Geotechnical And Coastal Engineering Aspects Of Risk Assessment For Coastal Protective Works And Assets

There are numerous coastal assets in NSW that are located in areas subject to beach erosion and hence are at potential risk of damage in coastal storms. Two risk assessment procedures are presented herein, namely:

• a geotechnical risk assessment of foreshore stability and protective works that was applied by Jeffery and Katauskas on the north coast of NSW and
• a coastal engineering risk assessment of damage to assets along beaches in Warringah as applied by WorleyParsons for Warringah Council.

The geotechnical assessments of risk to property and risk to life were based on the AGS (2007) procedures. These risk assessments are seen to be useful in informing emergency services of the potential need for evacuation of some properties in coastal storms, and allowing a framework for monitoring of the foreshore to be developed and implemented.

The coastal engineering risk assessment comprised the development of:

• an inventory of individual property details relevant to consideration of risk,
• resistance ratings for existing protective works located along the beachfront (e.g. based on toe levels and rock size),
• procedures for assigning likelihood ratings for occurrence of damaging events (based on the position of the Immediate Coastline Hazard Line relative to the seaward face of an asset, assuming no protective works),
• procedures for assigning consequence ratings to expected property damage (including consideration of whether the asset was supported on piles and the likely effectiveness of protective works seaward of the asset) and
• an overall risk analysis matrix used to derive a risk rating from different combinations of likelihood and consequence ratings.

These coastal risk assessment procedures are noted as being useful in preparing in advance for coastal storm
events.