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Open AccessArticle

Role and Impact of Hydrograph Shape on Tidal Current-Induced Scour in Physical-Modelling Environments

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Ludwig-Franzius-Institute for Hydraulic, Estuarine and Coastal Engineering, Leibniz Universität Hannover, 30167 Hannover, Germany
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Leichtweiß-Institute for Hydraulic Engineering and Water Resources, Technische Universität Braunschweig, 38106 Braunschweig, Germany
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Department of Harbor and River Engineering, National Taiwan Ocean University, 2 Pei–Ning Road, Keelung 20224, Taiwan
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Author to whom correspondence should be addressed.
Water 2019, 11(12), 2636; https://doi.org/10.3390/w11122636
Received: 14 November 2019 / Revised: 10 December 2019 / Accepted: 11 December 2019 / Published: 13 December 2019
(This article belongs to the Section Hydraulics and Hydrodynamics)
For physical model tests, the time-varying characteristics of tidal currents are often simplified by a hydrograph following a shape of a unidirectional current or by resolving the tidal velocity signal into discrete steps of constant flow velocity. The influence of this generalization of the hydrograph’s shape on the scouring process in tidal currents has not yet been investigated systematically, further increasing the uncertainty in the prediction of scour depth and rate. Therefore, hydraulic model tests were carried out to investigate and quantify the influence of the hydrograph shape on the scouring processes under tidal currents. Several different hydrographs including those with continuously changing velocities, constant unidirectional currents, square-tide velocities and stepped velocity time series were analyzed. Results show that the scouring process in tidal currents is characterized by concurrent sediment backfilling and displacement which can only be reproduced by hydrographs that incorporate a varying flow direction. However, if only a correct representation of final scour depths is of interest, similar scour depths as in tidal currents might be achieved by a constant, unidirectional current, provided that a suitable flow velocity is selected. The effective flow work approach was found capable to identify such suitable hydraulic loads with reasonable practical accuracy. View Full-Text
Keywords: scour; tidal currents; unsteady flow; sediment transport; hydrograph; laboratory tests; temporal scour development scour; tidal currents; unsteady flow; sediment transport; hydrograph; laboratory tests; temporal scour development
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Schendel, A.; Welzel, M.; Hildebrandt, A.; Schlurmann, T.; Hsu, T.-W. Role and Impact of Hydrograph Shape on Tidal Current-Induced Scour in Physical-Modelling Environments. Water 2019, 11, 2636.

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