Gold Coast

Innisfail

Townsville

Cardwell

Cairns

Coral Sea

Gulf of Carpentaria

Brisbane (Moreton Bay)

Sunshine Coast

Mackay

Hervey Bay

Bowen

ReefBarrier

Great

Gladstone

0 200km

N

Queensland

Storm Surge: Know your risk in Queensland!

The Queensland coastline is highly vulnerable to storm surge. This is due to the frequency of tropical cyclones, the wide continental shelf and relatively shallow ocean floor in both the Great Barrier Reef lagoon and in the Gulf of Carpentaria, as well as the low lying nature of many coastal cities and towns.

While the highest storm surges are more likely to occur in North Queensland and the Gulf of Carpentaria, they can also develop in southeast Queensland affecting the Sunshine Coast, Moreton Bay and the Gold Coast. Storm surges may reach magnitudes of 1 to 10 metres above the tide depending on the intensity of the cyclone, its size and the local characteristics of the coastline.

ImpactsStorm surge can be very dangerous and poses a critical risk to human life during tropical cyclones.

The length of coastline affected by a storm surge can be tens to hundreds of kilometres wide. The rise in sea level can be rapid and high in velocity, inundating the ground floor of buildings, even up to the roof.

Storm surge has the power to easily move cars, even houses, can damage roads and buildings and can be almost impossible to manoeuvre through. Additionally, the storm surge can carry dangerous debris, which can cause structural damage to buildings and pose a high risk to life.

Storm surge is a rise in sea level above the normal tide usually associated with a low pressure weather system such as a tropical cyclone. Storm surge develops due to strong winds pushing water towards the coastline as well as the low atmospheric pressure drawing up the sea surface.

This information booklet was prepared by Griffith Centre for Coastal Management to educate Queensland’s coastal communities about storm surge.

Storm surge destruction from Tropical Cyclone Yasi (February 2011), Tully Heads, Qld (Source: Marc McCormack, News Limited).

Budds Beach during ex-TC Oswald, Gold Coast, 28th January 2013 (Source: GCCM, 2013)

High tide

Mean sea levelLow tide

Storm surge - measured fromheight of the tide at the time the cyclone crosses the coast.

Storm tide

High tideMean sea level

Low tide

A. Normal tidal conditions

B. Cyclone conditions

A. Water level during normal conditions. B. Conditions during a cyclone showing elevated sea level due to storm tide.

FloodingStorm surge can travel many kilometres inland and rising waters may come from estuarine waterways as well as the open coast. Low lying areas surrounding estuaries are vulnerable to the combination of storm surge and upstream flooding from heavy rainfall. Properties on the beachfront are also at risk from sea water inundation due to storm surge as well as wind-induced waves.

Storm TidesThe impact of a storm surge is highly dependent on the phase of the tide and the surge will have greater impact if it arrives during a high tide. This may result in extremely high water levels. When forecasting the cyclone, the timing of cyclone landfall is uncertain, making it difficult to predict an exact water level. The peak of the storm surge may occur prior to or after the cyclone making landfall. It can also occur without the cyclone crossing the coast.

WavesStorm surge is usually accompanied by extreme ocean waves created by hazardous winds during the cyclone event. These add to the total water level through wave run-up.

Wave run-up is the maximum height of the waves rushing up on the beach. This is due to both wave set-up as well as the swash of broken waves on the shoreline.

Wave set-up is the elevation of sea level above the storm tide level as a result of water piling up against the shoreline due to the momentum of the breaking waves.

These conditions can lead to beach erosion and add further impact to beach front properties.

What is a storm tide?Storm tide is the water level resulting from the combination of the storm surge with the astronomical tide, and is referred to a vertical datum such as Lowest Astronomical Tide, Highest Astronomical Tide or Australian Height Datum, AHD (equivalent to Mean Sea Level at major ports).

Total Water Level = Storm Surge + Tide + Freshwater Flooding + Wave Run-up

Storm surge flows through bottom storey of house at Tully Heads during TC Yasi, 2011 (Source: JCU, 2011)

Total Water LevelThe total water level experienced on land during a cyclone is made up of contributions from the storm surge, tide, freshwater flooding and wave run-up.

Tropical Cyclone Yasi making landfall in February 2011 (Source: www.bom.gov.au).

Storm surge is ampli�ed in shallow water Wind set-up

Atmospheric pressure increasing Low pressure

Onshore winds Cycloneeye

Pressure induced rise in sea level

Forecasting Every cyclone is unique in its behaviour resulting in a high level of uncertainty when it comes to forecasting where and when they will cross the coast. A cyclone can travel for hundreds of kilometres, may move erratically, even making sharp turns or loops, and change intensity rapidly. In Queensland, a cyclone may form in the Coral Sea and cross Cape York into the Gulf of Carpentaria or vice versa, and can track parallel to the coastline either north or south.

The Australian cyclone season extends from November through to April with an average of 10 cyclones per year, although not all make landfall.

Cyclone Category

Sustained Wind Speeds (km/hr)

Wind Gusts (km/hr)

Typical Damage

1. Tropical cyclone 62-88 90-125 Negligible house damage; damage to crops, trees and caravans.

2. Tropical cyclone 89-117 125-164 Minor house damage; significant damage to crops, trees and signs.

3. Severe tropical cyclone 118+ 165-224 Roof and structural damage; power failure likely

4. Severe tropical cyclone 118+ 225-279 Significant roof loss and structural damage; widespread power failure; dangerous airborne debris

5. Severe tropical cyclone 118+ 280+ Extremely dangerous with widespread destructionSource: www.bom.gov.au/cyclone/about/intensity

Tropical Cyclone Categories

Cross section of a cyclone showing the storm surge due to both the wind set-up and pressure induced rise in sea level.

Nott et al., 2013 The world record storm surge and the most intense southern hemisphere tropical cyclone - new evidence and modelling. Bulletin of the American Meteorological Society.

Tropical Cyclone Monica’s track across Queensland and the Northern Territory in April 2006 (Source: Bureau of Meteorology).

Most severe cyclones in Queensland1. Tropical Cyclone Monica (2006) was the highest intensity cyclone on record to impact the east coast of Australia, making landfall as a Category 5 system close to Lockhart River in Far North Queensland. The storm surge magnitude for this event is unknown given the remote nature of the impact area.

2. Tropical Cyclone ‘Mahina’, occurring in 1899, caused the largest death toll of any natural disaster in Australian history. Over 400 people were killed on shipwrecks in Bathhurst Bay in Far North Queensland due to extreme waves and storm surge.

Tropical CyclonesA tropical cyclone is a violent storm characterised by a calm low pressure eye surrounded by strong winds rotating clockwise in the Southern Hemisphere. They form over tropical waters of temperatures greater than 26.5°C and can persist over oceans with lower temperatures, although the energy tends to dissipate over cooler waters and land. A cyclone’s intensity is categorised based on the severity of its wind (see below).

Tropical Cyclone Yasi In 2011, Severe Tropical Cyclone Yasi made landfall over South Mission Beach as a marginal Category 5 system with maximum wind gusts of 285 km/hr. It produced a storm surge peaking at 5.3 m at the town of Cardwell. TC Yasi made landfall at close to low tide, and the storm tide was 4.5 m relative to mean sea level (AHD). If TC Yasi crossed the coast at high tide, the storm tide could have reached over 7 m AHD.

TC Yasi was a large cyclone and storm surge over 1 m affected the Queensland coast from Port Douglas to Bowen.Waves over 9 m high were recorded in Townsville. In the towns of Tully Heads, Hull Heads, Cardwell and Port Hinchinbrook, houses were inundated and in some cases completely destroyed or washed away. Robust evacuation strategies meant that no fatalities occurred.

Tropical Cyclone LarryTropical Cyclone Larry made landfall over Innisfail in North Queensland in 2006 and was a Category 5 system prior to

landfall. While Larry was classed as a ‘midget’ cyclone with a small radius of just 30 km, it was associated with strong wind speeds and storm surge peaking at 2.3 m at Clump Point. Inundation along the coastline was higher that this level, generally around 3.5 m, reaching up to 5.2 m AHD. This was due to a combination of wave set-up, onshore wind forcing and local coastal bathymetric (sea floor) and topographic effects.

Tropical Cyclone Oswald Tropical Cyclone Oswald developed in the Gulf of Carpentaria in January 2013 and tracked as an ex-tropical cyclone down much of the east coast of Queensland. This brought gale force winds, high swell, intense rainfall and some storm surge. The persistent northerly wind direction caused storm surge of over 1 m in southern Moreton Bay. While the storm surge alone did not cause appreciable flooding on the open coast, when combined with flooded estuaries and high waves, it contributed to inundation in small urban catchments and significant beach erosion along the Sunshine Coast and Gold Coast beaches.

For more informationBureau of Meteorologywww.bom.gov.au/cyclone/about

Queensland Fire and Emergency Services www.emergency.qld.gov.au/emq/css/cyclone.aspwww.emergency.qld.gov.au/emq/css/storm_surge.asp

Department of Environment and Heritage Protection www.ehp.qld.gov.au/coastal/development/assessment/coastal_hazards__storm_tide_inundation.htmlwww.ehp.qldgov.au/coastal/monitoring/storm-tides/index.php

See your local Government website for local details regarding storm surge.

Be aware of your storm tide risk and be prepared to evacuate when directed.

Recent Storm Surge Events in Queensland

Storm surge and high tide covering a boat ramp at Biggera Creek, Gold Coast, during ex-TC Oswald (Source: GCCM, 2013).

Sea foam and an uprooted tree at Burleigh Beach, Gold Coast, during ex-TC Oswald (Source: GCCM 2013).

Damage to building at Clump Point during TC Larry (Source: EHP, 2007)

Damage to external shed wall by storm surge at Tully Heads during TC Yasi (Source: JCU, 2011).