GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 32 Figure 19 Mataura Stream shown in the NZ Flood Statistics Henderson Collins V2 Layer The flow calculated was sense checked using the Rational method, rainfall statistics from NIWA’s high intensity rainfall design system and the following assumptions: Catchment area – 5.7 km2 Runoff coefficient (C) – 0.5 Length of catchment – 4.58 km Time of concentration (based on the Bransby-Williams formula) – 100 mins 100 year rainfall intensity – 75 mm/hr (including a climate change factor of 1.2) Table 9 Estimation of 100 year ARI flood flow in Mataura Stream adjacent to proposed portal infrastructure Mataura Stream reach Source Climate change factor Catchment area (km2) 100 year flow (m3/s) Reach adjacent to portal Rational Method 1.2 5.70 59 NZREACH 3009169 NIWA - 6.58 60 Reach adjacent to portal Scaled from NIWA 1.2 5.70 62 Flooding extent from the model can be seen in Figure 20. Flood levels adjacent to proposed WSFA shown in Appendix D are summarised in the Table 10. The model result indicates overbank flooding in some locations however there is no modelled flooding risk present for a 100 year ARI event to infrastructure positioned in the Wharekirauponga General Site Layout Plan shown in Appendix C. Table 10 Flood levels in the Mataura Stream adjacent to proposed portal infrastructure Location Water level (mRL) Model cross section chainage (m) Workshop 148.83 5,343 Office and change room 148.41 5,197 Switch room 148.06 5,133
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