This report provides the Flood Study component of the floodplain risk management process and details the investigation of flood behaviour associated with the ‘urban’ area of Boomi. Boomi is situated south of the Boomi River floodplain and north of Whalan Creek and has been subjected to various degrees of flooding over the years. The township and surrounding areas are flat, and flooding is dominated by Boomi River ‘backwater’ and breakout flows from Whalan Creek. The Boom River offtakes from the Macintyre River and joins the Barwon River west of Mungindi. Breakout flows from Whalan Creek are conveyed in a northwest direction before joining the Boomi River floodwater. This study has involved the establishment of historic and design storm flows using flood frequency analysis and the set-up of a two-dimensional, dynamic hydraulic model.

The approach undertaken for this flooding investigation has included the following key work items:

1. Identification of areas requiring additional ground survey and collation of this survey with existing photogrammetric data;
2. Site Inspections and Historic Flood Data Gathering;
3. Extraction of discharges and water levels from the existing Border Rivers Mike 11 model for use as boundary conditions in the 2D hydrodynamic modelling of historic events used for calibration purposes.
4. Flood frequency analysis to determine design flows for the 20%, 10% and 1% AEP.
5. Detailed hydraulic modelling of historic flood events for calibration purposes followed by modelling of the design flood events for the AEPs mentioned above.
6. Estimation of the Probable Maximum Flood (PMF) if practical.