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 276

the action of predominant wave approach from the west. Consequently, the sedi-
ment compartments are relatively large and there is an active littoral drift to the east.
Under such conditions, the classical dynamic balance of open ocean beaches hosting
considerable sediment transit is combined here with a seasonally varying balance
between the wave-induced longshore transport and river-flow-induced cross-shore
transport at river mouths (Laanearu et al. 2007 ) .
The basic advantage of the analysis of such beaches is that various concepts
applicable for equilibrium systems can be used to forecast their properties as well
as their reaction to human intervention, either in the form of various coastal engi-
neering structures that disturb the flow of natural processes or of coastal protection
measures. One has, of course, to account for the intermittency of wave climate
when calculating basic properties of equilibrium profiles such as the closure depth
(Soomere et al. 2008b ) . Also, one has to critically evaluate many results of cal-
culations of sediment transport. For example, the formal estimates of the potential
transport rate are frequently overestimated by several orders of magnitude simply
because the active layer of sediments may be very thin and/or be present only at
specific places.
One of the largest advantages, however, can be achieved by combination of the
theory of (basically one-point) equilibrium beach profile with the almost equilibrium
state of the entire beach. In such cases, greatly simplified methods, based on a few
parameters of the beach and the local wave climate, can be used for estimation of
such necessary parameters for coastal management as the overall net sand loss.
The above analysis has also shown that the equilibrium of the beaches in ques-
tion is largely based on a specific long-term balance of the sediment properties,
geometry of the coast, and the forcing conditions. In this respect, the beaches are
apparently very sensitive with respect to changes in the external forcing. Numerous
changes in the forcing conditions (such as an increase in the average wind speed
along the northern coast of the Gulf of Finland (Soomere and Keevallik 2003 ) or
rapid decrease in the length of the ice season (Sooäär and Jaagus 2007 ) ) and in the
reaction of the water masses of the Gulf (such as an increase in the variability of
sea level (Johansson et al. 2001 ) ) have been identified during the latter decade; see
The BACC Author Team ( 2008 ) for more examples. Moreover, the trends of the
average and of extreme values of certain properties are different. This feature has
been recently identified, among other processes, for wave conditions (Soomere and
Healy 2008 ) . Both instrumental wave data from Almagrundet (Broman et al. 2006 )
and visual wave data from Vilsandi (Soomere and Zaitseva 2007 ) suggest that dur-
ing the 1980s there was an increase in the annual mean wave height in the northern
Baltic Proper but a drastic decrease in the wave activity has occurred since 1997. At
the same time in December 1999 (Kahma et al. 2003 ) and at the turn of 2004/2005
(Soomere et al. 2008a ) extremely rough seas occurred. The beaches in question may
be used for early detection of consequences of such changes.
Acknowledgements The chapter is based largely on two presentations to the 33rd International
Geological Congress, Oslo, 6-14 August 2008: “Sediment transport patterns and rapid estimates of
net loss of sediments for “almost equilibrium” beaches of tideless embayed coasts” by T. Soomere,
A. Kask, and T. Healy, and “Formation of sand deposits in Estonian coastal sea” by A. Kask,