Three-dimensional Sediment Transport Model Research Articles

Incorporating a backward-forward stochastic particle tracking model into a hydraulic modeling framework to identify probable sedimentation sources during typhoons

Study regionShih-men Reservoir, Taiwan Study focusThe primary purpose of this research is to integrate the novel backward-forward stochastic particle tracking model (BF-SPTM) into a three-dimensional sediment transport model for the Shih-men Reservoir. This integration aims to simulate the distribution of sediment during typhoon events and effcientlyidentify probable sedimentation sources . Additionally, a Genetic Algorithm (GA) is developed to optimize the critical parameters of the EFDC hydrodynamic module and sediment transport module. New hydrological insightsIn the proposed BF-SPTM, the influence function is applied for the first time in a three-dimensional hydraulic model to integrate the backward and forward particle tracking processes, thereby providing more precise probable sources. In this study, a 'probable source' is considered a grid cell rather than a point, which substantially reduces the computational time in the BF-SPTM model. A case study using BF-SPTM during Typhoon MEGI demonstrates its capabilityto identify probable sources in natural water using the EFDC model. The output of the BF-SPTM can be effectively used to identify potential sources of sedimentation. Additionally, this study incorporated more realistic boundary and flow conditions from a natural river to enhance the practical application of BF-SPTM. These conditions included flow velocity, diffusivity, water surface, and bed topography.

Uncertainty in complex three-dimensional sediment transport models: equifinality in a model application of the Ems Estuary, the Netherlands

Estuarine suspended sediment transport models are typically calibrated against suspended sediment concentration data. These data typically cover a limited range of the actual suspended sediment concentration dynamics, constrained in either time or space. As a result of these data limitations, the available data can be reproduced with complex 3D transport models through multiple sets of model calibration parameters. These various model parameter sets influence the relative importance of transport processes such as settling, deposition, erosion, or mixing. As a result, multiple model parameter sets may reproduce sediment dynamics in tidal channels (where most data is typically collected) with the same degree of accuracy but simulate notably different sediment concentration patterns elsewhere (e.g. on the tidal flats). Different combinations of model input parameters leading to the same result are known as equifinality. The effect of equifinality on predictive model capabilities is investigated with a complex three-dimensional sediment transport model of a turbid estuary which is subject to several human interventions. The effect of two human interventions (offshore disposal of dredged sediment and restoration of the tidal channel profile) was numerically examined with several equifinal model settings. The computed effect of these two human interventions was relatively weakly influenced by the model settings, strengthening confidence in the numerical model predictions.

Shelf sediment transport during hurricanes Katrina and Rita

Hurricanes can greatly modify the sedimentary record, but our coastal scientific community has rather limited capability to predict hurricane-induced sediment deposition. A three-dimensional sediment transport model was developed in the Regional Ocean Modeling System (ROMS) to study seabed erosion and deposition on the Louisiana shelf in response to Hurricanes Katrina and Rita in the year 2005. Sensitivity tests were performed on both erosional and depositional processes for a wide range of erosional rates and settling velocities, and uncertainty analysis was done on critical shear stresses using the polynomial chaos approximation method. A total of 22 model runs were performed in sensitivity and uncertainty tests. Estimated maximum erosional depths were sensitive to the inputs, but horizontal erosional patterns seemed to be controlled mainly by hurricane tracks, wave–current combined shear stresses, seabed grain sizes, and shelf bathymetry. During the passage of two hurricanes, local resuspension and deposition dominated the sediment transport mechanisms. Hurricane Katrina followed a shelf-perpendicular track before making landfall and its energy dissipated rapidly within about 48h along the eastern Louisiana coast. In contrast, Hurricane Rita followed a more shelf-oblique track and disturbed the seabed extensively during its 84-h passage from the Alabama–Mississippi border to the Louisiana–Texas border. Conditions to either side of Hurricane Rita’s storm track differed substantially, with the region to the east having stronger winds, taller waves and thus deeper erosions. This study indicated that major hurricanes can disturb the shelf at centimeter to meter levels. Each of these two hurricanes suspended seabed sediment mass that far exceeded the annual sediment inputs from the Mississippi and Atchafalaya Rivers, but the net transport from shelves to estuaries is yet to be determined. Future studies should focus on the modeling of sediment exchange between estuaries and shelves and the field measurement of erosional rates and settling velocities.

Impact of winter storms on sediment erosion in the Rhone River prodelta and fate of sediment in the Gulf of Lions (North Western Mediterranean Sea)

In this study a three-dimensional sediment transport model was developed. The model accounts for both current and wave forcing on the sediment and was implemented over the Gulf of Lions. A two-way nesting technique was used to focus on the Rhone River prodelta which is considered as a sink for riverine sediment. In addition, to understand the resuspension of trapped sediment over the Rhone prodelta, an in situ experiment, called SCOPE, was conducted during the winter 2007–2008. The experiment consisted of measuring hydro-sedimentary parameters using a mooring station comprising a current profiler (ADCP) and an altimeter (acoustic transducer) located in the eastern part of the Rhone prodelta. The three-dimensional transport model was validated using these data, and used to investigate the effect of sediment dynamics at the prodelta and Gulf of Lions scale. Both modelling and data analysis highlighted the impact of the two strong storms from the south-east which characterised the experimental period. Erosion of bed material (about 2cm) and an increase in suspended material (up to about 50–100mg/l) in the water were the result of each storm as recorded at the mooring station. The erosion capacity due to waves, combined with a strong current, due to both wind and wave forcing, resulted in strong south-westward export over the whole prodelta. Each storm was responsible for an off-prodelta export estimated at around 2.1Mt. This study demonstrates that the Rhone River sediments trapped over the Rhone prodelta are subject to strong resuspension during episodic events.

Satellite data assimilation and estimation of a 3D coastal sediment transport model using error-subspace emulators

This paper describes sequential assimilation of data into a three-dimensional coastal ocean model using fast and cheap statistical surrogates of the model (emulators). The model simulates resuspension and deposition of fine sediments in a macro-tidal environment of the Fitzroy Estuary and Keppel Bay, North-East Australian coast. The assimilation algorithm was applied first to synthetic observations produced by a twin model run, and then with real data obtained from satellite observation. The latter are derived from remote sensing algorithms customised to the study region. The main objective of simulations was to test the data assimilation scheme using synthetic observations and identify potential issues and challenges when assimilating real data sets. The assimilation algorithm proved capable of substantially reducing a prior uncertainty of the model for both the scenario with the synthetic observations and the scenario with the satellite data. Significant remaining error in western Keppel Bay after assimilating satellite data is diagnostic of an underlying error in the system conceptualisation – in other words, it indicates that the primary source of error is not in the parameter values specified, but in the model structure, in the interpretation of satellite data or in the other input data. The results of our study show the utility of the developed technique for the data assimilation into the three-dimensional sediment transport model of the Fitzroy estuary and Keppel Bay. More research is required to understand the capacity of this technique to generalise to other models and regions.

Daily and seasonal dynamics of suspended particles in the Rhône River plume based on remote sensing and field optical measurements

Satellite ocean colour remote sensing can serve as a powerful tool to assess river plume characteristics because it provides daily mapping of surface suspended particulate matter (SPM) concentration at high spatial resolution. This study’s ultimate objective was to better understand daily and seasonal particle dynamics in a coastal area strongly influenced by freshwater discharge and wind—the Rhone River (France), this being the major source of terrestrial input to the Mediterranean Sea. SPM concentrations and biogenic composition (chlorophyll a, organic carbon) were investigated during several bio-optical field campaigns conducted in spring–autumn of 2010 both from aboard a research vessel and by means of an autonomous profiling float. Freshwater discharge and wind velocities varied significantly during the year, associated with marked fluctuations in surface SPM (upper 1 m), even within hours and not restricted to any specific season. Thus, the range was ca. 12–25 g m–3 (dry mass basis) on 9 April (spring), and ca. 3–39 g m–3 on 4–5 November (late autumn). Short-term variations were observed also in SPM composition in terms of POC (albeit not chl a), with POC/SPM ratios ranging between ca. 3 and 11% over ca. 3 weeks in spring. Nevertheless, the particulate backscattering coefficient (b bp) proved to be a robust proxy of SPM concentration in the river plume (b bp(770) = 0.0076 × SPM, R2 = 0.80, N = 56). It has recently been demonstrated that 80% of the Rhone’s terrestrial discharge occurs during flood events. The results of the present study revealed that, under these conditions, SPM is constrained largely within surface waters (i.e. at depths <5 m), with only weak daily vertical variability. By implication, ocean colour satellite data are highly suitable in meaningfully estimating the overall SPM load exported by the Rhone River to the Mediterranean. These findings make a solid contribution to future improvements of three-dimensional sediment transport models for the region and similar settings.

Modeling Transport and Distribution of Suspended Sediments in Pearl River Estuary

Abstract The Pearl River, one of the seven largest rivers in China, drains into the South China Sea. To simulate the transport and distribution of non-saturated suspended sediments in the Pearl River Estuary, a three-dimensional sediment transport model coupled with a three-dimensional hydrodynamic model has been developed. The model was validated by comparing simulation results with suspended sediment concentrations measured on July 25–26, 1999 at four sites within the study area. The validation indicated that the model can simulate the transport and distribution of suspended sediments reasonably well. The simulated surface suspended sediment concentrations matched the satellite images qualitatively. It was found that suspended sediments in the study area exhibit strong vertical stratification, and sediment concentrations near the river gates are generally lower in the surface layer of the water column and increase with water depth while the minimum concentrations may be observed in the middle layer of w...

Three-dimensional numerical modeling of reservoir sediment release

For the computation of flow field and bed evolution in a water reservoir during the flushing process a fully three-dimensional hydrodynamic model, using a finite volume method to solve the Reynolds averaged Navier–Stokes equations, has been developed and combined with a three-dimensional sediment transport model. The hydrodynamic model is based the equations of mass and momentum conservation along with a standard k–e turbulence closure model. The sediment transport model is based on the equation of convection/diffusion of sediment concentration and sediment continuity equation for calculating the sediment concentration and bed level change in the reservoir flushing process, respectively. Both the hydrodynamic and sediment transport models are developed in a boundary-fitted curvilinear coordinate system. The grid is adaptive in the vertical direction, and changes according to the calculated bed level. The hydrodynamic section of the model was verified using experimental and direct numerical simulations data, and the sediment concentration calculations compare well with the experimental results. Also a physical model study was carried out to verify the results of bed evolution at the upstream of a sluice gate. Good agreement is found between bed evolution in the numerical and physical models.

Field Verification of 2–D and 3–D Suspended‐Sediment Models

A tidal channel in the eastern Scheldt estuary in the Netherlands was closed by pumping a sand-water mixture into the closure gap. During the closure, fields measurements of flow velocities and sand concentrations are carried out. Based on the results of the field measurements, computations with two- and three-dimensional sediment transport models are carried out. The two-dimensional computations show that the depth-integrated transport rates can be reasonably predicted in case of diverging flow. But less satisfactory results are obtained for converging flow. The three-dimensional computations show quite good agreement between measured and predicted flow velocities, sediment concentrations and transport rates, both for flood and ebb flow. A sensitivity analysis with respect to the time-dependent concentration term, the shape of the velocity profiles, the turbulent mixing coefficients and the bed material gradiation is carried out. The results show no significant influence of these parameters. The main reason for the difference between measured and predicted results is caused by the formula modelling the sediment pickup rate.