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Zhilin Zhang, Bensheng Huang, Hongxiang Ji, Xin Tian, Jing Qiu, Chao Tan, Xiangju Cheng. A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-019-0000-0
 Citation: Zhilin Zhang, Bensheng Huang, Hongxiang Ji, Xin Tian, Jing Qiu, Chao Tan, Xiangju Cheng. A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation[J]. Acta Oceanologica Sinica.

# A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation

##### doi: 10.1007/s13131-019-0000-0
Funds:  The National Key Research and Development Program of China under contract No. 2016YFC0402607; Key Research and Development Projects in Guangdong Province under contract No. 2019B111101002; 2018 Guangzhou Science and Technology Project under contract No. 201806010143; Water Resource Science and Technology Innovation Program of Guangdong Province under contract No. 2017-17.
• Vegetation in wetlands is a large-scale nature-based resource that can provide multiple benefits to human beings and the environment, such as wave attenuation in coastal zones. Traditionally, there are two main calibration approaches to calculating the attenuation of wave driven by vegetation. The first method is a straightforward one based on the exponential attenuation of wave height in the direction of wave transmission, which, however, overlooks the crucial drag coefficient (${C}_{D}$). The other method is in accordance with more complicate equations for predicting the damping factor, which is regarded as a function of ${C}_{D}$. In this study, a new relation, combining these above two conventional approaches, is proposed to predict the drag coefficient (${C}_{D}$) in an operative approach. Results show that values yielded by the new assessment method perform a strong linear relationship with a collection of historical observations, with a promising R2 value of 0.90. Besides, the linear regression derives a new predictive equation for the bulk drag coefficient. Additionally, a calibrated value of 4 for the empirical plant drag coefficient (${C}_{P}$) is revealed. Overall, this new equation, with the superiority of the convenient exponential regression, is expected to be a rapid assessment method for calculating wave attenuation by vegetation and predicting the drag coefficient.
•  [1] Anderson M E, Smith J M, McKay S K. 2011. Wave dissipation by vegetation. Coastal and Hydraulics Engineering Technical Note ERDC/CHL CHETN-I-82. Vicksburg, MS: U. S. Army Engineer Research and Development Center [2] Chen Hui, Ni Yan, Li Yulong, et al. 2018. Deriving vegetation drag coefficients in combined wave-current flows by calibration and direct measurement methods. Advances in Water Resources, 122: 217–227. [3] Dalrymple R A, Kirby J T, Hwang P A. 1984. Wave diffraction due to areas of energy dissipation. Journal of Waterway, Port, Coastal, and Ocean Engineering, 110(1): 67–79. [4] Danielsen F, Sørensen M K, Olwig M F, et al. 2005. The Asian tsunami: a protective role for coastal vegetation. Science, 310(5748): 643. [5] Dean R G. 1979. Effects of vegetation on shoreline erosional processes. In: Wetland Functions and Values: The State of Our Understanding. Minneapolis, MN: American Water Resources Association, 415–426 [6] Ghazali N, Zainuddin K, Zainal M Z, et al. 2016. The potential of mangrove forest as a bioshield in Malaysia. In: Proceedings of 2016 IEEE 12th International Colloquium on Signal Processing & Its Applications (CSPA). Malacca City, Malaysia: IEEE, 322–327 [7] Houser C, Trimble S, Morales B. 2015. Influence of blade flexibility on the drag coefficient of aquatic vegetation. Estuaries and Coasts, 38(2): 569–577. [8] Hu Zhan, Suzuki T, Zitman T, et al. 2014. Laboratory study on wave dissipation by vegetation in combined current-wave flow. Coastal Engineering, 88: 131–142. [9] Keesstra S, Nunes J, Novara A, et al. 2018. The superior effect of nature based solutions in land management for enhancing ecosystem services. Science of the Total Environment, 610-611: 997–1009. [10] Knutson P L, Brochu R A, Seelig W N, et al. 1982. Wave damping in Spartina alterniflora marshes. Wetlands, 2(1): 87–104. [11] Kobayashi N, Raichle A W, Asano T. 1993. Wave attenuation by vegetation. Journal of Waterway, Port, Coastal, and Ocean Engineering, 119(1): 30–48. [12] Liu Xin, Wang Yebao, Costanza R, et al. 2019. The value of China’s coastal wetlands and seawalls for storm protection. Ecosystem Services, 36(3): 100905 [13] Losada I J, Maza M, Lara J L. 2016. A new formulation for vegetation-induced damping under combined waves and currents. Coastal Engineering, 107(1): 1–13 [14] Mazda Y, Magi M, Kogo M, et al. 1997. Mangroves as a coastal protection from waves in the Tong King delta, Vietnam. Mangroves and Salt marshes, 1(2): 127–135. [15] Peruzzo P, De Serio F, Defina A, et al. 2018. Wave height attenuation and flow resistance due to emergent or near-emergent vegetation. Water, 10(4): 402. [16] Quartel S, Kroon A, Augustinus P G E F, et al. 2007. Wave attenuation in coastal mangroves in the Red River Delta, Vietnam. Journal of Asian Earth Sciences, 29(4): 576–584. [17] Reguero B G, Beck M W, Bresch D N, et al. 2018. Comparing the cost effectiveness of nature-based and coastal adaptation: A case study from the Gulf Coast of the United States. PLoS One, 13(4): e0192132. [18] Schaubroeck T. 2017. Nature-based solutions: sustainable?. Nature, 543(7645): 315 [19] Suzuki T, Hu Z, Kumada K, et al. 2019. Non-hydrostatic modeling of drag, inertia and porous effects in wave propagation over dense vegetation fields. Coastal Engineering, 149: 49–64. [20] Tanaka N, Sasaki Y, Mowjood M I M, et al. 2007. Coastal vegetation structures and their functions in tsunami protection: experience of the recent Indian Ocean tsunami. Landscape and Ecological Engineering, 3(1): 33–45. [21] Thampanya U, Vermaat J E, Sinsakul S, et al. 2006. Coastal erosion and mangrove progradation of Southern Thailand. Estuarine, Coastal and Shelf Science, 68(1–2): 75–85. [22] Wu W C, Cox D T. 2015. Effects of wave steepness and relative water depth on wave attenuation by emergent vegetation. Estuarine, Coastal and Shelf Science, 164: 443–450. [23] Wu W C, Cox D T. 2016. Effects of vertical variation in vegetation density on wave attenuation. Journal of Waterway, Port, Coastal, and Ocean Engineering, 142(2): 04015020. [24] Wu W C, Ma G F, Cox D T. 2016. Modeling wave attenuation induced by the vertical density variations of vegetation. Coastal Engineering, 112: 17–27. [25] Wu W M, Ozeren Y, Wren D G, et al. 2011. Investigation of surge and wave reduction by vegetation. SERRI Report 80037-01, Southeast Region Research Initiative [26] Yanagisawa H, Koshimura S, Miyagi T, et al. 2010. Tsunami damage reduction performance of a mangrove forest in Banda Aceh, Indonesia inferred from field data and a numerical model. Journal of Geophysical Research: Oceans, 115(C6): C06032 [27] Yao Peng, Chen Hui, Huang Bensheng, et al. 2018. Applying a new force–velocity synchronizing algorithm to derive drag coefficients of rigid vegetation in oscillatory flows. Water, 10(7): 906.
###### 通讯作者: 陈斌, bchen63@163.com
• 1.

沈阳化工大学材料科学与工程学院 沈阳 110142

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## A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation

##### doi: 10.1007/s13131-019-0000-0
###### 1. Guangdong Research Institute of Water Resources and Hydropower, Guangzhou 510630, China2. State and Local Joint Engineering Laboratory of Estuarine and Hydraulic Technology, Guangzhou 510630, China3. Guangdong Key Laboratory of Hydrodynamic Research, Guangzhou 510630, China4. Technical Research Center of Guangdong-Hong Kong-Macao Greater Bay Area’s Water Safety Guarantee, Guangzhou 510630, China5. Department of Water Management, Delft University of Technology, Delft 2611 CD, the Netherlands6. School of Civil Engineering and Transportation, South China University of Technology, Guangzhou, 510641, China
Funds:  The National Key Research and Development Program of China under contract No. 2016YFC0402607; Key Research and Development Projects in Guangdong Province under contract No. 2019B111101002; 2018 Guangzhou Science and Technology Project under contract No. 201806010143; Water Resource Science and Technology Innovation Program of Guangdong Province under contract No. 2017-17.
###### Corresponding author:E-mail: bensheng@21cn.com

Abstract: Vegetation in wetlands is a large-scale nature-based resource that can provide multiple benefits to human beings and the environment, such as wave attenuation in coastal zones. Traditionally, there are two main calibration approaches to calculating the attenuation of wave driven by vegetation. The first method is a straightforward one based on the exponential attenuation of wave height in the direction of wave transmission, which, however, overlooks the crucial drag coefficient (${C}_{D}$). The other method is in accordance with more complicate equations for predicting the damping factor, which is regarded as a function of ${C}_{D}$. In this study, a new relation, combining these above two conventional approaches, is proposed to predict the drag coefficient (${C}_{D}$) in an operative approach. Results show that values yielded by the new assessment method perform a strong linear relationship with a collection of historical observations, with a promising R2 value of 0.90. Besides, the linear regression derives a new predictive equation for the bulk drag coefficient. Additionally, a calibrated value of 4 for the empirical plant drag coefficient (${C}_{P}$) is revealed. Overall, this new equation, with the superiority of the convenient exponential regression, is expected to be a rapid assessment method for calculating wave attenuation by vegetation and predicting the drag coefficient.

Zhilin Zhang, Bensheng Huang, Hongxiang Ji, Xin Tian, Jing Qiu, Chao Tan, Xiangju Cheng. A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-019-0000-0
 Citation: Zhilin Zhang, Bensheng Huang, Hongxiang Ji, Xin Tian, Jing Qiu, Chao Tan, Xiangju Cheng. A rapid assessment method for calculating the drag coefficient in wave attenuation by vegetation[J]. Acta Oceanologica Sinica.
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