As part of the Mangrove Living Lab project, this research examines how multiple drivers influence coastal erosion in Bạc Liêu, Vietnam. Currently, observed erosion in this region cannot be explained by natural sediment redistribution, and literature suggests that tidal flows are more cross-shore dominated in Bạc Liêu compared to adjacent provinces. Consequently, four key anthropogenic drivers that primarily act in the cross-shore direction are explored: (1) land subsidence due to increased groundwater extraction, (2) reduced sediment availability, (3) foreshore degradation leading to higher waves, both induced by fluvial sediment deficit, and (4) the construction of sea dikes and fishpond dams in the intertidal zone, resulting in tidal flow restriction, wave reflection and coastal squeeze.
Two main methods are applied: a cross-shore elevation level analysis to assess spatial differences in subsidence and sediment supply, and a numerical model to assess the influence of each driver individually and combined. The elevation analysis revealed that subsidence varies spatially along the coast. Moreover, historic satellite images show that a site without subsidence has been accreting in the past, while a site experiencing subsidence remained stable during the same period. After 2004, they both began eroding. This suggests that differences in subsidence rates largely explain spatial variations in current coastline positions, while the erosion itself is likely driven by additional drivers. However, the limited spatial and temporal coverage of elevation transects highlights the need for more extensive data collection. Numerical modeling indicates that reduced wave heights and increased suspended sediment greatly reduce erosion rates, and can even overshadow the effect of subsidence when combined. This demonstrates that historic and ongoing fluvial deficit is likely the main driver of the current erosion. The role of intertidal structures remains inconclusive due to model limitations and differing theoretical interpretations. Refining the current model or developing more advanced alternatives will help improve understanding of these coastal erosion processes. This is needed to support the development of integrated solutions that protect both the communities and ecosystems of Bạc Liêu. ... Read more

The Vietnamese Mekong Delta, a vital region in the country’s economy, faces the dual challenges of coastal erosion and mangrove degradation, which threaten its long-term sustainability and flood protection capabilities. This research focuses on the coastal area of the Bac Lieu province, characterized by severe erosion and degrading mangrove forests. The study investigates the applicability and potential impacts of hydraulic measures to decrease the net rate of coastal erosion, utilizing numerical modeling with Delft3D and a comprehensive socio-economic analysis. The research hypothesizes that the coastal erosion is partly driven by the placement of a sea-dike to protect aquaculture farms, initiating a positive feedback loop. This loop explains the relation between coastal erosion and mangrove degradation. The proposed hydraulic measures to interfere with this feedback loop are a porous detached breakwater, a shoreface nourishment and the removal of the existing sea-dike. The socio-economic analysis involves questionnaires for local residents, field investigations, and insights from experts in Ho Chi Minh City. While the questionnaires provide inconclusive results, the overall socio-economic impact of the nourishment and breakwater is deemed positive and worth further exploration, particularly in light of the critical role of mangroves in future flood protection. On the other hand it is concluded that the measure of removing the sea-dike will have a negative impact on the coastal area of Bac Lieu due to the intensive land-use and the lack of individual protection of the farms and villages. Therefore, this measure is not modelled. Numerical modeling with Delft3D assesses the hydraulic impact of the breakwater and nourishment on the heavily eroded and partially eroded coasts of Bac Lieu. Results indicate that the nourishment method exhibits a positive effect in reducing net erosion, especially in low energy conditions. Conversely, the porous breakwater shows minimal impact on cumulative erosion and sedimentation. Since this is against all expectations, the validity of the schematization of the porous breakwater is questioned. It is observed that the schematization does not grasp the complex behaviour of the breakwater and therefore it is concluded that Deft3D is not a suitable modelling tool for modelling a porous breakwater. The findings suggest that the nourishment method is a promising approach for reducing erosion in Bac Lieu, benefiting both the heavily and partially eroded coasts. To determine the best course of action for Bac Lieu, further research into the long-term effects and configurations of nourishment is recommended. Additionally, informing local inhabitants on the threats of relative sea-level rise and flood protection, and fostering consensus between the government and engineering agencies on the importance of protecting the Mekong Delta and its mangrove ecosystems are essential steps toward a more resilient future. ... Read more