Bottom type distribution based on wave friction velocity in the Baltic Sea

Surface waves play an important role for the sediment distribution in the shallow Baltic Sea. This paper presents the large-scale spatio-temporal distribution of wave-induced bottom friction velocity, u * , based on modelled wave data for the years 1999 and 2000. The highest values of u * are found along the eastern coasts of the Baltic Proper and Bothnian Sea—areas characterised by long fetches for the dominant winds. Temporally, the dynamics follow that of the wind climate with higher velocities during winter and lower during summer. th bottom is assumed for the calculations. To test this assumption, u * is compared to other estimates of u * assuming rough bottoms. The spatio-temporal patterns are similar, although the present approach gives a slight underestimation of u * at areas with coarse grain sizes. pare the results, the co-variation between the u * distribution and bottom type distribution from a digitised sediment map is analysed. It shows upon a good agreement. This is also found when comparing critical levels for resuspension found in the literature with the same from modelled u * . In addition, other processes important for bottom stress, such as mesoscale eddies and coastal jets, are discussed.