River Thames Bathymetric Data Analysis

DRAFT REPORT REV 3 River Thames Bathymetric Data Analysis Prepared for Environment Agency January 2016 Burderop Park Swindon SN4 0QD United Kingdom Contents Section Page Acronyms and Abbreviations ............................................................................................................ vii 1 Summary ............................................................................................................................ 1-1 2 Scope ................................................................................................................................. 2-1 2.1 Need for study ................................................................................................................. 2-1 2.2 Objectives ........................................................................................................................ 2-2 3 Data ................................................................................................................................... 3-1 3.1 Data sources .................................................................................................................... 3-1 3.2 Bathymetric surveys ........................................................................................................ 3-1 3.2.1 Available data ..................................................................................................... 3-1 3.2.2 Survey methods .................................................................................................. 3-3 3.2.3 Survey data resolution ........................................................................................ 3-5 3.2.4 Survey data uncertainty ...................................................................................... 3-5 3.2.5 Confidence levels ................................................................................................ 3-7 3.3 Flow data.......................................................................................................................... 3-7 3.4 Previous studies and dredging records ............................................................................ 3-8 4 Methodology ...................................................................................................................... 4-1 4.1 Bathymetric survey processing ........................................................................................ 4-1 4.1.1 Pole & SBES cross-section data (St John’s to Radcot) ......................................... 4-1 4.1.2 MBES data (Rushey to Teddington) .................................................................... 4-2 5 Results ................................................................................................................................ 5-1 5.1 Overview .......................................................................................................................... 5-1 5.2 Geomorphology ............................................................................................................... 5-4 5.2.1 Overview ............................................................................................................. 5-4 5.2.2 Limitations .......................................................................................................... 5-5 5.2.3 River scale changes ............................................................................................. 5-6 5.2.4 Local scale changes ........................................................................................... 5-10 5.2.5 Jubilee River ...................................................................................................... 5-15 5.2.6 Summary ........................................................................................................... 5-17 5.3 Flood conveyance .......................................................................................................... 5-18 5.3.1 Sample locations assessment ........................................................................... 5-19 5.3.2 Relative changes in cross-section conveyance ................................................. 5-21 5.3.3 Gauge records ................................................................................................... 5-23 5.3.4 Conclusions ....................................................................................................... 5-26 5.4 Dredging ......................................................................................................................... 5-27 5.4.1 Design dredge depths ....................................................................................... 5-27 5.4.2 Dredged conveyance ........................................................................................ 5-33 5.4.3 Dredging quantities and costs .......................................................................... 5-33 5.5 Navigation ...................................................................................................................... 5-36 5.6 Environment .................................................................................................................. 5-40 5.6.1 Legislative Background ..................................................................................... 5-40 5.6.2 Water Framework Directive Status .................................................................. 5-40 5.6.3 Conservation designations in the Thames ........................................................ 5-40 5.6.4 Dredging ............................................................................................................ 5-42 III CONTENTS Section Page 6 Dredging strategy ............................................................................................................... 6-1 6.1 Overview .......................................................................................................................... 6-1 6.2 Discussion ........................................................................................................................ 6-2 6.3 Monitoring ....................................................................................................................... 6-3 6.3.1 Bathymetric surveys ........................................................................................... 6-3 6.3.2 Navigation and Dredging .................................................................................... 6-3 6.3.3 Key locations ....................................................................................................... 6-3 6.3.4 Remote monitoring ............................................................................................. 6-3 6.4 Data analysis .................................................................................................................... 6-5 7 References .......................................................................................................................... 7-1 Appendices Appendix 1 Reach Location Maps Appendix 2 Detailed Reach Results Appendix 3 Reach Activity Plans Appendix 4 Sample Cross-section Conveyance Calculations Appendix 5 Dredge Level Plans for Penton Hook Reach Appendix 6 Potential Locations for Shoal Removal Tables Table 1. Bathymetric Surveys Table 2. River Thames flow gauge data Table 3. Summary Results of Bathymetric Surveys Table 4. Change in bed level and conveyance with dredging Table 5. Indicative Dredging Volumes and Costs Table 6. Navigation Standard of Service Table 7. Shoals recorded in 2014 and 2015 Surveys Table 8. Potential gauges for remote monitoring of conveyance Figures Figure 1. Study area Figure 2. Example Processed Survey Data (Pole and SBES) Figure 3. Example Processed Survey Data (SBES) Figure 4. Example Processed Survey Data (MBES) Figure 5. MBES Survey Ground Truthing Results IV CONTENTS Section Page Figure 6. Summary of average reach bed level changes Figure 7. Average reach bed levels for all reaches since end of reach dredging relative to current level Figure 8. Changes in reach bed level and river flow (Old Windsor to Teddington) Figure 9. Changes in bed level and river flow (Penton Hook reach and Staines flow gauge) Figure 10. Changes in reach bed level and river flow (Caversham to Romney) Figure 11. Changes in reach bed level and river flow (Iffley to Mapledurham) Figure 12. Changes in reach bed level and river flow (Rushy to Osney) Figure 13. Example of meander behaviour : Bell Weir reach Figure 14. Example of Active Meander : Eynsham Reach Figure 15. Example of Planform Change in an Active Meander : Eynsham Reach Figure 16. Example of behaviour at islands Figure 17. Effect of Jubilee River operation on flow in the River Thames Figure 18. Change in flow frequency due to Jubilee River operation Figure 19. Changes in average bed level : Caversham to Teddington (2003-2008 and 2008-2014) Figure 20. Definition of cross section properties Figure 21. Changes in average bed level and corresponding change in conveyance at sample cross- sections Figure 22. Relationship between change in cross-section conveyance and average bed level at sample cross-sections Figure 23. Potential relative changes in channel cross-section conveyance in each reach Figure 24. Flow record for Bray reach Figure 25. Gauged Flow and Water Level in Bray Reach Figure 26. Changes in conveyance in Bray Reach Figure 27. Changes in conveyance in Penton Hook Reach Figure 28. Effect of structures on flood levels Figure 29. Channel dredging limit (Appendix 2, River Thames Dredging Study, July 1998)

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