Laboratory Study of Turbulent Kinetic Energy within Mangrove Forest under Waves

Abstract

Laboratory study was set out to investigate the flow structure and turbulent kinetic energy ($TKE$) within mangrove forest considering flexible canopies and rigid stems under various wave conditions. Canopies and stems have different effects on turbulence generation. The flexible leaves in canopy scale can promote the dissipation of $TKE$ and the rigid stem scale contribute to the generation of turbulence. Importantly, the difference of $TKE$ with and without vegetation, $\Delta TKE$ varied with wave frequency and peaked at 0.833 Hz for the canopy and vegetation-free upper layer, but increased with wave frequency in stem scale. Moreover, $TKE$ in mangrove forest increased monotonically with ${u_{w,RMS}}^2$ for each stem density. This study proposed a modified model for the $TKE$ prediction within canopy scale considering the role of flexible leaves and rigid stems together. Besides, $TKE/{u_{w,RMS}}^2$ presented a good correlation with the ratio of wave excursion (${A_w}$) to stem spacing ($S$), ${A_w}$/$S$ and declined rapidly with ${A_w}$/$S$ especially when ${A_w}$/$S$ <0.1 for both stem and canopy scale. This empirical relationship can be a predictor for $TKE$ within mangrove forest. Further, considering the scale between wave energy dissipation by vegetation and production of $TKE$, the third model was validated in mangrove forest and predicted well.