The Port Phillip Bay Coastal Hazard Assessment

The DEECA Port Phillip Bay Coastal Hazard Assessment is sobering reading that has strong implications for the City of Port Phillip.

The Victorian Department of Energy, Environment and Climate Action, DEECA, has recently released its assessment of the risks faced by Port Phillip Bay because of climate change. It is available at DEECA Port Phillip Bay Coastal Hazard Assessment.

It seems very clear that climate change will not be avoided and will have major impacts and costs. Inaction by global and Australian political and business leaders is coming home to roost.

The risk assessment document is very careful to simply lay out what is likely to happen in the future with the impacts of climate change. At the same time it very carefully does not spell out the implications of these changes, which I found quite disappointing.

Another major gap in the assessment is the run-off water coming from inland sources. For example, a major part of the Elster Creek catchment actually comes from Glen Eira, which is inland from Elwood. Rainfall hitting roads and buildings in Glen Eira is mostly caught and directly into storm water drains that outfall at the Elster Creek and may cause inundations there. Thus, works to correct coastal hazards can require substantial inland investments.

The main risks considered are rising sea levels, inundations of low-lying areas during severe weather events, coastal erosion and increasing water table salinity because of sea level rises and more violent weather events associated with climate change. Generally, we can expect to see more temporary inundations because of storms, more coastal erosion and more saline water tables along coasts (which may adversely affect tree canopy coverage, among other issues). All this will inevitably lead to significantly rising insurance costs and strongly increasing investments in infrastructure to mitigate the coming problems. It should be noted that many of the problems are already starting and will progressively get worse over the next 25-50 years.

Along with Williamstown, parts of Geelong and Queenscliff, the City of Port Phillip is especially vulnerable because it is a relatively densely populated, low lying coastal region. Within the City of Port Phillip, the low lying areas around:

  • Fisherman’s Bend and Port Melbourne,
  • between Southbank, South Melbourne and Albert Park to Middle Park, and
  • Elwood (especially near the Elster Creek and Canal)

are the most at risk.

Interpreting the risk assessment, it seems clear that the more extreme weather events that are coming can quite conceivably lead to temporary ½m deep inundations of low lying areas that may persist for several days. The severe storms will result in more local water, and the sea level rises will mean that this water will only drain away slowly. Increasing drainage infrastructure will likely have limited benefits because rising sea levels will mean that the water has nowhere to drain to. Increasing ground permeability and ground sinks by removing asphalt may also bring some benefits (and also help limit groundwater salinity increases).

Because much of the coastline between Port Melbourne and Elwood already has seawalls, coastal erosion should be limited. However, these clearly need extensive reinforcing and will need to be raised higher in many places, which is very expensive. The banks of the Elster Creek and Canal will also need to be extensively raised to limit inundations of the surrounding low lying areas during storm tides. Also, the rising sea levels will clearly shrink many of our beaches and make them less attractive for swimming and lead to flooding of coastal roads during storms.

The combination of reduced average rainfall and rising sea levels will most likely significantly raise the salinity of the groundwater along the coast. This is very problematic for coastal vegetation, and especially for larger trees that have deeper root systems. There are risks for significant parts of the tree canopy along the coastal parks and in the Albert/Middle Park and Elwood areas, which are areas with the highest tree canopy coverage within our municipality. This is best mitigated by making the ground in these areas more porous by removing asphalt so that rainfall increasingly soaks into the ground. As they die off, existing trees will likely need to be replaced with more salt tolerant, and hopefully, more locally native species. The costs of not taking action are going to be very high for all residents.

It finally seems clear that homeowners insurance costs will rise significantly in the low lying areas of the City of Port Phillip in the future. Similarly, bank loans for home improvements and redevelopments are also likely be much more difficult get in these locations. The climate change mitigation costs are also likely to be large, so that Council Rates will also likely have to increase more than than keeping pace with inflation in the future. There are sure to be difficulties in getting the State and Federal Governments to pay for much of the infrastructure works that will be needed.

Major investments will be needed in coming years in the City of Port Phillip to combat climate change. Making the land more porous by removing asphalt should slow down groundwater salinity increases and let inundations drain more quickly. It should also have the added benefits of making these areas more livable and walkable. Much will also need to be spent on expanding and raising seawalls, and especially, on raising the banks along the Elster Creek/Canal. The rising groundwater salinity may kill many trees and these will need to be progressively replaced by more salt resistant  (locally native) species. All this will be very expensive, and it is better to start now to proactively spread the investments over as long a time period as possible.

Lastly, many investments will also be needed in adjacent inland areas and will require considerable collaboration and coordination with other Councils and State authorities. These inland investments will mostly be concerned with minimizing rainfall run-off entering the storm water system, and increasing the capacity of this system to deal with severe weather events.

Richard Whitfield