Spatial Differences of Wave Energy Dissipation in the Mangrove Forests Along the South China Sea

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Haijin Cao, Yujun Chen, Marcel Stive, Weibing Feng

Friday 3 july 2015

12:15 - 12:30h at North America (level 0)

Themes: (T) Hydro-environment, (ST) Ecohydraulics and ecohydrology

Parallel session: 15F. Environment - Ecohydraulic

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This study investigates the buffering effect on ocean wave energy due to the coastal mangrove forests of the South China Sea on the basis of field measurement data, which are collected from two different sites under different tidal levels and wave climate. The intention of this paper is to find out the exact wave damping rate with the presence of mangroves, to figure out the results due to spatial distinction and the reasons of that. The measured sites named Lianhua Shan in Panyu and Leizhou Bay were chosen for their representative characteristics------therein the pass-by tropical storms usually stir up onshore and offshore wind. Wave gauges were mounted in line perpendicular to the coastline to record the time history of surface displacement synchronously during certain time periods. The data analysis indicates that both sites witness prominent wave damping, and coupled with bottom friction after 100 meters the measured maximum dissipation rate of wave height reaches 80%. Wave energy spectrum analysis is done as well to show the differences in energy dissipation under different water levels. Further insight into the wave damping rate manifests that spatial difference is significant particularly during the typhoon period due to its position relative to the storm route. What’s more, examining the spectral wave energy dissipation pattern tells that water depth is a determinant factor to the spectrum shape and the dissipation capability of vegetation is distinct at different frequencies. Serving as natural coastal protection schemes, mangrove forests effectively mitigate the coastal hydrodynamics and reversely are greatly affected by hydrodynamics, contributing to an interactional stable aquatic ecosystem. Nevertheless, each specific location has its own proper features.