144 • Stream diversions are to convey clean surface water (i.e., uncontaminated by construction or operational activities). • The design of the diversion channels should meet ecological objectives through the creation of a range of stable microhabitats for fish and invertebrates, including the creation of stable pool, run and shallow riffle habitats and the inclusion of gravel and cobble habitat, that at least reach a level of stream function to that predicted through the offset (SEV) calculations. • The substrate of the diversion channels should optimise conditions for trout spawning (including spawning gravels) and suitable habitat for juvenile trout. • Riparian vegetation should extend to at least 10 m either side (on OGNZL owned land or with other landowner approval) of the channel and must include low-growing species with overhanging cover. • Where possible, diversions should be constructed prior to the reclamation of the original channel. Where a diversion is required but it is not possible to replicate the habitat value (such as the upper reaches of the Ruahorehore Stream Tributary diversion channel) or where construction is taking place, then a clean water cut off drain should be created. This clean water cut off drain is not considered (and therefore not included) to be part of any offset for stream impacts but retains hydrological connectivity to the upper catchment. Design principles for the design of the stream diversions are shown in Appendix 4 and examples of cross-sections of the indicative diversion channels are provided in Appendix 11. 22.2.5 Bulk earthworks and sediment generation Sediment entering waterways can have significant impacts on the flora and fauna living within watercourses. This includes: • Changes to water clarity that affects the ability for fish to feed and follow visual cues. • Decrease in water clarity effects light penetration and potential plant and algal growth. • Settled sediment smothering the bed habitat thus reducing habitat for macroinvertebrates and periphyton. To address these effects, a range of erosion and sediment control measures must be implemented to minimise the quantum of sediment entering the receiving environment. These recommendations include the following: • Sediment and erosion control should reflect best practice and as a minimum the design criteria for all erosion and sediment control measures will be based on WRC TR 2009/02. • Open area limits will be in place. • Construction period monitoring of sediment discharges and the implementation of corrective actions where required. • The development and construction of the culverts are to be undertaken utilising current best practise to minimise the impacts on water quality and instream disturbance.
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