106 18.2.3 Erosion and Sediment Control Erosion and sediment control measures will be established before undertaking preparatory works. This will include appropriate silt control to avoid discharge of excessive suspended solids to the Ohinemuri River. Similar techniques as used for the construction of the TSFs will be used as outlined in section 17.3.2. 18.2.4 Loss and Diversion of Waterways The formation of the NRS will result in the diversion of aquatic habitat within the works footprint. The diversion will result in some 1,391 m length (approximately 2,086 m2 (0.2 ha) of stream area) of permanent and intermittent streams of TB1 to be replaced via a 3,522 m length diversion. The offset has been calculated for sections of TB1 with ECRs ranging from 1.11 to 2.97. Details of the offset calculations and assumptions are included in Appendix 8. Surface water entering the headwaters of TB1 will be diverted through a diversion channel located between the NRS and the Significant Ecological Area to the north-east of the footprint. The diversion is to convey clean surface water (i.e. uncontaminated by mining activities) from above the site to a new confluence with the lower reaches of TB1. 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. Riparian vegetation should extend to at least 10 m either side of the channel and should include low-growing species with overhanging cover. Principles of diversion design are detailed in Appendix 11. In addition to the principles, the following recommendations are specific to the TB1 Stream diversion: • Surface water entering the headwaters of TB1 will be diverted through a diversion channel located between the NRS and the Significant Ecological Area to the north-east of the footprint. The diversion is to convey clean surface water (i.e., uncontaminated by mining activities) from above the site to a new confluence with either the lower reaches of TB1, or direct with the Ohinemuri River. • The design of the new channel should meet ecological objectives through the creation of a range of stable microhabitats for fish and invertebrates, including the creation of stable pool habitats and the inclusion of gravel and cobble habitat. The stream gradient may be difficult to maintain fish passage for general fish species, so the design should allow the passage of migrating eels, allowing them to access the remaining upstream habitat. • Riparian vegetation should extend to at least 10 m either side of the bed and must include low-growing species with overhanging cover. Additional recommendations for management of effects include: • The selection and construction of culverts is to be undertaken utilising current best practise to minimise impacts on water quality and in-stream disturbance, and to meet the requirements of the NPSFM. All work is to be undertaken in accordance WRC’s ‘Erosion and Sediment Control Guidelines’ (WRC 2009) to minimise the impacts of sediment entering the waterway. • Water flow is to be diverted around the working area by using an open diversion channel or by pumping the water around the work area.
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