Perimeter bunding above the uphill clean water diversion drain 263mm 7.6ha 2.622 0.5 3% 400 700 General site activities 263mm 5ha 1.725 0.5 2% 250 550 The permanent uphill clean water diversion design details are provided by Engineering Geology Limited. 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 NRS site and northern stockpiles 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 General site activities 263mm 5.0ha 2.121 0.5 2% 300 600 Northern Stockpiles 263mm 3.2ha 1.358 0.5 2% 250 550 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 5: Cross-section of a dirty water diversion.
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