Community Information Session 26 November - Denham Town site Coastal Hazard Risk Management and Adaptation Plan (CHRMAP)

Published: Wednesday, 13 November 2019 at 1:30:01 PM

 Denham Town site Coastal Hazard Risk Management and Adaptation Plan - Community Information Session 26 November

The Shire of Shark Bay has been undertaking a Coastal Hazard Risk Management and Adaptation Plan (CHRMAP) for the town of Denham to address the risks of coastal hazards both now and over the next 100 years. Undertaking a CHRMAP is a recommendation of the Western Australian Planning Commission’s (WAPC) State Planning Policy 2.6 (SPP2.6). 

The Shire has already held two community workshops to discuss and inform the project and now the draft is ready for presentation to the community.

There will be a Community Information Session at 6.30pm on Tuesday 26th of November held at the Shark Bay Recreation Centre, Francis Street, Denham to discuss the recommendations from the CHRMAP as well as the potential adaptation options proposed for the future.

As part of this project, the Shire has identified all assets within the town that may be subject to coastal inundation or erosion over the next 100 years. Due to Denham’s coastal setting, many of the town’s public and private assets are at risk or will be at risk by 2118. The CHRMAP has been undertaken to identify the level of risk and develop adaptation options to ensure Denham is ready for coastal hazards.

All community members are welcomed for the upcoming session. Whether you directly own assets, community consensus is important for achieving coastal management that meets the community values.

A link to the online coastal hazard mapping can be found below.

Further text explaining the hazard maps is also outlined below. It should be noted that the hazard zones are not predictions of future coastline locations, they are planning tools to be utilised by community members and decisions makers to help accommodate coastal evolution and extreme weather-related inundation.

In conjunction with Water Technology, the Shire has developed a number of recommendations, planning controls and coastal adaptation strategies that will be presented at the upcoming meeting. These strategies were designed with the stakeholders’ values in mind and have been assessed to ensure that they will provide a benefit to the community and be financially viable.

We highly encourage any members of the community who have any questions or wish to raise any concerns to attend the upcoming meeting.  The meeting is open to all members of public.

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Online Coastal Mapping

Short link: http://bit.ly/2WKX8Kd

Full link: https://watech.maps.arcgis.com/apps/webappviewer/index.html?id=6e092b4d0f044e038a721705e907c084

This online map and asset database has been prepared to display the results of the Denham Town site Coastal Hazard Risk Management and Adaptation Plan. Important terms to assist in interpreting these maps are shown in the table below.

The aim of this project is to identify assets at risk of coastal hazards (erosion and inundation) at the present and over the next 100 years due to sea level rise, and to develop adaptation options to accommodate these risks.

The purpose of the maps is to show the community the extent of the hazard zones on the town’s assets. Selecting the key assets layer displays assets identified within the hazard zone under four categories.

Selecting the coastal processes assessment layer displays the various coastal processes allowances identified as part of the project. These include the HSD, present-day, 2030, 2050 and 2118 allowances. Note that these allowances are not a prediction of future erosion. They are a planning tool calculated by methodology described by the WAPC including different mechanisms of erosion and a safety factor. They are designed to assist decision makers in the adaptation planning process.

Selecting any of the inundation layers overlays the modelled flood results for four different storms over the four project timeframes (present-day, 2030, 2050, 2118) which differ due to predicted sea level rise. Note that the WAPC requires finished floor levels of new development to meet or exceed the 2118 500-year ARI storm level. As a result, this is the most important inundation level to consider for long-term adaptation. The other storms provide users with an indication of the level of risk for existing developments. Note that the map height data does not include specific development footprint levels, only the height of the surrounds, and as such some raised developments may be within the shaded area but at reduced or no risk of flooding from a given storm.

Table 3-1             Online Mapping Definitions

Term

Definition

AHD

Australian Height Datum, a sea level reference generally fairly close to mean sea level

ARI

Average Recurrence Interval: the estimated time period (in years) between events of equal or greater magnitude, e.g.: at present-day sea levels, the water level is expected to reach 2.7 m AHD once every 100 years.

Coastal Processes Allowance

The potential hazard zone from erosion as calculated by the recommendations provided by the Western Australian Planning Commission. This zone moves landward over time due to the allowance for long-term erosion, sea level rise and a safety factor. Coastal protection structures designed for less than 100 years may reduce long-term erosion calculations, but do not affect the potential for erosion due to sea level rise, or the safety factor, which both must still be included.

HSD

Horizontal Shoreline Datum, the present-day landward limit of influence from coastal processes. Generally, this is taken as the level where vegetation begins growing on the beach. May be taken as the location of a seawall in built stretches of Denham’s coast. Erosion allowances are calculated from this line moving inland.

Inundation

In this case refers to flooding from the coast due to extreme weather events that result in a coastal storm surge. Coastal storm surges from events such as cyclones can cause the sea level to rise significantly above the high tide lines for a period of minutes to hours, causing significant damage to low lying assets and allowing for waves to cause erosion much further inland than normal. When coinciding with a high tide (generally rare) this can be particularly devastating.

 

 

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