2nd Annual Dredged Material Management Summit Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 2nd Minimization Of Sedimentation In Harbors And Marinas Eric Smith and John.
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2nd Annual Dredged Material Management Summit Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 2nd Minimization Of Sedimentation In Harbors And Marinas Eric Smith and John Headland, Moffatt & Nichol 6 October, 2005 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas PRESENTATION TOPICS • Why do We Dredge? • Why Does Sedimentation Happen? • How Can We Minimize Sedimentation? • Examples • Conclusions 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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) 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas FLOW-THROUGH HARBORS/MARINAS Berths Parallel To Flow Newark Bay, NJ Wilmington, DE 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas SEDIMENTATION IN DEEPENED CHANNELS Sediment Transport In Qs in = uin cin hin Sediment Transport Out Qs out = uout cout hout Dredged Area Un-Dredged Area Qs in, uin hin Qs out, uout hout Sedimentation Because Qs out < Qs in 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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) 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas KSM- FLOW TRAINING STRUCTURES MAINTAIN VELOCITY IN A DEEPENED AREA Yangtze River, China Shooters Island, NY 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas KSM- FLOW TRAINING STRUCTURES Delaware Bay Mississippi River 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas KSM- FLOW AUGMENTATION WITH SCOUR JETS 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas KSM- FLOW AUGMENTATION WITH PROPELLOR JETS Propeller Jet System, Scour Systems 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas HARBOR/MARINA BASINS Quiescent Basins Port Elizabeth Channel, NJ Manten, Holland 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas SIMPLIFIED PHYSICS OF SEDIMENTATION IN IN BASIN HARBORS 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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) 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas HORIZONTAL EDDY EXCHANGE- HARBOR BASINS 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas SALT/FRESH WATER DENSITY CURRENTS- HARBOR BASINS Channel Incoming Tide: Brings Saltier/Heavier Water To Basin Fresher Water Saltier Water Channel Outgoing Tide: Brings Fresher/Lighter Water To Basin Harbor Basin Fresher Water Harbor Basin Saltier Water Even A Small Change In Salinity (i.e., 1-2 ppt) Can Exchange A Tremendous Volume Of Water, More Than Tide Or Eddy Exchange!! 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas METHODS TO REDUCE FLOW VOLUME EXCHANGEIN 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas CLOSE SECOND ENTRANCE PORT OF BREMEN, GERMANY SECOND ENTRANCE 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas IN-SITU TREATMENT- PORT OF EMDEN, GERMANY SEDIMENTATION REDUCTION 67% 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas GROIN PILE FIELD- REDUCES fh By 30% CAN INTERFERE WITH NAVIGATION! 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas CURRENT DEFLECTING WALL- REDUCES fh By 30% Kohlfleet Harbor Basin Hamburg, Germany 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas CURRENT DEFLECTING WALL- KOHLFLEET BASIN 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas CURRENT DEFLECTING WALL- PRINCIPLES Without CDW With CDW CDW 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas CURRENT DEFLECTING WALL- FLOW PATTERNS 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas KOHLFLEET BASIN CDW REDUCES fh By ~35% 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas CURRENT DEFLECTING WALL FOR DENSITY CURRENTS 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas Dye Mass In Basin (g) CURRENT DEFLECTING WALL FOR DENSITY CURRENTSPHYSICAL MODEL TESTS Without CDW With CDW & Sill TIME (Sec) 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas KSM- FLOW AUGMENTATION WITH WATER INJECTION DREDGING (WID) European Water Injection Dredger 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas KSM- FLOW AUGMENTATION WITH WATER INJECTION DREDGING (WID) FAST-MOVING RIVER QUIESCENT BASIN BREMERHAVEN, GERMANY 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas IN-SITU TREATMENT- PORT OF EMDEN, GERMANY QUIESCENT BASIN FAST-MOVING RIVER 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas FLUID MUD THICKNESS- PORT OF EMDEN, GERMANY 3.3 m thick 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas FLUID MUD THICKNESS PORT OF EMDEN, GERMANY -5 July April -5 -10 210 kHz 3.3 m Thick 15 kHz 210 kHz 3.5 m Thick 15 kHz FLUID MUD IS IN EQUILIBRIUM WITH RIVER/SEDIMENT CONDITIONS THICKNESS REMAINS CONSTANT OVER TIME! 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas IN-SITU TREATMENT- PORT OF EMDEN, GERMANY DEPTHS FLUID MUD THICKNESS 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas IN-SITU TREATMENT (IST)- PORT OF EMDEN, GERMANY 2nd Annual Dredged Material Management Summit Minimizing Sedimentation In Harbors and Marinas 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