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NZ Transport Agency and Tauranga City Council Mangatawa Drain Flood Bypass and TEM Stormwater AEE 7.2 TEM Roadway Stormwater The package of activities this part of the report refers to are between chainage 5250 – to 10850 in the Mangatawa catchment. This part of the report describes the devices and design related to controlling and treating the stormwater generated by the road up to the point it leaves the swales to discharge to the surrounding land/drains or water. It should be noted that NZTA has received consent (albeit appealed to the Environment Court) for stormwater resource consents for the remaining three catchments that are affected by the TEM, i.e. Te Maunga, Bell Road and east of the Kaituna River. The stormwater system that is subject to this application is shown in Appendix 3. 7.2.1 TEM Stormwater Management Philosophy The main method for stormwater management is to use swales for stormwater treatment, attenuation and conveyance, with discharge into the existing drainage network. In this area ALL the stormwater generated by the road will be treated and attenuated in swales on the northern side of the alignment. Water will be collected in catch pits from the southern side of the road and piped to the swales which represent a change from the present situation where the water from the existing Sate Highway drains into the Mangatawa Drain. The following summary sets out the principal elements of the approach proposed for the TEM component of this proposal. 1. Treatment and conveyance in Maranui catchment using the TCC drainage system; 2. Swales in the Wairakei catchment providing treatment in accordance with TP10, plus flood storage in accordance with the TCC Wairakei stormwater discharge consent (currently subject to appeal); 3. Fit in with existing land drainage system as far as practicable; 4. Discharge frequently to existing streams or drains, to avoid the concentration of large flows at fewer discharge points; 5. Design using Tauranga City Council (TCC) updated rainfall values that account for climate change (2055); 6. Design consideration up to 1% Annual Exceedance Probability (AEP) storm, but with pipe systems designed for the 10% AEP storm with the balance as secondary flow. 7.2.2 Swales The drainage system will generally consist of kerb and channel on the southern side of the proposed TEM collecting runoff and piping it north at regular intervals under the TEM to swales along the northern side. Within the Wairakei catchment (from chainage 8,200 to 10,850), these swales will provide treatment and attenuation before discharge with a pond within the designation North West of the Domain Road interchange. Within the Maranui catchment, the swales are principally for conveyance, as the treatment will occur in the Status: Final Page 73 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 Maranui stormwater wetland, and the Maranui swale has significant capacity to accept the flows. In the section east of Bruce Road (chainage 9200 to 9,950) the swales will provide attenuation as they will be discharging initially to an existing drainage system which then joins the Maranui swale. West of Bruce Road discharge will be direct to the Maranui swale, as a separate TEM swale system is not necessary. The swales will be at relatively flat grades, often less than 1%. Given that the land being traversed is either peat or soft alluvial silts (using wetland swales at or near groundwater level) the flat grades are not expected to be a problem in terms of ponding of water. However, the swales and associated pond at the Domain Road interchange will provide attenuation of flood peak flows from the motorway, and have been designed to meet the requirements of the TCC comprehensive catchment consent for Wairakei catchment. Some restriction of outlet flows from the swales to the receiving drains is needed to achieve a neutral effect on peak flows and fully mobilise the in-swale storage. A drawing of a typical road side swale is also provided in Appendix 12 Drawing 2036-ck227 Rev D. Between chainage 5700 and chainage 7900 the TEM will drain directly to the Maranui swale and receive treatment in the enlarged TCC wetland at the end of Truman Lane (see Appendix 4 drawing no: 3932036- ck073). Status: Final Page 74 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 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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