Queensland storm tide maps and sea level rise: what they show

Queensland's storm tide maps show which coastal land a storm tide would temporarily cover. Two statewide sets are public. The State Planning Policy coastal hazard maps divide the storm tide inundation area into high hazard (one metre or more of water) and medium hazard (less than one metre), and include a 0.8 m sea level rise by 2100. The NDRP Storm Tide Hazard Interpolation series maps water level, depth and extent along the whole Queensland coast for a set of storm tide events, including the 20, 100 and 1000 year ARI events. Sea level rise projections are published separately, at tide gauges, as a change in metres from a baseline period.

What is a storm tide?

A storm tide is the sea level reached during a severe storm: the storm surge, which is the rise in water pushed up by strong onshore winds and low air pressure, added to the normal astronomical tide at the time. A cyclone surge that arrives at high tide gives a higher storm tide than the same surge at low tide. Storm tide flooding is temporary. It lasts hours, not the permanent loss of land that coastal erosion or sea level rise causes.

What do Queensland's coastal hazard maps show?

The Queensland Government's coastal hazard area maps, used under the State Planning Policy, show three things for a coastal lot:

• Storm tide inundation area, high hazard: land that would be covered by one metre or more of water in the defined storm tide event.
• Storm tide inundation area, medium hazard: land that would be covered by less than one metre.
• Erosion prone area: the width of coast considered vulnerable to erosion and permanent inundation over a 100-year planning period.

The storm tide areas include the state's 0.8 m sea level rise allowance to 2100. They are development assessment triggers: land inside them may need a coastal hazard assessment or minimum floor levels for new building work. The maps can be viewed in the State Planning Policy interactive mapping system and the coastal hazard map application, or requested by lot on plan.

Several councils also publish their own storm tide mapping in their planning schemes or flood maps, for example Brisbane City Council's storm tide inundation areas and the Gold Coast's storm tide surfaces for 2010 and 2100. Where a council has its own mapping, its planning scheme sets out which map applies.

What does the NDRP storm tide mapping show?

The NDRP Storm Tide Hazard Interpolation series was prepared by GHD in 2014 for the Queensland Government and is published on Open Data Queensland under CC BY 4.0. It takes modelled storm tide levels at points along the coast and spreads them across a digital elevation model in three regions, North, Central and South. For each event it publishes a water level in metres AHD, a depth in metres and an inundation extent.

The series covers a range of return periods from 20 year ARI to 10,000 year ARI, plus a theoretical maximum storm tide (TMST). The events most often used are compared below. The chance over 30 years is the chance of at least one event of that size in that time.

Event	Chance in any year	Chance over 30 years	How it is usually read
20 year ARI	about 5%	about 78%	A frequent storm tide
100 year ARI	about 1%	about 26%	The usual planning benchmark
1000 year ARI	about 0.1%	about 3%	A rare event, relevant to evacuation and critical uses
Theoretical maximum (TMST)	no stated chance	not applicable	An upper bound, not a likelihood

Three limits apply. The method is an interpolation onto a ground model, often called bathtub mapping: it does not model water flowing across land, waves breaking or seawalls holding water back. The ground model dates from the study, so filling and development since then are not reflected. And the Open Data Queensland listing does not describe a sea level rise allowance for the series, so it should not be read as a 2100 map. The State Planning Policy hazard areas are the ones that carry the 0.8 m allowance.

How are sea level rise projections shown for the Queensland coast?

Sea level rise projections are published at tide gauges, not at addresses. The IPCC's sixth assessment (AR6) gives projections at named Australian gauges, including Queensland gauges such as the Gold Coast Seaway. Each projection is:

• a change in relative sea level, in metres, compared with the 1995-2014 average
• given for a year, usually 2050 and 2100
• given for an emissions scenario, most often SSP1-2.6 (low), SSP2-4.5 (intermediate) and SSP5-8.5 (high)
• given as a median with a likely range, the 17th to 83rd percentile

At most gauges the scenarios sit close together to 2050 and spread apart by 2100. The figures and how to read them for one gauge are set out in sea level rise for an address.

Can I add sea level rise to a storm tide level?

No. A projected rise at a gauge is a change in sea level, not a flood level, and adding it to a storm tide level does not give a future storm tide level for a lot. Wave setup, the shape of the coast and the ground between the sea and the lot all sit between the two. For development, the State Planning Policy mapping already includes the 0.8 m allowance, and the council's coastal hazard overlay sets the levels a building application is assessed against.

Where does the LayeredGeo report show storm tide and sea level rise?

The Flood Model Report reads the NDRP storm tide series at the property as a published study: the water level for the 20, 100 and 1000 year ARI events and the theoretical maximum, and the depth where the series publishes a depth grid for that event. Coastal addresses within 10 km of the coast or a tidal river, and within 100 km of a tide gauge, also get a Sea Level Rise Indication page with the AR6 figures for 2050 and 2100 at the nearest gauge, the gauge named and its distance stated.

The Property Report shows the NDRP storm tide inundation extents for the same four events and the state's storm tide high hazard area on its Flood: Risk & Hazard page, with council storm tide mapping where it is held. A declared erosion prone area appears on the Geotechnical & Natural Hazards page. How the flood maps in a planning report differ from modelled numbers is covered in flood overlays versus actual flood risk.

Common questions

Where can I find storm tide maps for Queensland?

The State Planning Policy coastal hazard maps are in the Queensland Government's interactive mapping system and coastal hazard map application, and can be requested by lot on plan. The NDRP Storm Tide Hazard Interpolation series is on Open Data Queensland. Some councils publish their own storm tide maps in their planning schemes.

What is the difference between a storm tide and a storm surge?

A storm surge is the rise in sea level caused by a storm's winds and low pressure. A storm tide is the total water level reached: the storm surge plus the normal tide at the time.

Does the Queensland storm tide map include sea level rise?

The State Planning Policy storm tide inundation areas do: they include a 0.8 m sea level rise by 2100. The Open Data Queensland listing for the NDRP interpolation series does not describe a sea level rise allowance.

What does storm tide high hazard mean in Queensland?

It is land the Queensland coastal hazard maps show would be covered by one metre or more of water in the defined storm tide event. Medium hazard is land covered by less than one metre.

The free coverage check shows whether published flood or storm tide modelling reaches an address. The coastal and flood planning maps for a lot are in the Property Report.

LayeredGeo's Flood Model Report collects every published flood model that reaches a property, with modelled depth, velocity and flood level for each event, and a sea level rise indication for coastal addresses.

Sources

• Queensland Government. About coastal hazards. qld.gov.au
• Queensland Government (GHD 2014). NDRP Storm Tide Hazard Interpolation Series. Open Data Queensland, CC BY 4.0. data.qld.gov.au
• Garner, G. G. et al. (2021). IPCC AR6 Sea Level Projections. Zenodo, doi:10.5281/zenodo.6382554 (CC BY 4.0). doi.org
• Fox-Kemper, B. et al. (2021). Ocean, Cryosphere and Sea Level Change. In Climate Change 2021: The Physical Science Basis, IPCC AR6 WG1, Chapter 9. ipcc.ch

About this article. Published by LayeredGeo and written from the published research cited in the Sources section above. It is general information about how property and ground conditions are assessed in Australia, not engineering, planning, legal or financial advice, and it is not specific to any property. Check anything that matters against the source dataset or a suitably qualified professional before you rely on it. If you spot something wrong, tell us at hello@layeredgeo.com.au and we will fix it.

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