Greenough River 2D Flood Modelling

Project: Greenough River 2D Flood Modelling
Client: Main Roads Western Australia

BG&E were commissioned by Main Roads Western Australia to provide specialist flood modelling services of the Greenough River in support of the upgrade and realignment of Brand Highway to the south of Geraldton in the Mid-West region of Western Australia.

The Brand Highway bridge, south of Geraldton is to be upgraded following the recent flood events and road closure. The Brand Highway is a major transport corridor and the bridge is a vital crossing of the Greenough River. During flood events, a watershed along the southern boundary of the floodplain breaches from the river banks and water flows southwards into the low-lying Flats. Due to the flat topography the water is unable to escape. The area becomes essentially a retention basin without exit, and flood waters can potentially remain for long periods of time.

BG&E has provided a comprehensive hydrological and hydraulic model of the flat areas from the Brand Highway Bridge south to the lowest lying areas in order to assess the flood levels, flood extents and probable closure periods for Brand Highway and local road network.

BG&E used the latest 2D modelling techniques combined with an extensive area survey. The modelling results were calibrated with gauged flows and levels to provide informed and better design parameters for the design of the new Brand Highway alignment and bridge.

The work included:

• Detailed hydrological assessment of the Greenough River catchment, including RORB runoff routing Flood Frequency Analysis on gauged flow data.
• Development of 2D flood model using Mike 21 software.
• Calibration of 2D flood model with recorded flood levels and extents.
• Mapping of flood levels and extents.
• On-going technical support for road designers, including 100 Year ARI flood levels.
• Communication of outcomes hydrological study with Department of Water.