surface water drainage strategy document ......1. testing undertaken in general accordance with bre...

PROPOSED EXTENSION TO

STEPHENS AND GEORGE PRINTERS

AT

GOAT MILL ROAD, MERTHYR TYDFIL

SURFACE WATER DRAINAGE STRATEGY

DOCUMENT

IN SUPPORT OF PLANNING APPLICATION

PREPARED BY

BRADLEY ASSOCIATES LIMITED

31 CARDIFF ROAD, TAFFS WELL

CARDIFF

CF15 7RB

May 2018

BACKGROUND

Stephens and George Printers have been based at Goat Mill Road Merthyr since 1995 and

through a series of expansions now employ 220 people on the site. As part of further

business growth Stephens and George Printers have acquired additional land from Merthyr

Tydfil Council to the south of their existing production facility, to construct a proposed

1,050m2 extension to house additional printing lines.

The development site is located on the south side of Goat Mill Road on the south eastern

margins of Dowlais, Merthyr Tydfil. The National Grid Reference of the centre of the site is

(S0) 30667 207430 and the postcode is CF48 3TD. A site location plan is presented in

Appendix A.

The site comprises a rectangular shaped parcel of land of around 90m in length (east to

west) and 20m width (north to south), occupying an area of around 0.18Ha. It is currently

occupied by scrubland to the rear of the factory buildings. The site area is bounded by:-

• To the north: the existing factory buildings housing the print works.

• To the east: sloping scrubland extending for approximately 200m.

• To the south: scrubland extending for 150m followed by the A4060.

• To the west: the existing factory buildings, parking and service yards.

EXISTING SITE RESTRICTIONS

The extension to the side of the existing Print Works is severely restricted by the sharp rise

in levels to the south with a substantial retaining structure required to be incorporated into

the proposals to facilitate the development.

There is a lined open ditch located to the south of the site which will need to be re-aligned

diverted along the top of the new retaining wall to accommodate construction of the

extension and the wall. The ditch will re-modelled and tumble back to the existing levels to

the west of the development.

Reference to statutory Authority record drawings would suggest that the area is free from

main services.

FLOODING FROM RIVERS AND SEAS

From a review of topographical plans and NRW published flood maps, the site is not

indicated to be at risk of flooding by rivers or reservoirs and does not lie within a Flood Alert

or Warning Area. However, the area is indicated to be potentially at risk from flooding by

surface water, the risk appearing to emanate from the cut-off ditch mentioned above. An

extract from the NRW Flood Map is contained within Appendix B.

EXISTING SURFACE WATER DRAINAGE

The existing surface water system for the original development Phase combines both the

rainwater discharge from the roof areas and car parking prior at MHSW3, all as notated on

the drawing No. 419.D1 prepared by Chris Hyatt Partnership and contained within Appendix

C. From MHSW3 we understand the surface water sewer leaves the site before discharging

beneath Goat Mill Road and entering the Morlais Culvert to the north of the site. Discharge

from the Morlais Culvert eventually entering the River Taff further downstream.

PROPOSED SITE DEVELOPMENT

The proposed site development comprises the construction of a new extension new

1,050m2 extension to the existing print works 72m x 14.50m in the form of a portal frame

construction built of the existing structural frame. The works incorporates approximately

90m of a 4m high proprietary retaining wall to retain the ground to the south and part east

and west of the development. The development is reliant on the existing infrastructure

including car parking and service yards to support the development and no additional

external hard areas are proposed.

PROPOSED SURFACE WATER DRAINAGE PHILOSOPHY

As part of an initial Geo-Environmental and Geo-Technical Report carried out for the site in

August 2017 by Earth Science Partnership a single soakaway infiltration test was carried out

in accordance with the method described in BRE Digest 365. The test was undertaken at a

depth of 1.05m in the weathered coal measures. The test failed.

The report extrapolated potential infiltration rates for the site based on the results received

recommending a percolation rate of 1 X 10-6m/s be considered subject to future full size

extended testing. The report also states that any soakaway must be located a minimum of

10m from and building and that any soakaway discharge point be kept as high as possible

within the ground to maximize the thickness of soils between the discharge point and the

ground water below there-by maximising the attenuation potential of the soils.

A copy of the soakaway test result and extracts from the Earth Science Partnership Geo-

environmental and Geo-technical Report is contained within Appendix D.

Whilst the development would discharge clean roof water only to soakaway the location

and linear nature of the development would limit the practicality of use of soakaways as the

carrier drains would be at significant depth prior to discharge to any soakaway chamber.

Given the extrapolated potential percolation rate advised, the size of any soakaway

chamber would also need to be significant to accommodate the discharge from the

developed roof area. The soakaway chambers would also need to be located a minimum of

10m from the proposed and existing building structure further limiting the practicality of

utilizing such an option in this instance.

Given the foregoing consideration has been given to providing an attenuated discharge from

the development to the existing surface water system and the Morlais Culvert downstream.

However, again given the location and orientation of the extension it would be impractical

to provide direct attenuation of run-off from these areas. As such the surface water

proposals rely on direct discharge of the proposed 1,050m2 roof to the existing roof

drainage system serving the phase 1 development with the additional flow generated by the

proposed roof area compensated by the interception of approximately 1,550m2 of car

parking to the north of the development with run-off from this area attenuated to 5L/s for

all rainfall events, up to the 1 in 100yr event plus a 30% increase in rainfall intensity as an

allowance Climate Change. Attenuation to be provided in the form of underground storage

crates sized to suit the critical 240min. winter storm equating to a critical storage volume of

61m3.

The cellular storage crates shall be stacked to be 500mm high and will be of approximate

dimensions 21.60m x 7.20m with two 3.6 x 3.6m cut outs to suit the location of two existing

car park lighting columns, which shall remain. Two rodding access sleeves through the

crates will be provided with access chambers positioned either end to facilitate future

inspection and maintenance. One of these access points will take the form of a catch-pit

manhole which will serve to alleviate silt and debris entering the attenuation system. The

cellular crate system shall be capable of supporting car parking loadings under a minimum

cover of 600mm and shall be Hewitech Variobox or similar approved.

The preliminary surface water proposals are as indicated on drawing No. 15948/10[P0]

contained within Appendix E. The through flow control will be provided by the construction

of a new manhole notated SW8A over the existing 150mm dia. surface water drain between

existing manholes SW8 and SW9. An ACO Q-Brake vortex type flow control devise will

restrict the flow to a maximum of 5L/s under the design head of 0.685m. Micro Drainage

calculations indicating the storage requirements and outflow control are contained within

Appendix F.

The proposals as detailed will essentially result in zero increase in surface water discharge

from the site with the area intercepted within the car park exceeding the area of the

proposed extension by circa 500m2 which based on a rainfall intensity of 35mm/hr equates

to a runoff of 4.8L/s which is less than the through flow allowance generated by the control.

Details of the principles of the realignment of the open ditch located to the south of the site

has also been shown on drawing No. 15948/10[P0]

Report prepared by: -

Paul Bradley BSC CEng MICE

Director

Bradley Associates Limited

APPENDIX A

SITE LOCATION PLAN

09/05/2018 Google Maps

https://www.google.co.uk/maps/@51.7570297,-3.3564865,17z 1/1

Map data ©2018 Google 50 m

APPENDIX B

EXTRACT FROM NRW FLOOD MAPS

09/05/2018 Geocortex Viewer for HTML5

https://maps.cyfoethnaturiolcymru.gov.uk/Html5Viewer/Index.html?configBase=https://maps.cyfoethnaturiolcymru.gov.uk/Geocortex/Essentials/REST/sites/Flood_Risk/viewers/Flood_Risk/virtualdirectory/Resources/Config/Default

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100m

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Basemap

Options

APPENDIX C

EXISTING DRAINAGE LAYOUT DRAWING

NO.419.D1 PREPARED BY CHRIS HYATT PARTNERSHIP

APPENDIX D

SOAKAWAY TEST RESULTS AND EXTRACTS FROM EARTH SCIENCE PARTNERSHIPS

GEO-ENVIRONMENTAL AND GEO-TECHNICAL REPORT

Project Name:

Project Ref: 6665b

Test Location: TP1/SA1 test failed m/sec

Fill Number: 1

Test results: Pit Dimensions (m)length

width0 0.52 depth1 0.563 0.60 0.525 0.62

10 0.65 Ground Conditions:19 0.6880 0.75

175 0.79380 0.83

V p75 - 25 0.19

α p50 1.9455

tp75 - 25 n/a

ƒ

ƒ

Remarks:

Extremely weak grey MUDSTONE recovered as angular fragments of sizes betweengravel and cobbles. (GRADE B/C SOUTH WALES LOWER COAL MEASURESFORMATION)

Proposed Industrial Extension, Goat Mill Road

Water Level(m bgl)

Assumed Invert Level (m bgl)

Soil Infiltration Rate

α p50 x t p75 - 25

V p75 - 25

1. Testing undertaken in general accordance with BRE Digest 365:2007

no value

Effective depth storage volume of water in the trial pit between 75% and 25% effective depth

The internal surface area of the trial pit up to 50% effective depth and including the base area

The time for the water level to fall from 75% to 25% effective depth

test failed

Soil Infiltration Rate (m/sec) 0.186

Soil Infiltration Rate (m/sec) ƒ

SOAKAWAY INFILTRATION TEST RESULTSBRE 365 method

2.00

0.351.05

Time(mins)

2. Trial pit was not filled with aggregate for test.

0.0 - 0.13Soft dark brown slightly gravelly slightly sandy organic CLAY with roots. (PLACEDTOPSOIL)

0.13-0.55Soft to firm dark brown slightly gravelly slightly sandy CLAY with a low cobble content.Cobbles and gravel are angular to rounded and of mudstone with some coal. (MADEGROUND)

0.55-1.05

0.00

0.20

0.40

0.60

0.80

1.000 100 200 300 400

Wat

erLe

vel(

mbg

l)

Time (mins)

Fall in Water over Time

Water depth

25% Effective Depth

75% Effective Depth

6665bGoat Mill Road, Dowlais

August 2017

APPENDIX E

PROPOSED DRAINAGE LAYOUT DRAWING No. 15948/10[P0]

APPENDIX F

MICRO-DRAINAGE CALCULATIONS

Bradley Associates Page 1

31 Cardiff Road Extension to

Taffs Well Steven & George

Cardiff CF15 7RB 15948

Date 01/05/2018 Designed by PB

File STORAGE.SRCX Checked by

Micro Drainage Source Control 2017.1

Summary of Results for 100 year Return Period (+30% )

©1982-2017 XP Solutions

Half Drain Time : 109 minutes.

StormEvent

MaxLevel

(m)

MaxDepth

(m)

MaxInfiltration

(l/s)

MaxControl

(l/s)

MaxΣ Outflow

(l/s)

MaxVolume

(m³)

Status

15 min Summer 291.321 0.196 0.0 5.0 5.0 24.2 O K30 min Summer 291.404 0.279 0.0 5.0 5.0 34.5 O K60 min Summer 291.485 0.360 0.0 5.0 5.0 44.4 O K

120 min Summer 291.532 0.407 0.0 5.0 5.0 50.2 O K180 min Summer 291.543 0.418 0.0 5.0 5.0 51.6 O K240 min Summer 291.548 0.423 0.0 5.0 5.0 52.2 O K360 min Summer 291.544 0.419 0.0 5.0 5.0 51.7 O K480 min Summer 291.530 0.405 0.0 5.0 5.0 50.0 O K600 min Summer 291.511 0.386 0.0 5.0 5.0 47.7 O K720 min Summer 291.490 0.365 0.0 5.0 5.0 45.0 O K960 min Summer 291.441 0.316 0.0 5.0 5.0 39.0 O K

1440 min Summer 291.319 0.194 0.0 5.0 5.0 23.9 O K2160 min Summer 291.209 0.084 0.0 5.0 5.0 10.4 O K2880 min Summer 291.153 0.028 0.0 4.8 4.8 3.4 O K4320 min Summer 291.125 0.000 0.0 4.2 4.2 0.0 O K5760 min Summer 291.125 0.000 0.0 3.5 3.5 0.0 O K7200 min Summer 291.125 0.000 0.0 3.1 3.1 0.0 O K8640 min Summer 291.125 0.000 0.0 2.8 2.8 0.0 O K

10080 min Summer 291.125 0.000 0.0 2.5 2.5 0.0 O K15 min Winter 291.350 0.225 0.0 5.0 5.0 27.8 O K30 min Winter 291.448 0.323 0.0 5.0 5.0 39.9 O K60 min Winter 291.546 0.421 0.0 5.0 5.0 52.0 O K

120 min Winter 291.609 0.484 0.0 5.0 5.0 59.8 O K180 min Winter 291.615 0.490 0.0 5.0 5.0 60.6 O K

StormEvent

Rain(mm/hr)

FloodedVolume

(m³)

DischargeVolume

(m³)

Time-Peak(mins)

15 min Summer 100.646 0.0 29.2 2130 min Summer 74.363 0.0 43.1 3660 min Summer 52.662 0.0 61.3 64

120 min Summer 35.497 0.0 82.4 108180 min Summer 27.508 0.0 95.7 142240 min Summer 22.929 0.0 106.3 176360 min Summer 17.658 0.0 123.2 246480 min Summer 14.625 0.0 135.9 316600 min Summer 12.613 0.0 146.8 386720 min Summer 11.163 0.0 155.6 456960 min Summer 9.187 0.0 171.0 592

1440 min Summer 6.965 0.0 194.3 8282160 min Summer 5.294 0.0 221.3 11722880 min Summer 4.365 0.0 243.7 15044320 min Summer 3.346 0.0 280.1 05760 min Summer 2.792 0.0 311.6 07200 min Summer 2.438 0.0 340.0 08640 min Summer 2.180 0.0 365.0 0

10080 min Summer 1.984 0.0 387.4 015 min Winter 100.646 0.0 32.8 2130 min Winter 74.363 0.0 48.2 3660 min Winter 52.662 0.0 68.5 64

120 min Winter 35.497 0.0 92.2 118180 min Winter 27.508 0.0 107.5 148








Summary of Results for 100 year Return Period (+30% )


StormEvent

MaxLevel

(m)

MaxDepth

(m)

MaxInfiltration

(l/s)

MaxControl

(l/s)

MaxΣ Outflow

(l/s)

MaxVolume

(m³)

Status

240 min Winter 291.619 0.494 0.0 5.0 5.0 61.0 O K360 min Winter 291.604 0.479 0.0 5.0 5.0 59.1 O K480 min Winter 291.575 0.450 0.0 5.0 5.0 55.6 O K600 min Winter 291.541 0.416 0.0 5.0 5.0 51.3 O K720 min Winter 291.503 0.378 0.0 5.0 5.0 46.6 O K960 min Winter 291.415 0.290 0.0 5.0 5.0 35.8 O K

1440 min Winter 291.234 0.109 0.0 5.0 5.0 13.5 O K2160 min Winter 291.129 0.004 0.0 4.7 4.7 0.4 O K2880 min Winter 291.125 0.000 0.0 4.0 4.0 0.0 O K4320 min Winter 291.125 0.000 0.0 3.1 3.1 0.0 O K5760 min Winter 291.125 0.000 0.0 2.6 2.6 0.0 O K7200 min Winter 291.125 0.000 0.0 2.2 2.2 0.0 O K8640 min Winter 291.125 0.000 0.0 2.0 2.0 0.0 O K

10080 min Winter 291.125 0.000 0.0 1.8 1.8 0.0 O K

StormEvent

Rain(mm/hr)

FloodedVolume

(m³)

DischargeVolume

(m³)

Time-Peak(mins)

240 min Winter 22.929 0.0 119.6 188360 min Winter 17.658 0.0 137.9 266480 min Winter 14.625 0.0 152.1 342600 min Winter 12.613 0.0 163.9 418720 min Winter 11.163 0.0 174.4 492960 min Winter 9.187 0.0 191.1 640

1440 min Winter 6.965 0.0 217.5 8442160 min Winter 5.294 0.0 248.1 11282880 min Winter 4.365 0.0 272.8 04320 min Winter 3.346 0.0 313.7 05760 min Winter 2.792 0.0 349.0 07200 min Winter 2.438 0.0 380.8 08640 min Winter 2.180 0.0 408.8 0

10080 min Winter 1.984 0.0 433.9 0








Rainfall Details


Rainfall Model FSR Winter Storms YesReturn Period (years) 100 Cv (Summer) 0.750

Region England and Wales Cv (Winter) 0.840M5-60 (mm) 20.000 Shortest Storm (mins) 15

Ratio R 0.200 Longest Storm (mins) 10080Summer Storms Yes Climate Change % +30

Time Area Diagram

Total Area (ha) 0.155

TimeFrom:

(mins)To:

Area(ha)

TimeFrom:

(mins)To:

Area(ha)

0 4 0.000 4 8 0.155








Model Details


Storage is Online Cover Level (m) 292.230

Cellular Storage Structure

Invert Level (m) 291.125 Safety Factor 2.0Infiltration Coefficient Base (m/hr) 0.00000 Porosity 0.95Infiltration Coefficient Side (m/hr) 0.00000

Depth (m) Area (m²) Inf. Area (m²) Depth (m) Area (m²) I nf. Area (m²) Depth (m) Area (m²) Inf. Area (m²)

0.000 130.0 0.0 0.500 130.0 0.0 0.501 0.0 0.0

ACO Q-Brake Outflow Control

Design Head (m) 0.680 Design Flow (l/s) 5.0 Diameter (m m) 102 Invert Level (m) 290.945

Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s) Depth (m) Flow (l/s)

0.100 3.6 0.800 5.4 2.000 8.5 4.000 12.0 7.000 15.90.200 4.8 1.000 6.0 2.200 8.9 4.500 12.8 7.500 16.50.300 5.0 1.200 6.6 2.400 9.3 5.000 13.4 8.000 17.00.400 4.6 1.400 7.1 2.600 9.7 5.500 14.1 8.500 17.50.500 4.3 1.600 7.6 3.000 10.4 6.000 14.7 9.000 18.00.600 4.7 1.800 8.1 3.500 11.2 6.500 15.3 9.500 18.5

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