Time for a Geelong flood levee?

On November 14, 2009 The Australian Government Department of Climate Change released a report on the risks from climate change facing coastal communities. I receive about 2-4 media releases per day from Penny Wong’s office announcing the Government’s latest policy position on climate change or heralding the publication of the associated White Papers, Green Papers and studies. However, as a resident of the coastal and low-lying town of Geelong I took particular interest in this policy document.

A couple of days after I received this media release Peter Farago of the Geelong Advertiser published an article on the report entitled ‘Drowntown Geelong’. Farago opened the article with the line, ‘Up to 6600 Geelong homes will be under water if a frightening climate change forecast comes true … and there’s nothing you can do about it’. While Farago is correct that there is nothing we can do about the climate change that will cause the estimated 1.1m sea level rise (because sea level rise has a lag time, so the earliest future sea level rise is the result of past climate warming), he is just plain wrong that there is nothing you can do about it. The whole purpose of the Government’s report is to propose adaptations that communities can make to avoid the flooding or inundation of low-lying areas when sea levels do rise. As Penny Wong states in the aforementioned media release, the report ‘shows that Australia must plan to adapt to the climate change we can’t avoid’. So although there is nothing you can do to mitigate the climate change that will cause the estimated seal level rise referred to in the report, there is plenty you can do to adapt to that rise in sea level.

Cheetham Salt Works, from Pt Henry Rd

Cheetham Salt Works, from Pt Henry Rd

One of the areas of Geelong particularly at risk from any rise in sea level encompasses Moolap and Newcomb — two low-lying suburbs adjacent to the Cheetham Salt Works on Corio Bay. Many of the low-lying coastal areas of Australia at risk from sea level rise are limited in the measures they can take to adapt because they lack a significant buffer zone between the sea and existing infrastructure on which to build sea walls, dykes or levees. Moolap and Newcomb, however, have in the salt pans of the Cheetham Salt Works (right) a 100-200 metre wide buffer zone between low-lying established infrastructure (the residential and industrial areas of Moolap and Newcomb and Portarlinton Road) and Corio Bay. This buffer zone provides Geelong with the perfect location to build some sort of infrastructure to hold back the rising bay. One of the possible measures that the State or Federal Government, Geelong Council or residents could take to adapt to sea level rise in these areas is to build a levee, like the one pictured below.

Sacramento River levee (USA)

Sacramento River levee (USA)

If you wish to read on, the remainder of this post looks in more detail at the options the people of Geelong have for protecting Moolap and Newcomb from rising sea levels.

The science, the risk and Council’s position

Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) data shows that sea levels are rising at approximately 3.3mm per year. At these rates much of Newcomb and Moolap, two suburbs just east of Geelong, will be inundated with seawater in the coming decades. Fortunately there is a stretch of land running from Eastern Park to Pt Henry (the Cheetham Salt Works, 11-129 Portarlington Rd, Moolap) on which to build a levee. Such a levee would delay flooding of these low-lying areas for some time. Should we build the levee?

On November 17th, 2009 the Geelong Advertiser published a few responses to a small poll it conducted on the issue. Some of the respondents were residents that live in low-lying coastal areas. The published responses, supposedly credible because they came from people who live in Geelong’s low-lying areas, were cursory analyses of the issue at best. Any person who (1) believes the primary national scientific research organisation’s data on sea level rise, (2) knows that Newcomb and Moolap lie just above sea level and (3) can add up will infer that the area is at risk of seawater inundation in the coming decades.

Council is aware of the issue. A 2008 Community Emergency Risk Management (CERM) plan produced by the Municipal Emergency Management Planning Committee rated sea level rise a ‘low risk’ for Geelong, stating that:

There is a risk of inundation of low lying areas with the exact extent unknown due to lack of data to predict sea level rises. It is unlikely that inundation would involve habitable buildings
and would most likely be limited to flooding of shorelines and roads located near the shore. Drain outfalls may be submerged thus leading to potential flooding upstream of the outlet. Long term road closures may be requires [sic] as well as the abandonment of low lying residential areas leading to displaced families/individuals as well as insurance issues.
(CERM Municipal Workbook No. 2, p. 46)

The first thing one notes about this statement is that it is contradictory. How can it be ‘unlikely that inundation would involve habitable buildings’ but ‘the abandonment of low lying residential areas leading to displaced families’ may be required? One would think that families would only be displaced when there is a risk that their habitable buildings will be inundated by flood waters. Another thing of note about the CERM report is that it lists sea level rise as a natural risk (p. 46). I guess Council’s position on global climate change is clear.

Presently the risk is low that residents of Moolap and Newcomb will have to abandon their homes. However, sea level rise is not like other risks. It occurs on a cycle so large that it is almost better to consider the risk to be cumulative. It does not come and go on a short cycle like, for example, the risk of fire.

The risk of fire increases over a number of years, peaking during the hottest months of summer. Eventually a fire breaks out and burns the existing fuel load. This reduces the risk of fire for the coming few years becasue the fuel load has been burnt in the previous season. The same is not true of the sea level rise cycle. The ‘fuel load’ for the risk of sea level rise is linked to the amount of water released into the ocean from ice at or near the poles. A reduction in this fuel load only occurs when water freezes in the polar caps. Unlike the fire fuel load which can be controlled at the local level, sea level rise is a global problem that moves on a much greater cycle of polar ice expansion and contraction. Accordingly, the risk accumulates until the next polar ice expansion — i.e. the next time the cycle shifts from the poles melting to the poles freezing, thus reducing the sea level by drawing seawater into the poles’ frozen stores. So although the risk of flooding in the Geelong area is low at present, the risk continues to increase as polar ice melts.

So should Geelong at least place a planning overlay on the Cheetham Salt Works so that if and when the time comes we can build a flood levee to hold off flooding of Moolap and Newcomb?

I have compiled a few images of the potential site for such a seawall, levee, floodbank, or whatever one wishes to call it. From satellite imagery and initial inspection of the site I have estimated that a 3.5km levee could be built to prevent flooding of Newcomb and Moolap to a height of approximately 3m above sea level. This is the approximate height above sea level of the lowest natural embankment at the Eastern end of the levee (Buckley Grove). The natural embankment at the Western end (Eastern Park/Limeburners Point) rises much higher above the present sea level. At current rates of sea level rise a 3m levee would keep Moolap and Newcomb dry for about 100 years.

Proposed site for Geelong levee

Proposed site for Geelong levee. The white building on the left is the Australian Animal Health Laboratory (AAHL) and marks the beginning of the Western natural embankment. Pt Henry Rd (on the right) or Buckley Grove would mark the Eastern natural embankment. The grey markers indicate 1km increments along the proposed levee.

The cost and the risks associated with building a levee

What is the cost? A very rough estimation of the cost, based on a US design firm’s costings, is AUD $20,000 per linear metre or AUD $70mil for a 3.5km levee.

Cheetham Salt Works, zoned Special Use, Schedule 1

Cheetham Salt Works, zoned Special Use, Schedule 1

Gretna levee, Louisiana (USA)

Gretna levee, Louisiana (USA)

Levee breach (USA)

Levee breach (USA)

The benefits: an opportunity in the waiting?

Does the Cheetham Salt Works provide a large, undeveloped area on which to build and test sea level rise adaptation measures? If CSIRO predictions prove correct, this will be a booming industry and Geelong has, in the Moolap salt works, a prime site to establish a controlled levee test facility.

Moolap Cheetham Salt site in the news

» ‘Residential plan for saltworks site’, Geelong Advertiser, 17 September 2012, Peter Begg.
» ‘EDITORIAL: Public must get say on land’, Geelong Advertiser, 17 September 2012.
» ‘New life set for salt sites’, Geelong Independent, 20 April 2012, John van Klaveren.
» ‘Ridley chief John Murray reviews Cheetham Salt business’, The Australian, 9 April 2012, Michael Bennet.
» ‘Waterside housing development on cards for Moolap plains’, Geelong Advertiser, 1 November 2011, Anthea Cannon.
» Ridley Corporation 2011 Annual Report, [PDF 3MB]. (Access all Ridley Corp. Annual Reports.)
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