Geological Hazard Potential at the Baltic Sea and Its Coastal Zone: Examples from the Eastern Gulf of Finland and the Kaliningrad Area - The Baltic Sea Basin - page 354

of their relatively small depths. Erosion furrows were traced along all coastal lines
in the western direction. On the bottom surface of the erosion furrows, there are
very distinct current ripples (up to 20 cm high) turned perpendicularly to the runnel
direction and composed of coarse-grained sand. The distance between ripple crests
ranges from 40 cm to 1 m (Fig. 16.8b ) . Investigation has shown that they are the
ways of near-bottom currents, removing sand material offshore.
Offshore sand movement and its redeposition at depths of more than 10 m
lead to sediment loss and disturbance of the dynamic equilibrium. This occurs
during storms when dunes and foreshores are eroded. During these events,
material is transported seaward to be deposited outside the break point, while
during calmer weather, sandbars are shifted toward the coastline (Schwarzer
et al. 2003 ) .
Repeated profiling of the submarine terrace located between capes Peschany
and Repino (Fig. 16.9 ) and the comparison of our results with old nautical maps
revealed the progressive erosion of the marine edge of the terrace. As long as the
terrace exists with its surface at the depth of 3-5 m, it protects the coast from ero-
sion. Accordingly, erosion of the terrace itself is a rather dangerous process, which

(a) (b)

Fig. 16.9 Bottom erosion. a Changing of the depths in the nearshore zone as a result of the sub-
marine terrace erosion. Red lines - isobaths of the navigational chart edited in 1989; blue lines -
results of the depth measurements made by VSEGEI in 2005. b 3D diagram showing submarine
terrace erosion