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

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• Added primary drain cross-sections to reflect updated topographic data • Adjusted Kairua road culverts to reflect existing situation • Included the Maranui catchment of which the details are: - Catchment and natural storage areas - Swales - Culverts - Outlet to harbour 2.1.2 Mitigation Using the above update, various mitigation options were investigated and the options that provided satisfactory results and were cost effective are: • Additional storage within the drains. • Stop banks along the drain located at the two known spill points. • Drain improvements, clearing of vegetation and replant with vegetated lining. • Protection and stabilisation of drain bank in specific locations. • Decrease secondary losses through the railway bridge crossing. • An alternative outlet from the Maranui swale to the Mangatawa Drain was included through the inclusion of the following details: - - Additional culverts below the highway and the railway track. A weir to allow flood spill but contain and bypass the first flush water to the Maranui swale and pond. 2.1.3 Inclusion of MPBI land Further refinement in the model was later carried out to address the effects on the MPBI industrial land south of the State highway. The aim of the refinement was to optimise the available MPBI land. This refinement in the model included the following amendments: • Replace the open drain with an extension of the current 1.8m diameter Maranui Swale outlet pipe culvert from its current outlet up to the treatment pond. • Optimise both the Maranui swale and Mangatawa drain floodway corridor options. • Improve the current pond to a stormwater wetland area that provides treatment for MPBI, TCC and NZTA. 2.1.4 Summary The following is a summary of the mitigation work that is included in the modelling and is illustrated in the drawings in Appendix A: • Provide stopbank and flood retention “bund”. • Enlarge the flood storage area within the drain. • Drain improvements, clearing of vegetation and replant with vegetated lining. • Protection and stabilisation of drain bank in specific locations. • Decrease secondary losses through the railway bridge crossing. • Deepening of Maranui swale. • Additional culverts to drain from the Maranui swale to the Mangatawa Drain. • Improve the lower Mangatawa drain conveyance capacity. • Extend the existing Maranui outlet culvert. • Extend the Maranui stormwater treatment pond as a wetland. Beca // 17 March 2009 // Page 7 3932036 // NZ1-1604459-15 0.15 Rev A
2.2 Hydrological Assessment 2.2.1 Catchments The Papamoa Hills area is the major catchment contributing to the Mangatawa Drain runoff; see Appendix A for the illustration of the catchment boundaries. The southern rural catchments flow directly into the drain and thence without treatment into the harbour, at Rangataua Bay. The northern (urban) catchment drains into the Maranui swale and is treated in the Maranui Pond before also discharging to Rangataua Bay. The current SH2 runoff is partly to the Mangatawa drain, and partly to the Maranui swale. For the proposed TEM this will change, with both the southern and northern carriageway draining into the Maranui swale and being treated in the Maranui Pond. The following table summarise the catchments and the pervious and impervious areas. Table 2 - Catchment Areas (km 2 ) Catchment Residential lots Pervious Imperv. Roof Roads Pervious Imperv. Rural Total P1 – central Lots 10.75 10.75 P2 – east 2.69 2.69 P3 – west 3.03 3.03 Maranui 0.685 0.279 1.167 0.102 0.305 0.606 3.14 SH2/ TEM 0.030 0.148 0.18 Total 0.685 0.279 1.167 0.132 0.453 17.076 19.79 This does not include the MPBI land to the south west, which does not directly affect the principal flood management works addressed in this report. 2.3 Rainfall The TCC design rainfall estimates based on 2055 projected climate change 3 were used. Temporal patterns from that report were used to develop hydrographs that were included in the hydraulic model software. The 6 hour storm was used by Beca as it was identified in the initial work as producing the highest flow rate for the central catchment (P1) of Papamoa Hills. For the Maranui catchment the 5 hour storm produced the critical storm. The following table summarises the input data used in the model work for the catchments. 3 Tauranga City High Intensity Rainfall Update, October 2005, and Tauranga City Temporal Rainfall using the Average Variability Method, May 2006, both produced by Opus International Consultants Ltd Beca // 17 March 2009 // Page 8 3932036 // NZ1-1604459-15 0.15 Rev A
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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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Page 209 and 210: 2 INTRODUCTION Project Background T
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Page 215 and 216: 8 Figure 6. Part ML 8133 showing Pt
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Page 277 and 278: 1 Introduction This report describe
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concrete contamination as well as s
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Pahse 1 consists of the western sec
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• Installation of Stage 2 decanti
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Appendix A Erosion and Sediment Con
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Activity Status Mangatawa Drain 1.1
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(b) Natural State (River) Water Qua
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6. Reclamation or drainage of the b
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APPENDIX 15 - Legal Descriptions of
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Path: P:\393\3932036\TGI\55_Project
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32 Harington Street PO Box 903, Tau
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32 Harington Street PO Box 903, Tau
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