Erosion and Sediment Control Assessment Report Rev. 0 This is an uncontrolled copy if photocopied or printed from the Intranet. Copyright © 2016, SouthernSkies Environmental Ltd. All rights reserved. Page 25 of 30 Once the initial earthworks for the GOP are completed water runoff will accumulate in the pit. This water will be pumped to the WTP. The southern stockpile will be treated by a SRP and discharged directly off site. The catchment area of this SRP is significantly smaller than those proposed for the NRS and TSF3. As a result, the USLE calculation focuses on the NRS and TSF3 sites. The results are provided in Table 3 below, which compares the estimated sediment yield from the existing land area with the proposed earthworks phases. As shown, increases in the catchment sediment yield during stages of earthwork that discharge off-site are predicted to vary, ranging from 11% to 8% for TSF3 and 2% to 0.4% for NRS. When the NAF earthworks are completed and the importation of PAF is underway, the sediment yields will reduce by 7.5% and 16% respectively, because those areas will discharge via the permanent collection ponds to the WTP. The USLE undertaken at this stage is based on annual yields. It is conservative as it assumes that the earthworks stages will be exposed to erosion for the full year of calculation, whereas in practice those areas will be further staged and progressively stripped and stabilised. Nor does it assume a winter works closedown period. Table 3: USLE results. In summary, the proposed earthworks will result in a small increase in sediment yield to the Ruahorehore Stream and Ohinemuri River during the initial stripping and establishment of each site. The outer batters of the new landforms created will be progressively stabilised. Once PAF is imported to the sites, runoff will be diverted to the WTP and sediment yield from these
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