Continuing to dump dredged spoil from Otago Harbour's shipping channel at existing sites will not negatively affect the protected nationally significant surfing breaks at Aramoana and Whareakeake, Port Otago specialists say.
An Otago Regional Council hearing of Port Otago's application for a three-year renewal of its consent to dispose of 450,000cu m of spoil per year from maintenance and incremental capital dredging of the harbour to sites at Heyward Point, Aramoana Spit and Shelly Beach is being heard by an independent panel in Dunedin this week.
The consent was opposed by five out of eight submissions, mostly from people wanting to protect the nationally significant surf breaks near the dump sites.
Counsel Len Andersen, for Port Otago, said a short-term application had been applied for so the company could find the best long-term solution for the disposal of spoil. A longer-term consent would then be applied for.
For the renewal, Port Otago had agreed to change the ratios of deposits at two sites so no more than 350,000cu m was dumped at Heyward Point, up from the present 200,000cu m, and up to 50,000cu m would be discharged at Aramoana spit. Fifty thousand cubic metres would also be deposited at Shelly Beach.
Port general manager infrastructure Lincoln Coe said a range of consultant groups would be set up as part of the company's New Generation project after channel-deepening consents were granted late last year. Until the capital dredging began, it proposed continuing with its existing working party but would add a surfing representative, he said.
Coastal specialist Dr Martin Single said there was no evidence of any adverse effects from the disposal of dredged sediment at the Shelly, Aramoana and Heyward Point beach sites. Surveys of the beaches showed they were healthy, he said.
Dr Single considered that there were beneficial effects to Shelly and Aramoana Beaches because the dredged sediment provided extra sand and reduced erosion of the dunes.
Dredge spoil placement appeared to be lessening the erosion by supplying sediment to the general area next to the Heyward disposal site, he said.
The proposed conditions provided ongoing assessment of effects and provided for adaptive management.
Benthic (sea floor) ecologist Dr Brian Paavo said, from the research he had been involved in, he considered the continued disposal of dredging material, of the quantity and quality so far, was not expected to have ''onerous deleterious ecological effects'' on the sea floor environment for the short duration of the consent.
Physical oceanographer Dr Peter McComb said a detailed analysis of the surfing wave dynamics had been undertaken.
The presence of the offshore bar and dredged channel was the main feature creating the unique surf conditions at Aramoana. The spit ''mound'' had a secondary, modifying effect.
The proposed deposit at Shelly Beach was not expected to produce outcomes different from those in the past 10 years, he said.
Depositing similar amounts at the spit ground was not expected to result in long-term effects on the sedimentary environment of Aramoana Beach.
''This region has the capacity to absorb this volume and cumulative negative impacts over the long term are not anticipated.''
Some short-term effects on the surfing wave climate were expected but would not be dissimilar to the effects experienced in the past 10 years as both surf breaks had been influenced by port activities for many years, he said.
The Heyward Point deposits had the potential to alter the ''wave-focusing effect'' within the dominant swell corridor to the Whareakeake surf break.
Judicious placement of spoil on the deeper parts of the ground could be used to minimise effects, he said.
Planner Mary O'Gallahan said the proposed monitoring work was expected to result in a better understanding of the relationship between disposal and ''surfability'' and help develop a management plan which minimised any long-term negative effects on the surf breaks.
The conditions of the consent provided appropriate safeguards in the event the effects on surf quality were to change in the future, she said.
''A sustainable approach needs to take into account the economic benefits of the proposal as well as the potential effects on surf quality.''
The hearing continues today.
Day 1
Where: Southern Cross, Dunedin.
Application: Three-year renewal of consent to dispose of dredged spoil at three sites.
Independent hearing panel: John Lumsden (chairman), Mike Johnston, Martin Ward.
Evidence: Port Otago, counsel Len Andersen, general manager infrastructure Lincoln Coe, coastal geographer Dr Martin Single, marine benthic ecologist Dr Brian Paavo, physical oceanographer Peter McComb and planner Mary O'Callahan.
