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 b. Wairakei Catchment The Wairakei Catchment covers most of Papamoa and is a sensitive catchment to stormwater runoff. It is covered by a comprehensive consent that this application has taken account of. The Wairakei comprehensive stormwater management consent has included in its calculations an expected spill over from the Mangatawa catchment as part of the conditions of consent for the 48 hour 50 ARI storm event. c. Mangatawa Catchment The Papamoa hills area is the major catchment contributing to the Mangatawa Drain. The southern part of the catchment flows directly into the drain and thence without treatment into the harbour, at Rangataua Bay. The current SH2 runoff in this catchment 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. 5.12.2 Catchment Hydrology The Mangatawa Drain is about 2,500m long where it is alongside the proposed Tauranga Eastern Motorway (TEM). The drain has a vegetated, earth lined channel that is tightly constrained between the railway (to the south) and the motorway (to the north). There is some uncertainty as to who is responsible for its maintenance, although in the past Tauranga City Council has undertaken maintenance. It is generally located on either road reserve or railway land. In larger flood events excess flow spills north across the motorway at two locations, and into the Papamoa urban area. The two locations are identified in this report as “Top Spill” and “Bruce Road Spill” (although the spill covers several hundred metres of highway in the general vicinity of Bruce Road). While the discharge can be volumetrically large, it is generally spread as a shallow overflow (a few hundred millimetres deep) or ponding across several hundred metres length of highway, and has resulted in highway closure in the past. The most recent closure was in May 2005, and lasted for 14 to 18 hours. The frequency of spills appears to be about 5 yearly on average at present. TCC has updated their design rainfall figures and these have been applied to this investigation and modelling. These design rainfall figures are based on predicted climate changes to 2055. With the climate adjusted rainfall figures the frequency of spills is predicted to increase to about 3 yearly. In addition to closing the motorway, the spills discharge into developing urban areas on the northern side of the motorway, with potential consequences for TCC for flood risk management. The Top Spill discharge flows to the Wairakei Stream, where there is significant existing urban development, plus plans for growth. This stream predominantly relies on ground soakage, with additional discharge to Harrisons Cut and the Grant Place discharge, so is sensitive to additional flood flow volumes. The Bruce Road Spill discharges to TCC’s Maranui Swale (across private land), and conveys urban stormwater along the northern side of the highway. It then travels under the highway and the railway to the wetland treatment ponds, before discharge to the Tauranga Harbour at Rangataua Bay. The swale was originally designed without Status: Final Page 49 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 accounting for climate change, or for the effects of the Mangatawa Spill, and therefore will need significant upgrading to meet maximum flood level standards in the urban area. 5.13 Ecology 5.13.1 Mangatawa Drain The Mangatawa drain flows within a well-defined channel, northwest along the southern side of State Highway two (SH2). The drain veers southwest past Mangatawa Lane and discharges to Rangataua Bay. The channel is predominantly shaded by the steep banks as the riparian vegetation is minimal, generally consisting of rank grasses and weeds, and the occasional tree. One site was sampled (April 2008) within the upper Mangatawa drain between Mangatawa and Domain Road (Site 5; E: 2798350 N: 6383240). At this site various components of the aquatic ecosystem were sampled and sediment and water quality samples were collected for laboratory analysis. At the time of sampling the drain had formed ponded habitats at both ends of the culvert beneath Kairua Road, and some of the bank vegetation had been cleared as a result of recent instream works. a) Sediment Quality Sediment quality data were compared with the ANZECC (2000) guidelines for the common metals, copper, lead and zinc. Levels recorded in the upper Mangatawa drain at Site C fell below the lower Interim Sediment Quality Guidelines (ISQG) for metals, indicating that the likelihood of adverse effects on instream organisms would be low. Hydrocarbon levels within the upper Mangatawa drain were also below the laboratory detection limit, however no guidelines exist for hydrocarbons for the protection of aquatic life. b) Water Quality Overall, the upper Mangatawa drain at Site 5 had good water quality as determined by spot measurements, with the water being cool (16oC), having high levels of dissolved oxygen (8mg/L & 81%) and moderate conductivity (107 μS/cm), however clarity was poor (0.2m) (Table 5). Status: Final Page 50 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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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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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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