Emu Bay boat ramp construction material justified

Kangaroo Island councillor and retired engineer Ken Liu has questioned the use of limestone in the construction of the Emu Bay boat ramp upgrade.

Limestone is relatively soft, did not bind together well and would not stand up to constant erosion and wave action of an open ocean location such as at Emu Bay, Cr Liu said.

“My concern is the structural integrity and safety of the boating public,” he said. “I have always thought we should have built a breakwater around the existing structure first and then done the upgrade of the actual ramp second.” 

KI Council CEO Andrew Boardman however said that while the initial specification was to use harder igneous rockfor the rock armour elements of the new boat ramp, it was later deemed that more plentiful limestone would be sufficient and would present a better “whole-of-life cost outcome”.

Mr Boardman said harder rock of the size consistency required was not available in the area and, while the igneous rock that was available on the island was very hard, it was also was brittle and difficult to produce in sizes consistent with the specification for the rock armour.

He acknowledged that the limestone rock armour might need supplementing in 20 or 30 years, but this was no different than at the island’s other ramps at Bay of Shoals and American River, where limestone was also used, despite the specification originally calling for igneous rock there as well.

The council had sent samples of the limestone off to a laboratory to have a suite of standard tests carried out including a chemical decomposition test to demonstrate the rocks suitability for purpose. These results are expected back by the end of this month.

Mr Boardman said the construction was proceeding at a faster pace with the contractor now building the walls of the temporary coffer dam that will enclose the ramp area and allow new concrete to be poured.

The contractor was still hoping to have the ramp complete by the end of October, start of November. The temporary side launching area that had been open during construction was now closed.

The ramp upgrade had originally been budgeted at $1.9 million with a commitment from the Minister for Transport, on advice from the SA Boating Facilities Advisory Committee, to meet up to 50 per cent of that cost or $950,000.

The tenders came in lower than budget with a gross project cost, including a project contingency sum, of $1.6 million and the council wrote to the minister seeking a higher percentage contribution towards the project offset with a lower overall cost to the State to assist in minimising the  the council’s contribution to the overall cost of the project.

As part of their election commitments, the Liberal Party stated that they would be looking to fund regional projects to a higher level of 80 per cent of ramp projects and Mr Boardman said the council had contacted the committee to confirm its position in light of this. The council is yet to receive a response.

The council has also been questioned on what size of boats would be able to use the new boat ramp and Mr Boardman said the ramp had specifically designed as a recreational boating facility for vessels up to 1 tonne.

Given the ramp comprises two separate ramps of 4m and 8m, the larger ramp has the capability to be used by significantly larger commercial vessels under permit from the council.

The council will assess each application on its merits once it understands the weight of boat and trailer, configuration of trailer and likely frequency of launching.

There was also the issue of how rough seas will impact the ramp that currently was deemed a “fair-weather ramp”.

 Mr Boardman said the two jetties extending out on either side of the new 8-metre and 4-metre wide ramps would feature wave attenuation boards that would minimize the impact of all waves coming in at an angle, except those coming in at 90 degrees to the ramp.

The council is researching options for floating “swell-breakers” which could be moored directly in front of the ramp to reduce the impact of swell,  similar to those used at other ramps or harbours around South Australia, including Port Lincoln. 

These devices consisted of large plastic pipes, some flooded, some empty, lashed together and moored to the seafloor, floating perpendicular to the shore and ramp. 

Deputy mayor and boating facilities committee member Larry Turner had checked out the use of these devices at two locations elsewhere in South Australia and had reported his views back to the committee.

Mr Boardman said that he was hopeful of the capability to fund something like this from uncommitted project contingency funds and the opportunity for this would be evaluated closer to the completion of the project. 

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