Flooding is a major issue across the Illawarra. It has diverse impacts, many of them obviously negative, particularly on buildings and infrastructure, with flow-on impacts on personal well-being, community connections, and economic value and activity.
It can be hard to see the positives. But relatively high rainfall and weather systems that bring heavy and intense rain at times are important parts of the ecology of the region, and the Illawarra's native plants have adapted over millions of years to local conditions, including regular floods.
In this piece, I'll look at flooding and the Illawarra's native vegetation.
Prior to European settlement, the Illawarra region was strongly characterised by the presence of water. Water flowed rapidly down the steep escarpment slopes, with short, narrow waterways punctuated by waterfalls. It then crossed the wide floodplains via meandering, often-shifting channels leading into coastal wetlands, salt marshes and lagoons.
Much of the coastal vegetation was flood-tolerant or indeed depended on regular inundation or the presence of permanent water. The First Nations people who have cared for this country for tens of thousands of years lived on and from the lands and waters, and did not substantially alter the flow of water from the escarpment to the sea, although they certainly substantially influenced (and were influenced by) their surroundings and local plants and animals.
All that water is no longer so readily visible in the landscape, because of the huge changes made since European settlement, including extensive vegetation clearing, filling in wetlands, and channelising, piping or even relocating whole creeks to create flat land suitable for more roads and buildings.
As a result, water now moves through the Illawarra landscape in very different ways. Many of the early European depictions of the Illawarra region featured creeks, lakes and other water bodies. Prout's engravings show Lake Illawarra, Tom Thumb Lagoon, and the now-vanished Fairy Lake. These give us glimpses of what the place was like then.
You can also see the significance of water in the pre-clearing landscape via the fascinating Trees Near Me app, created by staff at the NSW Department of Climate Change, Energy, the Environment and Water. It includes a reconstruction of pre-clearing vegetation patterns.
Here are the names of some of the common plant communities, clearly indicating their wet and swampy character:
- Estuarine Swamp Oak Twig-rush Forest
- South Coast Floodplain Grassy Swamp Forest
- Samphire Saltmarsh
- Southern Estuarine Swamp Paperbark Creekflat Scrub
The mapping is copyrighted but you can check it out here (use the tab labelled pre-clearing to explore and see just how much of the area is estimated to have been covered by these vegetation communities).
The changes wrought since colonisation have had major implications for the Illawarra's native vegetation.
First and foremost, a huge amount of vegetation has been lost through clearing, including the habitat and conditions required for natural regeneration. It is no coincidence that many of the plant communities listed above are threatened with extinction.
It is a testament to the adaptability of the local plants that so many individual species are still present. And many are able to cope with both flooding and drought, such as the outstandingly tough Swamp Oak (Casuarina glauca), the local Paperbarks (Melaleucas decora, hypericifolia, linariifolia and styphelioides), and the mighty Swamp Mahogany (Eucalyptus robusta), not to mention dozens of ground covers, reeds, rushes and herbs (non-woody plants).
Loss of native vegetation has also reduced the capacity of the ground to absorb rainfall, which in turn exacerbates the severity of flooding as more and more rain flows overland rather than soaking into the soil.
An established forest can absorb 100-200mm of rainfall, 10 times as much as an area under turf (10-20mm; figures taken from Grant Witheridge's Creeks and Catchments, 2023), let alone concrete or asphalt. So we're all doing this place and each other a favour if we use suitable local native species in gardening and landscaping, contribute to urban greening efforts, avoid adding more hard surfaces such as paths and paving, do the 'rewilding' thing or help care for natural areas.
Conversations with Leon Fuller, Penny Thompson, Ruth Garland, Elena Martinez, George Takacs, Michael Andrews and others have contributed to my views on this topic.