Sediment Management Technologies W. H. McAnally PhD, PE, D.CE, D.NE, F.ASCE Research Professor of...

Sediment Management Technologies  

W. H. McAnally PhD, PE, D.CE, D.NE, F.ASCE Research Professor of Civil & Environmental Engineering

Mississippi State University, USA. mcanally@cee.msstate.edu

 R. Kirby BSc, PhD, C.Geol, Dist.D.NE, FGS

Director & Board Member Sediment Innovation Centre (SICEM)Emden, Germany. robkirby@globalnet.co.uk

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.