The lessons learned by Wollongong City Council in the flood aftermath

Wollongong City Council staff have found what it tagged "introduced materials" like river stones, concrete, vegetation not from the foothills, even a 10-metre long bridge.

Structures like backyard bridges can serve as a dam, as more debris builds up behind them.

"In this circumstance, a lot of material has come down from the escarpment as well as through properties and a lot of those properties on those particular water courses have introduced things," Wollongong Mayor Gordon Bradbery said.

"They've created gardens and put in materials, landscaping materials that have also been caught up in the rain event. They've been brought down into properties and caused difficulties and backed up and caused the blockages.

"So it's a matter for the citizens of this city as well as council to make sure that that is managed more appropriately."

In a city where more than 60 per cent of the water courses run through private property, the reality is that in flood events, debris can come from suburban backyards.

The weekend's event was also unusual in terms of the volume, so some of the city's drainage infrastructure was put beyond the limits of its capacity.

In terms of the council response, that started before the storm. The council monitors long-range forecasts and headed out to hotspots in advance to ensure they were clear.

This also happened four weeks ago, though the predicted storm moved out to see and didn't threaten the Illawarra.

Immediately after the storm, council crews were out clearing the areas that were a high priority for safety, and also lobbying higher levels of government to make a disaster declaration, which would trigger funding.

There was also the clean-up; picking up rubbish residents had left on the side of the road. Where possible, council staff had asked them to sort it when putting it out to make the pick-up go smoothly.

The silt scraped off the road and collected from the kerbside is being stored while it dries and the council will work with the Environment Protection Authority on a disposal solution.

Over the weekend, the amount of rubbish dropped off at Whytes Gully ballooned 900 per cent from the usual 30 tonnes, to 300 tonnes.

"We're picking up material from people's front yards," said the council's Infrastructure Director Joanne Page.

"We're asking them to put it into different piles so that we can manage the silt and sediment a certain way, recyclables a certain way and other material that is flood damage that can't be recovered.

"At the moment, the majority of that except for the silt is going to Whytes Gully, but we're looking at options with the EPA and with the Reconstruction Authority so that we can actually look at other sites because could have an issue with Whytes Gully filling up."

Cr Bradbery said the data from the weekend would feed into the city's flood studies, which along with climate change may see restrictions placed on future development in the city.

"We're going to have to go back and rethink for instance, some of those locations and liaise with state planning and other agencies as to how to manage the city better," Cr Bradbery said.

"But it's a continuous improvement, taking on board new data, new information, the intelligence and then applying that to the modelling and making decisions as best we can.

"There are certain locations in the city where you would not allow any building to take place [today]. But those decisions were made decades ago or even in the middle of the early part of the 20th century.

"So it's a continuous improvement in the light of data and the information that's before us."