Coastal hazards and mapping
Queensland’s coastal communities are vulnerable to impact from coastal erosion and storm tide inundation. These are termed coastal hazards and are generally caused by extreme weather events such as cyclones. Each of these is a current day risk to people and property on the coast. Sound planning and development decisions are required to protect lives and property exposed to coastal hazards.
Each of the hazard types—and their relative impacts at a given location—are products of a complex interplay of physical factors. These factors include wind, waves, tidal flows, sediment transport, shoreline type (rock versus sand), sea depth (bathymetry), land elevation and longer-term geophysical processes. Coastal hazards can only be considered in planning and development decision making where the threat is understood and areas at risk have been assessed. Detailed investigative studies are required to provide this critical information at local levels.
- Erosion prone area maps
- Storm tide inundation
- Coastal Hazard Technical Guide
- Guideline for Developing a Coastal Hazard Adaptation Strategy
- Townsville Coastal Hazard Adaptation Strategy Pilot Project
- A risk assessment approach to development assessment in coastal hazard areas
- Coastal hazard area maps
Coastal erosion occurs when waves or water currents remove sediment from the shoreline. This can be a temporary cyclical process and the coast can rebuild over time, or be a permanent loss where sediment is not returned.
Changes in the sediment movement pattern; channel migration; or an elevation of sea level, may also accelerate erosion and cause permanent changes to the coastline. Sediment movement may be disrupted by natural processes (such as climatic or geophysical changes), or development (such as coastal protection structures like seawalls and groynes). A sea-level elevation will cause permanent inundation of low lying areas. It will also result in a morphological response of the coast, which will be observed as new or accelerated coastal erosion of higher areas.
Using defense works such as rock walls, to protect development at risk from coastal erosion impacts, can be expensive for landholders and the community. In addition, defense works can alter physical coastal processes, which can prevent a beach from reforming and accelerate erosion on adjacent beaches.
Other impacts of ongoing erosion include the loss of recreational and scenic amenity of the beaches, economic loss as tourism declines, and the loss of foreshore ecosystems.
The Department of Environment and Heritage Protection (EHP) has assessed the erosion vulnerability of the Queensland coast, and erosion prone areas have been declared to inform planning and development decisions. Find out more about erosion prone areas.
As a severe storm or cyclone approaches land, water levels may be elevated by a reduction of air-pressure and wind effects on the water surface. The increased height of the water appears as a rapidly rising tide but well above normal levels—a storm tide. If a cyclone makes landfall, especially during a high tide, the increased height of the water can result in the inundation or flooding of land up to several metres high. High storm tide inundation levels are infrequent but the effects on people and property can be disastrous. It is not always practical to use hard defensive structures to protect communities from impacts associated with storm tide inundation.
To assist decision makers and inform the public, the Queensland Government has encouraged and supported local government to undertake storm tide inundation studies and has acquired high resolution digital elevation data to help map areas vulnerable areas.
The Coastal hazard technical guide provides information about coastal hazards (coastal erosion and storm tide inundation) and guidance on the methodology used to determine areas at risk from coastal hazards.
The guideline Developing a Coastal Hazard Adaptation Strategy: Minimum Standards and Guideline for Queensland Local Governments has been prepared to help local governments prepare and implement coastal hazard adaptation strategies for urban areas at risk from coastal erosion and storm tide inundation.
To demonstrate how adaptation planning may be undertaken, the Local Government Association of Queensland, Townsville City Council and the Queensland Government have finalised a pilot coastal hazard adaptation strategy for Townsville.
A guideline has been prepared to assist local government in assessing development applications to address the coastal hazard(s) and associated risks to people, property, economic activity, social wellbeing and the environment.
Coastal hazard area maps indicate the footprint of the following coastal hazards:
- inundation from a defined storm event or storm tide event with a 1% (or one-in-100) annual return probability
- declared erosion prone areas
A detailed storm tide assessment specific to the location is generally required to determine the area that will be affected by a defined storm tide event. Where a detailed storm tide assessment has not been undertaken, the government has prepared default storm tide inundation mapping to assist with land use planning and development assessment decisions as follows:
- For South East Queensland, including the Sunshine Coast Regional Council area, the default storm tide inundation area is all land between the high water mark and 1.5 metres above the level of highest astronomical tide (HAT)
- Outside South East Queensland, the default storm tide inundation area is all land between the high water mark and the level of 2 metres above HAT.
Each of these includes the effect of a projected 0.8m sea-level rise.
EHP’s storm tide inundation area maps are categorised as either high or medium hazard areas. High hazard areas are the parts of the storm tide inundation area that are projected to be temporarily inundated to a depth of one metre or more during a defined storm tide event. The medium hazard areas consist of land within the storm tide inundation area that is projected to be temporarily inundated to a depth of less than one metre during a defined storm tide event.
Erosion prone areas are determined by a formula which considers:
- short-term erosion from storm events long-term erosion from sediment supply deficit, channel migration or tidal flow
- scarp slumping after the erosion event has ceased
- erosion due to future sea level rise from climate change, both by permanent inundation of land by tidal water and the coast’s morphological response to an elevated water level
- a 40% safety factor.
The coastal hazard area maps can be downloaded at a property scale by filling in an electronic form that requires a valid email address and the lot and plan details of the property of interest. An A4 size PDF map will be emailed to the address supplied. Alternatively, local area maps can be downloaded from a map sheet index. These maps will open as PDF documents and can be saved or printed.
Questions and answers that address coastal hazards area maps are also available.