Application of a multivariate transport model for understanding cohesive sediment dynamics

Abstract. Sediment dynamics play a major role in the agricultural and fishery productivity of the Mekong Delta. However, the understanding of sediment dynamics in the 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 deposition in the whole Mekong Delta. To this end, a quasi-2D hydrodynamic model is combined with a cohesive sediment transport model. The combined model is calibrated 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 2 validation years with very different flood characteristics. It is shown how sediment transport and sediment deposition is differentiated from Kratie at the entrance of the delta on its way to the coast. The main factors influencing the spatial sediment dynamics are the river and channel system, dike rings, 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, annual sediment loads reaching the coast vary from 48 to 60% of the sediment load at Kratie. Deposited sediment varies from 19 to 23% of the annual load at Kratie in Cambodian floodplains, and from 1 to 6% in the compartmented and diked floodplains in Vietnam. Annual deposited nutrients (N, P, K), which are associated with the sediment deposition, provide on average more than 50% of mineral fertilizers typically applied for rice crops in non-flooded ring dike floodplains in Vietnam. Through the quantification of sediment and related nutrient input, the presented study provides a quantitative basis for estimating the benefits of annual Mekong floods for agriculture and fishery, and is an important piece of information with regard to the assessment of the impacts of deltaic subsidence and climate-change-related sea level rise on delta morphology.

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Cohesive sediment transport model with consideration of flocculation, concentrated benthic suspension flow, and bed consolidation

Journal of Japan Society of Civil Engineers Ser B2 (Coastal Engineering) ◽

10.2208/kaigan.68.i_516 ◽

2012 ◽

Vol 68 (2) ◽

pp. I_516-I_520

Author(s):

Toyoaki MISHIMA ◽

Tomoaki KOMAGUCHI ◽

Takao YAMASHITA

Keyword(s):

Sediment Transport ◽

Transport Model ◽

Cohesive Sediment ◽

Suspension Flow ◽

Sediment Transport Model ◽

Cohesive Sediment Transport

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A Methodology for Estimating the Parameters in Three-Dimensional Cohesive Sediment Transport Models by Assimilating In Situ Observations with the Adjoint Method

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-16-0194.1 ◽

2017 ◽

Vol 34 (7) ◽

pp. 1469-1482 ◽

Cited By ~ 3

Author(s):

Daosheng Wang ◽

Jicai Zhang ◽

Ya Ping Wang ◽

Xianqing Lv ◽

Yang Yang ◽

...

Keyword(s):

Sediment Transport ◽

Adjoint Method ◽

Settling Velocity ◽

Transport Model ◽

Three Dimensional ◽

Temporal Variations ◽

Cohesive Sediment ◽

Cohesive Sediment Transport ◽

Resuspension Rate

AbstractThe model parameters in the suspended cohesive sediment transport model are quite important for the accurate simulation of suspended sediment concentrations (SSCs). Based on a three-dimensional cohesive sediment transport model and its adjoint model, the in situ observed SSCs at four stations are assimilated to simulate the SSCs and to estimate the parameters in Hangzhou Bay in China. Numerical experimental results show that the adjoint method can efficiently improve the simulation results, which can benefit the prediction of SSCs. The time series of the modeled SSCs present a clear semidiurnal variation, in which the maximal SSCs occur during the flood tide and near the high water level due to the large current speeds. Sensitivity experiments prove that the estimated results of the settling velocity and resuspension rate, especially the temporal variations, are robust to the model settings. The temporal variations of the estimated settling velocity are negatively correlated with the tidal elevation. The main reason is that the mean size of the suspended sediments can be reduced during the flood tide, which consequently decreases the settling velocity according to Stokes’s law, and it is opposite in the ebb tide. The temporal variations of the estimated resuspension rate and the current speeds have a significantly positive correlation, which accords with the dynamics of the resuspension rate. The temporal variations of the settling velocity and resuspension rate are reasonable from the viewpoint of physics, indicating the adjoint method can be an effective tool for estimating the parameters in the sediment transport models.

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Modelling impacts of spatially variable erosion drivers on suspended sediment dynamics

10.5194/esurf-2019-59 ◽

2019 ◽

Cited By ~ 1

Author(s):

Giulia Battista ◽

Peter Molnar ◽

Paolo Burlando

Keyword(s):

Suspended Sediment ◽

Transport Model ◽

Empirical Studies ◽

Surface Characteristics ◽

Sediment Dynamics ◽

Catchment Scale ◽

Landscape Characteristics ◽

Variable Surface ◽

Deterministic Modelling ◽

Suspended Sediment Concentrations

Abstract. The estimate of suspended sediment load in rivers is often highly problematic because of the strong variability in suspended sediment concentrations with discharge. Previous studies that investigated the sources of this variability highlight the need to explicitly account for the main hydrological processes controlling sediment erosion and transport at the catchment scale, their spatio-temporal variability and interactions with the topography and surface characteristics of the basin. In this paper we propose a novel physically explicit spatially distributed hillslope erosion and sediment transport model including these erosion drivers, based on the computationally efficient hydrological model TOPKAPI-ETH. We investigate its suitability to reproduce the variability of sediment concentrations at the outlet of a pre-alpine river basin in Switzerland and quantify the impacts of key spatially variable erosion drivers – rainfall and surface erodibility – on sediment dynamics. Our analysis shows that deterministic modelling can capture a significant part of the variability in suspended sediment concentrations. Spatial variability of erosion drivers affects sediment yield by (i) increasing sediment production due to a spatially variable precipitation, while decreasing it due to a spatially variable surface erodibility, (ii) favoring the clustering of sediment source areas, and (iii) decreasing their connectivity to the river network by magnifying sediment buffers. Finally, we discuss the results in the context of the geomorphology and landscape characteristics of our study area and compare our findings with other modelling and empirical studies on sources of sediment concentration variability.

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