The Challenge

In 2014, Toowoomba Regional Council successfully completed 42 flood studies for 35 locations in the region. Following this, multiple community consultation events were held where the community was encouraged to submit flood evidence to Council. Water Modelling Solutions was commissioned by Council to review the submitted flood evidence to determine if it would change the outcomes of the flood studies. The review concluded that a revision of the East Greenmount flood study was required.

Approach and Outcomes

The original model had utilised SRTM digital elevation data. As considerably more accurate LiDAR had become available in the interim period a new XP-RAFTS hydrological model and new TUFLOW hydraulic model were developed. The TUFLOW model utilised a three metre grid resolution and contained eleven 1D structures. A joint calibration was undertaken for the December 2010 and January 2011 flood events. Simulations were then undertaken for 1%, 5% and 20% AEP design events.  Maps were created for peak flood depths, peak water levels, peak velocities, peak flood hazard and peak flood risk. The study revision showed a significant reduction in flood extent attributable mostly to the change in terrain data input. This also resulted in significant reductions of peak flood hazard and peak flood risk.