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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/hess-2019-64
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/hess-2019-64
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 19 Feb 2019

Research article | 19 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).

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

Vo Quoc Thanh1,2,3, Dano Roelvink1,2,4, Mick van der Wegen1,4, Johan Reyns1,4, Herman Kernkamp4, Giap Van Vinh5, and Vo Thi Phuong Linh3 Vo Quoc Thanh et al.
  • 1Department of Water Science and Engineering, IHE Delft, the Netherlands
  • 2Faculty of Civil Engineering and Geosciences, Delft University of Technology, the Netherlands
  • 3College of Environment and Natural Resources, Can Tho University, Vietnam
  • 4Deltares, Delft, the Netherlands
  • 5Cuu Long River Hydrological Center, Southern Regional Hydro-Meteorological Center, Vietnam

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.

Vo Quoc Thanh et al.
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Short summary
The Vietnamese Mekong Delta (VMD) is a rice bowl of not only Vietnam, but also the world since 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 in the VMD downstream. If the VMD floodplains are completely protected by dykes, yearly mean water levels can increase by 3 cm (at Can Tho) and 1.5 cm (at My Thuan).
The Vietnamese Mekong Delta (VMD) is a rice bowl of not only Vietnam, but also the world since...
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