Monday the 10th of January started out like a typical wet summer day in Toowoomba. A monsoonal trough that had been delivering rain to the central QLD coast was travelling south and combined with another system moving in from the east resulting in significant rainfall across the entire south east of the state. By Monday morning the Toowoomba catchment was saturated, with a combined 80 mm of rainfall falling on Sunday and the early hours of Monday morning.
At around 11am a major storm developed on to the north east of Toowoomba and began travelling south-west (in the opposite direction typical storms in this region). The rain started falling at around Midday and finished by 3pm dumping between 100-150 mm, the heavy falls occurred between 1-2pm. At least six of the official automatic rain gauges in Toowoomba recorded one and two hour rainfall intensities greater than the 100-Years ARI. In basic terms this means that the rainfall was greater than the theoretical 1 in a 100 year storm. For example Prince Henry Drive received 64mm in 30 minutes.
The resulting rain quickly overwhelmed Toowoomba's drainage system which rely on the two major creeks, East and West Creek. These creeks merge in the middle of the CBD (downstream of the cache) which suffered the greatest from the event. Contrary to the media reports on the day, all the Toowoomba floodwater flows westward in Gowrie creek towards Dalby. The flooding in Grantham and the Lockyer valley occurred due to the rain falling on the other side of the dividing range just east of Toowoomba.
Many people were caught in the path of the unprecedented flood wave which tragically took the lives of two people in East Creek. In the days following the event many people were in a state of shock, no-one expected something like this could happen on top of a mountain. To further complicate matters the city’s residents were cut off from outside supplies including fuel, food and milk for several days due to flooding of all major roads into the city.
The site of the cache is on West creek, some distance upstream from the worst of the flooding but images from this spot made national and international news with cars being violently swept downstream. These images should serve as a warning whenever thinking about driving in flooded creeks.
Here is a video showing one of the unfortunate cars caught up in the creek https://www.youtube.com/watch?v=S6oLoKvMLf4