100 17.3.4 Topsoil Stripping Topsoil stripping will be required over an area of approximately 80 ha. This includes approximately 5 ha on the existing TSF1A embankment. Stripping of topsoil will be undertaken in stages as required. Vegetation will need to be removed from an estimated area of 5.7 ha in the SNA and 1.3 ha outside the SNA designation. The vegetation will likely be mulched on site and taken to stockpile. Topsoil and vegetation will be stockpiled preferentially in the smaller west and east TSF3 stockpiles. Further information on terrestrial ecology values and effects is reported by Bioresearches (2021). 17.3.5 Cutting of additional farm drains The preparatory works may result in the development of additional farm drains to expedite the drainage of surficial soils. We have no design of the extent or depth of these drains at the time of writing. The Ruahorehore Stream catchment is already subject to numerous drains and we do not expect the additional drains at the time of the construction of TSF3 to result in changes to the aquatic ecological values of the Ruahorehore Stream 17.4 Effects on construction of TSF3 on Freshwater Ecological Values 17.4.1 Loss and Diversion of Waterways The construction of the TSF3 will result in the diversion of some 2,111 m of permanent and aquatic habitat within its footprint, including within the SNA. The waterways to be lost include permanent, intermittent and ephemeral streams, as well as artificial watercourses of the Ruahorehore Stream catchment. As outlined above, a section of the Ruahorehore Stream meets the ecological significance criteria. A stream diversion of some 4,024 m will be created to convey surface water from the upper Ruahorehore Stream to its lower reaches. We have calculated ECRs for different sections (upper and lower catchment sections) of the Ruahorehore Stream that range from 1.41 to 4.84 and providing for some 4,024 m (8905.2 m2 of stream surface area) of diversion length. Calculations for stream offset are provided in Appendices 5 and 9, and summarised (along with our assumptions) in section 22 and Appendix 8. The design of the diversion channel is planned to replicate aquatic habitat attributes with a range of suitable stable microhabitats for fish and invertebrates, including the creation of stable pool habitats, the inclusion of gravel and cobble riffle habitats, and provide for the passage of climbing fish, especially eels. Maintaining connectivity between the lower and upper catchment will be important. All new sections of the diversion channel will be installed off-line and fully stabilised before flows are directed into them. Once the flows are diverted, the existing stream channels will be off-line and can be worked as part of the overall earthworks footprint, with sediment-laden runoff being treated via the main sediment controls (OGNZL 2021). Indicative designs of diversion channels are detailed in Appendix 11. In addition to the principles, the following recommendations are specific to the Ruahorehore Stream diversion:
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