GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 27 Figure 14 Mataura Stream AWBM synthetic stream flow compared with M1 flow gauging data The effects on the flow in the Mataura Stream as a result of the proposed development at the WSFA are expected to be minimal. The footprint of the facilities is small compared to the total catchment area. The footprint of the WRS (5.5 Ha, or less than 1%) will be removed from the catchment during peak development and runoff will be collected and diverted to the WTP. This is not expected to have a noticeable effect of the Mataura Stream flow. All land disturbing activities carried out onsite will be in accordance with the Waikato Regional Council’s Erosion and Sediment Control Guidelines for Soil Disturbing Activities (WRC, 2009). Due to the size of the WKP portal infrastructure footprint, a number of sediment ponds will be required to manage sediment laden runoff to protect Mataura Stream from excessive sedimentation. Details of these ponds including operational stormwater management are detailed in the erosion and sediment control assessment report (Southern Skies, 2022). Clean stormwater from the site will be discharged in its ‘current state’ through appropriate diversion and is detailed in BECA (2022). 3.2.2 Wharekirauponga Stream The Wharekirauponga Stream catchment area was determined from NIWA online application “NZ Rivers Flood Statistics” (WSP, 2020), which indicated an approximate total area of 40 km2. The catchment is steep and covered in native bush, and has several small tributaries discharging into the Wharekirauponga Stream, including: Edmonds Stream, Adams Stream, Thompson Stream, and multiple unnamed streams. Baseline flow data for the Wharekirauponga Stream was collected between January 2019 and May 2021, which is described in the OGNZL Baseline Report (WSP, 2020), included in Appendix A. The data includes manual flow gauging and continuous flow data recorded by automated pressure transducers (monitoring locations shown in Figure 15). The continuous flow data was corrected using a two-point correction to calibrate the continuous level data to the gauged flows, which is displayed in Figure 16. Flow duration curves (Figure 17) were completed to indicate the percentage of time the calculated flows are exceeded. The graph demonstrates that the streams typically observe a sustained flow throughout the year; however, a steep curve within the high flows indicates that rain-caused flooding can occur during short periods of time. The dashed lines in the figure represent an assumed flow, as the manual flow gauging events were below these flow values.
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