Mount Morgan Mine Upper Mundic Gully TSF EA Amendment

Figure 2.1 presents an overview of overtopping and piping failure configurations.

Figure2.1

Overtopping and piping failure configurations (US Army Corps of Engineers, 2014)

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:

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.

Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals

WSP May 2026 Page 6

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