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Boat liftsThe waterfront, read like a tide gauge

Boat lifts · Guide 6 of 6 · High water

Mark 6 · Above the highest tide

Storm tide and flooding on the waterfront

A storm tide is a storm surge added to the normal tide, and the Queensland Government says the worst impacts come when the surge arrives on a high tide, when it can reach areas that might otherwise have been safe. Its advice is to ask your council whether your home is in a storm tide evacuation area and, if it is, to arrange a safer place to go as part of your preparations.

General information, not emergency advice for your address. In Queensland, follow your council and the Queensland Government’s disaster pages; in NSW, follow NSW SES.

6.1

Surge plus tide

What makes a storm tide

The Queensland Government’s storm tide glossary defines a storm surge as an abnormal rise in water above the predicted tide, caused by a storm: the combined effect of wind set-up, wave set-up and falling air pressure. A storm tide is that surge combined with the normal astronomical tide, and the flooding it causes is often made worse by waves running up the shore, waves overtopping levees, and heavy local rain.

The government’s emergency page describes a surge as a raised dome of sea water, typically 60 to 80 km across and 2 to 5 metres above normal sea level, that comes in like a rapidly rising tide. It lists what decides how high it gets:

  • the intensity of the storm: stronger winds, higher surge;
  • the angle it crosses the coast, with a right-angle crossing raising the surge;
  • the shape of the sea floor, where a gentler slope means a greater surge;
  • local features such as bays, headlands or islands, which can funnel and amplify it;
  • the tide, with flooding worst if a cyclone crosses at high tide.
The parts of a storm tide A stacked column. At the bottom, the predicted tide rises from chart datum. On top of it sits the storm surge, made of wind set-up, wave set-up and the effect of low air pressure. Wave run-up rushes higher still. A bracket marks the predicted tide plus the surge as the storm tide. Predicted tide sun, moon and earth Storm surge wind set-up wave set-up low air pressure Wave run-up chart datum Storm tide
The parts of a storm tide as the Queensland glossary lists them, stacked on the predicted tide. A diagram, not to scale.

Maritime Safety Queensland makes the same point about its tide tables: the highest astronomical tide is not the highest the water can go, because storm surges can push levels considerably higher. How those levels are measured is on the home page.

6.2

The record

Queensland’s storm surges, and one near miss

The Queensland Government says cyclones and storm surges can reach every part of Queensland’s coast, and that destructive surges are rare but the risk grows as the coastal population grows. Its examples:

  1. 1899 · Bathurst, near Cape YorkA huge storm surge left more than 300 people dead.
  2. 1918 · MackayA storm surge drowned 13 people and damaged or destroyed around 1,000 homes.
  3. 1971 · Townsville, Cyclone AltheaA 2.8 metre surge arrived near low tide, so flooding was minor. Had Althea struck at high tide, just five hours later, the page says a tragedy could have occurred.
  4. 2011 · Tropical Cyclone YasiOne of the most powerful cyclones to affect Queensland. State coastal scientists advised disaster managers on surge levels around the clock as it approached, then surveyed 230 km of the worst-hit coast, from Townsville to Bramston Beach.

6.3

Warnings

How the warnings work in Queensland and NSW

Queensland

The state runs a network of storm tide gauges and wave buoys along the coast that send real-time water levels, and works with Bureau of Meteorology forecasters, who predict surge heights. During a cyclone its coastal engineers give emergency management centres advice on surge levels around the clock. Maritime Safety Queensland points boat owners to its own dashboard for maritime warnings and to the state’s disaster management dashboard for storm, flood and cyclone warnings.

New South Wales

NSW SES is responsible for emergency management of coastal erosion and flooding from severe storms, and issues coastal erosion warnings at three levels: Advice, Watch and Act, and Emergency Warning. The Bureau of Meteorology’s severe weather warnings can include abnormally high tides and unusually large surf. NSW SES suggests the Hazards Near Me app, with watch zones set, to receive its warnings.

6.4

The boat at the jetty

Preparing a boat for severe weather in Queensland

Maritime Safety Queensland says the severe weather season generally runs from November to April, and that boat owners are responsible for making sure their boat is maintained and equipped to survive it. Its preparation list:

  • know when and where your boat needs to be in an evacuation or port closure;
  • carry plenty of line to secure it, since rope has more give than chain;
  • secure loose articles below deck, and all hatches;
  • check the boat is watertight;
  • reduce wind loading by removing furled sails, covers, bimini tops and clears.

Anyone going away between November and April should either leave a key and contact details with a responsible, licensed person who knows when and where to move the boat if a warning is issued, or ask the local marine rescue unit whether it can move boats in an emergency. MSQ also asks owners to follow every direction of the Regional Harbour Master and not to leave a cyclone or emergency mooring until the all clear; it lists a fine of up to $32,260 for failing to follow those directions, on a page last updated in October 2024.

Caught out on the water

MSQ’s advice if severe weather arrives while you are out: put life jackets on everyone at the first sign, look for shelter in a mangrove-fringed river or creek if you cannot get back, remember that heavy rain and wind can raise tides even in creeks and rivers, and in a marina or hardstand, ask the manager for instructions. It also says to check its dashboard and the state’s disaster management dashboard for warnings, and to follow any directions from the Regional Harbour Master, police or emergency services.

6.5

The house behind it

When a storm surge looks likely, and leaving

The Queensland Government’s storm surge page sets out two lists, given here in its order.

When a severe surge seems likely

  • Listen to local radio for warnings and advice; a battery-powered radio is a good idea.
  • Prepare to move vehicles, outdoor equipment, rubbish, chemicals and poisons to higher places.
  • Decide which indoor items to raise, and which appliances to empty, such as fridges and freezers.
  • Check your emergency kit, and plan for your pets.

If you need to evacuate

  • Be ready to follow local authorities and leave quickly; the safest choice is to decide early.
  • Pack warm clothes, essential medicines, valuables, papers and photos in waterproof bags with your kit.
  • Raise furniture, clothes and valuables onto beds, tables and into the roof space, electrical items highest.
  • Empty and turn off fridges and freezers, doors left open.
  • Turn off power, water and gas, and take your mobile phone.
  • Put sandbags in toilet bowls and over laundry and bathroom drains to stop sewage backflow.
  • Lock up, take your keys, and use the recommended evacuation routes.

The Queensland Government page adds a warning after the second list: “Don’t drive into water of unknown depth and current. If it’s flooded, forget it.”

6.6

After the flood

What floods do to pontoons

Queensland’s guideline to the prescribed tidal works code explains that pontoon floats are commonly an expanded polystyrene core wrapped in a thin polyethylene liner, and that river floods dislodge and break pontoons, tear the liners and scatter the polystyrene widely, harming the environment and leaving costly clean-ups. It says this was particularly evident after the South East Queensland floods of 2022.

The code requires prescribed tidal works to be structurally sound with regard to flooding, storm tide, overtopping waves, projected sea-level rise, tides and water forces, and to be built from materials that resist breaking in the marine environment. The guideline says a pontoon that is easily damaged in a flood, or releases polystyrene, does not meet those outcomes. For rivers and large creeks with high flood flows, it recommends this float design, developed with Maritime Safety Queensland, as advice that the design engineer remains responsible for:

  1. Wrap all of itAll the polystyrene in a float is wrapped or encased in a core protection liner.
  2. Use a tough linerThe liner is a rotomoulded tub, a welded high-density polyethylene membrane, or a composite; concrete shells are allowed if they meet the concrete cover requirements of AS 3600.
  3. Make it thickAt least one layer on the sides, ends and base, a minimum of 6 mm thick, to protect the core from debris and sharp objects.

The guideline says this design is necessary in South East Queensland, should be considered elsewhere in the state depending on flood risk, and may not be needed in canals, marinas, small creeks or other protected places; an application proposing a liner thinner than 6 mm should include an engineer’s statement explaining why it suits the site. The rest of the code is in Queensland tidal works, and NSW’s approach to the same structures in boat lifts and jetties in NSW.