Funding urged for rock slides

Gosford Council officers have recommended funding to correct possible rock slides near public roads at several locations on the Peninsula, with some funds already committed to the projects.

The three locations include Memorial Ave at Blackwall, Mt Ettalong Rd in southern Umina and Patonga Dr.

A rockfall hazard was found in Memorial Ave on the southern face of Blackwall Mountain between the intersections of Barrenjoey Rd and Lurline St.

A geotechnical consultant was appointed to assess the condition of the area and the risks posed to the area.

The consultant was also asked to recommend appropriate remedial action, if required.

The consultant also strongly recommended that the most cost-effective measure over the long term was, "to move the road about 4.5m away from the cutting to create a drop zone for small to moderate size blocks of rock, coupled with some bolting of large masses of rock and the removal of three angophoras".

Rock bolting and tree removal works in the area were completed in January last year.

Ongoing monitoring of the face for further deterioration continued with assistance from the geotechnical consultant which led to further measures being undertaken on the rock face in January.

Council staff are currently developing project details for the recommended Memorial Ave road realignment, including structural plans for a required retaining wall and service relocation designs.

A preliminary estimate for the design and construction of the work is $670,000.

Funding assistance for the work was declined by the RTA and the Department Infrastructure Planning and Natural Resources (DIPNR).

Council officers have recommended that a further report be made to council once project details have been finalised and costed.

Council officers have recommended that funding be allocated to immediate slope stabilisation works at Memorial Ave worth $25,000.

In another incident, a letter was received in April 2003 with a geotechnical report from a resident describing a potential rockfall hazard near a house at number 139 Mount Ettalong Rd, Umina.

The hazard identified was a slippage of the fill embankment on the northern side of Patonga Dr, near the lookout at the southern end of Umina Beach.

The embankment is constructed mainly of large boulders.

The report noted that the embankment showed some signs of failure and advised that further failure could result in several tonnes of rock sliding into the lower lying house.

Upon receiving this advice a second geotechnical consultant was engaged by council to assess the area and, if required, to recommend remedial works.

The report concluded that, "The overall risk of slope instability for the road reserve above Lot 4 ... is assessed to be high" and "remedial works should be carried out."

The report recommended the erection of a rock safety catch fence in the road reserve along the boundary of Lot 4 near the bottom of the road fill embankment.

A structural engineer completed the detailed design of the rock safety catch fence in February.

Council's preliminary estimate for the construction of the fence, including its design, is $65,000.

A council report on the matter stated that in view of the high priority of this project the work would be undertaken as soon as it could be scheduled, with funding to be provided in the next budget review.

In a third incident, residents informed council staff of concerns at rocks and debris falling onto Patonga Dr from the overlying slope on the north side.

The section of Patonga Dr was narrow and provided the only vehicular access to Patonga.

In response, a geotechnical consultant was engaged to assess the area and provide a report.

The report was completed in June last year and identified 18 individual hazards.

It recommended immediate remedial works to address 10 of those hazards, including rock scaling, tree removal and shotcreting.

Ongoing monitoring, including the use of precise survey to detect rock movement, was recommended for the remaining hazards.

Council's construction operations section completed the remedial works in November last year at a final cost of $24,000.

The asset management unit is undertaking ongoing monitoring, including detailed survey, until further notice.

Council agenda EO.13, April 5