Sediment Management Technologies

Transcription

1 Sediment Management Technologies W. H. McAnally PhD, PE, D.CE, D.NE, F.ASCE Research Professor of Civil & Environmental Engineering Mississippi State University, USA. R. Kirby BSc, PhD, C.Geol, Dist.D.NE, FGS Director & Board Member Sediment Innovation Centre (SICEM) Emden, Germany.

2 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

3 Engineering Solutions Krone s 3 ways to address sediment deposition: Keep sediment out Keep it moving Remove it Photos courtesy of Corps of Engineers

4 PIANC WG 102: Minimizing Harbor Siltation Six Methods Taxonomy METHOD 1. Keep Sediment Moving (KSM) and mainly passive: DESCRIPTION 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 5. KSO Through Passive Structures: 6. Keep Sediment Navigable (KSN) and passive/active For impounded docks, adopt low solids, surface water intakes, or resort to intermediate settlement basins, etc. For impounded docks, adopt low solids, surface water intakes, or resort to intermediate settlement basins, etc. Adopt Passive or Active Nautical Depth and Conditioning

5 COPRI: Sed Solutions Taxonomy CATEGORY STRATEGY EXAMPLES Prevention Treatment Accommodation KSP Keep Sediment in Place KSO Keep Sediment Out KSM Keep Sediment Moving KSN Keep Sediment Navigable DRS Dredge and Remove Sediment DPS Dredge and Place Sediment Adapt (to Changing Sediment Regime) Erosion control on land and/or bed and banks Sediment Traps, Gates and Dikes, Channel Separations Training Structures, Agitation, Flocculation Reduction, Flows Nautical Depth Definition, Aerobic Agitation Placement in confined disposal facilities or offshore, Permanent beneficial uses Bypass sediment (KSM), Temporary beneficial uses Flexible infrastructure, opportunistic agriculture, coastal setbacks

6 Fine, Cohesive Sediments Diameter < 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

7 Nautical Depth Fluid Mud COUNTRY The Netherlands Belgium China China China UK France France France Germany Thailand PORT Rotterdam Zeebrugge Yangtze Liang yungang Tianjing xingang Avonmouth Dunkirk Bordeaux Nantes - Saint Nazaire Emden Bangkok Firm Bottom Surinam Paramaribo French Guiana Cayenne

8 Fluid Mud in Sediment Profiles Sediment transport depth X Mixed layer mobile suspension Secondary lutocline Suspension Sediment concentration or density X Stratified mobile suspension (zero effective stress) Primary lutocline Zero velocity plane Lutocline shear layer X Fluid mud Stationary fluid mud Deforming bed Bed Fluid Mud Stationary (measurable effective stress) Depth below water surface bed

9 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

10 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

11 Emden: Self-propelled hopper with low power underwater pump for infrequently fluidising, raising, oxidising and redepositing fluid mud. (Wurpts, 2005).

12 Emden Active Nautical Depth Maintenance dredging reduced from 4X10 6 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

13 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.

14 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

15 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.