Arguments against development of the proposed canal estate in Ralphs Bay

The proposed development cannot be described as environmentally sustainable in the light of these short, medium and long term impacts on the water quality of Ralphs Bay and its parent water body, the Derwent River, and the flow-on effects to marine life, the aquaculture industry and public health.

Quotes (in red) and page references are taken from the the Lauderdale Quay Draft Integrated Impact Statement its appenices, its appenices or its Executive Summary

• The mudflat / sandflat ecosystem plays a complex and vital role in moderating water quality especially through the nitrogen cycle. Loss of this ecosystem would impact adversly on water quality,

• Possible impact from acid sulfate soils (ASS).

•   Resuspension of Ralphs Bay sediments as a result of the initial construction process and ongoing dredging to keep waterways open would result in increasing turbidity, and distribution of highly toxic heavy metals (lead, zinc, mercury, cadmium, copper) throughout the water column. This would threaten:
  • marine life in Ralphs Bay and its parent water body, the River Derwent (especially the critically endangered Spotted Handfish)
  • the aquaculture industry, if the heavy metals spread around the South Arm peninsula to Pipeclay Lagoon

Here are some concerning and conflicting findings on heavy metals from Appendix M4 Water and Sediment Quality of the Draft Integrated Impact Statement:

"Arsenic levels are at some sites marginally above ANZECC guideline levels." Appendix M4 of the DIIS, Water and Sediment Quality, Section 4.2.2 and
" Zinc levels are consistently above ANZECC guideline levels." Appendix M4 of the DIIS, Water and Sediment Quality, Section 4.2.3.
However there is no mention of arsnic in the summary statement on water quality: "The water quality of Ralphs Bay exhibits slightly elevated nutrients and elevated zinc levels,.." Appendix M4 of the DIIS, Water and Sediment Quality Summary, piii.

"Mercury was detected above screening [acceptable] levels in 6 of 152 core samples". Appendix M4 of the DIIS, Water and Sediment Quality, Section 4.2.

"Nickel was detected above screening [acceptable] levels in 17 of 155 samples." Appendix M4 of the DIIS, Water and Sediment Quality, Section 4.2.

• More conflicting statements on zinc levels; from Appendix M4 of the DIIS, Water and Sediment Quality.

In the Summary we read: "all metals in the bed and sub-bed sediments of Ralphs Bay fall underneath ANZECC (2000) guidelines for the 95% upper confidence limits, though slightly elevated levels of mercury and nickel were detected." Appendix M4 of the DIIS, Water and Sediment Quality, Summary, piii.

While in Section 4.4 a conflicting statement tells us there are: "...elevated zinc levels in sediments across Racecourse Flats..." Appendix M4 of the DIIS, Water and Sediment Quality, Section 4.4

• And on the risk of zinc leaching; from Appendix M4 of the DIIS, Water and Sediment Quality.

We find in the Summary: "Sediments in Racecourse Flats contain high levels of zinc, however the overall risk of metals leaching to the water column ...... is low" Appendix M4 of the DIIS, Water and Sediment Quality, Summary, piii.

but in Section 4.2: "In relation to bed sediments in Ralphs Bay, a preliminary investigation was completed by Lois Koehnken in January 2007. That study concluded that all but one surface sediment sample tested met ANZECC guidelines, with cadmium levels slightly exceeded at the one site, and that arsenic, lead and zinc were the metals that were more susceptible to mobilization through leaching." Appendix M4 of the DIIS, Water and Sediment Quality, Section 4.2.

• Possible petrochemical pollution into Ralphs Bay as a result of the presence of heavy trucks and vehicles working in the bay itself, during the extended construction phase.

• Possible pollution in Ralphs Bay as a result of a wide range of building materials used during construction.

• Runoff from gardens, roads and driveways in the proposed development, directly into Ralphs Bay could introduce fertilizers, pesticides, petrochemicals, dog faeces, general rubbish into the water.

• possiblilty of antifoulants, paint and fuel spills from the marina and moorings.

• Interruption of existing patterns of water movement in Ralphs Bay.

• The potential for poor flushing of the canals in the canal estate, partly because the proposed Ralphs Bay development is “back to front” in the sense that the prevailing strong winds would push polluted water from the canal estate back to the landward edge of the bay, instead of encouraging flushing towards the open sea. Poor flushing leads to the buildup of turbid, anoxic, polluted water in the canals, and frequently results in algal blooms and the buildup of other nuisance species (eg thick encrustations of tubeworms on underwater pilings).