1 McWilliam Flood Risk Assesment and Drainage Report · 2.2 Site Visit ... interception for...

Sustainable Drainage Systems (SuDS) and Flood Risk Assessment (FRA) Report

Our Ref: BE1062

DATE: 19 September 2017

Prepared in support of: Erection of Two Dwellings with Access off

McWilliam Road and Associated Landscaping: Land rear of 1 McWilliam Road,

Bournemouth, BH9 3BA

Prepared on behalf of: Edward Covell Architects

Second Floor 14 High Street

Poole BH15 1BP

The present document, its content, its appendices and/or amendments (“the Document”) have been created by Build Energy Limited

(“Build Energy”) for informative purposes. They contain private information referring to Complete and/or its subsidiaries (the “Company”),

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Table of Contents 1.0 Summary of Context and Objective of the Report ........................................................................... 4

1.1 Context ........................................................................................................................................ 4

1.2 Aim .............................................................................................................................................. 6

1.3 Objective ..................................................................................................................................... 6

2.0 Summary of Site Characteristics and Setting .................................................................................... 8

2.1 Site Details .................................................................................................................................... 8

2.2 Site Visit....................................................................................................................................... 10

2.3 Information Obtained from the Site Owner ............................................................................... 13

2.4 Information Obtained from Wessex Water Developer Services ................................................ 13

2.5 Ground Conditions ...................................................................................................................... 13

3.0 Flood Risk Assessment (FRA) .......................................................................................................... 15

3.1 Flooding from Rivers and Sea ..................................................................................................... 15

3.2 Flooding from Land ..................................................................................................................... 15

3.3 Flooding from Groundwater ....................................................................................................... 16

3.4 Flooding from Sewers ................................................................................................................. 16

3.5 Flooding from Reservoirs, Canals and Other Artificial Sources .................................................. 16

3.6 Conclusion ................................................................................................................................... 16

3.6.1 Entry through gaps around pipes and cables that pass through walls and floors ............... 18

3.6.2 Entry through party walls from property next door if it is flooded ..................................... 18

3.6.3 Entry through cracks in brickwork ....................................................................................... 18

3.6.4 Entry at airbricks .................................................................................................................. 18

3.6.5 Entry at gaps and cracks in joint sealant around doors and windows ................................. 18

3.6.6 Seepage through the ground entering through the floors of basements and cellars ......... 18

3.6.7 Entry through permeable brickwork and weathered or damaged mortar .......................... 19

3.6.8 Entry at the damp-proof course .......................................................................................... 19

3.6.9 Backflow through overloaded drainage/sewer system blocked by flooding ...................... 19

4.0 SuDS Selection................................................................................................................................. 20

5.0 Planning and Agreement of Design Criteria .................................................................................... 23

5.1 Hydraulic Design Criteria ............................................................................................................. 23

5.1.1 Type B Partial Infiltration Pervious Pavement ..................................................................... 23

5.2 Water Quality Design Criteria ..................................................................................................... 23


5.3 Amenity Design Criteria .............................................................................................................. 23


5.4 Biodiversity Design Criteria ......................................................................................................... 24


6.0 Management of Surface Water Run-off ......................................................................................... 25

6.1 Site Information .......................................................................................................................... 25

6.2 Peak Rate and Volume of Runoff ................................................................................................ 25


6.3 Management and Maintenance Requirements .......................................................................... 29


6.3.2 Skeletank® Controflow Mini Flow Control Chamber ........................................................... 29

Figures and Cross Sections .................................................................................................................... 30

Figure 1 Site Location Plan ................................................................................................................ 30

Figure 2 Proposed Site Plan .............................................................................................................. 30

Figure 3 Proposed Sustainable Drainage Plan .................................................................................. 30

Cross Section A-A’ (Generalised) ...................................................................................................... 30

Appendices ............................................................................................................................................ 31

Appendix A Wessex Water Sewer Plan ............................................................................................. 32

Appendix B Sketched Section Showing Externally Applied Resilience Measures for Cavity Wall

Construction ...................................................................................................................................... 33

Appendix C Rate and Volume of Runoff Calculations ....................................................................... 34

Appendix D Type B Partial Infiltration Pervious Pavement Infiltration Calculations ........................ 35

Appendix E Type B Partial Infiltration Pervious Pavement Sub Base Slope Calculations ................. 36

Appendix F Skeletank SELH03001 ‘Controflow’ Mini Flow Control Unit and Permavoid Rainwater

Diffuser Unit Data Sheets .................................................................................................................. 37

1.0 Summary of Context and Objective of the Report

1.1 Context

It is proposed to erect two Dwellings with access off McWilliam Road and associated

landscaping at a site currently occupied by hedges; trees and scrubland (Photographs 1-4).

Photograph 1

Photograph 2

Photograph 3

Photograph 4

The Site Location Plan is included as Figure 1. Please see Figure 2 for the Proposed Site Plan

and Figure 3 for the Proposed Sustainable Drainage Plan. Cross Section A-A’ shows a

generalised section through the proposed Type B Partial Infiltration Pervious Pavement.

1.2 Aim

The aim of this report is to ensure:

• the best scheme for the management of surface water run-off from the development,

maximising opportunities for Sustainable Drainage Systems (SuDS) and utilising

existing surface water drainage pipework/routes where possible; and,

• that either there is a low risk of flooding from all sources or that the development is

appropriately flood resilient and resistant, including safe access and escape routes

where required, and that any residual risk can be safely managed.

1.3 Objective

The objective of this report is to provide a Sustainable Drainage Systems (SuDS) and Flood

Risk Assessment (FRA) Report at the planning stage that details:

• How flood risk on and off site has been evaluated;

• The scope of SUDS measures appropriate for the site;

• How the SUDS system will meet local and national standards;

• Scaled sustainable drainage plan indicating the extent, position and type of all

proposed hard surfacing (e.g. drives, parking areas, paths, patios) and roofed areas;

• Details of the method of disposal for all areas including means of treatment or

interception for potentially polluted run off;

• Scaled drawings including cross section, to illustrate the construction method and

materials to be used for the hard surfacing (sample materials and literature

demonstrating permeability may be required);

• Maintenance arrangements / management plan for the lifetime of the development.

2.0 Summary of Site Characteristics and Setting

2.1 Site Details

The development site is located at land to the rear of 1 McWilliam Road, Bournemouth (Figure

1).

The site is approximately 40m long by 25m wide; circa 0.083ha in area; and the National

Ordnance Survey (OS) Grid Reference is 409124,094795.

The main site area appears to be approximately level with land falling towards it from the

north, south and west (Photographs 5-8).

Photograph 5

Photograph 6

Photograph 7

Photograph 8

The site is bounded to the north, east, south and west by similar residential development

(Figures 1 - 2).

2.2 Site Visit

A site visit was undertaken on Friday 11 August 2017.

The residential building roofs and driveways to the north and northeast of the site were noted

to discharge towards the development site area (Photographs 9-10).

Photograph 9

Photograph 10

A foul sewer manhole is located around 36.8m Above Ordnance Datum (AOD) in the vehicle

access to land to the rear of 1 McWilliam Road (Photograph 1). The 100mm diameter foul

sewer flows towards McWilliams Road at a depth of around 3.60m below ground level (bgl),

with a second 100mm diameter inlet noted at a depth of around 0.85m bgl (Photograph 11).

Photograph 11

In total 3 No. surface water gullies serve the upgradient McWilliams Road, with one appearing

to be blocked (Photograph 12).

Photograph 12

2.3 Information Obtained from the Site Owner

Information obtained from the owner of the site indicates that there is surface water drain

running across the site. No further information is available.

2.4 Information Obtained from Wessex Water Developer Services

Please see Appendix A for the sewer plan provided by Wessex Water. The plan shows that

the foul sewer manhole located in the vehicle access to land to the rear of 1 McWilliam Road

(Photograph 1) serves No.3 McWilliam Road and discharges to a 225mm diameter sewer

under McWilliam Road.

2.5 Ground Conditions

Cranfield Soil and Agrifood Institute (CSAI) Soilscapes Map provides information on the soil

underlying the site - ‘Freely draining very acid sandy and loamy soils’1.

The BGS Geoindex website also provides information on the superficial deposits and bedrock

geology underlying the site - ‘gravel, sand and clay depending on upslope source and distance

from source’2 and ‘Fine- to medium-grained sand, partly cross-bedded, with lenticular units

of rounded flint pebble- and cobble-gravel’3. The nearest available borehole log on the BGS

Geoindex website is 610m south southeast of the site4.

Groundwater beneath the site location is not associated with a source protection zone5.

The hydrological characteristics of the site location are:

• Average annual rainfall (AAR) mm 794

• Soil runoff coefficient (SPR) 0.1

• Growth curve factor 1 0.85

1 http://www.landis.org.uk/soilscapes/ 2 http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=HEAD 3 http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BOSS 4 http://mapapps2.bgs.ac.uk/geoindex/home.html 5 http://maps.environment-agency.gov.uk/wiyby/wiybyController?value=BH9+3BA&lang=_e&ep=map&topic=groundwater&layerGroups=default&scale=9&textonly=off&submit.x=10&submit.y=9#x=409131&y=94842&lg=1,10,&scale=8

http://www.landis.org.uk/soilscapes/

http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=HEAD

http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BOSS

http://mapapps2.bgs.ac.uk/geoindex/home.html

http://maps.environment-agency.gov.uk/wiyby/wiybyController?value=BH9+3BA&lang=_e&ep=map&topic=groundwater&layerGroups=default&scale=9&textonly=off&submit.x=10&submit.y=9#x=409131&y=94842&lg=1,10,&scale=8





• Hydrological region (R) 76.

6 http://www.uksuds.com/surfacewaterstorage_js.htm

http://www.uksuds.com/surfacewaterstorage_js.htm

3.0 Flood Risk Assessment (FRA)

3.1 Flooding from Rivers and Sea

The lowest point at the site appears to be around 33.2m AOD. The site appears to be

approximately level with land falling towards it from the north, south and west (Photographs

5-8).

A review of the Environment Agency (EA) Flood Map for Planning (from Rivers and the Sea)7

indicates that the:

• site lies within Flood Zone 1 i.e. land assessed as having less than a 0.1 per cent (1 in

1000) chance of flooding occurring each year; and,

• nearest area that could be affected by river flooding is approximately 1.2km north of

the site. This area lies within Flood Zone 3 i.e. land assessed as having a 1 in 100 or

greater annual probability of river flooding occurring each year.

3.2 Flooding from Land

A review of the EA’s risk of flooding from surface water map indicates a predominantly low

risk - between 1 in 1000 (0.1%) and 1 in 100 (1%) chance of flooding each year - and a localised

medium risk - between 1 in 100 (1%) and 1 in 30 (3.3%) chance of flooding each year - in the

development site area8.

Where a low risk is indicated, the surface water depth is predominantly below 300mm - with

a localised 300mm to 900mm depth - and a surface water velocity of over 0.25 m/s9. The

direction of water flow is west to east10.

Where a localised medium risk is indicated, the surface water depth is 300mm to 900mm

7 https://flood-map-for-planning.service.gov.uk/summary/409125/94789 8 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 9 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 10 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850

https://flood-map-for-planning.service.gov.uk/summary/409125/94789

https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850






depth and the surface water velocity is less than 0.25 m/s11.

3.3 Flooding from Groundwater

Appendix 6 of the Bournemouth Borough Council Local Flood Risk Management Strategy12

indicates that the site is not located in an area at risk of groundwater flooding.

3.4 Flooding from Sewers

Volume II, Tile Set 1 of the Level 1 Strategic Flood Risk Assessment13 indicates that the area in

which this site is situated has not experienced sewer flooding of property.

3.5 Flooding from Reservoirs, Canals and Other Artificial Sources

The site is not located in an area at risk of inundation should large reservoir flooding occur14.

3.6 Conclusion

The site is situated in Flood Zone 1 (i.e. land assessed as having less than a 0.1 per cent (1 in

1000) chance of river flooding occurring each year as defined in Planning Policy Guidance

(PPG) Flood Risk and Coastal Change15) but the FRA indicates that there is a low and localised

medium risk of flooding from land close to the curtilage of the property.

Where a low risk is indicated, the surface water depth is predominantly below 300mm - with

a localised 300mm to 900mm depth - and a surface water velocity of over 0.25 m/s16. The


11 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 12 Bournemouth Borough Council Local Strategy for Flood Risk Management, April 2015. 13 Halcrow Group Limited, Bournemouth, Christchurch, East Dorset, North Dorset and Salisbury SFRA, Level 1 Strategic Flood Risk Assessment, Volume I (Final Report), February 2008. 14 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 15 http://planningguidance.planningportal.gov.uk/blog/guidance/flood-risk-and-coastal-change/ 16 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 17 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850





http://planningguidance.planningportal.gov.uk/blog/guidance/flood-risk-and-coastal-change/







Based on the type of flooding (from land), the expected duration is likely to be short.

The picture below from the EAs Practical Guidance for Property Level Flood Protection19

illustrates potential routes for water entry.

Figure 3.1

18 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 19 Environment Agency, Dave Bartram - ncpms Innovation Manager, Practical Guidance for Property Level Flood Protection



3.6.1 Entry through gaps around pipes and cables that pass through walls and floors

See section 3.6.8.

3.6.2 Entry through party walls from property next door if it is flooded

Not applicable.

3.6.3 Entry through cracks in brickwork

See section 3.6.8.

3.6.4 Entry at airbricks

See section 3.6.8.

3.6.5 Entry at gaps and cracks in joint sealant around doors and windows

A flood resistant door is recommended. ‘Although this option is obviously more expensive, it

does have the benefit that as long as the door is shut, that opening is protected. Other

benefits include:

• They require no fitting prior to flooding so are suitable for areas where no flood

warning facility is available and areas susceptible to flash flooding.

• They come in a large range of styles and are virtually indistinguishable from normal

doors and so overcome many of the aesthetic objections to door barriers20.

3.6.6 Seepage through the ground entering through the floors of basements and cellars

Not applicable.

20 Environment Agency, Dave Bartram - ncpms Innovation Manager, Practical Guidance for Property Level Flood Protection

3.6.7 Entry through permeable brickwork and weathered or damaged mortar

See section 3.6.8.

3.6.8 Entry at the damp-proof course

Assuming a concrete slab foundation and a standard brick built wall cavity, at the request of

Gray Environmental Limited, Delta Membrane Systems Limited provided a sketched section

showing externally applied resilience measures for cavity wall construction (Appendix B).

Once further details on the type and form of construction, sections and plans have been

developed for the project, Delta Membrane Systems Limited can assist with the detailing for

the flood resilience measures.

3.6.9 Backflow through overloaded drainage/sewer system blocked by flooding

It is recommended that post development, all inspection chambers are fitted with non-return

valves.

Discharge pipes from washing machines or sinks can also provide a route for water entry, if

they are below the expected flood level. ‘There are a number of smaller easy fit NRVs on the

market especially for this purpose’21.

It is also recommended that a CCTV survey is undertaken of the surface water drain running

across the site to both locate the drain and ensure that any required repairs to the pipework

/ inspection chambers are completed prior to completion of the redevelopment.

21 Environment Agency, Dave Bartram - ncpms Innovation Manager, Practical Guidance for Property Level Flood Protection

4.0 SuDS Selection

The main site area appears to be approximately level with land falling towards it from the

north, south and west (Photographs 5-8).

The residential building roofs and driveways to the north and northeast of the site were noted

to discharge towards the development site area (Photographs 9-10).

In total 3 No. surface water gullies serve the upgradient McWilliams Road, with one appearing

to be blocked (Photograph 11).

Information obtained from the owner of the site indicates that that there is surface water

drain running across the site. No further information is available.

Cranfield Soil and Agrifood Institute (CSAI) Soilscapes Map provides information on the soil

underlying the site - ‘Freely draining very acid sandy and loamy soils’22.

The BGS Geoindex website also provides information on the superficial deposits and bedrock

geology underlying the site - ‘gravel, sand and clay depending on upslope source and distance

from source’23 and ‘Fine- to medium-grained sand, partly cross-bedded, with lenticular units

of rounded flint pebble- and cobble-gravel’24.

The FRA indicates that there is a low risk - between 1 in 1000 (0.1%) and 1 in 100 (1%) chance

of flooding each year - and a localised medium risk - between 1 in 100 (1%) and 1 in 30 (3.3%)

chance of flooding each year - of flooding from land close to the curtilage of the property.

Where a low risk is indicated, the surface water depth is predominantly below 300mm with a

localised 300mm to 900mm depth and a surface water velocity of over 0.25 m/s25. The



22 http://www.landis.org.uk/soilscapes/ 23 http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=HEAD 24 http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BOSS 25 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 26 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850

http://www.landis.org.uk/soilscapes/

http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=HEAD

http://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=BOSS






Based on the type of flooding (from land), the expected duration is likely to be short.

Characteristics were reviewed to allow appropriate selection of SuDS components for the site.

The main constraints/opportunities driving SuDS selection are summarised below and based

on Table 5.4 of CIRIA C69728.

Characteristic Constraint/Opportunity

Soils (permeable) Opportunity for retention, wetland,

infiltration, filtration and source control. Area draining to a single SUDS component

(<2ha)

Groundwater (>1m bgl)

Site topographic characteristics (0-5%)

Available head (0-1m)

Available space (low)

Initially, there appears to be opportunities for surface water runoff to discharge to the public

surface water sewerage system via retention (subsurface storage), wetland (pocket wetland

with surface baseflow), infiltration (infiltration trench, soakaway), filtration (perimeter sand

filter, filter trench) and source control (green roof, rainwater harvesting system, permeable

pavement).

Table 5.9 of CIRIA C69729 indicates:

• retention (subsurface storage) requires low maintenance, has high community

acceptability, requires medium cost and has low habitat creation potential;

• wetland (pocket wetland with surface baseflow) requires high maintenance, has

medium community acceptability, requires high cost and has high habitat creation

potential;

• infiltration (infiltration trench) requires low maintenance, has medium community

acceptability, requires low cost and has low habitat creation potential;

27 https://flood-warning-information.service.gov.uk/long-term-flood-risk/map?easting=409099&northing=94827&address=100040751850 28 CIRIA C697, The SuDS Manual, 2007 29 CIRIA C697, The SuDS Manual, 2007



• infiltration (soakaway) requires low maintenance, has medium community

acceptability, requires medium cost and has low habitat creation potential;

• filtration (perimeter sand filter) requires medium maintenance, has low community

acceptability, requires high cost and has low habitat creation potential;

• filtration (filter trench) requires medium maintenance, has medium community

acceptability, requires high cost and has low habitat creation potential;

• source control (green roof) requires high maintenance, has high community

acceptability, requires high cost and has high habitat creation potential;

• source control (rainwater harvesting system) requires high maintenance, has medium

community acceptability, requires high cost and has low habitat creation potential;

• source control (permeable pavement) requires medium maintenance, has medium

community acceptability, requires medium cost and has low habitat creation

potential.

The disruptive aspects of incorporating source control (green roof, rainwater harvesting) and

wetland (pocket wetland with surface baseflow) into the development design - coupled with

the high maintenance and high cost - indicates that there are no opportunities for these SuDS

techniques.

There are opportunities for the following SuDS techniques:

• retention (subsurface storage) prior to release at a controlled rate;

• infiltration (infiltration trench, soakaway);

• filtration (perimeter sand filter, filter trench); and,

• source control (permeable pavement).

5.0 Planning and Agreement of Design Criteria

5.1 Hydraulic Design Criteria

• discharges from the site to be limited to pre development flow rates;

• attenuation storage volume required to cater for the 100 year critical event;

• long term storage required to prevent increase in downstream flood risk;

• uplift on extreme rainfall intensities of 40% when designing for the ‘2080s’ (2070 to

2115)30; and,

• risk associated with blockage at key locations to be identified and accommodated

appropriately.

5.1.1 Type B Partial Infiltration Pervious Pavement

Please see Section 20.5 of CIRIA C753, The SuDS Manual, 2015 for Hydraulic Design

Requirements for Pervious Pavements.

5.2 Water Quality Design Criteria

In accordance with CIRIA C753, The SuDS Manual, 201531 runoff discharged from the site

should be of an acceptable water quality to protect surface water and groundwaters

effectively (Section 4.2.2 of CIRIA 753, 2015) and the SuDS treatment design should take into

account the potential impacts of climate change on the system processes and associated

performance (Section 4.2.3 of CIRIA 753, 2015).


Please see Section 20.6 of CIRIA C753, The SuDS Manual, 2015 for Treatment Design


5.3 Amenity Design Criteria

Indicators can be used to evaluate the extent to which the amenity design criteria are being

30 https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances 31 CIRIA C753, The SuDS Manual, 2015

https://www.gov.uk/guidance/flood-risk-assessments-climate-change-allowances

delivered by a SuDS design. The amenity design criteria and example indicators are presented

in Table 5.2 of CIRIA 753, 201532.


Please see Section 20.7 of CIRIA C753, The SuDS Manual, 2015 for Amenity Design


5.4 Biodiversity Design Criteria

Indicators can be used to evaluate the extent to which the amenity design criteria are being

delivered by a SuDS design. The amenity design criteria and example indicators are presented

in Table 6.1 of CIRIA 753, 201533.


Please see Section 20.8 of CIRIA C753, The SuDS Manual, 201534 for Biodiversity Design


32 CIRIA C753, The SuDS Manual, 2015 33 CIRIA C753, The SuDS Manual, 2015 34 CIRIA C753, The SuDS Manual, 2015

6.0 Management of Surface Water Run-off

6.1 Site Information

The site area is circa 830m2.

The percentage impermeable area (PIMP) of the site pre development is 0%. The percentage

impermeable area (PIMP) of the site post development is 43%.

6.2 Peak Rate and Volume of Runoff

Rate and volume of runoff calculations are included in Appendix C.

The calculated greenfield runoff rate is 0.02 l/s (based on 0.1 ha which is minimum value when

using the www.uksuds.com greenfield runoff tool).

The discharge rates have been set as low as possible while also ensuring that there is not a

risk to the development in case of blockage (see below and section 6.2.1).

The calculated attenuation storage volume for the post development area - based on the 100

year critical event with 40% uplift for extreme rainfall intensities and a 0.2 l/s gravity flow

control - is 47.91m3 with a time to empty of 9.48hrs

http://www.uksuds.com/


Please see Figure 3 Sustainable Drainage Plan and Generalised Cross Section A-A’.

It is proposed the Type B Partial Infiltration Pervious Access / Drive / Turning area (190m2)

will comprise of:

• 50mm decorative gravel bedding layer, 80mm thick permeable block paving with

50mm thick bedding layer (Type 2/6.3mm or similar) or 40mm porous asphalt 10

surface course and 80mm porous asphalt 14 binder course with 50mm thick bedding

layer (Type 2/6.3mm or similar);

• 125mm Hydraulically bound coarse graded aggregate (HBCGA) sub base; and,

• 150mm Coarse graded aggregate sub base - Type 4/20mm or similar (BS 7533-

13:2009).

‘HBCGA refers to hydraulically bound coarse graded aggregate (conforming to BS EN 14227-

1:2013), minimum cement content 3%, strength class C5/6 as defined in BS EN 14227-1 and

minimum permeability 10,000 mm/hr when tested in accordance with ASTM C1701M-09 or

other suitable test)’ 35.

35 CIRIA C753, The SuDS Manual, 2015

Figure 6.1

The storage volume of the access / drive / turning area 275mm thick sub base is calculated to

be 16m3 (based on a graded gravel porosity of 0.336).

Based on a plane infiltration system of areal dimensions 190m2; an infiltration coefficient of

1x10-5 m/s (Silty clayey SAND37); a minor inconvenience factor of safety (2); and a void ratio

of 0.3 (coarse graded aggregate), the critical depth of water (hmax) for the proposed access /

drive / turning area is 0.29m with a time to half empty (t1/2) of 2.41hr for the 1 hour 100 year

event with a 40% allowance for climate change (Appendix D). This depth will be mitigated by

the minimum 275mm coarse graded aggregate sub-base and the 0.2 l/s gravity flow control

outlet.

A check dam with 150mm flow control to restrict flow between compartments and optimise

the use of available storage space is calculated to be required every 9m in the sub-base

(Appendix E).

36 CIRIA C753, The SuDS Manual, 2015 37 CIRIA C753, The SuDS Manual, 2015

Figure 6.2

A perforated drainage pipe will convey surface water runoff from the sub-base to the on-site

surface water drain via a 0.2 l/s Skeletank SELH03001 ‘Controflow’ Mini Flow Control Unit

(Appendix F) or similar.

Figure 6.3

Rainwater runoff from the building roof downpipes can drain directly to the Type B Partial

Infiltration Pervious Pavement sub-base via Permavoid Rainwater Diffuser Units (Appendix F)

or similar.

External Parking Spaces can be constructed with nominal fall toward Type B Partial Infiltration

Pervious Access / Drive / Turning Area.

Infiltration and CBR testing of the sub grade is required. If saturated CBR of sub grade less

than 5%, a coarse graded aggregate capping layer is also required38.

Lastly, also recommend installation of bull nose kerb with 25mm upstand at site access from

McWilliam Road.

6.3 Management and Maintenance Requirements

Responsibility for the management and maintenance of the pervious pavement drainage will

rest with the property owners.

Periodic inspection is essential and should be carried out to ensure that the pervious

pavement drainage infrastructure is free from debris which could impair its performance.

Inspection and cleaning of silt and other debris from the roofs, inlets, outlets and filters should

be undertaken annually and after severe storms/poor performance.


Please see Section 20.14 of CIRIA C753, The SuDS Manual, 2015 for Operation and

Maintenance Requirements for Pervious Pavement.

6.3.2 Skeletank® Controflow Mini Flow Control Chamber

Maintenance Schedule

Required Action Frequency

Regular Maintenance Remove & rinse filter 3 monthly

Remedial Action Remedial Action Repair/ rehabilitation of inlets, outlets, overflows and vents.

As required

Monitoring Inspect/check all inlets, outlets, vents and overflows to ensure that they are in good condition and operating as designed.

Annually and after large storms.

38 Table 8, Interpave, GUIDE TO THE DESIGN, CONSTRUCTION AND MAINTENANCE OF CONCRETE BLOCK PERMEABLE PAVEMENTS, January 2010 - Edition 6

Figures and Cross Sections

Figure 1 Site Location Plan

Figure 2 Proposed Site Plan

Figure 3 Proposed Sustainable Drainage Plan

Cross Section A-A’ (Generalised)

6462

68

36

35

38

10

12

21

8280

7173

34

61

59

7

36

37

7

MOORDOWN13

17

7a

15

51

8a

60

25

KING EDWARD AVENUE

23

37

39 50

8b

27

48

447

34

60

El Sub Sta

6

36

28

63

Mc WILLIAM ROAD

26

33

78a

4

76

31

67MAY

FIEL

D RO

AD

76a78

3a

36

6

6a

3

8a8

2a

2

SITE LOCATION PLANScale 1:1250

Pln.001

NORTH

DRAWING NO.

SHEET TITLE

PROJECT TITLE

ISSUE DATE:

SCALE

Second Floor, 3Winchester Place, NorthStreet, Poole BH15 1NX

E:[email protected]: eca-p.com

T: 01202 675 152

1 McWILLIAM ROAD

140_PL_001

22/10/2014

SITE LOCATION PLAN

1:1250

DRAWING NO.

-

SHEET TITLE

Mark Date Description

CAD FILE NAME

DRAWN BY

CHECKED BY

PROJECT ID

ISSUE/REVISION

ISSUE DATE:

SCALE

Second Floor3 Winchester Place

North StreetPoole

BH15 1NX

E:[email protected]: eca-p.com

T: 01202 675 152

140

19/08/2016

MR

1:200 @ A3

AC

KEY

LICENSE

NO IMPLIED LICENSE EXISTS. THIS DRAWING

SHOULD NOT BE USED TO CALCULATE AREAS

FOR THE PURPOSES OF VALUATION.

DO NOT SCALE THIS DRAWING.

NOTES

SURVEY NOT FOR CONSTRUCTION.

FOR PLANNING , DESIGN AND LAYOUT

PURPOSES ONLY.

140_PL_003B

PROPOSED

MCWILLIAM ROAD

B

A

1 2

1 2 3

3

C

B

A

C

D D

4

4

5

5

B

A

1 2

1 2 3

3

C

B

A

C

D D

4

4

5

5

B

A

1 2

1 2 3

3

C

B

A

C

D D

4

4

5

5

SITE PLAN

ARROWS INDICATE DWELLINGASPECT

1000mE

KING EDWARD AVENUE

2350

3

0 5 10 MRPZ AS PER PREVIOUSTREE SURVEY

1

2

0 5 10 MRPZ AS PER PREVIOUSTREE SURVEY (BLUE)

UPDATEDRPZ 10.8m RADIUS

AA -140_PL_300

REV A 05/10/15 REPOSITION UNITS

REV B 19/04/16 REMOVE UNIT

Key

Impermeable external Parking Spaces to be constructed with nominal fall toward Type B Partial Infiltration Pervious Access / Drive /

Turning Area.

Infiltration and CBR

testing of subgrade is

required. If

saturated CBR of sub

grade less than 5%, a

coarse graded

aggregate capping

layer is also required.

NotesFigure 3 Proposed Sustainable Drainage Plan

Check Dam with 150mm flow control to restrict flow between compartments and optimise use of available storage space.

A perforated drainage pipe will convey surface water runoff from the sub-base to the on-site surface water drain via a 0.2 l/s orifice

flow control (Skeletank SELH03001 ‘Controflow’ Mini Flow Control Unit or similar).

Run-off from building roofs will be collected into downpipes and flow into a back inlet gully incorporating an internal filter or catchpit

inspection chambers. The back inlet gully or chamber discharges the filtered stormwater into the permeable sub-base via Heavy Duty

Permavoid diffuser units encapsulated in a 2mm mesh fabric.

Also recommend

installation of bull

nose kerb with

minimum 25mm

upstand at site

access from

McWilliam Road

Type B Partial Infiltration Pervious Access / Drive / Turning Area comprising of 50mm decorative gravel bedding layer, 80mm thick

permeable block paving with 50mm thick bedding layer (Type 2/6.3mm or similar) or 40mm porous asphalt 10 surface course and

80mm porous asphalt 14 binder course with 50mm thick bedding layer (Type 2/6.3mm or similar) underlain by 125mm Hydraulically

bound coarse graded aggregate and 150mm coarse graded aggregate.

GR2 GR1

GR3

A

A'

Appendices

Appendix A Wessex Water Sewer Plan

Reproduced from the Ordnance Survey map by permission on behalf of the Controller of Her Majesty's Stationery Office © Crown Copyright . Licence 100019539.

Centre:

N

EW

S

Printed on:

Information in this plan is provided for identification

purposes only. No warranty as to accuracy is given or

implied. The precise route of pipe work may not exactly

match that shown. Wessex Water does not accept liability

for inaccuracies.

Sewers and lateral drains adopted by Wessex Water under

the Water Industry (Schemes for Adoption of Private

Sewers) Regulations 2011 are to be plotted over time and

may not yet be shown.

In carrying out any works, you accept liability for the cost

of any repairs to Wessex Water apparatus damaged as a

result of your works. You are advised to commence

excavations using hand tools only. Mechanical digging

equipment should not be used until pipe work has been

precisely located.

If you are considering any form of building works and pipe

work is shown within the boundary of your property or a

property to be purchased (or very close by) a surveyor

should plot its exact position prior to commencing works or

purchase. Building over or near Wessex Water’s apparatus

is not normally permitted.

WATER MAINS Public Private

Public

Raw Water

Abandoned

Valve Hydrant PRV Meter

SEWERS Public - Section 104 - Private

Foul

Combined

Surface

Abandoned sewers

OTHER WESSEX PIPES

Rising Mains

Effluent Disposal Main

Overflow

NON-WESSEX PIPES

Private Rising Mains

Culverted Water Course

Highway Drain

Land to the rear of 1

McWilliam Road

29/08/2017 12:25

409098.84 , 94808.90

Appendix B Sketched Section Showing Externally Applied Resilience Measures for Cavity

Wall Construction

Appendix C Rate and Volume of Runoff Calculations

This report was produced using the greenfield runoff tool developed by HR Wallingford and available at www.uksuds.com. The use of this tool is subject to the UK SuDS terms and conditions and licence agreement, which can both be found at http://uksuds.com/terms-and-conditions.htm. The outputs from this tool have been used to estimate storage volume requirements. The use of these results is the responsibility of the users of this tool. No liability will be accepted by HR Wallingford, the Environment Agency, CEH, Hydrosolutions or any other organisation for use of this data in the design or operational characteristics of any drainage scheme.

Greenfield runoff estimation for sites

www.uksuds.com │ Greenfield runoff tool

This is an estimation of the greenfield runoff rate limits that are needed to meet normal best practice criteria in line with Environment Agency guidance “Preliminary rainfall runoff management for developments”, W5-074/A/TR1/1 rev. E (2012) and the SuDS Manual, C753 (Ciria, 2015). This information on greenfield runoff rates may be the basis for setting consents for the drainage of surface water runoff from sites.

Site name:

Calculated by:

Latitude:

Longitude:

Reference:

Date:

Site coordinates

Site location:

Site characteristicsTotal site area (ha)

MethodologyQbar estimation methodSPR estimation method

Default Edited

SOIL typeHOST classSPR/SPRHOST

Hydrological characteristics Default Edited

SAAR (mm)Hydrological region Growth curve factor: 1 year Growth curve factor: 30 year Growth curve factor: 100 year

Notes:(1) Is QBAR < 2.0 l/s/ha?

(2) Are flow rates < 5.0 l/s?

(3) Is SPR/SPRHOST ≤ 0.3?

Greenfield runoff rates Default Edited

Qbar (l/s)1 in 1 year (l/s)1 in 30 years (l/s)1 in 100 years (l/s)

Methodology IH124

0.1

0.02

2.3 for disposal of surface water runoff.

0.06

0.85 0.85

Lower consent flow rates may be set in which case blockage

7

0.1

2017-08-29T14:37:10

Bournemouth

--- 5.0l/s if blockage from vegetation and other materials is possible.

1.872° W

0.02

Land rear of 1 McWilliam Road

0.02

Chris Gray

3.19

0.02

Calculate from SOIL type

50.75265° N

794794Where groundwater levels are low enough the use of

11

0.06

3.19

Calculate from SPR and SAAR

7

---

0.04 0.04

soakaways to avoid discharge offsite may be a requirement

are set at 2.0 l/s/ha.

Normally limiting discharge rates which are less than 2.0 l/s/ha

2.3

6084772

work must be addressed by using appropriate drainage elements.

0.1

Where flow rates are less than 5.0 l/s consents are usually set at

Detailed Assessment of Gravity Outlet Storage Volumes (Allowable Discharge 2 l/s)

DETAILED ASSESSMENT OF INTERCEPTION STORAGE VOLUMEAbbreviation Calculations Value

Total site area TS A 829.32 m2

Total site area converted

to hardstandingHS A 353.87 m2

Total volume from 5mm

rainfall

5mm x 100% x

H/S A4.15 m3

DETAILED ASSESSMENT OF 100 YEAR ATTENUATION STORAGE VOLUME

Allowable Discharge AD 2.00E-04 m3/s

Discharge Coefficient C 1.0 Pumped

Discharge Coefficient C 0.5Gravity Outlet (e.g.

orifice)

Discharge Coefficient C 0.7 Vortex Flow Control

A B C D E F G H I J

Storm Duration D (Hours) Rainfall Depth (mm)

Revised Depth +

40% Climate

Change (mm)

Rainfall Rate i

(mm/hr)

Rainfall

Rate i +

40%

Climate

Change

(mm/hr)

Inflow rate - 2.78 HS A i -

(l/s)

Inflow volume - rate x

3.6D - (m3)

Outflow volume - C x AD x

3.6D - (m3)

Storage

required V -

in - out -

(m3)

Time to

empty -

0.277V/A

DC -

(Hours)

0.17 10 14.00 84.00 117.60 11.57 6.94 0.06 6.88 1.36

0.50 30 42.00 84.00 117.60 11.57 20.82 0.18 20.64 4.08

1 40.51 56.71 56.71 79.40 7.81 28.12 0.36 27.76 5.49

4 57.37 80.32 20.08 28.11 2.77 39.82 1.44 38.38 7.59

6 63 88.20 14.70 20.58 2.02 43.73 2.16 41.57 8.23

12 72.21 101.09 8.42 11.79 1.16 50.12 4.32 45.80 9.06

18 78.36 109.70 6.09 8.53 0.84 54.39 6.48 47.91 9.48

47.91 m3Maximum Storage Required

Page 1

Appendix D Type B Partial Infiltration Pervious Pavement Infiltration Calculations

Desk Based Infiltration Coefficient - Silty clayey SAND

CHALK INFILTRATION COEFFICIENTNo. Abbreviation Calculations Value

1

The time taken for the pit to empty from

75% to 25% of the depth tp75-25 minutes

2

Storage volume of pit between 75% to

25% depth Vp75-25 m3

3

Area of the base and sides of pit at 50%

depth ap50 m2

4 Soil infiltration coefficient q 1.00E-05 m/s

Factor of safety F 2 5.00E-06 m/s

5 Soil infiltration coefficient q 3.60E-02 m/h

Factor of safety F 2 1.80E-02 m/h

Page 1

Proposed Pervious Pavement

No. Abbreviation Calculations Value

1 Area to be drained AD 353.87 m2

2 Base area of infiltration system Ab 191.72 m2

3 Porosity of fill material n 0.3

4 Intensity of rainfall events i 0.014 m/h

5 Duration of rainfall events D 0.166 h

6 Infiltration coefficient from percolation test adjusted by the appropriate factor of safety q 0.0180 m/h

7 Ratio of drained area to infiltration area R 1.85

hmax D/n(i-q) 0.00 m

Time for half emptying plane infiltration system t1/2 n hmax/2q -0.02 hr

Acceptable infiltration coefficient n hmax/48 0.0000 m/h

hmax D/n(Ri-q) 0.00 m

Time for half emptying plane infiltration system t1/2 n hmax/2q 0.04 hr







5 Duration of rainfall events D 0.5 h














5 Duration of rainfall events D 1 h


DETERMINATION OF MAXIMUM DEPTH OF WATER FOR 10 MINUTES, 30 MINUTES, 1,4,6,12 and 18 HOUR 100 YEAR EVENTS (PLANE INFILTRATION

SYSTEM)

Page 2































hmax D/n(i-q) -0.07 m










Page 2








Acceptable infiltration coefficient n hmax/48 -0.0024 m/h

hmax D/n(Ri-q) -0.10 m














hmax D/n(Ri-q) -0.41 m



Page 2

Appendix E Type B Partial Infiltration Pervious Pavement Sub Base Slope Calculations

Pervious Pavement Slope Calculations

Total storage Volume

W 17.84 NA m3

L 13.13 NA m3(Reduced to 30%)

D 0.275

Ratio 1 in 32

deg 1.745 0.030456 Radians

0.030465 tan of Radians

9.0 m Length of sub-base where water can be stored.

Page 1

Appendix F Skeletons SELH03001 ‘Controflow’ Mini Flow Control Unit and Permavoid

Rainwater Diffuser Unit Data Sheets

Skeletank®

DesignThe Skeletank Mini Flow Control Chamber is specifically designed for use within a Skeletank attenuation system. The standard 11mm diameter orifice, protected by a removable filter, allows for surface water runoff to be restricted to a flow rate of 0.2l/s, preferably within the curtilage of each plot to suit the site layout.

Orifices to suit higher flow rates of 0.4l/s and 0.6l/s are available should the drainage system need to accommodate more than one property for genuine design reasons.

SpecificationFilters are removable to allow for cleaning and/or replacement. A specialised tool is required to facilitate removal and it is essential that filters are fixed back into position before replacing the filter tube.

Each chamber has a 200mm deep sump to accommodate the deposition of any suspended solids remaining in the runoff which has passed through the Skeletank RWP Filter Chambers positioned on the downpipes.

The chamber spigots are sized to fit standard 110mm diameter underground push-fit PVC-u drainage sockets.

Installation1. Set out the location of the chamber

2. Excavate to the required depth. Set the chambers on a bed of concrete in accordance with the standard detail drawing. The chambers are supplied with a secondary cover; this cover must be left in place during construction to prevent any debris i.e. Stone, mortar, bricks etc falling into the chamber. It is recommended that this cover be left in place when the brickwork and final choice of cover & frame has been fixed. Before completion ensure that the secondary cover is not trapped by mortar and can easily be removed.

3. If it is necessary to reduce the height of the chamber, remove the secondary cover, cut the chamber to the required height and replace the secondary cover before installation.

4. Connect the pipe work using standard underground pipes and fittings.

5. Backfill in accordance with the standard detail drawing or specific Contract requirements.

6. To complete the installation, a manhole cover to suit loading requirements should be procured and positioned using brickwork to adjust levels.

Copyright Skeletank Ltd © 2016 SELH3001-V.03.3

Element Dimensions

Chamber diameter 315mm

Inlet spigot diameter 110mm

Outlet spigot diameter 110mm

Sump depth 200mm

Overall depth 847mm

Material Polyethylene

Filter Details Specification

Filter tube material Polyethylene

Removable Yes

Filter tube perforation size 5mm

Flow rate Specification

Max flow rate through filter 0.2 l/s Approx.

Maintenance Specification

Interval - visual inspection Remove and rinse filter if required

3 monthly

ControFlow

PRODUCT SPECIFICATION SHEET

Product Code: SELH03001

Mini Flow Control Chamber

Technical SupportDetailed guidance and assistance is available.

For further information, please contact our Technical Team

on +44 (0) 1509 615 100 or email [email protected]

ELEMENT VALUE

PHYSICAL PROPERTIES

Weight per unit 3kg

Length 708mm

Width 354mm

Depth 150mm

SHORT TERM COMPRESSIVE STRENGTH

Vertical 715kN/m²

Lateral 156kN/m²

SHORT TERM DEFLECTION

Vertical 1mm per 126kN/m²

Lateral 1mm per 15kN/m²

TENSILE STRENGTH

Of a single joint 42.4kN/m²

Of a single joint at (1% secant modulus) 18.8kN/m²

Bending resistance of unit 0.71kN/m

Bending resistance of single joint 0.16kN/m

Volumetric void ratio 95%

Average effective perforated surface area 52%

OTHER PROPERTIES

Intrinsic permeability (k) Minimum 1.0 x 10-5

AncillaryPermavoid Permatie

Permavoid ShearConnector

Material Polypropylene (PP)

Run-off from building roofs is collected into downpipes and � ows into a back inlet gully incorporating an internal � lter or catchpit inspection chambers. The back inlet gully or chamber discharges the � ltered stormwater into the permeable sub-base via Permavoid Rainwater Diffuser Unit encapsulated in a 2mm mesh fabric. The run-off will then diffuse out of the Permavoid Rainwater Diffuser Unit and into the modi� ed granular sub-base layer. The Permavoid unit is a 150mm deep modular interlocking plastic unit storage system designed for use as a combined drainage component and sub-base replacement system, ideal for shallow in� ltration/attenuation.

Polypipe Civils,

Charnwood Business Park, Loughborough, Leicestershire LE11 1LE

Tel: +44 (0) 1509 615100 Fax: +44 (0) 1509 610215 Email: [email protected]

www.polypipe.com/wms

Permavoid Rainwater Diffuser Unit Data SheetPRODUCT INFORMATION P1 ISSUE 2 - MAY 2017

All descriptions and illustrations in this publication are intended for guidance only and shall not constitute a ‘sale by description’. All dimensions given are nominal and Polypipe may modify and change the information, products and speci� cations from time to time for a variety of reasons, without prior notice. The information in this publication is provided ‘as is’ on May 2017. Updates will not be issued automatically. This information is not intended to have any legal effect, whether by way of advice, representation or warranty (express or implied). We accept no liability whatsoever (to the extent permitted by law) if you place any reliance on this publication you must do so at your own risk. All rights reserved. Copyright in this publication belongs to Polypipe and all such copyright may not be used, sold, copied or reproduced in whole or part in any manner in any media to any person without prior consent. is a registered trademark of Polypipe. All Polypipe products are protected by Design Right under CDPA 1988. Copyright © 2017 Polypipe. All rights reserved.

Permavoid Rainwater Diffuser Unit -Con� guration Options

Depths available are either 150mm or 300mm.Connections available are either Ø110mm or Ø160mm.

Catchpit: 460mm diameter catchpit with 160mm inlet - PSMST 160 460mm diameter catchpit with 110mm inlet - PSMST 110

Width

Leng

th

354mm 708mm 1062mm 1416mm 2124mm

708mm 1062mm 1416mm 2124mm

Incomingpipe fromroofwaterdrainage

460mm catchpit inspectionchamber with min. 300mm sump

Connection through membranewith preformed spigot connectorwith weldable membrane

Permavoid diffuser wrappedin 2mm mesh (size varies)

Sub-base

Typical Layout - Rainwater downpipedrainage into sub-base reservoir

HYDRAULIC PERFORMANCE

3 units wide, 1 unit deep (1.06m x 0.15m)

FREE DISCHARGE

Gradient (%) 0 1 2 3 4 5

Flow rate (l/m/s) 8 13 15 17 19 21

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