Stranraer Flood Protection Scheme: a Case Study

Stranraer Flood Protection Scheme: A case Study

Juan Fernandez, Simon McGee, Alasdair Fraser

Mouchel 4th International Symposium on Flood Defence: The Beta Centre Managing Flood Risk, Reliability and Vulnerability Stirling University Innovation Park Toronto, Ontario, Canada, May 6-8, 2008 Stirling, FK9 4NF Scotland, UK 0 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 1 Stranraer Watercourses - Black Stank -Town Burn - Laundry Burn - Sheuchan Burn - Surface water sewers

Stranraer watercourses 2 Data Gathering

-Site visits - Topographic survey - Watercourse survey - Floodplain survey - Structural survey -3D survey - CCTV survey - DAP survey - Manhole survey Stranraer topography - Pumping Station survey - CCTV survey -CSO survey

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

3 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 Extreme water Return Period (year) 2.33 5 10 25 50 100 200 500 (years) level (m AOD) Black Stank 3.16 4.38 5.24 6.66 7.83 8.98 10.35 12.48 1 2.65 Town Burn 1.26 1.62 1.88 2.22 2.4 2.53 2.65 2.81 10 3.00 Reach B 1.09 1.58 1.89 2.34 2.81 3.27 3.82 4.68 25 3.14 Sheuchan Burn Reach A 1.06 1.57 1.89 2.36 2.75 3.21 3.77 4.63 50 3.23 Whole 2.5 3.66 4.39 5.46 6.42 7.51 8.78 10.76 100 3.38 Laundry Burn 1.22 1.82 2.21 2.77 3.26 3.73 4.37 5.35 250 3.52

Estimated Peak Flows (m3/s) for Stranraer Watercourses Extreme Water Levels for Stranraer

4 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

5 Hydraulic Modelling – Upper Town Burn

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

37.0

35.0

33.0

31.0

29.0

27.0

25.0

23.0 m AD

21.0

19.0

17.0

15.0

13.0

11.0 MH9N MH9J MH9L MH9W MH9V MH9U MH9T MH9S MH9R MH9Q MH9P 9.0 m 70 136 220 300 333 403 452 500 562 628 762 809 899 1034 1062 1142 1220 12851307 1343 Link MH9X.1 MH9W.1 MH9V.1 MH9U.1 MH9T.1 MH9S.1 MH9R.1 MH9Q.1 - MH9N.1 - - MH9K.1 MH9L.1 05599901.1 06590901.1 - - 06591819.1 MH14.1 06602005.1 - - - - width (mm) 375 375 375 450 600 750 750 750 - 750 900 900 900 900 1050 1200 - - 1200 1200 1400 1200 - - - us inv (m AD) 34.900 29.990 23.290 16.650 14.380 13.860 13.430 13.260 - 12.880 - 12.716 12.410 11.965 11.802 11.380 - - 10.659 10.267 10.105 - - - - ds inv (m AD) 29.990 23.290 16.650 14.380 13.860 13.430 13.260 13.040 - 12.790 - 12.510 11.965 11.802 11.380 10.670 - - 10.267 10.105 9.970 - - - - pf c (m3/s) 0.471 0.567 0.497 0.486 0.769 0.749 0.600 0.743 - 0.434 - 1.163 1.060 1.060 1.827 2.683 - - 2.661 1.732 2.951 - - - - Node MH9X MH9W MH9V MH9U MH9T MH9S MH9R MH9Q MH9PMH9N - - MH9J MH9K MH9L 05599901 06590901 06591804 - - MH14 06602005 - - - - ground (m AD) 36.745 33.865 25.623 19.310 16.513 16.312 16.434 16.464 - - - - - 15.190 14.484 14.802 13.560 13.079 - 13.280 12.993 13.255 12.250 - - - 6 Upper Town Burn inlets and profile Hydraulic Modelling – Upper Town Burn 2D -Detailed topographic survey -Data Processing to get 3D model

3D model and survey data gathered for the Ochtralure area

-MIKE21 HD module -Manhole spills (from InfoWorks) -Assessment of several scenarios and return periods

-Appropriate Manning numbers and grid size 2D model Ochtralure 1:200 year results

7 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

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

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

Flow

2.0

1.5 Flow (m3/s) Flow

1.0

0.5

0.0 2400 0200 0400 0600 0800 1000 1200 1400 1600 01/01/1999 Time

Town Burn 1:200 year predicted hydrograph Town Burn culvert 8 Hydraulic Modelling – Black Stank and Town Burn

1:200 year Town Burn and Black Stank combined model results 9 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

b Bi The Firs d r n ch i gr Cr ov Fence End Ro s s e rn W D a e Greenmount l a i t A ga Sc otby 22.9m E S th e d O r b ie u a R e W Englecot S t B G i ll r s o Ha wk s wo rt h a p R w L ef i c A ie A r ld h o Lorien R L ft G C W A H Sand V St IT E o n E NU e l H E eig OU White House h SE Tigh-na-Mara Canisbay K L u R ilm ya O o Ambles AD Ryanbank R ry a t hla rg Legend Ca Sa r C n nr H M os U ar Birchwood e RC c o B HI r L L aid A High Thornbank Sl ipway w VE Water Depths (m) o o N The Moorings 19.5m L d U ym E Cluden ph o y Se Farha afo rt BM 3.51m C h ra igo ch R Thornbank il l Da o b H 3.5 l in ' s ry H Whinlatter ay ill nn Ha D Du n c l i f fe or ys s t B on Ka d Pos ts s am a n R 0.7 a O l S t Knockhaar 16.5m s A a n e D d Westrig S W Ravenna S T a h O n Glenkens w e d M C M a a N E h u u E S L t i H i t r 0.2 l- z - A E r F A e e h D S io W n r R i O W a n be n W n T r O g B A g HO g B A LT n R A le N R i N ri D K O K R a A O Clairmont rb D A r F D a a e 0.01 ir f ield Lochlea

D G 1 A l Ga ra g e 6. e 5 O m n y R o r 0 K c No r-Is l e h Craigleach N y Sand and Boulders A 2.7m B e r N o R Wks m O n C H W ra u E t m D T ST r o E le e n N k f d D r f TE Masonry culvert i R M A n R A e AC Y l E F G MS IE e L al Loch Ryan D d BM 13.04m A n V y E L 11.0m Tw in pipe culvert N U n y E r B n t o Seaforth s l A 7 e 18 v a ld Waters r Main rectangular culvert R e k e 7 ea t 3 Edge n l e l 7 D u n O A a a n L D d B S E y t e l c C R oa a El RE l G u S F rb Sub C a EN n Sta T k E l S u N b T A Seapark R S R t U a R T A O H C E d LB n G U R

O V C E O 6.7m RSE Pond WA LL CRE SCE NT

Kinty re C a r

Court P ar Issues k Si nk s El Sub Sta Sheuchan Bridge

Glenesk Pi c ni c Sand and Shingle Northbrae Covington MILLBANK ROAD Area Glengorm Ca l a d h Co l l e c ts Gl a s m o n t l e gda M an B Liddesdale Cottage L il l R C bu Issues Spreads O o r u n FB Liddesdale House R O rt u e K b l F Sannox rda is e IE ood ilv T w la S L nch a W S re M F w D y h p a

B B e C a e I a r Keldeen r R n r d R R S n b k O O v B H L r e E E o o d Lochend O O r U w o le S y D K k K C C As c og i Vil la W u F e F F t T E H h f a IE IE o L a f C A t N ILLOWDEN E e r W R M Liddesdale Farm L L N r o ic y T E Millhouse r c c K n S H D r a D C S e S o h n i a p o n E T C A r s m N R n i l s F T n m R V E H g o a s E E s E ig u ir k N n T le n 8.2m m Liddesdale S h M a y U t e K C L b Bungalow D il a ag W R y a e o E E B e t m r c t a r u u S a N h o o M n Seabank t n e r m C T g e n i n e IL r g l D a d House i s o A L i lo S t O o n g F w R p t a K C o g M IE h n N R r A D L i B n a A G D g r N n I L R s P Tyrol R A L Co l i n d a Wemyss o S I A V y c A n s Ai ls a h e D E re v A a rt o N ou n A U ir F e B V E Craigallen e E i Ch i rm a N PO th U ir E a R n o F g S i i w O b a a D R r b Heugh A C a n Penryan E C b Brae RO r A ld L K a r N MingaryHa wth o rn L u b a E la in A i S nis a B lo A c i e e str A N h e R I C W Gl e SE Bank c n Cl h D e O c h A nd n h e L l a Sandyways g W y r T e Laing ts P A r r a m os L i a y H H n P th N b e A a IG arm Ho u s e 3 n a C 'S k H S . 7 E H R h m B IL Melita W O ait u r L c S ns T i A ns a id h C nd D Du n e Th e R r d e S E u m a A h B S sh 0.7 n ei Homelandr 1 d Sand D n l a C OA ch in S R L o g n E h K ID r d N i n N D ag e g A E e T Co l a rn As hgrov e le G B S lh IN DA o PR L M w S e E il Ceud Mile s R ha u O v L Failte ha AD en a a r d A D R o March Carnbo a o rv Bank im Torvaig w e Spring Bank a a n r n Lifeboat Windarra s H Stati on ill n Dunryan l l a n l i n R W a Pos ts a a y L e d m L Road Bridge i I o M n e A d H de Sheuchan G y 'S l r e Pos ts i N Milleur B n S d A n In a S y n nd g W Primary School F e tr a a a Wi lton to Sw H) n O l (P d th R o r Sh m Dean r in o a g le re Eldon E e N r Y LA o DR Anmaro nm Trentham N w OU a F F P Ps Dr u mj a E rgo n Pos t l Sub G St l e Ps a n w s ie TCB B hie v Issues M l rn 2 i 0 a . C W Pond k 18.0m 37 h ra c m Seaforth El Sub Sta T Springbank D it e Cottage A Nu rs e ry c H ro a O a f m R st t Lismore 1 i D i 1. lt V 9 o Si nk s N n D a m A n C 3.0m L L o o Mast IE B u D rt F Pl ay Area O C FB A O Pen Hil l g l E n u L Lintrathen 2m b L W a ID r 3 D O . E 9 S i t w D k Ambleside ro M A u b B

L B T y Ag new Park E d Bowli ng

N n Issues R i

E Gr e e n OA W D C S d

E a e Kil v ern R h Da rk a

C r a n ro P e A e ch h R

S A m S N L h D I o Pos ts E r O

A U L D P E L N H E A N BM 3.69m E L A A O A n F V L i R N IE A E a L K r D D R D A D A N O b a R e C P A r rle k I L O r r S a o a i h E D W m g F c p A 3 L lo I n w G O H . in N y 1 c N A o le N O C 2 d h H r E u A u W E m W R D C M E T R O E B A C t S K T R n Ca CE Issues L C E o r N Springbank A B S m ra T N C a ig D E tr a G Pos ts L N s c r H A B a o G e 14.9m I V T C v a e Linden B L E A t n e LH N e nv U s H i E E ig re e A Elv hf o D et ie m U ha m 3.0m D B l d ns G li Sink s r ir le di a 7 a n a i 37 Om e g a C ti n lt A 718 B S D R H Springbank E a 7 A ho IL L O R t 3 E van H E A C S E 7 ia A Structure 503 K N n D LH L T b A Kinneil El A L R u L P A S L I o Sub N I H in t D D N l E Bre D F ez A IN E e E F Sta V BM 19.62m S F I BM 13.43m a Issues E D r L a N A C U L Avalon g VE E N Enc l iffe n L O E RO E o E R o A G A D W D D r F L The Stables a IE ZE O darra in L A O Wi n D H D Ca ri b e UE Ce m e t e ry Sheuchan L N 17.1m A VE Lodge N A A BM 20.7 Ce m e t e ry RD LE 9m Thornfield O IG D Palm y r RA OA A C L R D L WE ING PR S B Thistleycroft Issues 20.7m A C Lamarton K NK L R A Falhaar E BM 22.10m A B Woodlea S Manse M W W De p o t O A P El m LL L A I T R Ho u Structure 676 W T H The High Kirk IG H 18.9m of Stranraer R O A Ha l l D

E t NU o VE p A e Y Linden R D SE House UR N illc L Sheuchan H A U Co tt R Park Hous e E L

G Q R U O E V E Lady Stewart Park E N B 'S L S T E EN Sheuchan Burn area Sheuchan Burn 1:200 year results 10 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 11 Wide Stranraer Results

Stranraer 1:200 year floodplain outline 12 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)

13 Stranraer Flood Alleviation Schemes (FAS)

Loch Ryan

Loc h Ryan FAS-1: Sheuchan

Loch Ryan Sheuchan Burn Outfall

Sand Sheuchan Burn FAS-8: Black Stank Mouth Diversion

Sand Town Burn

FAS-2: Upper

St r anr aer Academ y Sheuchan

Laundry Burn Black Stank

FAS-7: Localised Bunding

FAS-3: Thorney FAS-6: Town Burn Croft Inlet Railway Culvert Town Burn Legend FAS-5: Stoneykirk Blac k par ks Industrial Flood Alleviation RoundaboutEs t at e Scheme Option Black Stank

Historical Flooding FAS-4: Ochtralure

InletOchtrelure Predicted Floodplain

Big Plantation Watercourse

Stranraer FAS areas 14 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 15 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.

Sheuchan Outfall location and profile

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

16 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 4 diversion location and profile

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

17 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

Town Burn Railway Culvert

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

18 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

B M Forfield 4 . 3 3 Court m ge rid n B ur B op sh Bi

vron Che

op sh Bi n d ur De n v e r l an B ch s Au ott K C i ld o n a n Cairnview

Auld Lochview Ay re Hous e

Mira 3 2 Mare Route A Hi -L i te

5 Option 2 - Excess Flow

L 4 O C H V I E W

C R E 8 S

13 1

1 AD RO W VIE CK LO 11

9 2

1 B U

a N 2 R S E ID P

H E

8 1 b A T

3 2 D E R C R R A E C S n E ur C B E op N ish

T B

7 2

2 4

1 6

2 4

1 15 4

1 2 FAS 8 diversion option 19 Stranraer Discarded Options

Culvert Loc h Ryan Replacement Loc h Ryan Outfall

Loch Ryan Diversions Sheuchan Burn Channel Culvert Realignment Replacement Sand Sheuchan Burn

Storage

Sand Town Burn Railway Overflow

Channel Realignment

St r anr aer Academ y

Laundry Burn Black Stank

Open Section Storage Culverted

Black Stank & Town Burn Storage Connector Channel Town Burn

Culvert Pipe Upsizing Improvements

Blackparks I ndust r ial Estate Black Stank

Ochtrelure Legend Storage Discarded Option Big Plant at ion Surface water pipe Foul or Combined pipe Cacthment Diversion to Ballyferry Burn Watercourse Storage

20 Stranraer Preferable Options

Loch Ryan

Loch Ryan FAS-8: Black Stank FAS-1: Sheuchan Outfall Diversion Loch Ryan Sheuchan Burn New Outfall

Sand Sheuchan Burn FAS-2: Upper Sheuchan Bunding

Sand Town Burn

Stranraer Academy

Laundry Burn FAS-6: Railway Culvert Black Stank

FAS-5: Stoneykirk Roundabout Culverts

FAS-7: Black Stank Bunding

Town Burn

FAS-3: Thorney Croft

Inlet Improvements Blackparks Industrial Estate Black Stank Legend

Discarded Option Ochtrelure

Surface water pipe Big Plantat ion Foul or Combined pipe Watercourse FAS-4: Ochtralure Diversion

21 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