Greater Dandenong Council’s drainage system dates up to 100 years.
The system of stormwater entry pits, pipes, channels, retention basins and outflow points were given a “one in a 100 year” workout by a 48.6 millimetre deluge on 28 January.
Engineering director Paul Kearsley said flash-flooding in Springvale, Noble Park North and Dandenong North flowed down to lower-lying parts of the landscape.
“Council’s drainage system is designed to overflow and follow a flood path when rainfall and stormwater flows are greater than the drainage system’s designed capacity,” he said.
“Stormwater flows can become heavily concentrated and rapid outflow (drainage) can be restricted in these type of locations.
“Historic development in these areas can become flooded during intense rainfall events.”
Due to being naturally “flat and low lying”, areas like Bangholme and Keysborough receive flood water from the Dandenong Ranges and plains and valleys on the way to Port Phillip.
Waterways like Dandenong Creek and Patterson River carry flood waters to Port Phillip but can spill over into surrounding flood plains during intense rainfall, Mr Kearsley said.
This year, the council plans to upgrade two of its 55 drainage catchments. The works cover much of Noble Park and Noble Park North between the railway line and Princes Highway.
Future works are being planned for three other catchments in Noble Park North.
In the past, housing areas had drainage that could handle once every 5-10 year rainfall events and commercial areas up to 20 years.
In newly developed areas, local roads were designed for once-a-century stormwaters, he said.
“Standards and expectations of drainage infrastructure have been updated and become more targeted and precise to reflect the improved understanding of rainfall frequency and intensity, and the volumes of stormwater that flow through the municipality, based on rainfall records.”
