quantification of sediment concentrations and fluxes a comparison between optical and acoustic...
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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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