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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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Earth Surf. Dynam., 5, 731-756, 2017
https://doi.org/10.5194/esurf-5-731-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
28 Nov 2017
Turning the tide: comparison of tidal flow by periodic sea level fluctuation and by periodic bed tilting in scaled landscape experiments of estuaries
Maarten G. Kleinhans1, Maarten van der Vegt1, Jasper Leuven1, Lisanne Braat1, Henk Markies1, Arjan Simmelink2, Chris Roosendaal1, Arjan van Eijk1, Paul Vrijbergen1, and Marcel van Maarseveen1 1Faculty of Geosciences, Utrecht University, P.O. Box 80115, 3508 TC Utrecht, the Netherlands
2formerly at: Consmema Metalworking, Hattem, the Netherlands
Abstract. Analogue models or scale experiments of estuaries and short tidal basins are notoriously difficult to create in the laboratory because of the difficulty to obtain currents strong enough to transport sand. Our recently discovered method to drive tidal currents by periodically tilting the entire flume leads to intense sediment transport in both the ebb and flood phase, causing dynamic channel and shoal patterns. However, it remains unclear whether tilting produces periodic flows with characteristic tidal properties that are sufficiently similar to those in nature for the purpose of landscape experiments. Moreover, it is not well understood why the flows driven by periodic sea level fluctuation, as in nature, are not sufficient for morphodynamic experiments. Here we compare for the first time the tidal currents driven by sea level fluctuations and by tilting. Experiments were run in a 20  ×  3 m straight flume, the Metronome, for a range of tilting periods and with one or two boundaries open at constant head with free inflow and outflow. Also, experiments were run with flow driven by periodic sea level fluctuations. We recorded surface flow velocity along the flume with particle imaging velocimetry and measured water levels along the flume. We compared the results to a one-dimensional model with shallow flow equations for a rough bed, which was tested on the experiments and applied to a range of length scales bridging small experiments and large estuaries. We found that the Reynolds method results in negligible flows along the flume except for the first few metres, whereas flume tilting results in nearly uniform reversing flow velocities along the entire flume that are strong enough to move sand. Furthermore, tidal excursion length relative to basin length and the dominance of friction over inertia is similar in tidal experiments and reality. The sediment mobility converges between the Reynolds method and tilting for flumes hundreds of metres long, which is impractical. Smaller flumes of a few metres in length, on the other hand, are much more dominated by friction than natural systems, meaning that sediment suspension would be impossible in the resulting laminar flow on tidal flats. Where the Reynolds method is limited by small sediment mobility and high tidal range relative to water depth, the tilting method allows for independent control over the variables flow depth, velocity, sediment mobility, tidal period and excursion length, and tidal asymmetry. A periodically tilting flume thus opens up the possibility of systematic biogeomorphological experimentation with self-formed estuaries.

Citation: Kleinhans, M. G., van der Vegt, M., Leuven, J., Braat, L., Markies, H., Simmelink, A., Roosendaal, C., van Eijk, A., Vrijbergen, P., and van Maarseveen, M.: Turning the tide: comparison of tidal flow by periodic sea level fluctuation and by periodic bed tilting in scaled landscape experiments of estuaries, Earth Surf. Dynam., 5, 731-756, https://doi.org/10.5194/esurf-5-731-2017, 2017.
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Short summary
Creating estuaries in the laboratory has been challenging. When the ebb and flood currents are driven by ebb and flood in the sea, they are too weak to move sand. Here we describe how the periodic tilting of an entire experimental set-up leads to ebb and flood currents with similar behaviour as in nature and with enough strength to move sand. This means that this novel set-up now allows for the creation of estuarine landscapes in experiments.
Creating estuaries in the laboratory has been challenging. When the ebb and flood currents are...
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