Deriving vegetation drag coefficients in combined wave-current flows by calibration and direct measurement methods

Deriving vegetation drag coefficients in combined wave-current flows by calibration and direct measurement methods

Chen, Hui (Sun Yat-sen University; State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology; Guangdong Province Engineering Research Center of Coasts)
Ni, Yan (Shanghai Waterway Engineering Design and Consulting Co., Ltd.)
Li, Yulong (Sun Yat-sen University; State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology; Guangdong Province Engineering Research Center of Coasts)
Liu, Feng (Sun Yat-sen University; State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology; Guangdong Province Engineering Research Center of Coasts)
Ou, Suying (Sun Yat-sen University; State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology; Guangdong Province Engineering Research Center of Coasts)
Su, Min (Sun Yat-sen University; State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology; Guangdong Province Engineering Research Center of Coasts)
Peng, Yisheng (Sun Yat-sen University)
Hu, Zhan (Sun Yat-sen University; State and Local Joint Engineering Laboratory of Estuarine Hydraulic Technology; Guangdong Province Engineering Research Center of Coasts)
Uijttewaal, W.S.J. (TU Delft Environmental Fluid Mechanics)
Suzuki, T. (TU Delft Environmental Fluid Mechanics; Flanders Hydraulics Research)

2018-12-01

Coastal vegetation is efficient in damping incident waves even in storm events, thus providing valuable protections to coastal communities. However, large uncertainties lie in determining vegetation drag coefficients (C_D), which are directly related to the wave damping capacity of a certain vegetated area. One major uncertainty is related to the different methods used in deriving C_D. Currently, two methods are available, i.e. the conventional calibration approach and the new direct measurement approach. Comparative studies of these two methods are lacking to reveal their respective strengths and reduce the uncertainty. Additional uncertainty stems from the dependence of C_D on flow conditions (i.e. wave-only or wave-current) and indicative parameters, i.e. Reynolds number (Re) and Keulegan-Carpenter number (KC). Recent studies have obtained C_D-Re relations for combined wave-current flows, whereas C_D-KC relations in such flow condition remain unexplored. Thus, this study conducts a thorough comparison between two existing methods and explores the C_D-KC relations in combined wave-current flows. By a unique revisiting procedure, we show that C_D derived by the direct measurement approach have a better overall performance in reproducing both acting force and the resulting wave dissipation. Therefore, a generic C_D-KC relation for both wave-only and wave-current flows is proposed using direct measurement approach. Finally, a detailed comparison of these two approaches are given. The comprehensive method comparison and the obtained new C_D-KC relation may lead to improved understanding and modelling of wave-vegetation interaction.

Drag coefficient
Flume experiment
Keulegan-Carpenter number
Vegetation
Wave dissipation
Wave-current interaction

http://resolver.tudelft.nl/uuid:74d8487d-dee0-4448-9ed0-cedcdffc701c

https://doi.org/10.1016/j.advwatres.2018.10.008

2019-04-16

0309-1708

Advances in Water Resources, 122, 217-227

Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.

Institutional Repository

journal article

© 2018 Hui Chen, Yan Ni, Yulong Li, Feng Liu, Suying Ou, Min Su, Yisheng Peng, Zhan Hu, W.S.J. Uijttewaal, T. Suzuki