Figure 2: Cross-section of a clean water diversion bund. 3.2. Dirty Water Diversions Dirty water diversions will direct sediment laden runoff to the sediment control measures. The dirty water diversions have been sized to provide diversion capacity up to the 5% Annual Exceedance Probability (AEP) storm event, plus a freeboard of 300mm. Perimeter bunds located around the GOP excavation area and Southern Stockpile will be a minimum of 600mm high. Calculations are provided in Table 3. Table 3: Dirty water diversion details assuming maximum dirty water catchment area. Perimeter Bunds (dirty water diversion) Area 5% AEP rainfall depth (mm) Catchment Area (maximum) Peak Flow (m3/s) Base Width (m) Slope (minimum) Minimum Design Flow Depth (mm) Including Minimum 300mm Freeboard Gladstone Open Pit 263mm 7.0ha 2.416 0.5 5% 300 600 Southern Stockpile 263mm 1.2ha 0.414 0.5 2% 150 450 For simplicity, the earthworks associated with the GOP will adopt the larger of the two dirty water diversion sizing and construction dirty water diversion at a minimum of 600mm high. Figure 3: Cross-section of a dirty water diversion. 3.3. Sediment Retention Ponds Two Sediment Retention Ponds (SRPs) will be constructed to capture sediment laden water during the earthworks associated with the GOP.
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