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November 2014

NEWQUAY CORNWALL AIRPORT

MASTERPLAN;

SURFACE WATER MANAGEMENT

PLAN AND FOUL DRAINAGE

STRATEGY

Cornwall Development Company

[Final Draft]

Newquay Cornwall Airport Masterplan;

Surface Water Management Plan and Foul Drainage Strategy

287301A

Prepared for Cornwall Development Company

Pydar House Pydar Street

Truro TR1 1EA

Prepared by Parsons Brinckerhoff

The Forum, Barnfield Road Exeter EX1 1QR

01392 229700 www.pbworld.com

DOCUMENT HISTORY AND STATUS

Document control

Prepared by C Uzzell Checked by (technical)

M Bugbee

Approved by U Stevenson Checked by (quality assurance)

M Bugbee

Revision details

Version Date Pages

affected Comments

B October

2014 1

st issue

C November

2014 2

nd issue

D December

2014 3

rd issue – logo’s added

Newquay Cornwall Airport Masterplan; Surface Water Management Plan

Newquay Cornwall Airport Masterplan SWMP rev D docx_v1 Prepared by Parsons Brinckerhoff October 2014 for Cornwall Development Company - 7 -

CONTENTS Page

1 Introduction 8

2 Surface Water Management Plan Study 8

2.1 Definition of a Surface Water Management Plan 8

3 Phase 1; Preparation 9

3.1 SWMP Study and Scope. 9

3.2 NQY Existing Conditions and Site Background 9

4 Phase 2; Risk Assessment 16

4.1 Overview 16

4.2 Risks 16

4.3 Water Quality 16

4.4 Summary 17

5 Phase 3; Options 18

5.1 Development considerations 18

5.2 Calculated flows and attenuation 19

6 Phase 4; Implementation & Review 21

6.1 Action Plan: 21

6.2 SuDS Principles and Design Parameters 21

6.3 Management 23

6.4 Construction 23

6.5 Assumptions and Limitations 23

7 Foul Water drainage 24

7.1 Existing Conditions 24

7.2 Proposals 24

8 References 26

Appendices:

Appendix A – Background Documents

Appendix B – Recent NQY Site Studies

Appendix C – Summary of Meeting of “Partners”



1 INTRODUCTION

Cornwall Development Company (CDC), on behalf of Cornwall Airport Limited (CAL) has engaged Parsons Brinckerhoff (PB) to prepare a Surface Water Management Plan (SWMP) for Newquay Cornwall Airport (NQY), which includes the Aerohub Business Park and solar farm sites to the south. This commission also requires a foul water drainage strategy. For completeness, the foul water drainage strategy has been included within this SWMP. Given the relatively small and self-contained nature of this site, a “High Level” version of the standard Defra SWMP is used.

2 SURFACE WATER MANAGEMENT PLAN STUDY

2.1 Definition of a Surface Water Management Plan

Defra guidance provides a phased process for a SWMP incorporating “Preparation; Risk Assessment; Options; and Implementation & Review”, as illustrated in the wheel diagram below. As defined by the Defra guidance of March 2010, titled Surface Water Management Plan Technical Guidance “a Surface Water Management Plan (SWMP) is a plan which outlines the preferred surface water management strategy in a given location. In this context surface water flooding describes flooding from sewers, drains, groundwater, and runoff from land, small water courses and ditches that occurs as a result of heavy rainfall. A SWMP study is undertaken in consultation with key local partners who are responsible for surface water management and drainage in their area.” “A SWMP should establish a long-term action plan to manage surface water in an area and should influence future capital investment, drainage maintenance, public engagement and understanding, land-use planning, emergency planning and future developments.”



3 PHASE 1; PREPARATION

This step includes: identifying the need for a SWMP study; establishing the partnership; scoping the SWMP study, and undertaking a strategic assessment.

3.1 SWMP Study and Scope.

This SWMP aims to identify existing conditions, current and future proposals and identify how this site can be developed sustainably with regards to surface water runoff without increasing flood risk at or downstream of the NQY site, as well as maintaining or improving the quality of surface water discharges. This site and the downstream receiving watercourses are not defined as critical drainage areas. However, this largely greenfield site may be subject to considerable development over the coming years through the development of the site-wide Masterplan. With respect to new development, a SWMP study offers the opportunity to reduce existing surface water flood risk downstream or to create capacity in the drainage system through improvements in runoff from development sites.

3.2 NQY Existing Conditions and Site Background

The NQY site is located some 5km north east of Newquay. The site sits near the top of two river catchments, the Menalhyl flows to the north and the Porth Stream to the south. The northern tributary of the Porth Stream flows from east to west through the southern part of the site. It is formed from two small streams which rise within the site. A further tributary rises within RAF St Mawgan flowing into the tributary just downstream of the site boundary. It joins the southern tributary of the Porth Stream approximately 5km downstream, just before it drains into the sea at Porth Beach. Several minor tributaries of Menalhyl rise from springs along the northern boundary of the site, within Carnanton Woods to the north east and near Little Acre to the north-west. The Mehalhyl discharges into the sea at Mawgan Porth approximately 1.5km downstream of the Airport. There is a further minor watercourse which rises on the western boundary of the site near Penvose Farm and discharges to the sea at Watergate Bay. An indication of existing drainage systems are shown in Figure 1 below. This is dated 2005, when the Ministry of Defence (MOD) site was separated from the NQY site. Most shared utilities were severed at the time. The Masterplan red-line boundary is as shown on Figure 1. The site has an area of approximately 350Ha and a perimeter of some 13.8km.



Figure 1: Existing Services and drainage features (refer to larger scale drawing DR01 for detail)

3.2.1 Surface water characteristics

Runoff from runway hard-standings at NQY are understood to be directed to interceptor chambers, which are pumped out or discharge to the water courses to the south of the site. The land to the south of the site primarily drains to the Porth Stream Tributary with a small component from the Business Park site draining towards the A3059 along the southern boundary. A new compound hardstanding at the St Mawgan Building, east of the terminal building, drains to a soakaway beneath the access road. From the associated design report, permeabilities in this area are variable with values in this vicinity varying between 1x10

-6 m/s and 2x10

-5 m/s.

At the interface between the NQY and the MOD site, existing connections were severed and routed south east towards the Porth tributary. Figure 1 shows drainage catchment ridgelines across the site indicating in which direction surface water runoff will discharge. The southern side of the site drains south and west towards a tributary of the Porth River. The Aerohub site and the Solar Farm sites drains north to the Porth tributary. The west end of the site drains to a minor watercourse which discharges at Watergate Bay The north side of the site drains towards St Mawgan and the Menalhyl River. Figure 1 also indicates Environment Agency (EA) surface water runoff mapping for low to high risk areas. The site is currently shown as low risk.



Figure 2 shows the site sitting within Flood Zone 1, whereby flooding from rivers or the sea is very unlikely with less than 0.1% (1 in 1000) chance of occurring each year.

Figure 2 - Newquay Airport area EA flood mapping

Courtesy: Environment Agency, http://maps.environment-agency.gov.uk/

The site currently comprises the following principal impermeable elements: Table 1.

Site impermeable elements Area (Ha) % Total

Runways, taxiways and associated aprons & hardstandings 83 24

Terminal and associated office and commercial buildings to the north of the site

0.38 0.1

Old bunkers and storage structures and hangars to the west of the site

1.1 0.3

Hangars to the south of the site 0.01 0.003

Southern Access Road (SAR) 1.35 0.38

Impermeable areas 86 25

Grassed / permeable areas 264 75



3.2.2 Surface water runoff characteristics:

The Wallingford procedure provides the following data:

Soil Class (WRAP is high) = 2; SOIL = 0.30

M5-60 = 17mm

Ratio r = 0.3

SAAR = 1000mm Following Institute of Hydrology Report 124 methodology, runoff from greenfield areas of this site, based upon the above parameters will be 6.8 l/s/Ha for a 1:100 year return storm event, 5.3 l/s for a 1:30 year event and 2.1 l/s/Ha for a 1:1 year event. These runoff figures were also adopted for the Aerohub (Business Park phase 1) site. 3.2.3 Groundwater

Figure 3 indicates that the site is not located within a groundwater source protection zone; although the site is classified as a Secondary A Aquifer, which is associated with the Meadfoot Beds underlying geology. These are permeable layers of rock capable of supporting water supplies at a local rather than strategic scale. These are generally aquifers formerly classified as a minor aquifer. The EA Groundwater Vulnerability Map of West Cornwall (Sheet 53) indicates that the bedrock underlying the airfield is classified as a Minor Aquifer of Intermediate Leaching Potential. The leaching classification indicates that soils across the majority of the airfield are considered to have moderate ability to attenuate diffuse source pollutants, with small areas categorised as having a high leaching potential which may readily transmit liquid directly to the underlying strata and groundwater.

In terms of aquifer protection, the EA generally adopts a three-fold classification of Source Protection Zones (SPZ) for public water supply abstraction. A review of the data held on the EA website indicates that the site is not situated in a SPZ. However there are local SPZ’s located south and north east of the site; three outer zone 2 and three inner zone 1 some 1.1km to the south west; two outer zone 2 and two inner zone 1 located some 2.2km to the north east. The inner zone is defined as the 50 day travel time from any point below the water table to the source which has a minimum radius of 50m.



Figure 3 – Groundwater source protection zones


3.2.4 Water abstractions

Surrounding the site are a number of water abstraction licence locations, indicating that water can be abstracted from groundwater, surfaces water, and or tidal water. To do this, abstraction licences are required and are publicised on the EA website, see Figure 4. Figure 4 shows the river catchment boundaries. North east of the site a small groundwater abstraction licence is shown for industrial use for the holiday park. To the south is a small and medium groundwater abstraction licence for general agricultural and industrial use such as holiday camp sites and golf courses. The south catchment also includes a large and medium surface water abstraction licences for public water supply and agricultural use. Further details of the current licences can be found on the EA website.



Figure 4 - Newquay Cornwall Airport area EA Water Abstraction Licences


3.2.5 Landfill

There are historic landfill sites located close to the development; one to the south of the site, along Porth River at St Columb Minor; the land fill site is known as Priory Road. Another is located north east of the site along the River Menalhyl; the landfill site is known as Little Halveor. Historic landfill sites have the potential to pollute groundwater, however given the distance and topography it is not considered further in the context of the proposed development. 3.2.6 Background documents

These have been reviewed as part of this Masterplan process and are described further in Appendix A and include:

Drainage Guidance for Cornwall Council, v2, January 2010 3

East Cornwall, Catchment Flood Management Plans, June 2010 4

Cornwall Council Local Development Framework Strategic Flood Risk Assessment Level 1, November 2009

1

River Basin Management Plans 6

Safeguarding of Aerodromes

3.2.7 Recent NQY site studies

These have been reviewed as part of this Masterplan process and are described further in Appendix B and include:

Solar Park: Flood Risk Assessment, 2011



Aerohub Business Park: Flood Risk Assessment, 2012

Newquay Cornwall Airport, Draft Masterplan Strategic Environmental Assessment, 2008

South West Geotechnical, 2013, Newquay Cornwall Airport, Aerohub Enterprise Zone: Geotechnical and Geo-environmental Investigation.

3.2.8 The Partners

The following authorities have been identified as having knowledge of, or involvement and responsibility for, this scheme:

Cornwall Council (CC)

Environment Agency (EA)

Cornwall Airport Limited (CAL)

Cornwall Development Company (CDC) Whilst the requirements of a SWMP are well defined and may normally be considered for larger sites with known flooding issues, discussions with the above mentioned authorities suggest that this site currently has no recorded issues of flooding on site or downstream. However, given the proposals which may constitute considerable development over the coming years, the intention is to maintain or preferably improve flood risk and water quality and provide a consistent approach to surface water runoff. In terms of objectives and responsibilities, it is suggested that all parties will have a role to play in the provision of advice regarding flooding history and that CC and CAL will be engaged regarding future development proposals, recommendations for defining objectives and on-going maintenance. From this, a plan for new and existing drainage systems can be developed based upon risk, cost and on-going operation and maintenance. The Flood and Water Management Act 2010 establishes that unitary and county local authorities will lead new local flood risk management activities as the Lead Local Flood Authority. Cornwall Council (CC) is the local unitary authority. However until they formally take the role as Sustainable Drainage Systems (SuDS) Approving Body (SAB) now expected in 2015, the EA will continue to have a lead role. A meeting of the Partners was held at the CDC Truro office on 22 May 2014 and is summarised at Appendix C. This identified the principal objectives for surface water management at the site. Given the relatively small size and low risk nature of the site, a High Level “SWMP” was agreed.



4 PHASE 2; RISK ASSESSMENT

4.1 Overview

This step includes a strategic, intermediate and/or detailed assessment, depending upon the scale of scheme and known risks, and mapping and communicating of these risks. The following sources of flooding may be considered:

Surface Water / overland flows (pluvial)

Groundwater

Sewerage

Fluvial

4.2 Risks

Surface Water Runoff: Generated due to rainfall causing water to flow overland before entering underground systems. Runoff volumes may increase as a result of insufficient capacity within the underground systems. There is some available data for existing stormwater drainage systems, but this is limited. This primarily relates to building drainage, with some limited detail regarding the capture and discharge of runoff from the runway and associated taxiways. The highest risk of flooding at this site will be downstream from new developments, by creating impermeable areas which will intensify runoff rates and volumes. This risk will be mitigated by controlling runoff to greenfield rates using best practice SuDS techniques. Groundwater flooding: There are no reports of groundwater flooding. However, this would need to be considered more carefully where the site abuts the Porth tributary, as historical trial pits show water levels within 0.5m of the surface. The water table, particularly closer to the stream must be avoided for any below ground storage with infiltration.

Sewerage flooding: There are no reports of flooding from sewers. However, existing systems should be assessed in more detail and upgrades considered where existing systems lack capacity or require rehabilitation and as the proposed sites are developed. Refer to the WRc Sewerage Rehabilitation Manual. Fluvial: The site falls within flood zone 1; that is a low probability and less than 1 in 1000 annual probability of river or sea flooding in any year. Refer to Figure 2 for EA mapping. From discussions with the Partners, there are no known historical flooding problems, although there is anecdotal evidence of some flooding and pollution issues on the minor tributary west of the site which discharges to Watergate Bay. The strategy for surface water runoff will be to maintain or improve the existing condition in terms of runoff so that there is no increase in surface water leaving the site and therefore no increase to flood risk in downstream watercourses.

4.3 Water Quality

Although not flood related, this has the possibility of impacting upon all downstream receiving watercourses and features. Whilst new proposals can be more readily controlled, existing systems may not be designed or maintained to control the quality of discharges. There are various abstraction points downstream of the Business Park sites which may be at risk from infiltration drainage if not carefully considered.



Similarly, there are no known details of contamination across the site. This will require further investigation, particularly where infiltration devices are proposed. Potential sources of contamination affecting water quality may include the fire fighting training area, runway runoff, foul pump station and treatment units (indicated on Drainage Strategy drawing DR01). Without direct quantification, water quality can be controlled through the appropriate usage and combination of SuDS techniques. This should be developed further during the detailed design stages. Table 3.7 of the Ciria 609 report, Sustainable Drainage Systems indicates the pollutant removal efficiencies for various forms of SuDS technique.

Similarly, Ciria 697 “The SuDS Manual”, table 3.3, 5.6 and 5.7 recommends the number and type of SuDS treatment train components to more efficiently deal with various types of pollutant.

A water quality calculator “Water quality SuDS calculator” has been developed by HR Wallingford, on their web page “UK Sustainable Drainage” http://www.uksuds.com/. This calculator takes in to account the development proposals compared with the sensitivity of the receiving waters to pollution from runoff. A high “good” result would be desirable for this site.

4.4 Summary

Flood risks to the site are considered to be low due to the topography and location of the site at the top of a ridge/catchment and the surrounding system of watercourses. The highest perceived risks are considered to be:

Unknown quantity and quality of runoff from existing systems, particularly the runway drainage network and associated infrastructure such as the fire-fighting training area;

Risk to the Porth, its tributary and the River Manalhyl from foul discharges from sewage treatment units and polluted surface water runoff;

Risk to local groundwater abstraction points;

Existing site contamination, e.g. fuel storage areas;

The residual risks following development, which in terms of quality and quantity, should be no greater than the existing conditions;

Construction phase risks, in terms of silt and fuel runoff;

On-going Operation & Maintenance liabilities in terms of controlling and maintaining quality and quantity of runoff from existing systems and proposed development plots.

http://www.uksuds.com/



5 PHASE 3; OPTIONS

This step is to identify and assess options.

5.1 Development considerations

The Masterplan development proposals for the site are highlighted in Figure 5 below for the 10 proposed Development Zones. These are defined in three specific areas:

North side: Terminal, North and Northern Loop

South side: DZ1, DZ3, Business Park phases 1 to 3

West: HAS and DZ2.

Figure 5: Development Zones

The Solar Farm Site (not a development zone, but within the red-line boundary) has already been developed with minimal impact upon existing runoff conditions, as defined in the FRA reference 6. The Business Park phase 1 has already been designed as defined in reference 7 and construction for the infrastructure in phase 1 has commenced.



Options for discharge locations of storm drainage are relatively limited due to the topography and location of receiving waters. Under SuDS best practice (e.g. the SuDS Manual Ciria 697), infiltration is the preferred method of discharge. However, permeability rates across the site are currently unknown. Infiltration testing will be required before further design is undertaken. Following this, discharge at existing greenfield runoff rates is the next preferred option, ideally utilising some infiltration and filtration through filter drains, grassed swales and other SuDS features to optimise the SuDS principles of improving quality, quantity and amenity/biodiversity. The primary stormwater drainage options considered were discussed with the Partners. This broadly concluded that:

The existing runway and associated taxiways should ideally be kept separate from future developments where a better understanding of existing drainage is required, where operational boundaries can best be defined and where upgrading could benefit the quality and quantity of runoff.

Development to the south; whereby a drainage approach similar to that adopted for the Aerohub drainage strategy (Business Park phases 1 & 3) could be adopted.

Development to the north and west; with drainage primarily to infiltration features or beyond to existing watercourses.

One alternative option would be to link runoff from the various development zones. However, given the distance and physical barriers between them, this is not considered practical.

5.2 Calculated flows and attenuation

As defined above under “surface water runoff characteristics”, the existing greenfield equivalent runoff from the site amounts to 6.8l/s/Ha for a 1:100 year return storm event. Although existing runoff from some development zones is higher than for the existing greenfield conditions, with modifications to existing impermeable areas the opportunity exists to develop a more efficient SuDS based approach. If the new Development Zones can limit runoff from plots to at least existing rates, including for suitable levels of climate change, downstream flood risk is not increased and can be reduced. Similarly, by adopting a SuDS approach, in accordance with BS 8582:2013, Ciria 738 and Ciria 697 the SuDS Manual and providing suitable elements in the SuDS Train, a series of SuDS elements to improve water quality, then water quality can also be optimised. Indicative areas and attenuation volumes for the 10 proposed Development Zones are shown in the following Table 2. Pending geotechnical investigations, these indicative volumes are based upon zero infiltration and a 1m depth for the proposed additional impermeable development areas in a greenfield environment. They adopt an allowable outflow rate of 6.8l/s/ha and include an allowance for 30% climate change. These attenuation features can be located in one or more locations and be above or below ground. These will require updating as design progresses and ground conditions can be assessed.



Table 2.

Development Zone

Gross Area (Ha)

Existing impermeable

area (Ha)

Area / ( % Area)

Proposed impermeable

area (Ha)

Additional / Total

Existing 1

discharge Q100 (l/s)

Greenfield 2

discharge Q100 (l/s)

Indicative 3

storage area – new

development (m

2)

Northern Loop 17.48 5.16 (29%) 2.0 / 7.2 156 118 1500

North 5.31 3.34 (62%) 2.2 / 5.5 65 36 1620

Terminal 6.95 4.79 (69%) 2.2 / 7.0 89 47 1620

HAS 14.23 2.09 (15%) 2.4 / 4.5 112 97 1630

DZ1 23.41 8.81 (37%) 9.4 / 18.3 228 159 5900

DZ2 19.68 12.54 (64%) 10.6 / 2.1 241 134 6550

DZ3 18.69 1.13 (6%) 5.4 / 6.5 134 127 3600

Business Park phase 1

23.84 0 4 162 162

4

B / Park phase 2 (west)

20.76 0 4 141 141

4

B / Park phase 3 (east)

12.52 0 4 85 85

4

Sum 163 38 (21%)

1. Estimated, based upon existing impermeable area of each Development Zone. 2. Based upon existing “greenfield” conditions; 6.8l/s/Ha maximum runoff (1:100) for each Development Zone. 3. Excludes infiltration pending site investigations and adopts 6.8l/s/Ha maximum allowable runoff for the proposed additional impermeable development. 4. Already under design or construction.

High risk elements of the development will require additional attention in terms of pollution control and proprietary devices may be required. Further work is required to assess the condition and operational efficiency of the existing systems, particularly the runway drainage networks. Similarly, to implement any of these options infiltration testing is required.



6 PHASE 4; IMPLEMENTATION & REVIEW

This step identifies an action plan for implementation and review.

6.1 Action Plan:

The proposals for the site are as follows and indicatively summarised on Drawing DR01-B. 6.1.1 General

Future stormwater drainage features should adopt best practice “SuDS Principles and Design Parameters” as defined below, similar to those proposed for the Aerohub site. Allowable runoff rates shall be taken as matching the existing green or brownfield condition plus an allowance for at least a 10% betterment should be included along with appropriate climate change inclusions as recommended below. Water quality should be considered to reduce impact upon receiving waters. Where possible amenity factors should be considered and whilst water features are not acceptable due to the hazard of attracting birds, green spaces can be promoted. 6.1.2 Existing Runways, taxiways and associated infrastructure

Review and assess the condition and capacity of the existing systems in more detail, including an assessment of the quality of discharge. Upgrade or rehabilitate systems where required, to reduce or minimise local or downstream flood risk and to clarify water quality to ensure downstream receptors are protected. 6.1.3 DZ1 & DZ3

Stormwater to discharge at no greater than existing greenfield runoff rates towards the Porth tributary south of DZ1 & DZ3, adopting infiltration and other SuDS best practice. 6.1.4 HAS & DZ2

Stormwater to discharge at less than existing runoff rates, adopting principally infiltration and other SuDS best practice, with overflows north towards the minor tributary north of the HAS. 6.1.5 Terminal, North & Northern Loop

Stormwater to discharge at less than existing runoff rates, adopting principally infiltration and other SuDS best practice, with overflows north towards the River Menalhyl in the Vale of Mawgan.

6.2 SuDS Principles and Design Parameters

All stormwater systems are to provide amenity and biodiversity, discharging to infiltration devices or watercourses, adopting suitable SuDS features such as:

Green corridors with suitable outfalls for swales, filter strips, drains and ecology.

Green roofs, porous paving and car parks (for non-adopted areas only), swales, filter strips, dry ponds / infiltration areas, filter / infiltration drains / tanks.



No low points where flooding could exceed the design flows and flood property.

6.2.1 Attenuation should ideally be located close to source, although it will often be in the lower parts of the site. These areas could include un-adopted parking areas, recreation / landscape areas etc. Permanent water bodies should be avoided due to the proximity to the Airport. However, short term above ground storage features are considered acceptable, although this still requires verification from the Airport authorities.

6.2.2 Storm water drainage design parameters (external to buildings)

Quantity - The site and downstream watercourses are at low risk of flooding, provided that appropriate SuDS drainage systems are implemented to mitigate increased runoff from the proposed development.

Quality - Pollution control must be considered and the appropriate treatment procedures put in place for the construction stage and the permanent works.

Amenity should be gained through the use of open swales and “normally dry” ponds where appropriate to enhance landscape features and bio-diversity whilst also improving water quality.

6.2.3 Adoptable highway drainage shall conform to CC guidance and discharge via suitable SuDS systems to suitable attenuation/infiltration features and adopt a maximum allowable offsite discharge rates of 6.8l/s/ha, or existing runoff rates with 10% betterment.

6.2.4 Storage for water above the design events could be accommodated above ground within open space areas such as car parks, but this will be dependent upon finished levels and sensitivity of the area.

6.2.5 Individual plots and associated impermeable areas, including related public realm areas, shall drain surface water via soakaway features, such as permeable car parks; but where conditions prevail can adopt a maximum allowable discharge from the plots to the stream of 6.8l/s/ha of impermeable surface, or where less than 5 l/s/plot, be limited to 5 l/s/plot.

6.2.6 Individual plot tenants shall be responsible for pollution and storm water discharge control from their specific plot.

6.2.7 No storage/infiltration tanks within 5m of roads or buildings

6.2.8 SuDS designs shall follow the principles of the SuDS Manual, (Ciria 697) and the guidance within the NPPF, including adherence as required to the Building Regulations. A 30% allowance for climate change is to be included in new storm drainage design at a 100 year storm event; 10% for a 30 year event.

6.2.9 Adoptable drainage works shall be constructed in accordance with CC specifications, otherwise in accordance with Sewers for Adoption 7th edition.

6.2.10 Water quality will require careful consideration in terms of impact upon groundwater and ultimately the receiving stream. Treatment procedures need to be considered in accordance with the SuDS Manual (tables 3.3 & 5.10) and Ciria 609 and would typically include, porous pavements, infiltration devices and filter drains, swales and ponds. Use Ciria 609 or other similar procedures to show no reduction to water quality reaching receiving waters.



6.2.11 Exceedance flows, i.e. those flows which exceed the design capacity of the proposed site drainage system, or in the event of system failure, must be given free passage away from the site to avoid flooding of buildings or other sensitive property.

6.2.12 All designs shall be discussed in advance, and ultimately approved by, CC or their delegate.

6.3 Management

CC will retain responsibility for the development of site infrastructure.

Individual plot tenants will be responsible for discharge of storm water quality and quantity to the agreed rates.

6.4 Construction

The construction stage needs to be considered during design in terms of erosion control and protection of new SuDS facilities and receiving waters. Procedures defined within the SuDS Manual (Ciria report C697), section 21 should be considered and adopted as required during the construction stage.

6.5 Assumptions and Limitations

This approach to the stormwater drainage should satisfy a flexible Masterplan, but will need to be carefully monitored by CC to ensure that appropriate common infrastructure is put in place and that future sites are developed in accordance with this drainage strategy.



7 FOUL WATER DRAINAGE

7.1 Existing Conditions

The current foul water drainage systems at the site either connects the terminal and adjacent offices to an existing pump station at St Mawgan, 1km to the north, or is allowed to discharge into individual septic tanks or package treatment units. South West Water (SWW) has advised that there may be some spare capacity at the St Mawgan pump station, but given the long term aspirations of the Newquay Cornwall Airport Masterplan, these capacity issues are likely to change over time. The southern part of the site adjacent to the proposed Aerohub Business Park site is not currently connected to the Airport in terms of foul drainage. A new pumped sewage connection for the Aerohub Business Park (Business Park phase 1) is proposed to be provided with a rising main along the A3059 to St Columb Minor, some 3.5km to the west, under a requisition with SWW. A secondary treated sewage effluent discharge consent is extant via the EA which discharges to the tributary of the Porth Stream close to where the Southern Access Road (SAR) crosses the stream. This is for 20m

3/day (20/30/20, BoD/solids/N) and serves a sewage treatment plant for airport

hangars, offices and workshops. Kelda Water, who acts on behalf of the MoD site, operates a sewage treatment works approximately 1.5km downstream of the SAR on the Porth Stream tributary. Connection to the Kelda Water works is an option depending upon site levels; however, the works are close to the extent of their capacity so an upgrade may be required. Depending upon eventual flows, NQY could also develop a separate sewage works which Kelda Water, or others, could adopt and run in perpetuity through an inset agreement with Ofwat. The EA has previously advised (Aerohub Enterprise Zone @ Newquay Cornwall Airport; Drainage Strategy & Flood Risk Assessment, December 2012) that the Porth tributary is at capacity for ammonia levels, therefore unless there is consolidation and/or improvement of other local discharges, additional treated discharge to the stream is likely to be impractical.

7.2 Proposals

7.2.1 Existing Runways, taxiways and associated infrastructure

Review and assess the condition and capacity of the existing systems in more detail. Upgrade or rehabilitate systems where required. 7.2.2 DZ1 & DZ3

There will be a need for a phased approach to foul drainage from DZ1 and DZ3, dependent upon the development timing for Business Park phases 1 and 3. In the short term this may be drained to the Business Park phase 1 foul pump station up to a joint rate of 9l/s. In the longer term another solution will be required; this should include running a parallel pipe or duct with the Business Park phase 1 rising main so DZ1+3 can connect at a later date with a separate pump station. Other options considered include:

1. Pump DZ1 & DZ3 to St Mawgan via the terminal building – not favoured due to the crossing of the runway.



2. Connect (possibly with a pump) DZ1 & DZ3 to the Kelda Water treatment works approximately 1km downstream on the Porth Tributary. Kelda Water has already suggested that they would consider taking flow from plots HAS + DZ2.

3. Although the EA has previously advised that the Porth tributary is at capacity for ammonia, other options for foul treatment, perhaps in combination with positive systems should also be considered, e.g. treatment units with drainage fields / filter beds where space and suitably permeable soils permit.

7.2.3 HAS & DZ2

Kelda Water operates and maintain a sewage treatment works immediately south of the HAS & DZ2 site on the north side of the Porth tributary. Kelda Water has agreed in principle for new connections, pending upgrade works and associated contributions. Alternative options would be:

1. Direct flows to the discharge point for DZ1 & DZ3. 2. Treatment units with drainage fields / filter beds, although the sensitivity of receiving waters

will require confirmation. 7.2.4 Terminal, North & Northern Loop

Discharge via existing routes to the existing SWW foul pump station at St Mawgan. Upgrades to the systems may be required. For all foul water drainage systems, standards should be adopted as defined in Sewers for Adoption, 7th edition.



8 REFERENCES

1. Cornwall Council Local Development Framework Strategic Flood Risk Assessment

Level 1, November 2009 http://www.cornwall.gov.uk/media/3639947/Cornwall-

SFRA-Level-1-FINAL-version-Dec-09.pdf

2. Surface Water Management Plan Technical Guidance March 2010, Defra

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/69342/

pb13546-swmp-guidance-100319.pdf

3. Drainage Guidance for Cornwall Council, v2, January 2010

http://www.cornwall.gov.uk/media/3639948/Drainage-Guidance-for-Cornwall-Council-

Jan2010-final.pdf

4. East Cornwall, Catchment Flood Management Plans, June 2010 https://www.gov.uk/government/publications/east-cornwall-catchment-flood-management-plan

5. South West River Basin Management Plan, Environment Agency, 2008

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/292791/gesw0910bstp-e-e.pdf

6. Proposed solar park development at Treisaac Farm, St Mawgan, Cornwall; Flood

Risk Assessment Incorporating Sustainable urban Drainage System, 2011

7. FRA “Aerohub enterprise zone @ Newquay Cornwall, airport drainage strategy &

flood risk assessment, 2012. http://www.cornwall.gov.uk/media/3628654/Newquay-

Aerohub-Concept-drainage-strategy-FRA-incl-Foul-Utilsa.pdf

8. The Sewerage Rehabilitation Manual; WRc

9. BS 8582:2013, Code of practice for surface water management for development sites

10. Ciria 738a, Managing urban flooding from heavy rainfall – encouraging the uptake of

designing for exceedance

11. Ciria 697, The SuDS manual

12. Ciria 609, “Sustainable Drainage Systems”

13. South West Geotechnical, 2013, Newquay Cornwall Airport, Aerohub Enterprise Zone: Geotechnical and Geo-environmental Investigation.

http://www.cornwall.gov.uk/media/3628654/Newquay-Aerohub-Concept-drainage-strategy-FRA-incl-Foul-Utilsa.pdf

http://www.cornwall.gov.uk/media/3628654/Newquay-Aerohub-Concept-drainage-strategy-FRA-incl-Foul-Utilsa.pdf



Appendix A – Background Documents 1. Drainage Guidance for Cornwall Council, v2, January 2010 This Guidance considers the impact that drainage can have on flood risk. It complements Cornwall Councils Strategic Flood Risk Assessment - Level 1 (SFRA 1) which considers wider flood risk. This is “an area within Flood Zone 1 which has critical drainage problems and which has been notified… [to]…the local planning authority by the Environment Agency”. NQY is not within a critical drainage area.

2. East Cornwall, Catchment Flood Management Plans, June 2010

Catchment Flood Management Plans (CFMP’s) are intended to help understand scale and extent of flooding now and in the future and set policies for managing flood risk within these catchments. Newquay town is identified as having some properties at risk of flooding in a 1:100 year storm, the policy for this sub-catchment is principally to ensure that the guidelines of PPS25 (now Technical Guidance to the NPPF) are adopted along with adopting a SWMP policy for major developments around Newquay. 3. Cornwall Council Local Development Framework Strategic Flood Risk Assessment Level 1, November 2009 A Strategic Flood Risk Assessment (SFRA) is a tool for planning authorities to identify and evaluate the flood risk in their area. Information from the SFRA will form the basis for applying the sequential test to the selection of sites for development, with the aim of directing development to areas at lowest risk of flooding. This SFRA forms part of the evidence base for the emerging Cornwall Local Development Framework (LDF) and will help form the basis for preparing appropriate policies for flood risk management. The SFRA covers the county of Cornwall and has a planning time horizon extending to 2026. This SFRA references various data bases to provide details of flood risk in the area. The extract below indicates that the NQY site is at low flood risk and falls within Flood Zone 1. The NQY site is not a critical drainage area and similarly, the streams downstream of NQY are not defined as critical drainage areas.



Figure 6: Cornwall SFRA flood zones. Source: http://mapping.cornwall.gov.uk/website/sfra

4. River Basin Management Plans River Basin Management Plans (RBMPs) are prepared to implement the Water Framework Directive (WFD). The Environment Agency published a draft South West RBMP for consultation in December 2008. It sets out the current chemical, biological and ecological status of water bodies in the South West river basin district and sets objectives for individual catchments, to be met by 2015 and beyond. It divides the South West RBMP district into nine inland planning catchment groups that are broadly similar to the Catchment Flood Management Plan districts. The RBPM districts in Cornwall are: West Cornwall, East (North) Cornwall and Tamar. For the Menalhyl and the Porth Stream, the overall status and ecological status are both currently classified as moderate. The Porth Stream aims to achieve good ecological status by 2027 and the Menalhyl aims to achieve good chemical status by 2015 and good ecological potential by 2027 (it is classified as heavily modified). All the local coasts are classified as having moderate ecological status and are designated under the EU Bathing Water Directive This site principally drains south to the Porth, and north to the Menalhyl. Figure 7 below indicates the status of catchment water features.



Figure 7: Ecological status/potential of rivers, canals and surface water in the North Cornwall catchments (NTS). Source: RBMP https://www.gov.uk/government

5. Safeguarding of Aerodromes The Airport Operators Association & General Aviation Awareness Council, Advice Note 6, Potential Bird Hazards from Sustainable Urban Drainage Schemes (SuDS), recommends avoiding the use of features that would attract birds in the vicinity of airports. This is primarily related to permanent water features and areas which would attract bird life, which should be avoided.



Appendix B – Recent NQY Site Studies

1. Solar Park: In 2011 a Flood Risk Assessment (FRA) was undertaken for the solar park to the

west of the Aerohub site; “PROPOSED SOLAR PARK DEVELOPMENT AT TREISAAC FARM,

ST MAWGAN, CORNWALL; FLOOD RISK ASSESSMENT INCORPORATING SUSTAINABLE

URBAN DRAINAGE SYSTEM”. This recommended the installation of infiltration swales of

0.15m base width and 0.15m depth. The total length of these swales was 850m to provide a

storage volume of 85m3.

2. Aerohub Business Park: In 2012 an Environmental Statement and FRA “AEROHUB

ENTERPRISE ZONE @ NEWQUAY CORNWALL, AIRPORT DRAINAGE STRATEGY &

FLOOD RISK ASSESSMENT” was undertaken for CDC. This FRA concluded and

recommended the following:

Quantity - The site is at low risk of flooding, provided that appropriate SuDS drainage

systems are implemented to mitigate increased runoff from the proposed development.

Quality - Pollution control must be considered and the appropriate treatment procedures put

in place for the construction stage and the permanent works.

Amenity can be gained through the use of open swales and ponds where appropriate to

enhance landscape features and bio-diversity whilst also improving water quality.

Adoptable highway drainage shall conform to CC guidance and discharge via suitable SuDS

systems to a suitable attenuation/infiltration feature(s) at the north, north-west sides of the

site. This shall drain surface water via an infiltration feature but where ground conditions

prevail can adopt a maximum allowable discharge to the stream of 6.8l/s/ha of impermeable

surface.

Individual plots and associated impermeable areas, including related public realm

areas, shall drain surface water via soakaway features, such as permeable car parks; but

where conditions prevail can adopt a maximum allowable discharge from the plots to the

stream of 6.8l/s/ha of impermeable surface, or where less than 5 l/s/plot, be limited to 5

l/s/plot.

Individual plot owners shall be responsible for pollution and storm water discharge

control from their specific plot.

SuDS designs shall follow the principles of the SuDS Manual, (Ciria 697) and the

guidance within the NPPF, including adherence as required to the Building

Regulations. A 30% allowance for climate change is to be included in new storm

drainage design at a 100 year storm event; 10% for a 30 year event.

All highway and other storm drainage shall discharge towards the stream and be kept

separate from existing highway drains. Storm drainage from development plots shall

preferably drain towards the stream via green corridors through SuDS features such as

swales and/or filter drains.

Adoptable drainage works shall be constructed in accordance with Cornwall Council

specifications, otherwise in accordance with Sewers for Adoption 7th edition.

All designs shall be discussed in advance, and ultimately approved by, Cornwall

Council or their delegate.

This approach to the stormwater drainage should satisfy a flexible Masterplan, but will

need to be carefully monitored by CDC to ensure that appropriate common

infrastructure is put in place and that future sites are developed in accordance with this

drainage strategy.



3. Newquay Cornwall Airport, Draft Masterplan Strategic Environmental Assessment Report,

November 2008.

This considered the following key objectives:

Protecting and enhancing all water supplies and resources

Promoting the efficient use of water

Minimising flood risk and improving flood control infrastructure

The principal conclusions regarding water were summarised as:

Ensure that high quality, sustainable design and sustainable construction, including a

consideration of flooding and transport, is central to any proposals for redevelopment.

Adopt an Integrated Water Management Strategy

Ensure pollution-prevention, management and mitigation measures for effects on

surface water features take place during the construction phase.

Undertake drainage capacity investigations and maximise the use of SuDS

throughout the development area following best practise guidance (CIRIA SuDS

Manual) appropriate for an Airport (e.g. avoiding Birdstrike).



Appendix C – Summary of Meeting of “Partners”

Meeting of Partners to discuss options and strategies for the future development of the NQY site.

Location: CDC Truro office

Date: 22 May 2014

Attendees:

Dave Watkins, Cornwall Council

Simon Jeffery, Environment Agency

Jackie George, Cornwall Development Company

James Evans, Cornwall Development Company

Christopher Uzzell, Parsons Brinckerhoff

Apologies:

Steve Gardner, Newquay Cornwall Airport

The site:

There are no known flood issues at the site or downstream

There is a flood defence scheme at St Mawgan which appears successful

The Porth tributary has some erosion issues and cannot accept further treated foul discharge

There is no source protection zone in the area, so SuDS drainage should be suitable

The area within the red-line boundary is owned by Cornwall Council, with the exception of the search and rescue site. Development plots will be leased under design & build arrangements for development. Cornwall Council will be responsible for the design and maintenance of drainage systems. In terms of future development, Development Zones 1 and 2 are likely to be developed first.

Options were considered for how individual development plots should be dealt with and given the 2.5km length of the NQY site, the proposed plots would best be considered on an individual basis, albeit under a consistent framework of design, operation and maintenance parameters.

The site was deemed to be split in to 3 components, with initial suggestions considered for a surface water drainage approach:

The existing runway; which should ideally be kept separate from future developments and where a better understanding of existing drainage is required, and where upgrading could benefit the quality and quantity of runoff.

Development to the south; whereby a drainage approach similar to that adopted for the Aerohub FRA strategy could be adopted.

Development to the north and west; with drainage primarily to infiltration features.

Issues to be considered include a better understanding of how the existing drainage networks function and how these could be improved, e.g. interceptors, emergency isolation controls and what happens to de-icing chemicals.

Quality of runoff is deemed important and the various stages of the SuDS “train” would assist.

Ponds or other features which could attract birds to the area are to be avoided as per the CAA Safeguarding of Aerodromes Advice Note 6.