Figure 4.5
Comparison of historical dam failure release volumes and estimated released volumes
The estimated outflow volume for the STSF falls within the upper range of the general envelope of historical failure releases. This is due to the relative shape of the STSF and higher storage capacity in its upper section relative to historic failure cases. The adopted estimates are therefore considered appropriate for this assessment.
4.2 Dam break parameters Breach parameters including width, side slopes and formation times have been estimated using empirical relationships based on historical failure events. Studies by Knight & Froehlich [20] recommend using empirical equations derived by Froehlich [21] for breach widths greater than 5 m and MacDonald & Lanagridge Monopolis [22] 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 [21] set of equations, as the preliminary results were within the range of applicability of this methodology.
Table 4.3
Sandstone Gully TSF breach parameters
Parameter
Scenario 1
Scenario 2
Scenario 3
Failure mode
Piping
Piping
Piping
Embankment crest level (RL m)
297.0
313.0
330.0
Dam bottom invert (RL m)
237.1
236.1
246.2
Height of the embankment (RL m)
59.9
76.9
83.8
Estimated released volume (Mm 3 )
5.5
10.0
14.5
Project No PS213278 Sandstone Gully TSF Dam Break and Consequence Category Assessments Mount Morgan Gold Mine Heritage Minerals
WSP January 2025 Page 18
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