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

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The longest section of culvert works is from the existing 1.8 metre Maranui culvert to the wetland. The Maranui culvert travels beneath SH2 and the rail track conveying stormwater from the existing swale discharging 120 metres upstream of the wetland area to an open drain. The existing culvert will be extended to the wetland where a concrete outlet structure will be constructed. The total extension is 80 metres long and will result in some earthworks to re-grade the drain but is expected to be no greater than 2,000m 3 . 3.1.4 Lower Mangatawa Drain The Lower Mangatawa Drain flows in a south-westerly direction towards Rangataua Bay from Chainage 6800 to Chainage 6100. Works along the Lower Mangatawa Drain include reshaping of the existing floodplain and the installation of an earth bund along both sides of the drain. Along the Lower Mangatawa Drain construction will occur in two stages due to the large area of earthworks required. Due to the low lying nature of the lower reaches of the drain, and the risk of regular flooding, it is expected that work will progress from upstream down progressively improving fill to form the bund. As the bund is formed it will be stabilised as soon as practicable to protect it from storms and flooding. Due to the ecological significance of the drain (see Section 2.2) no works shall occur within the waterway. The Lower Mangatawa Drain construction is expected to require approximately 14,00m 3 volume of earthworks that will primarily be fill. Material excavated will either be reused for the proposed bund along the western and eastern side of the drain or appropriately removed off site. 3.1.5 Stormwater Treatment Wetland The existing wetland covers an area of approximately 3.2ha. In order to adequately treat stormwater from the TEM and surrounding area the wetland will be resized to expand the current treatment area. The total volume of earthworks proposed in this area is approximately 45,000m 3 . Stormwater treatment wetland works will be undertaken in two phases. Phase 1 includes the main body of works on the north-west section of the stormwater treatment wetland; this portion will receive stormwater primarily from the TEM Maranui swale as well as the Arataki and Papamoa residential areas. Phase 2 includes the smaller south-east section which will receive stormwater from the proposed Mangatawa Papamoa Blocks Incorporated (MPBI). The eastern section will eventually be linked with the main wetland area following Phase 2 works. NZTA is responsible for the initial stage of stormwater wetland works. The remaining works will be the responsibility of TCC and MPBI (see Section 4.2.5 for further detail). Stormwater treatment wetland works include extensive excavation works so as to establish a greater ponding area across the stormwater treatment wetland. The excavated material not used to reshape pond margins will be used to establish a bund along the eastern boundary of the Phase 1 area or appropriately removed off site. This material is likely to generally consist of sands, gravels and silt. During construction of the TEM there is potential to take advantage of the proposed stormwater treatment wetland works and utilise some of the area as a temporary sediment retention pond. By constructing the proposed forebay of the stormwater treatment wetland prior to drainage works the potential effects of the project on the SES13 (see section 2.2 for further details) beyond the stormwater treatment wetland can be further mitigated. Diverting runoff from the works area through the forebay will remove sediment before water enters the main stormwater treatment wetland. Further treatment within the stormwater treatment wetland will result in relatively clean water discharging to the SES13. Beca // 1 April 2009 // Page 4 3932036 // NZ1-1453076-10 0.10
3.2 Construction Sequence The typical sequence for the earthworks in fill areas is as follows: • Temporary access road and associated drainage; • Perimeter drains and bunds installed along the boundary to divert clean water and to contain runoff on site; • Erosion and sediment controls installed; • Placement and compaction of fill; • Stabilise with clean aggregate or hydroseed; • Install permanent drainage works. The typical sequence for the earthworks in cut areas is as follows: • Temporary access road and associated drainage; • Perimeter drains and bunds installed along boundary to divert clean water and to contain runoff on site; • Erosion and sediment controls installed; • Strip topsoil and stockpile for later reuse; • Excavate material and place in fill elsewhere on the project site; • Stabilise the exposed surface as soon as practical after excavation with either clean aggregate or hydroseed; • Install permanent drainage works. 3.3 Permanent Stormwater Management Permanent stormwater management will be through the construction of open drains and swales to collect, treat and transport the water to the modified stormwater wetland system before discharging via existing discharge points. Where practicable permanent stormwater drainage will be installed and utilised for erosion and sediment control purposes during the construction period (e.g. as clean water diversions). 4 Erosion and Sediment Control 4.1 Principles of Erosion and Sediment Control The key principles to be employed for an ESCP are to undertake land disturbing activities in a manner that reduces the potential for erosion of bare soils to occur (erosion control) and, to employ treatment devices to treat all sediment laden water prior to discharging from the site (sediment control). The basic erosion and sediment control principles applicable to this project are as follows: 1 Minimise disturbed areas and time of exposure: Only work those areas required for construction to take place. 2 Progressively stabilise disturbed areas. 3 Control erosion at the source. 4 Keep onsite runoff velocities low. 5 Install Perimeter Controls: Divert clean water away from areas of disturbance and divert runoff from areas disturbed to sediment control measures. 6 Retain sediment on site. Beca // 1 April 2009 // Page 5 3932036 // NZ1-1453076-10 0.10
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APPENDIX 1 - Drawing 3932036 ck301R
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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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Hydraulic Modelling: Mangatawa Drai
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undertake investigations into the d
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2. Mangatawa catchment consents for earthworks, storm water ...

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