The Bristol Port Company
The Hydrographic Society – Plymouth 1st March 2016 Mark Burrows – Deputy Haven Master (Conservancy) Monitoring and Measuring the Dynamic Seabed in the Port of Bristol . Overview of The Bristol Port Company
. Survey Capabilities . Dredging Operations . Monitoring Fluid Mud Overview
. In 1991 First Corporate Shipping, a private company, purchased a 150 year lease of the Avonmouth and Royal Portbury Dock Estate from Bristol City Council (Now freehold). . Since 1991, over £0.5 bn has been invested in the dock estate. . This has resulted in tonnage throughput increasing from 4m to 12.5m tonnes and annual revenue increasing from £22m to £77m. Avonmouth & Portbury Dock Areas
Royal Portbury Avonmouth Dock Docks 7000m of berths 2100m of permanent deep water berths 1991
2014 Portbury Lock
Portbury has one of the largest locks in Europe and can handle ships up to 130,000 dwt, 40 metres beam and 14.5m draft What is Conservancy?
CONSERVANCY
…/kən’sзvənsι/kən’sɜːvənsɪ/ n. …having authority to preserve a port, river or area of countryside…
Provision of a Safe Harbour Conservancy’s Contribution to a Safe Harbour
. A Competent Harbour Authority (CHA) has a duty to: – Survey – Find best navigable channels – Place navigation marks to their best advantage – Monitor variations in sea bed – Maintain hydrographic records – Provide information to vessels – Mark or remove obstructions/ wrecks Port of Bristol Limits
Surveys within the Bristol Port Company Jurisdiction are conducted at intervals and accuracies in accordance with International standards (IHO SP 44).
Statutory Harbour Area covers 160 km2 (62 miles2) Survey Vessels
SV Investigator 7.9m GRP Catamaran - Survey / Conservancy Vessel
SV Isambard Brunel 20m Survey / Relief Pilot Vessel Depth Measurements
Atlas Deso 17 . High accuracy, digital/analogue echo sounders are used. . Dual Frequency Atlas Deso 17 . Dual Frequency Navisound 420 . Dual Frequency Teledyne Odom CV200 . Low Frequency 33 kHz / 24kHz CV200 . High Frequency 210 kHz Navisound 420
Dual frequency Transducer 210 & 33 kHz Multibeam
. Teledyne-Reson 7101 – shallow water system – upgraded from 8101 in June 2013 . Installed in moon-pool – hydraulically operated . Swath accuracy to IHO standards . 240 kHz & up to 50 Hz ping rate . 101 beam transducer – (511 equidistant beams) . Angular sector 150 degrees . 12mm accuracy . Titanium housing King Road Multibeam 2013 King Road Multibeam 2014 Portishead Point Sandwaves 2014 Sand Waves – Portishead Point
4m Port of Bristol (Avonmouth) Tides
Bristol experiences the 3rd highest tidal range in the world – (The highest are in the Bays of Fundy and Ungava – Canada – extreme ranges around 16.8m) Bristol - HAT 14.7 m, MHWS 13.2m, MHWN 9.8m (Mean Spring Range 12.2m) Tidal currents can reach 8 knots, especially after heavy rainfall FLUID MUD Fluid Mud Challenges
. 30 million tonnes of sediment in suspension between Watchet Harbour and Second Severn Crossing on spring tides. . 1.5 million tonnes of material removed from the entrances of Portbury and Avonmouth annually.
. Siltation rate approximately 0.1m a week. . Port declares least depth available above the dock sills to the 1.2 tm-3 horizon. Mud Definitions
. Mud forms in 4 stages: . Silt-laden water . Flocculated water . Fluid Mud . Firm Mud Fluid Mud in Dock Entrances
Top of Fluff
1.2 t m-3
Hard Marl
Top of Fluff
1.2 t m-3
Hard Marl Single Beam Echo-Sounder Image of Settled Fluid Mud – Main Channel Deposit Site Overview Deposit Site on Spring & Neap Tides
Neap tide Spring tide 29th Oct ‘13 5th Nov ’13 HW 9.8m HW 13.6m TSD Hopper Discharge Deposit Site 1 Hour after Disposal Mud “Slug” – King Road Fluid Mud in Suspension Fluid Mud De-Watering Swath Widths in Turbid Water
Severn Bar Survey – May 2014
20th May HW 12.1m
29th May HW 12.8m Portbury Entrance – Pre-dredge
Data processing……. 7101 mbs Surveying Fluid Mud
SOL – running into Portbury Entrance – good swath, good data
20 seconds later – unusable swath data Portbury Entrance – Pre-dredge Portbury Entrance – Post-dredge How is the Nautical Horizon Quantified?
The nautical horizon is defined as…
” the level where the physical characteristics reach a critical limit, beyond which contact with a ship’s keel causes either damage or unacceptable effects on controllability and manoeuvrability”. (PIANC 1997) Stema System Stage 1: Calibrate the Mud Stage 2: Collect Bathymetric Data Stage 3: Collect Density Profiles Stage 4: Correlate bathymetric data with density profiles Stage 5:Silas software computes 1.2 tonnes m-3 nautical horizon Final Chart – Avonmouth Entrance Avonmouth Entrance DREDGING Deep Draft Vessel entering Portbury Dock
mv Selandia - 230m x 32 m, draft 14.05 metres Under keel clearance (UKC) 1.2 metres Two pilots and 5 tugs to manoeuvre vessel into lock Tidal window was nearly two hours but can be as low as one hour if draft was deeper or tide was lower. Trailer Suction Dredger (TSD) – UKD Orca
UKD Orca 2400 cu. metre hopper capacity Twin dragheads Plough and Cutter Suction Dredger (CSD)
Weighs 11 tonnes, 12 metres BPC CSD Malago wide and towed by tug with 23 Dredges around 8000 cu.metres tonne bollard pull in 12 hours. 30 metre wide cut. 1200 metres dredge pipe. Avonmouth Swinging Basin Finally, we grab dredge too!
Padstow Harbour Commissioners’ Grab Dredger “Mannin”: Hopper capacity 100 cu. metres. Able to squeeze into dock areas where other dredgers can’t and very capable of removing debris (especially scrap which damages our CSD) from berths and in particular behind lock gates. Acknowledgements
. Photographs - Martin Pick – BPC Survey Cox’n . UK Dredging . Padstow Harbour Commissioners . Chart Images – UKHO . Crown Copyright and/or database rights. Reproduced by permission of the Controller of Her Majesty’s Stationery Office and the UK Hydrographic Office (www.ukho.gov.uk)