Impact of extreme sea levels and waves in the bay of Lundåkra - present situation and future scenarios

Abstract: This report is a study of the impacts of extreme sea levels and waves on the coastal area of the bay of Lundåkra. The bay is characterized by shallow sea bottoms and a flat topography, particularly in the north. Analyses have been based on historical data. To expand the analyses to apply for a future scenario a change in mean sea level has been considered. Based on general recommendations from the Swedish Meteorological and Hydrological Institute (SMHI) and recent research from the Arctic Monitoring and Assessment Program (AMAP) two future scenarios have been chosen, a sea level rise of 1 m and 1.6 m respectively, for the year of 2100. The bay of Lundåkra is a Natura 2000 area and also contains smaller areas of nature reserves. The bay area holds many conservation values. Some of the most important ones are found in an area of coastal meadows in the northernmost part close to the Saxån estuary. This site is important to many red listed birds. This area is particularly threatened since the highway E6 runs very close to the coast here. The bay area is also of great importance for fish and other animals. Bathymetry and topography data collected by a laser scan method have been obtained from the municipality of Landskrona and Kävlinge and combined with the New National Height Model (NNH) from Lantmäteriet. Modeled wave data (1994-2011) have been extracted for the bay from the company Denmark’s Hydrological Institute, DHI. Sea levels (1992-2012) have been obtained from SMHI and combined with a longer series extracted from a previous study by Karlsson Green and Martinsson (2010). Return periods have been estimated for sea levels and waves by fitting the data to Weibull and Gringorten distribution functions. For the extreme event of the November storm in 2011-11-27 the waves reached 2.2 m, which has the estimated return period of 32.5 years. The sea level reached at the same time 1.47m, with the estimated return period of 27.5 years. Applying the Bruun rule to the future scenarios a risk has been estimated of a coastline retreat of several hundreds of meters along the entire bay area. The northernmost part with the important coastal meadows will likely be flooded already at a sea level rise of 0.75 m. An analysis for calculating the wave runup levels indicate that the highway may be exposed to wave runup at extreme events in the future scenario of a 1 m sea level rise. The wave runup analysis further shows some indications that some sections of the coastline will be more exposed to wave erosion than others.