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Hong Kong's waters are characterised by the interaction of oceanic and
estuarine water masses which vary in relative effect throughout the year.
The variable freshwater discharge from the Pearl River has a marked influence
on Hong Kong waters.
During the summer, an oceanic flow from the south-west
to the north-east brings the warm, high-salinity water of the Hainan Current
into Hong Kong waters. This interacts with fresh water from the Pearl
River and divides Hong Kong into three distinct zones. In the west, where
the fresh water influence is greatest, the environment is estuarine and
the water is brackish. In the east, the water is mainly oceanic with relatively
minor dilution from rainfall and runoff from streams. The limits of the
central transitional zone vary depending upon the relative influence of
Pearl River water and marine currents.
During the winter dry season, the Kuroshio oceanic
current brings warm water of high salinity from the Pacific through the
Luzon Strait. The freshwater discharge of the Pearl River is much lower
than in the summer and salinity is more uniform across Hong Kong. The
coastal Taiwan current also brings cold water from the north-east down
the South China coast, affecting inshore waters.
The normal tidal range in Hong Kong waters is between
one and two metres, depending on the relative influence of the moon and
sun. The tidal pattern is complex due to the relative effects of the diurnal
and semi-diurnal components. The basic pattern during flood tides is for
oceanic water to flow north into Mirs Bay and west through Lei Yue Mun
into Victoria Harbour and through Kap Shui Mun and the Ma Wan Channel.
This flow is reversed during the ebb tide. Maximum tidal currents generally
range from 0.5 to 1.5 knots, peaking at up to five knots in narrow channels. |
