2. Mangatawa catchment consents for earthworks, storm water ...

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. Sandhurst The installation of the Sandhurst culvert includes 2,000m 3 of excavation. The Maranui swale entering the culvert will be blocked off so as to avoid clean water entering the dirty works site. During rainfall events water will back up in the swale where it will be stored. Clean water diversions will be in place so no clean water will enter the site. Upon completion of the culvert installation the Maranui swale will be reconnected and clean water can continue to flow towards the wetland. c. Extension of Maranui Culverts The extension to the Maranui culvert includes 2,000m 3 of excavation. During works the drain will likely continue to convey clean water from the existing highway. To avoid clean water entering the open site the existing culvert will be dammed; as such clean water will back up the existing swale where it can adequately be stored until works are complete. Upon the completion of the culvert extension the dam shall be removed and water will return to flowing through the culvert to the stormwater treatment wetland. 4.2.4 Lower Mangatawa Drain Plan 3932036-CK467A Plan 3932036-CK467A illustrates perimeter controls and sediment treatment devices that may be used. It shows the different sections of the drain that are to be constructed and gives the approximate area that will be worked. Given the area of earthworks required along the drain; works will be undertaken in stages. Stage 1 will include an area of approximately 3ha on the west side of the drain. Clean water diversions will be placed along the northern boundary to divert clean flows from the working footprint and reduce the catchment requiring treatment. A stabilised earth bund will be installed along the length of the northern embankment of the existing drain so as to divert sediment laden flows away from the drain. A sediment retention pond will be installed in the lower south west corner of the works area to treat sediment laden flows from the open works area. Treated water will be discharged to the drain. A silt fence will extend around the boundary of the ecological wetland area so that any water entering the ecological area from the site will be treated by the fence. Stage 2 also covers an area of approximately 3ha along the eastern side of the drain. Stage 2 works include batter reshaping. Clean water diversions will be installed to divert clean flows from the working footprint and reducing the catchment that requires treatment. As per the west side a stabilised earth bund will be installed along the length of the northern embankment of the existing drain so as to divert sediment laden flows away from the drain. A sediment retention pond will be installed in the lower south west corner of the works area so as to treat sediment laden flows from the open works area. Treated water will be discharged to the drain. Stabilisation of the batters using hydroseed or other approved methods will be undertaken as works are completed. 4.2.5 Stormwater Treatment Wetland Plan 3932036-CK461 Plan 3932036-CK461 gives perimeter areas for stages of works and sediment treatment devices that may be used. There are three stages of works for Phase 1 of the stormwater treatment wetland; where as Phase 2 can be undertaken in a single stage of works. NZTA will be responsible for the works associated with Stage 1 of Phase 1 as outlined below. Tauranga City Council will be responsible for the Stage 2 and 3 works of Phase 1, with MPBI responsible for Phase 2. Beca // 1 April 2009 // Page 8 3932036 // NZ1-1453076-10 0.10
Pahse 1 consists of the western section of the proposed works and includes the existing wetland. The majority of the area is currently dry vegetated land making earthworks possible without the need for clean water diversions. Completing the works in three stages will minimise the potential for sediment to enter the clean water system by maintaining a separation between the open earthworks areas and existing channels. Stage 1 consists mainly of forebay works and requires a volume of 5,500m 3 of earthworks. Excavated material will be utilised in the eastern boundary bund or temporarily stockpiled on the existing vegetated areas to allow for drainage. Stockpiles will be positioned away from the clean water areas. Water will continue to enter the existing wetland via the open drain along the eastern boundary. A silt fence will be installed between the forebay works and open drain so as to avoid sediment from the works mixing with clean water flows. Upon completion of the forebay, water shall be diverted to the west of the silt fence so that works can be undertaken on the existing open drain. Undertaking the forebay works first will allow for the existing pond to be used as a temporary sediment retention pond. The forebay will be utilised to remove sediment from dirty water entering the wetland from the Maranui culvert. This approach will reduce the potential for adverse affects of the project on the SES13 beyond the stormwater treatment wetland as potentially sediment laden water from the Marunui catchment works will be treated. The total volume of earthworks required for Stage 2 and Stage 3 works is approximately 20,000m 3 . Plan 3932036-CK461 shows the perimeter of Stage 2; just under half of which is area to be excavated. Material excavated from the area will be reused as fill material for a bund along the boundary of the stormwater treatment wetland and the SES13; excess material not used for batter shaping will be appropriately stockpiled and removed off site. A silt fence will be installed around the eastern perimeter of Stage 2 prior to works beginning. All machinery will be kept out of the waterway on dry land and stable areas within the works site and excavated materials will be placed well away from the waterways. Prior to Stage 3 works beginning the existing wetland pond located in the centre of the Stage 3 area will need to be drained. To allow the wetland system to continue functioning and to drain the central area, stage 2 works will be opened and a temporary dam structure will be constructed in the existing channel as shown on plan 3932036-CK461. Water entering the system will now flow around the western channels of the constructed stormwater treatment wetland, away from the centre. This will allow for stage 3 earthworks to be undertaken in a clean water free section. To further mitigate the effects of sediment entering the clean water, the Stage 2 silt fence along the eastern boundary will remain and an additional silt fence will be constructed along the northern boundary of Stage 3 during the works. As the stormwater treatment wetland will continue to be operational, outlet works will be undertaken during periods of extreme low flows and any water discharged shall be pumped around the works if necessary. As the eastern boundary bund from the Phase 1 works will remain in place, Phase 2 earthworks can be undertaken without disturbing the stormwater treatment wetland. Phase 2 includes a volume of 24,000m 3 of earthworks; more than half of which is area to be excavated. Material excavated from the area will be reused as fill material for a bund constructed along the boundary of the stormwater treatment wetland and the SES13 as well as for fill material along the central ridge of the Phase 2 area. Excess material not used for bund shaping will be appropriately removed off site. 4.2.6 Ingress/Egress Points A stabilised entranceway, with a wheel wash if required, will be constructed at the ingress/egress points to help in the removal of sediment before reaching the public road. If earth is tracked onto Beca // 1 April 2009 // Page 9 3932036 // NZ1-1453076-10 0.10
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Mangatawa Drain Flood Bypass and TE
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APPENDIX 1 - Drawing 3932036 ck301R
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APPENDIX 3 - Drawing 3932036 ck119
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APPENDIX 5 - Bioresearches Report:
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APPENDIX 7 - Archaeological Assessm
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ARCHAEOLOGY B.O.P. HERITAGE CONSULT
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2 INTRODUCTION Project Background T
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4 ARCHAEOLOGICAL LANDSCAPE Previous
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6 U14/1708 & 1709 Figure 3. Cadastr
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8 Figure 6. Part ML 8133 showing Pt
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10 Hungahunga & Toroa A further ton
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12 APRIL 2008 ARCHAEOLOGICAL SURVEY
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14 Historic Places Act In addition
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APPENDIX 8 - Hydraulic Modelling: M
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Hydraulic Modelling: Mangatawa Drai
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undertake investigations into the d
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Discharge to Papamoa Beach To disch
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• Riparian planting adjacent to t
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Page 245: Appendix A Mangatawa Drain Layout P
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Page 289: Appendix A Erosion and Sediment Con
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Page 301 and 302: APPENDIX 15 - Legal Descriptions of
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Page 311 and 312: 32 Harington Street PO Box 903, Tau
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