Limestone Rock for Artificial Reef

During the 2014 State Election the labor government promised grants for recreational fishers. This included the construction of an artificial reef.

In 2016 Rogues Point a few kilometers south of Ardrossan was chosen as the location for the reef. A mixture of concrete structures and rows of limestone would be used to make the reef. Limestone was chosen because it has similar properties to native oyster shells in terms of calcium. An initial tender processes followed this in mid 2016. A trial reef of approx 4 hectares would be constructed with an expansion of 20 hectares expected to follow.

In mid 2016 we were contacted by a marine construction company to supply limestone rock for the project which we submitted a price however the project didn't take off as early as predicted.

In early 2017 we were contacted again by a second construction company to supply rock for the project. However after reviewing the criteria and desired time frame we declined the offer as we already had many work commitments for that period.

A few weeks later I was contacted by a couple of representatives from PIRSA http://www.pir.sa.gov.au/ who were in the area and were interested on visiting us to have a look at our product and discuss the project. After meeting with PIRSA and talking about our product and process for collecting and processing limestone they were quite interested in our product and I felt more comfortable about supplying it.

After the PIRSA visit we were then contacted by Maritime Constructions and agreed on the specified size of material and price delivered either locally or to Port Adelaide.

Maritime Construction won the tender for the project using limestone mainly supplied by Redding Crushing with a trial of dolomitic limestone supplied by Arrium at Ardrossan also being used. For the reef trail project the rock needed to be delivered to Port Adelaide as local boat loading facilities could not be arranged in time for the project. We had suggested that sizing approximately 100mm - 250mm product would be an achievable sizing within their time frame.

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While discussions were taking place about the project and the tender process continued, we started stockpiling raw material in our yard at Mt Rat. This would have taken place regardless of the reef project as we are always sourcing product to crush for our local market.

The limestone material we collect has been picked off of farming land over the years and been stockpiled in paddocks or along fence lines. Today we still have a number of farmers willing to let us come in and remove their rock piles as they are in the way of larger farming machinery, havens for pests and weeds or are in the way of fences in need of repair.

For this project we sourced the rock from the Wauraltee area through to Port Rickaby, as the closer you get to the coast the harder the surface limestone is.

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To size material it is usually dropped onto a vibrating screen with woven steel screen mesh with the holes being set at the desired size of material. The smaller material is shaken through the screen mesh and the larger material shaken across the top.

To size 100-250m creates some problems as generally most of our material is graded less than 50mm.

We could easily grade the less than 100mm product out but to grade the larger than 250mm would be more difficult.

We purchased and placed a 100mm screen into our vibrating scalper screen. This allows anything less than 100mm to fall through, it then ends up on a discharge conveyor belt which puts it on the ground away from the plant where a front end loader can pick it up and stockpile it for reprocessing later.

The material over 100mm is then shaken onto a conveyor belt which runs through our picking station allowing an operator to remove any foreign objects.

We do not have a machine capable of vibrating and sizing 250mm and because that size rock is quite heavy it would be very hard to get enough vibration to make it jump over screen mesh.

The only other option was a grid, with long straight bars set on a steep angle to get the rock to either fall through or slide along the bars. While this doesn't achieve an accurate size as large flat rocks will slip between the bars it will achieve a basic grading.

So we constructed a grid to be placed underneath of our picking station belt. With the bars set at 250mm this meant that the product that fell through the grid would be used for the reef and the larger rocks that rolled over the top would be stockpiled for crushing at a later date.

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While we were setup we processed all of the raw material we had stockpiled. This resulted in over 100o tonnes of 100mm-250mm, approx 2000 tonnes of less than 100mm and 100 tonnes of larger than 250mm rocks. The sizing of the material was done over a two week period.

The limestone rock that was graded for the reef was stockpiled in our yard until construction of the reef started.

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In early June Maritime Constructions had an area at the Port Adelaide wharf to stockpile the rock. We then sub contracted the delivery of rock to Yorke Peninsula Earthworks at Minlaton. 100 tonnes of rock was needed to be delivered every two to three days. All of the rock contracted for the project was delivered by July.

This project attracted a lot of media attention as it is the first of its kind to be built in South Australia.

http://indaily.com.au/news/2017/06/30/reef-fishers-tourism-ardrossan-gulf-st-vincent/

http://indaily.com.au/eat-drink-explore/features/2017/06/28/restored-sa-reef-seeks-to-turn-the-tide-for-oysters/

http://www.abc.net.au/news/rural/2017-06-28/australias-largest-shellfish-restoration-underway-in-sa/8658778

https://www.youtube.com/watch?v=b1Nr6XL0Gv4

Our local paper the Country Times also featured a story on our rock supply.

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If you are looking for some more background on the project the links below may be of some interest.

https://yorke.sa.gov.au/news/largest-recreational-marine-reef-in-australia-to-be-built-on-yp/

http://pir.sa.gov.au/__data/assets/pdf_file/0010/289594/Yorke_Peninsula_Trial_Shellfish_Reef_FAQ_Updated_May_2017.pdf

http://www.pir.sa.gov.au/alerts_news_events/news/fisheries_and_aquaculture/yorke_peninsula_reef_work_underway

http://pir.sa.gov.au/fishing/recreational_fishing/yorke_peninsula_shellfish_reef/shellfish_reef_construction