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OVERLAND FLOW PATH ASSESSMENT FOR 45 MOUNT EDEN ROAD AT MOUNT EDEN FOR ANSCOT PROPERTY LTD FOR RESOURCE CONSENT

Job No | 38555

Date | 6 June 2017

Anscot Property Ltd

45 Mount Eden Road

Overland Flow Path Assessment – Revision B

MSC Ref: 38555 | 6 June 2017 i | Page

Document History and Status

Issue Rev. Issued To Qty Date Reviewed Approved

1 A ASC Architects 1 24/04/17 CH CH

2 B ASC Architects 1 06/06/17 CH CH

File Name: O:\Letters\2017\BDOC0005818751

Job Manager: Craig Horwood

Design Engineer: Luke Pyle

Name of Client: Anscot Property Ltd

Name of Job: 45 Mount Eden Rd

Location of Job: Mt Eden

Name of Document: Overland Flow Path Assessment

Document Version: B - Final

MSC Reference: 38555C

Anscot Property Ltd

45 Mount Eden Road

Overland Flow Path Assessment – Revision B

MSC Ref: 38555 | 6 June 2017 ii | Page

CONTENTS

1. INTRODUCTION ...................................................................................................................... 1

Existing Site .................................................................................................................................................. 1

Proposed Works ........................................................................................................................................... 1

2. OVERLAND FLOW PATH ASSESSMENT .............................................................................. 2

3. IMPACTS OF PROPOSED WORKS ON THE OVERLAND FLOW PATH ............................... 3

4. CONCLUSION ......................................................................................................................... 4

Anscot Property Ltd

45 Mount Eden Road

Overland Flow Path Assessment – Revision B

MSC Ref: 38555 | 6 June 2017 1 | Page

1. INTRODUCTION

MSC has been engaged to assess the impact of proposed works on a potential overland flow path located across the property at 45 Mount Eden Road as detailed on the Auckland Council GIS. The assessment of effects is based on a site walkover and a review of the Auckland Council GIS. Refer to Appendix A for a site plan from the Auckland Council GIS.

Existing Site The proposed site is located at 45 Mount Eden Road, Mount Eden, Auckland. The property has an area of approximately 464 m

2. The site and the surrounding area slopes from north-east to south-west at a

gradient of approximately 24%. There is an existing commercial/office building located on the eastern half of the site with grass along the northern boundary and parking located on the western edge of the site.

There is an overland flow path crossing the property, flowing across the north-west corner of the site as shown on the Auckland Council GIS.

Proposed Works The proposed works is to remove the existing building and construct a new mixed use commercial/office and residential building. The proposed building covers the entire lot, including the overland flow path as shown on the ‘Proposed Site Plan’ under Appendix B.

Anscot Property Ltd

45 Mount Eden Road

Overland Flow Path Assessment – Revision B

MSC Ref: 38555 | 6 June 2017 2 | Page

2. OVERLAND FLOW PATH ASSESSMENT

A site walkover was undertaken to validate the existence and actual location of the overland flow path as shown on the Auckland Council GIS. Refer to the site photos in Appendix C. According to the Auckland Council GIS, the overland Flow Path begins at 230-250 Symonds Street, approximately 135 m to the north of the site. The flow then travels south onto Mount Eden Road, continuing south along the road until it reaches 39 Mt Eden Road. The overland flow path then travels towards the south-west, flowing down the public walkway between 39 Mount Eden Road and the proposed site. The overland flow path then crosses the north-west corner of the existing site before flowing south-west along Shaddock Street. The overland flow path catchment is assessed to be approximately 10,952 m

2 as measured from the

Auckland Council GIS and has a calculated flow of 294 L/s, this is however likely to be overestimated. As the overland flow path travels south down Mount Eden Road, the Auckland Council GIS shows the overland flow path diverting from Mt Eden Road and flowing towards the south-west down the public walkway between 39 Mt Eden Road and the proposed site. It is expected that the kerb and channel along Mt Eden Road will contain a portion of the overland flow and ultimately divert it towards the south along Mt Eden Road. An assessment of the kerb and channel on Mount Eden Road has determined a capacity of 193 L/s. At the exit point of the existing site the overland flow has a calculated volume of 101 L/s. Refer to Appendix D for Overland Flow Path Calculations.

Anscot Property Ltd

45 Mount Eden Road

Overland Flow Path Assessment – Revision B

MSC Ref: 38555 | 6 June 2017 3 | Page

3. IMPACTS OF PROPOSED WORKS ON THE OVERLAND FLOW PATH

It is likely that the overland flow volume traveling down the public walkway between 39 Mt Eden Road and the proposed site as shown on the Auckland Council GIS will be reduced due to 101 L/s. As the overland flow travels down the public walkway between 39 Mt Eden Road and the proposed site, the Auckland Council GIS shows the overland flow path crossing the north-west corner of the proposed site before entering Shaddock Street to the west. Under the proposed development, the location where the overland flow path enters the site will be obstructed by a solid basement wall. This is expected to deflect the overland flow path so that it continues down the property boundary between the public walkway and the proposed site before entering Shaddock Street. The overland flow path will ultimately enter Shaddock Street at the same location as existing. There will be no scouring and erosion as the public walkway adjacent to the site is concrete pavement. There will be no increase in adverse effects on any upstream or downstream properties as a result of the diversion of the overland flow path. It is our opinion that the walkway between 39 Mount Eden Road the proposed site will adequately contain the overland flow path. Refer to Appendix E for the diverted overland flow path plan.

Anscot Property Ltd

45 Mount Eden Road

Overland Flow Path Assessment – Revision B

MSC Ref: 38555 | 6 June 2017 4 | Page

4. CONCLUSION

Based on the site walkover and assessment of the site, surrounding area, and the potential volumes in the overland flow path we believe that:

• The overland flow volume of 294 L/s entering the existing site as shown on the Auckland Council GIS is overestimated. It is our opinion that 193 L/s of the overland flow will be contained by the kerb and channels on Mount Eden Road and will be diverted to the south down Mount Eden Road. This will result in a flow volume of 101 L/s entering the existing site.

• The overland flow will not cross the proposed site as it will be diverted by the solid basement wall as part of the proposed development.

• The diverted overland flow will continue down the public walkway between 39 Mount Eden Road and the proposed site and will ultimately enter Shaddock Street to the west of the site at the same location as existing. The overland flow path both upstream and downstream of the site will be maintained.

• There will be no increase in adverse effects on any upstream or downstream properties as a result of the diversion of the overland flow path.

Yours faithfully

MSC CONSULTING GROUP LTD Luke Pyle Civil Engineer Reviewed By: Craig Horwood

Appendix A – Auckland Council GIS

Appendix B – Proposed Site Plan

Appendix C –Site Photos

Overland flow path travelsdown public walkway asper Auckland Council GIS

A portion of the overlandflow path is expected to becontained by the kerb andchannles in Mt Eden Road

A portion of the overlandflow path is expected to becontained by the kerb andchannles in Mt Eden Road

Overland flow path travelsdown public walkway andinto Shaddock Street asper Auckland Council GIS

Appendix D – Overland Flow Path Calculations

OVERLAND FLOW PATH CALCULATIONS

13-04-17 By: LP Reference No: 38555

Project: 45 Mount Eden Road

Assumptions:

c=0.90 for roof/carpark/driveway design rainfall (mm/hr) HIRDS plus 2.1 C increase

c=0.3 for permeable surafces 107.4 1% AEP

Overland Flow Path on Mt Eden Road

Area (ha) C No. Int (mm/hr) Q = 2.78CiA

1.0240 0.90 107.4 275.16 roof/carpark/driveway

0.0000 0.30 107.4 0.00 grassed

Max.Flow (L/Sec) 275.16

Assumed 100% impermiable surfaces. Assume full blockage of stormwater network.

Overland Flow Path 275.16 L/s

Overland Flow Path at bottom of footpath

Area (ha) C No. Int (mm/hr) Q = 2.78CiA

1.0952 0.90 107.4 294.30 roof/carpark/driveway

0.0000 0.30 107.4 0.00 grassed

Max.Flow (L/Sec) 294.30

Assumed 100% impermiable surfaces. Assume full blockage of stormwater network.

Overland Flow Path 294.30 L/s

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Appendix E – Diverted Overland Flow Path