Articles | Volume 9, issue 4
Research article 12 Aug 2021
Research article | 12 Aug 2021
Dynamics of salt intrusion in the Mekong Delta: results of field observations and integrated coastal–inland modelling
Sepehr Eslami et al.
No articles found.
Maarten G. Kleinhans, Lonneke Roelofs, Steven A. H. Weisscher, Ivar R. Lokhorst, and Lisanne Braat
Earth Surf. Dynam. Discuss.,
Preprint under review for ESurfShort summary
Floodplain formation in estuaries limit the ebb and flood flow, reducing channel migration, and shortening the tidally-influenced reach. Vegetation establishment on bars reduces local flow velocity and concentrates flow into channels, while mud flats fill accommodation space and reduce channel migration. These results are based on experimental estuaries in the Metronome facility supported by numerical flow modelling.
Christopher R. Hackney, Grigorios Vasilopoulos, Sokchhay Heng, Vasudha Darbari, Samuel Walker, and Daniel R. Parsons
Earth Surf. Dynam., 9, 1323–1334,Short summary
Unsustainable sand mining poses a threat to the stability of river channels. We use satellite imagery to estimate volumes of material removed from the Mekong River, Cambodia, over the period 2016–2020. We demonstrate that current rates of extraction now exceed previous estimates for the entire Mekong Basin and significantly exceed the volume of sand naturally transported by the river. Our work highlights the importance of satellite imagery in monitoring sand mining activity over large areas.
Chloe Leach, Tom Coulthard, Andrew Barkwith, Daniel R. Parsons, and Susan Manson
Geosci. Model Dev., 14, 5507–5523,Short summary
Numerical models can be used to understand how coastal systems evolve over time, including likely responses to climate change. However, many existing models are aimed at simulating 10- to 100-year time periods do not represent a vertical dimension and are thus unable to include the effect of sea-level rise. The Coastline Evolution Model 2D (CEM2D) presented in this paper is an advance in this field, with the inclusion of the vertical coastal profile against which the water level can be altered.
Paula Camus, Ivan D. Haigh, Ahmed A. Nasr, Thomas Wahl, Stephen E. Darby, and Robert J. Nicholls
Nat. Hazards Earth Syst. Sci., 21, 2021–2040,Short summary
In coastal regions, floods can arise through concurrent drivers, such as precipitation, river discharge, storm surge, and waves, which exacerbate the impact. In this study, we identify hotspots of compound flooding along the southern coast of the North Atlantic Ocean and the northern coast of the Mediterranean Sea. This regional assessment can be considered a screening tool for coastal management that provides information about which areas are more predisposed to experience compound flooding.
Arya P. Iwantoro, Maarten van der Vegt, and Maarten G. Kleinhans
Earth Surf. Dynam., 8, 413–429,Short summary
We investigated the effect of tides on the morphodynamic evolution of bifurcations in tide-influenced deltas. Using results from a numerical morphodynamic model (Delft3D), we found that tides cause less asymmetric bifurcations and thereby keep both downstream channels open. Our results explain why avulsion rarely occurs in tide-influenced deltas, whereas it occurs more often in river-dominated deltas.
Vo Quoc Thanh, Dano Roelvink, Mick van der Wegen, Johan Reyns, Herman Kernkamp, Giap Van Vinh, and Vo Thi Phuong Linh
Hydrol. Earth Syst. Sci., 24, 189–212,Short summary
The Vietnamese Mekong Delta (VMD) is a rice bowl of not only Vietnam, but also the world; agriculture is the main source of livelihood in the delta. The VMD is facing threats related to water management and hydraulic structures. Dykes are built to protect agricultural crops in the floodplains and may influence water regimes downstream in the VMD. If the VMD floodplains are completely protected by dykes, yearly mean water levels could increase by 3 cm (at Can Tho) and 1.5 cm (at My Thuan).
Alistair Hendry, Ivan D. Haigh, Robert J. Nicholls, Hugo Winter, Robert Neal, Thomas Wahl, Amélie Joly-Laugel, and Stephen E. Darby
Hydrol. Earth Syst. Sci., 23, 3117–3139,Short summary
Flooding can arise from multiple sources, including waves, extreme sea levels, rivers, and severe rainfall. When two or more sources combine, the consequences can be greatly multiplied. We find the potential for the joint occurrence of extreme sea levels and river discharge to be greater on the western coast of the UK compared to the eastern coast. This is due to the weather conditions generating each flood source around the UK. These results will help increase our flood forecasting ability.
Ivar R. Lokhorst, Lisanne Braat, Jasper R. F. W. Leuven, Anne W. Baar, Mijke van Oorschot, Sanja Selaković, and Maarten G. Kleinhans
Earth Surf. Dynam., 6, 883–901,Short summary
In estuaries, mud sedimentation enhances salt marsh accretion. Here we explore system-scale effects of plants and mud on planform shape and size of estuaries. We coupled Delft3D for hydromorphodynamics with our vegetation model and ran controls for comparison. Effects are greatest at the fluvial–tidal transition, where for the first time in a model, a bedload convergence zone formed. Regardless of local vegetation effects, mud and vegetation cause gradual filling of estuaries over time.
Dung Duc Tran, Gerardo van Halsema, Petra J. G. J. Hellegers, Long Phi Hoang, Tho Quang Tran, Matti Kummu, and Fulco Ludwig
Hydrol. Earth Syst. Sci., 22, 1875–1896,Short summary
We modeled hydrological changes under impacts of large-scale dike constructions for intensive rice production in the floodplain of the Vietnamese Mekong Delta. Four scenarios show a significant increase in peak water levels in the upstream rivers, but very few water level changes are found downstream. Water balance calculations show where the floodwater goes under four dike construction scenarios. Its impacts on the tidal areas need to be clarified in the future with a 3-D hydraulic model.
Wietse I. van de Lageweg, Stuart J. McLelland, and Daniel R. Parsons
Earth Surf. Dynam., 6, 203–215,Short summary
Sticky sediments are an important component of many rivers and coasts. Stickiness depends on many factors including the presence of micro-organisms, also known as biofilms. We performed a laboratory study to better understand the role of biofilms in controlling sediment transport and dynamics. We find that sand with biofilms requires significantly higher flow velocities to be mobilised compared to uncolonised sand. This will help improve predictions of sediment in response to currents and waves.
Maarten G. Kleinhans, Maarten van der Vegt, Jasper Leuven, Lisanne Braat, Henk Markies, Arjan Simmelink, Chris Roosendaal, Arjan van Eijk, Paul Vrijbergen, and Marcel van Maarseveen
Earth Surf. Dynam., 5, 731–756,Short summary
Creating estuaries in the laboratory has been challenging. When the ebb and flood currents are driven by ebb and flood in the sea, they are too weak to move sand. Here we describe how the periodic tilting of an entire experimental set-up leads to ebb and flood currents with similar behaviour as in nature and with enough strength to move sand. This means that this novel set-up now allows for the creation of estuarine landscapes in experiments.
Lisanne Braat, Thijs van Kessel, Jasper R. F. W. Leuven, and Maarten G. Kleinhans
Earth Surf. Dynam., 5, 617–652,Short summary
Mud raises concern in the short-term management of estuaries, but it is not known whether cohesive mud affects the long-term development of estuaries. We discovered that a small supply of mud from the river confines the estuary by forming stable mudflats on the sides in centuries, whereas estuaries with only sand continue to grow. Mudflats also reduce the shifting of channels and bars. This implies that changes in mud supply in estuaries may have led to changes in shape and dynamics in the past.
Jannis M. Hoch, Arjen V. Haag, Arthur van Dam, Hessel C. Winsemius, Ludovicus P. H. van Beek, and Marc F. P. Bierkens
Hydrol. Earth Syst. Sci., 21, 117–132,Short summary
Modelling inundations is pivotal to assess current and future flood hazard, and to define sound measures and policies. Yet, many models focus on the hydrologic or hydrodynamic aspect of floods only. We combined both by spatially coupling a hydrologic with a hydrodynamic model. This way we are able to balance the weaknesses of each model with the strengths of the other. We found that model coupling can indeed strongly improve discharge simulation, and see big potential in our approach.
Heiko Apel, Oriol Martínez Trepat, Nguyen Nghia Hung, Do Thi Chinh, Bruno Merz, and Nguyen Viet Dung
Nat. Hazards Earth Syst. Sci., 16, 941–961,Short summary
Many urban areas experience both fluvial and pluvial floods, thus this study aims to analyse fluvial and pluvial flood hazards as well as combined pluvial and fluvial flood hazards. This combined fluvial–pluvial flood hazard analysis is performed in a tropical environment for Can Tho city in the Mekong Delta. The final results are probabilistic hazard maps, showing the maximum inundation caused by floods of different magnitudes along with an uncertainty estimation.
W. A. Marra, S. J. McLelland, D. R. Parsons, B. J. Murphy, E. Hauber, and M. G. Kleinhans
Earth Surf. Dynam., 3, 389–408,Short summary
Groundwater seepage creates valleys with typical theater-shaped valley heads, which are found on Earth and on Mars. For a better interpretation of these systems, we conducted scale experiments on the formation such valleys. We find that entire landscapes, instead of just the shape of the valleys, provide insights into the source of groundwater. Landscapes filled with valleys indicate a local groundwater source in contrast to sparsely dissected landscapes formed by a distal source of groundwater.
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Increased salt intrusion jeopardizes freshwater supply to the Mekong Delta, and the current trends are often inaccurately associated with sea level rise. Using observations and models, we show that salinity is highly sensitive to ocean surge, tides, water demand, and upstream discharge. We show that anthropogenic riverbed incision has significantly amplified salt intrusion, exemplifying the importance of preserving sediment budget and riverbed levels to protect deltas against salt intrusion.
Increased salt intrusion jeopardizes freshwater supply to the Mekong Delta, and the current...