Nearshore morphodynamics along the coastline of southern Sweden from detailed surficial mapping and hydrodynamic modelling

With a view to assessing morphodynamic responses of the southern Swedish coast to predicted future sea level rise, the Geological Survey of Sweden has conducted detailed onshore and offshore sediment mapping and commissioned modelling of nearshore wave and current dynamics. Seamless, full coverage land and seabed mapping from approximately 3 m above sea level to 1000 m offshore has been completed along 500 km of coastline. On land, mapping of surficial sediments was done using conventional field-based methods and a high-resolution LIDAR-based digital elevation model. For the seabed, sediment and bathymetric mapping was based on ship-borne hydroacoustic surveying data, as shallow and close to shore as permitted by the ship draught, involving multibeam, swath-sonar, side-scanning sonar, sediment profiling and reflection seismics. For the white ribbon zone, i.e., the nearshore zone that is too shallow for the ships to enter, airplane-borne LIDAR and orthophoto-data were acquired. Ground-truthing in the form of sediment-sampling and visual observations was also done to verify sediment interpretations in the hydro-acoustical data. The exposure of the coast to waves and currents was modelled from several decades of historical wind data.  The sediment-, bathymetric- and topographic data were then combined with the modelled data of exposure to wind, waves, and currents to analyze spatial patterns of sediment erosion, transport and deposition. The results have been compiled into maps showing the location and distribution of mobile sediments, their transport pathways and storage compartments in the nearshore and deeper offshore zones, whether these compartments are closed or leaky, and their onshore-offshore exchange, including long-term trends in coastline accretion and erosion. The results show the coastline adapting to sea level rise that is associated both with the cessation of postglacial isostatic uplift and global warming, and to other climatic factors such as long-term changes in dominant wind direction.  At present, erosion causing long-term shoreline recession is localized. However, there is high potential for this to become a much more general and high magnitude problem in coming decades along this heavily populated, low lying, sedimentary coastline.