Morphological Evolution of an Intertidal Area Following a Set-Back Scheme: A Case Study From the Perkpolder Basin (Netherlands)

Abstract

In 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 per year −1. The average deposited sediment was about 100 g per 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 onset 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.

Evaluating Short-Term Tidal Flat Evolution Through UAV Surveys: A Case Study in the Po Delta (Italy)

“…For example, the Venice Lagoon (Italy) has a very low rate of accretion ranging between millimetres and a few centimetres per year [90,91] which means that even UAV surveys would have difficulty evaluating volume and vertical changes; this is the reason why different on-field methodologies, like sedimentation plates, are used in the Venetian lagoon. The opposite situation can be found in the Perkpolder tidal basin (Netherlands) where the sedimentation rates are very high (> 6 cm/year) and constant; wide vertical changes allow Lidar methodology to be quite accurate with a time interval of one year [105]. As explained in the previous section, it is necessary to find a compromise between the extent of the study area and the resolution of the survey.…”

“…It appears evident that microtidal wetlands are highly dynamic and, in most cases, their sediment transport is dominated by episodic events (i.e., storms, floods) occurring during specific seasons; the influence of these factors on the morphology seems to be higher than in meso and macrotidal environments. In fact, although tidal flats and salt marshes in high tidal regimes are influenced by seasonal variations as well, the amount of deposited sediment is more impactful (e.g., Van Proosdij (2006); Brunetta et al ( 2019)) [104,105]. Microtidal wetlands need these events in order to survive.…”

Drainage-Improved Sediment Strength Enhances Saltmarsh Seedling Establishment Chance

“…In 2015, the dike preventing water from entering Perkpolder was breached, and sea water from Western Scheldt estuary was introduced to the area (Rijkswaterstaat, 2015). After the breach, a soft mud layer has quickly evolved to equilibrium on top of the former agriculture land (Bruneta et al, 2019).…”

The complexity of studying coasts: From forms and processes to management

“…Regarding impacts on salt marshes and estuaries, urban and industrial settlements eliminate valuable habitats (Fig. 9C), while salt harvesting modifies the geometry of natural tidal channels, altering tide dynamics and sedimentation rates (Gracia et al, 2017;Brunetta et al, 2019). Nevertheless, the abandonment of traditional salinas maintaining sluice gates open allows the system to rapidly recover its naturalness through plant colonization (Fig.…”