Reports Page 52 2 June 2009
MATTERS SUBMITTED BY THE DIRECTOR - CITY SERVICES
CIT.27 PEARL BEACH ROCK POOL CLIFF FACE STABILISATION (IR 4553172)
Directorate: City Services
Business Unit: Open Space and Leisure Services
BACKGROUND
This item was considered at the Strategy/Policy Workshop held on 18 March 2008 and the Council
Meeting of the 6 May 2008 (Attachment A) due to the risk considerations and funding required to
undertake the stabilisation of the cliff face.
On the 6 May 2008, Council resolved to;
A Option 2 for stabilisation works be adopted as the preferred option.
B Works commence immediately with the funding of $180,000 to be sourced through a
Council's budget review.
Since Council resolved the item above, concerns have been raised by the local residents (via Pearl
Beach Progress Association) and The National Trust of Australia (NSW) (the cliff face is registered
by the Trust as part of the tidal baths) in relation to the preferred treatment by Council. Based on
the letter from The National Trust dated 11 September 2008 (Attachment B) the Trust appears to
favour a mesh covered and reshaped rock face as per Option 3.
The report that follows outlines the preferred option for all parties concerned.
REPORT
The details of Option 3 (Combination of Mesh, shotcrete and rockbolts) are;
This method comprises a mixture of wire mesh, rock bolts, shotcrete and other works as
described below:
• Preparing the face of the cliff removing loose blocks, soil, trees and vegetation.
• Draping and pinning double dip galvanised 4mm mesh loosely to the rock face.
• Installing rock bolts to the rock face.
• 50m2 of shotcrete sprayed where appropriate to prevent further erosion or
detachment of blocks.
Estimated Cost: $140,000
It is important to note that although Option 3 is $40,000 cheaper than Option 2 to complete, there
will be an ongoing maintenance cost which will need to be covered by Council. This would be
funded by Open Space & Leisure Services as required.
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A revised design has been undertaken and reviewed by Council Officers. This design has
subsequently been forwarded to the Pearl Beach Progress Association and The National Trust of
Australia (NSW).
Letters have been received from both organisations confirming their support for the revised design.
Attachments: A SF.16 Pearl Beach Rock Pool - First Report (6 May 2008)
B Recommendations from The National Trust of Australia (NSW)
C Design for Pearl Beach Rock Pool cliff face stabilisation - Option 3
Tabled Items: Nil
FINANCIAL IMPACT STATEMENT
The estimated cost of the design option 3 is $140,000. This is a reduction of $40,000 from the
previous design and will be funded through the Budget Review Process as per previous Council
Resolution.
The necessity for ongoing maintenance will be funded through the recurrent budget of Open Space
& Leisure Services as required.
RECOMMENDATION
A Proceed with Option 3 as being the preferred plan by the local residents and The National
Trust of Australia (NSW) at an estimated cost of $140,000.
B As per resolution 6 May 2008 (IR 4553172) the works be funded through a budget review.
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ATTACHMENT A
TITLE COUNCIL REPORT PEARL BEACH ROCK POOL - CLIFF FACE
STABILISATION (IR 4553172)
Directorate: City Services
Business Unit: Open Space and Leisure Services
BACKGROUND
This item was considered at the Strategy/Policy Workshop held on 18 March 2008 due to the risk
considerations and funding required to undertake the stabilisation of the cliff face.
The Pearl Beach rock pool was constructed in 1929 by excavating the natural rock shelf located at
the southern end of the beach. The pool received an upgrade in the late 1950's, mid 1980's and
the latest inspection (2007) has deemed the pool in need of another substantial upgrade (at a cost
of $202,000).
The pool has high importance to the local community primarily used as a venue for recreational
swimming. The Umina Blue Swimmers Club has swum at the pool since 1969 with a current
membership of 50 swimmers. The pool has also been classified by the National Trust.
The cliff face located on the south-eastern side of the rock pool has suffered some substantial rock
fall in recent years. As a result of this, Council contracted an external risk management report from
Logov, Risk Management Services.
The report identified that the cliff face appeared unstable over a distance of approximately 50
metres and recommended a number of actions to be undertaken.
Logov recommended that Council undertake engineering investigations into the stability of the rock
face and rectification works necessary to make the area safe.
The following Councillors were present for this item:
Councillor Maher, Holstein, Scott, Macfadyen, Brooks, Hale, and Drake.
REPORT
Council Officers engaged engineers Pells, Sullivan, Meynink Engineering Consultants (PSM) to
investigate the rock face adjacent to Pearl Beach Pool.
The report deemed that rock falls of rocks of up to 1 metre in size is considered to be moderate to
high in risk, with the risk of falls of larger rock sizes to be low.
Options for Consideration
The Engineers report has recommended three appropriate engineering solutions to prevent further
rock fall.
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Option 1 Protective Wall
Construct a structural wall approximately 8 metres in height and 50 lineal metres in length at the
base of the cliff and backfilled with gravel. The wall geometry would be such to cover the entire
length of the pool and 10 meters each side.
Possible constructions types include,
• Reinforced concrete
• Steel columns with timber wall lagging
• Copper log wall
Estimated cost on Option 1 is $220,000 - $270,000.
Option 2 Shotcrete and Rock Bolts
Apply a shotcrete membrane over the entire rock slope.
A rock bolt reinforced concrete membrane would remove the risk of rock fall. This option may be
considered unsightly, however colouring the concrete may reduce this impact. Trees at the crest of
the cliff would have to be removed.
Estimated cost on Option 2 is $180,000 and will require minimal ongoing maintenance.
Option 3 Combination of Mesh, shotcrete and Rockbolts
This method comprises a mixture of wire mesh, rock bolts, shotcrete and other works as described
below;
• preparing the face of the cliff removing loose blocks, soil, trees and vegetation,
• draping and pinning double dip galvanised 4mm mesh loosely to the rock face,
• installing rock bolts to the rock face,
• 50m2 of shotcrete sprayed where appropriate to prevent further erosion or detachment of
blocks.
This method would capture any blocks of rock (up to 250mm) that may be detach from the rock
face, however blocks would have to be removed periodically from the base of the wall.
Estimated cost on Option 3 is $140,000 and will require ongoing maintenance.
In determining the best option for consideration, Option 2 was deemed suitable as;
• The pool has high aesthetic significance due to it sitting on a rock shelf at the base of a cliff.
• Reactive measures that catch falling rocks as identified in option 1 are typically hefty in
design and expense.
• Preventative measures to prevent rock fall as identified in options 2 & 3 are more practical.
• All options would require some form of ongoing maintenance while options 2 & 3 involving
regular inspections to be undertaken by an engineer.
• The galvanised mesh attached to the cliff face as identified on option 3 will corrode
within 10 - 30 years, and therefore would require considerable ongoing maintenance.
• Whilst Option 3 is the least expensive initial cost, the likelihood of further expense to Council
in the long term is higher through ongoing maintenance. As the galvanised mesh is
exposed, it is more susceptible to the elements, and may require repairs and replacement.
It is recommended that Option 2 be pursued as the preferred works. Once Council has approved
the preferred option, PSM can provide technical drawings and specifications required for the next
phase of the project.
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Option 2 Cost Estimate
Shotcrete and rock bolts
ITEM QUANTITY COST ESTIMATE
Prepare face (remove loose 50 lm (about 500m2 ) $35,000
blocks, soil, trees and
vegetation).
Install rockbolts over 50 lm of Nominally 100 x 2.1m rock $75,000
rock face. bolts
Spray shotcrete Nominally 500m2 $60,000
Detailed design & Allow $10,000
documentation
TOTAL ESTIMATE $180,000
Attachments: NIL.
Tabled Items: NIL
FINANCIAL IMPACT STATEMENT
The cost of the preferred option is an estimated $180,000 to shotcrete and rockbolt the cliff face.
No funding is currently available through the current Capital Works budget for these works. Based
on the urgency of the works, consideration should be given to obtaining funding through the budget
review process.
Should the project be unsuccessful in the budget review process, the project should be given
further consideration through a future Capital Works budget.
RECOMMENDATION
A Option 2 for stabilisation works be adopted as the preferred option.
B Works commence immediately with the funding of $180,000 to be sourced through a
Council's budget review.
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ATTACHMENT B
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ATTACHMENT C
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