Spatial distribution of surface velocities on the ebb tidal delta near Ameland

Master thesis (2018)

Authors

T.A. Vos Civil Engineering & Geosciences

Contributors

M.F.S. Tissier (mentor)
S.G. Pearson (graduation committee member)
F.P. de Wit (graduation committee member)
Faculty
Civil Engineering & Geosciences, Civil Engineering & Geosciences
Copyright: © 2018 Thomas Vos
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Published Date

12-03-2018

Language

English

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Faculty

Civil Engineering & Geosciences

Abstract

Drifters equipped with GPS-trackers have been widely used to investigate surface velocities in a wide range of coastal and oceanic settings. A detailed description of a new, cell-phone based, budget drifter system is given, along with an overview of the potential error sources and the magnitude of these sources. Drag related “windage” errors were found to be significant. As a part of the SEAWAD research project, the surface velocities on the ebb tidal delta of the
Amelander Zeegat (the Netherlands) are measured over a period of two weeks. The drifters performed well in the field (no drifter losses) but the results showed relatively frequent data gaps and filtering resulted in significant data loss. The signal quality in the area appeared to significantly influence the data loss.
The velocities on the ebb tidal delta vary around 0.7 [m/s], depending on location, depth, tidal phase and wind. The spatial structure of the velocities shows generally a uniform flow structure. Different wind conditions caused the most significant changes in the spatial distribution of the velocities, followed by the effect of the tidal range. Waves were found to have an insignificant effect
on the flow velocities. A number different deployment configurations were investigated in order to shorten the measurement interval as much as possible. Due to the absence of spatial structure, spatial “resolution” can be exchanged for a shortened measurement interval by deploying the drifters in two or more groups across the research area. Methods for measurement verification using nearby ADCP-equipped measurement points are presented but not performed.
Overall, the described drifter measurement method provides a cheap way of measuring the spatial distribution of velocity in an area. However, the accuracy of the measurement has not been verified. Until then, the accuracy of the results is uncertain.