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 273

relevant EBP) and the closure depth. The potential gain or loss of the dry land area
is then calculated under an assumption of zero net loss from the Bruun Rule. This
potential gain is then compared with the factually measured gain or loss.
Kask et al. ( 2009 ) illustrate the method based on two examples. The coastline
changes at Pirita Beach were first quantified from topographical maps based on
measurements with a time lag of about 15 years (1986 and about 2000). The uplift
rate at Pirita is about 2.5 mm/year (Vallner et al. 1988 ) . If the sand volume were
constant at Pirita, the expected coastline shift within approximately 15 years would
have been about 4 m and the gain of dry land in the entire sandy beach with a length
of about 2 km to about 8,000 m 2 . In reality, the total gain of land is about 3,000 m 2 ,
which corresponds to a mean coastline shift of about 1.5 m seawards. Consequently,
the net loss of sand from the beach is about 5,000 m 2 12,500 m 3 . The net × 2.5 m =

annual loss of sand is thus of the order of 1,000 m 3 .
Another example of a similar estimate is obtained from the comparison of the
results of two high-resolution surveys from 1997 and 2006, during which the area
of dry beach remained practically unchanged. The expected coastline shift within 10
years, however, would have been about 2.5 m and would have resulted in the gain of
about 5,000 m 2 of dry land. Therefore, the net loss of sand during these years is also
about 12,500 m 3 . The net loss of sand from the beach is thus about 1,250 m 3 /year
during this decade.

13.5.3 Interplay of Littoral Transport and River Flow
at Narva-Jõesuu

While there is fairly weak net longshore transport in the middle sections of bay-
head beaches (Soomere et al. 2008b ) , the situation is completely different in the
eastern section of the North Estonian coast. The dominant wave approach direction
along a long section of the almost straight coast is from the northwest. Although at
times waves generated by easterly winds cause westward sediment drift, the basic
geomorphic features reflect the overall intense sediment transport to the east. This
transport leads to the formation of sand bars across river mouths.
The intensity of wind waves has a pronounced seasonal cycle in the entire Baltic
Sea (Soomere 2005 , Bromanetal. 2006 , Soomere and Zaitseva 2007 , Räämet and
Soomere 2010 ) . The monthly mean wave height at Pakri (the only wave observation
point, in the western part of the Gulf of Finland) varies from 0.38 m during spring
and early summer (April-June) to 0.75 m in late autumn and early winter. The sea-
sonal cycle is also clearly visible in the most typical wave conditions, dominant
wave periods, and higher percentiles of observed wave heights (Zaitseva-Pärnaste
et al. 2009 ) . The similar cycle in the intensity and direction of littoral transport is
much more strongly pronounced, because (i) westerly winds dominate during the
later autumn and (ii) relatively strong easterly winds usually occur in early spring
when much of the near-coastal wave activity is damped by the presence of ice.
The interplay of seasonal variation of wave intensity and river discharge leads to
an interesting pattern of seasonal variation of the river mouth bar or sill height at