The Challenge

Isaac Regional Council commissioned WMS to undertake the hydrologic and hydraulic analysis and design of the Drummond Creek floodway crossing upgrade. The existing crossing had a low flood immunity and was inundated and impassable several times a year.

Approach and Outcomes

Two preliminary design options were developed to provide immunity options (63.2% and 10% AEP). Following the hydrologic and hydraulic assessment of the two preliminary design options and discussions with Council, the preferred design option for the Drummond Creek crossing upgrade was chosen. The final design for this option was however modified from the preliminary design with changes made to the width, alignment, crossfall and batters to ensure that the proposed roadworks will cater for the requirements of a 90 km/hr design speed environment.  The aim was to minimise the extent of these works while ensuring that the design speed was achieved.
Several iterations of the design were tested, with model results being used to inform the design process. Final design mapping and drawings as well as details on the scour assessment, proposed scour protection and flood impact assessment for the final design were provided. The bill of quantities and a detailed cost estimate to enable Council to solicit bids for project construction was also delivered as part of the project.