3 October 2012 — A report and case studies, commissioned by the Department of Climate Change and Energy Efficiency and completed by a consortium led by AECOM, will help infrastructure investors, owners and managers make informed building decisions in a changing climate.

The Economic framework for analysis of climate change adaptation options report, and three associated case studies, focus on the impact of climate change on infrastructure networks and coastal settlements.

The reports aim to provide infrastructure investors, owners and managers, as well as all tiers of government, with the most cost-effective ways to prepare for the more extreme climate of the future.

  • Photo: Narrabeen Lakes

They show how a cost-benefit approach can be used to look at options that would reduce vulnerability to climate change impacts, and how to select the option which offers the best long-term value for money.

Domestic Adaptation branch director John Higgins said the reports bridged the gap between climate science and effective decision-making in an uncertain environment.

“The Adaptation Policy team has worked closely with AECOM to ensure these reports will be invaluable to infrastructure planners,” he said.

The main report sets out the methods for building during a changing climate.

The three case studies apply the methodology to:

  • flood mitigation around Narrabeen Lagoon in Sydney’s northern beaches
  • securing a long-term water supply for towns in the Central Highlands region of Victoria
  • reducing the impacts of heatwaves on Melbourne’s urban rail network

In the first case study, Coastal inundation at Narrabeen Lagoon – Optimising adaptation investment, the impact of climate change on flooding from Narrabeen Lagoon in the northern Sydney local government area of Pittwater is analysed.

It found the best “socially and economically justifiable strategy” was to immediately institute an early flood warning system, amend planning regulations, and build the Lake Park Road levee, followed by channel widening in 2035.

“Narrabeen Lagoon is the smaller body of water to the north and east of Pittwater Road. Narrabeen Lakes is the larger body of water to the south of Pittwater Road and Wakehurst Parkway,” the report says.

“Narrabeen Lagoon is one of about 70 intermittently closed and open lakes and lagoons spread along the coast of New South Wales.

“Storms can block ocean entrances to lagoons by depositing sand but, in combination with floodwaters from creeks that feed into a lagoon, they will occasionally also flush away deposits in the entrance.

“When its entrance is blocked, rain and floodwaters will generally fill a lagoon like a bathtub, and can therefore flood the land and houses around it.

“Because climate change is expected to increase the frequency and intensity of storms and rainfall in the Narrabeen catchment over the coming century, as well as rising sea levels, decision makers need a better understanding of the social costs and benefits to their communities of the different adaptation measures that could be implemented to reduce inundation.

“This pioneering study estimates the social benefits of adaptation to climate change in terms of willingness to pay, rather than just costs avoided. It also employs Monte Carlo analysis to generate more realistic probabilities of overall costs and benefits, as well as modelling the expected future values of variables such as rainfall using extreme value analysis rather than just taking averages.

“Six possible adaptation measures are analysed in detail. These are:

  • Lagoon entrance opening
  • Lake Park Road levee
  • Progress Park levee
  • Nareen Creek levee 2
  • Flood awareness
  • Planning control

The report found that opening the ocean entrance to Narrabeen Lagoon permanently by excavating a channel through the headland rock shelf would lower the water level by up to one metre.

“Modelling suggests that a 70-metre wide channel is economically viable now, but the benefits increase if deferred until 2035. However, the study suggests that a 100-metre wide channel would be far more expensive, with little additional benefit, and could therefore not be justified economically.

“Construction today of a three-metre high levee on Lake Park Road along the southern boundary of the Sydney Lakeside Holiday Park would generate net economic benefits of $0.9 million, and is therefore a viable proposition. However, a similar levee at Progress Park is unlikely to generate sufficient social benefit to outweigh the costs involved.

“A floodwall and floodgates along Wakehurst Parkway would prevent rising floodwaters in the lagoon from backing up into Nareen Creek, which feeds into it. Although almost 300 houses would be protected, the study suggests that the cost involved outweighs the benefits.

“A system to provide Pittwater residents with early warning of floods would be relatively inexpensive, and would allow them to move valuable belongings and business merchandise to higher ground to avoid damage. With net benefits of $12 million in present value terms, it would be worthwhile implementing this strategy immediately.

“Amending planning regulations to require an increase in floor height by at least one metre for all new buildings and renovations to existing buildings would reduce flood damage over time.

“Although an average house is renovated only every 40 years on average, the beneficial net present value from immediate adoption of this measure would be at least $13.8 million.

“Overall, a socially and economically justifiable strategy for the Narrabeen community would be to immediately institute an early flood warning system, amend planning regulations, and build the Lake Park Road levee, followed by channel widening in 2035.”

The other two reports can be viewed here: