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 16.2 Effects of construction of GOP on Headwater Gully Approximately 47 m of intermittent stream channel length (~ 47 m2) of the headwater gully will be reclaimed as part of the GOP. In addition, there is potential for sediment to enter the gully as a result of the proposed activities. A small area (approximately 47 m length and 0.001 ha) of planted riparian vegetation will be removed from the headwater gully as part of the proposed works for the GOP. The loss will include an assortment of manuka and kanuka along with a mix of wet-tolerant plants such as Carex secta, C. lessoniana, harakeke and cabbage trees. 16.3 Effects of construction of GOP on ecological values of Gladstone Wetland The vegetation removal and earthworks from the headwater gully is greater than 100 m upslope of the Gladstone Wetland and consequently does not trigger any of the provisions of the NESF. Earlier in our report, it was established that the Gladstone wetland was maintained by groundwater and interflow, and there was no significant hydrological connection between the upper headwater gully and the wetland. GWS (2022) concluded that after prolonged rainfall, interflow contributions are made from the headwater gully section (see Figure 23). Flows from the upper headwaters at Gladstone Hill were in the order of 0.1 L/s and the outflow was 3 L/s. GWS (2022) assess the contribution of flow into the wetland as small, around 3%, and only occurs following rainfall. We understand it is this contribution that would be lost because of the development of the GOP. GWS (2022) go on to conclude that this loss of a small amount of interflow would result in a small loss of surface water flow through the wetland following rainfall and this is expected to be immeasurable. Similar conclusions were reached in a separate assessment by GHD (2022B) who concluded that the effects of the GOP and subsequent TSF are very similar. GHD (2022B) concluded that the reduction in groundwater discharge by approximately 33% and reduction in groundwater level of approximately 0.5 m adjacent to Gladstone wetland is expected to be unmeasurable given the natural variability within the wetland. Both GWS (2022) and GHD (2022B) have indicated that a reduction in catchment and groundwater inflow may result in a less frequent saturation of the wetland. We have noted above that the level control at the outlet of the wetland provides for water saturation in the wetland and buffers the wetland against more frequent periods of drying. We expect the wetland to continue to dry during periods of low rainfall. Accordingly, we conclude that there are unlikely to be any direct or indirect (hydrological) effects on the Gladstone wetland resulting from the loss of 0.14 ha of the upper headwater gully and development of the GOP and related TSF. Nevertheless, we recommend that baseline monitoring of the Gladstone wetland vegetation be undertaken prior to GOP commencement and re-assessed periodically (e.g., every five years) to ascertain whether hydrological changes, however immeasurable, have resulted in changes in the existing wetland flora or soil moisture levels.
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