Figure 2.1: Overtopping and piping failure configurations [7]
2.2
Sunny day and flood day scenarios
The potential for dam failure and the consequence category for a dam is estimated by assessing the consequence of dam failure under two different climatic scenarios, including: — Sunny day failure: failure occurring without any natural rainfall or flooding, giving rise to the ‘Sunny Day’ consequence category. The consequence of failure is taken as the impact of the entire inundation extent. — Flood day failure: failure that occurs in association with a natural flood event, giving rise to the flood consequence category. The consequence of failure is taken as the impact of the incremental increase in flood extent from the natural flood extent.
2.3
Breach locations
The breach location is the position or section of embankment where the failure originates from. When undertaking a dam break assessment, the breach location chosen has a direct influence on the potential estimated impact. For the current assessment, the following items were considered when selecting appropriate breach locations: — Maximising of potential outflow volume, i.e. typically equal to the location with the largest outer embankment height.
— Resulting in large failure reach length, i.e. proximity to natural watercourses that would carry the outflow further.
— Population density and degree of environmental significance in expected downstream inundation extent area.
2.4
Flow behaviour
A tailings dam breach analysis is generally more complex than a water dam failure analysis. The outflow can possess Newtonian (water flood) characteristics, or non-Newtonian (mud flood or mud flow) characteristics, depending on the
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP JUly 2025 Page 6
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