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Based on measurements of waves and currents obtained for a period of 302 days with a bottom-mounted RDCP (Recording Doppler Current Profiler) at two differently exposed locations, a model for significant wave height was calibrated separately for those locations; in addition, the Gulf of Riga-Vainameri 2D model was validated, and the hydrodynamic conditions were studied. Using wind forcing data from the Kihnu meteorological station, a set of current, water exchange and wave hindcasts were obtained for the period 1966–2011. Current patterns in the Gulf and in the straits were wind-dependent with characteristic wind switch directions. The Matsi coast was prone to upwelling in persistent northerly wind conditions. During the hindcast period, currents increased along the Koiguste coast and in the Suur Strait, waves decreased noticeably off Koiguste but fluctuated without a clear linear trend near Matsi. The spatially contrasting results for differently exposed coasts were related to the corresponding variations in local wind conditions and to changes in atmospheric circulation patterns over northern Europe.
Wind, flow and wave measurements were performed in November–December in 2008 in the relatively narrow and shallow Suur Strait connecting the waters of the V¨ainameri and the Gulf of Riga. During the measurement period wind conditions were extremely variable, including a severe storm on 23 November. The flow speed along the strait varied between ±0.2 m s−1, except for the 0.4 m s−1 that occurred after the storm as a result of the sea level gradient. The mean and maximum significant wave heights were 0.53 m and 1.6 m respectively. Because of their longer fetch, southerly winds generated higher waves in the strait than winds from the north. All wave events caused by the stronger southerly winds induced sediment resuspension, whereas the current-induced shear velocity slightly exceeded the critical value for resuspension only when the current speed was 0.4 m s−1. A triplenested two-dimensional high resolution (100 m in the Suur Strait) circulation model and the SWAN wave model were used to simulate water exchange in 2008 and the wave-induced shear velocity field in the Suur Strait respectively. Circulation model simulations demonstrated that water exchange was highly variable, that cumulative transport followed an evident seasonal cycle, and that there was an gross annual outflow of 23 km3 from the Gulf of Riga. The horizontal distribution of waveinduced shear velocity during the strong southerly wind event indicated large shear velocities and substantial horizontal variability. The shear velocities were less than the critical value for resuspension in the deep area of the Suur Strait.
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