Wharf and Jetty Demolition: Working Over Water Without Leaving Anything In It

Wharf and jetty demolition is marine civil work with a demolition licence attached. Half the structure is under water or in the tidal zone, the deck will not carry the plant you would normally use, the timber is treated with chemicals that make it hazardous waste, and anything you drop goes into a harbour or river where someone else has to get it out. Get the sequence and the environmental controls right and it is a clean, well paid job. Get them wrong and the EPA and the port authority are both on site.

This is how we approach it, what will hurt you, and the mistakes we see when a land based crew has had a go first.

What you are actually dealing with

• Timber piles and decking treated with creosote, CCA or similar. All of it is regulated waste; none of it can go to a general landfill or be burnt.
• Steel piles, often badly corroded at the splash zone, with concrete or timber headstocks and a deck that may be concrete, timber or both.
• Services run along or under the deck: water, fuel lines to a refuelling berth, power, firefighting mains, sometimes sewer. Fuel lines on an old fishing or ferry wharf are the ones that surprise people.
• Marine growth, sediment and the sea bed itself. Disturbing contaminated sediment can trigger controls that stop the job.
• Tides, swell and weather windows. The job is planned around the tide tables, not the calendar.
• Navigation. Other vessels keep using the waterway, so exclusion zones and marine notices are part of the method.

Step one: work out what the deck will carry

The first engineering question is whether any plant can sit on the wharf at all. Old timber wharves often cannot carry a 20 tonne excavator; older concrete wharves have been losing section to chloride attack for decades. The answer decides whether the job is done from the deck with light plant, from the shore with a long reach excavator, from a barge mounted crane or excavator, or a mix. It also decides the price, so it comes first.

Step two: survey, services and sediment

A dive or sonar survey of the piles and the sea bed, a hazardous materials survey of the deck structures (asbestos in old wharf sheds and switchrooms, lead paint on steel, treated timber everywhere), a services search with the port or council, and a sediment assessment if piles are to be pulled rather than cut. Pulling a pile disturbs the sea bed; cutting it at or below the mud line does not. Which one the approval allows shapes the whole method.

Step three: isolate and protect

Services are disconnected and capped at the shore end. Silt curtains go in where sediment will be disturbed. Floating booms and debris screens are set so nothing drifts away. Catch platforms or barges sit under the work face so cut material lands on something we control. Exclusion zones are marked for other water users and the port is notified.

Step four: deck first, then headstocks, then piles

The deck comes off in sections, working from the outer end back towards the shore so plant always has a sound structure or the shore behind it. Headstocks and bearers follow. Piles are the last element: cut at the agreed level below the mud line by divers or a hydraulic pile cutter, or extracted with a vibrating hammer or crane where the approval allows and the sediment permits. Every piece is lifted onto a barge or the shore laydown, never dropped into the water to be fished out later.

Step five: the waste

Treated timber goes to a facility licensed to take it, and the volumes are larger than they look because the piles are long. Steel is recovered and credited. Concrete can usually be recycled once any coatings are dealt with. Sediment and marine growth on recovered material can change its classification, so material is drained and inspected on the barge before it is loaded for transport.

Step six: handing the waterway back

The sea bed is surveyed again at the end to show nothing was left behind, the pile stubs are at the approved level, and the shore abutment is made safe or prepared for the new structure. The port or council will want that survey on file.

What not to do

• Do not put plant on a wharf deck without an engineer's rated load. The deck is the first thing to fail.
• Do not drop material in the water and plan to recover it later. Recovery costs more than prevention and the regulator counts it as pollution.
• Do not burn or landfill treated timber as general waste. It is regulated and the fines follow the site owner.
• Do not pull piles if the approval says cut. Disturbed sediment can stop the job.
• Do not start without the tide tables and a weather plan. A barge job runs on the tide.

Approvals and notifications

Marine works approval from the port authority or the state maritime agency, council consent where the structure is on council land, environmental approvals for work in the waterway and for sediment disturbance, licensed demolition and asbestos notifications to the state regulator, and marine notices for navigation. Heritage listing is common on older wharves and brings its own process. Start early; approvals on the water are slower than on land.

Who should be doing this

A contractor with marine experience and its own plant, including long reach excavators that can work from the shore, with a dive and barge partner it has used before, and with the asbestos and demolition licences in its own name. Perfect Contracting carries out wharf, jetty and port infrastructure demolition across Australia from its Sydney and Brisbane bases. Read more about our industrial demolition and site remediation work, or send us the details.