scholarly journals Flooding in the Mekong Delta: Impact of dyke systems on downstream hydrodynamics

2019 ◽  
Author(s):  
Vo Quoc Thanh ◽  
Dano Roelvink ◽  
Mick van der Wegen ◽  
Johan Reyns ◽  
Herman Kernkamp ◽  
...  
Keyword(s):  
Mekong Delta ◽  
River System ◽  
Dry Season ◽  
Water Levels ◽  
Mekong River ◽  
Flood Season ◽  
Tidal Propagation ◽  
River Outflow ◽  
Year 2000

Abstract. Building high dykes is a common measure to cope with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes cause considerable changes in hydrodynamics of the Mekong River. Therefore, this paper aims to assess the impacts of the high dyke system on water level fluctuation and tidal propagation on the Mekong River branches using a modelling approach. In order to consider interaction between rivers and seas, an unstructured modelling grid was generated, with 1D–2D coupling, covering the Mekong Delta and extending to the East (South China Sea) and West (Gulf of Thailand) seas. The model was manually calibrated for the flood season of the year 2000. To assess the role of floodplains, scenarios consisting of high dykes built in different regions of the Long Xuyen Quadrangle (LXQ), Plains of Reeds (PoR) and TransBassac were carried out. Results show that the percentage of river outflow at Dinh An sharply increases in the dry season in comparison to the flood season while the other Mekong estuarine outflows rise slightly. In contrast, the lateral river flows of the Mekong River system to the seas by the Soai Rap mouth and the LXQ decrease somewhat in the dry season compared to the flood season due to overflow reduction at the Cambodia–Vietnam border. Additionally, the high dykes in the regions that are directly connected to a branch of the Mekong River, not only have an influence on the hydrodynamics in their own branch, but also on other branches because of the connecting channel of Vam Nao. Moreover, the high dykes built in the PoR, LXQ and TransBassac regions are the most important factor for changing water levels at Tan Chau, Chau Doc and Can Tho, respectively. The LXQ high dykes result in an increase of daily mean water levels and a decrease of tidal amplitudes on the Song Tien (downstream of the connecting channel of Vam Nao). A similar interaction is also found for the the PoR high dykes and the Song Hau.

scholarly journals Flooding in the Mekong Delta: the impact of dyke systems on downstream hydrodynamics

2020 ◽  
Vol 24 (1) ◽  
pp. 189-212 ◽  
Author(s):  
Vo Quoc Thanh ◽  
Dano Roelvink ◽  
Mick van der Wegen ◽  
Johan Reyns ◽  
Herman Kernkamp ◽  
...  
Keyword(s):  
Mekong Delta ◽  
High Flow ◽  
Water Levels ◽  
Mekong River ◽  
Low Flow ◽  
Water Level Fluctuations ◽  
Tidal Propagation ◽  
Extreme Flood ◽  
Year 2000 ◽  
The Impact

Abstract. Building high dykes is a common measure of coping with floods and plays an important role in agricultural management in the Vietnamese Mekong Delta. However, the construction of high dykes causes considerable changes in hydrodynamics of the Mekong River. This paper aims to assess the impact of the high-dyke system on water level fluctuations and tidal propagation in the Mekong River branches. We developed a coupled 1-D to 2-D unstructured grid using Delft3D Flexible Mesh software. The model domain covered the Mekong Delta extending to the East (South China Sea) and West (Gulf of Thailand) seas, while the scenarios included the presence of high dykes in the Long Xuyen Quadrangle (LXQ), the Plain of Reeds (PoR) and the Trans-Bassac regions. The model was calibrated for the year 2000 high-flow season. Results show that the inclusion of high dykes changes the percentages of seaward outflow through the different Mekong branches and slightly redistributes flow over the low-flow and high-flow seasons. The LXQ and PoR high dykes result in an increase in the daily mean water levels and a decrease in the tidal amplitudes in their adjacent river branches. Moreover, the different high-dyke systems not only have an influence on the hydrodynamics in their own branch, but also influence other branches due to the Vam Nao connecting channel. These conclusions also hold for the extreme flood scenarios of 1981 and 1991 that had larger peak flows but smaller flood volumes. Peak flood water levels in the Mekong Delta in 1981 and 1991 are comparable to the 2000 flood as peak floods decrease and elongate due to upstream flooding in Cambodia. Future studies will focus on sediment pathways and distribution as well as climate change impact assessment.

scholarly journals THERAVADA BUDDHISM IN KHMER PEOPLE’S LIFE IN THE MEKONG DELTA – FROM THE ANGLE OF MARRIAGE

2011 ◽  
Vol 14 (3) ◽  
pp. 79-86
Author(s):  
Oanh Thi Kim Dang
Keyword(s):  
Family Life ◽  
Social Relationship ◽  
Mekong Delta ◽  
Mekong River ◽  
Theravada Buddhism ◽  
Marriage And Family ◽  
Agricultural Society ◽  
Indirect Impacts ◽  
Social Management

Theravada Buddhism, although it is a religion based on the principle of “ly gia cat ái” which means “leaving family and cutting off love, in reality, for the Khmer people in the Mekong River Delta, Theravada Buddhism has very clearly shown secularization into all aspects of Khmer people’s life. In Khmer traditional society, Theravada Buddhism teachings are the foundation for rules which operate social relationship, social management including both the power of community and of pagodas, which creates special features of Khmer traditional agricultural society, completely different from Vietnamese villages and communes. Particularly, in the field of marriage and family, from concepts, rules to wedding rituals, from rites and customs in daily life to funeral rituals of family life etc. all are absorbed and profoundly influenced by Theravada Buddhism ideology and philosophy. The paper aims to learn about influences, and direct as well as indirect impacts of Theravada Buddhism on marriage and family life of the Khmer in the Mekong Delta, contributing more data to prove the role of Theravada Buddhism in the life of Khmer people in the Mekong Delta.

scholarly journals Socio-hydrology: conceptualising human-flood interactions

2013 ◽  
Vol 10 (4) ◽  
pp. 4515-4536 ◽  
Author(s):  
G. Di Baldassarre ◽  
A. Viglione ◽  
G. Carr ◽  
L. Kuil ◽  
J. L. Salinas ◽  
...  
Keyword(s):  
Flood Control ◽  
Technological Development ◽  
River System ◽  
High Water ◽  
Social Processes ◽  
Individual Characteristics ◽  
Water Levels ◽  
Control Structures ◽  
Flooding Events

Abstract. Over history, humankind has tended to settle near streams because of the role of rivers as transportation corridors and the fertility of riparian areas. However, human settlements in floodplains have been threatened by the risk of flooding. Possible responses have been to resettle away and/or modify the river system by building flood control structures. This has led to a complex web of interactions and feedback mechanisms between hydrological and social processes in settled floodplains. This paper is an attempt to conceptualise these interplays for hypothetical human-flood systems. We develop a simple, dynamic model to represent the interactions and feedback loops between hydrological and social processes. The model is then used to explore the dynamics of the human-flood system and the effect of changing individual characteristics, including external forcing such as technological development. The results show that the conceptual model is able to reproduce reciprocal effects between floods and people as well as the emergence of typical patterns. For instance, when levees are built or raised to protect floodplain areas, their presence not only reduces the frequency of flooding, but also exacerbates high water levels. Then, because of this exacerbation, higher flood protection levels are required by the society. As a result, more and more flooding events are avoided, but rare and catastrophic events take place.

scholarly journals Mechanism of Formation and Estuarine Turbidity Maxima in the Hau River Mouth

Water ◽  
2020 ◽  
Vol 12 (9) ◽  
pp. 2547
Author(s):  
Nguyen Ngoc Tien ◽  
Dinh Van Uu ◽  
Do Huy Cuong ◽  
Le Dinh Mau ◽  
Nguyen Xuan Tung ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Dry Season ◽  
River Delta ◽  
Mekong River ◽  
Suspended Sediment Transport ◽  
Mechanism Of Formation ◽  
Mekong River Delta ◽  
Flood Season ◽  
Estuarine Turbidity Maxima

Observation of the Hau River distributary of the Mekong River delta in Vietnam, conducted in dry and flood season (2009, 2014, and 2015), is utilized to investigate the mechanism of formation, distribution of estuarine turbidity maxima (ETM), and links with sediment transport in the system. Additionally, 3D (three-dimensional) numerical models are applied to simulate the seasonal tidal variation (flood and dry seasons) of the water and suspended sediment transport processes of the Mekong River Delta. The 3D model, with a combination of hydrodynamic-wave and suspended sediment transport, was set up and validated with measured data in the study area. The mechanism that measures ETM is the process of suspended sediment from the river when it interacts with seawater and speeds up the flocculation, combined with the asymmetry of the tidal current, which will create the region with ETM by moving in/out with the tidal current’s ups and downs. As there is surface flow velocity towards the sea, the bottom baroclinic flow has a decisive role in deposition and erosion, and it causes the suspended sediment concentration (SSC) to be maximized. During the flood season, the salt wedge near the river’s mouth, at the peak of the tide, pushes towards the sea’s direction when there are ebbing tides, with a scope of about 20 km. In the dry season, there is estuary disturbance as well; the salt wedge forms, but is relatively weak or does not exist, depending on the time of the tide. The maximum turbidity zone in the flood season moves the subaqueous delta with a scope of about 20 km and SSC of about 0.1 to 0.6 g L−1, whereas in the dry season, the seawater has high salinity, and seaward SSC penetrates the estuaries to cause a disturbance and flocculation. The penetration scope is up to 50 km and creates a water mass that has high SSC, from 0.2 to 0.7 g L−1, to run in/off by the tidal current’s ups and downs for several kilometers in the tidal phase.

scholarly journals Socio-hydrology: conceptualising human-flood interactions

2013 ◽  
Vol 17 (8) ◽  
pp. 3295-3303 ◽  
Author(s):  
G. Di Baldassarre ◽  
A. Viglione ◽  
G. Carr ◽  
L. Kuil ◽  
J. L. Salinas ◽  
...  
Keyword(s):  
Flood Control ◽  
Technological Development ◽  
River System ◽  
High Water ◽  
Social Processes ◽  
Individual Characteristics ◽  
Water Levels ◽  
Control Structures ◽  
Flooding Events

Abstract. Over history, humankind has tended to settle near streams because of the role of rivers as transportation corridors and the fertility of riparian areas. However, human settlements in floodplains have been threatened by the risk of flooding. Possible responses have been to resettle away and/or modify the river system by building flood control structures. This has led to a complex web of interactions and feedback mechanisms between hydrological and social processes in settled floodplains. This paper is an attempt to conceptualise these interplays for hypothetical human-flood systems. We develop a simple, dynamic model to represent the interactions and feedback loops between hydrological and social processes. The model is then used to explore the dynamics of the human-flood system and the effect of changing individual characteristics, including external forcing such as technological development. The results show that the conceptual model is able to reproduce reciprocal effects between floods and people as well as the emergence of typical patterns. For instance, when levees are built or raised to protect floodplain areas, their presence not only reduces the frequency of flooding, but also exacerbates high water levels. Then, because of this exacerbation, higher flood protection levels are required by society. As a result, more and more flooding events are avoided, but rare and catastrophic events take place.

scholarly journals Trophic ecology of the ichthyofauna of a stretch of the Urucu River (Coari, Amazonas, Brazil)

2013 ◽  
Vol 25 (1) ◽  
pp. 54-67 ◽  
Author(s):  
Igor David da Costa ◽  
Carlos Edwar de Carvalho Freitas
Keyword(s):  
Trophic Structure ◽  
Trophic Ecology ◽  
Fish Assemblages ◽  
Hydrological Cycle ◽  
Taxonomic Diversity ◽  
Dry Season ◽  
Water Levels ◽  
Seasonal Fluctuations ◽  
Flood Season ◽  
Wide Range

INTRODUCTION: The floodplains of the large Amazonian rivers are very productive as a result of seasonal fluctuations of water levels. This favors the fishes as they are provided with a wide range of habitats and food resources; AIM: In this study, we identified the trophic structure of fish assemblages in the upper river Urucu area (State of Amazonas - Brazil), observing seasonal changes determined by the hydrological cycle; Methods: Samples were collected with the aid of gillnets, during the flood season (April/2008) and the dry season (August/2008) in areas upstream and downstream of ports of the Urucu river within the municipality of Coari, Amazonas, Brazil; RESULTS: 902 individuals of seven orders, 23 families and 82 species were collected. Fishes were more abundant in the dry season than in the flood season, and the piscivores and carnivores (Serrasalumus rhombeus and Osteoglossum bicirrhosum) were the most significant trophic categories in the dry season whereas piscivores and insectivores (Serrasalumus rhombeus, Bryconops alburnoides and Dianema urostriatum) were more abundant in the flood season. The trophic diversity, dominance and evenness were very similar in all sampling periods and show lower values than taxonomic index patterns, except for the trophic dominance in the dry season. Taxonomic diversity and dominance were higher in the flood season if compared to the dry season, but figures were quite uniform and there were no great discrepancies between seasons. CONCLUSION: We found through our studies that the dry and flood seasons work as regulatory factors of abundance of fishes of certain trophic categories in the Urucu river, what can be possibly explained by the availability of resources and the food spectrum of each category.

scholarly journals Water discharge and sediment flux changes in the Lower Mekong River

2005 ◽  
Vol 2 (6) ◽  
pp. 2287-2325 ◽  
Author(s):  
X. X. Lu ◽  
R. Y. Siew
Keyword(s):  
Water Discharge ◽  
Sediment Concentration ◽  
Dry Season ◽  
Water Levels ◽  
Sediment Flux ◽  
Mekong River ◽  
Water Level Fluctuations ◽  
Main Stream ◽  
Discharge Water ◽  
Ecological Changes

Abstract. The Lower Mekong River has witnessed extremely low water levels over the past few years. There is speculation that the changes are a consequence of the construction and operation of the Chinese cascade dams in the upper part of the Mekong main stream, the Lancang River. Dam construction on upper streams can produce a series of induced effects downstream, particularly in terms of water, sediment, channel and ecological changes. The infilling of the Manwan reservoir in 1992 caused water levels to fall to record lows in various parts of the Mekong River, and sediment concentration values decreased similarly. Analyses of discharge and sediment flux at various gauging stations on the Lower Mekong River have indicated a disruption in water discharge, water fluctuations and sediment transport downstream of the Manwan Dam, after its reservoir was infilled in 1992. Dry season flows showed a declining trend, and water level fluctuations in the dry season increased considerably in the post-dam (1993–2000) period. Monthly suspended sediment concentration (SSC) has also decreased significantly in several gauging stations in the post-dam period. The estimation of sediment flux is challenging since the measurements of SSC were sporadic. Our estimation based on the available data indicated that the areas along the upper-middle and lowermost reaches of the Mekong River have experienced a decline in sediment flux, possibly due to sedimentation in the Manwan Dam. However, the decrease is only statistically significant at Chiang Saen. Areas located in the mid-length of the river show less sensitivity to the operation of the Manwan Dam, as sediment fluxes have remained stable or even increased in the post-dam period.

scholarly journals Water discharge and sediment flux changes over the past decades in the Lower Mekong River: possible impacts of the Chinese dams

2006 ◽  
Vol 10 (2) ◽  
pp. 181-195 ◽  
Author(s):  
X. X. Lu ◽  
R. Y. Siew
Keyword(s):  
Water Discharge ◽  
Sediment Concentration ◽  
Dry Season ◽  
Water Levels ◽  
Sediment Flux ◽  
Mekong River ◽  
Water Level Fluctuations ◽  
Main Stream ◽  
The Past ◽  
Ecological Changes

Abstract. The Lower Mekong River has witnessed extremely low water levels over the past few years. There is speculation that the changes are a consequence of the construction and operation of the Chinese cascade dams in the upper part of the Mekong main stream, the Lancang River. Dam construction on upper streams can produce a series of induced effects downstream, particularly in terms of water, sediment, channel and ecological changes. Analyses of discharge and sediment flux at various gauging stations on the Lower Mekong River have indicated a disruption in water discharge, water fluctuations and sediment transport downstream of the first Chinese dam among the 8 cascades (i.e. the Manwan Dam), after its reservoir was infilled in 1992. Dry season flows showed a declining trend, and water level fluctuations in the dry season increased considerably in the post-dam (1993–2000) period. Monthly suspended sediment concentration (SSC) has also decreased significantly in several gauging stations in the post-dam period. The estimation of sediment flux is challenging since the measurements of SSC were sporadic. Our estimation based on the available data indicated that the areas along the upper-middle and lowermost reaches of the Mekong River have experienced a decline in sediment flux, possibly due to sedimentation in the Manwan Dam. However, the decrease is only statistically significant at the nearest gauging station below the Dam (i.e. Chiang Saen). Areas located in the mid-length of the river show less sensitivity to the operation of the Manwan Dam, as sediment fluxes have remained stable or even increased in the post-dam period.

scholarly journals River Discharge and Water Level Changes in the Mekong River: Droughts in an Era of Mega-Dams

2021 ◽  
Author(s):  
XiXi Lu ◽  
Samuel Chua
Keyword(s):  
Water Level ◽  
Water Discharge ◽  
Dry Season ◽  
Water Levels ◽  
Mekong River ◽  
Wet Season ◽  
Discharge Data ◽  
Mekong Basin ◽  
Lower Mekong Basin ◽  
Dry Conditions

While 1992 marked the first major dam – Manwan – on the main stem of the Mekong River, the post-2010 era has seen the construction and operationalisation of mega dams such as Xiaowan (started operations in 2010) and Nuozhadu (started operations in 2014) that were much larger than any dams built before. The scale of these projects implies that their operations will likely have significant ecological and hydrological impacts from the Upper Mekong Basin to the Vietnamese Delta and beyond. Historical water level and water discharge data from 1960 to 2020 were analysed to examine the changes to streamflow conditions across three time periods: 1960-1991 (pre-dam), 1992-2009 (growth) and 2010-2020 (mega-dam). At Chiang Saen, the nearest station to the China border, monthly water discharge in the mega-dam period has increased by up to 98% during the dry season and decreased up as much as -35% during the wet season when compared to pre-dam records. Similarly, monthly water levels also rose by up to +1.16m during the dry season and dropped by up to -1.55m during the wet season. This pattern of hydrological alterations is observed further downstream to at least Stung Treng (Cambodia) in our study, showing that Mekong streamflow characteristics have shifted substantially in the post-2010 era. In light of such changes, the 2019-2020 drought – the most severe one in the recent history in the Lower Mekong Basin – was a consequent of constructed dams reducing the amount of water during the wet season. This reduction of water was exacerbated by the decreased monsoon precipitation in 2019. Concurrently, the untimely operationalisation of the newly opened Xayaburi dam in Laos coincided with the peak of the 2019-2020 drought and could have aggravated the dry conditions downstream. Thus, the mega-dam era (post-2010) may signal the start of a new normal of wet-season droughts.

CURRENT STATE OF SALT INTRUSION IN THE MEKONG DELTA IN VIETNAM

2020 ◽  
pp. 74-80
Author(s):  
Nguyen Thi Thuy Nhung Nguyen Thi Thuy Nhung ◽  
Keyword(s):  
Power Plants ◽  
Salt Water ◽  
High Tide ◽  
Mekong Delta ◽  
Dry Season ◽  
Mekong River ◽  
Circulation System ◽  
Deep Penetration ◽  
Hydroelectric Power ◽  
Salt Intrusion

The study aims to determine the evolution of salt intrusion in the Mekong Delta in Vietnam. Salt water appeared in the mouths of rivers many years ago, but its values in 2019-2020 are considered the highest in the history of observations and surpass the data of 2016 (the year with the highest salinity). In 2020, the phenomenon of salt invasion will strongly manifest itself in the Mekong Delta in Vietnam (in the lower reaches of the Mekong River), the penetration of salt water deep into the mainland and the marginal salinity of 4 (g/l) deeper than 5-25 km, depending on the range. The main reason for this is the change in the flow of water from the headwaters. During the dry season, the flow in the estuary is completely dependent on the flow of water from the upper Mekong River, and the construction of hydroelectric power plants affects the water content of the river below the dams. The second reason is the inefficient operation of the fresh water circulation system between rivers during the dry season in Vietnam. Some other causes are related to climate change, such as rising sea levels at high tide, which allows salt water to flow inland from the mouth, as well as a rather wide shape of the mouth and deep penetration into the land, which contributes to faster penetration. All this negatively affects the environment and sustainable economic development of the Mekong Delta in Viet Nam.

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