72 Boffa Miskell Ltd | Waihi North Project | Terrestrial Ecology Values and Effects of the WUG | 22 June 2022 6.5.4 Dewatering Effects on Vegetation and Fauna The potential of the WUG to reduce surface water volumes and moisture content in soils is assessed in the Assessment of Effects on Groundwater (GWS, 2022) and we rely on this assessment to inform our report. Potential adverse effects associated with dewatering or drying out of regolith and soils are that the roots systems of old-growth forest are stressed and lead to wholesale forest decline, habitat loss and fauna mortality, or that there may be changes to surface water bodies that could impact aquatic species including Hochstetter’s frogs. The risk to soil regolith and therefore trees and vegetation from dewatering is assessed in the GWS and FloSolutions reports. Trees and other vegetation source soil water from the regolith to survive and the root zone depth of most plant species is limited to 2 m depth. Tap roots can go deeper but these are structural meaning the plant does not depend on them for water to live. Dewatering of the rock mass does not affect the soil water balance in the regolith as the regolith sits above the permanent water table in the unsaturated zone. The soil water balance in the regolith is controlled by rainfall and climatic conditions and dewatering the rock mass as a whole will have no effect on plant health. Further work is required to understand the groundwater system around surface water bodies. This risk will be avoided through the management measures detailed by Valenza Engineering such that the activity does not cause any measurable dewatering of the soil regolith or surface water bodies which could have an adverse effect on vegetation or streams. Proposed consent conditions do not allow for the mine to proceed if there is a risk of measurable changes to surface hydrology. The magnitude of effect of dewatering is Nil (not technically possible) and the ecological value vegetation / fauna habitats is Very High. The level of effect of the project will be None (i.e. no dewatering and loss of forest). 6.6 Level of Effects on Terrestrial Vegetation, Habitats and Species The level of effect on native species and communities is set out in Sections 6.3 – 6.5 and summarised in Table 13 and includes the effects management described throughout that section. The primary mechanism to reduce the level of effect is to avoid and minimise the impact on the ecological parameters considered through design and management (Table 12). Although the risk of introducing kauri dieback disease to Wharekirauponga is always present, it is not specific to the activities associated with the WNP. Both animals and recreational users of the forest may also contribute to the spread of the disease. We consider that the proposed surveillance protocols for kauri dieback infection (described in CFP KDMP) will allow for early detection of the presence of the disease within the forest.
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