Abstract
IIn the present context of sea-level rise, the reconstruction of previously reclaimed intertidal areas represents an opportunity to build dynamic coastal defences, to decrease flooding under storm conditions by the dissipation of wave and surge energy across the vegetated domain. In Europe, this approach started in the late 1990s along the coast of eastern and southern England but it is becoming common to many European countries around the North Sea margin. The process of salt-marsh restoration normally develops around the opening or removal of flood protection structures and gradual flooding of the hinterland. If the intertidal zone starts to experience vertical accretion, vegetation will colonize the area and a saltmarsh will develop. This paper presents the morphological evolution and sediment distribution in the Perkpolder basin, SW Netherlands (NL), following the conversion of a reclaimed area into a tidal flat, after the opening of an inlet in the flood defence structures in June 2015. The main focus of this study is the description of the evolution of the tidal flat since the opening of the inlet and the identification of spatio-temporal conditions for the evolution of a salt marsh. To reach this objective, several topographic surveys were undertaken, together with sediment surface sampling. Sedimentation rates at fixed sampling stations were assessed during the transition between neap and spring tides over a period of 1 month and 2 weeks. The morphological analysis of the inlet evolution proved that 6 - 8 months after the opening the inlet reached an equilibrium state. The average accretion rate across the whole study area was about 6 - 7 cm year-¹. The average deposited sediment was about 100 g m-² per day. Considering the sedimentation rates in the most elevated regions, 80-110 cm above NAP (Normaal Amsterdams Peil), and assuming that the sedimentation rate will remain constant in time, the conditions for the on-set of salt-marsh formation will not be reached before 8-10 years. Projections indicate that the area located at +50 cm above NAP will not become a mature marsh before 50 years.
Highlights
Tidal flats are intertidal, non-vegetated, soft sediment habitats generally composed of mud and sand (Dyer et al, 2000), often backed by salt marshes that grow at higher elevations within the intertidal fringe
In order to assess the morphological evolution of the tidal flat through time, three Lidar surveys, with a 2 m x 2 m resolution, and uploaded on the GPS datalogger to collect the points along selected orientations; during the successive surveys, the points of measurements where repeated with absolute care
From a sedimentological point of view, the conditions found on this reconstructed tidal flat reflect the typical characteristics of back-barrier flats as outlined by Friedrichs (2011); the pattern of the sediment distribution, defined by coarser sediment in the creeks and on lower flats grading to finer sediment on upper flats reflect the hydrodynamic energy level and sediment supply (Mai and Bartholomä, 2000)
Summary
Non-vegetated, soft sediment habitats generally composed of mud and sand (Dyer et al, 2000), often backed by salt marshes that grow at higher elevations within the intertidal fringe. Several studies have discussed the benefits derived from these environments to nature and mankind: (i) they support fisheries as they host economically and ecologically important fish species (Boesch and Turner, 1984; MacKenzie and Dionne, 2008; Barbier et al, 2011); (ii) they play a role in the carbon cycle as they are able to shift carbon sequestering from the short-term (10–100 years) to the long-term (1000 years) (Mayor and Hicks, 2009); (iii) they can host leisure activities and have an important role in local cultural aspects (Weis, 2016) The decline of these environments during the last 50 years has caused an important loss of ecosystem services (Millennium Ecosystem Assessment, 2005). Several local-scale studies demonstrated that coastal wetland loss can be avoided by using nature-based adaptation in coastal management solutions (Schuerch et al, 2018)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
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 call
