Figure 4.4
Comparison of historical dam failure release volumes and estimated released volumes
The estimated outflow volume for the Upper Mundic Gully TSF falls within the general envelope of historical failure releases, and, therefore, were considered reasonable estimates for this assessment.
4.2
Dam Break parameters
Dam Break breach parameters (including width, side slopes and formation times) have been estimated using empirical relationships based on historical failure events. Studies by Knight & Froehlich [19] recommend using empirical equations derived by Froehlich [20] for breach widths greater than 5 m and MacDonald & Lanagridge‐Monopolis [21] for those smaller than 5 m. These recommendations are due to the sample data used in developing the respective equations. Table 4.3 presents the estimated breach parameters for the proposed scenarios using the Froehlich [20] set of equations, as the preliminary results were within the range of applicability of this methodology.
Table 4.3
Upper Mundic Gully TSF breach parameters
Parameter
Stage 1
Stage 2
Unit
-
Failure mode
Piping
Piping
Water surface level
358.2
388.6
RL m
RL m
Breach bottom elevation
353.5
350.1
Breach height
6.5
39.9
m
Estimated released volume
0.75
3.6
Mm³
m
Bottom breach width
16.3
12.5
Project No PS213278 Upper Mundic Gully TSF Stage 1 and 2 DBA and CCA Mount Morgan Gold Mine Heritage Minerals
WSP JUly 2025 Page 16
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