Quantification of sediment concentrations and fluxes A comparison between optical and acoustic...

Quantification of sediment concentrations and fluxes

A comparison between optical and acoustic measurements

Utrecht, 11 June 2013 – Emile Lemey

ManagementJDN

Departments

DREDGING

Marine Environmental Department

MARINE ENVIRONMENTAL DEPARTMENT

SEDIMENTS SOIL

GROUNDWATERSPECIAL WASTE

Envisan

WHO?

ENVIRONMENTAL

QUALITY HEALTHSAFETY

SECURITY ENVIRONMENT

QHSSE

ManagementJDN

Departments

DREDGING

Marine Environmental Department

MARINE ENVIRONMENTAL DEPARTMENT

SEDIMENTS SOIL

GROUNDWATERSPECIAL WASTE

Envisan

WHO?

ENVIRONMENTAL

QUALITY HEALTHSAFETY

SECURITY ENVIRONMENT

QHSSE

WHEATSTONE Secondary Stabilisation Project

WHAT?

Dredging near sensitive marine habitats Intensive dredge plume monitoring Hind cast hydrodynamic modelling

WHEATSTONE Secondary Stabilisation Project

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?

MONITORING METHODS

3) Integration positioning system / loggings

- Through software (QINSy and Visea PDT)

- GPS/DGPS data absolute flow velocity and direction

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?

- 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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