Geoscience Reference
In-Depth Information
Chapter 13
On the Dynamics of “Almost Equilibrium”
Beaches in Semi-sheltered Bays Along
the Southern Coast of the Gulf of Finland
Tarmo Soomere and Terry Healy
†
Abstract
Beache
s
along the northern coast of Estonia form an interesting class of
almost equilibrium, bayhead beaches located in bays deeply cut into the mainland
in an essentially non-tidal, highly compartmentalised coastal landscape, and that
develop mostly under the influence of wave action. These beaches, although often
suffering from a certain sediment deficit, are stabilised by the postglacial land uplift.
We describe the basic features of their appearance and functioning from the view-
point of sediment transport processes. Wave action normally impacts a relatively
narrow nearshore band and additionally stabilises the beaches through littoral drift
of sandy sediment and gravel towards the bayheads. Eolian transport and fluvial
sediment supply have typically very modest magnitude. Such beaches, in general,
evolve quite slowly and may represent an almost equilibrium stage, even when the
active sand mass is very limited. The concept of the equilibrium beach profile is an
adequate tool for their analysis. As an example, its parameters and longshore trans-
port patterns are evaluated for Pirita Beach based on a granulometric survey and
long-term simulation of wave climate. It is demonstrated that net sand changes for
such beaches can be estimated directly from the properties of the equilibrium pro-
file, land uplift rate, and loss or gain of the dry beach area. Another type of highly
dynamic equilibrium exists owing to interplay of the effects of river flow and wave
action at the mouths of large rivers such as the Narva River.
Keywords
Beaches
·
Gulf of Finland
·
Baltic Sea
·
North Estonian coast
·
Sediment
transport
·
Almost equilibrium beaches
·
Equilibrium beach profile
·
Wave
climate
·
Sediment loss
