum of eustatic sea level rise, natural and human induced subsidence (2) sediment transport rate changes at some sections due to change of wave condition by climate change (3) change of sediment sources from the Mekong estuaries by dam construction and sand mining and (4) mangrove degradation. A coastline monitoring is the basis to understand and manage coast. This study utilizes integrated techniques of remote sensing, geographic information system and statistics to monitor coastline change over the period of 1973 to 2015 from Landsat images of Multispectral (MSS), Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), Operational Land Imager (OLI) at coastal area of Mekong delta. An advanced toolbox is developed for the work of atmospheric and radiometric correction of Landsat images as well as influence of tidal range is taken into account to obtain mean water level. Tasseled Cap and Normalized Difference Water Index (NDWI) algorithm is applied to separate land-water interface for extracting shorelines. Besides, a digital shoreline assessment system (DSAS) tool is used to analyze shoreline rate by statistic parameters as Shoreline Change Envelope (SCE), End Point Rate (EPR) and Linear Regression (LRR). Furthermore, uncertainty assessment for this methodology based on topographic surveying and Google Earth images. Moreover this research explored relationships between the accretion and erosion of land and the sediment load of the Mekong River. The results revealed a general pattern of accretion and erosion. The eastern coast, which is fragmented by 9 estuaries, was significant accretion and erosion, especially annual erosion rate of around 40 meter at Bo De estuary is noted. Meanwhile the western coast is rather stable, particularly annual accretion rate of up to 90-95 meter at Datmui commune of Camau province. This study indicated there is relative difference of coastline change rate among periods of 1973-1990, 1990-2005 and 2005- present. And the study illustrates the rate of shoreline change is significantly associated with sediment discharge on Mekong River through statistic approach, especially the phase of sediment flow decrease by dam and sand mining on Mekong River in recent 15 years. The results of methodology and maps from this research may be useful in planning and management of this exposed coastline.
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The coastal zone of Mekong delta is suffering under intense pressures from climate change as well as human intervention. Currently, the coastline evolution of Mekong delta is a complex combination of impacts due to (1) relative sea level rise i.e. the sum of eustatic sea level rise, natural and human induced subsidence (2) sediment transport rate changes at some sections due to change of wave condition by climate change (3) change of sediment sources from the Mekong estuaries by dam construction and sand mining and (4) mangrove degradation. A coastline monitoring is the basis to understand and manage coast. This study utilizes integrated techniques of remote sensing, geographic information system and statistics to monitor coastline change over the period of 1973 to 2015 from Landsat images of Multispectral (MSS), Thematic Mapper (TM), Enhanced Thematic Mapper Plus (ETM+), Operational Land Imager (OLI) at coastal area of Mekong delta. An advanced toolbox is developed for the work of atmospheric and radiometric correction of Landsat images as well as influence of tidal range is taken into account to obtain mean water level. Tasseled Cap and Normalized Difference Water Index (NDWI) algorithm is applied to separate land-water interface for extracting shorelines. Besides, a digital shoreline assessment system (DSAS) tool is used to analyze shoreline rate by statistic parameters as Shoreline Change Envelope (SCE), End Point Rate (EPR) and Linear Regression (LRR). Furthermore, uncertainty assessment for this methodology based on topographic surveying and Google Earth images. Moreover this research explored relationships between the accretion and erosion of land and the sediment load of the Mekong River. The results revealed a general pattern of accretion and erosion. The eastern coast, which is fragmented by 9 estuaries, was significant accretion and erosion, especially annual erosion rate of around 40 meter at Bo De estuary is noted. Meanwhile the western coast is rather stable, particularly annual accretion rate of up to 90-95 meter at Datmui commune of Camau province. This study indicated there is relative difference of coastline change rate among periods of 1973-1990, 1990-2005 and 2005- present. And the study illustrates the rate of shoreline change is significantly associated with sediment discharge on Mekong River through statistic approach, especially the phase of sediment flow decrease by dam and sand mining on Mekong River in recent 15 years. The results of methodology and maps from this research may be useful in planning and management of this exposed coastline.