Quantification of sediment concentrations and fluxes A comparison between optical and acoustic measurements Utrecht, 11 June 2013 – Emile Lemey

Management JDN Departments DREDGING Marine Environmental Department MARINE ENVIRONMENTAL DEPARTMENT SEDIMENTS SOIL GROUNDWATER SPECIAL WASTE Envisan WHO?WHO? ENVIRONMENTAL QUALITY HEALTH SAFETY SECURITY ENVIRONMENT QHSSE

Management JDN Departments DREDGING Marine Environmental Department MARINE ENVIRONMENTAL DEPARTMENT SEDIMENTS SOIL GROUNDWATER SPECIAL WASTE Envisan WHO?WHO? ENVIRONMENTAL QUALITY HEALTH SAFETY SECURITY ENVIRONMENT QHSSE

WHEATSTONE Secondary Stabilisation Project WHAT?WHAT? Dredging near sensitive marine habitats  Intensive dredge plume monitoring  Hind cast hydrodynamic modelling

WHEATSTONE Secondary Stabilisation Project WHAT?WHAT? Dredge plume monitoring -Daily transects around CSD -Perpendicular to current direction -Downstream of turbidity source

MONITORING METHODS 1)Optical measurements -YSI 6920 V2 multi-parameter probe -Davit with an electrical winch -Undulating motion -Turbidity, depth, temperature, conductivity and salinity -Turbidity  SSC with conversion coefficient 2)Acoustic measurements -Acoustic Doppler Current Profiler (ADCP) Workhorse Mariner (Teledyne RD Instruments) -VISea Plume Detection Toolbox (PDT) software (Aqua Vision) -Mounted in moon pool of vessel, fixed depth -Current speed and direction -Backscatter data  SSC HOW?HOW?

MONITORING METHODS 3)Integration positioning system / loggings -Through software (QINSy and Visea PDT) -GPS/DGPS data  absolute flow velocity and direction HOW?HOW?

POST PROCESSING 1)Acoustic method -Sediment flux calculation in Visea PDT 2)Optical method -Data outlier removal -Surfer surface modelling software (© Golden Software) -Quantification of total flux (kg/s)  HOW?HOW?

-Most transects: similar sediment profiles RESULTS Optical: Acoustic:

-Some differences in profiles RESULTS Optical: Acoustic:

-Some differences in profiles RESULTS Optical: Acoustic:

RESULTS -Quantification of fluxes

RESULTS -Quantification of fluxes

-Point measurement comparison RESULTS

Both methods yield similar profiles Real-time vs. Intensive post processing Flux quantification results differ TSS concentrations by acoustic measurement overestimated?  Maybe due to Algorithm used in processing ADCP + PDT very useful as visualisation tool Not yet alternative for optical TSS quantification of complex dredge plumes CONCLUSIONS

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