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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.
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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 2004-09-24
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