Primary ship waves generated by conventional marine vessels were investigated in the Furusund fairway located in the Stockholm archipelago, Sweden. Continuous water level measurements at two locations in the fairway were analyzed. In total, 466 such events were extracted during two months of measurements. The collected data were used to evaluate 13 existing predictive equations for drawdown height or squat. However, none of the equations were able to satisfactorily predict the drawdown height. Instead, a new equation for drawdown height and period was derived based on simplified descriptions of the main physical processes together with field measurements, employing multiple regression analysis to derive coefficients in the equation. The proposed equation for drawdown height performed better than the existing equations with an R² value of 0.65, whereas the equation for the drawdown period was R² = 0.64. The main conclusion from this study is that an empirical equation can satisfactorily predict primary ship waves for a large data set.

From November 12th to 13th in 1872, an extreme coastal flood event occurred in the south Baltic Sea. An unusual combination of winds created a storm surge reaching up to 3.5 m above mean sea level, which is more than a meter higher than all other observations over the past 200 years. On the Danish, German, and Swedish coasts, about 300 people lost their lives. The consequences of the storm in Denmark and Germany were more severe than in Sweden, with significantly larger destruction and higher numbers of casualties. In Denmark and Germany, the 1872 storm has been more extensively documented and remembered and still influences local and regional risk awareness. A comparative study indicates that the collective memory of the 1872 storm is related to the background knowledge about floods, the damage extent, and the response to the storm. Flood marks and dikes help to remember the events. In general, coastal flood defence is to the largest degree implemented in the affected areas in Germany, followed by Denmark, and is almost absent in Sweden, corresponding to the extent of the collective memory of the 1872 storm. Within the affected countries, there is local variability of flood risk awareness associated with the collective memory of the storm. Also, the economic dependency on flood-prone areas and conflicting interests with the tourism industry have influence on flood protection decisions. The processes of climate change adaptation and implementation of the EU Floods Directive are slowly removing these differences in flood risk management approaches.

Hallin, C.; Almström, B.; Larson, M., and Hanson, H., 0000. Longshore transport variability of beach face grain size: Implications for dune evolution. This study investigates grain-size sorting through longshore transport processes and how it influences dune evolution. The analysis is based on a data set of 58 sediment samples distributed alongshore over a 6.5-km-long sandy beach in Ängelholm, Sweden. Grain size differs significantly from north to south, where median grain size varies from about 0.4–0.15 mm. The long-term coastal evolution is derived from shoreline change analysis of a series of aerial photos from the 1940s until today and from longshore sediment transport rates calculated on the basis of wave data simulated by the SWAN wave model employed in the Coastal Engineering Research Center (CERC) formula. The results show an almost unidirectional longshore transport from north to south; the beach is eroding in the northern part and accreting in the southern part. The McLaren model, a grain size–based model to predict transport direction, was tested against the grain size data. The test indicated transport in the opposite direction. This result supports previous studies suggesting that the McLaren model has limited applicability for sandy beaches with a dominant longshore transport. The sediment samples were collected at the mid–beach face position in an area where sediment is supplied to the beach during accreting conditions. Sediment in the appropriate grain size to build dunes—at this beach, 0.2–0.3 mm—was found in the parts of the beach where the dunes are growing. In the eroding parts, the sediment was coarser, suggesting that the longshore transport influences the supply of sediment for aeolian transport. The gradients in longshore transport rate were also found to affect dune morphology; the dunes were higher in the eroding and stable parts of the beach and lower in the accreting parts.

Problems related to shipping have increased worldwide during the last decades as a result of more traffic travel-ling at higher speeds and using larger vessels. When ships move in a restricted fairway they generate primary (drawdown) and secondary (transverse and divergent) waves (Bertram 2000) that often cause adverse impact to adjacent shores. An example of this is the Furusund fairway in Sweden, which since the 1980’s has experienced increased traffic and larger ships. This has resulted in a loss of natural fine sediment habitats along the shores as well as structural damages to piers and jetties (Granath 2015). Furusund is an important fairway into Stockholm, the capital of Sweden, and is located about 25 km north of the city within the Stockholm archipelago. It is mainly trafficked by large ferries (length/width/draft: 200x30x7m). The wind-wave regime in the fairway can be described as a low-energy environment, due to the short fetches and no swell. Hence, ship waves have a significant impact on the shores in terms of bed and bank erosion. This study aims at determining the primary ship wave characteristics and their relationship to ship properties and bathymetric conditions in the Furusund fairway. Measured water levels were collected for this purpose during three months at three locations. Existing empirical formulas for drawdown are evaluated based on the measurements and compared with a new formula derived for the specific fairway. The results are used for designing nature-based protection against ship-generated waves along the shores and to validate analytical and numerical models that can be employed for ship wave generation and propagation.

The October 2023 storm surge, denoted Babet, caused severe flooding and unprecedented damage along the southwestern Baltic Sea coasts. The beginning of October 2023 was dominated by several westerly low-pressure systems over the Baltic Sea region. The abundance of westerly winds pushed water into the Baltic Sea basin through the Danish straits resulting in elevated water levels of +50 cm above normal in the basin. Around the 18th of October the wind direction shifted from west to north and subsequently to east while also increasing in intensity, with mean wind speeds of 25 m/s and gusts exceeding 30 m/s. This gave strong wind setup in the southwestern part of the Baltic Sea and the strong winds generated large waves as well as increasing the water levels further. Notably, the area experienced the most extreme storm conditions in over a century with the storm peak was reached during the night between the 20th to 21st October.We present a study with results of the numerical model simulation using SWAN set up for the southwestern part to the Baltic Sea basin. The simulation combines the wave conditions derived from wind forcing and observed water levels from a network of observation gauges. These levels are compared to historical event statistics from an existing long-term hindcast model of wave climate conditions for the region. Finally, the results of storm surge levels are assessed in relation to observed flooding and erosion impact on natural coastal areas and impact to existing coastal protection.