What happens next? Coffs Council backs flood plan to reduce impact of future severe weather events

The City of Coffs Harbour council have backed a plan focused on reducing the impacts of flooding in the future.

The Coffs Creek Floodplain Risk Management Study and Plan was endorsed on Thursday, June 19, at the monthly council meeting as councillors resolved to support the plan which includes a prioritised list of potential measures and strategies to mitigate flood risks. 

The list includes:

• Upgrading the Bennetts Rd detention basin  

• The removal of Finch Crescent embankmentRevising the City’s Development Control Plan 

• Providing ongoing flood awareness campaigns and provision of flood information 

• Improving flood warning systems 

However, whether these plans go ahead or not depends on funding and feasibility. 

The Flood Risk Management Study and Plan was put on public exhibition in January. Only two formal submissions were received.

In a media release published on Wednesday, council noted one of two submissions suggested the dredging of Coffs Creek, however, that will be more appropriately considered in the Central Coffs Coastal Management Program.

Council said minor amendments were made to the Study following community feedback. They include:

• Further information to clarify why dredging was not included for investigation as part of the Study.  

• Amendments to include an assessment of the sea level rise values used in the modelling against the latest Intergovernmental Panel on Climate Change sixth assessment report. 

• Update to the rankings of the projects within the plan.

Flood basins reduce water levels

Coffs Harbour has four flood detention basins located at Bakers Road, Bennetts Road, Spagnolos Road, and Upper Shephards Lane. These basins were recommended as part of the 2005 Coffs Creek Floodplain Risk Management Plan and were constructed between 2010 and 2018.  

A City of Coffs Harbour spokesperson told the Mid North Coaster the basins work by temporarily storing stormwater runoff during heavy rainfall and then releasing it slowly into the creek system, reducing downstream flood levels.

City Planning and Communities Acting Director Ian Fitzgibbon said the four detention basins in Coffs Creek worked well during the May flood event, however, he acknowledged the flooding in the area was minor compared to what was experienced to the south of Coffs – in the Nambucca, Macleay, Hastings and Manning River catchments.

“At their peak, the detention basins within Coffs Creek were about five to 20 percent full, which played a part in reducing peak flood flows and levels within Coffs Creek,” Fitzgibbon said.

“It is estimated the May flood event in Coffs Harbour was roughly a 1-in-2 to 1-in-10 chance per year event dependent on location, so it was considered a relatively frequent event. 

“The basins were designed to reduce peak flood flows up to a 1-in-100 chance per year flood event, however it should be noted they were not designed to completely stop flooding but rather to reduce how often floods occur, how severe they are, and their overall impact.” 

The spokesperson stated the above statistics were derived by the council’s technical staff, using observed rainfall and river level data and flood modelling outputs developed for the study.

Experts say flooding will only get more intense in the future

Councillor with the Climate Council and Professor Emeritus at the University of Melbourne, Professor David Karoly, told the Mid North Coaster extreme rainfall events have become more frequent and intense in Australia due to the rising of global temperatures caused by pollution from coal, oil and gas.

Karoly said the rise of ocean and atmospheric temperatures is leading to more moisture in the atmosphere causing an increase in extreme downpours.

“We've seen record-high atmospheric temperatures in the spring and summer in Australia, which are also the result of rising climate pollution, not just in Australia, but globally.”

Karoly said increasing temperatures are down to human-induced climate change, due to the burning of fossil fuels, which led to the high concentrations of carbon dioxide and methane in the atmosphere: 

The increasing frequency and severity of extreme events means communities are facing successive disasters with little time in between to recover, while national disaster support is costing government billions with the costs continuing to rise. The frequency of intense rainfall events is expected to almost double with each degree of global heating.

Study used by emergency services

Mayor Nikki Williams said the study has improved council’s understanding of flood behaviour in the Coffs Creek Catchment.

“The information from the study will be used by the State Emergency Service (SES) during flood emergencies and assist the City in managing development in areas that are at risk of flooding, as well as informing flood mitigation efforts,” Williams said. 

The Study was jointly funded by the council and NSW government.

Thumbnail image: 2009 flooding in Coffs Harbour. Supplied The City of Coffs Harbour.