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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-141
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
07 Apr 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
Assessing impacts of dike construction on the flood dynamics in the Mekong Delta
Dung Duc Tran1,5, Gerardo van Halsema1, Petra J. G. J. Hellegers1, Long Phi Hoang2, Tho Quang Tran3, Matti Kummu4, and Fulco Ludwig2 1Water Resources Management group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands
2Water Systems and Global Change group, Wageningen University, P.O. Box 47, 6700 AA Wageningen, The Netherlands
3Southern Institute for Water Resources Planning, 271 An Duong Vuong Street, District 5, Ho Chi Minh City, Vietnam
4Water & Development Research Group, Aalto University, P.O. Box 15200, Aalto, Finland
5Centre of Water Management and Climate Change, Vietnam National University Ho Chi Minh City, Ho Chi Minh City, Vietnam
Abstract. There is a large public concern about recent increases in flood risks in the downstream part of the Vietnamese Mekong Delta. Pronounced recent expansion of high-dike constructions in the floodplains of the upper delta are associated with observed increases in river water levels in the downstream province of Can Tho. In this paper the hydraulic impact of upstream dike construction on the flood hazards downstream the Mekong Delta is assessed through modelling of dike density scenarios in the flood hydrographs of 2011 and 2013. To do this, the existing Mekong delta one-dimensional (1D) hydrodynamic model was combined with a quasi-two dimensional (2D) approach to explore the change in water dynamics downstream under extensive high-dike developments in An Giang and Long Xuyen Quadrangle. Most studies are unable to explain where the floodwater goes. To address this, water balances have been established to trace the propagation and redistribution of flood volumes over the delta, which provides an extension of current work in this field. Model results indicate that the extensive construction of high dikes in the upstream floodplains have only limitedly impacts upon the downstream peak river water levels in Can Tho. Instead, model impacts on peak river water levels are concentrated and amplified in the upstream reaches of the delta. The water balance analysis shows the model is able to return fairly stable river water levels at Can Tho by diverting floodwater volumes away for the Long Xuyen Quadrangle in excess of the retention volume lost due the dike construction. This reduced inflow into the Quadrangle, and subsequent diversion of flood volumes to the Plain of Reeds and Cambodian floodplain can, however, not be fully validated due to a lack of monitoring data. The model's spatial re-distribution of flood volumes can be induced by the way the model is calibrated. As dike construction results, according to the model, in a reduction of floodwater volumes reaching the Long Xuyen Quadrangle, high-dike scenarios for the whole of An Giang province or for the entire Long Xuyen Quadrangle indicate only limited increases in upstream and downstream peak river water levels. Future assessments will have to be conducted on the scale of the entire Cambodia-Vietnamese Mekong Delta, with explicit calibration and validation of the Cambodian floodplain as a means to trace the re-distribution of flood volumes and peaks across the delta.

Citation: Duc Tran, D., van Halsema, G., Hellegers, P. J. G. J., Phi Hoang, L., Quang Tran, T., Kummu, M., and Ludwig, F.: Assessing impacts of dike construction on the flood dynamics in the Mekong Delta, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-141, in review, 2017.
Dung Duc Tran et al.
Dung Duc Tran et al.
Dung Duc Tran et al.

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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 of peak water levels in the upstream rivers but very little 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 3D hydraulic model.
We modeled hydrological changes under impacts of large-scale dike constructions for intensive...
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