U.S. Army Corps of Engineers Investigation on the Implementation of Nautical Depth

Transcription

1 U.S. Army Corps of Engineers Investigation on the Implementation of Nautical Depth Tim Welp, Steve Reid, and Dennis Webb Tim Welp Research Hydraulic Engineer ERDC Coastal and Hydraulics Laboratory 25 October 2012

2 Definition of Fluid Mud Fluid mud is a high concentration aqueous suspension of fine-grained sediment in which settling is substantially hindered by the proximity of sediment grains and flocs, but which has not formed an inter-connected matrix of bonds strong enough to eliminate the potential for mobility, leading to a persistent suspension. McAnally et al. 2007

3 What is Fluid Mud?

4 Problem Statement Why Is It A Problem? Sounding pole, lead line, and acoustic echo sounding will generally not correlate with one another, or give consistent readings from one time to the next when the same type of instrument is used in fluid mud (Hydro EM). Measurement ambiguity has hindered optimization of Corps management of Gulfport Ship Channel.

5 Source: Kirby and Parker 1978

6 $1,000,000 $181,455

7 Nautical Bottom Definiton PIANC-IAPH 1997: the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship s keel causes either damage or unacceptable effects on controllability and manoeuvrability Nautical Bottom Approach Requires: practical fluid mud criterion & critical value practical, continuous survey method minimum underkeel clearance value knowledge about ship behaviour

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10 Fluid Mud Field Drop Admodus 10A Admodus 10B Admodus 10C BV Rheotune 10 (9/19) Rheotune 10 comp (9/21) SILAS Water/Silt interface SILAS g/ml boundary SILAS g/ml boundary SILAS seafloor CTD 1 (9/19) Depth (ft) Water / Silt Interface khz Depth Density (g/ml)

11 Practical Continuous Survey Method Rheotune Density Probe SILAS

12 Practical Continuous Survey Method SILAS DIGITAL RECORDING LINE 17 LEGEND TOP SILT LAYER 1.200kg\liter DENSITY LEVEL TOP CONSOLIDATED MATERIAL SILAS SURVEY GULF PORT DIGITAL RECORDING OF ODOM ECHOTRACK MK III 24 khz FEQUENCY

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14 World Wide Nauical Depth Criterion Critical Limits Density (g/cm 3 )

15 Economic Impact Study Results - 800,000 yd 3 /9 months, $2.1M -$5.6M - Estimate that if fluid mud layer excluded could reduce dredging in excess of 250,000 yd 3 - annual savings $550,000 to $1.4M - 50 year project life potential savings $28 to $70M - build acre new CDF $28 -$49M - extend CDF life 10 years

16 SAM Hydro Survey Using SILAS & Rheotune

17 Nautical Bottom Definiton PIANC-IAPH 1997: the level where physical characteristics of the bottom reach a critical limit beyond which contact with a ship s keel causes either damage or unacceptable effects on controllability and manoeuvrability Nautical Bottom Approach Requires: practical fluid mud criterion & critical value practical, continuous survey method minimum underkeel clearance value knowledge about ship behaviour

18 Implementation Plan Upgrade SAM with state-of-practice fluid mud surveying equipment and train personnel on its use to determine where nautical bottom is (1.2 gm/cm 3 horizon). Develop hydrodynamic model for ERDC ship simulator to calculate ship response to the variety of forces (Gulfport-specific environmental and mariner controlled) being exerted upon the vessel w/o fluid mud. Modify ship simulator with Ghent University/Flemish Hydraulics Institute fluid mud/ship maneuverability hydraulic coefficients. Have Gulfport Pilots drive simulator with fluid mud, then with different fluid mud densities and underkeel clearances to accept nautical depth criteria. Monitor dredging to optimize maintenance dredging contract management.

19 Dr. Marc Vantorre EXPERIMENTAL PROGRAM Source: Dr. Marc Vantorre 2005 Towing tank for maneuvers in shallow water co-operation Flanders Hydraulics Laboratory & Belgium Ghent University, Belgium

20 ERDC Ship Simulator Collection & Rendering of Visuals

21 Implementation Plan Upgrade SAM with state-of-practice fluid mud surveying equipment and train personnel on its use to determine where nautical bottom is (1.2 gm/cm 3 horizon). Develop hydrodynamic model for CHL ship simulator to calculate ship response to the variety of forces (Gulfport-specific environmental and mariner controlled) being exerted upon the vessel w/o fluid mud. Modify ship simulator with Ghent University/Flemish Hydraulics Institute fluid mud/ship maneuverability hydraulic coefficients. Have Gulfport Pilots drive simulator with fluid mud, then with different fluid mud densities and underkeel clearances to accept nautical depth criteria. Monitor dredging to optimize maintenance dredging contract management.

22 Atchafalaya Bar Channel

23 Atchafalaya Bar Channel

24 High Resolution Density Profiler