6 October, 2005

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

• Why do We Dredge?
• Why Does Sedimentation Happen?
• How Can We Minimize Sedimentation?
• Examples
• Conclusions

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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

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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)

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HOW CAN WE MINIMIZE SEDIMENTATION?

• Build Marine Facilities In Naturally Deep Water
  (i.e. Dont Deepen)
• Otherwise, Simply
• Keep Sediment Moving (KSM) Through The Harbor
• Keep Sediment Out (KSO) of the Harbor
• Both Strategies Involve Controlling Flow
  Conditions

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FLOW-THROUGH HARBORS/MARINAS
Berths Parallel To Flow
Newark Bay, NJ
Wilmington, DE
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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 lt Qs in
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SIMPLIFIED PHYSICS OF SEDIMENTATION FOR FLOW
THRU HARBORS CHANNELS

• Sedimentation Sediment In Sediment Out
• ?Qs Qs in Qs out
• ?Qs cin Uin din cout Uout dout
  
• Where ?Qs Sedimentation Rate, c sediment
  concentration
• No Sedimentation When U,d are constant
• Sedimentation When Uout lt Uin (i.e., dout gt din)

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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

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• KSM- FLOW TRAINING STRUCTURES MAINTAIN VELOCITY
  IN A DEEPENED AREA

Yangtze River, China
Shooters Island, NY
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KSM- FLOW TRAINING STRUCTURES
Delaware Bay
Mississippi River
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KSM- FLOW AUGMENTATION WITH SCOUR JETS
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• KSM- FLOW AUGMENTATION WITH PROPELLOR JETS

Propeller Jet System, Scour Systems
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• KSM- PROPELLOR/SCOUR JETS

• Systems Have Been Installed
• Kings Bay, GA
• Savannah, NC
• Linden, NJ
• Grays Harbor
• Each Installation Has Eliminated Dredging
• Best-Suited For Berthing Areas
• System Keeps Sediment In The Natural System

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HARBOR/MARINA BASINS
Quiescent Basins
Port Elizabeth Channel, NJ
Manten, Holland
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SIMPLIFIED PHYSICS OF SEDIMENTATION IN IN BASIN
HARBORS
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SIMPLIFIED PHYSICS OF SEDIMENTATION IN IN BASIN
HARBORS

• ?Qs 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

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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)

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HORIZONTAL EDDY EXCHANGE- HARBOR BASINS
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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!!
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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

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CLOSE SECOND ENTRANCE PORT OF BREMEN, GERMANY
SECOND ENTRANCE
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IN-SITU TREATMENT- PORT OF EMDEN, GERMANY
SEDIMENTATION REDUCTION 67
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GROIN PILE FIELD- REDUCES fh By 30
CAN INTERFERE WITH NAVIGATION!
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CURRENT DEFLECTING WALL- REDUCES fh By 30
Kohlfleet Harbor Basin Hamburg, Germany
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CURRENT DEFLECTING WALL- KOHLFLEET BASIN
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CURRENT DEFLECTING WALL- PRINCIPLES
Without CDW
With CDW
CDW
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CURRENT DEFLECTING WALL- FLOW PATTERNS
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KOHLFLEET BASIN CDW REDUCES fh By 35
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CURRENT DEFLECTING WALL FOR DENSITY CURRENTS
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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

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CURRENT DEFLECTING WALL FOR DENSITY CURRENTS-
PHYSICAL MODEL TESTS
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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

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• KSM- FLOW AUGMENTATION WITH WATER INJECTION
  DREDGING (WID)

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

FAST-MOVING RIVER
QUIESCENT BASIN
BREMERHAVEN, GERMANY
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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

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

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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

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FLUID MUD THICKNESS- PORT OF EMDEN, GERMANY
3.3 m thick
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FLUID MUD THICKNESS PORT OF EMDEN, GERMANY
FLUID MUD IS IN EQUILIBRIUM WITH RIVER/SEDIMENT
CONDITIONS THICKNESS REMAINS CONSTANT OVER TIME!
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IN-SITU TREATMENT- PORT OF EMDEN, GERMANY
DEPTHS
FLUID MUD THICKNESS
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IN-SITU TREATMENT (IST)- PORT OF EMDEN, GERMANY
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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