The Challenge

Devastating flooding in January 2011 was not limited to water rising from the primary creek systems within Toowoomba.  Major overland flow paths were known to be active during this event seeing hazardous flows occurring kilometres from the named creek systems. Following completion of a detailed creek flooding study, questions still remained as to the extent and hazard of overland flow paths. This project sought to map the route that water travels in order to arrive in the named creek systems – East Creek, West Creek, Black Gully Creek and Gowrie Creek.
Toowoomba Regional Council (TRC) has undertaken the Toowoomba Overland Flowpath Mapping Study (TOFPS).  The primary objective of the TOFPS was to develop hydraulic models that utilised the direct rainfall approach in order to provide overland flowpath mapping for the Gowrie Creek catchment in Toowoomba.

Approach and Outcomes

Thirteen detailed TUFLOW direct rainfall models were developed of the catchment utilising a two-metre grid spacing derived from aerial and vehicle mounted LiDAR and incorporating the pit and pipe stormwater drainage network.
The TUFLOW models were validated against the 10th January 2011 flood event. Each model showed good agreement with anecdotal evidence (photos, depths and general flow path descriptions) obtained during the community engagement phase of the project.
The primary output of the project was mapping of overland flow paths for the 10% and 1% AEP events. The 10% AEP event was selected to assist in identifying stormwater pipe capacity constraints within Council’s existing network and the 1% AEP event to identify properties within major overland flow paths. Secondary outputs included a product for assisting with the management of drainage complaints.