The State of the Nearshore Bottom as an Index of the Shore State, South Baltic Coast Examples

Abstract

The aim of this work is to present the results of seabed surveys in the deeper nearshore zone, which indicate an intense transport of sandy bedload into the sea. This translates into a negative bottom sediment balance and erosive character of the shore incongruent with the intense protective actions including a lot of beach nourishment. The phenomenon of irrevocable transport of sandy bedload into the sea has not been sufficiently accounted for in the studies on the shore protection so far. This might be due to the fact that an assessment of bedload transport requires adequate knowledge of the character and state of the bottom in the deeper nearshore zone. Other basic requirements include multibeam echosounder, side-scan sonar measurements and seismic profiling supplemented with other methods such as collection of grab and core samples, underwater TV, etc.). The paper provides examples of the assessment of nearshore bottom state conducted in the vicinity of Ustka (where the dune shore is typical of the Polish coast) and near Kołobrzeg (where rocky outcrops occur on the nearshore bottom and which is a unique coastal form in this area). The state of the nearshore bottom in the deeper nearshore zone may constitute a relative state index in the assessment of the long-term state of the whole coastal zone, while the nearshore bottom of the shallower nearshore zone (including the sandbars zone) serves as a temporary state index. These results are important in the assessment of all the shores formed by wave activity.