Large-scale quantification of suspended sediment transport and deposition in the Mekong Delta

N. V. Manh, N. V. Dung, N. N. Hung, B. Merz, H. Apel
2014 Hydrology and Earth System Sciences Discussions  
Sediment dynamics play a major role for the agricultural and fishery productivity of the Mekong Delta. However, the understanding of sediment dynamics in the Mekong Delta, one of the most complex river deltas in the world, is very limited. This is a consequence of its large extent, the intricate system of rivers, channels and floodplains and the scarcity of observations. This study quantifies, for the first time, the suspended sediment transport and sediment-nutrient deposition in the whole
more » ... on in the whole Mekong Delta. To this end, a quasi-2-D hydrodynamic model is combined with a cohesive sediment transport model. The combined model is calibrated automatically using six objective functions to represent the different aspects of the hydraulic and sediment transport components. The model is calibrated for the extreme flood season in 2011 and shows good performance for the two validation years with very different flood characteristics. It is shown how sediment transport and sediment deposition vary from Kratie at the entrance of the Delta to the coast. The main factors influencing the spatial sediment dynamics are the setup of rivers, channels and dike-rings, the sluice gate operations, the magnitude of the floods and tidal influences. The superposition of these factors leads to high spatial variability of sediment transport, in particular in the Vietnamese floodplains. Depending on the flood magnitude, the annual sedimentation rate averaged over the Vietnamese floodplains varies from 0.3 to 2.1 kg m<sup>−2</sup> yr<sup>−1</sup>, and the ring dike floodplains trap between 1 and 6% of the total sediment load at Kratie. This is equivalent to 29 × 10<sup>3</sup>–440 × 10<sup>3</sup> t of nutrients (N, P, K, TOC) deposited in the Vietnamese floodplains. This large-scale quantification provides a basis for estimating the benefits of the annual Mekong floods for agriculture and fishery, and is important information for assessing the effects of deltaic subsidence and climate change related sea level rise.
doi:10.5194/hessd-11-4311-2014 fatcat:edi5mmqbcbgb3dntvy4eja2juy