82 14.2 Wharekirauponga Stream catchment 14.2.1 Warm spring 14.2.1.1 Effects of WNP on the warm spring We understand that the dewatering of the WUG is likely to cause the loss of the warm water spring. This is because the mine void will very likely intercept the flow of this spring and it will cease to emerge at the surface (instead needing to be collected and pumped from the mine void). This will result in a small reduction in flow to the main stem of the Wharekirauponga (GWS predict Ca. 2.5 L/s). The warm spring feature is of low value due to its condition and size. The complete loss of the warm spring feature in the absence of any other known warm water spring in the catchment is a moderate effect (i.e., as per the EIANZ - “loss of a moderate proportion of the known population or range of the element/feature”). There are few warm water springs and even though its ecological value is limited the feature in and of itself is unusual and the only known one in the catchment. The outcome of a low ecological value with a moderate magnitude of effect is a Low level of ecological effect. Effects management needs to consider management for the residual effects of the loss of the warm water spring. 14.2.1.2 Effects management for the warm spring As the warm spring appears to be the only warm water spring within the Wharekirauponga Stream catchment, there is no opportunity to look to a similar habitat to protect and enhance to provide additional ecological benefit. However, we recognise the ecological and water quality value (amongst other values) of all springs, and many of the watercourses around the Mataura Stream are fed by natural coldwater springs. For the most part, these coldwater springs are not protected and as for most springs in similar land use environments, are likely to be adversely affected by the current farming practices. We recommend an offset for the residual effects of the loss of the warm spring. The offset should focus on the springs and seepages with similar functional and habitat class types (but not with the same warm mineral-rich water attributes) but with better faunal potential and downstream benefit. We recommend that the offset for the loss of the warm spring be integrated into the wider package of freshwater mitigation and offset. Accordingly, we recommend that several headwater spring and seepage gullies of tributary 3 (tributary of Mataura Stream) be fenced for stock exclusion and planted with appropriate headwater vegetation. We estimate a ratio-based offset of a 12:1 gain : loss amounting to some 180 m in length of watercourse (approx. 51 m2 of freshwater habitat) for a loss of some 7 m length of warm spring length (9 m2 of freshwater habitat) will provide for a no net loss of springs.
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