6 october, 2005
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
6 October, 2005
Minimization Of
Sedimentation
In Harbors And Marinas
2nd Annual Dredged Material Management Summit
Eric Smith and John Headland, Moffatt & Nichol
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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
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
• 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
WHY DO WE DREDGE?
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
• 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)
WHY DOES SEDIMENTATION HAPPEN?
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
• 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
HOW CAN WE MINIMIZE SEDIMENTATION?
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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
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
SEDIMENTATION IN DEEPENED CHANNELS
Qs in = uin cin hin Qs out = uout cout hout
hin
hout
Because Qs out < Qs in
Sedimentation
Qs in, uin
Sediment Transport In Sediment Transport Out
Qs out, uout
Dredged AreaUn-Dredged Area
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
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)
SIMPLIFIED PHYSICS OF SEDIMENTATION FOR FLOW THRU HARBORS & CHANNELS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
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
KSM IN FLOW-THRU HARBORS & CHANNELS
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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
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
KSM- FLOW TRAINING STRUCTURES
Delaware Bay Mississippi River
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
KSM- FLOW AUGMENTATION WITH SCOUR JETS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
KSM- FLOW AUGMENTATION WITH PROPELLOR JETS
Propeller Jet System, Scour Systems
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
• 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
KSM- PROPELLOR/SCOUR JETS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
HARBOR/MARINA BASINS
Port Elizabeth Channel, NJ Manten, Holland
Quiescent Basins
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
SIMPLIFIED PHYSICS OF SEDIMENTATION ININ BASIN HARBORS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
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
SIMPLIFIED PHYSICS OF SEDIMENTATION ININ BASIN HARBORS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
FLOW PHENOMENA IN HARBOR BASINSQe Depends on 3 Mechanisms:
Horizontal Eddy Exchange (Can Be Reduced) Tidal Filling (Cannot Be Changed) Density Currents (Can Be Reduced)
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
HORIZONTAL EDDY EXCHANGE- HARBOR BASINS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
SALT/FRESH WATER DENSITY CURRENTS- HARBOR BASINS
Saltier Water
Fresher Water
Harbor BasinChannel
Fresher Water Saltier Water
Harbor BasinChannel
Incoming Tide:Brings Saltier/HeavierWater To Basin
Outgoing Tide:Brings Fresher/LighterWater To Basin
Even A Small Change In Salinity (i.e., 1-2 ppt) Can ExchangeA Tremendous Volume Of Water, More Than Tide Or EddyExchange!!
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
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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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
CLOSE SECOND ENTRANCE PORT OF BREMEN, GERMANY
SECOND ENTRANCE
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
IN-SITU TREATMENT- PORT OF EMDEN, GERMANY
SEDIMENTATION REDUCTION 67%
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
GROIN PILE FIELD- REDUCES fh By 30%
CAN INTERFERE WITH NAVIGATION!
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
CURRENT DEFLECTING WALL- REDUCES fh By 30%
Kohlfleet Harbor BasinHamburg, Germany
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
CURRENT DEFLECTING WALL- KOHLFLEET BASIN
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
CURRENT DEFLECTING WALL- PRINCIPLESWithout CDW
With CDWCDW
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
CURRENT DEFLECTING WALL- FLOW PATTERNS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
KOHLFLEET BASIN CDW REDUCES fh By ~35%
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
CURRENT DEFLECTING WALL FOR DENSITY CURRENTS
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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
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
CURRENT DEFLECTING WALL FOR DENSITY CURRENTS- PHYSICAL MODEL TESTS
TIME (Sec)
Dye
Mas
s In
Bas
in (g
) Without CDW
With CDW & Sill
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
• 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
KSM- WATER INJECTION DREDGING
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
KSM- FLOW AUGMENTATION WITH WATER INJECTION DREDGING (WID)
European Water Injection Dredger
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
KSM- FLOW AUGMENTATION WITH WATER INJECTION DREDGING (WID)
BREMERHAVEN, GERMANY
FAST-MOVING RIVER
QUIESCENT BASIN
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
• 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
KSM- WID, PORT OF BREMERHAVEN, GERMANY
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
IN-SITU TREATMENT- PORT OF EMDEN, GERMANY
FAST-MOVING RIVER
QUIESCENT BASIN
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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
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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
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
FLUID MUD THICKNESS- PORT OF EMDEN, GERMANY
3.3 m thick
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
FLUID MUD THICKNESS PORT OF EMDEN, GERMANY
210 kHz
15 kHz
210 kHz
15 kHz-10
-5
-5
3.3 m Thick 3.5 m Thick
April July
FLUID MUD IS IN EQUILIBRIUM WITH RIVER/SEDIMENT CONDITIONSTHICKNESS REMAINS CONSTANT OVER TIME!
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
IN-SITU TREATMENT- PORT OF EMDEN, GERMANY
DEPTHS FLUID MUD THICKNESS
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2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
IN-SITU TREATMENT (IST)- PORT OF EMDEN, GERMANY
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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