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 solids concentration of the released tailings. In general, the travel time and inundation area for water floods will be larger than for mud floods. Non-Newtonian assessments have a larger data requirement due to the need to characterise the tailings flow properties. As discussed in Section 1.2, the Upper Mundic Gully TSF embankment is proposed to be constructed immediately upstream of the OCP. In the event of an embankment failure, the mobilised tailings would discharge into the pit, displacing water that would then be released through the pit spillway. The solid outflow is expected to be mostly contained within the void, with primarily water flowing through the spillway. Therefore, only Newtonian flows will be considered for this analysis. 2.5 Flood severity classification The inundated area can be categorised by flood severity to assess the potential hazard. The flood severity indicates the likely impact/damage caused by the flood to people, vehicles, buildings and the environment. Guidance on categorisation of the flood severity provided in the Australian Rainfall and Runoff (ARR 2019) guidelines (Ball et al, 2019). Flood severity is described by six hazard classifications, based on the maximum flood depth, velocity, and depth-velocity product (DV) at a given location. The adopted hazard classifications are presented graphically in Figure 2.2 and are tabulated in Table2.1.
Figure2.2
Combined flood hazard curves (Smith et al . (Smith, Davey & Cox, 2014))
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP May 2026 Page 7
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