Simulating and classifying large-scale spatial sand-mud segregation using a process-based model for a tidal inlet system

Tidal inlet systems, as found in the Dutch Wadden Sea, often feature both sand and mud. Due to differences in sediment properties, sand and mud particles respond different to identical forcing conditions, like short waves and tidal currents. Because of this, sand and mud can get transported to different locations. This process is referred to by sand-mud segregation. Sand-mud segregation can have considerable influences on bathymetry, potential pollution and flora & fauna. It is because of these aspects that predictions on sand-mud segregation are needed. To predict sand-mud segregation, commonly for a practical scenario, a morphodynamic model can be used. Though, modelling a practical scenario often comprises a complex bathymetry and various non-linear processes, that contribute to sand-mud segregation, occur. Because of this, practical sand-mud segregation models are often hard to understand, give little insight in the overall processes and discrepancies with reality are often found within the results. These problems can be overcome by considering a schematized scenario, where only the overall forcing conditions (tidal currents and short waves) are considered, along with a schematized bathymetry and geometry. By considering a schematized scenario of the Amelander tidal inlet system, the large-scale sand-mud segregation patterns can be reproduced. It is found, e.g. in observations from the field and theoretical descriptions, that mud is commonly found in less hydrodynamic active areas (as long as mud is available). Within the Amelander tidal inlet system, mud is therefore found in the shallow intertidal areas, far from the deeper hydrodynamically active areas, like the tidal inlet and tidal channels. The schematized process-based model (a newly developed sand-mud version of Delft3D, which accounts for (non) cohesive regimes, a layered stratigraphy and consolidation lag) also reproduces these large-scale spatial sand-mud segregation patterns, with the schematized process-based approach. By combining the schematized model approach with variations in relative forcing domination (by tidal currents or short waves), various scenarios can be considered. From observations in the field and associated sand-mud segregation theory, one always expects mud deposition in less hydrodynamically active areas. Given the properties of tidal currents and short waves, it is hypothesized that mud is commonly found in deeper/shallow areas, respectively for a relative dominance of tidal currents/short waves. Results from the schematized process-based model support this hypothesis. Mud is transported to deeper areas when short wave domination is imposed, while mud is commonly found in shallow areas for a tidally dominated system. A schematized process-based sand-mud segregation model is able to reproduce large-scale spatial sand-mud segregation patterns for a practical case (the Amelander tidal inlet system). Furthermore, a classification can be set up, relating these large-scale spatial sand-mud segregation patterns to relative forcing dominance (from tidal currents or short waves), which is based on observations, theory and the schematized process-based model.Coastal EngineeringHydraulic EngineeringCivil Engineering and Geoscience

Simulating the large-scale spatial sand-mud distribution in a schematized process-based tidal inlet system model

Tidal basins, as found in the Dutch Wadden Sea, are characterized by strong spatial variations in bathymetry and sediment distribution. In this contribution, the aim is at simulating the spatial sand-mud distribution of a tidal basin. Predicting this spatial distribution is however complicated, due to the non-linear interactions between tides, waves, sediment transport, morphology and biology. To reduce complexity, while increasing physical understanding, an idealized schematization of the Amelander inlet system is considered. Delft3D is applied with a recently developed bed module, containing various sediment layers, combined with formulations for both cohesive and non-cohesive sediment mixtures. Starting with uniform mud content in the spatial domain, the development of the sediment distribution is simulated. Realistic sand-mud patterns are found, with accumulation of mud on the tidal flats. The schematization is further used to determine the sensitivity of the sand-mud patterns to changes in tide, while assessing the influence of tidal dominance on the large-scale sand-mud patterns. The patterns are enhanced/diminished under the influence of higher/lower tides.Hydraulic EngineeringCivil Engineering and Geoscience

On the Generic Utilization of Probabilistic Methods for Quantification of Uncertainty in Process-based Morhpodynamic Model Applications

A variety of uncertainty sources are inherent in process-based morphodynamic modelling applications. There is an increasing demand for the quantification of these uncertainties. This contribution introduces a probabilistic-morphodynamic (PM) modelling framework that enables this quantification. The PM modelling framework provides a systematic approach, while also lowering the required effort for inclusion of uncertainty quantification in morphodynamic model studies. Applicability and added value is shown using a pilot application to the Holland coast.Hydraulic EngineeringCivil Engineering and Geoscience

Performance evaluation of wave input reduction techniques for modeling inter-annual sandbar dynamics

In process-based numerical models, reducing the amount of input parameters, known as input reduction (IR), is often required to reduce the computational effort of these models and to enable long-term, ensemble predictions. Currently, a comprehensive performance assessment of IR-methods is lacking, which hampers guidance on selecting suitable methods and settings in practice. In this study, we investigated the performance of 10 IR-methods and 36 subvariants for wave climate reduction to model the inter-annual evolution of nearshore bars. The performance of reduced wave climates is evaluated by means of a brute force simulation based on the full climate. Additionally, we tested how the performance is affected by the number of wave conditions, sequencing, and duration of the reduced wave climate. We found that the Sediment Transport Bins method is the most promising method. Furthermore, we found that the resolution in directional space is more important for the performance than the resolution in wave height. The results show that a reduced wave climate with fewer conditions applied on a smaller timescale performs better in terms of morphology than a climate with more conditions applied on a longer timescale. The findings of this study can be applied as initial guidelines for selecting input reduction methods at other locations, in other models, or for other domains.Coastal EngineeringEnvironmental Fluid MechanicsRivers, Ports, Waterways and Dredging Engineerin

Understanding coastal erosion processes at the Korean east coast

Rivers, Ports, Waterways and Dredging EngineeringCoastal Engineerin