This paper presents five examples of Nature-based Solutions (NbS) to restore degraded mangroves and mangrove-mud coasts. These examples are meant to provide inspiration for the restoration of other such coasts. The designs are based on a qualitative/conceptual understanding of the bio-physical system. This is obtained mainly from an in-depth analysis of historic satellite images and historic maps, while quantitative data are scarce, as is generally the case in these environments. One example reflects the restoration of circulation and flushing in a small bay in the SW of the Caribbean Island Bonaire. Drainage channels were overgrown, and the forest was attacked from the back by hyper-salinity and the inflow of silts. The first, more urgent problem has now been addressed by re-opening a few channels, restoring circulation and flushing, and mangrove recruitment restarted. The other four examples are from Guyana and Suriname. Though all sites are part of the greater Guiana coastal zone and driven by the same physical processes, local conditions are so different that different NbS-solutions were required to catch and arrest sufficient sediments to recreate mangrove habitat. The examples show why and how one solution works at one location, while elsewhere another approach was successful. This paper can be regarded as a supplement to the Engineering with Nature Atlas issued by ERDC in 2024, which focuses on temperate climate environments though.

@en

Understanding the abiotic factors governing salt marsh dynamics is crucial to incorporate such ecosystems in holistic coastal risk management (Bouma et al, 2014). Process-based modelling of these ecosystems can help to gain insight into their response to changing environmental conditions. Therefore, a new process-based approach was applied to model establishment and survival of salt marsh vegetation, bridging the gap between geophysical and ecological models. A salt marsh ecosystem representative for the Western Scheldt Estuary, the Netherlands, which is characterized by semi-diurnal tides, locally generated waves and transport of fine sediments, was simulated starting from a bare mudflat. Salt marsh development is simulated in a Python script based on two concepts: Windows of Opportunity, accounting for seedling establishment (Poppema et al, 2019), and Population Dynamics, describing the growth and decay of established salt marshes (Temmerman et al, 2007). This external script is coupled to a morphodynamic Delft3D Flexible Mesh model through Basic Model Interface (BMI). The model results show that the establishment of pioneer vegetation on bare tidal flats governs the of tidal channels. The rate of seedling establishment affects the geometry of tidal channels, leading to narrow and deep channels aligned with the direction of tidal flow for fast colonizers (e.g. Salicornia europaea; glasswort) and wider, meandering channels for slow colonizers (e.g. Spartina anglica; cordgrass). Moreover, the response of the salt marsh-tidal flat system to changing abiotic conditions (e.g. waves, sediment influx) is assessed, showing that although fast colonizing salt marsh species are less resistant to physical forcing, they can adjust more rapidly to changes in environmental conditions. Concluding, a new process-based approach for biogeomorphological modelling has helped to improve the understanding of salt marsh development under changing environmental conditions, bringing incorporation of these ecosystems into coastal management a step further.@en