Modeling flow and sediment dynamics in an estuarine mangrove forest and adjacent areas: the impact of mangrove forest dynamics on landscape evolution

Mangroves, a coastal wetland ecosystem with complex above-ground root systems, are known to modulate flow and sediment transport and promote sedimentation – processes that could drive the long-term geomorphic evolution of mangrove forests. However, insights on how and to what extent mangrove forests impact the sedimentary processes and evolution of landscapes and their adjacent areas are limited. This study aims to address these challenges by using a hydrodynamic-sediment transport model and contribute to understanding the effective restoration and management of mangrove forests under the impact of climate change effects such as sea-level rise. A new model was developed to represent the impacts of species-specific three-dimensional root structures (e.g., “prop roots” of Rhizophora species and “pencil roots” of Avicennia and Sonneratia species) on flow and sediment transport and implemented in a hydrodynamic-sediment transport model. This model was applied to a restored estuarine mangrove forest in the Philippines influenced by tidal and fluvial processes. The results show the significant impacts of mangroves on the sedimentation of fluvially-transported sediments in the mangrove forest and nearby areas, which contributed to the areal expansion of the mangrove forest. In addition, due to the increased hydraulic resistance of the mangrove forest following restoration, significant amounts of river flow and sediment discharge are diverted to the other tributary, decreasing the sediment supply downstream of the mangrove forest, a phenomenon that could possibly explain the trend in sediment loss in the area. These results suggest the significance of mangrove forests in driving landscape evolution, not only within the mangrove forest itself but also in adjacent areas, highlighting the importance of considering these areas as a connected system for the management and restoration of mangrove forests.