Launching and Towing of the Deep Sea Release Pipe
A Deep Sea Release pipeline was constructed off Boambee Beach as part of the city's $170 million Sewerage Strategy.
The 1.5km pipeline is used to release excess reclaimed water into the ocean. The pipe is buried under the beach and out through the surf zone. The seaward section of the pipe sits on the seabed floor. At its deepest, the pipe is 20 metres below sea level.
The Operation
The first section of seaward pipe was successfully towed out of the harbour on 26 June 2004 and sunk onto the seabed off Boambee Beach.
Three tugboats towed the 360m pipeline around to the temporary trestle off Boambee Beach. A dredger had previously created a 150m trench for the pipe off the end of the trestle. The first section of pipeline was slowly sunk into this trench in a procedure which took about eight hours.
On 27 August 2004, the remaining two pipeline sections were joined underwater in the harbour before they were also towed by tugs to their final destination off the Boambee Beach temporary trestle.
The gap between the existing sunken pipe and the newly sunken pipe was then measured by divers. The measurements were sent to Melbourne where a connector, or make-up piece, was cut and welded to size. This was installed on 11 September, marking the end of the project to lay the seward pipeline.
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Above: The pipe being positioned in the harbour and the underwater jointing operation taking place, August 2004.
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Background
The operation had previously been delayed by damage to the pipes and equipment caused by adverse weather conditions.
< The launch of the first 360-metre pipe string on 6 February 2004
The pipe for the seaward section of the Deep Sea Release was joined into 84 metre lengths at the Corambirra compound. In the first week of February 2004, the three 360-metre pipe strings were anchored at temporary moorings in the harbour.
Sea Damage
Unfortunately, sea conditions prevented the next stage of the operation taking place as soon as scheduled.
Huge swells on the nights of 25 and 26 February subsequently caused two of the pipes to break free and float, undamaged, onto Jetty Beach. The third pipe string was then sunk onto the harbour seabed to protect it while preparations to complete the operation were finalised.
DSR Sunken Pipe Warning Notice March 2004
Sea anchors mooring the project's crane barge broke in six metre swells. The barge sustained damage and partially sank > |
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The tail end of cyclonic weather conditions off southern Queensland caused 6 metre swells in the harbour on the night of 5 March. Three of the five anchors mooring the Deep Sea Release crane barge (which is to be used to pick up the pipelines and join them together) broke and the barge partially sank after sustaining damage.
< The barge is being dismantled
Two-metre sea swells caused the barge to sustain further damage during the night of 22 March. The barge's owner, Barclay Mowlem Candac, and its insurers decided that the damage was so extensive that it would have to be dismantled. Work began on dismantling the barge on 9 August 2004 and took several months.
The pipes were removed from the beach using excavators, April 2004> |
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Meanwhile, four heavy lifting excavators were brought in to remove the two pipeline sections off Jetty Beach. Slings were placed under the pipes and the excavators progressively moved them, one by one, towards the waterline. The last pipe was refloated and sunk onto the harbour seabed to protect it on 21 April 2004.
Favourable weather and sea conditions allowed the first pipeline section to be raised on 26 June, towed to Boambee Beach and sunk on the deep sea release alignment.
