Drainage Statement on · 2016. 9. 29. · soakaways, infiltration trenches, permeable pavements,...

Prepared for

Norfolk County Council

Drainage Statement on:

Land west of Burlingham Road

South Walsham

RLC Ref. 161116 March 2016

alell20161643


Land west of Burlingham Road, South Walsham

Limitations

Rossi Long Consulting Ltd has prepared this Report for the sole use of Norfolk County Council (“Client”) in accordance with the Agreement under which our services were performed [letter dated 18 March 2016]. No other warranty, expressed or implied, is made as to the professional advice included in this Report or any other services provided by Rossi Long Consulting Ltd. This Report is confidential and may not be disclosed by the Client nor relied upon by any other party without the prior and express written agreement of Rossi Long Consulting Ltd.

The conclusions and recommendations contained in this Report are based upon information provided by others and upon the assumption that all relevant information has been provided by those parties from whom it has been requested and that such information is accurate. Information obtained by Rossi Long Consulting Ltd has not been independently verified by Rossi Long Consulting Ltd, unless otherwise stated in the Report.

The methodology adopted and the sources of information used by Rossi Long Consulting Ltd in providing its services are outlined in this Report. The work described in this Report was undertaken during March 2016 and is based on the conditions encountered and the information available during the said period of time. The scope of this Report and the services are accordingly factually limited by these circumstances.

Where assessments of works or costs identified in this Report are made, such assessments are based upon the information available at the time and where appropriate are subject to further investigations or information which may become available.

Rossi Long Consulting Ltd disclaim any undertaking or obligation to advise any person of any change in any matter affecting the Report, which may come or be brought to Rossi Long Consulting Ltd’s attention after the date of the Report.

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Copyright

© This Report is the copyright of Rossi Long Consulting Ltd. Any unauthorised reproduction or usage by any person other than the addressee is strictly prohibited.

Norfolk County Council Land west of Burlingham Road, South Walsham

Table of Contents

1 Introduction and Client’s Brief ......................................................... 5 2 Site Description ................................................................................. 6 3 Ground Conditions and Hydrology ................................................. 7 4 Existing Drainage .............................................................................. 9 5 Surface Water Drainage .................................................................. 10 6 Foul Drainage ................................................................................... 12 7 Conclusions and Recommendations ............................................ 13 8 Appendices ...................................................................................... 14 Appendix A – Preliminary Site Layout ......................................................................................... 15 Appendix B – Site Survey Drawing ............................................................................................. 16 Appendix C – Anglian Water Sewer Mapping ............................................................................. 17



Drainage Strategy March 2016 5

1 Introduction and Client’s Brief

1.1 We were instructed by NPS Group, on behalf of Norfolk County Council, to prepare a Drainage Statement for a proposed development at South Walsham.

1.2 Norfolk County Council is seeking Outline Planning Consent to develop the site for residential use and this report considers the drainage options available, taking into account National Planning Policy and the Building Regulations.

1.3 The preliminary site layout is shown on the drawing included at Appendix A.

1.4 This report is compiled with the benefit of our findings from desk study research and topographical survey information.




2 Site Description

2.1 The site is located on the west side of Burlingham Road in South Walsham, presently comprising an arable field. The Ordnance Survey grid reference for the site is TG359128. A location plan is shown below.

2.2 Ground levels on the site are falling towards the south-east corner with an approximate 3.0m fall across the site from the north-west corner. A site survey drawing is included in Appendix B.

2.3 The proposal for the site is for residential development with associated access road and landscaping.

Location Plan




3 Ground Conditions and Hydrology

3.1 British Geological Survey (BGS) mapping shows that the site is situated upon Superficial Deposits of Happisburgh Glacigenic Formation - Diamicton. The underlying bedrock geology is Crag Group – Sand and Gravel.

Geomap

The BGS describes Happisburgh Glacigenic Formation as a range of diamictons, sands and gravels, sands and laminated silts and clays. BGS hold no records of any nearby boreholes.

3.2 Site investigation has not yet been undertaken; however, by reference to CIRIA C753, The SuDS Manual 2015, Table 25.1 gives guidance on typical infiltration coefficients based on soil texture. For ‘loamy sand’ - slightly silty clayey SAND, typical infiltration coefficients are given in the range of 1.0 x 10-4 to 3.0 x 10-5 m/sec. For ‘loam’ – very silty clayey SAND, typical infiltration coefficients are given in the range of 1 x 10-7 to 5 x 10-6 m/sec.




3.3 The Environment Agency website shows the site is not within a Groundwater Source Protection Zone (SPZ). In terms of groundwater vulnerability, the site is within an area classified as Secondary B and a Principal Aquifer with respect to superficial and bedrock geology respectively.

Groundwater Plan

3.4 The nearest watercourses are situated west of the site at Hare Fen, which drains north towards South Walsham Broad. South Walsham Broad connects to the River Bure to the north via Fleet Dike.

THE SITE

GROUNDWATER SPZ




4 Existing Drainage

4.1 A plan showing the location of the Anglian Water public foul sewer is included in Appendix C with an extract shown below. This shows a 150mm diameter foul sewer that is located in Burlingham Road. There are no surface water sewers shown on the Anglian Water mapping.

4.2 We are not aware of any formal land drainage system serving the existing site. A shallow channel has been cut along the east site boundary running parallel with the rear garden fenceline of the houses fronting Burlingham Road. There is no apparent outfall to this channel, which is dry suggesting that any runoff soaks naturally into the ground.

4.3 A ditch is situated adjacent to Burlingham Road fronting some of the existing dwellings. It is understood that this ditch drains across Burlingham Road via. a culvert to Hare Fen. Hare Fen is located on land to the west of Burlingham Road flowing north towards South Walsham Broad and local ditch flow is assumed to follow this route.

Extract of Anglian Water Map




5 Surface Water Drainage

5.1 The proposal for the site is for a development of residential housing.

5.2 The Building Regulations 2000 Approved Document H3 requires that rainwater from buildings and paved areas shall discharge to one of the following, listed in order of priority:

a) An adequate soakaway or some other adequate infiltration system; or where that is not reasonably practicable,

b) A watercourse; or where that is not reasonably practicable,

c) A sewer.

The Building Regulations therefore adopt a design philosophy that accords with sustainable drainage systems (SuDS).

5.3 National Planning Policy also requires that, for planning applications relating to major development (development of 10 dwellings or more) or equivalent non-residential or mixed development, sustainable drainage systems for the management of run-off are put in place, unless demonstrated to be inappropriate.

Planning Practice Guidance considers what sort of sustainable drainage system should be considered. Generally, the aim should be to discharge surface run-off as high up the following hierarchy of drainage options as reasonably practicable:

1) Into the ground (infiltration);

2) To a surface water body;

3) To a surface water sewer, highway drain or another drainage system;

4) To a combined sewer.

Particular types of sustainable drainage systems may not be practicable in all locations.

This hierarchy follows the same order of priority of Approved Document H3 of the Building Regulations.

5.4 Norfolk County Council (NCC) is the Lead Local Flood Authority (LLFA) for this area and the Local Planning Authority (LPA) should consult with the LLFA on surface water drainage. NCC has published guidance on the use of sustainable drainage systems, which is an approach to managing surface water run-off which seeks to mimic natural drainage systems and retain water on or near the site, as opposed to traditional drainage approaches which involve piping water off-site as quickly as possible. SuDS involves a range of techniques including soakaways, infiltration trenches, permeable pavements, grassed swales, ponds and wetlands. SuDS offers significant advantages over conventional pipe drainage systems in reducing flood risk by attenuating the rate and quantity of surface water run-off from a site, promoting groundwater recharge and improving water quality and amenity.




5.4 It is a requirement of the National Planning Policy Framework (NPPF) that the development does not increase flood risk elsewhere. Regulators will normally require that, for the range of annual flow rate probabilities up to and including the 1% annual probability (1 in 100 year event), the developed rate of run-off should be no greater than the undeveloped rate of run-off for the same event. Exceptions only apply where it is not practical to achieve this due to the size of the hydraulic control unit. The purpose of this is to retain a natural flow regime in the receiving watercourse and not increase peak rates of flow for events of an annual probability greater than 1%.

5.5 Site investigation has not yet been undertaken but BGS mapping shows that the site is situated on superficial geology of Happisburgh Glacigenic Formation – Diamicton. The BGS describes the Diamicton as sands and gravels and laminated silts and clays. By reference to C753, The SuDS Manual, typical soil infiltration rates in the range of 1.0 x 10-7 to 1.0 x 10-4 m/sec are suggested for loam and loamy sand. For preliminary purposes and subject to site investigation at the detailed design stage, a sustainable approach to surface water management is proposed using ground infiltration for the disposal of surface water run-off.

5.6 Accordingly, surface water run-off from the proposed site will be managed as follows:

Surface water run-off from the roof areas will be directed to soakaways designed for the 100 year event +30% allowance for climate change;

The private driveways and parking areas will be constructed using permeable paving designed for the 100 year event +30% allowance for climate change;

The estate road will be designed to cross fall towards a filter strip falling to a drainage

swale. Any overflow from the drainage swale will be directed to highway soakaways.

5.7 Soakaways, permeable paving, filter strips and drainage swales provide a sustainable approach to surface water management, providing storage of peak flows and water quality benefits. The above drainage strategy will ensure that the requirements of the NPPF will be met.

5.8 BRE Digest 365 porosity testing should be completed prior to any detailed drainage design. In the event that infiltration rates do not form an adequate basis for design of a sustainable drainage system, then an off-site discharge to the local watercourse will be required. Any discharge should be limited to the equivalent ‘greenfield’ run-off rate for the pre-developed site for all storms up to and including the 1 in 100 year event plus 30% allowance for climate change.




6 Foul Drainage

6.1 Under H1 of the Building Regulations, a public sewer is the preferred option for all foul drainage. Only where a public sewer is not available should other alternatives be considered.

6.2 Anglian Water records confirm that the existing foul sewer system is available in Burlingham Road. Foul drainage from the development should connect to the existing public sewer at MH 0801. A pumping station may be required.

6.3 Connection to the public foul sewer will be subject to the approval of Anglian Water under Section 106 of the Water Industry Act.




7 Conclusions and Recommendations

7.1 The proposal for the site is for a development of residential dwellings, an access road and landscaping.

7.2 From BGS mapping, site ground conditions are recorded as Happisburgh Glacigenic Formation – Diamicton. Diamicton can be varying material ranging from sand, silts and clays with varying drainage characteristics. Subject to on-site testing at the detailed design stage, a sustainable approach to surface water run-off is proposed with soakaways for roof water run-off and permeable paving for the private drives and parking spaces. The proposed estate road will drain to soakaways via a filter strip and roadside swales. The use of sustainable drainage via infiltration will ensure that the proposals will not increase flood risk both on the site or elsewhere. Should subsequent testing confirm that infiltration drainage is not a viable option, then off-site discharge would be required to be restricted to the pre-development site ‘greenfield’ run-off rate.

7.3 Foul drainage should connect to the Anglian Water foul sewer in Burlingham Road, subject to approval via a Section 106 application to Anglian Water.




8 Appendices




Appendix A – Preliminary Site Layout




Appendix B – Site Survey Drawing

Stn

9001

8.322

Stn

9002

7.858

Stn

9003

8.752

Stn

9004

7.920

Stn

9002

10.003

8.54

8.45

8.37

8.33

8.26

8.25

8.14

8.12

8.21

8.27

8.39

8.72

8.69

8.78

8.82

8.87

8.84

8.81

8.74

8.68

8.64

8.15

8.06

8.03

8.10

7.98

7.88

7.93

7.93

8.43

8.45

8.40

8.88

8.85

9.15

8.95

8.96

O

H

E

L 16.89m

O

D

O

H

E

L 17.91m

O

D

c/l fence 1.00m

h

8.29

8.79

9.53

8.19

8.13

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1

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0

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h

8.32

8.50

8.37

8.33

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c

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8.36

8.35

8.30

8.24

8.34

8.24

c/b fence 1.70m

h

11.18

10.93

10.78

10.62

10.25

10.13

c/l fe

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ce

1

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0

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h

10.08

9.79

9.38

8.72

8.70

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1

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0

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m

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8.43

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c

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1

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8

0

m

h

8.10

7.67

7.66

7.45

7.40

7.96

8.02

8.04

IC

CL: 7.98

7.95

8.02

8.03

8.31

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10.97

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8.322

Stn

9002

7.858

Stn

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10.003

7.42

7.39

7.42

7.53

7.52

7.64

7.69

7.79

7.75

7.66

7.51

7.47

7.45

7.48

7.53

7.51

7.45

7.39

7.46

7.50

7.51

7.62

7.71

7.78

7.44

7.38

7.29

7.35

7.34

7.29

7.38

7.91

7.82

7.64

7.67

7.55

7.58

7.65

7.69

7.64

7.63

7.66

7.69

7.62

7.56

7.61

7.63

7.86

7.74

7.68

7.68

RS

7.89

7.85

7.62

7.70

7.63

7.64

7.55

7.78

8.00

8.04

7.82

7.69

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/

l

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1

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0

0

m

h

7.74

7.94

8.32

8.89

9.41

9.66

9.82

9.55

9.16

8.58

8.08

7.87

7.98

8.29

8.95

9.46

9.78

10.15

10.29

10.01

9.72

9.30

8.74

8.26

8.14

8.37

8.60

9.19

9.67

9.93

10.25

10.49

10.60

10.37

10.13

9.84

9.44

8.84

8.50

8.60

8.88

9.57

9.95

10.20

10.43

10.67

10.82

10.85

10.65

10.42

10.28

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10.19

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Project N

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Appendix C – Anglian Water Sewer Mapping

Thi

s pl

an is

pro

vide

d by

Ang

lian

Wat

er p

ursu

ant i

ts o

blig

atio

ns u

nder

the

Wat

er In

dust

ry A

ct 1

991

sect

ions

198

or

199.

It m

ust b

e us

ed in

con

junc

tion

with

any

se

arch

res

ults

atta

ched

. The

info

rmat

ion

on th

is p

lan

is b

ased

on

data

cur

rent

ly r

ecor

ded

but p

ositi

on m

ust b

e re

gard

ed a

s ap

prox

imat

e. S

ervi

ce p

ipes

, priv

ate

sew

ers

and

drai

ns a

re g

ener

ally

not

sho

wn.

Use

rs o

f thi

s m

ap a

re s

tron

gly

advi

sed

to c

omm

issi

on th

eir

own

surv

ey o

f the

are

a sh

own

on th

e pl

an b

efor

e ca

rryi

ng o

ut a

ny w

orks

. The

act

ual p

ositi

on o

f all

appa

ratu

s M

US

T b

e es

tabl

ishe

d by

tria

l hol

es. N

o lia

bilit

y w

hats

oeve

r, in

clud

ing

liabi

lity

for

negl

igen

ce, i

s ac

cept

ed b

y A

nglia

n W

ater

for

any

erro

r or

inac

cura

cy o

r om

issi

on, i

nclu

ding

the

failu

re to

acc

urat

ely

reco

rd, o

r re

cord

at a

ll, th

e lo

catio

n of

any

wat

er m

ain,

di

scha

rge

pipe

, sew

er o

r di

spos

al m

ain

or a

ny it

em o

f app

arat

us. T

his

info

rmat

ion

is v

alid

for

the

date

prin

ted.

Thi

s pl

an is

pro

duce

d by

Ang

lian

Wat

er S

ervi

ces

Lim

ited

(c)

Cro

wn

copy

right

and

dat

abas

e rig

hts

2016

Ord

nanc

e S

urve

y 10

0022

432.

Thi

s m

ap is

to b

e us

ed fo

r th

e pu

rpos

es o

f vie

win

g th

e lo

catio

n of

Ang

lian

Wat

er p

lant

onl

y. A

ny o

ther

use

s of

the

map

dat

a or

furt

her

copi

es is

not

per

mitt

ed. T

his

notic

e is

not

inte

nded

to e

xclu

de o

r re

stric

t lia

bilit

y fo

r de

ath

or

pers

onal

inju

ry r

esul

ting

from

neg

ligen

ce.

Pum

ping

Sta

tion

Man

hole

Inle

t

Out

fall

Sew

age

Tre

atm

ent W

orks

Fou

l Sew

er

Fin

al E

fflue

nt

Dec

omm

issi

oned

Sew

er

(Col

our

deno

tes

efflu

ent t

ype)

(Col

our

deno

tes

efflu

ent t

ype)

Sur

face

Sew

er

Com

bine

d S

ewer

(Col

our

deno

tes

efflu

ent t

ype)

(Col

our

deno

tes

efflu

ent t

ype)

(Col

our

deno

tes

efflu

ent t

ype)

Dat

e: 2

4/03

/16

Sca

le: 1

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0D

ata

upda

ted:

04/

12/1

5M

ap C

entr

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0,31

2800

(c)

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wn

copy

right

and

dat

abas

e rig

hts

2016

Ord

nanc

e S

urve

y 10

0022

432

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tew

ater

Pla

n A

2O

ur R

ef: 1

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1

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dy.n

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ross

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uk

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16

Ris

ing

Mai

n

Priv

ate

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er(C

olou

r de

note

s ef

fluen

t typ

e)

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hole

Ref

eren

ceLi

quid

Typ

eC

over

Lev

elIn

vert

Lev

elD

epth

to In

vert

0001

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31.

73

0801

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--

0901

F8.

787

7.36

71.

42

0902

F10

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8.77

51.

58

1001

F7.

516

5.38

32.

133

1901

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391

6.27

61.

115

1902

F-

--

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hole

Ref

eren

ceLi

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160324_161116_Drainage StatementSignature page160324_161116_Drainage StatementAppendix A Site Plan160324_161116_Drainage StatementAppendix B Survey160324_161116_Drainage StatementAppendix C AW Mapping

Drainage Statement on · 2016. 9. 29. · soakaways, infiltration trenches, permeable pavements,...

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Transcript of Drainage Statement on · 2016. 9. 29. · soakaways, infiltration trenches, permeable pavements,...