From Physical Experiments to 1D and 2D Numerical Models of Wave Propagation in Mangrove Forests: Implications for Nature-Based Solutions in the Mekong Delta

This study investigates the propagation and attenuation of short and long waves within mangrove forests by combining physical experiments at the experimental scale with 1D and 2D numerical wave models at the field scale along the Mekong Delta coast. Physical experiments were conducted in a wave flume at TU Delft laboratory to examine the transformation of short and long waves under different mangrove forest configurations. The separation of incident and reflected waves, as well as short- and long-wave components, was performed to quantify the relative contribution of different wave processes to overall wave attenuation. In parallel, numerical wave-flume models were constructed using XBeach and SWASH to mimic the experimental setup. Comparisons between measured and simulated wave parameters indicate a good model performance and support the scaling of experimental findings to real world conditions.

Building on these controlled investigations, the analysis was extended to the Mekong Delta by constructing detailed 1D and 2D numerical models of mangrove forests along the delta's Eastern coast. In addition to real bathymetry, idealised concave and convex cross-shore profiles with varying degrees of curvature were introduced to explore the effect of coastal squeeze and erosion processes on wave transformation. This unified modelling framework enables a systematic comparison of wave behaviour from the laboratory to the field scale. The results demonstrate relatively consistent trends in wave attenuation between physical experiments and numerical models, while also highlighting a strong sensitivity of wave-height transformation to cross-shore profile geometry, mangrove width, and the relative positions of the fish farms. These sensitivities are particularly evident in relation to the location of fish farms and sea dikes situated landward of the mangrove system. Results indicate that a concave profile offers more favorable natural conditions for mangrove development, particularly in terms of wave energy absorption and sediment accumulation, whereas convex profiles are more prone to wave reflection and exhibit lower attenuation efficiency.

The width of the mangrove forest and the location of fish farms or sea dikes landward of the system significantly affect wave-height behaviour both in front of and within the forest. A reduction in mangrove width, together with the landward structures being pushed closer to the shoreline, increases reflected wave energy and return currents at the mangrove edge. Consequently, it is hypothesised that mangrove removal and seaward expansion of fish farms enhance reflected wave heights and return-flow velocities near the forest edge, thereby promoting erosion in this zone. Such processes may induce a transition from convex to concave cross-shore profiles, thereby further accelerating erosion. The results highlight the importance of maintaining sufficient mangrove width and carefully positioning sea dikes and aquaculture infrastructure relative to the mangrove edge, particularly where cross-shore profiles evolve from concave to convex forms that increase wave reflection and reduce attenuation efficiency.