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Direct observations of estuarine dispersion: results of a recent dye experiment

Direct observations of estuarine dispersion: results of a recent dye experiment. Bob Chant Rutgers University. River. Pritchard’s Paradigm. Seaward at the surface. Pressure gradient and Velocity. But estuaries are often highly 3-dimensional with appreciable

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Direct observations of estuarine dispersion: results of a recent dye experiment

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  1. Direct observations of estuarine dispersion: results of a recent dye experiment Bob Chant Rutgers University

  2. River Pritchard’s Paradigm Seaward at the surface Pressure gradient and Velocity

  3. But estuaries are often highly 3-dimensional with appreciable cross channel gradients of salinity and velocity. Do these processes impact stream-wise dispersion? Not a new question-- But observations are lacking. Current understanding is based on models (Zimmerman, Okubo, Fischer, Smith) or indirect methods.

  4. “Lagrangain studies of secondary circulation and mixing in a stratified channel” NSF PI’s Chant, Geyer and Houghton. Salinity section May 21, 2001 2-days prior to injection

  5. Pilot Dye Study May 23-24, 2001. 4 more experiments planned for May, 2002 Pilot study coincided with microstructure measurements by Hartmut Peters. 2002 injections will occur at spring and neap tide conditions

  6. Ship Track and Dye Trace Currents and salinity Injection May 23, 2001 9:15-9:30 AM Salinity and velocity cross sections at time of release Figure 2 Study Site

  7. Dye’s salinity distribution at release Currents and salinity Upper layer Lower layer 39 kg of fluorecene dye

  8. Patch 2 (12:20 - 14:00) Depth integrated dye 1.8 kg 26 kg

  9. 40.94 40.9 Cross Channel Sections during Flood 2 hours after release

  10. Patch 2 (12:20 - 14:00) Integrated dye above 14 psu Depth integrated dye 26 kg 1.8 kg

  11. 25 kg 26 kg Patch 3 Patch 2

  12. Patch 3 (14:00 - 15:40) Depth integrated dye Integrated dye above 14 psu 2.3 kg 25 kg

  13. 44 kg Patch 3 (14:00 - 15:40) Patch 4 (15:00 - 17:10) Depth integrated dye Depth integrated dye

  14. A series of cross-channel section during late ebb Currents from ADCP

  15. 1 5 8 6 2 1 7 3 8 4

  16. Patch 4 (15:00 - 17:10) Integrated dye above 14 psu Depth integrated dye 16 kg 44 kg

  17. 1 0.5 0

  18. Vertical mixing estimates

  19. H > 10 m H < 10m <S>=15.8 <S>=15.5 we=0.09 mm/s Kv=2.3* 10-3 m2/s we=0.05 mm/s Kv= 1.0-3 m2/s <S>=15.4 <S>=15.2 we=0.05 mm/s Kv=1.7* 10-3 m2/s we=0.28 mm/s Kv=1.0* 10-2 m2/s <S>=15.2 <S>=14.4 Max Ebb we=0.3 mm/s Kv=1.3* 10-2 m2/s we=0.31 mm/s Kv=1.1* 10-2 m2/s <S>=14.2 <S>=13.3 Max Flood

  20. 1 0.5 0 ? Slack before flood Day 1 Slack before ebb Day 2

  21. +.5 12 16 m/s -1.0 Current May 24 30 hours after release End of Ebb

  22. FLOOD Along Channel sections during ebb 14:00 - 14:30 14:54 - 15:21 15:41 - 16:30 Dye Contour Intervals 0.2, 0.5, 1.0 2.0

  23. Patch 5 (15:45 - 18:45) Integrated dye above 14 psu Depth integrated dye 40 kg 20 kg

  24. Conclusions 1) Lateral iso-pycnal advection of dye on flood 2) Mixing rates on flood are 10-3 and confined to bbm, suggestive of weak entrainment rates and thickening of BBL is due to flow convergence. 3) Mixing increases an order of magnitude on ebb. Diapycnal transport occurs primarily on flank 4) Perfect dispersive process-- coupling between secondary flow spatial variations in mixing and strong ebb shears. Suggests artificial decomposition of diffusive processes is ... 5) Dye distribution after one tidal cycle is not consistent with simple tidal straining ideas. 6) While spread of dye is consistent with advection by estuarine flows (but mixing may not be correct) observations clearly show that dispersion of dye is due to a 3-D tidal straining effect. Are estuarine flows then influenced by this mixing process? 7) Closure over-entrains on flood.

  25. Fresh Salty

  26. 2 1 1 3 5 4 5 40 kg 16 kg 3 2 4 26 kg 25 kg 44 kg Max 35 36 kg

  27. Simulation of Dye Release in Hudson Ebb Flood *Simulation by Rocky Geyer

  28. Patch 1 (11:00 - 12:15) Integrated dye above 14 psu Depth integrated dye 16 kg 0.6 kg

  29. * H > 10m * H < 10m Dye weighted salinity of each cast

  30. .. Or is it driven by secondary circulation and mixing on the margins? “Lagrangain studies of secondary circulation and mixing in a stratified channel” NSF PI’s Chant, Geyer (WHOI) and Houghton (LDEO) Is diapycnal transport primarily associated with vertical mixing? Note: May dominate diapycnal mixing process in global ocean

  31. End of Ebb End of Flood End of Flood

  32. Two crude estimates of effective horizontal dispersion…. …both suggest Aeff=1000 m2/s 30 hours after release

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