proposed development of solar photovoltaic panels and associated ...

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proposed development of solar photovoltaic panels and associated ...

PROPOSED DEVELOPMENT OF

SOLAR PHOTOVOLTAIC PANELS

AND ASSOCIATED WORKS AT

SOUTHFIELD FARM,

BRIDGEHAMPTON

FLOOD RISK ASSESSMENT

INCORPORATING SUSTAINABLE

DRAINAGE SYSTEM


PROPOSED DEVELOPMENT OF

SOLAR PHOTOVOLTAIC PANELS

AND ASSOCIATED WORKS AT

SOUTHFIELD FARM,

BRIDGEHAMPTON

FLOOD RISK ASSESSMENT

INCORPORATING SUSTAINABLE

DRAINAGE SYSTEM

Report No. Issue Detail Originator Date Checked By Date

03 JCh 18/03/2013 JC 18/03/2013

For: British Solar Renewables Job No: J-4119.12-FM

Higher Hill Farm Date: March 2013

Butleigh Edition: 03

Glastonbury

Somerset

BA6 8TW


CONTENTS

Item Content Page No.

1.0 Introduction 2

2.0 Site Location and Description 3

2.1 Site Location 3

2.2 Existing Usage 3

2.3 Proposed Usage 3

3.0 Existing Hydrology 5

4.0 Flooding Mechanisms 7

4.1 Groundwater Flooding 7

4.2 Overland Sheet Flow 7

4.3 Fluvial (River) Flooding 8

4.4 Tidal Flooding 8

4.5 Flooding as a Result of Development 8

5.0 Design Standards 10

5.1 The CIRIA SUDS Manual 10

5.2 Building Regulations Part H 10

5.3 The Wallingford Procedure 10

5.4 National Planning Policy Framework 10

6.0 Proposed Sustainable Drainage Scheme (SuDS) 11

6.1 Overview 11

6.2 Percolation Testing 11

6.3 Surface Water Drainage 11

6.4 Maintenance Requirements 13

6.5 Summary 13

7.0 Affect on Adjacent Sites 14

8.0 Residual Risks After Development 15

9.0 Conclusions and Recommendations 16

APPENDICES

Appendix A

Appendix B

Appendix C

Site Location Plan

Proposed Site and Drainage Layout

Calculations


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1.0 INTRODUCTION

British Solar Renewables Ltd are currently investigating the development of Solar PV farm

sites around the UK. They are currently investigating the possibility of developing agricultural

land near Bridgehampton, Yeovil. The current proposal is to accommodate a photovoltaic

solar park of around 23.0ha.

Inspection of the Environment Agency (EA) indicative flood mapping shows that a small

section of the development site boundary is located within Flood Zone 3, however, no panels,

infrastructure or fencing will be located in this area, therefore the developable area of the site

is located entirely within Flood Zone 1.

As the development site is over 1 hectare (ha) in area, any application for planning permission

must be accompanied by a Flood Risk Assessment (FRA). The primary aim in this situation is

to assess the surface water runoff produced by the development and if necessary outline

measures to ensure flood risk is not increased downstream of the site.

In order to address this requirement British Solar Renewables Ltd has commissioned H 2 OK

Systems Ltd. The objective of this appointment is to prepare a FRA and a Surface Water

Drainage Strategy for the development in accordance with the best practice principles of

Sustainable Drainage Systems (SuDS), the National Planning Policy Framework and its

associated technical guidance regarding flood risk. This report describes the findings of the

study.

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2.0 SITE LOCATION AND DESCRIPTION

2.1 Site Location

The proposed solar park development is to take place on agricultural land approximately 7km

north of Yeovil. The subject site (red line boundary) covers an area of approximately 23.0 ha,

over 3 fields. The Ordnance Survey Grid Reference for the centre of the site is approximately

ST 57500 23621.

In a wider context, the site is largely surrounded by agricultural land. An unnamed road runs

along the western boundary of the site, Southfield Farm is located on the northern boundary

of the site.

With respect to topography, the northern half of the site falls from north-south from an

elevation of approximately 30 mAOD to 23 mAOD, the southern section of the site falls from

the north-east to south-west from an elevation of approximately 25 mAOD to 21 mAOD.

The site location is included in Appendix A and in figure 2.1 below.

Site Location

2.2 Existing Usage

Figure 2.1 Site Location Plan

The site currently consists of 3 agricultural fields totalling 23.0ha, typically used for arable

crops.

2.3 Proposed Usage

It is proposed to install a solar PV farm consisting of approximately 46,800 modules, which

are supported by a table/racking system which typically holds 40 or 80 modules each.

The 80 module steel support tables will be supported by a steel pile system, providing 12

support posts for each table, the 40 module tables will have 7 support piles. The piles are

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likely to be around 0.2m diameter and will elevate the tables between 0.8m and 2.4m above

ground level, allowing vegetation to grow below the panels.

The 994mm high by 1642mm wide modules will be aligned horizontally in rows of 4. A 22mm

gap will allow water to drain off each module (the 22mm gap surrounds all sides of each

module) an indicative detail of the panels is included in Appendix B. Therefore the

drainage path across the units will be less than 1m. This is shown in Figure 4.1.

The modules will be served by 7 inverter stations as indicated in Appendix B. These will be

accessed by 4m wide access tracks which will be constructed using permeable methods (likely

to be grass trackways). Further landscaping works are also put forward within the design

proposal, such as hedging, fencing and planting arrangements. There are 3 switch gear units,

2 are located in the southernmost field and 1 is located in the north-west field.

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3.0 EXISTING HYDROLOGY

The development site is located in adjacent to the Hornsey Brook, the River Cam is located

500m north of the proposed site; however, the proposed development land falls towards the

Hornsey Brook. The Hornsey Brook joins the River Yeo approximately 500m the west of the

site. The River Yeo joins the River Parrett near Langport before discharging into the Bristol

Channel at Burnham-on-sea.

According to FEH CD-ROM3, the upstream catchment of the development site is

approximately 14.23km 2 see Figure 3.2 below.

The existing greenfield surface water runoff rate for the site has been assessed using the

ADAS 345 method and WinDes Microdrainage software. The rates for several return periods

are included in Appendix C. A 1 in 1 year return period event produces a runoff rate of 117.9

l/s. A 1 in 100 year event is expected to produce a runoff rate of around 365.8 l/s, including

the effects of climate change (+20% to SAAR values) these values increase to 156.4 l/s and

485.4 l/s respectively. Assessment of the design rainfall for the site; for a 1 in 100 year

event, applying a 6 hour storm duration, gives a design rainfall depth of 65.6mm.

Analysis of the Environment Agency flood map shows the subject site has a small section

located within Flood Zone 3 associated with the Hornsey Brook; however, solar panels and

associated infrastructure have been removed from this area, effectively the developable area

of the site is located within Flood Zone 1. The relevant extract from the Environment Agency

indicative flood map is shown in Figure 3.1 below.

Main River (River Cam)

Flood Zone 3

Flood Zone 2

Site Location

Hornsey Brook

Figure 3.1

Environment Agency Indicative Flood Zone Map

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Site Location

Hornsey Brook

River Yeo

Figure 3.2

FEH CD-ROM 3 Extract

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4.0 FLOODING MECHANISMS

A number of possible flooding mechanisms have been considered at the site, and are

discussed below.

4.1 Groundwater Flooding

There are limited sources of information available to assess groundwater flood risk as

groundwater risk mapping is still in its infancy. Groundwater levels can be affected by periods

of sustained heavy rainfall which can cause groundwater levels to rise, potentially resulting in

periods of sustained flooding. This mechanism of flooding can be related to the presence of

aquifers. The EA have produced indicative mapping identifying and classifying areas based on

Bedrock and Superficial deposits.

Figure 4.1

EA Indicative Aquifer Mapping

Although no ground investigations have been conducted to establish groundwater levels, the

elevation of the site relative to surrounding features, suggests that ground water flooding

should not be a significant issue. It is expected that the nearby watercourses will act as

sumps, that will aid in draining/lowering groundwater levels.

Assessment of OS mapping shows no springs or issue points within the site boundary or in the

vicinity of the site.

Given the nature of the development, it is considered that groundwater flooding does not

pose a significant risk to the development site and will not be considered further within this

report.

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4.2 Overland Sheet Flow

The site is set in a rural environment with fields surrounding the majority of the site. The risk

of any significant overland flows being generated offsite that can affect the site are

considered to be small. Furthermore minor overland flows are not considered to pose a

significant threat to the site’s operation or infrastructure.

The majority of the site is covered with agricultural / permeable ground which provides

varying degrees of infiltration; these factors will serve to reduce the potential for overland

flows to develop.

Surface water runoff generated by the development of the site is considered further in

Section 6 of this report.

4.3 Fluvial (River) Flooding

The solar panels have been positioned outside of the flood zone within the site boundary,

therefore the EA’s Indicative Flood Map shown in Figure 3.1 illustrates that the entire

development is located within Fluvial Flood Zone 1 (low risk). This implies the site has lower

than a 1 in 1,000 year (>0.1 AEP) probability of being affected by fluvial flooding. As such the

fluvial flooding will not be considered further within this report.

4.4 Tidal Flooding

The site is well outside of any areas of tidal influence, located at a minimum elevation of

around 21m AOD. Given the nature of the site, and surrounding topography, tidal flooding has

not been considered further within this report.

4.5 Flooding as a Result of Development

The proposed development has the potential to introduce impermeable area around the site

where the land was previously permeable. This could have the potential to increase the runoff

rates across the site which could increase the flood risk to adjacent sites.

Following further inspection of the development layout (shown in Appendix B) it can be seen

that the proposed solar park infrastructure only introduces a small area of impermeable

surfaces through the foundations of the solar panel arrays, the inverter stations

and sub stations.

It is anticipated that rain falling on each solar panel will runoff the panels and flow/infiltrate in

the sheltered rain shadow area underneath the down-slope modules. The 994mm high by

1642mm wide modules will be aligned horizontally in rows of 4. A 22mm gap will allow water

to drain off each module (the 22mm gap surrounds all sides of each module). The existing

grass covered areas, which are likely to encourage / provide infiltration will only be marginally

reduced. This is demonstrated in figure 4.1 below.

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994 mm

Figure 4.1 Flow Path over PV modules

Any access and maintenance roads are proposed to be constructed from permeable materials

(likely to be grass trackways) and therefore will not contribute to increasing runoff rates from

the site. The impermeable area totals approximately 996m 2 , which is only around 0.4% of the

total site area. The drainage system need only contend with the volume of runoff from this

area to ensure flood risk is not increased. The potential for a sustainable drainage system to

be installed within the development is outlined further in Section 6.0 of this report.

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5.0 DESIGN STANDARDS

Design of the site drainage infrastructure and Sustainable Urban Drainage System (SuDS) is

to be carried out in line with best practice and to industry standard design procedures. A

number of publications, including design guidance and best practice guidance will be applied

to different components of the final infrastructure. The sections below provide an overview of

the design standards to be used on this project for various aspects of the infrastructure

design.

5.1 The CIRIA SUDS Manual

This document is a comprehensive publication covering design, construction, operation and

maintenance of SuDS. The advice and best practice outlined in this document has been

utilised in the design of the site SuDS features, which have been detailed in this report.

5.2 Building Regulations Part H

Building Regulations Part H ‘Drainage and Waste Disposal’ covers the design and installation

of surface water and foul water systems. All private drainage including pipes, manholes, down

pipes, and other drainage infrastructure on the site should be designed and installed in

accordance with this document.

5.3 The Wallingford Procedure

Developed by HR Wallingford this publication covers the design of urban drainage systems. In

addition, the document includes regional rainfall data for use in design for varying return

period events.

Basic sizing calculations for the swales and the estimation of the runoff volumes have been

made using this method. Further modification of these calculations, to enhance the design,

was carried out using WinDes software which is also based in part on the Wallingford

Procedure

5.4 National Planning Policy Framework

The National Planning Policy Framework (NPPF) contains the policy relating to the appropriate

assessment of flood risk within the UK. The associated technical guidance provides further

details on the definitions, classifications and constraints used to apply national policy to new

developments.

It contains details on flood zone definition, site specific FRA’s, vulnerability classifications,

appropriate development, climate change allowances, residual risk management, flood

resilience, the sequential test and the exception test.

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6.0 PROPOSED SUSTAINABLE DRAINAGE SCHEME (SUDS)

6.1 Overview

SuDS is a concept that incorporates long term environmental and social factors in order to

design surface water drainage systems, in accordance with the ideals of sustainable

development. SuDS takes into account the quantity and quality of surface water runoff, and

the value of surface water to the urban and rural environments. Many existing urban drainage

systems can cause problems of flooding, pollution or damage to the environment, so it is the

aim of the SuDS to avoid this in the future.

Most proposed urbanisation creates impermeable surfaces which will need drainage solutions

to remove surface water runoff. Traditionally it is only quantity of flow that has been

accounted for in drainage solutions, preventing floods locally by conveying the water away

from the site swiftly in underground pipes. These traditional methods frequently alter natural

flow patterns which can lead to problems elsewhere in the catchment area. More recently,

water quality issues must be accounted for, in order to avoid pollutants from urban areas

being transported into rivers or groundwater.

Other aspects, such as water resources, community facilities, landscaping and provision of

wildlife habitats have been largely ignored; a well designed and well managed SuDS can offer

the following benefits:

• management of runoff flow rates, reducing the environmental impact of urbanisation

• maintenance or enhancement of water quality

• consideration to the requirements of the local community

• enhancement of biodiversity in urban watercourses

• maintain the natural groundwater level

6.2 Percolation Testing

In view of the relatively small areas of impermeable surface being introduced across the site,

there will be a negligible impact in the runoff rates, resulting from the development.

Therefore percolation testing has not been conducted.

In addition, during the design of the SuDS across the site, it has been assumed that the

primary function of the SuDS will be the interception, storage and redistribution of the runoff

from the site with infiltration into the system a secondary benefit.

6.3 Surface Water Drainage

Environmental Considerations

The nature of the development means that runoff could originate from the solar panels

arrays, solar panel foundations, inverters and sub-station hut. The runoff from the panels

poses a low environmental risk. It has been assumed that any additional foul/industrial waste

from the maintenance and operation of the park will be disposed of elsewhere.

The use of heavy plant on wet arable/grazing land may cause the topsoil to be disrupted

which in-turn can pose a pollution risk to local watercourses. An intense rainfall event may

result in silt laden runoff being discharged from the site polluting local

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watercourses. Although the swales may provide some benefits, it is advised that silt fences

are installed to during the construction phase of the project to intercept silt laden runoff.

SuDS Design

The impermeable areas across the site are small, therefore no formal drainage is required. As

such a pragmatic approach has been taken to promote infiltration and create storage across

the site. This involves the installation of swale and scrape features running parallel to the site

contours within downstream areas of the site. These features will intercept flows, create

storage, attenuate runoff and promote infiltration across the site.

It is anticipated that rain falling on each solar panel table will runoff the panels and

flow/infiltrate in the sheltered rain shadow area underneath the down-slope modules.

However where the panels are aligned at variance to the contours then intensification of the

runoff into rivulets or small channels could occur beneath the lower end of the panels.

Conceivably this could result in a slight increase in the amount of runoff when compared to

the undeveloped condition. The swales and scrapes discussed below have been put in place to

deal with this effect.

In addition the SuDS design will not consider the runoff from the access and maintenance

roads as these will be constructed of unbound crushed stones / gravel or similar permeable

materials, which will allow infiltration of water on these areas. The access roads will therefore

not increase surface water runoff rates from the site.

The enclosed layout indicates the solar PV tables will support up to 80 modules each. Based

on 12 support posts for each table 80 module table and 7 posts for the 40 module table which

are set on 0.2m diameter screw piles, the increase in impermeable area has been calculated

as 230m 2 . Including the 7 new inverter stations with a plan area of around 50m 2 each and the

3 switchgear units of 50m 2 each, the total impermeable area is around 830m 2 . Applying a

20% increase for inconsistencies gives around 996m 2 . Therefore the volume of runoff from

the total impermeable area has been calculated to be approximately 78.4m 3 for a 6 hour

duration, 1 in 100 year rainfall event.

In order to adopt a pragmatic approach and promote infiltration across the site a swale

system is proposed to managed the runoff. It is therefore proposed to install swales of 0.2m

base width and 0.3m depth with side slopes of 1 in 4 at the down slope edges of the site.

The total length of these swales is expected to be approximately 1,030m, providing a storage

volume of 412m 3 . The layout of these swales is shown in more detail in Appendix B. In order

to ensure interception of flows and a maintainable system, an oversized system has been

implemented which will serve to reduce the runoff rate to less than the pre developed rates.

Thus reducing the potential flood risk created by the site.

It is proposed to install scrape features at specific locations on the site to limit the erosion risk

posed by the intensification of rainwater as a result of the solar arrays, in line with advice

given by the Environment Agency. The scrapes will also improve interception, storage and

infiltration across the site. The indicative layout in Appendix B shows the proposed locations

for the scrapes.

Provided the scrapes and swale structures outlined above are installed prior to other on site

construction works, it is anticipated that the runoff from the construction phase would be

suitably managed. The scrapes/swales will also serve to improve the water quality of runoff

discharged from the site.

For more detail on calculations of runoff refer to Appendix C.

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6.4 Maintenance Requirements

Maintenance of the drainage network is essential to ensure optimal performance of the

drainage elements. As such maintenance requirements for the drainage system will include

but not be limited to:

• Inspection and cleaning of the swales and scrapes to ensure that the capacity and

infiltration rates are maintained.

The drainage system is likely to remain in private ownership; the site operator would

therefore be responsible for the maintenance of the drainage features within the site. The

developer of the site should make this responsibility clear to the site operator by providing a

maintenance plan for the development.

6.5 Summary

Percolation testing has not been conducted at the proposed development site, due to the

small area of impermeable surface introduced by the development. It is anticipated that there

will be only a slight increase in runoff from the development which can be adequately

managed on site by the swales outlined in Section 6.3.

The conceptual design of a surface water drainage scheme has been carried out based on the

current proposed development layout. This has demonstrated that the surface water runoff

from the development can be managed entirely on site so as not to unduly affect the flood

risk to neighbouring areas. Furthermore the proposed system serves to reduce runoff rates to

less than the undeveloped rate.

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7.0 AFFECT ON ADJACENT SITES

As outlined in Section 6.0, the extent of the impermeable areas introduced across the site by

the proposed development is extremely small. Therefore any additional runoff from the

impermeable areas will be small and more than adequately managed by the swale system

outlined in Section 6.3. As such there will be no impact on the nearby watercourses and

neighbouring sites as a result of the proposed development.

In addition, the pragmatic approach to the design of the swales will provide an improved

storage and interception capacity. This capacity will reduce flood risks to adjacent sites that

are created by surface water runoff, when compared to the pre-development situation.

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8.0 RESIDUAL RISKS AFTER DEVELOPMENT

The capacity of the scrapes and swales has been oversized to manage the small additional

runoff and to promote infiltration across the site. As such the scrapes/swales have ample

capacity to contend with runoff from the impermeable areas of the site under rainfall events

in excess of the 1 in 100 year storm. Despite the relatively large capacity of the swales there

is still a risk that shallow surface water pooling could occur across the site in events in excess

of the 1 in 100 year storm.

The drainage system proposed has been specifically designed for the volume of surface runoff

resulting from the solar panel foundations and inverter stations. Therefore, any unauthorised

future connections into the site drainage network will potentially overload the system.

Therefore any future development on the site, beyond the current proposal, should be

suitably planned and considered, especially if new impermeable areas are to be introduced to

the site.

As long as these factors are considered in the design of the development there is the capacity

to manage any associated residual risks.

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9.0 CONCLUSIONS AND RECOMMENDATIONS

The study has investigated the mechanisms for flooding at the proposed Solar PV site on land

at Southfields Farm. It has identified that the development site is not in any direct risk of

flooding. The solar panels and the associated infrastructure will be positioned outside of the

Flood Zones 2 and 3, therefore the whole development is in Flood Zone 1 (low risk). As such

this report has focused on reducing the risks associated with surface water runoff.

Developments over 1ha in size; in Flood Zone 1, are required to ensure flood risk is not

increased to areas downstream of the development site. This study has investigated the

impact that the development proposal will have on the surface water runoff rates from the

site. It has been shown that the impermeable area created by the development is very small,

relative to the site area and as such will have a small impact on the runoff rates from the site.

The SuDS scheme proposed will effectively reduce the runoff rate to less than the

undeveloped (current) runoff rates, as storage and infiltration on site will be improved. A

Swale and Scrape system; shown in J-4119.12-FM 3001, has been proposed to allow the

interception, redistribution and infiltration of the flows from across the site,

If the recommendations made in this report are followed during the development of the site,

there is likely to be a reduction in the surface water discharge rate from the site and therefore

flood risk will be minimised.

On the basis of this report and by reference to EA flood maps, it is concluded that the site is

located within Flood Zone 1 and is therefore not at any direct risk of flooding. The National

Planning Policy Framework and associated Technical Guidance therefore states ‘All uses of

land are appropriate in this zone’ from a flooding perspective. Consequently, with regard to

flood risk, the proposed development is entirely appropriate in this area.

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APPENDIX A

SITE LOCATION PLAN


APPENDIX B

PROPOSED SITE AND

DRAINAGE LAYOUT


IH C

357343.812 E

123578.085 N

23.200 L

29.17

29. 8

29.87

29.57

29.64

22. 4

2.40

2.26

22.28

IH D

357554.741 E

123848.005 N

26.696 L

24.28

IH A

357594.498 E

123321.360 N

21.386 L

24.42

2.81 22.84

2.83

24.66

2.80

24.85

24.83

21.14

24.91

24.83

21.21

21.36

21.24

21.29

21.21

25.01

24.98

21.22

25.21

25.25

21.24

25. 0

25. 0

25.21

21.28

25.01 25.14

21.43

25.07

21.36

21.41

25.41

21.39

25.42

21.27

21.49

21.51

25.45

21.48

21.55

21.29

21.35

21.51

25.59

21.48

21.49

21. 4

21. 4

25.72

25.78

25.97

21.71

21.79

26.18

26. 3

21.14

21.05

21.19

26.36

26.39

26.53

26.56

26.64

26. 6

26.73

26.85

26.75

26.74

IC 26.82

22.36

2.38

2.54

2.52

24.63

24.51

24.39

24.39

24.45

24.46

24. 4

24. 5

24.45

24.50

24.49

24.43

24.45

IH B

357910.538 E

123420.043 N

24.440 L

23.83

23.82

24.10

23.73

23.69

23. 7

23.52

23.65

23.67

23.34

23.60

23.43

23.29

2.94

El Sub Sta Ordnance Survey, (c) Crown Copyright 2012. All rights reserved. Licence number 100020449

29.5m

Chantry House

Chantry

Depot

31.2m

Pond

Southfield Farm

Pond

Hornsey Brook

Pond

Pond

Pond

Collects

Pond

Pond

Ordnance Survey, (c) Crown Copyright 2012. All rights reserved. Licence number 100020449

Pond

29.5m

30.6m

27.7m

Lambrook

Bungalow

Snowdrops

Lambrook

Cottage

The Hawthorns

24.0m

23.2m

29.17

26.80 26.85

29.28

29.15

29.17 29.32

Canopy Level Approx 34.0

26.54 26.72

Canopy Level Approx 36.7

29.5m

Canopy Level Approx 34.3

Slurry Ponds

Canopy Level Approx 35.4

Canopy Level Approx 35.4

Canopy Level Approx 38.7

Canopy Level Approx 32.1

Canopy Level Approx 35.3

Canopy Level Approx 35.1

Canopy Level Approx 33.1

25.7425.86

Canopy Level Approx 39.2

Canopy Level Approx 31.7

Canopy Level Approx 33.3

Canopy Level Approx 34.7

Canopy Level Approx 39.3

Canopy Level Approx 35.9

30.6m

Canopy Level Approx 42.7

Canopy Level Approx 33.9

Pond

Canopy Level Approx 31.5

24.98

Canopy Level Approx 30.5

24.94

24.58

Canopy Level Approx 34.0

24.59

24.62

24.50

24.43

24.38

24.7824.76

Canopy Level Approx 36.3

Canopy Level Approx 37.3

Pond

Canopy Level Approx 35.2

Canopy Level Approx 36.0

Pond

Canopy Level Approx 39.4

Pond

Collects

G

Canopy Level Approx 33.2

G 22.82

Inv = 22.12

Slu ry Pit

Slu ry Ponds

Canopy Level Approx 33.9

Canopy Level Approx 30.0

Canopy Level Approx 31.5

Canopy Level Approx 30.6

Canopy Level Approx 32.7

Canopy Level Approx 32.3

Canopy Level Approx 33.2

Canopy Level Approx 32.4

Canopy Level Approx 31.4

22.43 2.47

Canopy Level Approx 31.0

Canopy Level Approx 39.5

Canopy Level Approx 30.3

Canopy Level Approx 39.9

Canopy Level Approx 27.9

Canopy Level Approx 29.7

Canopy Level Approx 30.2

Canopy Level Approx 27.9

Canopy Level Approx 28.9

Canopy Level Approx 33.6

21.47 21.56

Canopy Level Approx 28.5

21.52 21.85

Canopy Level Approx 31.7

Canopy Level Approx 35.6

Canopy Level Approx 30.3

Canopy Level Approx 31.5

Canopy Level Approx 35.8

Canopy Level Approx 34.7

Pond




Sewage Treatment

Industrial Effluent Treatment

AD/Biogas




Flood Risk Management/SUDS

Infrastructure

Service and Maintenance

Canopy Level Approx 33.3

Canopy Level Approx 31.0



Canopy Level Approx 29.5




Canopy Level Approx 30.3

Canopy Level Approx 34.9

Pond

22.57 22.58

Canopy Level Approx 30.4

Canopy Level Approx 29.4

Canopy Level Approx 30.4

Canopy Level Approx 28.0

Canopy Level Approx 25.7

21.23 21. 3

Canopy Level Approx 30.0

21.18 21.18

Canopy Level Approx 27.1

Canopy Level Approx 27.1

Canopy Level Approx 30.5

Canopy Level Approx 29.3

Canopy Level Approx 26.5

Canopy Level Approx 26.2

Canopy Level Approx 32.3


APPENDIX C

CALCULATIONS


H2OK Systems Limited Page 1

Nanjerrick Court

Allet, Truro

TR4 9DJ

Date 19/02/2013 15:11 Designed by jchapman

File

Checked by

Micro Drainage

Source Control W.12.6.1

ADAS 345 Mean Annual Flood

Input

Area (ha) 26.200 Soil Type Factor (St) 0.800

Length (m) 300.000 Paved Area (%) 0.000

Average Slope (1:X) 50.0 Region Number Region 8

AAR (mm) 750

Results

l/s

Q0 - Peak Flood Flow 133.6

Total Q0 133.6

QBAR 151.2

Q100 years 365.8

Q1 year 117.9

Q2 years 133.6

Q5 years 185.9

Q10 years 225.3

Q20 years 264.4

Q25 years 277.6

Q30 years 288.2

Q50 years 320.2

Q100 years 365.8

Q200 years 430.9

Q250 years 450.5

Q1000 years 591.1

©1982-2011 Micro Drainage Ltd


H2OK Systems Limited Page 1

Nanjerrick Court

Allet, Truro

TR4 9DJ

Date 19/02/2013 15:12 Designed by jchapman

File

Checked by

Micro Drainage

Source Control W.12.6.1

ADAS 345 Mean Annual Flood

Input

Area (ha) 26.200 Soil Type Factor (St) 0.800

Length (m) 300.000 Paved Area (%) 0.000

Average Slope (1:X) 50.0 Region Number Region 8

AAR (mm) 900

Results

l/s

Q0 - Peak Flood Flow 177.2

Total Q0 177.2

QBAR 200.6

Q100 years 485.4

Q1 year 156.4

Q2 years 177.2

Q5 years 246.7

Q10 years 298.8

Q20 years 350.8

Q25 years 368.2

Q30 years 382.3

Q50 years 424.8

Q100 years 485.4

Q200 years 571.6

Q250 years 597.7

Q1000 years 784.2

©1982-2011 Micro Drainage Ltd


Volume of Runoff Caculations

Client: AEE

Engineer: H2OK Consultants

Southfield Farm PV

Location:

Site

Site:

Date:

Southfield Farm PV Site

19/02/2013

SITE INFORMATION

Pre-development total area

Pre-development permeable area

Pre-development impermeable area

Post-development total area

Post-development permeable area

Post-development impermeable area

RAINFALL EVENT INFORMATION

Return period

Whole area greenfield runoff rate inclusive of 20% increase due to climate change (see attached MicroDrainage

calcs (SAAR values multiplied by 1.2))

Post-Development Greenfield Area runoff rate inclusive of 20% increase due to climate change (see attached

MicroDrainage calcs (SAAR values multiplied by 1.2))

Duration of rainfall event

Depth of Rainfall (calculated using Wallingford Procedure including 20% increase for climate change)

262000 m²

262000 m²

0 m²

262000 m²

261004 m²

996 m²

100 year

485.4 l/s

485.4 l/s

6 hours

78.7 mm

RUNOFF CALCULATION

Pre-development permeable area runoff

10484640 litres

Pre-development impermeable area runoff

0 litres

Total pre-development runoff

10484.6 m³

Post-development permeable area runoff

10484640 litres

Post-development impermeable area runoff

78385.2 litres

Total post-development runoff (without mitigation)

10563 m³

Difference in runoff 78.4 m³

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