A group of Dora Creek residents is urging Lake Macquarie City Council to clear vegetation growing in floodways off the creek to reduce the impacts on the town of the next big flood.
The residents said dense undergrowth and stands of causarina trees now posed obvious blockages to the floodways which would slow the dispersal of floodwaters and increase local flood levels.
But council said expert advice commissioned from the hydrologist consultancy WMAwater for the Dora Creek Floodplain Risk Management Study and Plan shows clearing the vegetation would not provide the benefit the residents expected.
"The question of vegetation within the floodway was specifically modelled and found to make a negligible difference (5cm) to flood levels upstream at Dora Creek, and makes no difference to flood levels downstream," the council said.
There are six floodways in Dora Creek, with the residents' main focus on the two floodways either side of the Eraring power station cooling canal on Stingaree Point Drive.
A floodway can be naturally occurring, or man made. If one thinks of a creek in flood as a water highway, then floodways are the off ramps.
The definition of a floodway given in the council study would seem to support the residents' concerns about blockages.
The study defines floodways as: Those areas of the floodplain where a significant discharge of water occurs during floods. They are often aligned with naturally defined channels.
Floodways are areas that, even if only partially blocked, would cause a significant redistribution of flood flows, or a significant increase in flood levels.
But Council said the trees growing in the two floodways on Stingaree Point Drive were deemed not to pose a threat.
"On the basis of modelling conducted to support the preparation of the Dora Creek Flood Study and Risk Management Plan, the casuarina growth does not constitute a blockage in the floodway," the council said.
"The Dora Creek Floodplain Risk Management Plan recommended weed control at the floodway in question to remove undergrowth at its entrance. This work has been undertaken and routinely checked and maintained."
Dora Creek resident Ron McCarthy, a retired engineer, said urban development in the Dora Creek catchment, coupled with an expected increase in intense rain events and sea-level rise all added to the potential for future flood events in the town to be increasingly destructive.
"Clearing floodway 5 (on Stingaree Point Drive) will save lives, decrease enormous property costs, and minimise dangers to Eraring power station," he said.