In December 2005, North Queensland Water completed installation of a new six point eight kilometre potable water submarine pipeline from Pallarenda Beach to Magnetic Island through the Great Barrier Reef Marine Park.

The old pipeline, originally constructed in the mid 1970s was in need of replacement due to increasing maintenance costs and forecast water supply requirements. The new pipeline is expected to supply fresh water to Magnetic Island residents for 30-50 years.

Sensitive Environments

The pipeline was installed through a range of environments of varying ecological sensitivity including sandy beach, seagrass meadows, silty clay seafloor, coral reef slope, reef and mud flat and mangrove communities. Additionally, the pipeline works were located near Middle Reef and Virago shoals in Cleveland Bay.

Sediments produced during trenching and pipe laying may pose a risk to seagrass meadows and reef areas through increased turbidity and deposition of sediments. The primary environmental objective was to minimise suspended sediments impinging on the sensitive environments near the works.

Pipe laying methods

The installation method through the dunes, intertidal area at Pallarenda and Magnetic Island reef flat utilised backhoes and excavators.

The main method of pipeline installation through the sub-tidal area in West Channel was by means of a pipe laying barge known as a ‘lay-barge’ incorporating an anchor block assembly platform.

The lay-barge and jetty-in system were effective at keeping turbidity and sedimentation to a minimum during construction and ensured the trenching through the channel was completed quickly.

Environmental monitoring programme

PallarendaNQWater1Trigger levels for turbidity were used to manage installation works in the sensitive areas. Baseline nephelometer readings were used to establish agreed trigger levels and measured in Nephelometric Turbidity Units (NTU) to provide weekly readings throughout the project. Trigger levels were set at 60 NTU, 100 NTU above 10 knots; 30 and 50 NTU below 10 knots dependant on weather conditions and measured at 300 metres from the pipeline installation point. Daily reactive monitoring was undertaken with hand held instruments.

Following several weeks of scientific monitoring under a range of environmental conditions, the data showed that turbidity and plume generation was minimal and not impacting on sensitive environments. Measurements taken of plumes during the works were generally within 5 NTU of background turbidity levels. Slightly increased turbidity levels, arising from the anchor movements for the lay barge, were detected during the monitoring. The structure of the approvals allowed for a review of the programme followed by the scaling back of scientific field monitoring requirements.

Internal environmental site supervision

Full-time independent supervision of this project was not considered necessary. Instead Queensland Parks and Wildlife (QPWS) and the Great Barrier Reef Marine Park Authority (GBRMPA) officers shared the role of targeted Environmental Site Supervision. Officers would oversee key parts of the installation to ensure the project was progressing as predicted, and would remain on call if needed to review any part of the works.

Adaptive management

Adaptive management principals allowed greater flexibility and responsiveness in all phases of the project. For example, a comprehensive program of water quality monitoring was required during the ‘jetting-in’ of the pipeline within the channel to ensure seagrass beds and reef areas were protected during the installation.

The ability for Agency staff to have close interaction with the client’s managers and administrators as well as the engineers, scientific team and construction workers on the ground, resulted in an ability to rapidly approve project modifications as necessary. A good example of this occurred during changes to the initial construction contractor, following commencement of in-water works.

Partnerships

This project represented a successful joint management effort between Queensland Parks and Wildlife (QPWS) and the Great Barrier Reef Marine Park Authority and other local and state government agencies.

The two main agencies adopted an adaptive and responsive management approach throughout all the phases of the project including the environment impact assessment, permit, Construction Environmental Management Plan (CEMP) , monitoring programme and installation of the pipeline, all of which required logistical, design and engineering changes to the project. The interactive role of government in the initial review, development, assessment, approval and field supervision of this project was integral to its successful completion.