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The reset of a subtidal bar during an energetic event : application to Le Truc Vert beach case (France)
A large number of beach morphologies across the world exhibits nearshore sandbars with complex 3D patterns. During large storms, these shapes disappear and the bars get to a certain extent alongshore uniform. This phenomenon is called a reset. Numerous studies have been conducted on the development of the bar shapes (3D) or on the cross-shore migration of sandbars (2D). The present work attends to determine the relevant processes involved in the reset of the three dimensional bars and to describe the relative influence of each of these processes. To perform this study, data collected during the ECORS campaign at Le Truc Vert (France) in 2008 are analysed. In addition, a numerical approach is performed using a new research Delft3D model forced by the Xbeach wave generator to investigate the processes involved in a reset-event. The effects of the hydrodynamic external conditions on the currents in the surfzone are investigated. Then the reset is studied in details in order to understand the role of the different processes taken into account by the numerical model. The significant role of the longshore currents induced by oblique wave incidence is clearly assessed. In addition, the long wave orbital velocities as well as the mean flow related to the short wave forcing control the stirring of sediments and influence the time scale of the reset-event.
Fast calculation of groundwater exfiltration salinity in a lowland catchment using a lumped celerity/velocity approach
To support operational water management of freshwater resources in coastal lowlands, a need exists for a rapid, well-identifiable model to simulate salinity dynamics of exfiltrating groundwater. This paper presents the lumped Rapid Saline Groundwater Exfiltration Model (RSGEM). RSGEM simulates groundwater exfiltration salinity dynamics as governed by the interplay between water velocity, gradually adjusting the subsurface salinity distribution, and pressure wave celerity, resulting in a fast flow path response to groundwater level changes. RSGEM was applied to a field site in the coastal region of the Netherlands, parameter estimation and uncertainty analysis were performed using generalized likelihood uncertainty estimation. The model showed good correspondence to measured groundwater levels, exfiltration rates and salinity response. Moreover, RSGEM results were very similar to a detailed,complex groundwater flow and transport model previously applied to this field site.
Bench-mark morphodynamic model Ameland Inlet
The bench-mark study specifically aims to identify which trends and patterns in morphodynamic behaviour can or can't be reproduced. The model results presented in the bench-mark simulation show that morphodynamically stable simulations over a timescale of 5 to 10 years can be obtained with Delft3D. The use of a parallel online approach, in combination with a low-resolution model grid, allows us to run with acceptable computational times. A qualitative comparison of bed-levels reveals a major short-coming of the bench-mark model. The modelled morphodynamic response overpredicts the measured changes of the ebb-tidal delta; the ebb-tidal delta develops beyond observed limits. However, the comparison of the observed trends shows, in the bench-mark simulation and all sensitivity tests, that the model is capable of reproducing the dominant trends. Conceptual descriptions show that wave-dominated ebb-tidal deltas tend to be pushed closer to the inlet throat. In the model, it is likely that the balance between the offshore directed tidal component, and the onshore directed wave-driven transports is not resolved accurately enough. By selecting a highly efficient bench-mark model we can easily implement, test and verify new insights, model developments and advances as these are obtained in the Kustgenese 2.0 project.
The contribution of mud to the net yearly sedimentation volume in the Dutch Wadden Sea : a review based on literature
This literature study describes the present knowledge on mud import, mud concentration and mud deposition in the Dutch Wadden Sea. It also discusses a method to convert between mud weight percentages and mud volume percentages. Knowledge on the mud contribution to the net annual sedimentation volume in the Wadden Sea is essential for future sustainable coastal management. An extensive summary of the main findings and their contribution to answering the research questions of sub-project 'Systeemkennis Zeegaten' of Kustgenese 2.0 is presented in the report. The main conclusions are: Various authors give estimates of recent mud deposition in the Wadden Sea between 1.2 and 3 *109 kg/year ; Only a small percentage of the gross mud transports is net deposited ; Mud only contributes to the sediment volume for mud weight percentages above 15%, because at that moment sand grain contacts start to be broken up ; The average mud deposition is estimated to be between 0.7 and 4,1 *109 kg/year in mass and between 0.7 and 3.4*106 m3/year in volume or between 8 and 37% of the total annual sedimentation volume.