Parramatta River Integrated 1D-2D Modelling, Australia
- Alastair Sheppard
- May 27, 2024
- 3 min read
What our customers say:
“Flood Modeller’s 2D ADI solver was chosen for its range of productivity tools, such as the spill generator, its speed and stability, and its ease of modelling direct rainfall in the 2D domain.”
Flood Modeller has been successfully utilised to simulate combined fluvial and direct rainfall flooding in a sub-catchment of the Parramatta River in Sydney, Australia. This floodplain modelling was conducted as part of a comprehensive floodplain risk management plan for a proposed riverbank development of a brownfield site for a multinational environmental services company. The goal was to evaluate the impact of site development on the surrounding water levels.
The initial phase of the project involved the development and calibration of a Flood Modeller 1D model of the Parramatta River. This model provided an initial assessment of the impacts of proposed bank-side regeneration works at the site, confirming the need for more detailed modelling for the site and surrounding sub-catchment.
In the second phase, a fully linked 1D-2D model was developed to simulate both fluvial and direct rainfall events. Flood Modeller’s 2D ADI solver was chosen for its range of productivity tools, such as the spill generator, its speed and stability, and its ease of modelling direct rainfall in the 2D domain. Rainfall hyetographs were developed for the catchment using locally accepted methods in Sydney, and existing hydrographs were used for the flow series in the river.
The 2D model was developed using available LiDAR and aerial imagery data, with more accurate site topographic data overlaid where appropriate. The domain covered the entire surrounding sub-catchment. Buildings in the catchment were modelled at ground level with high roughness to prohibit flow through them, while enabling water storage within them.
A sensitivity analysis concluded that a 5m grid size provided sufficient accuracy over the 100ha catchment. The surface water drainage network in the area was not included in the model, as the intensity of events being analysed would render it ineffective.
Key Facts
Optimal solver performance: Flood Modeller was chosen for its fast and stable solvers.
Phase one: Developed and calibrated a 1D model of the Parramatta River.
Phase two: Created a fully linked 1D-2D model to incorporate both fluvial and direct rainfall events.
Efficiency boost: Productivity tools like the spill generator significantly reduced model development time.
To analyse the impacts of both direct rainfall and fluvial flooding, the events were combined. The peak rainfall-runoff at the site was timed to coincide with the peak river levels adjacent to the site by adjusting the start of rainfall. The baseline model was evaluated for 20-year, 100-year, and Probable Maximum Flow events, considering the joint probability of both direct rainfall and fluvial events and their respective impacts on flood levels at the site.
A design scenario model was developed based on the site design drawings. This model was evaluated for the same events, and the results were compared. 2D flood maps of depth were used to analyse water levels on site and within the catchment. These maps were also used to determine hazard values along proposed evacuation routes from the site, ensuring a safe exit route would be available in the event of a large flood.
Using Flood Modeller, it was demonstrated that the proposed design could be implemented without increasing flood levels in the catchment or downstream water levels in the river, while providing sufficient flood protection for the site.
