BLANCHE BEACH SAND TRANSFER COMPLETE
Civil Contracting company, Gradco Pty Ltd, recently completed the sand transfer project at Blanche Beach St Helens.
BACKGROUND
A number of studies by coastal engineers have been done in the past, with the most recent report completed in 2007 by Dr Peter Riedel of Coastal Engineering Solutions.
The existing training wall at the entrance to Georges Bay was built to improve the navigation across the barway. After the training wall was completed in 1984, conditions on the bar were their best. However, there has been a decline in these conditions in recent years.
In a report completed in 2007, Dr Peter Riedel of Coastal Engineering Solutions, stated that although the rock wall was built to train tidal water flows and provide a stable navigation channel, it also acted as a sand trap. Dr Riedel estimated that about 10,000 cubic metres of sand entered the entrance to Georges Bay every year and this sand was trapped by the wall to form Blanche Beach. The benefit of the formation of Blanche Beach was that it trapped sand that would normally have deposited on the offshore shoals and therefore has improved conditions on the bar.
However in the 1990’s, Blanche Beach grew out to the end of the training wall. Once the beach reached full capacity, new sand entering the entrance to Georges Bay deposited on the shoals at the barway and within the entrance to the bay instead of accreting on the beach. Dr Riedel recommended that sand should be removed from Blanche Beach, so that sand on the offshore bar could again move ashore onto the beach and improve conditions for vessels. The option of extending the training wall was also considered, however it was recommended that beach sand removal would be a better and more cost effective approach.
MAST received State Government funding to remove the sand accumulation at Blanche Beach. With this funding, MAST removed approximately 250,000 cubic metres of sand and placed it to landward of the current beach by building up low-lying land to create dunes.
SAND TRANSFER PROJECT
Due to the scale of the project, there were significant environmental considerations. In 2008, MAST engaged GHD Pty Ltd to undertake environmental assessments of the site. These assessments led to the production of an Environmental Management Plan (EMP). The assessments included flora and fauna including threatened species, possible sand contamination and assessment of Aboriginal heritage. The EMP also set out criteria for weed and disease management and sand stabilisation and revegetation of the deposited sand.
As the area is within the St Helens Point Conservation Area, approval was then given by the Parks and Wildlife Service (PWS) via a Reserve Activity Assessment (RAA). The information gathered by GHD Pty Ltd was used to produce the RAA application.
After the RAA was approved, a development application was submitted to the Break’O’Day Council which was subsequently approved.
After the issuing of all approvals, MAST advertised for suitably qualified contractors to tender for the works to transfer the sand. This contract was awarded to Gradco Pty Ltd.
TRANSFER PROCESS
The works consisted of excavating sand from Blanche Beach, down to a level of
-1.0m AHD and transporting this sand to the low-lying areas behind the dunes, where it was deposited, spread and compacted. (As a reference the level of the top of the training wall is 2.2m AHD)
A sand bund was constructed along the seaward side of the excavation area to protect the machinery from waves and swell. Behind the bund, excavators loaded the excavated sand into six-wheel drive articulated trucks for transport to the deposit sites. At the completion of the excavation, the bund was removed and the wave action restored the beach to a natural slope.
Machinery used by Gradco Pty Ltd included two excavators (45 and 65 tonne), two D6, low ground pressure bulldozers and a fleet of 8 Volvo articulated dump trucks. Ancillary vehicles included a washdown trailer, a dedicated service vehicle and a dedicated fuel truck.
The position of the deposit sites were influenced by minimising the amount of vegetation that would be affected and by the topography of the area. These sites were situated on the low-lying areas behind the dunes. These areas were filled with sand, up to the level of the dunes immediately adjacent to a particular deposit site. Consequently, all deposit sites have different finished levels to match surrounding land.
All areas that were filled to a height greater than 2.0m had the vegetation removed before deposition. This allowed fauna to move elsewhere prior to the deposition of sand and as the native species were not expected to grow through sand greater than this depth, the stripped vegetation was stockpiled and where possible, placed back on top of the deposited sand to minimise wind erosion and to encourage seed germination.
The routes that the articulated trucks used to travel from the excavation site to the deposition site were carefully chosen to follow existing low-lying areas. The removal of vegetation from these routes and from the deposition areas only occurred where necessary.
Now that the deposition is complete, it is expected that marram grass will grow on top of these areas, giving some stabilisation in the short-term, then native species should revegetate and succeed the marram. If the native species do not germinate from seed, then tube stock that is currently being propagated will be planted.
PROJECT TIMEFRAME
On site works began in the first week of June 2009 which enabled completion to be reached by late-August 2009. This was important as one of the environmental conditions was that the contractor could not undertake any works on the beach between September and April due to the nesting of migatory birds species.
Consequently, Gradco Pty Ltd were very conscious of staying within the project timetable and had extra plant and operators on site to ensure this completion date was not delayed. Gradco Pty Ltd actually finished the project sooner than the original timetable and moved an average of around 5500 cubic metres per day.
Whilst the beach sand transfer should improve conditions at the barway, St Helens will never be an all weather port. Now that this project has been undertaken, it should minimise the amount of new sand entering Georges Bay, however it will not reduce the shoals that already exist inside the entrance. Preliminary work is also underway on assessments and approvals for dredging at Pelican Point. It is envisaged that these approvals to complete this dredging will be sought in the coming months.
FREQUENTLY ASKED QUESTIONS
How is the sand transfer expected to improve the navigability into Georges Bay?
Since the completion of the training wall, sand has been accumulating on Blanche Beach. When the beach area became full, the sand which would normally accrete on the beach, started to flow into the entrance to Georges Bay and also accumulate on the offshore shoals. Coastal engineering advice says that marine-driven sand should begin to accumulate on the beach again instead of on the shoals, improving the conditions on the barway.
Reducing the amount of sand that enters Georges Bay will also reduce the rate that the shoals within the bay develop.
How were environmental impacts assessed and managed?
MAST engaged GHD Pty Ltd to undertake extensive environmental assessments leading to the production of an Environmental Management Plan covering the scope of the works.
MAST then used this plan to gain approval for the project from the Parks and Wildlife Service via a Reserve Activity Assessment (RAA). A condition of the RAA approval was the requirement to provide a series of management plans. These plans outlined how the work was done and particular controls that were put in place including items such as weed and disease management, public safety and sand stabilisation.
A development application was approved by the Break’O’Day Council.
How did the sand transfer occur?
The sand transfer occurred by excavating sand from the designated excavation area on the beach, transporting it in six-wheel drive articulated trucks and then dumping it in the low-lying areas behind the dunes to the south of the beach. Once in the deposition areas, the sand was spread and compacted with bulldozers.
What impacts on access now exist on Blanche Beach area?
Now that the work has been completed, the training wall and beach itself are now open to the public again.
People wading and swimming at Blanche Beach should be aware that due to the nature of the sand transfer and the transient nature of sand accreting on the beach, water depth off the beach may be inconsistent and extreme caution should be taken.
What measures will be undertaken to ensure the site is remediated?
Prior to the transfer of sand, all the vegetation in the specific deposition areas was removed and stockpiled. This vegetation was then laid on the sand at the completion of the deposition. This was to limit wind erosion, but more importantly, allow seeds from the vegetation to germinate, allowing revegetation of native species.
Ongoing monitoring of the site will now occur to ensure no weeds are evident. MAST and PWS have plans in place, should weeds be detected. It is unlikely that any declared weeds will become evident as there were strict washdown procedures in place for all plant that was brought onto the site.
MAST will also monitor the revegetation of the site. Should seed from the existing native vegetation fail to germinate then tube stock that is currently being propagated will be used.
Who can you contact if you require further information or have concerns?
If you have any further queries contact Justin Foster at MAST on 0418 142 053 or via email at www.mast.tas.gov.
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