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 265

Natural supplies of sand to the beach originate from the Pirita River, littoral trans-
port along the western coast of Viimsi Peninsula, and sporadic erosion of sand from
a glacial till scarp at the northern end of the sandy sector as well as from the dunes
of the middle and the northern part of the beach (Soomere et al. 2007 ) . All these
sources have undergone major changes within the twentieth century. The construc-
tion of a small jetty out to about 3 m water depth in 1925-1927 just to the north of
the beach diminished the transport of coarser sediments. The quays of Miiduranna
Port, commenced in the 1970s, extend out to the natural depth of 6-8 m and almost
completely block wave-induced alongshore sediment transport. At the turn of the
millennium the depth of its fairway was dredged to 13 m. This blocking subse-
quently leads to sediment deficit and relatively fast erosion southwards from these
constructions.
The supply of fluvial sediments by the Pirita River (about 400 m 3 /year in the
past, Lutt and Kask 1992 ) is entirely blocked by the Olympic sailing harbour
that was built in the mid-1970s and today acts as a settling basin. A revetment
from granite stones was constructed along the dune toe in the 1980s to protect
dunes in the northern sections of Pirita Beach against erosion. The till scarp that
was subjected to direct wave action under storm surge conditions and also sup-
plied a certain amount of sand was protected by a new seawall in 2006-2007
(Soomere et al. 2007 , 2008b ) . There have been several attempts to increase the
active sand mass of the beach starting from the late 1950s by pumping sediments
from the river mouth to different sections of the beach. The joint effect of all the
human activities led not only to blocking of the major supplies of coarser sand
of relatively high recreational value but also to a gradual decrease of the beach
dominant grain size owing to the potential misbalance of the supply of different
fractions.
On the other hand, Pirita Harbour blocks the lateral sand loss from the beach.
The beach profile, therefore, should be relatively stable and the concept of the
equilibrium beach profile is accordingly an appropriate tool for its analysis.
The vicinity of the Narva River mouth that also hosts Narva-Jõesuu Beach
(Fig. 13.6 ) serves as an example of a littoral system that is completely open to the
Gulf of Finland. This river is the largest in Estonia. Its long-term mean volume dis-
charge is around 400 m 3 /s (Protasjeva and Eipre 1972 ) whereas considerably (up
to two times as large) larger monthly values occur during spring floods. The bay is
mostly sandy at the coast and is open to the dominating winds (Laanearu and Lips
2003 ) . The river mouth area therefore is an interaction zone between wave- and
current-induced sand motions.
According to the classification of Wright ( 1985 ) , the Narva River mouth belongs
to the Senegal type characterised by high wave energy, strong littoral drift, and rela-
tively steep offshore shoaling slope. The presence of littoral drift commonly results
in the formation of a submerged sand bar (sill) that gradually moves in the pre-
vailing direction of the littoral drift. The bar forces the river flow to bend in the
same direction and occasionally (for example, when the river flow is weak) it cre-
ates inconvenience by initiating flooding of the river delta or hindering navigation
(Carter 2002 ) . Indeed, the sand bar in the Narva River mouth presents a highly