Showing papers by "H.E. de Swart published in 2019"

Dynamics of offshore tidal sand ridges, a review

Abstract: Tidal sand ridges are large-scale rhythmic bedforms that are observed on the offshore parts of shelf seas where sand is abundantly available Spacings between successive ridges are several kilometres, they evolve on centennial time scales, and their crests are cyclonically rotated with respect to the direction of the principal tidal currents Here, an overview will be presented of the current knowledge about these ridges with respect to their manifestation in different seas, their observed behaviour, the basic mechanisms that explain their initial formation and their evolution towards finite heights and the ability to model them It will be shown that both tides, waves and changes in mean sea level have a profound impact on the evolution of the ridges

Sensitivity of tidal bar wavelength to channel width

Abstract: Tidal bars are repetitive estuarine bedforms with heights of several meters and wavelengths in the order 1–15 km. Understanding their formation and sensitivity to changes in channel characteristics is important as they hamper marine traffic and play a crucial role in the local ecosystem. Recent observations suggest that the local width of the channel is dominant in determining the tidal bar wavelength. However, theoretical studies could not reproduce the sensitivity of the tidal bar wavelength to channel width. This discrepancy between theory and observations suggests that a mechanism is missing. In this study, one of the theoretical models is extended and results in tidal bar wavelengths, lateral mode numbers, and growth rates that agree fairly well with those of natural tidal bars, including the wavelengths dependency on estuary width. An important extension of the model concerns the bed slope induced diffusive suspended load transport of sediments. With this, it is explained why previously, the modelled tidal bar wavelengths depend only weakly on estuary width and why in the extended model it does. This has, from a modelling point of view, general implications for morphological models using a total load sediment transport formulation with a so‐called bed slope parameter.

The Perfect in dialogue : Evidence from Dutch

Abstract: We investigate the use of the perfect in dialogue in Dutch and – for comparison – report on data from Dutch narrative discourse as well as on data from both registers in English. Our approach is corpus-based with data drawn from Harry Potter and the Philosopher’s Stone and its translation to Dutch. Our data reveal that the Dutch perfect is sensitive to the dialogue/narrative discourse distinction and competes with the past in dialogue along the event/state distinction. This is in line with earlier findings by Boogaart (1999) and de Swart (2007) and lays the foundation for an analysis of the perfect in which we bridge the gap between the English/dialogue oriented literature (Portner 2003; Nishiyama & Koenig 2010) and the variationist/narrative discourse oriented literature (de Swart 2007; Schaden 2009).

Closure of Secondary Basins Causes Channel Deepening in Estuaries With Moderate to High Friction

Abstract: Estuaries are often characterized by the presence of secondary basins (side embayments), which affect the estuarine hydrodynamics and sediment dynamics. Many of these basins have disappeared due to land reclamations, which might influence the estuarine morphodynamics. This study addresses how the presence and closure of secondary basins affect the estuarine channel depth using the Delft3D model. Results reveal that channels in estuaries with secondary basins are shallower than those in which these basins are absent, regardless of their location, length, or number. This shallowing is more pronounced for basins that are located at the northern estuarine margin due to the Coriolis force. The shallowing of channels increases if more secondary basins are present. Channels deepen after the closure of secondary basins, resulting from a decrease of the landward directed sediment transport that is driven by tidal asymmetry. Model results apply to estuaries with moderate to high friction.

Modelling the impact of a time-varying wave angle on the nonlinear evolution of sand bars

Abstract: Sandy beaches are often characterized by the presence of sand bars, whose characteristics (growth, migration, etc.) strongly depend on the wave conditions (wave height, angle of wave incidence, etc.). This study addresses the impact of a periodically time-varying wave angle of incidence with different time-means on the long-term evolution (order days to months) of sand bars. Model results show that heights of sand bars that form in the case of a time-varying angle around a zero-mean are on average larger than those in the cases of time-varying angles around an oblique mean, particularly for large variations in the angle of wave incidence.

Tense use in dialogue

Abstract: This paper reports on parallel corpus research that shows that there are differences in tense use in written texts between parts that represent dialogue, and parts that narrate the story. This calls for further study of tense use in dialogue, both in written representations, and in spoken dialogue. Yet, in the dialogue semantics literature almost no prior work exists that is devoted to tense use, neither from a formal, nor from a computational angle. We argue that this gap in dialogue research should be filled by further empirical investigation, as well as the development of computational tools for automated annotation of tense and temporal structure in dialogue. This will not only help understand how speakers track the temporal structure of dialogue, but also give theoretical linguistic literature on tense a wider empirical and computational dimension.