In 2018, the Shoalhaven Coastal Zone Management Plan Risk Assessment identified sewage pump stations (SPS) in the Mollymook Region that are considered to be exposed to a “high” or “extreme” degree of coastal hazard risk. In order to address this risk, Water Technology was engaged by Shoalhaven City Council to identify a range of potential coastal protection options for these assets, and identify cost-effective solutions.

The project looked at a range of potential coastal management adaptation options, including relocation of the assets (both passive and active relocation), adaptation of the structures (such as raising electronic components), coastal protections structures (such as geotextile sand container and rock armoured seawalls), as well as more environmentally friendly options such as coastal dune building and revegetation in front of the structures.

Scope:

Coastal Management Options Assessment of at risk infrastructure, including sewage pump stations.

Location:

Shoalhaven

Client:

Shoalhaven City Council

Options were assessed using a robust Cost Benefit Analysis (CBA). This included a sophisticated Monte-Carlo analysis of simulated storm events and the resulting cost of asset damage. For this analysis, the forward 30-years planning period was simulated over 1,000 times, and the range of potential outcomes were provided to inform Council decision making regarding protection of the assets. These costs were then assessed against social and environmental benefits in order to provide a cost-benefit ranking of the various options at each site and each asset.

The study looked at solutions over two forward time frames. “End State” solutions were assessed in order to determine long term solutions – and typically, these solutions involve active relocation, or the implementation of hard coastal protection structures such as revetments and seawalls.

In addition to identifying the long-term end state solutions, a series of “Transitional”, or “Interim” coastal management actions were assessed that can mitigate coastal hazard risk in the short to medium term. Whilst these do not represent long term solutions, they can be considered as transitional measures, assisting to provide a cost-effective level of protection against medium term risk over a nominal forward 30 years planning period.

The sophisticated use of cost-benefit analysis to inform coastal adaptation planning was presented at the NSW Coastal Forum in November 2020, with highly positive feedback.

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