Magnetic Island North Queensland
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A young koala's beach adventure

June 11th 2010
The ongoing price of Nelly Bay Harbour

Nelly Bay erosion in January this year “This problem is a direct result of the building and design of Nelly Bay Harbour,” was how Townsville City Council's Environment and Sustainability Committee Chair,Cr Vern Veitch described the ongoing erosion which has eaten deeply into the beach foreshore and has been the subject of a Shoreline Erosion Management Plan (SEMP) which has been given preliminary approval by Council's Environment and Sustainability Committee.

“We need it (SEMP) to get funding from a higher level of government. It's a professional study which suggests solutions to erosion at Nelly Bay,” said Cr Veitch.

Developed in consultation with the Townsville Port Authority, DERM, the Department of Employment and Economic Development, GBRMPA and the Department of Transport and Main Roads; adoption of the plan by full council later this month would allow the city to proactively plan for and manage erosion into the future.

Magnetic Times attended an impromptu meeting on the beach last year, after king tides and a storm had gouged out another large section of Nelly Bay, in which Cr Veitch and Cr Trevor Roberts heard the concerns of residents. The SEMP was developed since that meeting and an option that was discussed then which has been further developed in the SEMP is the construction of a “training wall” or groyne which would run approximately 70m out from the beach and 30 to 40 metres parallel to and south of the present breakwater. No decision has been made as to what materials might be used for the training wall but sand-filled geotextile bags or concrete cubes are considered options.

The idea is to “place sand to create a stable beach orientation in a fillet of sand against the southern flank of the training wall”. Although subject to further consideration the sand is expected to be sourced from lower Gustav Creek.


The recommended shoreline Erosion Management Plan for Nelly Bay
(courtesy Coastal Engineering Solutions)


The training wall, would, theoretically, still allow the movement of water under the bridge joining the breakwater with the mainland but is expected to stop the sand making its way beneath the bridge and into the harbour. Sand from Gustav creek would still be required to be transported to Nelly Bay beach and costings in the SEMP put this at an ongoing $60,000 per year.

Cr Veitch, said, “The causes of the problem are twofold. The moved headland (Nelly Bay Breakwall) two thirds of the way along the beach creates an erosion cutting point. The other part of the problem is wave set-up. The water going in has to get out somewhere and it goes sideways along the beach through to the harbour and it takes sand with it..”

“The problem is a direct result of the building of Nelly Bay harbour. Whenever you put in hard infrastructure you will change the pattern of beach sand distribution.”

Cr Veitch's observations are in line with predictions made by James Cook University's Marine Modelling Unit which Magnetic Times', (then) journalist, Wendy Tubman reported in February 1999, before the the present development was started, “The marina has altered the pattern of beach sediment transport in Nelly Bay ... there is some evidence that sand has begun to build up along the southwestern edge of the main breakwater. Because waves that will move this sand toward the southwest away from the marina no longer exist, sand will probably continue to move toward the marina. This change in sediment movement characteristics may cause loss of sand on the beach towards the middle of Nelly Bay, several hundred metres southwest of the marina”.

The SEMP asks that Council decide on a “design event”: the level of storm they might wish to seek “immunity” from and set a minimum 1 in 50 year event as the basis for costings. They also requires a decision as to the line of defence – the line at which replenished sand should aim to hold the erosion to.

According to SEMP early estimates are that it would take $754,000 to protect against a 1 in 200 year event – the rating achieved by the storm in February 2009.

While not ruling out stone or concrete to be employed as part of the training wall, Cr Veitch was adamant that a rock wall along the beach was no solution. “Rocks do not stop erosion they just move it somewhere else. Rocks bounce energy they don't absorb it. It just takes bigger waves to move them and in severe storms rocks are just like bigger grains of sand,” he said, adding that Cyclone Ului achieved just this at the Mackay breakwater in March this year. Cr Veitch also claimed that the rockwall approach costs about $1 million per 10 metres of beach to construct.

“This agreement is not a quick fix, it represents a long-term commitment to addressing the underlying causes of beach erosion and an ongoing commitment to protecting these shorelines.”

Adoption of this plan will not prevent our beaches from being eroded but it puts in place a strategic and manageable plan to defend our coast,” Cr Veitch said.

Story and photo at top: George Hirst

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The ongoing price of Nelly Bay Harbour
 
2 comments
 
chasmac
June 11th 2010
Oh dear. You remember that supposedly funny quip about a camel being the result of a committee sitting down to design a horse? Cr Veitch and this committee and the professional consultant paid to advise it have seemingly identified the bleeding obvious: that the problem has arisen as a "..direct result of the building and design of Nelly Bay Harbour". Looking at the proposed engineering solution (another bloody breakwater invading a new section of the Marine Park - and only 70 metres long this time, as if...) it is clear that the Presto Breakwater, the Constitution Bridge and the harbour itself are all inviolate constructions that can never be altered for any reason. But why not?
You can see what's happened here. The committee members know there's a problem right at the Constitution Bridge itself. They know that the water area inside the main part of the harbour (not in the inner marina or Gustav Creek) is still part of the Great Barrier Reef Marine Park - so long as the breakwater is separated from the land as an island, along the line of Mean Low Water - this is the constitutional boundary between the State and the Commonwealth. Maintaining that watery separation and spanning it with a bridge upholds the contrived fiction of a legal settlement but forces both State and Commonwealth governments to concoct these convoluted arrangements which they then expect Local Government to hold in place. That contrived solution also creates the erosion problem which cannot be addressed whilst ever that bridge opening remains.
What the individual members of the committee have not done, on the face of it, is place on the table the agenda/s of the government agency they represent. No one is saying why they wish to "... still allow the movement of water under the bridge". Blind Freddie can see that the bridge opening serves absolutely no hydrodynamic function. It is not involved in 'flushing' the harbour or relieving floodwaters or some other tidal function. Clearly, if they just blocked the opening under the bridge forever the so called 'sand fillet' could build up against the actual breakwater and never be able to get inside the harbour. There would be no need to build a new groyne or 'training wall' (how much practice does an engineer need?), no need to create a new intrusion into the Marine Park outside the harbour and in particular, no need to make the Nelly Bay harbour an even bigger blot on the Magnetic Island landscape.
Any chance of some transparency here? Not likely. Just the prospect of a future obligation for ugly rock protection structures at $1m/ten metres. Another committee, another Magnetic Quays saga. Do we really need this?
 
Tonia
September 8th 2013
It's 14 years since I last visited Maggy. I am shocked by Nelly Bay and saddened. It is insensitive, ugly and juxtaposed to the essence of Maggy. I embrace progress in general, but this is poorly conceived and executed. Shame.


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