5.11 Flood Potential A flood potential impact study was undertaken to determine impacts that might occur in the event of a catastrophic failure of the proposed Upper Mundic Gully TSF. A copy of the flood impact study is provided in the tailings management plan in Appendix D and summarised below. Given the total volume capacity of both assessed stages of the TSF, a flood included overtopping failure was deemed as non-credible. The following scenarios were identified as critical in terms of consequence and adopted in the assessment: ∕ Sunny day piping failure of the Stage 1 embankment layout; and ∕ Sunny day piping failure of the Stage 2 embankment layout, Sunny day piping failure (sometimes referred to as Seepage/internal erosion) is typically triggered by seepage flows concentrated along a path of high hydraulic conductivity. These seepage paths can be caused by cracking, combustion, animal activity, high hydraulic gradients, or relict structures in the foundation or embankment materials. The shear forces exerted by the escaping water can enlarge the seepage path until a portion of the embankment collapses. This results in a breach through overtopping and erosion of the caved area. A piping failure event may occur at any time and may not be a direct result of a storm event. Figure 31 presents an overview of overtopping and piping failure configurations.
Figure 31. Overtopping and piping failure configurations (US Army Corps of engineers, 2014)
The hydraulic modelling was undertaken using the TUFLOW software package. TUFLOW software can dynamically simulate linked one-dimensional (1D) and two dimensional (2D) hydraulic models and has the capacity to represent complex changes in topography, hydraulic structure, boundary conditions, land use classification, floodplain storage and floodplain/channel interaction. Resulting flood inundation results maps are provided in Appendix D. The results of the simulation testing indicated that the OCP is the primary receptor of breach outflows in all scenarios with these being heavily attenuated and controlled by its spillway discharge. The relatively smaller outflow volume discharge for Stage 1 Scenario was conveyed through the site drainage system and released to Dee River, completely contained within the
Project number: 25B061
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