Remediation of Piper Reef following the grounding of the Doric Chariot

On 29 July 2002 the 73,000 tonne Panamax class bulk carrier ‘Doric Chariot’ ran aground on the southeast side of Piper Reef in the Far Northern Section of the Great Barrier Reef Marine Park. The 225m long vessel was on route from Hay Point to India carrying 62,000 tonnes of coal, 375 tonnes of fuel oil and 37 tonnes of diesel. The ‘Doric Chariot’ was refloated nine days later without loss of fuel or cargo.

Piper Reef is an inshore reef in the Far Northern Section of the Great Barrier Reef Marine Park, situated 15 km off the mainland coast and over 600 km north of Cairns. Piper Reef supports a rich and relatively pristine ecosystem characterised by abundant marine life and high species diversity. The total cover of living benthic organisms ranged from 50-95 %, with hard coral mostly above 40% and up to 90% at some locations.

The physical impact of the vessel destroyed over 3500 m² of coral reef. Approximately 1000 m² of reef was pulverised and compacted under the weight of the vessel, resulting in a U-shaped gouge approximately 50 m long by 70 m wide and up to 5 m deep.

The hull of the ‘Doric Chariot’ had been antifouled with tributlytin-based (TBT) paint. As a result of the physical forces of the grounding event, TBT was smeared onto coral rock, reefal substrate and areas of hard surface sediments.

At the request of the Great Barrier Reef Marine Park Authority, the vessel owners, through their insurers, undertook clean up of contaminated sediments and remediation of the grounding site. The aim of the proposed works was to;

remove visible signs of antifoulant paint,
remove unconsolidated, loose and mobile sediment and rubble contaminated by TBT, and
stabilise the physical structure of the impact zone to restore biological functionality of the site.

Clean up of contaminated material and remediation of the physical structure of the reef occurred over a five-week period from 27 October to 30 November 2002.

Approximately 60 cubic metres of TBT contaminated sediment were removed from the impact site by divers vacumming sediment from the impacted area. Over 118 boulders ranging from <0.5m to 3.5m in size was used to create 32 constructed coral bommies. Broken pieces of coral resulting from the vessels impact were placed among the coral boulders in an effort to assist reattachment and recolonisation and to attract small coral associated fish to the constructed.

Overall, TBT concentrations at the site were unchanged following remedaitaion however the number of visible fragments were greatly reduced.

A key requirement of the remediation program was the implementation of a long term monitoring program to be established to test the efficacy of the clean-up effort and to document the recovery at the damaged site. The program will provide important information about the process and rate of recovery of the reef community and provide visual documentation of the recovery process. In the long term, results from the monitoring program will contribute to refinements of future grounding remediation programs while maximising environmental outcomes and minimising costs.