About the Dredging

Plans are for Port Otago’s ‘Next generation Project’ to dispose of up to 7.2 million cubic metres of dredged material from the inner Otago Harbour to deepen the channel to allow supersized cargo ships to berth at Port Chalmers. A new Wharf is also being constructed.

The disposal sites are at the current maintenance dredging sites at Heywards Point, The Spit and Shelly Beach, and a new site called AO situated 6.3 kilometres off the coast of Taiaroa Heads.

Extensive modelling has been made of the Environmental effects of dredged material on the marine ecology and sediment transport at the AO site. The surfing collective have been advised that effects from the proposed dredging will have virtually no impact on the surfing environment apart from a reduction in wave height by .01 of a metre because of the deeper channel at the heads.

Changes proposed from current disposal of maintenance dredging of up to 450,000 m3 a year to be spread between Heywards Point, The Spit (Aramoana Beach) and Shelley Beach, to the allowance of material dredged as part of Project Next Generation to be disposed of at these existing sites.

The Port Otago owned dredges, the New Era and the Vulcan, that currently carry out the maintenance dredging will step up operation from 48 hours per week to a 24/7 operation.  They will deepen the swinging area at Port Chalmers to a depth of 6m and widen the bends along the channel. Up to 100,000m3 of rock will be blasted from Acheron Head and Rocky Point to be used for foundations of the new wharf, the balance being dumped at Heywards Point.  We are told that up to 100,000m3 will be divided between the two existing disposal grounds. The Port Otago dredges are at most times unable to carry dredged material to the proposed dump site AO which is 6.3 ks off the coast of Taiaroa Heads. So ongoing dredging of Project Next Generation will use the existing dump sites until the much larger contract dredge is commissioned to complete the work and dump the remaining spill at the AO site 6.3 ks off the coast.

The Larger international dredge will NOT be commissioned until the large shipping companies have given the go ahead for their supersized ships to service Port Otago. No official decision has been made yet for them to do so, this decision will be dependant on the global economic climate and demand. This decision is expected to take from between 2 years to 15 years. In the mean time Port Otago is preparing the channel as far as possible to make ready for the tentatively expected event.

So at best there will be a period of 3 years of maximum capactiy dumping (450,000m3) at the existing disposal sites at Heywards Point and The Spit. (only minimal amounts are allowed at Shelley Beach)

Potential effects of PNG on surfing recreational values have been considered… The model results show no evidence to the wave environment at the shoreline, and (p91) Assesment of Environmental Effects: “there is no evidence that the changes would be detrimental to surfing conditions or give rise to adverse coastal change.” (p103) – “ NO noticible effect on surfing conditions” “Studies show effects negligible on physical coastal environment” (p136) “ The Surfing and Swimming environment along the Otago Coast will remain unchanged in giving effect to this proposal” “Patterns of beach response will stay the same”

Unfortunately these modelled results are from the AO dump site 6.3ks offshore, and are NOT based on the cumulative effect of AO and the existing dump sites at Heywards Point and The Spit, which could be potentially receiving dredged spoil for up to 12+ years at maximum capacity of 450,000m3.


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