| dc.description.abstract | Coastal protection in the Netherlands is essential. Since 1990, the policy called dynamic preservation has been in effect. This policy has paved the way for both a proactive approach to combat coastal erosion, by means of a baseline that is to be maintained by sand nourishment, and the explicit possibility to stimulate natural dynamics. The underlying idea is to have a sustainable coastal system that grows with sea-level rise (i.e., is safe) and a more integrated approach that also includes direct benefits to ecology and economy. Although the mitigation of structural erosion has been successful, natural dynamics, particularly in the dunes, remained restricted. This led to the initiation of active dynamic foredune management, which encompasses taking erosive measures in the foredune to enhance sand drift inland.
Active dynamic foredune management has been proposed from an ecological perspective in sections 6775 to 7025, which are part of the Holland coast. The water authority responsible, the Hoogheemraadschap van Rijnland, has special interest in the consequences this might have for safety of the sections under future uncertainties (e.g., climate change and infrastructure). Especially, in sections 6800 to 6875, as dune width is limited here. Therefore, through this study, it was aimed to assess the effect of beach-dune development, when met with active dynamic foredune management and future uncertainties, on safety and several other interest in sections 6775 to 7025.
The measures to be taken, the influencing factors and accompanied uncertainties, and the interests in the study area were explored through a literature survey and three interviews. This resulted in the formation of 8 scenarios that mimic morphological beach-dune development based on the size and further evolution of foredune notches and the rate of sea level rise. With MorphAn, the scenarios were translated into sequences of cross-shore profiles until the year 2093 of the most vulnerable section (6850) in the study area. These profiles were assessed in terms of dune safety with the DUROS+ module embedded in MorphAn and also used to assess the effect on habitat development and the local infrastrastructure (e.g., cycling track and gas pipe).
Results show that safety (with 1:30000 as the maximum allowable chance of flooding) is ensured in all scenarios. The development of large-scale dynamics, that is, with notches that facilitate direct aeolian transport from the beach into the inner dunes, results in a lower erosion volume during major storms (1:30000) than small-scale notching, in which such a sand influx is not present. However, large-scale dynamics cause a potentially undesirable conversion of grey to white dune habitats, while it may also jeopardize the future of the cycling track and gas pipe, because of excessive sand deposition. These results are, however, dependent on the assumptions made around notch development and nourishment in this study. | |
