The study area was located within the Bayside Council Local Government Area (LGA) in New South Wales, Australia. With a surface of approximately 5.4 sq.km, the area was fully developed with residential, commercial and industrial buildings. Due to the relatively flat nature of the topography in the catchment and the low-lying areas, the flooding issues were significantly impacted by the performance of the pit and pipe drainage networks and the tidal levels at the outlets.
The previous flood study was conducted in 2015 and was undertaken to define the nature and extent of flooding within the area. The study represented catchment conditions in 2015 and utilised Australian Rainfall and Runoff (ARR) 1987 methodologies to estimate rainfall runoff. Based on the data and model review report, it was recommended that the 2015 flood study be updated in accordance with the ARR 2016 guidelines, and recent topographic modifications and developments.
A full range of design flood events were simulated for the updated flood study. Design flood events includes the 20%, 5%, 2%, 1%, 0.5% and 0.2% Annual Exceedance Probability (AEP) events and the Probable Maximum Flood (PMF) event. As per new Australian Rainfall and Runoff guidelines (ARR2016), each design storm AEP and duration consists of an ensemble of 10 storm temporal patterns which define the timing and intensity of rainfall throughout a given storm event. Each storm in the 10 temporal pattern ensemble has an equal probability of occurring.
The 20% AEP, 5% AEP and 1% AEP events were simulated for the 10 temporal patterns for the full range of storm durations from 15 minutes up to 9 hours. The 2% AEP, 0.5% AEP and 0.2% AEP events were simulated for the identified critical storm and temporal patterns.
The large number of scenarios, more than 400 simulations needed to be run within TUFLOW, would require thousands of hours of computing time. Each of the TUFLOW simulations would have taken about 7.5 hours to complete using one of their local computers. Due to both hardware and software (TUFLOW licensing) restrictions, it meant that all the simulations could not be run concurrently to obtain results faster.