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

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NZ Transport Agency and Tauranga City Council Mangatawa Drain Flood Bypass and TEM Stormwater AEE excess flood waters from the Maranui swale south into the lower Mangatawa drain at Mangatawa Lane. These will be set so the ‘first flush’ stormwater travels to the TCC wetland via the Maranui Swale and the remaining diluted flood waters will travel down the Lower Mangatawa Drain. This element of the proposal is vital to this proposal as it conveys water in large scale flood events away from the Treatment wetland preventing potential damage to that facility from extreme flood events. This element of the proposal reduces the flood risk to the Papamoa catchments (Wairakei and Maranui) from the present situation. Mangatawa Flood Bypass i. Upper Mangatawa Drain (Domain Road – Bruce Road) The primary aim of the Mangatawa bypass is to control the number of motorway closures and the volume of water spilling into the Maranui and Wairakei catchments without negatively affecting the surrounding environment. The frequency and volume of water spilling across the motorway will decrease with the proposal. It is forecast that the spill occurrence will decrease from approximately 3 yearly events (at present with climate change) to 8. With the proposed mitigation measures the flooding across the motorway is expected about every 10 years. The effect of diverting this flood volume on the Mangatawa drain is considered to be minor and will have positive effect on the Maranui and Wairakei catchments. ii. Lower Mangatawa Drain (Bruce Road – Rangataua Bay) While there will be reduced risk of flooding in the Wairakei and Maranui catchments, there is potentially increased flood risk on the low lying land near the lower Mangatawa Drain (below Mangatawa Lane), south of the railway. The mitigation measures required to address this issue is to remove spoil and widen the flood plain and to provide an earth bund to contain the additional flow particularly the extra peak volume of water and convey it to the Rangataua Bay. Once past this area the discharge of the Mangatawa Drain to the harbour becomes diffuse, within the SES 13. The creation of capacity for flow in the lower Mangatawa Drain will provide the necessary mitigation to reduce the effects of increased volume and flow rate of water to no more than minor. 9.1.2 Water Quality The following information has been taken from the Bioresearches Report: Ecological Features of Some Habitats within Rangataua Bay Catchment (attached as Appendix 5) and the Tauranga Eastern Motorway Resource Consent application. The following focuses on the ecological effects of the TEM project and in turn the enlargement of the stormwater treatment pond at Te Maunga. Status: Final Page 83 April 2009 Project Number: 3932036 NZ1-1552092-Mangatawa Drain Flood Bypass and TEM Stormwater AEE
NZ Transport Agency and Tauranga City Council Mangatawa Drain Flood Bypass and TEM Stormwater AEE The water quality in the area is influenced by the source of the water. The Mangatawa Catchment in the Papamoa Hills lies within Western Bay of Plenty District. It is likely that the water quality is influenced by the rural runoff in this area but this proposal will not address that issue. However the existing State highway 2 as mentioned drains directly to the Mangatawa Drain and it is proposed to pipe this water to swales on the northern side of the alignment for treatment and attenuation. This represents a net improvement for the Mangatawa drain in terms of water quality. TEM Roadway Stormwater The southern side of State highway 2 currently drains directly to the Mangatawa drain and surrounding land drains. In addition the surrounding land use is predominantly rural which adds nutrients to the existing runoff from the area in the Mangatawa Drain. The stormwater generated by the road has the potential to contain contaminants, which can adversely affect receiving environments. The concentration of contaminants in stormwater varies during a storm, from storm to storm, and from catchment to catchment. Stormwater from high traffic areas has a greater potential to contain significant levels of contaminants and levels of contaminants in stormwater can change over time, for example as traffic volumes increase. The following are some of the contaminants that can be found in roadway derived stormwater. (a) Suspended sediments: These are soil, organic particles, and breakdown products of the built environment entrained in stormwater flow. (b) Oxygen demanding substances: These are soil organic matter and plant detritus which reduce the oxygen content of water when they are broken down by chemical action and by bacteria. (c) Metals: A variety of trace metal compounds are carried in stormwater in both solid and dissolved forms. The most commonly measured metals of concern are zinc, lead, copper and chromium. Metals are persistent; they don’t decompose and they accumulate in sediments, plants and filter feeding animals such as shellfish. (d) Hydrocarbons and oils: The hydrocarbons in stormwater are generally those associated with vehicle use. They may be in the form of a free slick, oil droplets, and oil emulsion and in solution or absorbed to sediments. (e) Litter: Litter in stormwater is often referred to as gross pollution. It has a high visual and amenity impact, but limited effect on public health and ecological standards. In addition to the above contaminants, stormwater discharges have other physical and chemical effects which affect aquatic organisms and change how contaminants react. These include increased temperature, altered pH, reduced dissolved oxygen, and changes to alkalinity, hardness and conductivity. From chainage 5900 to chainage 7900 the TEM discharges to the Maranui swale directly. The Maranui swale does not provide treatment as such but this water will be treated in an enlarged stormwater treatment wetland near the end of Truman Lane. This wetland will treat the stormwater to the ARC TP 10 level. Status: Final Page 84 April 2009 Project Number: 3932036 NZ1-1552092-Mangatawa Drain Flood Bypass and TEM Stormwater AEE
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Mangatawa Drain Flood Bypass and TE
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NZ Transport Agency and Tauranga Ci
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Page 116: APPENDIX 1 - Drawing 3932036 ck301R
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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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2.2 Hydrological Assessment 2.2.1 C
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The Maranui catchment area in the m
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Table 7 - 2% AEP Storm Event Top Sp
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These results include climate chang
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3.3 Maintenance Work in Mangatawa D
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stormwater from the Maranui catchme
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Appendix A Mangatawa Drain Layout P
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Appendix C Runoff Hydrographs
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Appendix E Proposed Lower Mangatawa
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APPENDIX 10 - Drawings 3932036 ck46
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APPENDIX 12 - Drawing 3932036 ck227
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Report Tauranga Eastern Motorway -
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1 Introduction This report describe
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embankment settlement rates, and th
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3.2 Construction Sequence The typic
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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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