Title

Victorian Coastal Cliff Hazard Assessment 2023 

Alternate title

Coastal_Cliff_Erosion_Assessment 

Purpose

Coastal planning and management 

Status

Completed  

Maintenance and update frequency

As needed  

Title

Shapefile, File geodatabase, MapInfo 

Topic category

• Environment

DELWP Categories

• Geological & GeophysicalEnvironmentOceans & Estuaries

Use limitation

Unknown 

Classification

Unclassified  

Statement

Areas susceptible to coastal cliff instability and/or erosion (ASCCIE) and Areas susceptible to Talus Runout (ASTaR) Consolidated shorelines, which include soil and rock cliffs, are not able to rebuild following periods of erosion but rather are subject to a one-way process of degradation. ASCCIEs typically have two components: • Toe Erosion A gradual retreat of the cliff toe caused by weathering, marine and bio-erosion processes. This retreat will be affected by global process such as sea level rise and potentially increased soil moisture. Future cliff toe position based on historical erosion rates with a factor applied to allow for the effect of future sea level rise. • Cliff Instability Episodic instability events are predominately due to a change in loading or material properties of the cliff or yielding along a geological structure. In soft cliffs, instability causes the cliff slope to flatten to a slope under which it is “stable” (geo-mechanically). Soil cliff slope instabilities are influenced by processes that erode and destabilise the cliff toe, including marine processes, weathering and biological erosion or change the stress within the cliff slope. Most of the hard cliffs are stable at very steep angles. Instability events may range from small-scale instabilities (block or rock falls) or discontinuities, to cliff slope instability cause by large-scale and deep-seated mass movement. The latter mode of failure in hard cliffs is rare. Risk Assessment Score The risk assessment framework defines risk as the “effect of uncertainty on objectives” and utilises likelihood and consequence to determine risk. Where likelihood is the probability of a coastal hazard occurring, and consequence is the impact of the coastal hazard on coastal values and uses, e.g. social, cultural, economic, and environmental. The first step of the risk assessment was the development of hazard extents and likelihoods based on the mapped ASCCIE and ASTaR. Likelihood defines the potential frequency of occurrence of a hazard occurring, and these were mapped to identify areas potentially at risk to cliff instability and/or erosion related to a likelihood. In this assessment a qualitative measure of likelihood was used. Likelihood is divided into five categories: rare, unlikely, possible, likely, almost certain. Each hazard scenario is assigned a particular likelihood and rated on this five-point scale which is considered increasingly likely over the long-term (2070-2100). Professional judgement was used to best define the likelihood of the hazard scenario for each timeframe. It is recognised that there are a range climate change trajectories and uncertainties regarding the impact of climate change on hazards. Note that the GIS exercise undertaken utilised only a single ASCCIE polygon (the most likely) for each timeframe in the analysis. The calculation of risk ratings assumes the same likelihood for each assessed timeframe across all coastal compartments, irrespective of differences in the underlying geology of coastal cliffs across coastal compartments. This limitation of the assessment is tied to the regional scale and deterministic approach adopted in the development of hazard inputs. For a regional/state-wide scale assessment it is not possible to adopt a probabilistic approach due to the large scale, total length of the shoreline and lack of site-specific data to build probability distributions around each parameter. The purpose of this regional/state-wide assessment is to identify high risk areas, where it would be prudent to undertake more detailed, probabilistic assessment on a local-scale or site-specific scale. 

Classification

Unclassified  

Attribute Quality

Positional Accuracy

Comments

The product is recommended for use at regional/state scale 

Conceptual Consistency

Missing Data

Excess Data