Date Published: April 19, 2019
Publisher: Public Library of Science
Author(s): Caroline Hallin, Magnus Larson, Hans Hanson, João Miguel Dias.
A numerical model for simulating beach-dune evolution at decadal to centennial time scales is developed. The work builds on an existing semi-empirical cross-shore model, the CS-model, to which the effect of sea level rise is added and the routines for aeolian transport and morphological dune evolution are improved. The model development is based on established conceptual models from the literature, which are translated into mathematical formulations and solved numerically. The capability of the proposed model is demonstrated through a case study at Ängelholm Beach, Sweden. The model is calibrated and validated against a seven-year long data set on morphological evolution and sediment grain-size samples. Beach and dune evolution is then simulated from 2018 to 2100 for a range of sea level rise scenarios. The model results are promising, and suggest that the model has potential to be used for long-term assessment of climate change impact on beaches and dunes.
Coastal dunes play an important role to protect against flooding and beach erosion, while providing nature and recreation values [1,2]. Therefore, both natural and artificial dunes are becoming increasingly popular flood protection methods in many coastal areas [3,4]. Meanwhile, rising sea levels increase the probability of flooding as well as the pressure on beaches and dunes [5,6]. The capability to predict future beach and dune evolution is thus of major importance for flood risk assessment and design of coastal protection. Several models have been developed to separately estimate dune erosion during storms [7–9], dune build-up due to aeolian transport [10–12], and long-term coastline evolution . However, models for the evolution of the beach and dune system at decadal time scales, which are of particular interest in coastal management , require a coupling between constructive and destructive nearshore, beach, and dune processes . In recent years, there has been advances in the coupling of cross-shore and longshore transport processes at decadal time scales, e.g., the CoSMoS-COAST model  and the LX-model ; but, these models do not include dune processes. To improve the understanding of how processes in the land-sea interface control the foredune evolution, Cohn et al  combined three process-based models—X-BEACH , CDM , and Aeolis —in the model framework Windsurf. Windsurf successfully simulated dune evolution in one cross-shore transect during one year, however, longer time and spatial scales require reduced complexity approaches. In this study, a model is developed that simulates sediment transport and morphological evolution of the beach and dune on time scales of decades to centuries. The aim is to create a robust, computationally efficient model that couples nearshore, beach, and dune processes.
The CS-model simulates sediment transport and the associated morphological evolution based on a set of transport and continuity equations . In this paper, the profile schematization is developed and routines are added for aeolian transport, morphological dune evolution, and the effect of SLR. For more detailed description of the other model components we refer to Larson et al .
To demonstrate the capability of the proposed model to simulate long-term beach and dune evolution, it was applied to a seven-year data set from Ängelholm Beach in south Sweden (Fig 6).
In this study, the CS-model was expanded to simulate beach and dune evolution at decadal to centennial time scales under SLR. Model development was based on morphological concepts from the literature, which were translated into mathematical formulations that were numerically solved. The proposed model was applied to a data set from Ängelholm Beach, Sweden. First, the model was calibrated and validated for a seven-year period, and then the beach and dune evolution was simulated from 2018–2100 for a range of SLR scenarios.