Port of Gdańsk and Port of Gdynia’s exposure to threats resulting from storm extremes

This study is intended to make a first estimate of the exposure of the two Polish largest ports – Gdańsk and Gdynia, localized in the Gulf of Gdańsk – to threats from storm extremes. These ports are elements of the Polish critical infrastructure and presented analysis is one of the tasks related to critical infrastructure protection. Hypothetical extreme meteorological conditions have been defined based on 138-year NOAA data and assumed wave fields for those conditions have been generated. Using HIPOCAS project database the 21 extreme historical storms over the period 1958–2001 were selected to simulate realistic conditions in the vicinity of the ports. The highest significant wave height was found to be nearly 4 m in the vicinity of Port of Gdańsk and nearly 2 m in the vicinity of Port of Gdynia. A future intensification of these wave conditions should be considered due to the climate change and sea level rise

Rip currents in the non-tidal surf zone with sandbars: numerical analysis versus field measurements

Rip currents, which are local seaward-directed jets with their mean velocity exceeding 0.5 m/s, have been a subject of many studies since the 1940s. They are an important part of the nearshore current system and in specific hydro- and litomorphological conditions can cause changes in the local bathymetry. Thus, a detailed analysis of the characteristics of this phenomenon is crucial both to public safety and hydroengineering. The main purpose of this research is to determine the wave conditions of a multi-bar non-tidal coastal zone environment in which rip currents can occur. In this study, we focus on a multi-bar non-tidal coastal zone environment located in the Southern Baltic Sea, where rip current driving forces are mostly reduced to the wind and wind-induced waves. This is one of very few comprehensive approaches to exploring the possibility of rip currents occurrence in such environmental conditions. During two field expeditions, there were carried out in situ measurements exploiting two GPS drifters. The results indicate the formation of irregular non-longshore flows (related to rip currents) in the studied area. To answer the question under what conditions the formation of rip currents takes place, an extended modelling experiment was performed. Deep-water wave conditions typical of the studied area were chosen due to bouy measurements. The total of 589 combinations of the significant wave height, the mean period and wave direction values were examined as test cases. The coastal flow in the area and tracks of virtual drifters were simulated by XBeach numerical model for all test cases. As a result, 589 nearshore currents fields were generated and two scenarios were indicated: a regular circulation (dominated by the longshore current) which is typical of this area (547 cases), and flows with rip current features (42 cases). This reflects the results of the field measurements carried out. It can be concluded that the wave direction is a dominating factor in the formation of rip currents. Namely the flows of this type may occur in the area of interest when the direction of a deep water wave is almost perpendicular to the shore. Such situations occur rarely. They cover about 7% of the days of the year. Thus, rip currents do not appear to be a significant factor in the reconstruction of the sea bottom in the studied area