The Structure of the Net Alongshore Sediment Transport in the Eastern Gulf of Gdansk

Resumo

The published schemes of the net alongshore sediment transport near the eastern coast of Gdansk Bay have been systematized. Considerable discrepancies have been identified in the structure and localization of the convergence zones of opposite currents. The results of station-based measurements of bottom currents near the Strait of Baltiysk at depths of 6–16 m were used to show that, at winds >6 m/s, the alongshore currents run along the alongshore wind component. The morphodynamic accumulation (filling of the entry corner and abrasion in the shadow zone of the obstacle) and abrasion (orientation of the abrasion depression at the extreme end of the harbor moles) criteria are discussed. The abrasion criterion is shown to work better than the accumulation criterion in determining the net sediment transport in the coastal reaches with a normal or near-normal approach angle of the wave energy flow toward the shore. The specific features of the mechanism of sediment transport from south to north, by-passing Baltiisk harbor moles, from the abrasion to accumulation shore segments are given. Two schemes of the opposite Vistula and Sambian alongshore sediment flows are proposed: before the construction of the entry harbor moles in the Baltic Strait with a vast migration zone near the northern end of the Vistula Spit and after the construction of these moles, which has narrowed this zone and shifted its southern boundary northward toward the moles.