On the Dynamics of “Almost Equilibrium” Beaches in Semi-sheltered Bays Along the Southern Coast of the Gulf of Finland - The Baltic Sea Basin - page 262

early winter (September-December) whereas the late spring and summer months
are relatively calm (Zaitseva-Pärnaste et al. 2009 ) .
For long and high waves excited by strong southwestern storms, the geometry of
the northern Baltic Sea and the Gulf of Finland suggests that full geometric block-
ing (Caliskan and Valle-Levinson 2008 ) should occur. Most of the waves affecting
beaches on the southern coast of the Gulf of Finland thus originate from the gulf
itself. Under specific conditions, however, western winds may still bring appreciable
amounts of wave energy stemming from the northern sector of the Baltic Proper to
certain coastal sections of the gulf (that are open to the west). If this happens, very
high and extremely long waves may penetrate deep into the gulf (Soomere et al.
2008a ) . Such wave systems have much longer periods ( T

=

12-14 s) and impact the
nearshore at much greater depths compared to local wind seas. As such events are
usually accompanied by high water levels, major damage may occur to beaches that
are widely open to the Gulf of Finland such as Narva-Jõesuu Beach.
The “memory” of wave fields is relatively short and the changes in the wind field
are fast reflected in the wave pattern. As a consequence, the instantaneous wave
fields in smaller sub-basins (such as Tallinn Bay or Narva Bay) rapidly mimic the
changes of the open-sea winds (Soomere 2005 , Laanearu et al. 2007 ) .
A specific feature of the northern coast of Estonia is the largely intermittent
nature of the local wave climate. As different from the classical examples of bay
beaches, the bayhead beaches here are only partially sheltered from intense waves.
Very high waves occasionally penetrate into such bays and cause intense erosion of
their coasts (Kask et al. 2003b ) . For example, the significant wave height in Tallinn
Bay usually exceeds 2 m each year, may reach 4 m in NNW and western storms
(Soomere 2005 ) , and may overshoot 2.5 m in the nearshore of Pirita Beach during
NNW storms (Soomere et al. 2007 ) . Such storms usually cause littoral transport
towards the bayhead beaches, but may severely damage coastal sections in their
neighbourhood.

13.2.3 Local Sediment Transport

As contemporary rivers in North Estonia are fairly small (except for the Narva River)
and cross mostly areas overlying limestone, they bring relatively little amounts of
sediments into the sea. Moreover, sand forms only a very little fraction of the fluvial
sediments. For example, the Pirita River provides about 400 m 3 of suspended mat-
ter annually. Most of its fluvial sediments (74%) possess a grain size from 0.01
to 0.05 mm and about a quarter has a size from 0.0025 to 0.01 mm (Lutt and
Kask 1992 , pp. 149-152). Only a few rivers cross sandstone layers and fairly small
sandstone sections of the North Estonian coast are open to wave action.
The largest source of sand are bluffs cut into glacial deposits (including eskers,
Estonia lies in the periphery of the esker distribution area of the Scandinavian glacia-
tion, Karukäpp 2005 ) and ancient beach ridges which are open to the wave action
along some sections of the coast. Their sand content is relatively small, usually
well below 25%. The material contains many cobbles, pebbles, and boulders which