The warning time for all breach locations has conservatively been assumed as little to none. The USBR (USBR, 2015) upper suggested limit curve (considering little to no warning) shown in Figure 6.2 with a maximum fatality rate of 75% PAR has been adopted for this study.
Figure6.2 Fatality rate vs. DV for cases with little or no warning time A fatality rate value of 0.01 has been adopted to account for uncertainties over areas where small DV values are reached for any values of DV below 30 ft 2 /s (2.8 m 2 /s) shown in Figure 6.2. 6.2.2.2 Results The maximum DV product at the locations where PAR was estimated to be impacted presented values up to approximately 2.8 m 2 /s. Areas where DV presented values beyond this threshold were only identified within the drainage features and channel banks. A fatality rate of 1% was deemed suitable for the PLL estimation reflecting the relatively mild flood severity of the impacts from the hydraulic modelling (H4 and below for the PAR locations as discussed in Section 5.2.2). Table 6.6 and Table 6.7 presents the estimated PLL for each failure runout scenario, according to ANCOLD (2012) and DETSI (2025), respectively. Table6.6 PLL estimates according to ANCOLD
PLL
Stage 1
Stage2
Mining operations
0
0.5
Township of Mt Morgan
0
0.1
Itinerant
0
0.0
Total
<0.1
0.6
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP May 2026 Page 28
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