Vegetation provides practical protective tools for estuarine and coastal regions. The roots, stems, and canopy systems of mangroves can divert and retard the flow field within and surrounding vegetation regions (Truong et al., 2019) and also absorb external forces from waves (Phan et al., 2015). The area within the vegetation is usually calmer compared to the unprotected region outside. Consequently, sediment tends to be deposited inside the vegetation region (Vargas Luna et al., 2015). The sediment deposited then may have feedback on the wave and flow field and the growth conditions of the vegetation (Truong et al., 2017). These mutual interactions between ecological area (vegetation), hydrodynamic conditsions (wave and flow field), and morphological conditions (sediment transport) are the crux of any proposed nature-based solutions (NbS). From a hydraulic engineering perspective, these dynamic interactions can translate into the momentum and mass exchange processes between vegetation and nearby areas. By observing the evolution of mangrove forests and associated with the rate of erosion/accretion of the shoreline, Phan, 2015 and Truong., 2017 proposed a hypothesis of “squeezed mangrove forest”, in which “the mangrove width” is considered a crucial length-scales that is related to the sustainable development of the mangroves. This length scale was physically interpreted and connected to the penetration of the mixing layer into the vegetation region (Truong., 2017; Truong et al., 2019). It is noted that whereas the characteristic of the incoming waves mainly controls the penetration of the mixing layer into the coastal mangroves, that of the estuarine mangroves is mainly governed by the characteristic of lateral flow. The latter is the primary focus of this study. Large vortex structures caused by the Kelvin-Helmholtz instability at the vegetation’s edge play an essential role in the transverse exchange of mass and momentum (White & Nepf, 2007; Truong et al., 2019). These structures are usually large compared to the water depths and are termed large horizontal coherent structures (LHCSs). The Reynolds Shear stresses (RSs) induced by LHCSs contribute more than 90% to the total turbulent shear stress at the edge of the floodplain vegetated region (Truong & Uijttewaal 2019).

Nevertheless, our understanding of this topic often stems from small-scale laboratory experiments. Whether the presence and characteristic of vortex structures at the interface of the low flow and fast flow region obtained from small-scale physical models remain true for estuaries and coasts has not yet been determined. In order to obtain more insight into the physics of the exchange processes occurring at the vegetation interface at different scales, two unique physical models of vegetated channels have been conducted. One small-scale and another large-scale experiment, both with and without vegetation, were conducted at TU Delft Water Lab and the Korea Institute of Civil Engineering and Building Technology - River Experiment Center (KICT-REC), respectively. Two digital twin models of this flume were subsequently constructed using Delft3D, which were calibrated and validated using the collected datasets. In this study, recent findings pertaining to these experiments are presented

Mangrove degradation and rapid coastline erosion have been widely observed at many locations along the Mekong Delta Coast. These locales frequently display narrow mangrove forests, occasionally spanning as few as 100 meters. This phenomenon of the narrower mangrove forests is supposed to be due to the construction of sea dikes in a search to establish room for agricultural purposes and to hinder the salinity intrusion, referred to as "mangrove squeeze". Within the context of monitoring mangrove forest evolution alongside the shoreline's dynamic processes of erosion and accretion, the hypothesis of a "squeeze mangrove forest" was advanced by Phan (2015) and Truong (2017). This conceptual construct underscores the fundamental importance of "mangrove width" as a critical length scale influencing the sustainable growth of a mangrove forest. The physical interpretation of this length scale is intricately tied to the extent of the mixing layer's intrusion into the vegetative domain (Truong et al., 2019). It is important to note that while the mixing dynamics of estuarine mangroves are primarily regulated by lateral flow events induced by large vortex structures moving along the vegetation edge, the characteristics of incoming waves primarily determine the length to which the mixing layer penetrates within coastal mangroves. The latter is the primary focus of this study.