STORMWATER REPORT

To:

AUCKLAND COUNCIL

On behalf of: COUNTIES RACING CLUB INC.

Manukau Road

Pukekohe

28 FEBRUARY 2019

BSL REF: 4204

REVISION C

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 1 of 9

BIRCH SURVEYORS LTD

Property House

2A Wesley Street, Pukekohe

PO Box 475, Pukekohe 2340, New Zealand

Telephone: 64 9 237 1111 Facsimile: 64 9 238 0033

Website: www.birchsurveyors.co.nz Email: Pukekohe@BSLnz.com

© BIRCH SURVEYORS LTD 2019 This document is and shall remain the property of Birch Surveyors Ltd. The document may only be used for the purposes for which it was commissioned and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited.

REPORT PREPARED BY REPORT REVIEWED BY REPORT AUTHORISED BY

KELLY BOSGRA SIR WILLIAM BIRCH SIR WILLIAM BIRCH

REGISTERED PROFESSIONAL

SURVEYOR

REGISTERED PROFESSIONAL

SURVEYOR

DATE: 01 MARCH 2019

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 2 of 9

CONTENTS

1 INTRODUCTION......................................................................................................................... 3

1.1 PROJECT ................................................................................................................................... 3 1.2 LEGAL DESCRIPTION ................................................................................................................... 3 1.3 SITE DESCRIPTION ..................................................................................................................... 3 1.4 BACKGROUND ........................................................................................................................... 3 1.5 PROPOSED DEVELOPMENT .......................................................................................................... 4 1.6 PLAN CHANGE REQUEST ............................................................................................................. 4

2 STORMWATER REPORT .............................................................................................................. 5

2.1 STORMWATER DISPOSAL ............................................................................................................. 5 2.2 OVERLAND FLOW ....................................................................................................................... 6

3 CONCLUSIONS ........................................................................................................................... 9

APPENDICES

APPENDIX A: PLANS: STORMWATER AND DEVICE TYPICAL DETAILS

APPENDIX B: CALCULATIONS: DETENTION, SWALE, HYDROLOGY (TP108), CULVERT (HY-8) AND SUPPORTING

INFORMATION FROM CMP

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 3 of 9

1 INTRODUCTION

1.1 PROJECT

The report comprises a Stormwater Assessment to support a proposed plan change for the use land

located at the north-western portion of 242 Manukau Road, Pukekohe. This site is currently zoned as

“Special Purpose” under the Auckland Unitary Plan and will be subject to a proposed plan change to

General Business Zone, to allow subdivision for commercial and retail activities at the site.

1.2 LEGAL DESCRIPTION

The legal description of the Land parcel is as follows-

Appellation: Part of Lot 2 DP 337473

Title Reference: Part of 153789

Plan Change Area: 5.8393Ha

1.3 SITE DESCRIPTION

The site is located adjacent to existing Commercial activities at the southern end of Manukau Road,

Pukekohe, and has multiple access points to both Manukau and Buckland Roads. It is bordered by

existing Commercial areas to the north and west, and existing rural (future urban and commercial)

activities to the south.

The land is generally falling from Southeast to the Northwest, with the receiving area being Peat

Land located on the Flood Plain of the Tutaenui Stream. This stream is located on the western side

of the Plan Change Area. This stream is highly modified and it is appears from historic images that

the current alignment was excavated in the 1940’s to facilitate the drainage of the low lying area that

is Manukau Road. The property is generally in grass and has direct road frontage onto Manukau

Road. The Area also contains a number of existing buildings totalling 655m² being one house of

approx 140m² and some Commercial Retail Space of that is currently occupied by Kia and Versatile

of approx 335m² and a shed used by Counties Racing of Homes of approx 180m². There are also

existing hardstand areas totalling 1.03Ha associated with access, parking and remains of the original

Formula 1 Track. This area is drained by the Tutaenui Stream, which flows into the Whakapipi

Stream, into the Waikato River and eventually to the Tasman Sea.

1.4 BACKGROUND

The site is situated near the bottom end of a small Stormwater Catchment with approximately

27.3Ha of upstream Catchment that is generally bounded by Webb Street to the South, the Old

Buckland Road Alignment to the East and the edge of a Gully to the West and as shown.

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 4 of 9

Most of the upstream Catchment is Future

Urban/Business with an underlying rural zone.

The existing landcover of the catchment is a

mix of Cropping and grazing.

This area does not contain any Public

Stormwater Infrastructure and is serviced by

open drains, culverts and historic private pipes

that directs surface water westward to the

Stream.

The proposal and its immediate Catchment

area fall within the area contained in the

Pukekohe South Stormwater Network

Discharge Consent (NDC), which regulates the

Stormwater Treatment and Disposal. The Pukekohe South Stormwater Catchment Management

Plan (CMP) is the Document that the NDC refers to in regards to Stormwater Modelling &

Calculations and Capital Works Required. We note that the CMP does not include a Climate Change

Factor and confirm that all values quoted from the CMP have been increased by the required

Climate Change Factor for a 2.1° increase in Temperature in line with MfE Guidelines. These being:

ARI →

Duration ↓ 2 Years 5 Years 10 Years 50 Years 100 Years

24 Hour +9% +11.3% +13.2% +16.8% +16.8%

To bring the proposal into context with the CMP Modelling, proposed Lots 1, 2 & 5 are contained in

the western portion of Catchment NW-b and Lots 3 & 4 are contained in the northern (lowest)

portion of Catchment NW-a.

The upstream Stormwater Network and Overland Flowpaths are a complicated affair, with the

Roading Network diverting Overland Flows into different catchments. The proposal is subject to

such a diversion which complicates the management of Overland Flows and this is addressed in

detail in Section 2.2.

1.5 PROPOSED DEVELOPMENT

The Proposal is to change the Underlying Zone from Special Purpose to General Business to allow a

Commercial Development of approximately 5.84Ha in the north western corner of Lot 2 DP 337473

abutting existing Commercial development within the neighbouring property.

1.6 PLAN CHANGE REQUEST

A Plan Change request is being sought from Auckland Council and this assessment supports that

application.

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 5 of 9

2 STORMWATER REPORT

2.1 STORMWATER DISPOSAL

In determining the appropriate Stormwater Treatment and Disposal for the proposed Activity, we

have designed a system to ensure compliance with the CMP and Condition 21 of the NDC. This sets

out the required Stormwater Management and for this site will require the treatment of runoff from

impervious surfaces to remove 75% TSS loads in accordance with TP10; to minimise changes to the

pre-development hydrological regime by attenuating runoff for the 2 and 10 year storm events, and

to detain the 34.5mm storm event and release over 24 hours (ED) when discharging to a Category 1

Watercourse (Permanently Flowing)

The proposal is to treat Carpark runoff in Bioretention Swales to suitable treat the runoff and

designed with sufficient Detention capacity to provide ED and attenuate runoff up to the 10yr ARI

Storm event. The roofs of any buildings will be constructed from inert materials, so the roof runoff

will be considered clean. This will be attenuated via stormwater cells under the floor slab to provide

ED and volumetric control for storm events up to the 10yr ARI.

TP108 was used as the basis for Stormwater Calculations and the results of these are attached in

Appendix B. The Hydrology of the rezoning to General Business will allow almost full impervious

coverage, and we have allowed for a Post Development Hydrology for 95% impervious, allowing 5%

pervious area for soft landscaping within the lots. The Curve Numbers used in the TP108

Calculations are Group B (Alluvial), consistent with the Geological description in the Geotechnical

Report.

The TP108 assessment shows that the proposal will increase both Peak Flows and Volumes for all

Storm Events. These will be attenuated to provide the Required Treatment as required by the NDC.

It is proposed to utilise Detention in the form of Stormwater Cells under the floor Slab for the

buildings, with strategically located outlets to achieve the desired Stormwater Controls. The Cells

are proposed to be single layer and will have a treatment area of 220m² for every 2000m² roof area.

Refer to Appendix B for Calculation Details. The future building sizes are unknown, and the size of

the Stormwater Management Device can be determined at the time of Building Consent on a pro-

rata basis. The Tanks afford 100m³ storage with 60m³ used to capture the 34.5mm Rainfall event

and releasing it over 24hours, and the remaining 40m³ as Detention for the 2-, 5- & 10-year storm

events to be released via orifice or weir at flowrates not exceeding the pre-development flowrates.

The same type of system is proposed to manage the Stormwater runoff from the sealed carpark and

access, except the surface water will be directed to vegetated swales to treat the water before

flowing into the stormwater cells. Swale Calculations are attached in Appendix B. It is anticipated

that for a vegetated swale of 3m wide, a length of 30m is required to treat the stormwater for a

2000m² Carpark/access. Refer to drawing Draft Stormwater, Flood and Overland Flow Paths. The

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 6 of 9

treated runoff will be directed to Stormwater Cells or similar under the carpark to ensure the

required Flow Regime is achieved.

The devices will be connected to a new internal Stormwater Network designed to convey the

attenuated 10% AEP flows to the Tutaenui Stream.

Any new Stormwater Infrastructure will need to convey the anticipated flows from all upstream

catchments, and there is allowance in the concept design to convey the runoff from the remainder

of catchment NW-a to the south. The NDC identifies that developments must maintain flows to the

pre-development rates. Therefore, the design criteria for any new Public Stormwater Network will

be to convey the existing 10% AEP runoff from all directly contributing catchments. Conceptual

Plans showing the layout and detail of the Stormwater Devices are attached in Appendix A. and the

anticipated flows are derived from the CMP calculations.

The combination of the Swales and controlled release underground storage will ensure the runoff

from any proposed buildings and associated parking and access are appropriately treated and the

flow rates are mitigated to pre-development conditions.

2.2 OVERLAND FLOW

In assessing the proposed Activity, Council must be satisfied that the locations of proposed new

buildings and access are safe & stable and not prone to be inundated. There has been a number of

Stormwater and Flooding Assessments for the Tutaenui Stream undertaken in the vicinity of the

proposal, and Council have undertaken most, if not all, the Capital Upgrade Works required in the

NDC and CMP. Synergine has completed a Flood Assessment for the Mega Centre Development

immediately adjacent to the proposal, and this part of the Stormwater Report (Overland Flow) draws

on those results, findings and recommendations of that report.

In terms of the Tutaenui Stream, we have undertaken a HY-8 Culvert Analysis of the Culvert under

Float Road, being node 7 RC culv u/s in the HEC-HMS analysis in the CMP. We have adjusted the

values for the 2.1° Climate Change Factor (CCF). This calculates that the maximum headwater level

required to convey the 1% AEP Storm with CCF is 53.65m. The CMP identified the Design 1% AEP

Flood Level for this culvert (before construction) at 53.70m and it has also been used as the

maximum flood level in the Synergine Flood Report for the Mega Centre.

This correlation enables us to use the CMP Flood Modelling levels as the target flood levels for

developing this site, even allowing CCF. The CMP identified 1% AEP Flood Level ranges from 53.7m

at the northern end of Lot 5 to 53.6m at the southern end of Lot 5. Lots 1, 2 & 5 range in elevation

from 54m to 53m, meaning these Lots will be inundated with up to 700mm flood water.

The Mega Centre has undertaken widening of the Stream profile above the base flow and filling in

the Flood Plain to convey the anticipated 1% AEP Flood Flows within the banks of the stream. This

was undertaken in accordance with the Synergine Report. Council has also recently completed

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 7 of 9

stream works just upstream of the development and we propose to undertake a similar widening,

increasing the width of the stream up to 35m wide for the 95m stretch of stream along the western

boundary of Lot 5, filling Lots 1, 2 & 5 to be above the 1% AEP Flood Level and maintaining the Flood

Level at its existing height.

We note that due the proximity of the RC Culvert and the RT Culvert (as identified on the HEC-HMS

modelling) the scope of the widening may not need to be 35m and may in fact be a lesser value as

the backwater effects of the downstream culvert may not require such a wide channel as a narrower

channel can allow the two culverts to act as a single entity in terms of flooded levels. This will be

modelled at Subdivision Engineering to determine the exact width of channel works required.

The current modelling determines the 1% AEP Flood Level at 53.7m and the maximum widening of

the stream along Lot 5 will be 35m.

This will allow Lots 1,2 & 5 to have fill placed to lift these properties to and above an elevation of

53.8m. Minimum Floor Levels of 54.4m are proposed for future Buildings on these Lots.

Comparing the CMP with Council’s GIS and the Ground profile, it is apparent that the site is subject

to a number overland flowpaths, these originate from upstream catchments and diversions from

other catchments.

The CMP modelling does not correctly identify these overland flows, and the modelling shows

overland flows from Kitchener Road being directed up Manukau Road. This is seen on the map of

the model as component J-3 K’Road (flows down Kitchener Road) is connected to node 8 MR culv u/s

(culvert under Manukau Road). The GIS above shows flows down Kitchener Road as flowing across

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 8 of 9

the proposed site. This effectively changes the designed flow regime and connects J-3 K’Road to

node 7 RC culv u/s. Using the Flows as calculated in the CMP, the overland flow is estimated to be in

the order of 12m³/s from Catchments RS, Y and NW-a. The latter being the only upstream

catchment. This flow will be conveyed along access roads to the Stream and is depicted as

Flowpath A. Presuming this is designed to convey the full overland flow, mannings calculation for

open channel flow determines that for a channel or road grade of 1:250, the anticipated flow depth

for 12m³/s is 400mm in an 11m wide flowpath.

With detailed Intersection Design AT Subdivision Engineering, some of this flow may be able to be

directed down Manukau Road, and down Float Road utilising the existing Flowpath Z.

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe Page 9 of 9

3 CONCLUSIONS

Areas of the site are currently subject to flooding in the 1% AEP Storm event and engineering works

are required to manage the stormwater flows. Overland Flowpaths are required to be formalised

and enlarged to convey excess surface flows through and past the site as outlined in this report. In

order to adequately protect future buildings, the site will be filled above the 1% AEP Flood Levels

and it will be necessary to impose Minimum Floor Levels of 54.4m to provide a minimum of 500mm

freeboard above Tutaenui Stream and 300mm above on site Overland Flowpaths.

The combination of the Storage and the Stormwater Treatment Swale will ensure the runoff from

the proposed buildings and yard are treated in accordance with TP10 to capture 75% of sediments

and that runoff flowrates are mitigated to pre-development rates up to the 10% AEP Storm.

If further information is required please contact, Kelly Bosgra on 09 237 0781 or by email

kelly@bslnz.com

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe

APPENDIX A

CATCHMENT PLAN

TYPICAL DEVICE DETAIL PLAN

Hz: 1:2000 @ A3

Project No.

Scale

4204

Drawn

Designed

Date

Approved

Date

Date

Surveyed Date

-

-

PROJECT MANAGER

-

-

TITLE

Rev.E

Drawing NameF:\..\CAD\SW 3054 E.dwg /

Rev.

PROJECT NAME

COUNTIES RACING CLUB

222 - 244 & 246 - 250 MANUKAU ROAD

PUKEKOHE

DRAFT STORMWATER, FLOOD AND OVERLAND

FLOWPATHS

PLANNING MAP

ZONING

COMPRISED IN

ACTIVITY

TOTAL AREA

REGISTERED OWNERS

LOCAL AUTHORITY AUCKLAND COUNCIL

SPECIAL PURPOSE - MAJOR RECREATION FACILITY ZONE

CFR 153788, 153789, NA54C/889

72.5221 ha

THE COUNTIES RACING CLUB INC

-

-

SUBJECT TO FINAL SURVEY

REV. BYDATE

COMMENT

ESS

12/18INITIAL DRAFT

QualityISO 9001

N

Birch

surveyors

Property House

2A Wesley Street, Pukekohe

PO Box 475,

Pukekohe 2340

Ph: 09 237 1111

Fax: 09 238 0033

pukekohe@bslnz.com

www.birchsurveyors.co.nz

S.Shuker 12/2018

SUBDIVISION

Hz: 1:20 @ A3

Project No.

Scale

3054

Drawn

Designed

Date

Approved

Date

Date

Surveyed Date

TITLE

Rev.E

Drawing NameF:\..\CAD\SW 3054 E.dwg /

Rev.

PROJECT NAME

COUNTIES RACING CLUB

222 - 244 & 246 - 250 MANUKAU ROAD

PUKEKOHE

TYPICAL DEVICE DETAILS

PLANNING MAP

ZONING

COMPRISED IN

ACTIVITY

TOTAL AREA

REGISTERED OWNERS

LOCAL AUTHORITY

CFR 153788, 153789 & NA54C/889

72.5221 ha

-

SUBJECT TO FINAL SURVEY

REV. BYDATE

COMMENT

EKB

03/19RELEASE

QualityISO 9001

Birch

surveyors

Property House

2A Wesley Street, Pukekohe

PO Box 475,

Pukekohe 2340

Ph: 09 237 1111

Fax: 09 238 0033

pukekohe@bslnz.com

www.birchsurveyors.co.nz

-

WB

KB

Project Manager

02/19

03/19

03/19

The Counties Racing Club Inc

SPECIAL PURPOSE

AUCKLAND COUNCIL

Counties Racing Club BSL Ref: 4204 Rev A Manukau Road, Pukekohe

APPENDIX B

SWALE CALCULATIONS

DETENTION TANK CALCULATIONS

HYDROLOGY CALCULATIONS (TP108)

CULVERT CALCULATIONS (HY-8)

SUPPORTING INFORMATION FROM CMP

2a Wesley Street

PO Box 475

Pukekohe 2340

BIRCH SURVEYORS LTDLand Surveyors • Resource Consultants • Planners

ph: 09 237 1111

fax 09 238 0033

Hydrological Soil Group Group_B

CN Area Product

Grassed 61 4.7438 289.3718

totals 4.7438 289.3718

% Impervious 0.00%

CN weighted 61.0000

la weighted 5.0000

Channelisation factor (C) 0.8000 ########

Catchment Length (l) 0.3290 km ########

Catchment Slope (Sc) 0.0073 m/m ########

Runoff Factor 0.4388 Group_A Group_B Group_C Group_D

Time of Concentration (tc) 0.3701 hrs 22.2 min 30 55 70 78

Use (tc) 0.3701 hrs 22.2 min 39 61 74 80

Catchment Area 0.0474 km² 72 81 88 90

CN 61.0000 76 85 89 91

Storage (S) 162.3934 mm 98 98 98 98

Group_A_ImperviousGroup_B_ImperviousGroup_C_ImperviousGroup_D_Impervious

WQV Ex. Det. 50% AEP 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP1/3 2yr 2yr ARI 5yr ARI 10yr ARI 20yr ARI 50yr ARI 100yr ARI

24 hour rainfall depth (P24) mm 23.3333 34.50 70 100 120 140 160 180

c* 0.0394 0.0701 0.1559 0.2170 0.2530 0.2858 0.3159 0.3436

q* from ARC Approx 0.024 0.024 0.039 0.053 0.060 0.065 0.070 0.074

Peak Flowrate (qp) cumecs 0.0269 0.0397 0.1290 0.2501 0.3393 0.4334 0.5312 0.6320

Peak Flowrate (qp) l/s 27 40 129 250 339 433 531 632

24 hour Runoff Depth (Q24) mm 1.86 4.54 18.58 35.06 47.68 61.28 75.69 90.77

24 hour Runoff Volume (V24) cu mtr 88 215 881 1663 2262 2907 3591 4306

Hydrological Soil Group

CN Area Product

Building 98 0.0655 6.4190

Seal 98 1.0300 100.9400

totals 1.0955 107.3590

% Impervious 100.00%

CN weighted 98.0000

la weighted 0.0000

Channelisation factor (C) 0.8000

Catchment Length (l) 0.3290 km

Catchment Slope (Sc) 0.0073 m/m

Runoff Factor 0.9608

Time of Concentration (tc) 0.2405 hrs 14.4 min

Use (tc) 0.2405 hrs 14.4 min

Catchment Area 0.0110 km²

CN 98.0000

Storage (S) 5.1837 mm

WQV Ex. Det. 50% AEP 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP1/3 2yr 2yr ARI 5yr ARI 10yr ARI 20yr ARI 50yr ARI 100yr ARI

24 hour rainfall depth (P24) mm 23.3333 34.50 70 100 120 140 160 180

c* 0.6924 0.7689 0.8710 0.9061 0.9205 0.9311 0.9391 0.9455

q* from ARC Approx 0.128 0.134 0.142 0.145 0.146 0.146 0.147 0.147

Peak Flowrate (qp) cumecs 0.0327 0.0507 0.1089 0.1584 0.1914 0.2244 0.2574 0.2904

Peak Flowrate (qp) l/s 33 51 109 158 191 224 257 290

24 hour Runoff Depth (Q24) mm 19.09 29.99 65.17 95.07 115.03 135.00 154.98 174.96

24 hour Runoff Volume (V24) cu mtr 209 329 714 1042 1260 1479 1698 1917

WQV Ex. Det. 50% AEP 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP1/3 2yr 2yr ARI 5yr ARI 10yr ARI 20yr ARI 50yr ARI 100yr ARI

24 hour rainfall depth (P24) mm 23.3333 34.50 70 100 120 140 160 180

Peak Flowrate (qp) cumecs 0.0595 0.0905 0.2380 0.4084 0.5307 0.6577 0.7886 0.9224

Peak Flowrate (qp) l/s 60 90 238 408 531 658 789 922

24 hour Runoff Volume (V24) cu mtr 297 544 1595 2705 3522 4386 5289 6223

Existing Flows

Group_B_Impervious

Counties Racing Club Zone Change

STORMWATER FLOWS - Site CatchmentExisting Pervious Area

STORMWATER FLOWS - Site CatchmentExisting Impervious

1

2a Wesley Street

PO Box 475

Pukekohe 2340

BIRCH SURVEYORS LTDLand Surveyors • Resource Consultants • Planners

ph: 09 237 1111

fax 09 238 0033

Hydrological Soil Group Group_B

CN Area Product

Grass 61 0.2920 17.8120

totals 0.2920 17.8120

% Impervious 0.00%

CN weighted 61.0000

la weighted 5.0000

Channelisation factor (C) 0.6000 ########

Catchment Length (l) 0.3290 km ########

Catchment Slope (Sc) 0.0073 m/m ########

Runoff Factor 0.4388 Group_A Group_B Group_C Group_D

Time of Concentration (tc) 0.2776 hrs 16.7 min 30 55 70 78

Use (tc) 0.2776 hrs 16.7 min 39 61 74 80

Catchment Area 0.0029 km² 72 81 88 90

CN 61.0000 76 85 89 91

Storage (S) 162.3934 mm 98 98 98 98

Group_A_ImperviousGroup_B_ImperviousGroup_C_ImperviousGroup_D_Impervious

WQV Ex. Det. 50% AEP 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP1/3 2yr 2yr ARI 5yr ARI 10yr ARI 20yr ARI 50yr ARI 100yr ARI

24 hour rainfall depth (P24) mm 25.3333 34.50 76 111 136 163 187 210

c* 0.0451 0.0701 0.1689 0.2372 0.2795 0.3202 0.3527 0.3811

q* from ARC Approx 0.027 0.027 0.047 0.063 0.071 0.078 0.084 0.088

Peak Flowrate (qp) cumecs 0.0020 0.0027 0.0104 0.0204 0.0283 0.0373 0.0457 0.0538

Peak Flowrate (qp) l/s 2 3 10 20 28 37 46 54

24 hour Runoff Depth (Q24) mm 2.26 4.54 21.60 41.86 58.49 77.92 96.18 114.39

24 hour Runoff Volume (V24) cu mtr 7 13 63 122 171 228 281 334

Hydrological Soil Group

CN Area Product

Building 98 2.7737 271.8226

Roads 98 2.7737 271.8226

totals 5.5474 543.6452

% Impervious 100.00%

CN weighted 98.0000

la weighted 0.0000

Channelisation factor (C) 0.6000

Catchment Length (l) 0.3290 km

Catchment Slope (Sc) 0.0073 m/m

Runoff Factor 0.9608

Time of Concentration (tc) 0.1804 hrs 10.8 min

Use (tc) 0.1804 hrs 10.8 min

Catchment Area 0.0555 km²

CN 98.0000

Storage (S) 5.1837 mm

WQV Ex. Det. 50% AEP 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP1/3 2yr 2yr ARI 5yr ARI 10yr ARI 20yr ARI 50yr ARI 100yr ARI

24 hour rainfall depth (P24) mm 25.3333 34.50 76 111 136 163 187 210

c* 0.7096 0.7689 0.8800 0.9146 0.9292 0.9402 0.9475 0.9530

q* from ARC Approx 0.142 0.147 0.156 0.159 0.160 0.161 0.161 0.162

Peak Flowrate (qp) cumecs 0.1989 0.2813 0.6587 0.9785 1.2072 1.4543 1.6740 1.8845

Peak Flowrate (qp) l/s 199 281 659 979 1207 1454 1674 1885

24 hour Runoff Depth (Q24) mm 21.03 29.99 71.15 106.05 131.01 157.98 181.96 204.94

24 hour Runoff Volume (V24) cu mtr 1167 1664 3947 5883 7267 8764 10094 11369

WQV Ex. Det. 50% AEP 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP1/3 2yr 2yr ARI 5yr ARI 10yr ARI 20yr ARI 50yr ARI 100yr ARI

24 hour rainfall depth (P24) mm 25.3333 34.50 76 111 136 163 187 210

Peak Flowrate (qp) cumecs 0.2009 0.2840 0.6691 0.9989 1.2355 1.4916 1.7196 1.9384

Peak Flowrate (qp) l/s 201 284 669 999 1236 1492 1720 1938

24 hour Runoff Volume (V24) cu mtr 1173 1677 4010 6005 7438 8991 10375 11703

Post Development Flows

Counties Racing Club Zone Change

STORMWATER FLOWS - Site CatchmentPost Development Pervious

STORMWATER FLOWS - Site CatchmentPost Development Impervious

Group_B_Impervious

2

Client Counties Racing Analysis Date

Address

Project Number 4254 10% AEP Flood Mitigation Required Yes

Extended Detention and Runoff Flow Mitigation

Site Data

New and Redeveloped Impervious Area 2000 m² Total Site Area 2000 m²

Percentage of Total Site Area 100% Total Site Post Development Impervious Area 2000 m²

Hydrographical Soil Group Group_B Impervious Area required to be Mitigated 2000 m²

34.5 mm Pervious Area required to be Mitigated 0 m²

Pre Development

Pre Developed Area to be Mitigated 2000 m²

Curve Number (CN) 74

Initial Abstraction (Ia) 5 mm

Storage (S) 89.24 mm

ARI

24 Hr Rainfall depth (P24) 34.5 mm

Runoff Depth (Q24) 7.33 mm

Runoff Volume (V24) 14.66 m³

Post Development

Area (m²) CN Product

Total Impervious Area to be Mitigated 2000 98 196000

Total Pervious Area to be mitigated 0 74 0

Total 2000 196000

% Impervious 100%

CN Weighted 98.00

Initial Abstraction Weighted (Ia) 0.00 mm

Storage (S) 5.18 mm

24 Hr Rainfall depth (P24) mm

Runoff Depth (Q24) mm

Runoff Volume (V24) m³

Extended Detention Volume Requirements

Total Extended Detention Volume Required 59.99 m³ (Post Dev - Pre Dev)

Average Outflow to Detention Volume in 24 hours 0.69 l/s for Pipe Tank use 0.86 reduction in flow

Peak Orifice Outflow (2x Average Flow) 1.39 l/s 1.19 l/s

Head above Orifice 0.28 m 0.28 m

Orifice discharge coefficient 0.62 0.62

Orifice Diameter (Orifice 1) 35.0 mm 32.5 mm

TYPICAL DETENTION CALCULATIONS - For a 2000m² Building

4-Mar-19

Manukau Road, Pukekohe

Capture the 34.5mm Rainfall Event and Release over 24 Hours if Discharging to a Category 1

(Permanently Flowing) Watercourse

Extended Detention Depth

Storm Event (ARI)

34.5

29.99

59.99

Storm Event

Mitigate the Post Development Flow Rates for the 2yr and 10yr Storm Events to not exceed the

Pre-Development Flow Rates

Extended Detention

Design Storm

Extended Detention

SURVEYORS | RESOURCE CONSULTANTSLAND DEVELOPMENT ENGINEERS | PLANNERS

3

Flood Mitigation for 2yr Event

Area (m2) CN 10% AEP P24 tc c* q* Q (l/s)

Pre Development (TP108 Calcs) 2000 74 70 17 0.2516 0.065 9.16

Peak Orifice Outflow (2yr Storm - Ex Det Storm) 7.8 l/s Imp Area 2000 0.95 1900 m²

Average Orifice Outflow (2yr Storm - Orifice 2) 3.9 l/s Per Area 0 0.4 0 m²

Reduced Area 1900 m²

Detention Tank Calcs (2yr storm with CC Factor)

Time Duration

(min)

Intensity

(mm/hr)

Reduced

Area

(m²)

Flow

(l/s)

Time to Fill

SMAF

(min)

Tank

Inflow

(m³)

Outflow

Orifice 1

(m³)

Outflow

Orifice 2

(m³)

50% AEP

Storage

(m³)

10 50.16 1900 26.5 37.8 0.00 0.42 0.00 -0.42

20 38.76 1900 20.5 48.9 0.00 0.83 0.00 -0.83

30 29.4 1900 15.5 64.4 0.00 1.25 0.00 -1.25

60 22.8 1900 12.0 83.1 0.00 2.50 0.00 -2.50

120 15.58 1900 8.2 121.6 0.00 5.00 0.00 -5.00

360 6.08 1900 3.2 311.6 9.33 17.01 11.29 -18.98

720 3.99 1900 2.1 474.8 30.99 40.21 57.19 -66.41

Minimum Detention Storage Required for 2yr Storm Event -0.42 m3

Flood Mitigation for 10yr Event

Area (m2) CN 10% AEP P24 tc c* q* Q (l/s)

Pre Development (TP108 Calcs) 2000 74 120 17 0.3813 0.087 20.93

Peak Orifice Outflow (10 yr Storm - SMAF Storm) 19.5 l/s Imp Area 2000 0.95 1900 m²

Average Orifice Outflow (10yr Storm - Orifice 3) 9.8 l/s Per Area 0 0.4 0 m²

Reduced Area 1900 m²

Detention Tank Calcs (10yr storm with CC Factor)

Time Duration

(min)

Intensity

(mm/hr)

Reduced

Area

(m²)

Flow

(l/s)

Time to Fill

SMAF

(min)

Tank

Inflow

(m³)

Outflow

Orifice 1

(m³)

Outflow

Orifice 3

(m³)

10% AEP

Storage

(m³)

10 89.76 1900 47.4 21.1 0.00 0.42 0.00 -0.42

20 69.36 1900 36.6 27.3 0.00 0.83 0.00 -0.83

30 50.4 1900 26.6 37.6 0.00 1.25 0.00 -1.25

60 40.8 1900 21.5 46.4 17.53 3.06 7.96 6.51

120 27.88 1900 14.7 67.9 45.96 7.17 30.52 8.27

360 10.88 1900 5.7 174.1 64.05 22.74 108.98 -67.68

720 7.14 1900 3.8 265.3 102.81 48.93 266.57 -212.70

Minimum Detention Storage Required for 10yr Storm Event 8.27 m3

for Pipe Tank use 0.86 reduction in flow

Peak Weir Outflow (10 yr Storm) 19.5 l/s 16.8 l/s

Head above Weir 0.10 m 0.10 m

Weir discharge coefficient 1.69 1.69

Weir Length 0.4 m 157.2 mm

Detention Tank Square Versitank

Tank Length L 12.00 m Tank Area 219.00 m²

Tank Width W 18.25 m Volume 98.55 m³ total

Tank Height h 0.45 m

Number of Tanks n 1

Number of Orifice Holes 2 total

Outlet Orifice Diameter d1 35.0 mm

Orifice 3 Diameter d3 0.4 mm

Orifice Discharge Coefficient 0.62

Consecutive

4

2a Wesley Street

PO Box 475

Pukekohe 2340

BIRCH SURVEYORS LTDLand Surveyors • Resource Consultants • Planners

ph: 09 237 1111

fax 09 238 0033

WQV 50% AEP 20% AEP 10% AEP 5% AEP 2% AEP 1% AEP1/3 2yr 2yr ARI 5yr ARI 10yr ARI 20yr ARI 50yr ARI 100yr ARI

Area Pervious ha 0.0000 0 0 0 0 0 0

Hydrological Soil Group Group_B Group_B Group_B Group_B Group_B Group_B Group_B

CN 61 61 61 61 61 61 61

P24 mm 25.3333 76 111 136 163 187 210

Peak Rainfall mm 17.1 51.3 74.9 91.8 110.0 126.2 141.8

Ia 5 5 5 5 5 5 5

S 162.39 162.39 162.39 162.39 162.39 162.39 162.39

c* 0.0881 0.3093 0.4181 0.4809 0.5379 0.5811 0.6170

Peak Runoff m³/s 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000 0.0000

Peak Runoff l/s 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Area Impervious ha 0.2000 0.2 0.2 0.2 0.2 0.2 0.2

CN 98 98 98 98 98 98 98

P24 mm 25.3333 76 111 136 163 187 210

Peak Rainfall mm 17.1 51.3 74.9 91.8 110.0 126.2 141.8

Ia 0 0 0 0 0 0 0

S 5.18 5.18 5.18 5.18 5.18 5.18 5.18

c* 0.9157 0.9856 0.9927 0.9950 0.9964 0.9972 0.9978

Peak Runoff m³/s 0.0087 0.0281 0.0413 0.0507 0.0609 0.0699 0.0786

Peak Runoff l/s 8.70 28.09 41.32 50.74 60.91 69.93 78.58

Combined Runoff l/s 8.70 28.09 41.32 50.74 60.91 69.93 78.58

Peak Flow in Swale l/s 7.74 25.00 36.78 45.16 54.21 62.24 69.93

Swale Channel Slope s m/m 0.005 0.005 0.005 0.005 0.005 0.005 0.005

length of Grass mm 75 75 75 75 75 75 75

Depth of Flow d m 0.077 0.115 0.132 0.141 0.150 0.157 0.164

manning n n 0.32 0.20 0.17 0.16 0.14 0.14 0.13

Flowrate Q m³/s 0.008 0.025 0.037 0.045 0.054 0.062 0.070

Side Slope Z 1/ 1 1 1 1 1 1 1

Bottom Width b m 2.50 2.50 2.50 2.50 2.50 2.50 2.50

Top width T m 2.65 2.73 2.76 2.78 2.80 2.81 2.83

cross sectional Area m² 0.1984 0.3007 0.3460 0.3724 0.3975 0.4171 0.4355

flow Velocity v m/s 0.04 0.08 0.11 0.12 0.14 0.15 0.16

WQ Event Velocity Check

Ultimate Velocity Check

time of flow t min 12

swale Length l m 28.09

maximum available swale length m 30.00

Design Top width T1 m 3.00 3.00 3.00 3.00 3.00 3.00 3.00

Design Depth of Swale d1 mm 250 250 250 250 250 250 250

Freeboard mm 173 135 119 109 100 93 87

SWALE DESIGN TO GD04 GUIDELINES (ARC TP10) - Typical Catchment 2000m²

Pervious Catchment

Impervious Catchment

STORMWATER SWALE

5

Client Counties Racing Analysis Date

Address

Project Number 4254 10% AEP Flood Mitigation Required Yes

Extended Detention and Runoff Flow Mitigation

Site Data

New and Redeveloped Impervious Area 2000 m² Total Site Area 2000 m²

Percentage of Total Site Area 100% Total Site Post Development Impervious Area 2000 m²

Hydrographical Soil Group Group_B Impervious Area required to be Mitigated 2000 m²

34.5 mm Pervious Area required to be Mitigated 0 m²

Pre Development

Pre Developed Area to be Mitigated 2000 m²

Curve Number (CN) 74

Initial Abstraction (Ia) 5 mm

Storage (S) 89.24 mm

ARI

24 Hr Rainfall depth (P24) 34.5 mm

Runoff Depth (Q24) 7.33 mm

Runoff Volume (V24) 14.66 m³

Post Development

Area (m²) CN Product

Total Impervious Area to be Mitigated 2000 98 196000

Total Pervious Area to be mitigated 0 74 0

Total 2000 196000

% Impervious 100%

CN Weighted 98.00

Initial Abstraction Weighted (Ia) 0.00 mm

Storage (S) 5.18 mm

24 Hr Rainfall depth (P24) mm

Runoff Depth (Q24) mm

Runoff Volume (V24) m³

Extended Detention Volume Requirements

Total Extended Detention Volume Required 59.99 m³ (Post Dev - Pre Dev)

Average Outflow to Detention Volume in 24 hours 0.69 l/s for Pipe Tank use 0.86 reduction in flow

Peak Orifice Outflow (2x Average Flow) 1.39 l/s 1.19 l/s

Head above Orifice 0.28 m 0.28 m

Orifice discharge coefficient 0.62 0.62

Orifice Diameter (Orifice 1) 35.0 mm 32.5 mm

Mitigate the Post Development Flow Rates for the 2yr and 10yr Storm Events to not exceed the

Pre-Development Flow Rates

Extended Detention

Design Storm

Extended Detention

29.99

59.99

Storm Event

TYPICAL DETENTION CALCULATIONS - For a 2000m² Parking/Sealed Area

4-Mar-19

Manukau Road, Pukekohe

Capture the 34.5mm Rainfall Event and Release over 24 Hours if Discharging to a Category 1

(Permanently Flowing) Watercourse

Extended Detention Depth

Storm Event (ARI)

34.5

SURVEYORS | RESOURCE CONSULTANTSLAND DEVELOPMENT ENGINEERS | PLANNERS

6

Flood Mitigation for 2yr Event

Area (m2) CN 10% AEP P24 tc c* q* Q (l/s)

Pre Development (TP108 Calcs) 2000 74 70 17 0.2516 0.065 9.16

Peak Orifice Outflow (2yr Storm - Ex Det Storm) 7.8 l/s Imp Area 2000 0.95 1900 m²

Average Orifice Outflow (2yr Storm - Orifice 2) 3.9 l/s Per Area 0 0.4 0 m²

Reduced Area 1900 m²

Detention Tank Calcs (2yr storm with CC Factor)

Time Duration

(min)

Intensity

(mm/hr)

Reduced

Area

(m²)

Flow

(l/s)

Time to Fill

SMAF

(min)

Tank

Inflow

(m³)

Outflow

Orifice 1

(m³)

Outflow

Orifice 2

(m³)

50% AEP

Storage

(m³)

10 50.16 1900 26.5 37.8 0.00 0.42 0.00 -0.42

20 38.76 1900 20.5 48.9 0.00 0.83 0.00 -0.83

30 29.4 1900 15.5 64.4 0.00 1.25 0.00 -1.25

60 22.8 1900 12.0 83.1 0.00 2.50 0.00 -2.50

120 15.58 1900 8.2 121.6 0.00 5.00 0.00 -5.00

360 6.08 1900 3.2 311.6 9.33 17.01 11.29 -18.98

720 3.99 1900 2.1 474.8 30.99 40.21 57.19 -66.41

Minimum Detention Storage Required for 2yr Storm Event -0.42 m3

Flood Mitigation for 10yr Event

Area (m2) CN 10% AEP P24 tc c* q* Q (l/s)

Pre Development (TP108 Calcs) 2000 74 120 17 0.3813 0.087 20.93

Peak Orifice Outflow (10 yr Storm - SMAF Storm) 19.5 l/s Imp Area 2000 0.95 1900 m²

Average Orifice Outflow (10yr Storm - Orifice 3) 9.8 l/s Per Area 0 0.4 0 m²

Reduced Area 1900 m²

Detention Tank Calcs (10yr storm with CC Factor)

Time Duration

(min)

Intensity

(mm/hr)

Reduced

Area

(m²)

Flow

(l/s)

Time to Fill

SMAF

(min)

Tank

Inflow

(m³)

Outflow

Orifice 1

(m³)

Outflow

Orifice 3

(m³)

10% AEP

Storage

(m³)

10 89.76 1900 47.4 21.1 0.00 0.42 0.00 -0.42

20 69.36 1900 36.6 27.3 0.00 0.83 0.00 -0.83

30 50.4 1900 26.6 37.6 0.00 1.25 0.00 -1.25

60 40.8 1900 21.5 46.4 17.53 3.06 7.96 6.51

120 27.88 1900 14.7 67.9 45.96 7.17 30.52 8.27

360 10.88 1900 5.7 174.1 64.05 22.74 108.98 -67.68

720 7.14 1900 3.8 265.3 102.81 48.93 266.57 -212.70

Minimum Detention Storage Required for 10yr Storm Event 8.27 m3

for Pipe Tank use 0.86 reduction in flow

Peak Weir Outflow (10 yr Storm) 19.5 l/s 16.8 l/s

Head above Weir 0.10 m 0.10 m

Weir discharge coefficient 1.69 1.69

Weir Length 0.4 m 157.2 mm

Detention Tank Square Versitank

Tank Length L 18.25 m Tank Area 219.00 m²

Tank Width W 12.00 m Volume 98.55 m³ total

Tank Height h 0.45 m

Number of Tanks n 1

Number of Orifice Holes 2 total

Outlet Orifice Diameter d1 35.0 mm

Orifice 3 Diameter d3 0.4 mm

Orifice Discharge Coefficient 0.62

Consecutive

7

HY-8 Culvert Analysis Report Float Road

node 7 RC culv u/s

Crossing Discharge Data

Discharge Selection Method: Specify Minimum, Design, and Maximum Flow

Minimum Flow: 7.50 cms

Design Flow: 37.50cms

Maximum Flow: 66.60cms

8

Table 1 - Summary of Culvert Flows at Crossing: CRC

Rating Curve Plot for Crossing: CRC

Headwater Elevation (m)

Total Discharge (cms) RC Discharge (cms) Roadway Discharge

(cms) Iterations

50.91 7.50 7.50 0.00 1 51.43 13.41 13.41 0.00 1 51.87 19.32 19.32 0.00 1 52.31 25.23 25.23 0.00 1 52.80 31.14 31.14 0.00 1 53.13 37.00 34.69 2.30 5 53.26 42.96 36.13 6.82 4 53.37 48.87 37.50 11.37 4 53.47 54.78 38.34 16.44 4 53.57 60.69 39.24 21.45 4 53.65 66.60 40.10 26.50 4 53.00 33.32 33.32 0.00 Overtopping

9

Table 2 - Culvert Summary Table: RC

********************************************************************************

Straight Culvert

Inlet Elevation (invert): 49.60 m, Outlet Elevation (invert): 49.55 m

Culvert Length: 22.10 m, Culvert Slope: 0.0023

********************************************************************************

Culvert Performance Curve Plot: RC

Total Discharge

(cms)

Culvert Discharge

(cms)

Headwater Elevation

(m)

Inlet Control

Depth (m)

Outlet Control

Depth (m) Flow Type

Normal Depth

(m)

Critical Depth

(m)

Outlet Depth

(m)

Tailwater Depth

(m)

Outlet Velocity

(m/s)

Tailwater Velocity

(m/s)

7.50 7.50 50.91 1.182 1.312 3-M1t 0.926 0.863 1.160 1.487 1.681 0.259 13.41 13.41 51.43 1.652 1.825 3-M1t 1.288 1.170 1.591 2.034 2.034 0.320 19.32 19.32 51.87 2.033 2.274 3-M1t 1.634 1.415 1.949 2.488 2.352 0.363 25.23 25.23 52.31 2.385 2.711 3-M2t 2.500 1.625 2.266 2.887 2.698 0.398 31.14 31.14 52.80 2.755 3.199 4-FFf 2.500 1.810 2.500 3.250 3.172 0.427 37.00 34.69 53.13 2.999 3.630 4-FFf 2.500 1.909 2.500 3.582 3.534 0.452 42.96 36.13 53.26 3.103 3.954 4-FFf 2.500 1.946 2.500 3.898 3.680 0.474 48.87 37.50 53.37 3.206 4.261 4-FFf 2.500 1.981 2.500 4.193 3.819 0.494 54.78 38.34 53.47 3.271 4.530 4-FFf 2.500 2.001 2.500 4.473 3.905 0.513 60.69 39.24 53.57 3.343 4.793 4-FFf 2.500 2.022 2.500 4.740 3.997 0.529 66.60 40.10 53.65 3.413 5.047 4-FFf 2.500 2.042 2.500 4.996 4.085 0.545

10

Water Surface Profile Plot for Culvert: RC

Site Data - RC

Site Data Option: Culvert Invert Data

Inlet Station: 0.00 m

Inlet Elevation: 49.60 m

Outlet Station: 22.10 m

Outlet Elevation: 49.55 m

Number of Barrels: 2

Culvert Data Summary - RC

Barrel Shape: Circular

Barrel Diameter: 2500.00 mm

Barrel Material:

Embedment: 0.00 mm

Barrel Manning's n: 0.0140

Culvert Type: Straight

Inlet Configuration: Grooved End in Headwall

Inlet Depression: None

11

Table 3 - Downstream Channel Rating Curve (Crossing: CRC)

Tailwater Channel Data - CRC

Tailwater Channel Option: Irregular Channel

Channel Slope: 0.0003

User Defined Channel Cross-Section:

Coord No. Station (m) Elevation (m) Manning's n

1 0.00 54.60 0.0500

2 4.70 49.50 0.0500

3 12.70 49.50 0.0500

4 13.00 49.80 0.0500

5 25.60 49.80 0.0500

6 30.00 54.60 0.0000

Roadway Data for Crossing: CRC

Roadway Profile Shape: Constant Roadway Elevation

Crest Length: 30.00 m

Crest Elevation: 53.00 m

Roadway Surface: Paved

Roadway Top Width: 21.00 m

Flow (cms)

Water Surface Elev (m)

Depth (m)

Velocity (m/s)

Shear (Pa)

Froude Number

7.50 50.71 1.21 0.33 3.56 0.11 13.41 51.14 1.64 0.41 4.83 0.11 19.32 51.50 2.00 0.47 5.88 0.12 25.23 51.82 2.32 0.52 6.81 0.12 31.14 52.10 2.60 0.55 7.65 0.12 37.00 52.37 2.87 0.59 8.43 0.12 42.96 52.62 3.12 0.62 9.17 0.12 48.87 52.85 3.35 0.65 9.86 0.12 54.78 53.07 3.57 0.67 10.51 0.12 60.69 53.29 3.79 0.69 11.14 0.12 66.60 53.49 3.99 0.71 11.74 0.12

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