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J. Nauw 1) , L. Merckelbach 2) , H. Ridderinkhof and H. van Aken

Ferry-based observations of the transport of total suspended matter through the Texel inlet Journal of Sea Research , 2014 , 87 , 17 - 29. J. Nauw 1) , L. Merckelbach 2) , H. Ridderinkhof and H. van Aken T. Gerkema 1) , C. van der Hout 1) , J. de Vries 3)

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J. Nauw 1) , L. Merckelbach 2) , H. Ridderinkhof and H. van Aken

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  1. Ferry-based observations of the transport of total suspended matter through the Texel inletJournal of Sea Research , 2014, 87, 17 - 29 J. Nauw1), L. Merckelbach2), H. Ridderinkhof and H. van Aken T. Gerkema1), C. van der Hout1), J. de Vries3) 1) Royal Netherlands Institute for Sea Research (a NWO institute) affiliated to Utrecht University 2) Helmholtz Zentrum Geesthacht, Germany 3) Van Oord

  2. Measurement locations in the Netherlands Vlie inlet Texel or Marsdiep inlet Kimstergat North Holland coastal zone

  3. Schulpengat Instrumentation ADCP • Ferry Schulpengat 17 km/h, 32 times per day, 7 days per week, 300 days per year (since 1998, less freq. since 2006) • Nortek 1.0 MHz Acoustic Doppler Current Profiler depth 4.3 m, sampling rate 0.26-0.35 Hz, 3 beams 25° angle, bin size: 0.5 m, profiles: -velocity in earth coordinates (u,v,w) -backscatter intensity per beam (N1,N2,N3) • Processing erroneous data profiles, data in harbor 50 gridpoints along streamlines tidal flow grid

  4. Calibration with Navicula Navicula 13-hours calibration with Navicula: • ADCP: sample rate 1 Hz • TSM: 1 surf+1 bot sample/20 min. • CTD + OBS: 1 profile/20 min. CAMPAIGNS • >25 13-hours stations in the Marsdiep inlet BESIDES THAT: • 3 13-hours transects in the Vlie inlet • 3 13-hours transects in the North Sea along Dutch coast • 6 13-hours transects in the Western Scheldt • 2 13-hours stations in the Kimstergat near Harlingen

  5. Instruments ADCPs Navicula pole OBS box Water samples Niskin CTD&OBS

  6. Filtration of water samples • Before: 0.7µm GF/F dried @ 110oC (2 hrs) • 1 hour acclimatization • Weighing Sartorius, 0.01 mg • Samples ~ 300 to 900 ml backpressure • Filters rinsed with milli-Q • After: Dried, acclimatize, weighing

  7. TSM (mg/l) TSM= 42∙OBS-9 OBS (Volt) Navicula Marsdiep Tracks ferry SPMmax ~200 mg/L)

  8. 2007-09-28, gusts of 9 Bft

  9. North Holland coastal zone SPMmax ~250 mg/L) robustfit (Matlab) Van der Hout et al. (2015)

  10. Calibration Vlie inlet • * Bottom • o surface • Both • bottom • surface Gerkema et al. (2014)

  11. Kimstergat (near Harlingen) Kimstergat (max ~800 mg/L) SPMmax ~600 mg/L)

  12. Theil-Sen fit Slopes between all pairs Histogram of slopes Slope of the fit = Median Intercept=median(TSM-slope*OBSbox)

  13. Calibration OBS box to OBS frame In the lab 2015-06-20 In situ: 2007-04-12

  14. TSM profile

  15. Theory Merckelbach (2006) Acoustics classical turbulent

  16. Grainsize Distribution Samples ~ 1 liter: every hour, surface & near-bottom Stored in fridge, reduced by syphoning Laser particle sizer Coulter LS after ultrasonic breakup flocs Error bar – variation within 13-hours measurement

  17. Calibrating ADCP NaviculaOnly Classical regime kt,nav=1.1·10-9

  18. Classical & Turbulent regime

  19. Surface boundary condition Measured concentration Classical regime Turbulent regime

  20. Calibration kfer ADCP ferry Ic,fer = Ic,nav -5.4 kt,fer=3.4·kt,nav= 3.7·10-9

  21. Conclusions • Measurements using ADCPs can be used to determine TSM concentrations and therefore TSM fluxes after calibration! • Due to turbulent regime – an independent measure of the TSM concentration is needed somewhere in the water column • OBS – TSM calibration lines vary with location and time • Theil – Sen fit provides better fit than linear regression (outliers)

  22. Daily values • - 14-day running mean +4.3˚ +3.9˚ S=32.2 S=27.2

  23. Samples OBS Time series, Bottom, 16 June Surface, 16 June Bottom, 17 June Surface, 17 June

  24. Time-series 2003-2005 Period 1 Period 2

  25. September 2003

  26. 14 day averages

  27. Daily residual transport vs daily mean windspeed transport windspeed

  28. Long-term averages Flux along Dutch Coast: De Kok2004: 10-25 Mton/yr Flux through Texel inlet (Delft3D): Ligtenberg1998: 0.53-1.59 Mton/yr This study: Flux=2.1-2.6∙102 kgs-1 ~8 Mton/yr Residual transport (·103 m3/s): Ridderinkhof1988: -0.82 Elias2006: -2.13 Buijsman2007: -2.91

  29. Conclusions • Measurements using ADCPs can be used to determine TSM concentrations and therefore TSM fluxes after calibration! • Residual water transport is small and can be towards the Wadden Sea or the North Sea. • Sediment flux is tide-driven – import of 8 M tons/year – previous estimates are probably highly underestimated.

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