Sediment Management Technologies
W. H. McAnally PhD, PE, D.CE, D.NE, F.ASCE Research Professor of Civil & Environmental Engineering
Mississippi State University, USA. [email protected]
R. Kirby BSc, PhD, C.Geol, Dist.D.NE, FGS
Director & Board Member Sediment Innovation Centre (SICEM)Emden, Germany. [email protected]
Port & Channel Sedimentation
• Sediment accumulation reduces available depth• Dredging & disposal are expensive• Dredging & disposal are often environmentally
disruptive• Environmental windows
limit dredging• Placement sites are limited
Engineering Solutions
Krone’s 3 ways to address sediment deposition:• Keep sediment out• Keep it moving• Remove it
Photos courtesy of Corps of Engineers
PIANC WG 102: Minimizing Harbor SiltationSix Methods Taxonomy
METHOD DESCRIPTION1. Keep Sediment Moving
(KSM) and mainly passive:
Locate/relocate port to deeper water, locate berths alongside channels rather than on waterway margin, apply equilibrium regime theory concepts, dredge channels parallel to natural flow, etc.
2. KSM and passive Longitudinal/perpendicular training walls/groins, dikes, or sills.
3. KSM and active Bed -mounted, automatic pumps fed by water injection, and applicable at impounded or semi-enclosed basins; early stage (i.e. before consolidation) water injection alone; bar/shoal removal, scour/propeller jets, etc.
4. Keep Sediment Out (KSO) and active
For impounded docks, adopt low solids, surface water intakes, or resort to intermediate settlement basins, etc.
5. KSO Through Passive Structures:
For impounded docks, adopt low solids, surface water intakes, or resort to intermediate settlement basins, etc.
6. Keep Sediment Navigable (KSN) and passive/active
Adopt Passive or Active Nautical Depth and Conditioning
COPRI: Sed Solutions TaxonomyCATEGORY STRATEGY EXAMPLES
Prevention
KSP – Keep Sediment in PlaceErosion control on land and/or bed and banks
KSO – Keep Sediment OutSediment Traps, Gates and Dikes, Channel Separations
KSM – Keep Sediment MovingTraining Structures, Agitation, Flocculation Reduction , Flows
Treatment
KSN – Keep Sediment NavigableNautical Depth Definition, Aerobic Agitation
DRS – Dredge and Remove SedimentPlacement in confined disposal facilities or offshore, Permanent beneficial uses
DPS – Dredge and Place SedimentBypass sediment (KSM), Temporary beneficial uses
AccommodationAdapt (to Changing Sediment Regime)
Flexible infrastructure, opportunistic agriculture, coastal setbacks
Fine, Cohesive Sediments
• Diameter < 20 – 40 μm • Form flocs – low density, mostly water• Form Fluid Mud in high concentrations• False acoustic “bottom” fathometer signals• Require dredging large volumes of muddy
water
Photos courtesy of Chris Zabawa, EPA
Nautical Depth
Firm Bottom
Fluid Mud
COUNTRY
PORT
The Netherlands
Rotterdam
Belgium Zeebrugge
China Yangtze
China Liang yungang
China Tianjing xingang
UK Avonmouth
France Dunkirk
France Bordeaux
France Nantes - Saint Nazaire
Germany Emden
Thailand Bangkok
Surinam Paramaribo
French Guiana
Cayenne
Fluid Mud in Sediment Profiles
Sediment concentration or density
Mixed layer mobile suspension
Stratified mobile suspension
Lutocline shear layer
Fluid mud
Deforming bed
Stationary fluid mud
Stationary
bed
Depth below water surface
Primary lutocline
Secondary lutocline
Zero velocity plane
Sediment transport depth
Suspension
(zero effective stress)
Bed
(measurable effective stress)
X
X
X
Sediment concentration or density
Depth below water surface
Fluid Mud
Passive Nautical Depth
• Map Fluid Mud Density• Dredge to keep
1.2 kg/cu m below channel prism
Zeebrugge Harbor entrance density contours at project depth
Active Nautical Depth• Create and maintain fluid mud in
channel/port by oxygenation & stirring• Presence of fluid mud prevents entry of
new sediment• Vessels sail
through muddy water
• Example: Emden Port
Emden: Self-propelled hopper with low power underwater pump for infrequently
fluidising, raising, oxidising and redepositing fluid mud. (Wurpts, 2005).
• Maintenance dredging reduced from 4X106 cu m/yr to 0
• Costs reduced from €12.5M to €2M/yr• Chemolithotrophic bacteria break down the Tri-
butyl Tin• Formerly intractable
problem has disappeared
Emden Active Nautical Depth
Gulf Ports Project
• PURPOSE: – Find feasible, affordable engineering solutions to reduce or eliminate
port maintenance dredging requirements.
• APPROACH: – Identify sedimentation problems and causes– Devise approaches to decrease dredging costs.
Pascagoula • Two harbors• Deep draft port ~ 40+ ft• Both local and federal channels• Top 20 largest U.S. ports
• Fluid mud• Dredged every 18 months• About $450,000 per cycle• Limited disposal space• Nautical depth would work
Conclusions
• Sediment Management:– Can reduce dredging costs– Is sustainable– Comes in many different forms
• Nautical Depth is a proven solution– Used ~40 years in Rotterdam & worldwide– Should be used in U.S.
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