15 July 2022
Landslides triggered by exceptional rainfall in Australia
The last few months have seen a series of exceptional rainfall events in the eastern part of Australia, triggering extensive flooding and landslides. In recent says this series of events has continued, with another major rainfall event causing extensive problems. Loyal reader Scott Johnson has kindly provided a series of updates to me as these events have developed.
The landslide with the largest long term impact occurred at Blackheath in New South Wales on Main Western Line, a major railway through the Blue Mountains. A set of images were posted to Facebook by Transport for NSW – this one shows the scale of the landslide:-
Clearly in global terms this landslide is not large, but it is undoubtedly serious. The nature of the terrain, and the remote location, means that mitigation is extremely challenging. Transport for NSW has posted a video update on the ongoing mitigation works. This still shows the scale of the excavations that have been necessary to reach a firm foundation, allowing a stable slope to be created to provide a secure track bed:-
The target date to get one line functioning is 24 July 2022, with a focus on night time freight traffic in the first instance. The line is a critical route for the transport of grain, coal, minerals and meat across the Blue Mountains to Sydney and the east coast area. Thus, the economic cost of this landslide is likely to be high.
Meanwhile, on the banks of the Hawkesbury River in NW Sydney, a rather different landslide problem has developed at Richmond Lowlands. ABC News has a good video report about this event, triggered by flooding on the river. This still from the video shows the scale of the problem:-
The house is, I believe, located at -33.5667, 150.7624. The flooded area on the right side of the image presumably indicates that the ground was saturated whilst the river was in flood at the time of the failure. A flood warning bulletin released on Sunday 10 July indicates that the river level was falling at that time. The landslide is reported to have occurred at about 10 am on Monday 11 July, indicating perhaps that it was a drawdown failure. The form of the landslide indicates that it might have been a retrogressive event, initiated by collapse of the riverbank at the toe.
It is not immediately obvious to me why such a large failure has developed at this particular location. Failures have developed at other sites too.