In 1978 Portsmouth Dr was opened, marking the completion of the Otago Harbour Board’s Southern Endowment reclamation project.
For decades before that, millions of cubic metres of saturated sediments were dredged from the upper harbour and pumped ashore as slurry into the area now roughly bounded by Andersons Bay Rd and Portsmouth Dr.
Those sediments began as water-logged sands. Over time they were drained, consolidated and stabilised. Today what was once harbour floor is now ordinary, functional land.
The proposed Tailings Storage Facility (TSF) at Santana’s Bendigo-Ophir project would also receive material as slurry.
Harbour reclamation material and gold tailings are not the same thing, but the underlying engineering principle of hydraulic deposition followed by progressive drainage and consolidation is well established in New Zealand and internationally.
Over the life of the mine, tailings would be deposited in stages and progressively dewatered. Like all large tailings facilities, the highest level of engineering scrutiny applies during the operational phase, when water is present and embankments are being raised.
Modern designs rely on staged construction, conservative slope geometry, internal drainage and continuous monitoring. These are precisely the aspects that deserve careful, independent oversight.
A recurring theme in articles written in opposition to the mine is that the mere presence of hazardous material in a sensitive Central Otago environment is too risky and should render the project unacceptable.
That position, however, is not consistent with how we manage risk in other sectors. For example, in Dunedin, up to 45million litres of diesel and petrol are stored adjacent to the open waters of Otago Harbour.
These facilities are not considered unacceptable simply because failure would be serious; they are permitted because the risk is actively reduced through engineering and management measures.
Similar engineering rigour will be applied to Santana’s tailings storage facility.
On mine closure, the tailings storage facility is proposed to be capped with up to 1.5m of waste rock, covered with soil and planted in native vegetation. By that stage, free water is intended to have been removed and the deposited material consolidated. The end state is designed to function as an engineered landform rather than an active slurry pond.
The fast-track application documentation is publicly available.
The documents indicate the front embankment (dam) of the TSF would reach about 100m in height with a base width of roughly 400m — a broad, pyramid-shaped engineered earth and rockfill structure rather than a narrow retaining wall.
On the downslope side of the dam, an Engineered Landform would form a substantial rockfill buttress extending for more than a kilometre and, in places, up to 200m deep. This mass of rock is intended to provide long-term stability and integrate the structure into the surrounding terrain once rehabilitated.
These are large dimensions. A structure of that scale demands conservative design, independent review and ongoing regulation. But scale alone does not determine safety; engineering methods and oversight do.
Central Otago is no stranger to engineered landscapes. Developments such as Jack’s Point, The Hills and Millbrook — all within Outstanding Natural Landscapes — have involved the movement of very large volumes of material to reshape terrain for residential and recreational purposes.
Those projects are not equivalent to a tailings facility, nor are their risks similar. The comparison is not about hazard, but about consistency: as a region, Central Otago has repeatedly accepted significant and permanent landform modification where wider benefits are considered sufficient.
Mining, like viticulture, dairying, hydro-electric power generation, tourism infrastructure and urban expansion, alters the landscape permanently.
Through this lens, claims that Central Otago is a region of pristine and untouched landscapes do not stand up to close scrutiny. The question is not whether change occurs, but whether it is responsibly engineered, transparently regulated and proportionate to the benefits delivered.
The Bendigo-Ophir proposal should be examined rigorously. Operational-phase risk, seismic performance and long-term water management are legitimate matters for scrutiny.
But discussion is best grounded in engineering reality rather than imagery. By closure, the TSF is intended to be a compacted, capped and vegetated landform subject to ongoing management — not an abandoned pond of untreated slurry.
Central Otago’s history shows that developers are capable of reshaping land carefully and living with those decisions for generations.
The challenge now is to assess Santana’s proposal on evidence, not assumption — applying the same standards of proportionality, consistency and technical rigour expected of any major development in the region.
- Steve Munro has a background in physical earth sciences. He has no financial interest in the Santana project.
