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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

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

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.


“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


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


Ship Track and Dye Trace for May, 2002

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


Dye’s salinity distribution at for May, 2002

release

Currents and salinity

Upper layer

Lower layer

39 kg of fluorecene dye


Patch 2 (12:20 - 14:00) for May, 2002

Depth integrated dye

1.8 kg

26 kg


40.94 for May, 2002

40.9

Cross Channel Sections during Flood

2 hours after release


Patch 2 (12:20 - 14:00) for May, 2002

Integrated dye above 14 psu

Depth integrated dye

26 kg

1.8 kg


25 kg for May, 2002

26 kg

Patch 3

Patch 2


Patch 3 (14:00 - 15:40) for May, 2002

Depth integrated dye

Integrated dye above 14 psu

2.3 kg

25 kg


44 kg for May, 2002

Patch 3 (14:00 - 15:40)

Patch 4 (15:00 - 17:10)

Depth integrated dye

Depth integrated dye


A series of cross-channel section during late ebb for May, 2002

Currents from ADCP


1 for May, 2002

5

8

6

2

1

7

3

8

4


Patch 4 (15:00 - 17:10) for May, 2002

Integrated dye above 14 psu

Depth integrated dye

16 kg

44 kg


1 for May, 2002

0.5

0



H > 10 m for May, 2002

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


1 for May, 2002

0.5

0

?

Slack before flood

Day 1

Slack before ebb

Day 2


+.5 for May, 2002

12

16

m/s

-1.0

Current

May 24

30 hours after release

End of Ebb


FLOOD for May, 2002

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


Patch 5 (15:45 - 18:45) for May, 2002

Integrated dye above 14 psu

Depth integrated dye

40 kg

20 kg


Conclusions for May, 2002

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.


Fresh for May, 2002

Salty


2 for May, 2002

1

1

3

5

4

5

40 kg

16 kg

3

2

4

26 kg

25 kg

44 kg

Max 35

36 kg


Simulation of Dye Release in Hudson for May, 2002

Ebb

Flood

*Simulation by Rocky Geyer


Patch 1 (11:00 - 12:15) for May, 2002

Integrated dye above 14 psu

Depth integrated dye

16 kg

0.6 kg


* H > 10m for May, 2002

* H < 10m

Dye weighted salinity of each cast


.. Or is it driven by secondary for May, 2002

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


End of Ebb for May, 2002

End of Flood

End of Flood


Two crude estimates of effective horizontal dispersion…. for May, 2002

…both suggest Aeff=1000 m2/s

30 hours after release


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