Baltic Sea coastal erosion; a case study from the Jastrzębia Góra region

Abstract

The coastline in the Jastrzębia Góra area can be divided into three major zones of general importance: a beach and barrier section, a cliff section, and a section protected by a heavy hydrotechnical construction. These areas are characterised by a diverse geology and origin, and hence different vulnerability to erosion. In addition, observations have demonstrated a different pace of erosion within each zone. Based on the results obtained by remote sensing methods (analysis of aerial photographs and maps), it has been determined that the coastline in the barrier area, i.e., to the west of Jastrzębia Góra, moved landwards by about 130 m, in a period of 100 years, and 80 m over about 50 years. A smaller displacement of the shoreline could be observed within the cliff. Between the middle of the twentieth and the start of the twenty-first centuries the shore retreated by about 25 m. However, in recent years, an active landslide has led to the displacement of the uppermost part of the cliff locally up to 25 m. Another issue is, functioning since 2000, a heavy hydrotechnical construction which has been built in order to protect the most active part of the cliff. The construction is not stable and its western part, over a distance of 50 m, has moved almost 2 m vertically downwards and c. 2.5 m horizontally towards the sea in the past two years. This illustrates that the erosional factor does not comprise only marine abrasion, but also involves land-based processes determined by geology and hydrogeology. Changes in the shoreline at the beach and barrier part are constantly conditioned by rising sea levels, the slightly sloping profile of the sea floor and low elevation values of the backshore and dune areas. Cliffs are destroyed by mass wasting and repetitive storm surges that are responsible for the removal of the colluvium which protects the coast from adverse wave effects. Presumably, mass movements combined with groundwater outflow from the cliff, plus sea abrasion cause destabilisation of the cliff protection construction.

The development of unconsolidated sedimentary coastal cliffs (Pobrzeże Kaszubskie, Northern Poland)

“…The con struc tion is meant to pro tect the cliff and land slide against ma rine ero sion. Yet, ero sion of the sea bed in front of the seawall oc curs be cause of a lack of thick sandy de pos its of the pro tec tive layer (Uoecinowicz et al, 2014).…”

“…The cliff slope reach ing the limit of equi librium is sub ject to trans for ma tion, in which the pri mary role is played by the com plex geo log i cal con di tions. Their neg a tive effects are in ten si fied by the com pli cated hydrogeological sit u ation (Uoecinowicz et al, 2014;Lidzbarski and Tarnawska, 2015). Col lu vium dis place ment is of ro ta tional or ro ta tion-with-flow char ac ter, which is caused by a con stant in flow of rain wa ter and ground wa ter.…”

“…There are three lev els of till interbedded with sandy de pos its and clays, ex posed in the west ern part of the cliff (Mas³owska et al, 2002;Uoecinowicz et al, 2014). Glaciotectonic struc tures were vis i ble in the west ern, edge part of the up land.…”

“…How ever, these sed i ments are of ten dis con tin u ous and have a small thick ness, so that the un der ly ing Mio cene strata, and lo cally glacitectonically de formed Oligocene(?) clays as well as Pleis to cene tills are re vealed in places (Zachowicz et al, 2007;Uoecinowicz et al, 2014).…”

The Impact of Sea Shore Protection on Aeolian Processes Using the Example of the Beach in Rowy, N Poland

“…Climatic change and rising sea level [4,[6][7][8][9], as well as the increasing number of storms [8][9][10][11] contribute to erosion of the Polish coast of the South Baltic [11][12][13][14], including west of Rowy [15,16]. In addition, breakwaters securing outlets from seaports demonstrate an impact on the erosion processes of seacoasts in Poland; they disturb the process of longshore sediment transport [17][18][19].…”