As global sea levels rise, local governments in Australia and New Zealand are being tasked with the protection of their communities and infrastructure.

During a vicious storm event in June 2016, the Fairy Bower Amenities building, located on the harbour-front promenade between Sydney’s Manly Beach and Shelly Beach, was irreparably damaged. Upon rebuild, Council ensured the new building was designed with climate change in mind.

Threats from climate change include higher sea levels and increasingly severe storm events. The sea wall in front of this building is currently overtopped to a depth of 0.2m of sea water during the once in 1 year 0.01% Annual Exceedance Probability (AEP) storm event, which increases to a 0.5m in a 1 in 100 year, 1% AEP storm event. By 2050, however, those figures would increase to an AEP of 0.4m and a one in 100-year event depth of 0.6m, as the result of a 0.4m sea level rise (above the 1990 mean sea level).

The new building design included marine grade, galvanised steel rafters in the roof, itself cast into the reinforced concrete block walls with galvanised reinforcement rods. Footings were held firm by a concrete layer of heavy duty waterproof membrane slab, anchored to the sandstone below with marine grade, stainless steel rods. Even the mosaic tile grout was sealed with a waterproof, penetrative sealer.

All of these design features, and many more, were introduced because of the predicted increase in severity of coastal storms.

The re-build was an example of a new focus required by local governments throughout Australia and New Zealand as they build resilience into their infrastructure to protect against sea level rises and other impacts of climate change.

What changes will global warming bring?

Published in 2018 in conjunction with Northern Beaches Council, IPWEA’s PN 12.1: Climate Change Impacts on the Useful Life of Infrastructure looks to the year 2100 to offer increased clarity to plan for the effects of climate change.

It discusses an asset’s useful life, bringing into consideration the new levels of physical wear and tear that will be introduced by aspects of climate change, including rising sea levels. It also suggests best practice processes for planning climate change adaptation measures, including a Decision Tree to aid asset managers in their development of solutions.

“According to the International Energy Agency, the current rate of greenhouse gas emissions continues to increase,” says the report’s author, Dr Jacqueline Balston, applied climatologist, climate consultant and adjunct senior research fellow at the University of South Australia. “A continued high-emissions scenario is associated with sea level rises between 45cm and 82cm along the Australian coastline by 2100. There is also the possibility of additional contributions to sea level from extreme events such as a large ice-shelf breakdown in Antarctica that may further add to those projected sea levels.”

When they include such events, many experts put the sea level rise at one metre, which will offer plenty of reason for concern.

“...it should be noted that even moderate increases in sea level rise can result in extreme sea level events associated with high tides and storm surges that occur hundreds of times more frequently than they currently do,” Balston wrote in the report. “As an example, an event that now occurs once every 100 years could be expected to occur two or three times every year by the end of the century.”

Professor Jean Palutikof, Director of the National Climate Change Adaptation Research Facility, agrees. “When you get a storm, if your sea levels are a metre higher than they are at the present day, the effect becomes magnified in terms of things like wave height and surge,” she says.

“So the damage that’s inflicted during a storm is considerably worse than it would be if sea levels were at present day levels.”

The ocean around Australia has also become more acidic, a trend that will continue as more carbon dioxide dissolves in sea water to produce carbonic acid.

These and other changes – including high wind events and cyclones, heatwaves, changes in rainfall intensity and more bushfires – will combine to introduce entirely new challenges to those whose responsibility it is to manage assets and infrastructure.

At-risk assets

Sea level rise puts an enormous amount of infrastructure at risk, Balston says. And it’s not just about flooding.

Assets along the coast may be affected by sea level rise on two fronts. First is the erosion of, or damage to, the coastline and potentially to any assets built along the coastline. This includes piers, jetties, storm walls, buildings, walkways, roads, pavements, curbing, etc.

“If these assets are inundated or undermined by sea level rise and they are not designed to withstand such events, then they’re likely to be damaged. That’s the first thing,” Balston explains.

“The second is that as the sea level rises, there is an infiltration of salt water into the underlying ground and in some cases ground water. So assets that have a concrete or steel footing going into the soil can be affected by rising salt that’s pushed into the landscape. In some cases that might occur some distance from the coast. The resulting rising salt causes problems that might not have occurred in that area before, including corrosion and subsequent damage.”

Dave Cull, President of Local Government New Zealand (LGNZ) and Mayor of Dunedin, says a recent national review highlighted three waters (drinking water, wastewater and stormwater) and roads as the major infrastructure affected by rising sea levels. Protection of roads and three waters against a rise of just half a metre, he says, will cost NZ$2.7 billion nationally. That amount doesn’t take into account any other private or central government infrastructure on top of or dependent on water and roads.

“The big issue in Dunedin is a relatively unusual one,” Cull says. “Sea level rise is expressed here through ground water rise in South Dunedin, because it was a reclaimed swamp. So we’ll see ponding as the sea level rises. It’s not the sea crashing through the dunes, but instead water rising from beneath the ground.”

What can be done?

One council in New Zealand, Cull says, spent half a million dollars on a seawall and the first storm to come along left it virtually destroyed. So not all current solutions are successful. But there is plenty that a council can do, and some are developing innovative solutions.

In Queensland’s Mackay, as reported by the Daily Mercury, the council is seeking innovative solutions to coastal erosion in partnership with local residents. The council owns the land on the immediate foreshore, and homeowners adjacent to that land are at risk from sea level rise. The council is seeking to break up the land it owns into lots that match the boundaries of the people living along the foreshore and handing those lots over to the householders, on the understanding they will pay for a seawall.

Cull says much of the solution begins with communication. Ratepayers have to fully appreciate the gravity of the risk before they can be convinced that a solution is worth paying for.

“The engineering feasibility stuff is part of the conversation, but you’ve first got to have the understanding of the risk before looking at your options,” he says.

“We’re following the Dynamic Adaptive Pathways approach, where you don’t try to solve the whole problem right now. We figure out what we need to do to ensure resilience until the water gets to a certain level a few decades from now. Then we’ll work out the next bit. So we’re spending about NZ$30 million over the next 10 years on enhanced groundwater drainage in South Dunedin.”

Speaking of communication, in Queensland’s Noosa, a council-run community forum about sea level rises attracted 60 residents. They heard about sections of the shoreline most at risk, were presented with scientific data, and concluded as a group that they would go ahead with ‘nature-based measures’ including dune revegetation and beach nourishment, rather than built structures such as rock walls.

In the Hawke’s Bay region of New Zealand, where the ocean is already reclaiming parts of the land, several councils including Hastings District Council, Napier City Council and Hawke’s Bay Regional Council have combined their resources to present a unified front in the battle against sea level rise. Together they develop and prioritise projects. It’s an excellent example of the new directions required in decision making as a result of climate change.

Jacqui Grove, Acting Executive Manager, Natural Environment and Climate Change at Northern Beaches Council in Sydney, says that infrastructure projects such as the Fairy Bower Amenities block have now incorporated measures to deal with the projected increasing severity of extreme coastal storm events.

“It’s an important factor that we now consider whenever we are renewing any infrastructure,” Grove says. “It’s one branch in the decision tree that helps us to make the best decisions as we plan to renew assets.”

Barriers to adaptation

Unfortunately, there are also several barriers to adaptation around rising sea levels. Grove says it can sometimes be difficult to convince the community to consider a problem that is 40 years in the future. Like Cull, Grove says success will have a lot to do with excellent communication.

Palutikof believes that a major barrier to adaptation is a lack of leadership – a problem which is not unique to Australia but is experienced globally. Local governments, Palutikof says, are understandably nervous about pushback from their communities and about the extent to which their state government will support them if the community reacts against long-term planning for sea-level rise. In fact, state governments are now putting in place support for coastal adaptation, although there still tends to be a barrier between the planning stage and the implementation stage.

“The first thing to realise is that climate change is happening now, that it’s affecting us already and that it will continue to do so beyond 2100,” Balston says. “Next is to identify the likely costs, damages and potential threats associated with it.”

“For assets along the coastline, assess where they sit in comparison to the projected sea level rises and events for the region. For long-lived assets, you might consider reducing the asset’s useful life, or looking at ways to adapt it, upgrade it or make other modifications so its useful life will remain the same.”

Finally, our experts say, remember that you’re not alone. From the Great Ocean Road to Surfers Paradise high rises and from Invercargill to Whangarei, local governments are facing the same challenges. The more they share insights, the more successful they will all be.”

“Sea level rise puts an enormous amount of infrastructure at risk.”

Case study: Ross River virus

The coastadapt.com.au website discusses the case study of Cairns Regional Council’s analysis of how climate change may increase mosquito-borne disease, particularly Ross River fever, in the region.

The council decided on a 20-year planning horizon as the most relevant timeframe for the application of a revised Mosquito Management Plan, which was informed by increases in sizes of mosquito breeding areas, heat-related hazards and rainfall-related hazards.

Case study: Stormwater management

The report titled PN12.1: Asset Management and Financial Management Guidelines: Climate Change Impacts on the Useful Life of Infrastructure, outlines in detail the case study of the Collaroy Beach stormwater outlet. In the storm event of June 2016, the outlet was destroyed. A replacement asset could not be like-for-like, as sea level rise meant it could be more exposed to severe storm events and a higher still water level.

If sea water covered the outlet during a severe rainfall event, stormwater would be unable to discharge and would instead flood the upstream catchment.

The new design incorporates a one-way rubber check valve to prevent salt water intrusion into the pipe and the use of High Density Polyethylene (HDPE) for the outlet to increase the useful life due to its corrosion, abrasion and chemical resistance.

Additionally, the HDPE pipe will be built into the sea wall being constructed in the area to protect it from erosion, including increased wind speed, during a storm event. Even if the asset is inundated, these measures are expected to protect its useful life.

Resources for council engineers

There are plenty of useful resources available for engineers wanting to find out more about planning for rising sea levels. Here’s where to start.

1 IPWEA’s Practice Note 12.1 – (an addendum to Practice Note 12: Useful Life of Infrastructure) Asset Management and Financial Management Guidelines: Climate Change Impacts on the Useful Life of Infrastructure

2 LGNZ’s report: Vulnerable: The quantum of local government infrastructure exposed to sea level rise

3 coastadapt.com.au – a website all about building knowledge, making assessments and taking action, developed by the National Climate Change Adaptation Research Facility

4 climatechangeinaustralia.gov.au – a website containing a broad selection of resources specific to climate change issues in Australia

5 mfe.govt.nz/climate-change – a website containing a broad selection of resources specific to climate change issues in New Zealand