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Sediment Management Technologies

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

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Sediment Management Technologies

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  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.mcanally@cee.msstate.eduR. Kirby BSc, PhD, C.Geol, Dist.D.NE, FGS Director & Board Member Sediment Innovation Centre (SICEM) Emden, Germany.robkirby@globalnet.co.uk

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

  4. PIANC WG 102: Minimizing Harbor SiltationSix Methods Taxonomy

  5. COPRI: Sed Solutions Taxonomy

  6. 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

  7. Nautical Depth Fluid Mud Firm Bottom

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

  9. Passive Nautical Depth • Map Fluid Mud Density • Dredge to keep 1.2 kg/cu m below channel prism ZeebruggeHarbor 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 4X106 cu m/yr to 0 • Costs reduced from €12.5M to €2M/yr • Chemolithotrophicbacteria break down the Tri-butyl Tin • Formerly intractableproblem has disappeared

  13. 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. Gulf Ports Project

  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.

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