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.

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Mangrove-mud coasts across the world erode because of uninformed management, conversion of mangrove forests into aquaculture ponds, development of infrastructure and urbanization, and/or extraction of groundwater inducing land subsidence. The accompanied loss of ecosystem values, amongst which safety against flooding, has far reaching consequences for coastal communities, exacerbated by sea-level rise. To halt erosion various nature-based solutions have been implemented as an alternative to hard infrastructure sea defenses, including mangrove planting and erection of low-tech structures such as bamboo fences, permeable brushwood dams, etc. These structures have been designed on the basis of best-engineering practice, lacking sufficient scientific background. This paper investigates the use and success of permeable dams over a period of about 15 years, describing their application in Guyana, Indonesia, Suriname, Thailand and Vietnam, summarizing the lessons-learned, and analyzing their functioning in relation to the physical-biological coastal system. Also an overview of relevant costs is given. The basic philosophy behind the construction of permeable dams is the rehabilitation of mangrove habitat through re-establishment of the (fine) sediment dynamics – we refer to Building with Nature as the overarching principle of this approach. Our main conclusions are that a successful functioning of permeable dams requires (1) a thorough understanding of the physical-biological system and analysis of the relevant processes, (2) patience and persistence, including maintenance, as the natural time scales to rehabilitate mangrove green belts take years to decades, and (3) intensive stakeholder involvement. We give a list of conditions under which permeable dams may be successful, but in qualitative terms, as local site conditions largely govern their success or failure.@en