SECTION 5 Groundwater Effects Assessment – WUG Dual Tunnels 28 Figure 21 Otahu Surface Water Catchment Extents and Dual Tunnel Alignment Hydraulic Gradients The hydraulic gradients will again be influenced largely by surface topography and the location within the catchment. For the purpose of the inflow assessment, hydraulic gradients from the Willows Farm observations have been adopted in the groundwater inflow model. Aquifer Parameters The hydraulic conductivity of the rockmass from the groundwater inflow assessment is 2.5x10-8 m/s. This value is considered reasonable by comparison to other locations such as the Kaimai Rail tunnel. The groundwater inflow assessment actually assigns various permeability values to different geologic units as present in in Table 6 and as described in Attachment B of this report.
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