140 No construction or earthworks works will be carried out within 10 m of the Gladstone Wetland boundary (Figure 31). The ESCP proposed for the pipeline installation will prevent sediment entering the wetland. As the pipeline follows the existing route no effects on the riparian planting alongside the Ohinemuri River is expected to occur. Ecological effects resulting from the installation of the pipeline will be minimal. 21.4 Diffuser installation The installation procedure for the diffuser is set out in Beca (2022) as follows: • The proposed outlet diffusers will be installed approximately 2 m from the existing diffusers. • A temporary cofferdam will be constructed to enclose the cast-in-situ concrete diffuser headwall construction area so that the construction can proceed in the dry. The river flow shall be maintained throughout construction. • Prior to construction work beginning, silt curtains will be installed to the surrounding area to manage sediment disturbance during installation of the diffuser on the riverbed. • A shallow depression within the riverbed will be created for the diffuser pipe to be placed within. • The diffuser pipe and supports will be installed. • Cast-in-situ shallow foundations will be constructed to anchor the diffuser pipe supports. • The temporary bunding will be removed. We understand that in addition to the ESCP, other necessary steps to control erosion and prevent sediment entering the waterways will be required e.g., construction of temporary berms and cutoffs, or stabilisation methods including use of clean aggregates, mulch, seeding, or geosynthetics and wheel washing facilities to prevent sediment leaving the site. 21.5 Effects of diffuser construction on aquatic ecological values The proposed diffuser installation will be carried out during summer low flows, and there will be no disruption to the flow within the Ohinemuri River. During construction, the presence of a temporary coffer dam across part of the riverbed will allow the construction of the diffuser headwall to occur in the dry but will concentrate flows across a smaller width of river. The narrower width of river means that there will be an increase in water velocities at this point across a small area of riverbed. As this will occur across a very small area of riverbed over a matter of days and during low flows this is not expected to result in any changes to the ecology of the riverbed. Fish passage will be maintained at all times. The current diffusers will remain operational within the riverbed during construction of the new diffusers and all diffusers will be operational in discharging the treated water to the Ohinemuri River.
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