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Saline
coastal lagoons have entrances to the sea which intermittently open and
close. They are estuaries that became separated from the ocean when
sediments in the entrance area were moved and redistributed by wind, wave
and tidal forces to form a barrier. Factors affecting the hydrodynamic
features of these lagoons are the coastal location and exposure; entrance
location and width; climate; size and shape; the size and nature of their
catchments; as well as the frequency of flooding and number and size of
the artificial and natural openings to the sea, the tidal range, and the
extent of percolation to the sea (NSW Fisheries 1998a).
Unlike
tidal estuaries, salinity changes typically occur slowly, over weeks or
months, rather than twice a day (tidally). They are also influenced
markedly by rainfall and dry periods, the latter often resulting in
salinities higher than normal seawater.
In
NSW, about 45% of major estuaries are intermittently opening coastal
lagoons (NSW Fisheries 1998a). Formation and breakdown of a barrier may
occur frequently (e.g., 5-6 times per year in Dee Why Lagoon) or
infrequently (e.g., 2-3 times per century in Lake Conjola). Around half
the NSW coastal lagoons have their entrances artificially breached from
time to time.
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