PB11207-CVR.qxd 1/9/05 11:42 AM Page 1 Joint Defra/EA Flood and Coastal Erosion Risk Management R&D Programme Understanding the lowering of beaches in front of coastal defence structures, Stage 2 Technical Note 3 R&D Project Record FD1927/PR3 Understanding the Lowering of Beaches in Front of Coastal Defence Structures, Phase 2 Assessment of beach lowering and toe scour 4.5 4 3.5 3 2.5 2 Beach level (mODN) level Beach Level Trend 1.5 1 1962 1966 1970 1974 1 1982 1986 199 958 978 0 Year Technical Note CBS0726/03 Release 3.0 Address and Registered Office: HR Wallingford Ltd. Howbery Park, Wallingford, OXON OX10 8BA Tel: +44 (0) 1491 835381 Fax: +44 (0) 1491 832233 Registered in England No. 2562099. HR Wallingford is a wholly owned subsidiary of HR Wallingford Group Ltd. Understanding the Lowering of Beaches in Front of Coastal Defence Structures, Phase 2 Assessment of beach lowering and toe scour Document Information Understanding the Lowering of Beaches in Front of Coastal Defence Project Structures, Phase 2 Technical subject Assessment of beach lowering and toe scour Client Department for Environment, Food and Rural Affairs Client Representative Mr Stephen Jenkinson Project No. CBS0726 Technical Note No. CBS0726/03 TN-CBS0726-03_Assessment_beach_lowering_toe_scour_Rel_3- Filename. 0.doc Project Manager Dr J Sutherland Project Sponsor Dr RJS Whitehouse Document History Date Revision Prepared Approved Authorised Notes 14/02/08 3.0 Sutherland Brampton Whitehouse Incorporation of client review and additional work on Bruun rule. Re- released to client. 1/09/06 2.0 Sutherland Brampton Whitehouse Released to client 28/08/06 1.0 Sutherland Brampton Whitehouse Internal review version HR Wallingford accepts no liability for the use by third parties of results or methods presented here. The company also stresses that various sections of this document rely on data supplied by or drawn from third party sources. HR Wallingford accepts no liability for loss or damage suffered by the client or third parties as a result of errors or inaccuracies in such third party data TN CBS0726/03 ii Rev 3.0 Understanding the Lowering of Beaches in Front of Coastal Defence Structures, Phase 2 Assessment of beach lowering and toe scour Contents 1. Introduction ...................................................................................................................... 1 2. Monitoring methods and other data sources ..................................................................... 3 2.1 Small Scale .......................................................................................................... 3 2.1.1 Linear arrays of point sensors ................................................................ 3 2.1.2 Underwater acoustic measurements of the seabed ................................. 5 2.1.3 Measurements of emerged toe levels ..................................................... 5 2.1.4 Measurements of mixing depth .............................................................. 5 2.1.5 Relative merits of small scale monitoring devices ................................. 6 2.2 Medium-scale ...................................................................................................... 7 2.2.1 Cross-shore profile surveys and topographic surveys ............................ 7 2.2.2 Total station ............................................................................................ 7 2.2.3 Kinematic GPS ....................................................................................... 7 2.2.4 Laser scanning systems .......................................................................... 7 2.2.5 Repeated digital photography................................................................. 7 2.2.6 X-band radar........................................................................................... 9 2.3 Large-scale ........................................................................................................ 10 2.3.1 Ordnance Survey Maps ........................................................................ 10 2.3.2 Orthorectified Aerial or Satellite Photos .............................................. 14 2.3.3 Topographic LIDAR ............................................................................ 15 2.3.4 Bathymetric LIDAR ............................................................................. 16 2.3.5 Synthetic Aperture Radar ..................................................................... 16 2.3.6 Advantages and disadvantages of medium and large scale survey techniques ............................................................................................. 16 3. Statistical analysis of beach level data ........................................................................... 18 3.1 Linear analysis of beach level data .................................................................... 18 3.1.1 Introduction .......................................................................................... 18 3.1.2 Usefulness of best-fit linear trend as predictor ..................................... 38 3.1.3 Gaussian distribution of elevations ...................................................... 42 3.1.4 Number of surveys in each year ........................................................... 46 3.1.5 Seasonal variations in beach levels at the toe of a structure ................ 48 3.2 Advanced linear analysis of beach level data .................................................... 50 3.2.1 Wavelet analysis ................................................................................... 50 3.2.2 Empirical Orthogonal Function (EOF) analysis ................................... 50 3.2.3 Canonical Correlation Analysis (CCA) ................................................ 51 3.2.4 Principal Oscillation Pattern (POP)...................................................... 51 3.3 Non-linear analyses of beach level data ............................................................ 51 3.3.1 Singular Spectrum Analysis ................................................................. 51 3.3.2 Fractal Analysis .................................................................................... 52 3.3.3 Neural Networks .................................................................................. 52 3.4 Shoreline or beach volume? .............................................................................. 52 3.5 Estimating shoreline change from maps and aerial photographs ...................... 54 3.5.1 Errors in OS County series maps ......................................................... 56 3.5.2 Errors in aerial surveys ......................................................................... 60 3.5.3 Rms Uncertainty of shoreline estimates in the UK .............................. 61 4. Process-based models ..................................................................................................... 63 4.1 Introduction ....................................................................................................... 63 4.2 One Line models ................................................................................................ 63 TN CBS0726/03 iii Rev 3.0 Understanding the Lowering of Beaches in Front of Coastal Defence Structures, Phase 2 Assessment of beach lowering and toe scour 4.3 Coastal Profile Models....................................................................................... 63 4.4 Coastal Area Models .......................................................................................... 64 4.5 systems model: SCAPE ..................................................................................... 64 4.6 Flood and Coastal Defence national overview of coastal erosion potential ...... 65 4.7 USGS Coastal Vulnerability Index .................................................................... 66 4.8 Storm erosion potential index ............................................................................ 68 4.9 Stochastic modelling .......................................................................................... 68 5. Geomorphological analyses ............................................................................................ 70 5.1 Sediment Budget ................................................................................................ 70 5.2 Futurecoast ......................................................................................................... 70 5.3 Eurosion ............................................................................................................. 71 6. Parametric equilibrium models ....................................................................................... 72 6.1 Equilibrium Beach Profile ................................................................................. 72 6.2 Bruun rule for coastal retreat ............................................................................. 72 7. Predicting bed levels at different timescales .................................................................. 75 7.1 Predicting bed levels at a scale of tides and storms ........................................... 75 7.1.1 Monitoring ............................................................................................ 75 7.1.2 Process-based modelling ...................................................................... 75 7.1.3 Empirical Scour Predictors ................................................................... 75 7.2 Predicting bed levels at the scale of weeks and seasons