Coastal management

Throughout our planet’s history, sea level has risen and fallen over millions of years. Strong scientific evidence indicates global sea level has risen more consistently over the past century. Current projections for sea level rise are based on a vertical sea level rise of 0.9 metres over a 100 year period to the year 2110 (SPP 2.6). Sea level rise is being linked to climate change which has been observed as an average rise in temperature of the Earth’s climate over the past century, also known as global warming.

Global warming causes a rise in sea level in two primary ways. First, as the global temperature increases the seawater expands, taking up more space in the ocean basin and causing a rise in water level. The second mechanism is the melting of ice over land which then adds water to the ocean.

Coastal vulnerability is the extent that an area of coastline is susceptible to the effects of erosion, storms and sea level rise. Coastal areas that are exposed, sensitive and less able to adapt are vulnerable. Part 1 of the CHRMAP process has identified areas of the City of Wanneroo that are vulnerable over the next 100 years.

In July 2013, the amended State Coastal Planning Policy No 2.6 (SPP 2.6) was gazetted. A new provision was included within this Policy requiring a Coastal Hazard Risk Management & Adaption Plan (CHRMAP) to be prepared by 'responsible management authorities’ (e.g. the City of Wanneroo), where existing or proposed developments are in an area at risk of being affected by coastal hazards over the planning timeframe. The main purpose of a CHRMAP is to define areas of the coastline that are vulnerable to coastal hazards and to develop an adaption plan to monitor and manage these hazards where required.

The City of Wanneroo has chosen to complete the CHRMAP in two main components. The first component is complete a coastal vulnerability study and hazard map (Part 1). The results of this study are available on the City’s website and mapping tool.

The second component of the CHRMAP utilises community feedback to help determine the potential risk and available adaptation strategies to manage coastal vulnerability along the City’s coastline.

The City of Wanneroo is responsible for managing 32 km of coast line along the rapidly expanding northern corridor of the Perth Metropolitan area. In addition to the existing infrastructure and assets along this coast line, there is significant development planned in this area. It is therefore of extreme importance to understand what the potential impacts of sea level rise are and to identify where this may occur. This enables all stakeholders to effectively plan how the potential risks of sea-level rise can be managed for both existing and planned infrastructure and assets.

The City’s CHRMAP does not include detailed information about the risk management and adaptation planning for undeveloped areas along the coastline for which the City is not currently managing. The relevant developer for each foreshore area is responsible for developing their own CHRMAP consistent with SPP 2.6 and the overall strategic direction of the City’s CHRMAP.

The City of Wanneroo engaged specialist coastal engineers M P Rogers & Associates Pty Ltd (MRA) to complete the CHRMAP Part 1 study. The study identified cultural, environmental and built assets that may be exposed to coastal erosion, storm surges and sea level rise over specified time frames, in accordance with SPP 2.6.

The study reviewed historical studies and used scientific methodology to identify coastal areas and associated assets that may be vulnerable to coastal processes.  How vulnerable an asset is depends upon how exposed the asset is to the sea inundation and erosion; the sensitivity of the asset; and the ability for that asset to adapt to these changes.  

Hazard maps were developed as a component of the CHRMAP Part 1 study to illustrate the areas of coastline that may be impacted over the next 100 years.   The vulnerability of the coastline is defined by the following timeframes:

• Present day – brown line;
• 2030 – green line;
• 2050 – blue line;
• 2070 – purple line;
• 2090 – pink line; and
• 2120 – red line.

Copies of the hazard maps are available within the CHRMAP Part 1 study, available by clicking below and within the City’s online mapping tool.

CHRMAP Part 1 study

Key areas that may be impacted over the next 35 years are included in Table 1:

Description	Suburb	Estimated Vulnerability Timeline
Priority Ecological Community	Two Rocks	2030
Sovereign Drive & residential lots	Two Rocks	From 2050
Beach access road to 'The Spot'	Two Rocks	2050
Capricorn Groyn car park	Yanchep	2050
Brazier Road car park adjacent to Yanchep Lagoon	Yanchep	2030
Residential lots west of Brazier Drive	Yanchep	From 2030
Heritage site Karli Springs	Alkimos/Jindalee	2050
Residential lots west of Clarecastle Retreat	Mindarie	2050
Priotiy Ecological Community	Mindarie	Present day

Table 1 The nine key areas of vulnerability along the City of Wanneroo’s coastline, as determined by Part 1 of the CHRMAP study.

The City has no control or influence in the calculation of property insurance as this is a matter for private insurers.

The residential property market is subject to a number of external factors that can influence property values. Therefore the City is unable to comment as to whether the CHRMAP findings will negatively impact the value of properties that have been identified as at risk over the next 100 years.

The City will consider all viable options that may assist in mitigating the risk of sea level rise on our coastline inclusive of placing a notification on the certificate of title for affected properties. The City has a duty of care to consider sea level rise in planning and development decisions now that the risks identified in the CHRMAP Part 1 are known.

Quinn’s Beach was not included in the CHRMAP Part 1 process as the Quinn’s Beach Long Term Coastal Management Study was not yet finalised at the time. The City reviewed the potential coastal hazard risk in Quinns Rocks in 2017 and subsequently completed a coastal hazard assessment for this area, which is now available on the City’s website and online mapping tool.

The City is now undertaking Part 2 of the study – Risk Assessment, Analysis and Adaptation Planning. This stage of the study involves assessing the risk and developing an adaptation plan to manage potential sea level rise and associated coastal erosion. The City has engaged coastal management consultants Cardno to assist in this process.

The City conducted a Values Survey in August 2016 to identify what the community values about the City’s coastline. The survey results have been combined with information on the potential impact and vulnerability of the City’s coast to sea level rise and erosion to complete a risk assessment for the high risk sites along the City’s coastline. The outcomes of the risk assessment will help the City to identify which sites should be prioritised in the future.

In September 2017, the City prepared draft preliminary adaptation options for the City’s coastline and each of the specific key risk areas. The community was invited to comment on potential adaptation options for vulnerable coastal areas, through a survey, open from the 20 November 2017 to the 18 December 2017.

The results from the survey were collated to help to determine the types of adaptation options that may be used along the City’s coastline in the future. A draft Final CHRMAP report is currently being drafted and will be presented to Council in late 2018.

The draft Final CHRMAP report will be considered by Council for adoption in late 2018. The City will then begin an implementation phase until the next review of the CHRMAP is required.

This study is planned to be repeated every five to ten years to ensure the vulnerability of assets are reassessed. This will assist in reviewing any potential changes in the impact of coastal processes and to review the effectiveness of implemented adaption plans.