PO Box 364 Whakatane 3158 Attention: Jill Owen Dear Jill Response to Section 92 RMA Request for Further Information - Donald Rodee, Matahui Peninsula -RM16-0068 1 Introduction Donald Rodee ( the applicant ) has forwarded us a copy of your email dated 14 March 2016 requesting further information under s 92 of the Resource Management Act 1991 ( RMA ) in relation to the above Resource Consent application. The applicant has asked us to provide a response to the request on his behalf. Consequently, we provide a response to the numbered items contained within your email below. 2 Item 1 Further drawings Please provide further description and detailed accompanying drawings of the proposed structure. Specifically requested is: A long section drawing of the structure; and A cross section profile representing the areas where there is a break in the crest. This request is based on Note 2 in the Typical Section of Proposed Reef Breakwater 851886.001-20 plan which mentioned 5m wide break in the crest at 30m. The body of the AEE does not address this aspect of the breakwater design. Please find attached updated Revision 1 drawings containing a long section encompassing two individual breakwaters and one connecting rock sill. We have not provided a long section of the entire 300 m longshore extent of the eight breakwaters, as the height of the proposed structures in relation to their overall aggregated length, would result in a drawing which contained little detail and associated value. Revision 1 drawings provide the following additional information and detail which should be treated as an update to the applicant s proposal. Sheet 01 shows that the proposal encompasses eight individual nearshore breakwaters with a low rock sill constructed in the gaps between the breakwaters. The rock sills act as control structures for The Hub on Cameron, Level 1, 525 Cameron Road, Tauranga 3110, New Zealand PO Box 317, Tauranga 3140 P +64-7-571 7360 F +64-9-307 0265 E tga@tonkintaylor.co.nz
2 sediments placed during construction, as well as sediments that naturally accumulate in the lee of the breakwater, due to coastal processes and weathering of the bank. The gaps between the breakwaters are required to ensure that tidal flows do not create a preferential scour channel along the back of a 300 m long continuous breakwater structure. That is, with multiple entry and exit points to foreshore area in the lee of the structures, the volumes and velocities of tidal water movements are reduced. More information on the rock sills is provided under Item 4 below. Sheet 01 shows that it is intended that the breakwaters will be constructed in three stages (Areas A, B and C). The first of the three breakwater areas will be constructed as soon as the Resource Consent is approved with two subsequent areas of breakwaters constructed in around 2018 and 2019 respectively. Sheet 02 shows that the relocated foreshore material placed in the lee of the breakwaters will be shaped into a profile such that most of the new profile will be located above MHWS. This will mean that intertidal vegetation will be established at the toe of the new profile and that coastal vegetation will be established near the toe of the existing bank with a transition between the two types of vegetation occurring along the profile. Further, due to the relocated foreshore material being comprised of mainly silts (see Item 4 below), a biodegradable matting (such as Biomac or Biocoir ) will be placed on top of the relocated foreshore material to assist with retaining the relocated foreshore material in situ and provide a medium for the vegetation to establish within. Lastly, the applicant now proposes to place rock at the toe of the existing bank as soon as the Resource Consent is approved. This placed rock would provide a degree of immediate short term mitigation against wave energy acting on the bank during storm events whilst the applicant commissions a detailed design and procures a contractor following the approval of the Resource Consent. The placed rock would be a temporary measure and would be sequentially removed as the permanent breakwaters are constructed along the area of foreshore occupied by the placed rock. 3 Item 2 Construction methodology Please provide a detailed construction methodology for review, including: Timing of the proposed works; Types and numbers of vehicles likely to be used and when; Map showing the access track of the vehicles down to the site in order to avoid disruption of ecological, historical and cultural sites of significance; and Proposed erosion and sediment controls to be undertaken (the necessity will be determined by what equipment is proposed to be used, whether or not the wall will be built to completion in any section, prior to moving to the next section, the length of breakwater structure proposed to be built at one time, and how much of the structure can be built over the hours either side of low tide). See response to Item 1 regarding staging and timing of construction works. We estimate it will take approximately 16 weeks to construct each stage of the breakwaters. We expect an excavator (approximately 12 tonne) would be used to build the structure with a tracked dump truck or tractor and trailer supplying the excavator with rock from a stockpile located on land; see Figure 1 overleaf. Access to the foreshore will be gained from the distal end of the peninsula; see Figure 1 overleaf. Access along the foreshore will be along the upper part of the foreshore when it is not inundated by seawater. The access will occur within the green shaded area notated as intertidal and coastal vegetation to be established within new beach profile behind breakwater on Sheet 01.
3 The following erosion and sediment controls are proposed: Avoiding working on the foreshore when the breakwater construction area and access to it is inundated by seawater; and Placing geotextile over or around the relocated foreshore material area in the lee of the breakwater until the relocated foreshore material has been shaped into the design profile, the biodegradable matting placed over it, and vegetation planted within the matting. Only one breakwater will be constructed at a time. This means that approximately 40-50 m of alongshore extent of foreshore will be disturbed through excavating the foundation of the breakwater and placing the relocated foreshore material behind the breakwater at any time. Figure 1: Stockpile and access locations Source LINZ 2017 4 Item 3 Breakwater core material Section 3.2.2 of the AEE suggests broken concrete will be supplied by the applicant as underlay rock. The quality of this material used could difficult to determine. It could be weak and degrade over time. This might result in damage to the geotextile and slumping of the breakwater. Please either confirm the specification of the proposed material (strength and grading) and its suitability for this application, or provide an alternative high quality form of concrete to be used to ensure the integrity of the structure is maintained from the time of construction. As part of the future detailed design process the specification of the breakwater core material will be confirmed. The detailed design process will ensure the material is suitable and does not cause the geotextile to become damaged and affect the structural integrity of the breakwater.
4 5 Item 4 Substrate composition Please provide comment in relation to the substrate that the breakwater structure is to be built of in relation to effects on ecology and water quality. Test pits have been dug on site to assess the type of sediments that will be excavated to form the breakwaters and placed behind the breakwaters to create the new profile. The sediments have been assessed to predominantly comprise silts with clay fractions mostly likely sourced from the adjacent eroding escarpment. Based on the sediment characteristics, it is considered that the relocated foreshore material will be more easily remobilised by coastal processes than if the sediment predominantly comprised sands. To assist with the retention of these smaller particle size sediments on the foreshore, the biodegradable matting is proposed and a low rock sill (as shown on Sheet 02) will act as a control structure for sediments to accumulate behind that would otherwise be lost to erosion, due to tidal water flows and wave actions/currents passing through the gaps between the breakwaters. The silts and clay fractions are part of the native material within the foreshore but at present they are covered by a layer of sand. Through excavating and replacing the silts and clay fractions on top of the foreshore in the lee of the breakwaters, the visual appearance of the foreshore along a narrow tract between the structures and the bank will be more like the sediments exposed within the bank face itself. To some extent, the proposed biodegradable matting and vegetation to be planted within it will mitigate any short term effects associated with the visual change of the upper component of the foreshore. Further, the proposal is likely to reduce the erosion of the escarpment and consequential deposition of silt and clay material into the Harbour. On the basis of the above and the discussion contained under Item 1 above, it is considered the potential effect on ecology (such as benthic organisms and zostera) due to increased suspended sediment loadings in the coastal water column attributable to the relocated foreshore material can be suitably mitigated to the extent that they will be minor. 6 Item 5 Sediment supply to Matahui spit The break wall will likely affect the delivery of sediment to sand spit, further exacerbating current erosion of the area. The sand spit has ecological value as a high tide bird roost. Sediment delivery to sand spit seems to be from eroding surfaces of Matahui Peninsula. Without hydraulic modelling it is difficult to correctly identify process occurring in area for sediment delivery. But from observations it is suggested this is case. Please provide comment regarding this. On our site visits we have not observed any issue with the distal end of the peninsula eroding. Having reviewed aerial imagery from (2003 to 2017) it is considered that the nett longshore sediment transport at the site is south to north with sediment being delivered to the distal end of the peninsula. A review of the aerial imagery does not suggest a sand spit is in place or that the spit has been prograding due to the longshore movement of sediments from south to north. It is considered that the breakwater structures and more elevated and vegetated foreshore behind them are likely to reduce the supply of eroded bank sediments to the distal end of the peninsula. However, the proposed structures are located relatively high up the beach profile and are shore
5 parallel and therefore are unlikely to significantly interrupt the existing longshore sediment transport at the site. It is considered that any reduction in sediment volume as a result of the construction of the breakwaters will be minor given the other sources of sediment within the wider embayment, estuary and stream systems. 7 Item 6 Relocated foreshore material There is very little sand and sediment present in area where seawall is to be constructed. The excavated clays from construction of the seawall will likely be unsuitable to back fill the breakwater as saltmarsh vegetation will likely not grow in this substrate. Further this fill material could create longer term impacts from increased turbidity due to erosion of this fill material. Please comment on the chosen fill material in relation to the suitability for use to support coastal vegetation and address potential erosion effects. Or, if an alternative fill material is to be used please provide comment regarding the suitability for use to support coastal vegetation and address potential erosion effects. See response provided under Item 4 above. Given the MHWS water level is near the toe of the proposed new foreshore profile, the bulk of the vegetation to be established will not comprise saltmarsh type species. It is envisaged the following species (or similar species) would be established: Oi Oi or similar other rush or sedge; Cabbage Tree; NZ Flax; Manuka and Kanuka; and Red Matipo. The BOPRC s Land Management Fact Sheets 7, 12, 14 and 15 provide useful guidance for coastal revegetation projects in terms of species selection and establishment. The applicant will select species and establish them on site in general accordance with the fact sheets. 8 Position of sub-tidal channel Please clarify the position of the channel and comment further on how you propose to manage this risk (potentially thickening the toe or monitoring and repairing at later date if required) with consideration to the theoretical depth of scour. The position of the sub-tidal channel has not been identified by a recent bathymetric survey. A review of the aerial imagery shows the sub-tidal channel being located approximately 20 m to the west of the Area A most southern breakwater and significantly more distant than 20 m for all other breakwaters. As part of the detailed design process the assessment of the wave climate and potential scour depth for the structures at the site will take into account the location and potential influence of the sub-tidal channel. If necessary, the location of the most southern breakwater will be adjusted further landward away from the sub-tidal channel.
6 9 Remediation of bank It is apparent that the existing bank has scoured significantly and now overhangs in excess of 2m in some places. Many of these overhangs support trees. Further information is required on what, if any, works are proposed to remediate or buttress these overhangs. We note drawing 85 1886.001 20 (Rev 0) does not show any overhang on the existing bank. The overhangs described are the main driver of the application. In most places there is no space between the toe of the bank and trees located right on the crest of the bank to trim the bank to a stable angle of repose without removing more shelter trees. Clearly, the applicant does not want to remove their shelter trees. Therefore, the placed rock and foreshore material won on site will be used to back fill these overhangs as far as practicable. It may even be necessary to import clean soil to fill these overhangs prior to the placed rock and relocated foreshore material won from the site being formed into the new profile. 10 Natural character assessment Due to the large scale of the proposed breakwater and the sensitivity of the site, I am not comfortable to assess the natural character of the proposal based on the limited information provided in the application. Therefore I will require a suitably qualified and experienced person to prepare a detailed Natural Character assessment of the proposal. Please find attached an assessment undertaken by Design Engine Landscape Architects.