An abnormal elevation of the sea level (a storm surge) over normal tide levels causes storm tide inundation (coastal flooding by the sea). Severe weather events, including cyclones in central and northern Queensland and east coast lows in southern Queensland, typically cause storm tides. Queensland’s coast is vulnerable to storm tide inundation as low sandy landforms dominate the coast.
Storm tide is the total sea level, including the tide and surge level. It can be destructive for human settlements. Large areas of major urban centres like Cairns, Townsville and Mackay are at risk from storm tide inundation.
Storm tides can seriously impact coastal ecosystems, but these usually recover naturally. Beneficial effects include sand deposits driven onshore to build up coastal landforms.
Severe Tropical Cyclone Megan
In March 2024, Severe Tropical Cyclone (STC) Megan made landfall on the southwest coast of the Gulf of Carpentaria in the Northern Territory. STC Megan was a large system, reaching category 4 strength and causing a storm surge of 1.5 metre at Karumba, which just exceeded the highest astronomical tide (HAT) level. STC Megan made landfall 450 kilometres east of Karumba. At Mornington Island, 250 kilometres from landfall, a storm surge of 1.17 metres was reported, with a minor inundation of 0.53 metres above the HAT level.
Tropical Cyclone Seth
In December 2021, a tropical low-pressure system moved across the top end of the Northern Territory and over the Gulf of Carpentaria and Cape York Peninsula onto the far northeast coast of Queensland. The low-pressure trough continued along the northeast Queensland coast and developed into a tropical cyclone on New Year’s Eve 2021. Tropical Cyclone Seth developed into a category 2 system while travelling southeast along the Queensland coast to Mackay where it was downgraded to a category 1 and continued travelling southeast.
Seth stalled offshore from Brisbane and degraded further to a sub-tropical low-pressure system, which moved slowly north-westerly towards the coast over the next two to three days. The system brought high winds, large waves, and storm surge to the Queensland coast with waves up to six metres. Ex-TC Seth generated a storm surge of 0.2 metres to 0.6 metres along the Southeast Queensland coast and inundation levels exceeding HAT at Mooloolaba, Golden Beach, within Moreton Bay and the Gold Coast. The combination of extremely high tides, large waves, and storm surge resulted in erosion and over-washed the dunes on northern Bribie Island. It cut a tidal channel through the island, creating a new entrance to the Pumicestone Passage from Moreton Bay. Since January 2022, the breakthrough of the island has widened to about one kilometre and has become the dominant tidal entrance to the Pumicetone Passage near Golden Beach.
Most coastal local governments have investigated the risks from storm tides. This information assists with evacuation planning, development assessment and planning.
