Coastal Hazard Management

2016 Coastal Hazard Risk Management and Adaptation Plan

The purpose of the CHRMAP is to provide strategic guidance on management and adaptation in areas potentially exposed to coastal processes, specifically sea level rise and storm erosion. The plan focuses on seven study areas, including Gracetown, Prevelly, Gnarabup, Hamelin Bay, Molloy Island, Augusta North and Augusta South and follows the process outlined in the State Coastal Planning Policy of risk identification, risk analysis and risk evaluation. A series of maps were prepared for each location, and risk categories developed as follows:

• Low coastal exposure (potential exposure to coastal processes in 20 -100 years)
  Medium coastal exposure (potential exposure to coastal processes in 10 – 20 years)
  High coastal exposure (potential exposure to coastal processes in 0 – 10 years)

The limited topographic and geotechnical data available means the analysis of inundation and influence of coastal processes (particularly along limestone cliffs) is limited to a very broad scale assessment. As a result, a conservative approach has been adopted. The intended outcome is to prioritise investment for further assessment and monitoring in these areas.

A copy of the 2016 Coastal Hazard Risk Management and Adaptation Plan (CHRMAP) mapping can be found here, and the detailed CHRMAP report can be found here

2017 Limestone Cliff Stability Assessment report

A Limestone Cliff Stability Assessment was prepared in 2017. The study was to provides a better understanding of how limestone cliffs will react to coastal processes i.e. from sea level rise, storm surges, wind, waves etc and to assess and manage the risk to recreational users and assets in close proximity to the coast. The assessment covers Gracetown, Prevelly and Gnarabup, and is based on a 100 year planning timeframe with a notional 0.9 m of sea level rise. 

A key outcome of the assessment was to refine hazard mapping identified in CHRMAP. The maps detail lower and upper extent hazard mapping with blue lines representing recreational users and red lines representing Shire assets. The lower extent of hazard lines defines the seaward side that may be impacted from rockfall collapse, while the upper extent shows the landward extent of the zone considered hazardous to Shire assets due to cliff regression over a 100-year period.

 A copy of the Limestone Cliff Stability Assessment mapping can be found here, and the full copy of the Limestone Cliff Stability Assessment Report can be found here

2019 Limestone Stability Report 

Following the 2017 risk assessment, modifications were made to stairs at Gracetown and Surfers Point, and additional signage installed throughout the Shire. In 2019, further investigations were undertaken at Gracetown, Surfers Point and Gnarabup. This resulted in 4 key actions being recommended:

• Removal of a small overhang at Gracetown;
• Installation of a protection fence at Riflebutts consisting of high tensile wires and posts that extend from the toe of the cliff into the surf zone; and
• Underpinning of the overhang under the concrete stairs that lead from the upper carpark down towards the cafe at Gnarabup; and
• Installation of additional fencing & signage at Surfers Point with possible future underpinning of an overhang near the main break access stairs;

Copies of the full report are available here and minutes of the Council resolution are available here.

2021 Update

Since late 2019, the Shire has implemented works at Gracetown, Gnarabup, Surfers Point and Riflebutts. It is expected to undertake a full review of coastal risk at all Shire managed locations in late 2021.

For more information on this work, please contact the Landcare and Environment Team at the Shire on (08) 9780 5255.