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6 October, 2005

2 nd Annual Dredged Material Management Summit. Minimization Of Sedimentation In Harbors And Marinas. Eric Smith and John Headland, Moffatt & Nichol. 6 October, 2005. PRESENTATION TOPICS. Why do We Dredge? Why Does Sedimentation Happen? How Can We Minimize Sedimentation? Examples

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6 October, 2005

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  1. 2nd Annual Dredged Material Management Summit Minimization Of Sedimentation In Harbors And Marinas Eric Smith and John Headland, Moffatt & Nichol 6 October, 2005

  2. PRESENTATION TOPICS • Why do We Dredge? • Why Does Sedimentation Happen? • How Can We Minimize Sedimentation? • Examples • Conclusions

  3. WHY DO WE DREDGE? • To Deepen Waters For Vessel Access (New Work Dredging • To Maintain Depths Subject To Sedimentation (Maintenance Dredging) • Dredged Material Can Be Managed By Managing Sedimentation • Reducing Sedimentation Keeps Sediment In The Natural System

  4. WHY DOES SEDIMENTATION HAPPEN? • Sediment Movement and Tidal/Wave Conditions Are Balanced in Most Natural Systems • Many Natural Systems Are Equilibrated And Free of Sedimentation or Scour • Sedimentation Occurs When: • There Is Sediment (Mud, Silt or Sand) In The Water Column • Flow Velocities Are Not Strong Enough To Keep Sediment Moving (Usually a result of deepening for navigation/harbor development)

  5. HOW CAN WE MINIMIZE SEDIMENTATION? • Build Marine Facilities In Naturally Deep Water (i.e. Don’t Deepen) • Otherwise, Simply: • Keep Sediment Moving (KSM) Through The Harbor • Keep Sediment Out (KSO) of the Harbor • Both Strategies Involve Controlling Flow Conditions

  6. FLOW-THROUGH HARBORS/MARINAS Berths Parallel To Flow Newark Bay, NJ Wilmington, DE

  7. SEDIMENTATION IN DEEPENED CHANNELS Sediment Transport In Sediment Transport Out Qs out = uout cout hout Qs in = uin cin hin Dredged Area Un-Dredged Area hin Qs out, uout Qs in, uin hout Sedimentation Because Qs out < Qs in

  8. SIMPLIFIED PHYSICS OF SEDIMENTATION FOR FLOW THRU HARBORS & CHANNELS • Sedimentation = Sediment In – Sediment Out • ΔQs = Qs in – Qs out • ΔQs = cin Uin din – cout Uout dout • Where: ΔQs = Sedimentation Rate, c = sediment concentration • No Sedimentation When U,d are constant • Sedimentation When Uout < Uin (i.e., dout > din)

  9. KSM IN FLOW-THRU HARBORS & CHANNELS • Strategy is to: • Place harbor & channels within naturally deep water • Increase velocity in deepened area by engineering works • Flow Training Structures That Maintain Velocities • By flow augmentation with jets or injection dredging

  10. KSM- FLOW TRAINING STRUCTURES MAINTAIN VELOCITY IN A DEEPENED AREA Shooters Island, NY Yangtze River, China

  11. KSM- FLOW TRAINING STRUCTURES Delaware Bay Mississippi River

  12. KSM- FLOW AUGMENTATION WITH SCOUR JETS

  13. KSM- FLOW AUGMENTATION WITH PROPELLOR JETS Propeller Jet System, Scour Systems

  14. KSM- PROPELLOR/SCOUR JETS • Systems Have Been Installed: • King’s Bay, GA • Savannah, NC • Linden, NJ • Gray’s Harbor • Each Installation Has Eliminated Dredging • Best-Suited For Berthing Areas • System Keeps Sediment In The Natural System

  15. HARBOR/MARINA BASINS Quiescent Basins Port Elizabeth Channel, NJ Manten, Holland

  16. SIMPLIFIED PHYSICS OF SEDIMENTATION IN IN BASIN HARBORS

  17. SIMPLIFIED PHYSICS OF SEDIMENTATION IN IN BASIN HARBORS • ΔQs = c p x Qe • Where: • c = sediment concentration outside of harbor • p = basin trapping efficiency • Qe = exchange rate through entrance of harbor • Best Way To Reduce Sedimentation is To Reduce Qe

  18. FLOW PHENOMENA IN HARBOR BASINS • Qe Depends on 3 Mechanisms: • Horizontal Eddy Exchange (Can Be Reduced) • Tidal Filling (Cannot Be Changed) • Density Currents (Can Be Reduced)

  19. HORIZONTAL EDDY EXCHANGE- HARBOR BASINS

  20. Harbor Basin Channel Fresher Water Saltier Water Channel Harbor Basin Fresher Water Saltier Water SALT/FRESH WATER DENSITY CURRENTS- HARBOR BASINS Incoming Tide: Brings Saltier/Heavier Water To Basin Outgoing Tide: Brings Fresher/Lighter Water To Basin Even A Small Change In Salinity (i.e., 1-2 ppt) Can Exchange A Tremendous Volume Of Water, More Than Tide Or Eddy Exchange!!

  21. METHODS TO REDUCE FLOW VOLUME EXCHANGE- IN HARBOR BASINS • Narrow Entrance • Use Only 1 Entrance • Change Entrance Orientation • Use Structures to Reduce fh • Pile Groin • Current Deflecting Wall (CDW) • Modified CDW For Density Currents

  22. CLOSE SECOND ENTRANCE PORT OF BREMEN, GERMANY SECOND ENTRANCE

  23. IN-SITU TREATMENT- PORT OF EMDEN, GERMANY SEDIMENTATION REDUCTION 67%

  24. GROIN PILE FIELD- REDUCES fh By 30% CAN INTERFERE WITH NAVIGATION!

  25. CURRENT DEFLECTING WALL- REDUCES fh By 30% Kohlfleet Harbor Basin Hamburg, Germany

  26. CURRENT DEFLECTING WALL- KOHLFLEET BASIN

  27. CURRENT DEFLECTING WALL- PRINCIPLES Without CDW With CDW CDW

  28. CURRENT DEFLECTING WALL- FLOW PATTERNS

  29. KOHLFLEET BASIN CDW REDUCES fh By ~35%

  30. CURRENT DEFLECTING WALL FOR DENSITY CURRENTS

  31. CURRENT DEFLECTING WALL FOR DENSITY CURRENTS • Creates A Vortex Over The Width of The Basin Entrance • CDW Decreases Water Exchange In Lower Layers By 40% During Flood Tide • CDW & Sill Reduce Same to 70% • Directs More Flow Into The Basin In Top Layers • Not Yet Tested in Field Conditions

  32. Without CDW With CDW & Sill Dye Mass In Basin (g) TIME (Sec) CURRENT DEFLECTING WALL FOR DENSITY CURRENTS- PHYSICAL MODEL TESTS

  33. KSM- WATER INJECTION DREDGING • Mobilize Sediments Near the Bottom Under Low Pressure • Used Extensively In Europe To Move Sediments From Quiescent Areas To Areas of High Velocities • Sediment Is Lifted Only A Few Feet Off Bottom Creating Little Turbidity • Can Be Used To Move Sediments Up to 1000m • 2 M m3 Are Managed This Way in Port of Hamburg

  34. KSM- FLOW AUGMENTATION WITH WATER INJECTION DREDGING (WID) European Water Injection Dredger

  35. KSM- FLOW AUGMENTATION WITH WATER INJECTION DREDGING (WID) FAST-MOVING RIVER QUIESCENT BASIN BREMERHAVEN, GERMANY

  36. KSM- WID, PORT OF BREMERHAVEN, GERMANY • Historical Sedimentation 350,000 m3 per year • WID Used For 11 Years • WID Reduced Sedimentation Rate To Zero • Eliminated Need For Upland Placement • Keeps Sediment In The System

  37. IN-SITU TREATMENT- PORT OF EMDEN, GERMANY QUIESCENT BASIN FAST-MOVING RIVER

  38. In-Situ Treatment, PORT OF EMDEN, GERMANY • Harbor Area Fronting Lock Subject To 2.5 cubic meters Per Year (deposited upland and/or offshore) • The Deposit Starts As Fluid Mud & Eventually Consolidates Into Mud • IST Consists of Removing Sediment From the Bottom into a Dredge Hopper, Exposing it to Oxygen (Oxygenating it), and Then Depositing it Back on the Bottom • Sediment Is Not Removed Or Suspended Above Bottom • Ships Sail Right Thru The Fluid Mud! • IST, Performed Every 3 Months, Eliminated the Need For Dredging

  39. IST, PORT OF EMDEN, GERMANY • Suspend Sediment: While Alive, Organisms Act as “Parachutes” to Keep Sediment Suspended • Fluid Mud: Organisms Form a Slime That Binds Particles To Form A Dense, Stable Suspension • Mud: Results From Consolidation In Absence of In-Situ Treatment, Organisms Die Owing To Lack Of Oxygen • IST Oxygenates Organisms In Order To Maintain Fluid Mud In Suspension

  40. FLUID MUD THICKNESS- PORT OF EMDEN, GERMANY 3.3 m thick

  41. -5 July April 210 kHz -5 210 kHz 3.3 m Thick 3.5 m Thick 15 kHz 15 kHz -10 FLUID MUD THICKNESS PORT OF EMDEN, GERMANY FLUID MUD IS IN EQUILIBRIUM WITH RIVER/SEDIMENT CONDITIONS THICKNESS REMAINS CONSTANT OVER TIME!

  42. IN-SITU TREATMENT- PORT OF EMDEN, GERMANY DEPTHS FLUID MUD THICKNESS

  43. IN-SITU TREATMENT (IST)- PORT OF EMDEN, GERMANY

  44. CONCLUSIONS • Dredged Material Can Be Managed Thru Sedimentation Management • There Are A Number of Strategies For Reducing Sedimentation Including New Developments Proven in Europe • These Strategies Keep Sediment In The System • These Systems Can Be Very Cost-Effective and Are Equally Applicable To Large and Small Harbors

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