Port Phillip Conservation Council Inc.

A0020093K Victoria    ABN 46 291 176 191   Founded in 1970

 

 

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Port Phillip Bay Environmental Study 1996 - Final Report: CSIRO

 

 

Click on a blue hyperlink of interest.

 

 

Selected sections of the above study can be viewed using the hyperlinks below:


Some of the pages from Page 19 to Page 51


Some of the pages from Page 52 to Page 62

 

Some of the pages from Page 63 to Page 76

 

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