Abstract
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.
Highlights
The objective of this paper is to present and discuss more than a decade of experience with the design, construction, maintenance and success of permeable dams along tropical mangrove-mud coasts
As early as the Roman era, small ridges of 0.1 – 0.2 m height were built in Europe around mean high water (MHW) on the lower supratidal marshes facing the North Sea (Lascaris and De Kraker, 2013)
Dams are meant to be temporary and may become obsolete after mangrove rehabilitation. Their construction can be relatively cost-effective and low-tech, im plying that they can be built and maintained by local coastal commu nities, provided they have the basic training. This nature-based adap tive approach can be regarded as an example within the Building with Nature (BwN) framework, applying natural forces in an integrated manner (De Vriend and Van Koningsveld, 2012; De Vriend et al, 2014), in concert with local communities to serve their socio-economic needs as well
Summary
Coastal protection is one of the many ecosystem services provided by mangroves. Its economic value is estimated between 2,000 and 9,000 USD per hectare per year (Spalding et al, 2010; UNEP-WCMC, 2006), worth an estimated 65 billion USD per year globally (Menéndez et al, 2020). Other efforts to stop erosion have been carried out using more traditional coastal defense structures as well, such as sea walls, groins, (porous) coast-parallel breakwaters, etc This is very expensive, does not work on the soft soils of muddy coasts (Kempfert and Raithel, 2002), and may lead to maladaptations, or path dependencies – “a response that does not succeed in reducing vulner ability but increases it instead” Disturbance of the fine sediment balance is a major, yet overlooked, root cause of the poor success of rehabilitation efforts on eroding coastlines (Winterwerp et al, 2005; Anthony and Gratiot, 2012; Besset et al, 2019) In these studies, the changes in sediment dynamics and bathymetry, which form the root cause of erosion, were found to prevent mangrove re-establishment, and resumption of their coastal protection services. These lessons include constructive aspects, the physics of the hydro-sedimentological system, the need for monitoring, and, last but not least, the socio-economic conditions re quired for success
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
