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CHAPTER
1: Port Phillip Bay
- Port Phillip Bay was
discovered by Lieutenant John Murray RN, in the
'Lady Nelson' on 5th January 1802.
- In October1803 an
exploration party under the leadership of
Lieutenant-Colonel Collins (later
Lieutenant-Governor of Van Diemen's Land) arrived
in HMS 'Calcutta'. Their mission was to examine
the potential for establishing a penal colony, but
unfavourable reports from the shore parties led
Collins to declare the place unsuitable for
settlement.
- The first European
settlement, apart from the ill-fated Sorrento
venture, which provided only one permanent
resident, the escaped convict William Buckley, had
to await the arrival of John Batman on the present
site of Melbourne in 1834.
- Port Phillip Bay is a large
marine embayment about 1,930 km2 in area and with a
coastline length of 264 km. It originated about
8,000 years BP (before the present) when eustatic
rise in sea level following an end the the last
ice age resulted in flooding of the delta of the
Yarra, Werribee and Little Rivers and Kororoit
Creek.
- The Bay is extremely
shallow for its size. The deepest portion is only
24 m, and half the volume is in waters shallower
than 8 m. The total volume of water in the Bay is
about 26 km3.
- The land catchment area
of the Bay is 9,790 km2, which consists of 21
natural drainage basins. Of these, only eight
deliver runoff directly to the Bay. Of the
remainder, six contribute diffuse runoff through
drains and seven contribute runoff to the Yarra
River.
- About three million
people live and work in the catchments, most of
them in Melbourne, which occupies the lower
reaches of the Yarra and Maribyrnong Rivers and
Moonee Ponds and Merri Creeks.
- Despite the large
population concentration, only 11% of the
catchment area is urbanized. However, the urban
runoff to the Bay is highly significant in its
contributions of nutrients, heavy metals like zinc
and lead and some organic contaminants such as
petroleum oils and industrial chemicals.
- That part of the
catchment utilized for agriculture and
horticulture provides major inputs of suspended
matter, nutrients and biocides, and some fixed
nitrogen derives from forested catchments.
- The Bay is also, of
course, the means of access to the Ports of
Melbourne and Geelong. Each year about 2,500 ships
cross the Bay to the Port of Melbourne, and 350 to
the Port of Geelong.
- Total shipping amounts
to 35,000,000 gross registered tonnes a year with
an average vessel size of 10,000 tonnes. This
traffic handles cargo worth $28,000,000,000 a year
through the Port of Melbourne. The port industry
involves 677 firms, 8,200 employees and an annual
turnover of $975,000,000.
- A significant use of the
Bay is the disposal of more than 400 megalitres a
day of treated sewage effluent from the Melbourne
Water Western Treatment Plant at Werribee. This
effluent contains large loads of nitrogen and
phosphorus, and much lesser loads of common
pollutants.
-
CHAPTER
3: The state of knowledge in 1992
- A mean tidal amplitude
of 0.4 m at Point Lonsdale falls to 0.2 m at
Williamstown. Correspondingly, maximum ebb and
flood velocities of 1 m/s or more at The Rip
decline to 0.05 m/s in the centre of the Bay, and
only 0.02 m/s in the north of the Bay.
- The average
tidal prism is 1 km3, and this was assumed
exchanged based on the proportion of drogues lost
to Bass Strait on the ebb. This would imply a
flushing time of 28 to 50 tidal cycles.
Calculations from solute inputs and Bay levels
give a flushing time range of 12-16 months or 700
to 1,000 tidal cycles. This poor real exchange
ratio of 0,035 is due to restriction of mixing
over the Great Sands.
- Most suspended matter is
inorganic and of the organic content only a small
proportion is living material. Total suspended
matter ranges from 2 to 30 mg/L whereas suspended
organic carbon levels are mainly 0.5 mg/L or less.
Only 20% or less of the latter is attributable to
living cells.
CHAPTER
7: Overview and Recommendations
Ecology
Recommendation
1.
The benthos are a vitally important component of the
Bay ecosystem. To protect the biodiversity of the
benthos and its key role in ecosystem function,
habitat destruction must be reduced to a minimum.
The effects of fishing, dredging and coastal
engineering on seagrasses and the benthos must be
minimized and should be closely monitored. The
disposal of dredged spoil must be confined to as
small an area as possible.
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Last
updated on 2016-04-21
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