|Coastal erosion, whether natural or anthropogenic induced, is a worldwide problem. Coastal areas are however often densely populated, making erosion mitigation solutions essential. However, solution knowledge is limited for tropical mud coasts and these mainly developing countries are characterized by weak coastal management. Traditionally hard solutions were implemented. They can cause biodiversity losses, potentially increasing community vulnerability. Furthermore, the instability of mud forms an engineering problem. This indicates the need for Nature Based Solutions (NBS). Although mud recharge and seagrass are identified in design guidelines as NBS, potential ways and success and failure factors of implementation and efficiency in erosion mitigating are absent. Furthermore, an erosion hotspots overview along tropical mud coasts is lacking.
This study firstly aimed to provide an erosion hotspot overview. Secondly, to evaluate restoration techniques of mud recharge and seagrass for tropical mud coasts, complemented by identifying their erosion mitigation effectiveness and success and failure factors of implementation. Identifying erosion hotspots was done with satellite data, complemented with qualitative literature the determine coastal sediment characteristics. Evaluation of restoration techniques was based on analysis of documented projects, backed up by qualitative and quantitative data from literature.
Erosion along tropical mud coasts occurs most often in Asia and North and South America. More erosion hotspots are found along open coasts compared to bays, estuaries and barrier coasts.
Evaluation of mud recharge schemes indicated direct confined intertidal placement and trickle charge aided in mitigating erosion in estuaries and bays intertidally. Seagrass has been restored with some success in bays, estuaries and barrier coasts. Restoration was achieved with planting subtidal sods or intertidal and/or subtidal anchored rhizome fragments to staples or weights. Erosion mitigation cannot be provided by every species in every location and/or scenario. Findings should be taken with caution due to limited availability of mud recharge and seagrass restoration projects.
Long term survival of seagrass is uncertain due to its vulnerability to anthropogenic threats. However, seagrass is linked to high fishery production. When energetic conditions are not restricting and ample of donor bed is available, choosing anchored rhizome fragments above sods is advised. The first is less labor intensive, costly and impacting to donor sites. Mud recharge is ill-advised in areas with sensitive marine life or commercial activities like shellfishery due to increased levels of turbidity. When chosen, trickle charge is advised above direct placement due to its lower recharge rate.