Upper Corindi rainfall and flash flooding a rare Coffs weather event

The downpour is somewhere between a 1-in-500 and 1-in-1000 year event.

Images from residents in Corindi who were impacted by the major storm event on Thursday February 25, 2021.

The extraordinary downpour in the Upper Corindi area last week is estimated to be between a 1-in-500 and 1-in-1000 year event.

The downpour on the night of Wednesday February 24 triggered flash flooding likened to a tsunami and contributed to a devastating train derailment at Nana Glen.

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The Boyles Bridge rain gauge recorded a peak rainfall over a six-hour period of 295mm.

Based on Intensity-Frequency-Duration (IFD) models, this equates to being somewhere between a 1 in 500 and 1 in 1000 rain event.

A shed is left in the middle of a field after being destroyed by flash flooding. Corindi was hit by an intense storm on Thursday February 25, which caused significant flash flooding which was described as being extremely fast moving and likened to a tsunami. Photo: Tim Jarrett

The rainfall at the Corindi River gauge at Solitary Islands Way, recorded a peak of 141mm over the six hours, equating to close to a 5 per cent AEP (or 1 in 20 year) rain event, meaning the extremely heavy rainfall was centred over the Upper Corindi area.

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River levels peaked at around 7.4m at the Corindi River gauge, which is about 1 metre higher than the current estimated 1 per cent AEP (1 in 100 year) flood level based on the RMS flood study completed for the highway upgrade.

Areas around Sherwood Creek and Corindi were also impacted by flash flooding on February 25, 2021. Coffs Harbour floods. Photo: Tim Jarrett

This is also much larger than the 2016 flood event which peaked around 6.13m, and it is estimated that the flood level was nearly one metre higher than the January 2012 flood event.

The Coffs Harbour SES was kept extremely busy throughout the weather event attending 59 jobs in a 24-hour period (23 in Corindi and 27 in Coffs/Sawtell and nine in other locations).

The Coffs Harbour State Emergency Service Photo: SES Coffs Harbour carried out 15 flood rescues in just eight hours on Thursday Feb 25.

Coffs Harbour City Council is currently undertaking a detailed Flood Study for Coffs Harbour LGA's northern coastal catchments, including Corindi River, Arrawarra Creek, Darkum Creek, Willis Creek, Double Crossing Creek (Hearnes Lake) and Fiddamans Creek.

The information gathered from this event will play a vital role in making sure the flood model reproduces observed flood behaviour as closely as possible.

The goal is to provide detailed mapping so that Council will have an even better understanding of potential flood risks to assist with future development, planning, community education and mitigation works.

RELATED:December 2020 floods on the Coffs Coast

Flooding at Edward Sharpe Bridge, Nana Glen on February 25 2021.

Busy summer for Coffs Harbour SES:

The Coffs Harbour SES attended 326 calls for assistance for the summer period (December to February).

This represents a 100 per cent increase in workload on the same time last year.

The Coffs Harbour State Emergency Service Photo: SES Coffs Harbour carried out 15 flood rescues in just eight hours on Thursday Feb 25.

Summer weather across the State:

Compared to last year's fires and heat, this year was marked by above-average rainfalls giving NSW its wettest summer in almost a decade.

Across NSW, the summer rainfall for 2020-21 was 29 per cent above the 1961-1990 benchmark used by the Bureau of Meteorology at 215.7 millimetres, making it the state's wettest summer since 2011-12.

The NSW mean temperature for summer was 0.03 degrees above the 1961-1990 benchmark, making it the state's coolest summer in nine years.