Structure of alongshore mobilization of sediments, eastern part of gulf of Danzig
Systematization of analyzed schemes of alongshore mobilization of sediments off the east coast of the Gulf of Danzig was conducted. Significant differences in the structure and localization of the countercurrent flows in convergence zones were detected. The results of near-bottom steady-state measurements of currents in the vicinity of the Baltic Canal in the depth range 6-16 m demonstrated that >6-m/s winds cause the alongshore currents to be reoriented in the direction of the alongshore wind component. The morphodynamic accumulative criterion (the filling of the re-entrant angle and abrasion in the obstacle-shadow zone) and “abrasive” criterion (the orientation of abrasion kettle holes at the ends of breakwalls) were examined. The abrasive criterion is apparently preferred over the accumulative one during transportation of sediments along segments of the coast where waves approach the coast at normal or near-normal angles. Peculiarities of the mechanism of the northward transportation of sediments, bypassing Baltiysk backwalls and changing from abrasive to accumulative criteria for different segments of the coast, are demonstrated. Two schema representing the opposite Vistula and Sambiysky alongshore flows of sediments are proposed: prior to construction of the backwalls facing Baltic Canal incoming waters with the vast area of migration at the north end of the Vistula bar, and the post-construction backwalls with the resulting narrowing of the area and displacement of its south boundary on the north side to the level of these backwalls.