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
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
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
• 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?
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?
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?
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
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
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
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
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
• 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
2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
HARBOR/MARINA BASINS
Port Elizabeth Channel, NJ Manten, Holland
Quiescent Basins
2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
SIMPLIFIED PHYSICS OF SEDIMENTATION ININ BASIN HARBORS
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
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)
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
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!!
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
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 BasinHamburg, 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- PRINCIPLESWithout CDW
With CDWCDW
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
CURRENT DEFLECTING WALL FOR DENSITY CURRENTS- PHYSICAL MODEL TESTS
TIME (Sec)
Dye
Mas
s In
Bas
in (g
) Without CDW
With CDW & Sill
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
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)
BREMERHAVEN, GERMANY
FAST-MOVING RIVER
QUIESCENT BASIN
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
2nd Annual Dredged Material Management Summit
Minimizing Sedimentation In Harbors and Marinas
IN-SITU TREATMENT- PORT OF EMDEN, GERMANY
FAST-MOVING RIVER
QUIESCENT BASIN
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
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!
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