scholarly journals Dynamics of salt intrusion in the Mekong Delta: results of field observations and integrated coastal–inland modelling

2021 ◽  
Vol 9 (4) ◽  
pp. 953-976
Author(s):  
Sepehr Eslami ◽  
Piet Hoekstra ◽  
Herman W. J. Kernkamp ◽  
Nam Nguyen Trung ◽  
Dung Do Duc ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Saline Water ◽  
Water System ◽  
Mekong Delta ◽  
Hydrological Regime ◽  
Salt Transport ◽  
Mixed System ◽  
Estuarine System ◽  
Salt Intrusion ◽  
Numerical Domain

Abstract. On the list of challenges facing the world largest deltas, increased saline water intrusion (SWI) in the surface water system and its role in jeopardizing freshwater supply are often ranked very high. Yet, detailed process-based studies of SWI at the whole delta scale are limited, and the trends are regularly associated with global sea level rise. Here, using field measurements and a sophisticated 3D model that integrates the riverine, rural, estuarine, and coastal dynamics within one numerical domain, we study SWI at the scale of the Mekong Delta in extensive detail. While many studies downscale the SWI problem to a topic within an estuary, we show that the physical processes on the continental shelf, such as monsoon-driven ocean surge, directly influence salinity dynamics within the delta. Typical values of 20–40 cm surge over the continental shelf contribute to up to 10 km of further SWI. The delta's estuarine system is also more sensitive than many other systems to variations of river discharge. Furthermore, spring–neap variability plays a key role in SWI in the delta. The estuarine variability from a stratified to a mixed system between neap and spring tides develops 3D processes such as estuarine circulation and tidal straining that become the main upstream salt transport mechanisms. The 3D nature of salinity dynamics, and the role of upstream and downstream processes, suggests that compromising on dimension or extent of the numerical domain can limit the accuracy of predictions of SWI in the delta. The study also showcases the fact that riverbed incision in response to anthropogenic sediment starvation in the last 2 decades has increased stratification and activated or magnified 3D salt transport subprocesses that amplify upstream salt transport. With all the external forces on the delta, namely climate change and an altered hydrological regime by the upstream dams, due to deeper estuarine channels (driven by sand mining and upstream impoundments) compared to its near past, the delta itself has become far more vulnerable to even mild natural events. This exemplifies the fundamental importance of preserving the sediment budget and riverbed levels in protecting the world's deltas against SWI.

scholarly journals Dynamics of salt intrusion in the Mekong Delta; results of field observations and integrated coastal-inland modelling

2021 ◽  
Author(s):  
Sepehr Eslami ◽  
Piet Hoekstra ◽  
Herman W. J. Kernkamp ◽  
Nam Nguyen Trung ◽  
Dung Do Duc ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Mekong Delta ◽  
Hydrological Regime ◽  
Field Measurements ◽  
Salt Transport ◽  
Mixed System ◽  
Estuarine System ◽  
Salt Intrusion ◽  
External Forces ◽  
Numerical Domain

Abstract. In the list of challenges facing the world largest deltas, increased salt intrusion and its role in jeopardizing freshwater supply is often ranked very high. Yet, detailed process-based studies of salt intrusion at the whole delta scale are limited and the trends are regularly associated to global sea level rise. Here, using field measurements and a sophisticated 3D model that integrates the riverine, rural, estuarine, and coastal dynamics within one numerical domain, we study salt intrusion at the scale of the Mekong Delta in extensive detail. While many studies down-scale the salt intrusion problem to a topic within an estuary, we show that the continental shelf is an intrinsic component of the delta, and its physical processes, such as monsoon-driven ocean surge, directly influence salinity dynamics within the delta. Typical values of 20–40 cm surge over the continental shelf contribute to up to 10 km of further salt intrusion. The delta's estuarine system is also more sensitive than many other systems to upstream discharge variations. Furthermore, spring-neap variability plays a key role in salt intrusion in the delta. The estuarine variability from a stratified to a mixed system between neap and spring tides develops 3D processes such as estuarine circulation and tidal straining that become the main upstream salt transport mechanisms. The 3D nature of salinity dynamics, and the role of upstream and downstream processes, suggests that compromising on dimension or extent of the numerical domain, can limit the accuracy of predictions of salt intrusion in the delta. The study also showcases that riverbed incision in response to anthropogenic sediment starvation in the last two decades, has increased stratification, and activated or magnified 3D salt transport sub-processes that amplify upstream salt transport. With all the external forces on the delta namely climate change and altered hydrological regime by the upstream dams, due to deeper estuarine channels (driven by sand mining and upstream impoundments), the delta itself is far more vulnerable to even mild natural events. This exemplifies the fundamental importance of preserving the sediment budget and riverbed levels in protecting the world's deltas against salt intrusion.

scholarly journals Response of Salt Transport and Residence Time to Geomorphologic Changes in an Estuarine System

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 1091 ◽  
Author(s):  
Wen-Cheng Liu ◽  
Min-Hsin Ke ◽  
Hong-Ming Liu
Keyword(s):  
Residence Time ◽  
Time Lag ◽  
High Tide ◽  
Freshwater Discharge ◽  
Salt Transport ◽  
Present Condition ◽  
Low Flow ◽  
Estuarine System ◽  
Salt Intrusion ◽  
Current Limit

Anthropogenic changes in tidal estuaries have significantly altered bathymetry and topography over the past half century. The geomorphic-driven changes in estuarine hydrodynamics and salt transport remain unclear. To explore this issue, a SELFE (Semi-implicit Eulaerian-Lagrangian Finite Element) -based model was developed and utilized in a case study in the Danshui River, Taiwan. The model was calibrated and validated using observed water level, current, and salinity data from 2015, 2016, and 2017. The performance of the SELFE model corresponded well to the measured data. Furthermore, the validated model was utilized to analyze the hydrodynamics, residual current, limit of salt intrusion, and residence time under the predevelopment (1981) and present (2015) conditions. The predicted results revealed that the time lag of water surface elevation at both high tide and low tide under the present condition was approximately 0.5–2 h shorter under the predevelopment condition. The residual circulation under the predevelopment condition was stronger than under the present condition for low flow, causing the limit of salt intrusion to extend further upstream under the predevelopment condition compared to the limit of salt intrusion under the present condition. The calculated residence time under the predevelopment condition was longer than the residence time under the present condition. The freshwater discharge input is a dominating factor affecting the salt intrusion and residence time in a tidal estuary. A regression correlation between the maximum distance of salt intrusion and freshwater discharge and a correlation between residence time and freshwater discharge were established to predict the limit of salt intrusion and residence time under the predevelopment and present conditions with different scenarios of freshwater discharge input.

scholarly journals Flow Division Dynamics in the Mekong Delta: Application of a 1D-2D Coupled Model

Water ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 837 ◽  
Author(s):  
Sepehr Eslami ◽  
Piet Hoekstra ◽  
Herman Kernkamp ◽  
Nam Nguyen Trung ◽  
Duc ◽  
...  
Keyword(s):  
Water Level ◽  
Irrigation System ◽  
Mekong Delta ◽  
Dry Season ◽  
Offshore Wind ◽  
Water Volume ◽  
Estuarine System ◽  
Tidal Amplitude ◽  
Tidal Dynamics ◽  
Salt Intrusion

The Mekong Delta constitutes a complicated multi-channel estuarine system, exchanging water with a delta-wide irrigation system. A 1D–2DH coupled numerical domain is calibrated and validated for water level and discharge during the dry season. This approach benefits from the simplicity of a 1D network within the estuarine and irrigation systems, while maintaining the interaction with the spatial tidal dynamics of the 2DH coastal domain. First, the role of the irrigation system on tidal dynamics is quantified; then, tidal propagation, freshwater budget, and the effect of offshore subtidal water level on discharge division are investigated. The results show that the complex irrigation system, in a friction-like manner, reduces the tidal amplitude up to 25%. The channels aggregate to 1% of the total water volume in the delta, while accommodating up to 10% of the tidal prism. Tidal amplitude reduces upstream, while subtidal water level is highly sensitive to upstream discharge, spring–neap cycles, and wind-generated offshore surge. Although cumulative discharge division within the estuarine network is consistent, temporal discharge division can be significantly sensitive to offshore wind-surge. During the dry season, it can reverse the expected subtidal discharge division within the time-scale of a few days and potentially influence salt intrusion.

Dinocysts as a Tool for Palaeoenvironmental Reconstruction in Vitória Bay, Brazil

Radiocarbon ◽  
2020 ◽  
Vol 62 (2) ◽  
pp. 289-311
Author(s):  
Alex da Silva de Freitas ◽  
Javier Helenes Escamilla ◽  
Cintia Ferreira Barreto ◽  
Alex Cardoso Bastos ◽  
Estefan Monteiro da Fonseca ◽  
...  
Keyword(s):  
Sea Level ◽  
Saline Water ◽  
Sediment Cores ◽  
Isotopic Analysis ◽  
Southeastern Brazil ◽  
Geochemical Data ◽  
Estuarine System ◽  
Marine Transgression ◽  
The Holocene ◽  
Energy Environment

ABSTRACTMicropaleontological and geochemical data were applied to sediments from southeastern Brazil to study the hydrodynamics associated with the Holocene sea level rise. Sediment cores were taken around Vitória Bay, examined for dinoflagellate cysts and subjected to isotopic analysis. The cyst assemblage mainly dominated by autotrophic species most notably O. centrocarpum, L. machaerophorum and T. vancampoae. The influence of the marine transgression and subsequent regression observed during the Holocene along the coast of Brazil could have initially favored the establishment of an oligotrophic and higher energy environment. The inflow of continental water from tributaries combined with a higher inflow of saline water into the estuarine system could have favored the establishment and subsequent deposition of the dinocysts.

scholarly journals Interplay between land-use dynamics and changes in hydrological regime in the Vietnamese Mekong Delta

2018 ◽  
Vol 73 ◽  
pp. 269-280 ◽  
Author(s):  
Thuy Ngan Le ◽  
Arnold K. Bregt ◽  
Gerardo E. van Halsema ◽  
Petra J.G.J. Hellegers ◽  
Lam-Dao Nguyen
Keyword(s):  
Land Use ◽  
Mekong Delta ◽  
Hydrological Regime ◽  
Land Use Dynamics

scholarly journals Impacts of Sea Level Rise and Groundwater Extraction Scenarios on Fresh Groundwater Resources in the Nile Delta Governorates, Egypt

Water ◽  
2018 ◽  
Vol 10 (11) ◽  
pp. 1690 ◽  
Author(s):  
Marmar Mabrouk ◽  
Andreja Jonoski ◽  
Gualbert H. P. Oude Essink ◽  
Stefan Uhlenbrook
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Driving Forces ◽  
Nile Delta ◽  
Saline Water ◽  
Groundwater Resources ◽  
Salt Transport ◽  
Groundwater Extraction ◽  
Fresh Groundwater ◽  
The Impact

As Egypt’s population increases, the demand for fresh groundwater extraction will intensify. Consequently, the groundwater quality will deteriorate, including an increase in salinization. On the other hand, salinization caused by saltwater intrusion in the coastal Nile Delta Aquifer (NDA) is also threatening the groundwater resources. The aim of this article is to assess the situation in 2010 (since this is when most data is sufficiently available) regarding the available fresh groundwater resources and to evaluate future salinization in the NDA using a 3D variable-density groundwater flow model coupled with salt transport that was developed with SEAWAT. This is achieved by examining six future scenarios that combine two driving forces: increased extraction and sea level rise (SLR). Given the prognosis of the intergovernmental panel on climate change (IPCC), the scenarios are used to assess the impact of groundwater extraction versus SLR on the seawater intrusion in the Delta and evaluate their contributions to increased groundwater salinization. The results show that groundwater extraction has a greater impact on salinization of the NDA than SLR, while the two factors combined cause the largest reduction of available fresh groundwater resources. The significant findings of this research are the determination of the groundwater volumes of fresh water, brackish, light brackish and saline water in the NDA as a whole and in each governorate and the identification of the governorates that are most vulnerable to salinization. It is highly recommended that the results of this analysis are considered in future mitigation and/or adaptation plans.

Synergistic effects of inorganic salt and surfactant on phenanthrene removal from aqueous solution by sediment

2014 ◽  
Vol 70 (8) ◽  
pp. 1329-1334
Author(s):  
Xiaoyan Zhang ◽  
Yaoguo Wu ◽  
Sihai Hu ◽  
Cong Lu
Keyword(s):  
Aqueous Solution ◽  
Inorganic Salt ◽  
Saline Water ◽  
Synergistic Effects ◽  
Water System ◽  
Water Quality Monitoring ◽  
Sodium Dodecylbenzene Sulfonate ◽  
Batch Method ◽  
Dodecylbenzene Sulfonate ◽  
Elevated Salinity

The economic and effective application of surfactant enhanced remediation (SER) technology in a sediment-freshwater/saline water system was investigated by batch method using the combined effects of inorganic salt (sodium chloride, NaCl) and anionic surfactant (sodium dodecylbenzene sulfonate (SDBS)) on phenanthrene (PHE) removal via sorption by sediment. In all cases, PHE sorption followed a linear equation and partition as the main mechanism for PHE removal from aqueous solution. Separate addition of SDBS (2 mmol L−1) and NaCl (2–100 mmol L−1) moderately enhanced PHE removal, while with their combined addition the enhancement was substantial, and the removal efficiency achieved a peak of 92.8%. The combined effect expressed a synergy, and the sorption enhancement increased by factors of 2.7, 3.2 and 3.4 when compared with the sum of the separate entities at elevated salinity. This was because the sorbed SDBS, with increasing amount and a high packing conformation at elevated salinity, outcompeted aqueous SDBS for PHE partition. Moreover, a combination of 2 mmol L−1 SDBS and 2 mmol L−1 NaCl was optimal for PHE removal. Therefore, SER technology appears more effective for PHE removal in saline water than in freshwater, and preliminary water quality monitoring is essential for economic and efficient SER application.

scholarly journals Salt intrusion in multi-channel estuaries: a case study in the Mekong Delta, Vietnam

2006 ◽  
Vol 10 (5) ◽  
pp. 743-754 ◽  
Author(s):  
A. D. Nguyen ◽  
H. H. Savenije
Keyword(s):  
River Discharge ◽  
Single Channel ◽  
Mekong Delta ◽  
Salt Intrusion ◽  
Predictive Equations ◽  
Alluvial Estuaries ◽  
Tidal Characteristics ◽  
Mixing Behaviour ◽  
Sloping Bottom

Abstract. There is a well-tested theory for the computation of salt intrusion in alluvial estuaries that is fully analytical and predictive. The theory uses analytical equations to predict the mixing behaviour of the estuary based on measurable quantities, such as channel topography, river discharge and tidal characteristics. It applies to single-channel topographies and estuaries that demonstrate moderate tidal damping. The Mekong delta is a multi-channel estuary where the tide is damped due to a relatively strong river discharge (in the order of 2000 m3/s), even during the dry season. As a result the Mekong is a strongly riverine estuary. This paper aims to test if the theory can be applied to such a riverine multi-channel estuary, and to see if possible adjustments or generalisations need to be made. The paper presents salt intrusion measurements that were done by moving boat in 2005, to which the salt intrusion model was calibrated. The theory has been expanded to cater for tidal damping. Subsequently the model has been validated with observations made at fixed locations over the years 1998 and 1999. Finally it has been tested whether the Mekong calibration fits the overall predictive equations derived in other estuaries. The test has been successful and led to a slight adjustment of the predictive equation to cater for estuaries that experience a sloping bottom.

Environmental forcing in a tropical estuarine ecosystem: the Palizada River in the southern Gulf of Mexico

2001 ◽  
Vol 52 (5) ◽  
pp. 735 ◽  
Author(s):  
César Fuentes-Yaco ◽  
David Alberto Salas de León ◽  
María Adela Monreal-Gómez ◽  
Francisco Vera-Herrera
Keyword(s):  
Sea Level ◽  
Saline Water ◽  
Estuarine System ◽  
Estuarine Ecosystem ◽  
Environmental Forcing ◽  
Hydrological Variability ◽  
Tropical Estuarine ◽  
Southern Gulf Of Mexico ◽  
Del Rio ◽  
Annual Signal

Environmental characteristics of the fluvial–deltaic–lagoon–estuarine system of the Palizada River were determined by the assessment of physical, environmental and hydrological variability. Environmental information comprised daily time series of precipitation (1971–85), Usumacinta River discharge (1948–94), sea level (1956–91) and wind patterns (1984–87). Hydrology was studied by weekly measurement of salinity, transparency,temperature, dissolved oxygen and pH at 18 stations during 19 months (September 1985 to March 1987). Water temperature reflected the climatic seasons: dry, rainy and winter frontal storms (‘Nortes’). During the rainy season fresh water dominated the whole area, but during the dry season a salt wedge entered as far as Del Este Lagoon.Northern winds allowed saline water to reach intermediate regions and occasionally the upstream freshwater head of the estuary. There are annual, 6-month and 3.2-month oscillations in the environmental records: the annual signal is modulated by precipitation, fluvial discharge and sea level; the 6-month signal has an implicit periodicity driven by the changes in the wind direction that affect all other parameters; and the 3.2-month period seems to be modulated by the rainy, dry and ‘Nortes’ seasons. Cluster analysis identified eight ecological regions based on the hydrological variables. Resumen. Las características ambientales del sistema fluvio–deltáico–lagunar estuarino del Río Palizada fueron determinadas a través del estudio de su variabilidad física, ambiental e hidrológica. La información ambiental comprende series de tiempo diarias de precipitación pluvial (1971–85), descarga fluvial del Río Usumacinta (1948-94), nivel del mar (1956–91) y dirección y velocidad del viento (1984–87). La hidrología comprende mediciones semanales de salinidad, transparencia, temperatura, oxígeno disuelto y pH en 18 estaciones durante 19 meses (Septiembre de 1985 a Marzo de 1987). La temperatura del agua refleja las estaciones climáticas: secas, lluvias y frentes invernales (‘Nortes’). Durante la época de lluvias el agua dulce predomina en toda el área, sin embargo durante la estación de secas la cuña salina llega hasta la Laguna del Este. Los vientos del norte promueven el avance del agua salina a las regiones intermedias y ocasionalmente hasta la cabecera del estuario. Las oscilaciones ambientales muestran períodos anuales, semestrales y de 3.2 meses: el ciclo anual está modulado por la precipitación pluvial, la descarga fluvial y el nivel del mar; el ciclo semestral tiene una periodicidad implícita gobernada por cambios en la dirección del viento que afecta los demás parámetros y el ciclo de 3.2 meses parece estar modulado por las estaciones climáticas de lluvias, secas y nortes. Los análisis Cluster basados en las variables hidrológicas permiten la identificación de ocho regiones ecológicas.

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