Flash flood warning system protects Parramatta, Sydney

24 March 2021

Sydney, 24 March 2021 – Extreme amounts of rainfall led to flooding in the state of New South Wales in Australia. Severe weather warnings were issued and thousands of people have been evacuated across the state in this natural disaster. Rainfall totals of up to 700 millimetres in a week were measured at Nambucca Heads, in the northern part of the state.

These extreme amounts of rainfall are associated with the weather phenomenon ‘La Nina’, caused by the stronger trade winds which blow warm water towards the coast of Australia, causing more rainfall there.

Royal HaskoningDHV (based in Sydney and Newcastle) and Nelen & Schuurmans (Dutch company) have implemented a flood warning system, called Flash, for the Parramatta River. The Parramatta River catchment is steep and highly urbanised, resulting in a rapid response to rainfall and potential flash flooding of its major CBD area. The Flash system comprises a hydraulic model predicting water level rises in the river over the next 12 hours. Using a mix of inputs from recorded rainfall to rainfall forecast data from the Bureau of Meteorology, Flash produces a new flood impact forecast every thirty minutes. The FloodSmart Parramatta dashboard allows emergency responders and local government to see all the catchment information in one place and to take appropriate action prior to a flood event including informing road closures, deployment of emergency response staff and sending public flood warnings.

Luckily, in this event Parramatta did not catch the full brunt of the weather. The Flash Flood Forecast technology allowed Council to know the severity of the flooding and to stand down response staff early once the forecasted rain showed no further impact on sensitive catchment areas. The Parramatta Flash system helped the authorities to take the right action at the right time.