0

Stranraer Flood Protection Scheme: A case Study

Juan Fernandez, Simon McGee, Alasdair Fraser

MouchelThe Beta Centre Stirling University Innovation ParkStirling, FK9 4NFScotland, UK

4th International Symposium on Flood Defence:Managing Flood Risk, Reliability and VulnerabilityToronto, Ontario, Canada, May 6-8, 2008

1

Introduction

- Stranraer is located in South West Scotland, in the Dumfries and Galloway Council

- Population of around 13,000- Ferry port connection- Historical flooding issues- October 2000 event- Scottish Water and Council competences - Drainage Area Plan Stranraer

October 2000 flooding around the Sheuchan Burn Stranraer Location

2

Stranraer Watercourses

- Black Stank- Town Burn- Laundry Burn- Sheuchan Burn- Surface water

sewers

Stranraer watercourses

3

Data Gathering

- Site visits- Topographic survey

- Watercourse survey- Floodplain survey- Structural survey- 3D survey

- CCTV survey- DAP survey

- Manhole survey- Pumping Station survey- CCTV survey- CSO survey

Stills from Millburn Court CCTV Survey (John Bunting, EEC - 7 July 2005)

Stranraer topography

4

Data Gathering

- Hydrology- Rainfall data from 4 raingauges (MET office, 2000)- Flood Estimation Handbook (FEH) methodology

- Climate Change (Price and McKenna, 2003)- Extreme sea-water levels for Stranraer (HR Wallingford, 2002)- Joint probability assessment (DEFRA, 2006)

Current Estimated Peak Flows (m3/s) Return Period (year) 2.33 5 10 25 50 100 200 500

Black Stank 3.16 4.38 5.24 6.66 7.83 8.98 10.35 12.48 Town Burn 1.26 1.62 1.88 2.22 2.4 2.53 2.65 2.81

Reach B 1.09 1.58 1.89 2.34 2.81 3.27 3.82 4.68 Reach A 1.06 1.57 1.89 2.36 2.75 3.21 3.77 4.63 Sheuchan Burn Whole 2.5 3.66 4.39 5.46 6.42 7.51 8.78 10.76

Laundry Burn 1.22 1.82 2.21 2.77 3.26 3.73 4.37 5.35

Estimated Peak Flows (m3/s) for Stranraer Watercourses

Return Period (years)

Extreme water level (m AOD)

1 2.65 10 3.00 25 3.14 50 3.23 100 3.38 250 3.52

Extreme Water Levels for Stranraer

5

Hydraulic Modelling

- Combination of different hydraulic software packages

- HEC-RAS (1D – open watercourses)

- InfoWorks CS (1D – long culverts and drainage system)

- MIKE21 (2D – overland flow)

- Watercourses and sewage system interactions

- Water depths were predicted at every single flooded property

6

Hydraulic Modelling – Upper Town Burn

- Highly modified- Wholly culverted- CCTV survey- InfoWorks Modelling- Draining assessment- Outputs for 1D/2D

70

MH

9W

136

MH

9V

220

MH

9U

300

MH

9T

333

MH

9S

403

MH

9R

452

MH

9Q

500

MH

9PM

H9N

562 628

MH

9J

762

MH

9L

809 899 1034 1062 1142 1220 12851307 1343

MH9X36.745

MH9W33.865

MH9V25.623

MH9U19.310

MH9T16.513

MH9S16.312

MH9R16.434

MH9Q16.464

MH9P-

MH9N-

--

--

MH9J-MH9K15.190

MH9L14.484

0559990114.802

0659090113.560

0659180413.079

--

-13.280

MH1412.993

0660200513.255

-12.250

--

--

--

MH9X.1375

34.90029.9900.471

MH9W.1375

29.99023.2900.567

MH9V.1375

23.29016.6500.497

MH9U.1450

16.65014.3800.486

MH9T.1600

14.38013.8600.769

MH9S.1750

13.86013.4300.749

MH9R.1750

13.43013.2600.600

MH9Q.1750

13.26013.0400.743

-----

MH9N.1750

12.88012.7900.434

-900---

-900

12.71612.5101.163

MH9K.1900

12.41011.9651.060

MH9L.1900

11.96511.8021.060

05599901.1105011.80211.3801.827

06590901.11200

11.38010.6702.683

-----

-----

06591819.11200

10.65910.2672.661

MH14.11200

10.26710.1051.732

06602005.1140010.1059.9702.951

-1200

---

-----

-----

-----

Nodeground (m AD)

Linkwidth (mm)us inv (m AD)ds inv (m AD)pfc (m3/s)

m A

D

9.0

37.0

11.0

13.0

15.0

17.0

19.0

21.0

23.0

25.0

27.0

29.0

31.0

33.0

35.0

m

Upper Town Burn inlets and profile

7

Hydraulic Modelling – Upper Town Burn 2D-Detailed topographic survey-Data Processing to get 3D model

-MIKE21 HD module-Manhole spills (from InfoWorks)-Assessment of several scenarios and return periods-Appropriate Manning numbers and grid size

3D model and survey data gathered for the Ochtralure area

2D model Ochtralure 1:200 year results

8

Hydraulic Modelling – Black Stank and Town Burn

-Topographic survey-Structures survey-Output from Upper Town Burn IW model-HEC-RAS modelling of both watercourses-Lateral structures definition-Peak flow in Town Burn caused by the Black Stank

Black Stank Flowing Into Town Burn (B. Eriksen, 2/1/98).

2400 0200 0400 0600 0800 1000 1200 1400 160001/01/1999

0.0

0.5

1.0

1.5

2.0

2.5Plan: final200yr07 River: TownBurn Reach: Upper Town RS: 1020

Time

Flow

(m3/

s)

Legend

Flow

Town Burn own peak

Black Stank caused peak

Town Burn culvertTown Burn 1:200 year predicted hydrograph

9

Hydraulic Modelling – Black Stank and Town Burn

1:200 year Town Burn and Black Stank combined model results

10

Hydraulic Modelling – Sheuchan Burn

- Topographic survey- CCTV survey- HEC-RAS modelling of Sheuchan A and B- InfoWorks CS modelling of Sheuchan culvert- MIKE21 modelling of Millburn Court manhole spills

Hillc

Palm y r

El mHou

Thi s tl ey c roft

Doon

gara

3 .0m

Pos ts

Pl ay Area

M

Ag new Park

TCB

Pos ts

Loch Ryan

Mean Low W

ater Spri ngs

FB

AGN EW CR ESCENT

A 718

HILLHEAD

Pos ts

BM 3.69m

Elvetha m

Pond

Glenti l t

Ca rraig

Uli dia

Benv ie

Pos ts

Li feboatStati on

Sand

Sand and Shing le

Sand and Shi ng le

Ca irnsmore

3.0m

18.9m

Sta

ElSub

Thornfi e ld

Av al on

BACKRAM

PART

Depot

Depo

t

BM 22.10m

LindenHous e

Hall

20.7mLam arton

Sheuc h anCo tt

Mans e

Park Hous e

The Hi gh Ki rkof Stranraer

LESWALT

HIGH R

OAD

Cemetery

Poin t Breez eBM 13.43m

CaribeSheuc hanCemetery

HIL LH EADRho vanian

Lodge

LBLady Stewart Park

Sand and Boul ders

El Sub Sta

Scaurbank

Gl enorc hy

Seaforth

WatersEdge

ARRA

N

THOR

NBAN

K RO

AD

WEST EN D TER RACE

B 73

7

COUR

T Seapark

Hawk s worth

Ry anbank

Birc hwood

The Moorings

Thornbank

A 718

2.7m

Sl ipway

Sand

BM 3.51m

Pos ts16.5m Sand a nd Shi n gle

Hannay' s H il l

BROADSTONE ROAD

Bri arbra e

Shea r-

water

Dunc li f fe

Cl a irmont

Rav enna

Whin latter

Hi gh Thornbank

M uizenberg

Wes trigKnoc k h aar

Cu i l-FionnHAWTHOR N ROAD

Ryan

leaFl

oatda

le

Glen

Otte

r

MS

Loc hlea

Nor-Is l e

Cra mond Dunm

ore

11.0 m

BM 13.04m

Bryn

Cl uden

Wes

tland

s

King

a rth

Rave

lston

Cra i g leac h

Fairfield

Dunk

e ld

Robin Hill

Farha

Braidwood

Seaforth

Greenm ount Sc otby

White Hous eTi gh-na-Mara

Fe nc e End

Birchgrov eCra iga the rie

Luya

Stone leigh

WHITE H OUSE ROAD

CHU RCHILL AVENU E

Am bles

San Marc o

Lori en

Chips

tead

Ki lm ory

Ca rnrose

Ra thla rg

LARG

RO

AD

Wind

b

Wi llowcroft

Cani s bay

Braefie ld

The Firs

ElSu

b Sta

L ARG AVENUE

Lynd

ale

Kas am a

Gl enk ens

Dorys ton

Da l ry

Craigoch

Lym phoy

Garage

Ark le

t

1 6.5m

Glen

i ffer

Wk s

19.5m

ElSubSta

LESWALT ROAD

MEADOWBANK

DALE CRESCENT

MAYFIELD AVENUE

Ros s ern

Englec ot

22.9m

HILLH

EAD

Falhaa r

B 737

El S

ub S

ta

Enc l if fe

The Stabl es

ENCL

I FFE

L ANE Ki nneil

Wi ndarra

17.1m

Woodl ea

BM 20.79m

QUEEN'S

Pos t

Om ega

Li nden

PARK

LAN

E

Mea n H

igh Wat er S pr i ngs

El Sub Sta

Posts

FORELAND PLACE

Swan Inn

(PH)

Hami l ton Court

FB

Sand and Shingl e

Spreads

Pi c ni c

M il lh ous e

Loc hend

M il lbu rnCou rt

Vil la

Area

SHEUCHAN STREET

Is s ues

Und

6.7m

Car Park

Kinty reCourt

WILLOWDEN ECRESC ENT

Ps

14.9m

Bowli ngGreen

BM 9.

32m

11.9m

3.7m

P

Seabank

Co ttageL och en d

As hgrov e

Bungalow

Sheuc han

PO

Highf iel d

Howpark

Darrochmhor

W indyb row

Parkhead

Sheena

Ancho rlea

Du rley

Ca stramont

Avoca Green

Gates

Club

By tor

Glen Fl ora

La i ngHous e

Cra ilo ch

HawthornBank

M ingary

Sandy way s

Craigal len

Col in da

Fourtrees

SeabankHous e

Prim ary Sc hool

RAND OLPH LANE

Ps

AILS

A CRE

SCEN

T

FINNART CRESCEN T

B 737

FOUN DRY LAN E

LESWALT HIGH RO

AD

DALRIADA AVENUE

MIL LFIELD AVENUE

SEABANK RO AD

21.3m

TCBLB

10.7m

ROWAN 'S H

ILL

OAKLAND AVENU E

LIDDESDALE ROAD

SPRING WELL ROAD

FINNART C

RES

LIDDESDALE

ENT

BM 19.62mAVENUE RO AD

CRAIG LEA AVENUE

Whitecro ft

Pen Hil l

Bona V

i sta

SeaforthNurs ery

Lin dumCraiglo ch

Buki t

Ora

ng

Aber

Fawnmo re

Wi ltonDean

Dunry an

M il leur

El don

Trentham

Lis m ore

Li ntrathen

Am bles i de

Ha mel and

Saarme n

Du nsc aith

Gle nis laCle strain

Lyna ire

Kil v ern

Cai rn

v iew

CR

Penry an

Cherrybank

Windrush

Col arn

L ad orven

Rowans Hill

RaymedeStra thmore

Torv aig

OAKLAND

WOOD

LANDRO

AD

WILLOWBANK

HAZEL GROVE

LAUREL GROVE

NUR SERY AVENUE

BM 20.37m18 .0m

BEEC

HWO

OD A

VENU

E

SE

8.2m

Inchyra

Wi ndarra

Anmaro

Mel ita

Chirma

Gl ens hie l

Ward Bdy

M ILLBANK ROAD

El Sub Sta

Ty ro l

CO RSEWALL CRESCENT

Sheuc hanBridge

BROOKF IELD CR

ESCENT

LEAFIELD

Dra in

Bra nd e lh ow

Da ima r

Homel and

ROWAN

'S HIL L CRESCENT

LB

Brae

Avon Beith

Heugh

SPRING BAN K R OAD

Cov i ngton

Gl enes k

Si nk s

Wi ndyridge

Drumj argonEl Sub Sta

WOO

DLA

NDR

OAD

NorthbraeGl engorm

CaladhGl as mont

Langdal e

Silv erdale

Ta yparkDuff ryn

Fairmile

In ver lei t hTo rcro ss

Frenchw ood

Fa ic an

Rub is law

Wem y s s

Mym

en sin ghKarori

Marn o ch

Ki nmo un tDru mlo gan

L och

Bank

Aodai

nn

Crai

gna ir Rowa nbrae

Sibb aldbie

Au chengith

The Anchorag e

The Sheil ing

M il hav en

Mea

ll an

CarnboM arc h

Ra n gi tot o

Sannox

Kel deen

As c og

Holmsle y

Ai ls a

Sherbro oke

L i ddes dale Hous e

Lidd es dale Cottage

Bungal owLiddes dal e

THE GROVE

BROOKF IEL D AVENU

E

BROOKFIEL D CR

ESCENT

Bu rnside

LEAFIELD

WOO

DLA

ND

ROAD

RI SE

Drai

n

Dra in

Aa rhauseCeud M il e

Fai lte

LIDDESDALE ROAD

SPRING BAN K R OAD

LEAF

IELD

Is s ues

Si nk s

Sink s

Is s ues

SpringbankCottage

Is s ues

Spri ngbank

Springb ank

Is s ues

Mas t

Coll ec ts

Is s ues

Track

Pond

Is s ues

y

Spring Bank Road Bridge

Liddesdale Farm

Structure 676

Structure 503

LegendWater Depths (m)

3.50.70.20.010

Masonry culvertTw in pipe culvertMain rectangular culvert

Sheuchan Burn area Sheuchan Burn 1:200 year results

11

Hydraulic Modelling – Laundry Burn

- CCTV survey- Totally culverted- Discharging into

the Town Burn- Reported capacity issues- No flooding predicted- Blockage issues

Laundry Burn location and 1:200 year profile

12

Wide Stranraer Results

Stranraer 1:200 year floodplain outline

13

Benefit / cost analysis

- Economic performance of flood protections schemes

- Benefits are measured in terms of the present value of damages avoided over the life of the scheme.

- Eight Flood Alleviation Schemes (FAS) identified through Stranraer Flood Study.

- For each FAS the following was considered in the modelling exercise:- Do nothing (current situation modelling results)- Do minimum- Do something (option modelling)

14

Stranraer Flood Alleviation Schemes (FAS)

Sand

Big Plant at ion

Blackpar ksI ndust r ial

Est at e

St ranraer Academ y

Loch Ryan

Sand

Loch Ryan

Loch Ryan

O cht r elur e

Black Stank

Black Stank

Town Burn

Laundry Burn

Town Burn

Sheuchan Burn

Sheuchan Burn

FAS-7: Localised Bunding

FAS-6: Town Burn Railway Culvert

FAS-8: Black Stank Mouth Diversion

FAS-2: Upper Sheuchan

FAS-3: Thorney Croft Inlet

FAS-4: Ochtralure Inlet

FAS-5: Stoneykirk Roundabout

FAS-1: Sheuchan Outfall

Legend

Watercourse

Predicted Floodplain

Historical Flooding

Flood Alleviation Scheme Option

Stranraer FAS areas

15

Stranraer Main Causes of Flooding

- Insufficient hydraulic capacity of culverts and inlets- Blocking issues in culverts and inlets.- Overland flow- Structural issues- Highly modified watercourses

Town Burn Downstream of Railway Culvert

16

FAS 1 and 2 – Sheuchan Outfall and Upper Sheuchan Burn- FAS 1 associated with flooding in lower Sheuchan due to lack of capacity- Structural issues- New Outfall designed.

- FAS 2 concerned with flooding along properties in Upper Sheuchan- Localised protection is the preferable option.

Sheuchan Outfall location and profile

17

FAS 3, 4 and 5 – Upper Town Burn- FAS 3 is associated with flooding in Thorney Croft Inlet whereas FAS 4 is

associated with Gallowhill Rise and Highcroft inlets- Inlets improvements is FAS 3 most practical solutions - Channel diversion is FAS 4 preferable option

- FAS 5 concerned with flooding in StoneyKirk Roundabout- Structural and hydraulic capacity issues.- Replacement not viable

FAS 4 diversion location and profile

18

FAS 6 - Town Burn Railway Culvert (Black Stank and Lower Town Burn)

- FAS 6 associated with flooding in the Station Road area (Town Burn)- Flooding caused by the Black Stank and Town Burn interaction- Poor culvert condition – Flow restriction

- Replacement of the railway culvert by a 750mm flow control - Modifications further downstream

Town Burn Railway Culvert

19

FAS 7 and 8 - FAS 7 associated with flooding in properties along the Black Stank- Localised protection proved to be the preferable option- FAS 8 concerned with alleviating flooding in the vicinity of properties at the

downstream end of the Black Stank- Diversion of the Black Stank peak flows

FAS 8 diversion option

12

25

39

1614

BURNSID

E TERRACE

Bishop Bur n

BM 4 .3 3m

De nv e r

Cairnv iew

Hi -Li te

Forf ie ld

Court

Loc hv ie wHous e

23

1

24

11

8 13

Bishop Burn Bridge

REPHAD C

RESCENT

LOCKVIEW ROAD

LOCHVIEW CRES

2

Chevron

1315

23

2

14

2a2b

Ay re

M ira

15

11

1

4

5

8

M are

Auld

Kildona n

Bishop

Burn

Cotts

1

2

1

7

9

Auchl and

Route AOption 2 - Excess Flow

20

Stranraer Discarded Options

Sand

Big Plant at ion

Blackpar ksI ndust r ial

Est at e

St r anr aer Academ y

Loch Ryan

Sand

Loch Ryan

Loch Ryan

O cht r elur e

Black Stank

Black Stank

Town Burn

Laundry Burn

Town Burn

Sheuchan Burn

Sheuchan Burn

Outfall Diversions

Culvert Replacement

Culvert Improvements

Storage

Storage

Black Stank & Town Burn Connector Channel

Railway Overflow

Cacthment Diversion to Ballyferry Burn

Open Section Culverted

Storage

Storage

Pipe Upsizing

Channel Realignment

Culvert Replacement

Channel Realignment

Storage

Legend

Watercourse

Surface water pipeFoul or Combined pipe

Discarded Option

21

Stranraer Preferable Options

Sand

Big Plant at ion

Blackpar ksI ndust r ial

Est at e

St r anr aer Academ y

Loch Ryan

Sand

Loch Ryan

Loch Ryan

O cht r elur e

Black Stank

Black Stank

Town Burn

Laundry Burn

Town Burn

Sheuchan Burn

Sheuchan Burn

FAS-8: Black Stank Outfall Diversion

FAS-7: Black Stank Bunding

FAS-6: Railway Culvert

FAS-5: Stoneykirk Roundabout Culverts

FAS-4: Ochtralure Diversion

FAS-1: Sheuchan New Outfall

FAS-3: Thorney Croft Inlet Improvements

FAS-2: Upper Sheuchan Bunding

Legend

Watercourse

Surface water pipeFoul or Combined pipe

Discarded Option

22

Summary and Conclusions

- A high level detail modelling identified properties at risk in Stranraer- Water depths were predicted at those properties - Eight flood alleviation schemes were assessed- Potential mitigation options were tested- A benefit/cost analysis approach was used- The diversion type option was the most viable for three FAS- Culvert or inlet improvements was the preferable options for other three FAS- Local bunding was the option chosen for two FAS