The Green, Northop Flood Consequences Assessment & Drainage Strategy

The Green,

Northop

Flood Consequences Assessment

Outline Drainage Strategy

Project number: 3010

Date: May 2016

Revision: 1

scott hughes design, the flint glass works, 64 jersey street, manchester, m4 6jw tel: 0161 605 0831 www.scotthughesdesign.com 3010: The Green, Northop Flood Consequences Assessment & Drainage Strategy

Document Control Sheet

Client: Peckforton Developments Ltd

Project No.: 3010

Project Title: The Green, Northop

Report Title: Flood Risk Assessment and Outline Drainage Strategy

Issue: 0

Status: Final

Control Date: 26 th May 2016

Document Revision Record:

Issue Status Author Approved Date

0 Draft Chris Finneran Paul Graveney 11.04.16

1 Final Chris Finneran Paul Graveney 26.05.16

Document Distribution Record :

Issue Organisation Quantity

0 Peckforton Developments Ltd 1

1 Peckforton Developments Ltd 1

This Flood Risk Assessment report is the property of Scott Hughes Design and is confidential to the client designated in the report. Whilst it may be shown to their professional advisers, the contents are not to be disclosed to, or made use of, by any third party, without our express written consent. Without such consent we can accept no responsibility to any third party.

Scott Hughes Design certify that they have carried out the work contained herein with due skill, care and diligence to their best belief and knowledge based on the time and information available.

This report is made on behalf of Scott Hughes Design. By receiving it and acting on it, the client – or any third party relying on it – accepts that no individual is personally liable in contract, tort or breach of statutory duty or otherwise (including negligence). Scott Hughes Design

3010: The Green, Northop Flood Consequences Assessment & Drainage Strategy

Table of Contents Executive Summary ...... 1 1.0 Introduction ...... 2 2.0 Development Description and Location ...... 3 2.1 Site Location ...... 3 2.2 Existing Site Description ...... 3 2.3 Development Proposals ...... 4 3.0 Planning Policy and Consultation ...... 5 3.1 Planning Policy Framework ...... 5 3.2 Local Flood Risk Management Strategy (LFRMS) ...... 5 4.0 Definition of Flood Hazard ...... 6 4.1 Sources of information ...... 6 4.2 Flooding from Rivers (Fluvial) ...... 6 4.3 Flooding From Land (Overland Flow) ...... 7 4.4 Flooding from Sewers and Private Drainage ...... 8 4.5 Flooding from Groundwater ...... 9 4.6 Flooding from Artificial Sources ...... 9 5.0 Assessment of Flood Risk on Development Site (Probability) ...... 10 5.1 Summary ...... 10 6.0 Outline Drainage Strategy ...... 11 6.1 External Consultation ...... 11 6.2 Existing Surface Water Runoff ...... 11 6.3 Geology ...... 11 6.4 Sustainable Drainage Systems ...... 11 6.5 Outline Surface Water Drainage Strategy ...... 17 6.6 Pollution Control ...... 18 6.7 Foul Water Strategy ...... 18 7.0 Management Measures, Off Site Impacts and Residual Risk...... 19 7.1 Flood Risk Management Measures...... 19 7.2 Off Site Impacts ...... 19 7.3 Residual Risk ...... 20

3010: The Green, Northop Flood Consequences Assessment & Drainage Strategy

Executive Summary

Flood Risk

The proposal is for the construction of a residential development on Greenfield land to the East of Northop Brook, off Capel Y Nant, Northop that will also include new highways and hard & soft landscaped external areas. The overall site is approximately 0.775Ha in plan footprint and to address the requirements of the local development plan, a Flood Risk Assessment is appropriate.

The development holds a Flood Zone A classification, i.e. land assessed as having less than a 1 in 1000 annual probability of river flooding (<0.1%) in any year. A fluvial flood impact assessment is therefore not required.

The development target has been assessed against the ‘Sequential Test’. Taking into consideration that the application is for a residential development in Flood Zone A, the Planning Policy Technical Advice Note has been appraised to confirm that 'Development is Acceptable'.

Other forms of flood risk have been considered and found not to be a risk to the development site. The only residual risk remaining is from exceedance drainage flooding beyond the 30 year design criterion. This however is only anticipated to be related to the external access road and soft landscaped areas.

There is no residual flood risk from the development site to the surrounding district due to the low storm water flow rates to the adjoining public sewers.

Drainage

Due to the reduced discharge rate to satisfy local criteria, Sustainable Drainage Systems (SUDS) will be incorporated to attenuate the peak surface water runoff. This will take the form of a attenuation pond located within the adjoining field.

Foul water generated by the development will be discharged unrestricted to the adjacent combined sewer via a new pumping chamber.

Summary

This report therefore demonstrates that the proposed scheme:

• Is not at risk from all flood sources. • Would be safe and flood resilient. • Would not adversely increase flood risk elsewhere as a result of the proposed development through increase in surface water run-off. • Incorporates a comprehensive and flood resilient drainage and SUDS strategy. • Has a statutory authority agreed foul discharge approval.

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1.0 Introduction

1.1 Scott Hughes Design (SHD) has been appointed by Peckforton Developments Ltd to prepare this Flood Consequences Assessment to support a planning submission for a new residential development on Land east of Northop Brook, Capel Y Nant, Northop. The assessment has been undertaken in line with the ‘Planning Policy Wales Technical Advice, Note 15: Development & Flood risk (TAN 15) 2004.’

1.2 This Flood Risk Consequences Assessment (FCA) has been commissioned by Peckforton Developments Ltd and is specific to their interests in the residential development as described by the Architectural plan in Appendix A. This report may not be assigned.

1.3 The report has been commissioned to identify any flood related issues associated with the proposed development and any likely constraints that could be imposed. The following issues have been suggested by the Environment Agency and subsequently addressed within this report;

• Identify available data relating to flood risk at the site. • Determine whether the site is at risk from flooding, including from breach or overtopping of any existing flood defenses, surface water flooding and/or ground water flooding. • Determine any the current surface water drainage regime and assess any potential increase in surface water runoff as a result of the proposed development. • Discuss Sustainable Drainage Systems (SUDS) as an option for reducing surface water flood risk. • Devise an appropriate outline surface water drainage strategy (including calculation where appropriate) to deal with any increase in surface water runoff and include for climate change. • Consider the recommendations of the Flintshire Local Flood Risk Management Strategy (LFRMS). • Consider the flood risk from all other sources. • Assess mitigation measures & off site impacts, and define any residual risks.

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2.0 Development Description and Location

2.1 Site Location

The site is referenced in Table 1, and a site location map is provided in Appendix A.

Table 1: Site Referencing Information

Item Brief Description

Site name The Green, Northop

Site address and Capel Y Nant, Flintshire location

Council Area Flintshire County Council

Approximate Grid OS: 324298,368095 Reference

The site is located to the east of Northop Road and Capel Y Nant, General Locality about 200m south from the centre of Northop village.

2.2 Existing Site Description

2.2.1 The development site (Red Line Boundary) is undeveloped and used for rearing livestock. The site is encompassed by Capel Y Nant on the eastern border, with grassland to the south and woodland and wetland to the north and west. Therefore the site can be classed as 'Greenfield'.

2.2.2 To the north and west of the boundary is low-lying wetland, with Northop brook flowing in a north-easterly direction within 100m of the northern boundary.

2.2.3 The site specific topographical survey has been perused and identifies that the site falls generally in a northerly direction from circa 108m AOD at the south to 101m AOD along the northern boundary.

2.2.4 There will be new vehicular access installed along the eastern boundary on Capel Y Nant Road.

2.2.5 The site is located some 200m to the south of the centre of Northop village and some 900m to the south of the A55 North Wales Expressway. Northop itself is some 16km west of Chester.

2.2.6 Figure 1 below identifies the overall site location details. Further details of the existing layout can be seen on the Red Line and site Plans in Appendix A and the Topographical survey in Appendix B.

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Figure 1: Site Location

Northop Brook

Capel Y Nant

Low-lying Wetland

The Green Development Site

2.3 Development Proposals

2.3.1 This report has been prepared to support a planning application for the construction of 17 two- storey properties with new hard and soft landscaped areas and access road.

2.3.2 The current outline Architectural site Master Plan as indicated in Appendix A provides an indication of the proposed development.

2.3.3 Development Design Life

The generally accepted design life for the proposed residential development for the assessment of flood risk is 100 years. This assessment therefore considers flood risk over the period 2016 to 2116.

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3.0 Planning Policy and Consultation

3.1 Planning Policy Framework

3.1.1 The flood maps provided by Natural Resources Wales locate the site within Flood Zone A. This is land assessed as having a less than 1 in 1000 annual probability of fluvial flooding (0.1%) in any year. As a requirement of the TAN 15 (2004), the proposed development has to satisfy the requirements of the Flood Consequences Test.

3.1.2 Flood Consequences Test:

Under the TAN 15 (2004), Zone A is defined as low probability flood risk. The proposal is for a residential development, which is classified as Zone A, ‘Highly Vulnerable’.

In light of this Highly Vulnerable development in Flood Zone A it is determined that ‘Development is acceptable'. Therefore the Exception test is not required.

It must be noted however that issues relating to offsite impacts need to be satisfied 3.2 Local Flood Risk Management Strategy (LFRMS)

3.2.1 LFRMS’s assess the risk associated with all types of flooding and provide the information required to identify the amount of development permitted in an area; how drainage systems in the area should function and also how risks in vulnerable areas can be reduced and/or mitigated. The Flood and Water Management Act (FWMA) 2010 states that Lead Local Flood Authorities (LLFA’s) should prepare LFRMS’s in consultation with the EA and other organisations.

3.2.2 Flintshire County Council have produced in 2013 the Local Flood Risk Management Strategy (LFRMS) for the area in accordance with criteria at that time. The purpose of the LFRMS is to assess and map all known sources of flood risk including fluvial, surface water, sewer, groundwater and all impounded water bodies, taking into account future climate change predictions.

3.2.3 A summary of the main elements from the LFRMS associated with the development sites are detailed below. The full report can be obtained from the Flintshire County Council website.

• LFRMS provides a detailed understanding of flood risks across Flintshire from all sources. • Development site located in FZ 1. • No recorded incidences of sewer flooding from the WW register. • Full sequential and exception tests to be carried out where applicable. • Development site not located in a Critical Drainage Area (CDA). • Development should be designed so that there is no flooding to the development in a 1 in 30 year event and so that there is no property flooding in a 1 in 100 year plus climate change event. Where possible SUDS should be implemented.

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4.0 Definition of Flood Hazard

Flood risk to the proposed development site is considered from all sources of flooding, as defined by the TAN 15 (2014).

4.1 Sources of information

The NPPF (2012) requires the developer to consider the impact of runoff generated by the proposed development onto the downstream catchment, and to assess the risk of runoff from the surrounding district impacting on the developments footprint. Further, the report is to consider flood risk from all other sources. The following section defines the flood risk receptors and anticipated flood risk. Section 5 then discusses in further the probability of flooding and the likely impacts.

Table 2 summarises the main sources of information used in the identification of flood risk.

Table 2: Sources of information used in the identification of flood risk

Source of Information Details

Natural Resources Wales Flood Map From EA website

Welsh Water WW Sewer Records

Flintshire LFRMS Various Maps

4.2 Flooding from Rivers (Fluvial)

4.2.1 There are no identified main rivers in close proximity of the site. The closest main river is the River Dee, located some 5km to the north of the site flowing generally in a north-westerly direction. There is a small watercourse some 100m beyond the northern boundary in an easterly direction. However the bed level is lower than the development site.

Natural Resources Wales Flood Zones

4.2.2 Figure 2 below locates the site on Natural Resources Wales’ indicative flood plain map. The site is shown by NRW’s Indicative Flood & Coastal Map in an area considered at low risk of flooding from river and is located within Flood Zone 1 (low probability of flooding), therefore classified as ‘Low Risk’. This is land assessed as having a less than 1 in 1000 annual probability of fluvial flooding (<0.1%) in any year.

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Figure 2 – NRW’s Indicative 100-year Flood Plain Map

The Green Development Site

NRW’s 100-year Indicative Flood Plain (Flood Zone 3)

NRW’s 1000-year Indicative Flood Plain (Flood Zone 2)

4.3 Flooding From Land (Overland Flow)

4.3.1 There is a nominal ground fall through the existing development site and the surrounding district in a northerly direction. The wetlands to the North of the site boundary have a high risk of surface water flooding, as shown below in figure 3. There is a medium risk of flow passing into the site from the higher ground to the south. However, this will be mitigated against by the inclusion of a raised mound along the boundary.

Figure 3 – NRW’s Indicative Surface Water Flood Risk Map

The Green Development Site

NRW’s High Risk Zone

NRW’s Medium Risk Zone

NRW’s Low Risk Zone

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4.4 Flooding from Sewers and Private Drainage

4.4.1 The Welsh Water (WW) sewer records have been reviewed and confirm that there are no public water sewers in the vicinity of the development site. Plans of the existing sewers can be found in Figure 4 and summarised below:

Combined Water Sewers: There is a 150/225mm diameter combined sewer flowing west to east, some 150m north of the site.

Surface Water Sewers: The only identified surface water in close proximity to the development site is located within Connah’s Quay road, some 150m north of the site.

Figure 4 –WW Sewer Records

The Green Development Site

4.4.2 The WW adopted drainage network serving the surrounding urban district ensures that the development footprint is protected from the impact of both upstream and downstream runoff. It is speculated that complete protection may well exist beyond a storm event equivalent to the 30-year statistical event. Beyond this projection, there may be a small degree of peripheral ‘Exceedance’ flooding within the highway areas above the sewers. However, this is expected to be localised and restricted to the location of specific manhole covers located outside the development footprint. Thus flood risk to the site from sewers is diminished to acceptable levels.

4.4.3 Beyond the public sewers, a ditch was located on the verge of the highway collecting the surface water runoff. This followed the line of the highway and outfalled to the small watercourse.

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4.5 Flooding from Groundwater

4.5.1 To date no intrusive site investigation has been provided to SHD for the site. It is unlikely due to the raised elevation that the site would be at risk of ground water flooding. However, ground water level data taken from the future Phase 2 site investigation will confirm this further.

4.5.2 The Flintshire Local Flood Risk Management Strategy (SFRA equivalent) would indicate that there are a total of 5 groundwater bodies in the county, all of which fall within the River Dee catchment area. The report also states that no groundwater flooding has been experienced in the locality of the development site.

4.6 Flooding from Artificial Sources

4.6.1 The closest waterbodies are several small ponds within 100m of the site. There is no apparent inflow to the ponds and no overflow water identified. The risk can therefore be considered low.

4.6.2 Natural Resources Wales map indicates that the site is in flood zone 1 for flooding from reservoirs or other artificial sources.

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5.0 Assessment of Flood Risk on Development Site (Probability)

5.1 Summary

5.1.1 Section 4 has defined the anticipated flood risks from all sources. Table 3 below considers each of the sources and defines in tabular format the Probability of Flood Risk associated to each and the likely impacts.

Table 3 – Flood Risk Summary

Probability Source Impacts Remarks of Flood Risk Development site is not in close Tidal Low Low proximity for it to be tidally influenced

Development site not within Fluvial (Watercourse) Low Low identified medium or high risk Flood Zone.

Raised mound to be constructed Surface (Overland along Southern boundary to Medium Low Flood Flow) prevent overland flows passing into the site.

Flooding from sewers speculated to be localised to the covers in Sewers Low Low the main highways, which are set at lower ground levels and away from the site.

Site levels raised in relation to locality and thus risk considered Groundwater Low Low low. No groundwater bodies in the vicinity of the site.

Closest artificial source is a small Artificial Sources Low Low off-site pond. This is at a distance and lower ground level.

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6.0 Outline Drainage Strategy

6.1 External Consultation

Flintshire Flood Risk Management Team

6.1.1 The Flintshire Flood Risk Management Team have been consulted and have indicated that there are no formal records of historical flooding at this location. In addition all new drainage should discharge at greenfield rates.

6.2 Existing Surface Water Runoff

6.2.1 The existing site is classed as Greenfield and therefore greenfield run off rates apply. Table 4 below defines the existing greenfield rates.

Table 4: Existing Surface Water Runoff (Area Method)

Greenfield Runoff Rates for the Total Area Respective Storm Events (ha) 1 Year 30 year 100 Year

0.775 1.6l/s 3.3/s 4.1l/s

6.3 Geology

6.3.1 No intrusive site investigation has been carried out at the site. However local boreholes would indicate the ground to be underlain with a mix of sands and clay. This would indicate that the ground is unlikely to be suitable for infiltration. 6.4 Sustainable Drainage Systems

6.4.1 SUDS Objectives: Sustainable drainage developed in line with the ideals of sustainable development is collectively referred to as Sustainable Drainage Systems (SUDS). At a particular site, these systems are designed both to manage the environmental risks resulting from the urban runoff and to contribute wherever possible to environmental enhancement. SUDS objectives are therefore to minimise the impacts from the development on the quantity and quality of the runoff and maximise amenity and biodiversity opportunities (CIRIA C753, 2015).

6.4.2 SUDS’s Design Themes A strong design theme is essential if the maximum aesthetic benefits are to be gained from the SUDS approach. At a more local scale the SUDS should link with the individuals plot structure, planting, public open space requirements and amenity areas, gaining multiple benefits from a limited area of land.

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6.4.3 The SUDS Management Train

The ‘Management Train Approach’ should be central to the surface water drainage strategy of the proposed site. The main objective is treatment and control of runoff as near to the source as possible protecting downstream habitats and further enhancing the amenity value of the site. This concept uses a hierarchy of drainage techniques to incrementally reduce pollution, flow rates and volumes of storm water discharge from the site, and is as follows:

1. Prevention – The use of good site design and housekeeping measures to prevent runoff and pollution and includes the use of rainwater reuse / harvesting. 2 Source Controls – Control of runoff at source or as close to source as possible (e.g. soakaways, green roofs, pervious pavements). 3. Site Control – Management of water in a local area and can include below ground storage / attenuation, detention basins, large infiltration devices. 4. Regional Control – Management of water from a site or various sites and can include wetlands and balancing ponds.

The drainage techniques for this development will seek to include Prevention and site control measures to satisfy the restricted discharge rates. This is due to the unknown permeability of the underlying ground. Once detailed analysis has been completed, this may change.

6.4.4 SuDS Methods

Tables 5 and 6, below, provide an assessment of various above and below ground SuDS methods that can provide water quality treatment and management of flows to reduce runoff rates and volumes and whether they can be suitably incorporated at this development site. The purpose of this assessment is to set out options to be considered at the planning stage with consideration to time constraints, viability and lifetime maintenance of the residential development.

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Table 5: Surface SuDS Methods

Method Comment Suitability for Development

Green Roofs • Can be used on suitable low Not suitable : rise buildings to provide • Architectural proposals for the retention, attenuation and development involve a pitched roof treatment of rainwater, and arrangement, which are not suitable promotes evaporation and for green roofs. local biodiversity. Water Butts • Plastic tanks placed at the Suitable: base of rainwater down pipes • To be included to the rear downpipes to collect rainwater runoff from of each unit. the roof areas. Rainwater • Rainwater harvesting reduces Not Suitable : Harvesting the total runoff volume from • Additional costs of installation would the developed site, and have severe effect on viability of the reduces treated water development. consumption. • Running and maintenance costs would not be acceptable to our client and future occupiers. • The ability to restrict peak flow rates and short term peak volumes is non- existent where a critical storm event occurs.

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Method Comment Suitability for Development

Permeable • Can be used to enhance Not suitable : Surfacing quality of runoff water. • Long term maintenance required (Standard) • Sub-base provides ‘source’ and risk of reduction in storage and reduces the permeability. volume of storage • Specialist maintenance required to downstream. maintain porous surfaces. • The storage can be created • No services to run beneath areas with selection of the stone fill of permeable surface (due to or use of plastic box stems. presence of base impermeable • Impermeable membrane at barrier which is very difficult to base of construction to excavate through and reinstate if prevent impact on pavement required), spatial constraints of site stability. do not allow alternative routes for services along plot frontages. • Difficult to install small areas of tanked systems that require very small flow controls which can lead to maintenance issues. Swales, • Provide areas for above Suitable : basins and ground surface runoff storage. • Space constraints on site do ponds • Swales also allow filtering of enable an attenuation pond to be particulate matter, improving located within the adjacent field water quality and used for flood storage.

Bio-Retention • Collect and retain run-off to Not suitable : help improve water quality, • Space constraints on site do not prior to discharge in piped permit large above ground areas system on infiltration. for flood storage. • No scope to reduce development area due to site viability.

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Table 6: Sub-Surface SuDS Methods

Method Comment Suitability for Development

Geocellular Not Suitable: • Suitable for sites with Storage insufficient space for basins • Geocellular storage is not adopted etc. by Welsh Water and so this would prohibit its use in the site. • Suitable for sites where topography prevents the use of open basins etc.

• Can be very effective infiltration devices subject to ground conditions. Large Suitable : • Suitable for sites with Diameter insufficient space for basins • Pipes, Oversized pipes more suited to etc. Culverts or adopted drainage network and so could be included if the pond • Tanks Provide a volume of below option is not feasible. ground storage with a high void ratio and good man entry • Downside is additional costs to provision to allow for future construct. maintenance and cleaning.

• Generally be suitable for adoption by the statutory water company (e.g. Severn Trent Water).

6.4.5 SuDS Hierarchal Approach

Based on the SuDS assessment in Tables 5 and 6, plus an assessment of the local site conditions, the SuDS hierarchal approach for discharge of surface water at the development site is considered in greater detail below:

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Table 7: SuDS Hierarchal Approach

Method Suitability Suitability for Development

Infiltration to Ground No Underlying ground unlikely to be suitable for infiltration

Connection to Watercourse in close proximity to the site and site Yes Watercourse currently drains into it.

Connection to No No surface water sewer in close proximity Surface Water Sewer

Connection to a Yes No combined sewer in close proximity Combined Sewer

6.4.6 SuDS Design Philosophy

The SuDS assessment and hierarchal approach discussed in Tables 5, 6 and 7 above has defined the overall SuDS strategy. Thus the SuDS philosophy for the development site is the promotion of Prevention, Source Control and Site Control techniques with discharge rates to mimic the predevelopment Brownfield rates, to reduce the risk of both site and downstream flooding.

The following design philosophy is proposed:

• Surface water treatment using the ‘Management Train’ approach to remove and isolate contamination at all SuDS facilities prior to conveyance to the ground or adjacent ditch network. • Restrict new development runoff peak flow rates to pre-development greenfield rates.

• Prevention measures by the inclusion of water butts.

• Site Control by the inclusion on an attenuation pond with controlled outflow to the adjacent watercourse to match predevelopment rates.

• Aim to limit where possible the impermeable fraction of development.

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6.5 Outline Surface Water Drainage Strategy

6.5.1 The general principal of the surface water drainage strategy is to collect the runoff from the new roof & access road areas and direct it to a new below ground surface water drainage network that will connect to a new surface water public sewer in the access road. This new sewer will then outfall into a new attenuation pond within the adjacent field and then outfall at agreed rates to the local watercourse.

6.5.2 The proposed private drainage layout for the new development site will be designed in accordance with Sewers for Adoption 7 th Edition. This is to indicate no surcharge for the 2 year storm event and no flooding for up to the 30 year storm event.

6.5.3 Flooding can occur on a local scale beyond the 30yr criterion due to runoff exceeding the capacity of the minor system during extreme events and it can only be addressed on a site specific basis. Sewers for Adoption (SfA) 7 th Edition (WRc, 2012) states that properties should be protected against flooding from extreme events (1 in 30 year) and that flood pathways are identified when the drainage system is exceeded.

6.5.4 In the case of this development, exceedance flows will be all those over and above the 30 year design criterion set by Building Regulations and SFA guidance. Using storage within the external hard standing and soft landscaping areas would be achievable and would direct flood water away from the new development with flows directed back into the surface water drainage network as the water levels in the sewers recede. The exceedance flows and volumes can be calculated for the new development drainage layout. In the case of this development and due to the fall across the site, consideration will be given to make sure all water is controlled so that it does not impact on adjoining properties or pass onto the highway.

6.5.5 Table 5 below defines the post development attenuation volumes based on the new impermeable areas and the reduced surface water discharge rates. Details of these outline calculations can be found in Appendix D. It is noted that the design and volumes identified are preliminary for this outline assessment and are likely to alter at detailed design stage when more site specific information is made available.

Table 5: Outline Attenuation Volumes

Approximate Greenfield Attenuation Volume for New Imp’ Area Runoff Rate Approximate 100yr Storm Event + (60% of Existing (Minimum rate to Attenuation Volume for 30% CC (Extra over 30yr Area - m2) cover all storm 30yr Storm Event could be retained in low events) lying external areas)

4650m2 5 l/s 112m3 214m3

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6.5.6 Any future drainage calculations carried out as part of a site wide drainage strategy or for the development layouts themselves must include the appropriate increase in rainfall to satisfy the future Climate change allowances. 6.6 Pollution Control

6.6.1 Silt is to be prevented from entering the drainage system by the use of trapped gullies, channels with silt traps, french drains with silt traps or by the use of Sustainable Drainage techniques. If appropriate, oil separators in line with Pollution Prevention Guidance 3 criteria will be provided. 6.7 Foul Water Strategy

6.7.1 The outline foul water drainage strategy is to construct a new private foul water drainage network to serve the new residential buildings. These will outfall to a new adopted foul sewer in the access road which will in turn outfall to the combined sewer via a new adopted pumping chamber.

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7.0 Management Measures, Off Site Impacts and Residual Risk

7.1 Flood Risk Management Measures

7.1.1 The surface water drainage strategy for the new development site will be to limit the surface water runoff to Greenfield discharge rates. Attenuation has been proposed in the form of an open attenuation pond. The new private surface water networks will be designed in line with current British Standard guidance up to the 100 year storm return period including an allowance for climate change. Beyond the 30yr criterion out of chamber flooding may occur with flood water directed away from the buildings to low lying areas including the highways and soft landscaped areas where it will then be directed back in to the drainage network as the pipe water levels recede.

7.1.2 The use of SUDS in the form of Site Control measures, with controlled (restricted) outflow to the watercourse in line with the required rates will help to minimise the flood risk impact to the surrounding district.

7.1.3 There will be a site management health and safety document prepared in respect of the final development. This will include the required maintenance regime for the on site drains and drainage facilities such as the channels, gullies, pipes, manholes and all SUDS facilities.

7.2 Off Site Impacts

7.2.1 The redevelopment of the site does not impair the hydraulic continuity of any watercourse and the current ‘‘local hydraulics’’ of distributing watercourses / outfalls.

7.2.2 The Development footprint does not cross or cover any existing or declared future catchment flood defences. Consequently, the Applicant does not propose to augment or compromise the current catchment defences.

7.2.3 Surface water runoff will be reduced to agreed rates and utilises SUDS solutions to satisfy the site constraints.

7.2.4 By reducing the pre development peak runoff at its point of discharge into the adjacent sewer by the inclusion of SUDS, this will reduce surface water flooding impact onto the downstream sewer network.

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7.3 Residual Risk

7.3.1 With careful design of the drainage elements as described above there will be no residual flood- related risks that will remain after the development has been completed.

7.3.2 Flood risk to people and property can be managed but it can never be completely removed; a residual risk remains after flood management or mitigation measures have been put in place. The only known flood related residual risk that will remain after flood management or mitigation measures have been put in place will be from drainage flooding beyond the designed 30 year storm event.

7.3.3 There will be no residual risks to any of the neighboring properties by any uncontrolled flood flows escaping from the proposed redevelopment.

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Appendix A –Architect Drawing

3010: The Green, Northop Flood Consequences Assessment & Drainage Strategy

Appendix B – Topographical Survey

c SEP (Site Engineering Personnel) Ltd. 2015 Reproduction in whole or in part by any means is prohibited without the prior permission of Site Engineering Personnel Limited. T. (01695) 729835 F. (01695) 725566 W. www.sepltd.com E. [email protected]

PLAN GRID NORTH

File Name: S11609-T.dwg

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NOTES: All levels relate to O.S (Newlyn) Datum, Established using network RTK. Survey plotted on a plane local grid, orientated to National Grid.

1 2

SHEET LAYOUT

0 2m 4m 8m 12m 16m

SCALE BAR

REV DATE DESCRIPTION

Client White Acre Estates Ltd 1 Beechwood lane Culcheth Warrington WA3 4HJ

Project Title Topographical Survey of Land at: Capel Nant Northop CH7 6DJ

Surveyed Drawn Checked C.Taylor A.Blackburn C.Sweeney

Scale Date Drawing Ref. No. Size Rev 1:200 Oct 15 S11609-T 01 A0 -- c SEP (Site Engineering Personnel) Ltd. 2015 Reproduction in whole or in part by any means is prohibited without the prior permission of Site Engineering Personnel Limited. T. (01695) 729835 F. (01695) 725566 W. www.sepltd.com E. [email protected]

PLAN GRID NORTH

File Name: S11609-T.dwg

LEGEND

NOTES: All levels relate to O.S (Newlyn) Datum, Established using network RTK. Survey plotted on a plane local grid, orientated to National Grid.

SHEET LAYOUT

0 2m 4m 8m 12m 16m

SCALE BAR

REV DATE DESCRIPTION

Client White Acre Estates Ltd 1 Beechwood lane Culcheth Warrington WA3 4HJ

Project Title Topographical Survey of Land at: Capel Nant Northop CH7 6DJ

Surveyed Drawn Checked C.Taylor A.Blackburn C.Sweeney

Scale Date Drawing Ref. No. Size Rev 1:200 Oct 15 S11609-T 02 A0 -- 3010: The Green, Northop Flood Consequences Assessment & Drainage Strategy

Appendix C – Scott Hughes Design Drawings

GENERAL NOTES

1. DRAWINGS ARE TO BE READ IN CONJUNCTION WITH ALL WATERCOURSE RELEVANT SPECIFICATIONS, ENGINEERS, ARCHITECTS & SERVICES DRAWINGS, INCLUDING APPROVED BUILDERS WORK CULVERTED BENEATH DRAWINGS. CONTRACTOR TO NOTIFY ENGINEER OF HIGHWAY DISCREPANCIES BETWEEN STRUCTURAL DRAWINGS AND SPECIFICATIONS OR OTHER DRAWINGS.

2. ALL DIMENSIONS ARE IN MILLIMETRES UNLESS NOTED N OTHERWISE. 3. DO NOT SCALE FROM THIS DRAWING, WORK TO DIMENSIONS OR CO-ORDINATES PROVIDED. ALL LEVELS ARE IN METRES AND WELSH WATER ADOPTED ALL DIMENSIONS ARE IN MILLIMETRES, UNLESS OTHERWISE FOUL PUMPING STATION NOTED. ANY AMBIGUITIES, OMISSIONS AND ERRORS ON DRAWINGSC, SHALL BE BROUGHT TO THE ENGINEERS AND TANKER LAYBY ATTENTION IMMEDIATELY. RISING MAIN TO OUTFALL TO PUBLIC SEWER AT JUNCTION OF CONNAH'S DRAINAGE KEY QUAY ROAD AND 'THE GREEN'

PROPOSED SW SEWER EXISTING SHALLOW LAYBY/ PROPOSED FW SEWER TANKER PARKING OPEN DITCH PROPOSED FW RISING MAIN

OUTFALLING TO EXISTING WATERCOURSE WATERCOURSE SITE BOUNDARY

The Green

Northop Road

WATERCOURSE

EXISTING ORIFACE PLATE ON OUTLET FROM POND TO RESTRICT FLOWS TO GREENFIELD RATES (5L/S)

ATTENUATION POND TO RETAIN PEAK SURFACE WATER DISCHARGES: · 1 IN 30Yr VOLUME = 112m³ · 1 IN 100Yr + CLIMATE CHANGE VOLUME = 214m³

P2 26.04.16 CF PG POND AND PUMP STATION UPDATE P1 19.04.16 CF PG PRELIMINARY ISSUE REV'D No DATE DRAWN ENG. AMENDMENT

STATUS PURPOSE OF ISSUE S2 FOR INFORMATION

COPYRIGHT: The concepts and the information contained in this document are the copyright of Scott Hughes Design Ltd. Use or copying of the document in whole or in part without written permission of Scott Hughes Design Ltd. constitutes and infringement of copyright.

Scott Hughes Design Ltd. The Flint Glass Works, 64 Jersey Street, Manchester M4 6JW   t. 0161 605 0831 f. 0161 605 0832 [email protected] Reg No. 4899745

CLIENT PECKFORTON DEVELOPMENTS LTD

PROJECT THE GREEN, NORTHOP

DRAFTER ENGINEER CF PG

TITLE OUTLINE DRAINAGE LAYOUT

SCALE SHEET DRAWING No REV 1:350 A1 3010-SHD-00-ZZ-DR-C-0001 P2 3010: The Green, Northop Flood Consequences Assessment & Drainage Strategy

Appendix D – Outline Surface Water Hydraulic Calculations

Scott Hughes Design Ltd Page 1 The Flint Glass Works Northop 64 Jersey Street 30 yr Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 30yr event.SRCX Checked by Micro Drainage Source Control 2015.1

Summary of Results for 30 year Return Period

Storm Max Max Max Max Status Event Level Depth Control Volume (m) (m) (l/s) (m³)

15 min Summer 99.246 0.246 5.0 44.6 O K 30 min Summer 99.322 0.322 5.0 62.1 O K 60 min Summer 99.389 0.389 5.0 79.7 O K 120 min Summer 99.437 0.437 5.0 93.3 O K 180 min Summer 99.449 0.449 5.0 96.8 O K 240 min Summer 99.449 0.449 5.0 96.8 O K 360 min Summer 99.441 0.441 5.0 94.3 O K 480 min Summer 99.428 0.428 5.0 90.7 O K 600 min Summer 99.413 0.413 5.0 86.4 O K 720 min Summer 99.397 0.397 5.0 81.9 O K 960 min Summer 99.365 0.365 5.0 73.0 O K 1440 min Summer 99.300 0.300 5.0 56.7 O K 2160 min Summer 99.214 0.214 5.0 37.8 O K 2880 min Summer 99.156 0.156 4.9 26.3 O K 4320 min Summer 99.111 0.111 4.3 18.0 O K 5760 min Summer 99.093 0.093 3.5 15.0 O K 7200 min Summer 99.083 0.083 3.0 13.3 O K 8640 min Summer 99.076 0.076 2.7 12.1 O K 10080 min Summer 99.071 0.071 2.4 11.2 O K 15 min Winter 99.275 0.275 5.0 51.0 O K 30 min Winter 99.356 0.356 5.0 70.8 O K

Storm Rain Flooded Discharge Time-Peak Event (mm/hr) Volume Volume (mins) (m³) (m³)

15 min Summer 64.939 0.0 56.1 47 30 min Summer 43.271 0.0 74.9 59 60 min Summer 27.653 0.0 96.2 78 120 min Summer 17.180 0.0 119.6 128 180 min Summer 12.869 0.0 134.4 182 240 min Summer 10.436 0.0 145.3 214 360 min Summer 7.724 0.0 161.3 280 480 min Summer 6.239 0.0 173.8 348 600 min Summer 5.283 0.0 183.9 414 720 min Summer 4.610 0.0 192.6 480 960 min Summer 3.716 0.0 207.0 610 1440 min Summer 2.738 0.0 228.8 862 2160 min Summer 2.015 0.0 252.8 1212 2880 min Summer 1.620 0.0 270.9 1540 4320 min Summer 1.189 0.0 298.2 2216 5760 min Summer 0.954 0.0 319.4 2944 7200 min Summer 0.804 0.0 336.4 3672 8640 min Summer 0.699 0.0 350.8 4400 10080 min Summer 0.621 0.0 363.6 5104 15 min Winter 64.939 0.0 62.9 50 30 min Winter 43.271 0.0 84.0 60

©1982-2015 XP Solutions Scott Hughes Design Ltd Page 2 The Flint Glass Works Northop 64 Jersey Street 30 yr Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 30yr event.SRCX Checked by Micro Drainage Source Control 2015.1

Summary of Results for 30 year Return Period

Storm Max Max Max Max Status Event Level Depth Control Volume (m) (m) (l/s) (m³)

60 min Winter 99.429 0.429 5.0 90.8 O K 120 min Winter 99.481 0.481 5.0 106.6 O K 180 min Winter 99.496 0.496 5.0 111.4 O K 240 min Winter 99.497 0.497 5.0 111.6 O K 360 min Winter 99.485 0.485 5.0 107.9 O K 480 min Winter 99.469 0.469 5.0 102.9 O K 600 min Winter 99.449 0.449 5.0 96.9 O K 720 min Winter 99.426 0.426 5.0 90.0 O K 960 min Winter 99.372 0.372 5.0 75.0 O K 1440 min Winter 99.268 0.268 5.0 49.3 O K 2160 min Winter 99.149 0.149 4.9 25.1 O K 2880 min Winter 99.112 0.112 4.3 18.3 O K 4320 min Winter 99.087 0.087 3.2 14.0 O K 5760 min Winter 99.075 0.075 2.6 12.0 O K 7200 min Winter 99.068 0.068 2.2 10.7 O K 8640 min Winter 99.062 0.062 1.9 9.8 O K 10080 min Winter 99.058 0.058 1.7 9.1 O K

Storm Rain Flooded Discharge Time-Peak Event (mm/hr) Volume Volume (mins) (m³) (m³)

60 min Winter 27.653 0.0 107.8 80 120 min Winter 17.180 0.0 134.0 128 180 min Winter 12.869 0.0 150.5 182 240 min Winter 10.436 0.0 162.8 232 360 min Winter 7.724 0.0 180.7 296 480 min Winter 6.239 0.0 194.7 372 600 min Winter 5.283 0.0 206.1 450 720 min Winter 4.610 0.0 215.8 526 960 min Winter 3.716 0.0 231.9 658 1440 min Winter 2.738 0.0 256.3 906 2160 min Winter 2.015 0.0 283.2 1212 2880 min Winter 1.620 0.0 303.5 1516 4320 min Winter 1.189 0.0 334.0 2216 5760 min Winter 0.954 0.0 357.7 2952 7200 min Winter 0.804 0.0 376.8 3680 8640 min Winter 0.699 0.0 392.9 4416 10080 min Winter 0.621 0.0 407.3 5016

©1982-2015 XP Solutions Scott Hughes Design Ltd Page 3 The Flint Glass Works Northop 64 Jersey Street 30 yr Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 30yr event.SRCX Checked by Micro Drainage Source Control 2015.1

Rainfall Details

Rainfall Model FSR Winter Storms Yes Return Period (years) 30 Cv (Summer) 0.750 Region England and Wales Cv (Winter) 0.840 M5-60 (mm) 18.000 Shortest Storm (mins) 15 Ratio R 0.349 Longest Storm (mins) 10080 Summer Storms Yes Climate Change % +0

Time Area Diagram

Total Area (ha) 0.465

Time (mins) Area Time (mins) Area Time (mins) Area Time (mins) Area From: To: (ha) From: To: (ha) From: To: (ha) From: To: (ha)

0 4 0.050 12 16 0.060 24 28 0.030 36 40 0.010 4 8 0.100 16 20 0.050 28 32 0.020 40 44 0.010 8 12 0.080 20 24 0.040 32 36 0.010 44 48 0.005

©1982-2015 XP Solutions Scott Hughes Design Ltd Page 4 The Flint Glass Works Northop 64 Jersey Street 30 yr Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 30yr event.SRCX Checked by Micro Drainage Source Control 2015.1

Model Details

Storage is Online Cover Level (m) 100.000

Tank or Pond Structure

Invert Level (m) 99.000

Depth (m) Area (m²) Depth (m) Area (m²) Depth (m) Area (m²) Depth (m) Area (m²)

0.000 150.0 1.400 0.0 2.800 0.0 4.200 0.0 0.200 200.0 1.600 0.0 3.000 0.0 4.400 0.0 0.400 280.0 1.800 0.0 3.200 0.0 4.600 0.0 0.600 360.0 2.000 0.0 3.400 0.0 4.800 0.0 0.800 440.0 2.200 0.0 3.600 0.0 5.000 0.0 1.000 580.0 2.400 0.0 3.800 0.0 1.200 0.0 2.600 0.0 4.000 0.0

Hydro-Brake Optimum® Outflow Control

Unit Reference MD-SHE-0111-5000-0600-5000 Design Head (m) 0.600 Design Flow (l/s) 5.0 Flush-Flo™ Calculated Objective Minimise upstream storage Diameter (mm) 111 Invert Level (m) 99.000 Minimum Outlet Pipe Diameter (mm) 150 Suggested Manhole Diameter (mm) 1200

Control Points Head (m) Flow (l/s)

Design Point (Calculated) 0.600 5.0 Flush-Flo™ 0.192 5.0 Kick-Flo® 0.427 4.3 Mean Flow over Head Range - 4.2

The hydrological calculations have been based on the Head/Discharge relationship for the Hydro-Brake Optimum® as specified. Should another type of control device other than a Hydro-Brake Optimum® be utilised then these storage routing calculations will be invalidated

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

0.100 3.8 1.200 6.9 3.000 10.6 7.000 15.9 0.200 5.0 1.400 7.4 3.500 11.4 7.500 16.4 0.300 4.8 1.600 7.9 4.000 12.1 8.000 17.0 0.400 4.5 1.800 8.3 4.500 12.9 8.500 17.5 0.500 4.6 2.000 8.7 5.000 13.5 9.000 18.0 0.600 5.0 2.200 9.1 5.500 14.1 9.500 18.5 0.800 5.7 2.400 9.5 6.000 14.7 1.000 6.3 2.600 9.9 6.500 15.3

©1982-2015 XP Solutions Scott Hughes Design Ltd Page 1 The Flint Glass Works Northop 64 Jersey Street 100yr + CC Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 100yr event.SRCX Checked by Micro Drainage Source Control 2015.1

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

Storm Max Max Max Max Status Event Level Depth Control Volume (m) (m) (l/s) (m³)

15 min Summer 99.398 0.398 5.0 82.2 O K 30 min Summer 99.503 0.503 5.0 113.7 O K 60 min Summer 99.597 0.597 5.0 145.3 O K 120 min Summer 99.669 0.669 5.2 172.2 O K 180 min Summer 99.695 0.695 5.3 182.5 O K 240 min Summer 99.703 0.703 5.4 185.6 Flood Risk 360 min Summer 99.697 0.697 5.3 183.2 O K 480 min Summer 99.688 0.688 5.3 179.7 O K 600 min Summer 99.678 0.678 5.3 175.6 O K 720 min Summer 99.666 0.666 5.2 171.2 O K 960 min Summer 99.643 0.643 5.1 162.1 O K 1440 min Summer 99.594 0.594 5.0 144.2 O K 2160 min Summer 99.520 0.520 5.0 118.9 O K 2880 min Summer 99.442 0.442 5.0 94.7 O K 4320 min Summer 99.273 0.273 5.0 50.4 O K 5760 min Summer 99.166 0.166 5.0 28.2 O K 7200 min Summer 99.122 0.122 4.7 20.2 O K 8640 min Summer 99.107 0.107 4.2 17.4 O K 10080 min Summer 99.097 0.097 3.7 15.6 O K 15 min Winter 99.439 0.439 5.0 93.7 O K 30 min Winter 99.548 0.548 5.0 128.4 O K

Storm Rain Flooded Discharge Time-Peak Event (mm/hr) Volume Volume (mins) (m³) (m³)

15 min Summer 108.950 0.0 94.4 53 30 min Summer 73.328 0.0 127.3 62 60 min Summer 47.182 0.0 164.3 82 120 min Summer 29.377 0.0 204.6 132 180 min Summer 21.965 0.0 229.5 188 240 min Summer 17.756 0.0 247.4 244 360 min Summer 13.049 0.0 272.7 316 480 min Summer 10.494 0.0 292.4 378 600 min Summer 8.854 0.0 308.4 444 720 min Summer 7.702 0.0 322.0 512 960 min Summer 6.176 0.0 344.2 652 1440 min Summer 4.516 0.0 377.5 926 2160 min Summer 3.295 0.0 413.5 1328 2880 min Summer 2.631 0.0 440.3 1732 4320 min Summer 1.913 0.0 480.0 2388 5760 min Summer 1.524 0.0 510.1 3016 7200 min Summer 1.276 0.0 534.1 3680 8640 min Summer 1.104 0.0 554.2 4408 10080 min Summer 0.977 0.0 572.1 5136 15 min Winter 108.950 0.0 105.8 54 30 min Winter 73.328 0.0 142.6 63

©1982-2015 XP Solutions Scott Hughes Design Ltd Page 2 The Flint Glass Works Northop 64 Jersey Street 100yr + CC Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 100yr event.SRCX Checked by Micro Drainage Source Control 2015.1

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

Storm Max Max Max Max Status Event Level Depth Control Volume (m) (m) (l/s) (m³)

60 min Winter 99.647 0.647 5.2 164.0 O K 120 min Winter 99.728 0.728 5.4 195.8 Flood Risk 180 min Winter 99.760 0.760 5.6 209.1 Flood Risk 240 min Winter 99.772 0.772 5.6 214.1 Flood Risk 360 min Winter 99.769 0.769 5.6 213.0 Flood Risk 480 min Winter 99.758 0.758 5.6 208.0 Flood Risk 600 min Winter 99.745 0.745 5.5 202.7 Flood Risk 720 min Winter 99.730 0.730 5.5 196.5 Flood Risk 960 min Winter 99.697 0.697 5.3 183.1 O K 1440 min Winter 99.625 0.625 5.1 155.7 O K 2160 min Winter 99.514 0.514 5.0 117.0 O K 2880 min Winter 99.371 0.371 5.0 74.7 O K 4320 min Winter 99.148 0.148 4.9 24.9 O K 5760 min Winter 99.107 0.107 4.2 17.5 O K 7200 min Winter 99.092 0.092 3.5 14.9 O K 8640 min Winter 99.083 0.083 3.0 13.3 O K 10080 min Winter 99.077 0.077 2.7 12.2 O K

Storm Rain Flooded Discharge Time-Peak Event (mm/hr) Volume Volume (mins) (m³) (m³)

60 min Winter 47.182 0.0 184.0 84 120 min Winter 29.377 0.0 229.2 132 180 min Winter 21.965 0.0 257.1 186 240 min Winter 17.756 0.0 277.1 242 360 min Winter 13.049 0.0 305.5 346 480 min Winter 10.494 0.0 327.6 400 600 min Winter 8.854 0.0 345.5 474 720 min Winter 7.702 0.0 360.6 552 960 min Winter 6.176 0.0 385.6 704 1440 min Winter 4.516 0.0 422.8 1000 2160 min Winter 3.295 0.0 463.2 1428 2880 min Winter 2.631 0.0 493.2 1800 4320 min Winter 1.913 0.0 537.6 2340 5760 min Winter 1.524 0.0 571.3 2952 7200 min Winter 1.276 0.0 598.2 3680 8640 min Winter 1.104 0.0 620.7 4408 10080 min Winter 0.977 0.0 640.8 5160

©1982-2015 XP Solutions Scott Hughes Design Ltd Page 3 The Flint Glass Works Northop 64 Jersey Street 100yr + CC Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 100yr event.SRCX Checked by Micro Drainage Source Control 2015.1

Rainfall Details

Rainfall Model FSR Winter Storms Yes Return Period (years) 100 Cv (Summer) 0.750 Region England and Wales Cv (Winter) 0.840 M5-60 (mm) 18.000 Shortest Storm (mins) 15 Ratio R 0.349 Longest Storm (mins) 10080 Summer Storms Yes Climate Change % +30

Time Area Diagram

Total Area (ha) 0.465

Time (mins) Area Time (mins) Area Time (mins) Area Time (mins) Area From: To: (ha) From: To: (ha) From: To: (ha) From: To: (ha)

0 4 0.050 12 16 0.060 24 28 0.030 36 40 0.010 4 8 0.100 16 20 0.050 28 32 0.020 40 44 0.010 8 12 0.080 20 24 0.040 32 36 0.010 44 48 0.005

©1982-2015 XP Solutions Scott Hughes Design Ltd Page 4 The Flint Glass Works Northop 64 Jersey Street 100yr + CC Attenuation Manchester M4 6JW Date May 16 Designed by PG File outline 100yr event.SRCX Checked by Micro Drainage Source Control 2015.1

Model Details

Storage is Online Cover Level (m) 100.000

Tank or Pond Structure

Invert Level (m) 99.000

Depth (m) Area (m²) Depth (m) Area (m²) Depth (m) Area (m²) Depth (m) Area (m²)

Hydro-Brake Optimum® Outflow Control

Control Points Head (m) Flow (l/s)

Design Point (Calculated) 0.600 5.0 Flush-Flo™ 0.192 5.0 Kick-Flo® 0.427 4.3 Mean Flow over Head Range - 4.2

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