Pacific Harbour maintenance dredging, Bribie Island

Pacific Harbour maintenance dredging project - dotted blue area is the dredge area.

Why is the project required?

Sediments wash into canal estates through natural tidal and drainage processes and require periodic removal to maintain navigational safety. The process of removal is by dredging.

Council’s Canal Estates Portfolio Asset Management Plan (CEPAMP) defines how Council will maintain canals to ensure safe navigation and mooring of vessels. Canal depths in the lower reaches of the Pacific Harbour canals, particularly the lower Skippers Canal and the Marina, have reached the depths nominated in the estates Long Term Maintenance Plan (LTMP) so maintenance dredging is now required.

The maintenance dredging will ensure safe navigation and mooring within Pacific Harbour.

This is the first large-scale maintenance dredging project undertaken at Pacific Harbour by Council. Smaller-scale maintenance dredging, of less than 2,500 cubic metres, was previously undertaken in 2005/06, 2013 and 2016. 

How long will the dredging take?

The planned maintenance dredging project is expected to start in 2022 and is to take approximately six to eight months to complete.

Once completed, the next major maintenance dredging project will be required in approximately 10 to 20 years.

What is the dredged material?

Detailed sampling and analysis of sediments from the bottom of Pacific Harbour canals was completed in 2020. Tests found that the material is mainly very soft, dark grey marine clays and sand with occasional clays.

The material has been tested and assessed against the relevant guidelines and is suitable for land-based disposal.

How much material will be dredged?

Based on bathymetric surveys of the canals, approximately 60,000 to 80,000 cubic metres of sediment material needs to be removed from the dredging area.

How is the project funded?

The cost of maintenance dredging and spoil disposal is funded by the Pacific Harbour Canal Maintenance Special Charge levied by Council to the canal fronting rateable land within Pacific Harbour.

In March 2021 Council confirmed cutter suction dredging and transport of material by pipeline via Ningi Creek to the Ningi DMMF would be used for the project to avoid an estimated 8,000 round-trips by trucks on local and state roads. This method has also been used on a number of similar dredging projects around Australia.

The dredged material will be transported by a temporary, submerged pipeline across Pumicestone Passage and a short way up Ningi Creek. The temporary pipeline will have a diameter of approximately 300-400 mm and a total length of approximately seven kilometres. To help move the dredged sediment, three to five booster pumps will be used along the length of the pipeline. One booster pump is expected to be placed onshore near the entrance to Pacific Harbour and the others on small floating pontoons/barges. The booster pumps and pipeline will be temporarily secured in place for the duration of the project using anchors.

During the dredging campaign, residents may notice temporary impacts as detailed:

Park and boat ramp temporary closures

Part of Council’s Sunset Park, at the south of the Pacific Harbour entrance, may be temporarily closed to public access to allow for the placement and operation of a booster pump for the duration of the works. Additionally, the Turners Camp or Kal Ma Kuta Drive Park boat ramp and adjacent car parking areas may be temporarily closed to allow for the assembly and disassembly of the temporary pipeline.

No local boat ramps or boating facilities will be permanently closed for the duration of the dredging. 

Noise

There may be noise from the temporary pipeline booster pump stations. To minimise noise impacts, the pumps will:

• only operate during daylight hours (7:00 AM to 5:00 PM, Monday to Saturday)
• be positioned as far as reasonably possible from residents’ properties
• include effective noise suppression and/or noise screening devices (e.g. mufflers)
• be monitored by the dredging contractor.

Marine areas

There may be minor impacts to the Marine Park environment of Pumicestone Passage and Ningi Creek due to the temporary pipeline and booster pump stations. These impacts will be temporary and are expected to naturally recover. Impacts to natural marine environments will be minimised as much as possible. These include:

• disturbance of seagrasses and mangroves where the temporary pipeline and anchors rest on the seabed
• the risk of vessel strikes to marine fauna, which would be controlled by use of exclusion zones and marine megafauna spotters during marine works.

Navigation and public use of waterways

The pipeline will be submerged across Pumicestone Passage and along most or all of its alignment within Ningi Creek to minimise impacts to navigation and marine-based activities. The exception will be where the pipeline connects to booster pumps, which will be floating. To avoid the pipeline and booster pumps moving, they will be anchored in place.

Closures of parts of Pumicestone Passage to recreational boating activities may be required during installation and removal of the temporary pipeline and booster pumps. Once operational, an anchoring exclusion zone will apply around the temporary pipeline, with additional exclusions also likely around the booster pump stations. Any required partial closures and exclusion zones will be advised by Maritime Safety Queensland (MSQ).

Cultural heritage

Council will continue to engage with the Kabi Kabi Indigenous Traditional Owners during the project to identify and ensure protection of any cultural heritage values that may be impacted by the project.