Erosion and Sediment Control Assessment Report Rev. 0 This is an uncontrolled copy if photocopied or printed from the Intranet. Copyright © 2016, SouthernSkies Environmental Ltd. All rights reserved. Page 26 of 30 areas will cease. At that time the sediment yield from each catchment will reduce from the existing vegetated situation and overall catchment load. While works within the NRS and TSF3 sites will include earthworks across steep land, this work will be undertaken and stabilised progressively, particularly the construction of the permanent stream diversions which rely on being progressively stabilised as a key component of site management. The majority of the NRS and TSF3 sites have relatively low gradients. This reduces the erosion potential and likely sediment yield. It is also noted that the USLE has assumed that sediment yield from the initial diversion of NAF runoff into the permanent stormwater ponds will be the same as that from a TR2009/02 SRP. However, the management of runoff via those stormwater ponds will likely result in a lower yield, as a result of the containment of runoff available within the ponds (particularly TSF3) and controlled pumping into and out of the ponds. 9.3. Streamworks The streamworks sections are shown on the SSESCPs for the NRS and TSF3. All new sections of stream channel (NRS diversion and TSF3 diversion) will be installed offline and fully stabilised before flows are directed into them. Once the flows are diverted, the existing stream channels will be off-line and can be worked as part of the overall earthworks footprint, with sediment-laden runoff being treated via the main sediment controls. The installation of temporary diversion pipes within the NRS footprint will be complex and will require specific design during construction. At this stage it is anticipated that those pipes can be installed at least partially off-line, with part or all of the stream channel remaining functional until such time as the flows are diverted into the pipes. Pumping may also be required at times, subject to confirmation by the contractor and certification via the corresponding final SSESCP. 9.4. Monitoring and Targets This ESCAR is based on the average efficiencies of the chemically treated SRPs proposed in combination with erosion control and staged construction methodologies. The SRP efficiencies have been assumed to vary throughout various rainfall events and are based on the average performance of the sediment retention devices proposed rather than a specific discharge limit. Further, the design and function of SRPs as recommended in TR2009/02 have been developed for Waikato conditions, which experience frequent and / or consecutive rainfall events, and sites that have steeper topography and spatial constraints. It is noted that this approach has now been adopted in the leading Australian ESC guideline17. The monitoring of the performance of SRPs, which are to service the largest earthworks areas, will be based on parameters that can be effectively measured in the field, and supported by laboratory analysis of water samples taken after trigger rainfall events. Those events are the times when the ponds are ‘working hard’ but should be expected to achieve an average compliance with the targets. The measurement of turbidity on site will allow an estimate of TSS to be made using the existing relationship. The laboratory analysis of turbidity and TSS will allow that relationship to be refined, both overall and for each site. The day-to-day monitoring and maintenance of the ESC measures throughout the construction period of the Project is the key element that will ensure that the anticipated level of performance and outcomes are achieved. The additional event-based monitoring will compliment that daily site management and will allow ongoing review and adjustment of the management system as 17 Best Practice Erosion and Sediment Control; November 2008 (updated April 2018), IECA Australasia
RkJQdWJsaXNoZXIy MjE2NDg3