U:\2021\BM210482_IBo_Waihi_North_Project\Documents\WNP_Freshwater_Report_May_2022\FINAL_Freshwater_Report_FOR DELIVERY_June 2022\FINAL DELIVERED 17 JUNE 2022\WAI-985-000-REP-LC-0007_Rev0_Freshwater_20220621_FINAL.docx Table 15: Summary of ecological values of the Gladstone headwater gully. EIANZ criteria Site Gladstone Headwater Tributary Ecological value Moderate Reasons for our assessment • Invertebrate community has moderate diversity. • Invertebrate community dominated by detritus eating taxa. • MCI score of 91 • No EPT taxa • SEV score of 0.617 • No fish present • Stream channel and banks unmodified, well established restored riparian 9.3.2 Gladstone Wetland 9.3.2.1 Vegetation Characteristics The Gladstone wetland contains substantial areas of raupō and Carex geminata, and local patches of giant umbrella sedge (probably naturally established), surrounded by a wide perimeter of dense flax interspersed with cabbage trees (Figure 9,Figure 11). The Gladstone wetland is not listed as an SNA in the HDP. However, the Gladstone wetland meets the WRC significance criteria based largely on the restoration of the wetland from what appears to have been an exotic, willow-dominated wetland[1], to an indigenous plant dominated wetland. Photographs of Gladstone wetland are shown in Figure 11 and historic photographs of the area are provided in Appendix 3. 9.3.2.2 Hydrological Characteristics GWS (2021) describes the Gladstone wetland as an expansive, flat section from around 92 mRL to 90 mRL with the length of the wetland having only a few meters fall. At the downslope end of the wetland, there is an earth embankment and culvert after which there is an approximate 2-3 m drop down to the Ohinemuri River. GWS (2021) goes on to describe the location of the wetland as an area of unstable ground formed due to repeated failures at the ash/regolith contact with the underlying volcanic geological layer. These materials are relatively porous and accumulation of water at the interface of the geologic units is the main destabilising mechanism. The pre-existing environment was likely one of wet ground. At some stage in the 1960s a farm track was constructed as a raised earth embankment with a culvert to allow surface water through flow. This earthwork essentially dammed the valley resulting in an area of standing water developing. Over time, the wetland developed naturally and since the mid 2000’s it was actively restored as a wetland by OGNZL (and its antecedent owners). GHD (2022C) has developed a conceptual assessment of the wetland hydrology. Flow from the catchment to the wetlands and drainage of stored water from the wetlands, which influences water levels and wetland drying, occurs via different modes and at different rates, creating a flow and water level recession response. The outcomes of this are not uniformly evidenced within the wetland and tributary, primarily owing to differences in wetland elevation. The wetland provides both a path for overland flow and dynamic storage for water which flows to the tributary and the Ohinemuri River.
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