Hepburn Shire Council
Creswick experienced significant flooding in late 2010 and early 2011 experiencing several large events in a short period. This had a devastating impact on the community.
Water Technology was commissioned to undertake a detailed flood study for Creswick to assist in providing the community with a greater level of protection from future flooding. The study involved detailed hydrological and hydraulic modelling of Creswick Creek, flood mapping, quantification and assessment of flood damages, and development and assessment of potential flood mitigation options.
A rainfall-runoff model was developed in RORB, which incorporated Creswick Creek, several tributaries and two upstream storages (Cosgrave Reservoir and St Georges Lake). A coupled 1D/2D hydraulic model was developed using MIKE FLOOD, to assess the extent of inundation, depths and water levels. Both models were developed using industry best practices and were rigorously calibrated and verified against historical flood events.
The hydraulic model was also used to test the effectiveness of a number of potential mitigation options, including deepening/widening of the creek, additional culverts and various levee alignments. A key element attributed to the success of this study was the active engagement of the community. This was developed over the course of the study and included community information sessions, questionnaires, media releases and meetings with the Technical Working Group and community based Steering Committee. The community concerns regarding levee heights were listened to and a level of protection was adopted to protect against the January 2011 flood level but which maintained the aesthetics of the township.
The final plan recommended a number of structural and non-structural options (warning systems, increased awareness and amended planning scheme overlays). As a result of extensive consultation, it was clear that the recommendations for Creswick had strong community support. Economic analysis indicated that the proposed mitigation option would reduce the cost of flood damages by up to 75%, with a benefit cost ratio of 0.8 (not including associated non-monetary costs).
The Creswick study has been held up as the example for all flood investigations to follow in Victoria. It led to an acceptable flood mitigation plan being developed and implemented in record time, and has dramatically reduced the flood risk for the Creswick community.