A numerical approach for approximating the historical morphology of wave-dominated coasts-A case study of the Pomeranian Bight, southern Baltic Sea

- A numerical approach to approximate historical coastal morphology is developed.
- The basic concept is a dynamic equilibrium of the coastal cross-shore profile shape.
- The approach can be potentially used for future projection of coastline changes.

Comparison between historical maps from the 1900s, 1980s and a modern map from the 2000s of the Pomeranian Bight at the southern Baltic Sea indicates that a major part of the coastline has been suffering continuous erosion. This also holds for a major part of other coasts on a global scale. Quantifying coastal geomorphological changes on a decadal-to-centennial temporal scale thus needs to be intensified for coastal protection activities and integrated coastal zone management. This study applies an estimation of sediment mass balance including the investigation of sediment source-to-sink transport. In the case of absent historical survey data, a numerical approach, namely the Dynamic Equilibrium Shore Model (DESM), is developed to approximate the historical morphology and to estimate sediment budget of wave-dominated coasts based on the information of historical coastline configuration derived from maps, a high-resolution modern Digital Elevation Model (DEM) and relative sea-level change. The basic concept of the model is a dynamic equilibrium of the coastal cross-shore profiles adapting to sediment mass balancing of a semi-enclosed coastal area, in which the unknown parameters of the cross-shore profile shapes are calculated by numerical iterations. The model is applied at the Pomeranian Bight, in order to validate its capability in reflecting the pattern of bed level change and estimating sediment mass volume. Two tests of the model are conducted in approximating historical DEMs in 1980s and ca. 1900. The changes of approximated DEMs from past to present are then respectively compared with the ones derived from a nautical sea chart in 1980s, and the ones produced by a complex morphodynamic model that uses the approximated DEM at ca. 1900 as a starting point to hindcast the coastal morphological evolution of the research area. The deposition/erosion patterns along the coastline are consistent in both comparisons. The pre-conditions and limitations of the model are discussed in detail. The model proposed here can serve as a useful tool for coastal morphological studies and potential applications for the future projection of coastal morphogenesis.