Sandbag plan for foreshore

The City of Wanneroo will consider sandbags like these at Watermans Beach in the City of Stirling. Picture: Kaity Malley
The City of Wanneroo will consider sandbags like these at Watermans Beach in the City of Stirling. Picture: Kaity Malley

City infrastructure maintenance manager Harminder Singh outlined the two short-term options for coastal protection works on about 280m of the beach at last week’s council briefing session.

The first, which administration recommended, would involve building a 4.5m high sloping revetment of sandbags and cost $2.813 million.

Above the sand bags there would be a batter slope, stabilised with fibre matting and revegetation, and it would make Frederick Stubbs Park 7m wide at the northern end, expanding to 15m to the south.

The second option would also require a revetment in the same location with the same dimensions, with the addition of a 9.2m limestone retaining wall between the sandbags and park.

That option would make the park about 12m wide at the northern end and 26m wide at the southern end.

Mr Singh said the first option was about $600,000 cheaper than the second and allowed for flexibility in the future.

‘Any work that we do here now should be adaptable to the ultimate option,’ he said.

‘To construct this (limestone) wall, we will have to pretty much dig up the whole park. If the revetments have to be changed (for future works) the wall will have to remain with no value to the erosion problem.’

As there would not be much space for a playground in the park under option one, Mr Singh said the City could investigate creating a playground area in the grassed area north of the car park access road using funds allocated to an access path to Quinns Beach.

He said each geo-synthetic sandbag was 2.5m long and 1m wide, weighed 4 tonnes and designed to withstand wave action.

According to Mr Singh, the sandbag revetment was designed to last five years but similar structures in other sites were in place for 12 years, with the potential to last another five.

He said the City had submitted an application for funds to the Department of Transport, having listed $1 million of state funding and $1 million of municipal funding for the project in 2014-15 in its 10-year capital works program.

Mr Singh said the City could also use funds from its strategic projects reserve without affecting the current capital works program because its balance was higher than anticipated.

‘Subject to council decision and allocation of funds, the coastal protection works are best undertaken during the forthcoming summer months (February to April, 2014), followed by revegetation works during May or June, 2014,’ his report said.

Replying to Mayor Tracey Robert’s question about the limestone wall’s vulnerability, Mr Singh said the revetment and a 7m buffer would have to fail before the wall would be undermined.

Nat Sangalli, a founder of the online campaign, Save Our Foreshore Quinns Beach, asked how construction vehicles would access the beach.

Mr Singh said the contractors appointed through a tender process this month would have to explain how they would access the site, but he expected it would be from the southern end.