Search

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.

Mangrove forests are well known as coastal ecosystem defences. Mangrove trees have a significant role in these systems as they attenuate hydrodynamic forces and contribute to the reduction of coastal erosion, (Horstman et al., 2014). However, a mechanistic understanding of the feedbacks of hydro- and morphodynamic stresses on mangrove seedling survival is lacking for the period after establishment (Balke et al., 2011). These feedbacks are key for the development and resilience of mangroves, particularly in an urban area where stressors such as limited accommodation space and reduced sediment supply are prevalent. In this work we address the effects of waves and tidal currents, including fluctuations therein over a seasonal timescale, on the morphodynamics and their combined impact on mangrove seedling development.