Stranraer Flood Protection Scheme: A case Study Juan Fernandez, - PowerPoint PPT Presentation

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

I ntroduction - 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 Stranraer - Drainage Area Plan Stranraer Location October 2000 flooding around the Sheuchan Burn 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 (m 3 /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 3.38 250 3.52 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 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 3 7 .0 3 5 .0 3 3 .0 3 1 .0 2 9 .0 2 7 .0 2 5 .0 m AD 2 3 .0 2 1 .0 1 9 .0 1 7 .0 1 5 .0 1 3 .0 MH9W MH9V MH9U MH9T MH9S MH9R MH9Q MH9P MH9N MH9J MH9L 1 1 .0 9 .0 m 7 0 1 3 6 2 2 0 3 0 0 3 3 3 4 0 3 4 5 2 5 0 0 5 6 2 6 2 8 7 6 2 8 0 9 8 9 9 1 0 3 4 1 0 6 2 1 1 4 2 1 2 2 0 1 2 8 51 3 0 7 1 3 4 3 L in k M H 9 X .1 M H 9 W .1 M H 9 V .1 M H 9 U .1 M H 9 T .1 M H 9 S .1 M H 9 R .1 M H 9 Q .1 - M H 9 N .1 - - M H 9 K .1 M H 9 L .1 0 5 5 9 9 9 0 1 .1 0 6 5 9 0 9 0 1 .1 - - 0 6 5 9 1 8 1 9 .1 M H 1 4 .1 0 6 6 0 2 0 0 5 .1 - - - - wid th (m m ) 3 7 5 3 7 5 3 7 5 4 5 0 6 0 0 7 5 0 7 5 0 7 5 0 - 7 5 0 9 0 0 9 0 0 9 0 0 9 0 0 1 0 5 0 1 2 0 0 - - 1 2 0 0 1 2 0 0 1 4 0 0 1 2 0 0 - - - u s in v (m A D ) 3 4 .9 0 0 2 9 .9 9 0 2 3 .2 9 0 1 6 .6 5 0 1 4 .3 8 0 1 3 .8 6 0 1 3 .4 3 0 1 3 .2 6 0 - 1 2 .8 8 0 - 1 2 .7 1 6 1 2 .4 1 0 1 1 .9 6 5 1 1 .8 0 2 1 1 .3 8 0 - - 1 0 .6 5 9 1 0 .2 6 7 1 0 .1 0 5 - - - - d s in v (m A D ) 2 9 .9 9 0 2 3 .2 9 0 1 6 .6 5 0 1 4 .3 8 0 1 3 .8 6 0 1 3 .4 3 0 1 3 .2 6 0 1 3 .0 4 0 - 1 2 .7 9 0 - 1 2 .5 1 0 1 1 .9 6 5 1 1 .8 0 2 1 1 .3 8 0 1 0 .6 7 0 - - 1 0 .2 6 7 1 0 .1 0 5 9 .9 7 0 - - - - p fc (m 3 /s) 0 .4 7 1 0 .5 6 7 0 .4 9 7 0 .4 8 6 0 .7 6 9 0 .7 4 9 0 .6 0 0 0 .7 4 3 - 0 .4 3 4 - 1 .1 6 3 1 .0 6 0 1 .0 6 0 1 .8 2 7 2 .6 8 3 - - 2 .6 6 1 1 .7 3 2 2 .9 5 1 - - - - N o d e M H 9 X M H 9 W M H 9 V M H 9 U M H 9 T M H 9 S M H 9 R M H 9 Q M H 9 P M H 9 N - - M H 9 J M H 9 K M H 9 L 0 5 5 9 9 9 0 1 0 6 5 9 0 9 0 1 0 6 5 9 1 8 0 4 - - M H 1 4 0 6 6 0 2 0 0 5 - - - - 6 g ro u n d (m A D ) 3 6 .7 4 5 3 3 .8 6 5 2 5 .6 2 3 1 9 .3 1 0 1 6 .5 1 3 1 6 .3 1 2 1 6 .4 3 4 1 6 .4 6 4 - - - - - 1 5 .1 9 0 1 4 .4 8 4 1 4 .8 0 2 1 3 .5 6 0 1 3 .0 7 9 - 1 3 .2 8 0 1 2 .9 9 3 1 3 .2 5 5 1 2 .2 5 0 - - - 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) 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