This paper aims to analyse the sensitivity of patterns of numerically simulated potential sediment transport along the eastern Baltic Sea coast. The study area extends from the Sambian (Samland) Peninsula to Pärnu Bay in the Gulf of Riga. The magnitudes of net and bulk transport depend largely on how the shoaling and refraction of the waves are resolved. The qualitative patterns of net and bulk sediment transport are almost insensitive with respect to the details of wave transformation in the nearshore and with respect to grain size. The overall counter-clockwise transport along the study area contains two persistent reversals along the coast of the Baltic Sea proper and two frequently recurring reversals along the eastern margin of the Gulf of Riga. Individual years with normal levels of wind speed may host completely different patterns of sediment transport. The location of the most persistent convergence and divergence areas of the net transport acceptably matches the granulometric composition of the nearshore seabed up to a few km from the shoreline.
We explore long-term variations in the properties of waves in the Baltic Sea and geostrophic air-flow over this water body. Records of visual wave observations from 1946 to 2012 at 8 observation sites at the eastern coast of the Baltic Sea reveal a multitude of changes. A substantial decrease in the wave heights took place until about 1970, and considerable decadal variations have occurred since then. The coherence between annual average wave heights at different locations was lost at the end of the 1980s. A rotation of the usual wave approach direction by almost 90° was identified at one location. We then coupled this data with a reconstruction of wave fields and wave-driven sediment transport for 1970 to 2007. The reconstruction is based on adjusted geostrophic winds from the Swedish Meteorological and Hydrological Institute. The simulated net potential sediment transport along the eastern coast of the sea reveals a major change at the end of the 1980s. This change is associated with an abrupt turn of the geostrophic air-flow over the southern Baltic Sea by ~40° around 1987. This change may serve as an alternative explanation for a radical decrease in the frequency of major inflows of saltier, oxygen-rich water into the Baltic Sea since the mid-1980s.
Numerically estimated wave properties and the associated closure depth along the eastern Baltic Sea coast from the Sambian (Samland) Peninsula up to Pämu Bay in the Gulf of Riga are compared against the existing data about accumulation and erosion. Typical values of the closure depth are about 5 6 m (maximum 6.58 m) at the open Baltic Sea coast, 3 4 m in the Gulf of Riga and 2 2.5 m in semi-sheltered smaller bays. The areas of intense accumulation or erosion (especially the areas of their high variability) generally coincide with the sections, hosting high wave intensity, except for a few locations, dominated by anthropogenic impact. It is shown that the longshore variations in wave intensity (or closure depth) can be used to identify the location of major accumulation and erosion domains. The sections that host the largest change in the wave height along the coast reveal erosion or accumulation features, depending on the predominant wave approach direction.
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