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Examples of secondary flows and lateral variability

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Examples of secondary flows and lateral variability

S4

S4

S3

S3

S2

U+DU

U-DU

U+DU

U-DU

U-DU

U-DU

S2

S1

S1

Differential Advection in channel with deep middle and

Shallow flanks Producing along channel salinity gradient

Fresh

Fresh

Salty

Effects of Differential Advection on Flood Tide

Nunes and Simpson (1985)

What’s the effect on stratification?

What’s the effect on the along channel momentum balance?

What happens on Ebb?

Requires Secondary flows

to balance forcing

Kalkwijk and Booij (1986)

Geyer (1993)

Pressure gradient

centrifugal acceleration

Secondary flows due to flow curvature

From Geyer (1993)

Baroclinic balance arrests

lateral flows

Chant and Wilson (1997)

Seim and Gregg (1997)

Pressure gradient

centrifugal acceleration

Chant and Wilson, 1997

Current Vectors

Upper layer

Lower layer

NY

NJ

CTD section

CTD section

NY

NJ

ADCP mooring

NOAA/NOS - PORTS mooring data.

Average ebb-dry period

Secondary circulation

Average ebb-wet period

No secondary circulation

Red - Surface

Blue -Middle

Purple- Bottom

Current Vectors

1 m/s

1 m/s

Dry Period

1.5 m

1m

2 m

Tidal Range

Wet Period

Currents during Maximum ebb

Wet Period

Red Surface Blue Bottom

Wet Period

1.5 m

1m

2 m

Depth

Depth

Tidal Range

Tidal Range

Along Channel Flow

Max Ebb

vs.

Tidal Range

Dry Period

Cross Channel Flow

Along Channel Flow

NeapTides

Depth

Depth

Cross Channel Flow

Springtides

Tidal Range

Tidal Range

Max Ebb vs. Tidal Range Wet Period

Wet Period - Maximum Ebb binned vs Tidal Range

Stronger shear in along

channel flow but weaker

cross channel flows.

Strong

Moderate

Weak

Complex

Lateral Sloshing??

Stratification

Tidal Range

Secondary flows driven by Coriolis (Lerczak and Geyer, 2004)

Lerczak and Geyer (2004) model set up.

Az=22*10-4 m2/s

Uf=0.25 cm/s

Max(V)=10 cm/s

Az=3.3*10-4 m2/s

Uf=7.0 cm/s

Max(V)= 2.6 cm/s

As stratification increases

Secondary flows decrease

Flood-ebb asymmetry in

Secondary flows

V~1/DS(z)

g ranges from 1 for weakly

Stratified case and approaces

100 during strongly case

(represents ratio of isopycnal tilting

To differential advection)

Lerczak and Geyer (2004)

Tidally mean vuy+wuz

Is dominated by flood

Tide.

Note where velocity max

Is on flood (red line)

Figure 4 Salt section along Hudson during moderate to high flow condition during spring tide (upper panel) and neap tide (Lower panel). See figure 2 for timing of transects relative to river flow and tidal range

April May June

Figure 5. (upper panel) along channel currents averaged between 1.35 and 6.1 meters above the bottom water from site 4 (blue line) and its low passed filtered component (green line). (lower panel) surface (green line) and bottom (blue line) salinity during the spring of 2002.

Exchange flow drops off more slowly than H&R predicts because

H&R neglected the effect of lateral circulation that becomes more

Important as mixing increases.

Including Coriolis produces lateral asymmetries. This would tend to transport

Sediment to the right (looking seaward) and thus produce a laterally asymmetric

Channel such as the Hudson.

Channel Cross-section at mooring array

1

2

3

4

Laterally Asymmetric Channel in Hudson

In the afternoon we’ll look at aspects of lateral circulation based

On data from the Hudson

Laterally Sheared

James Neap

James Spring

Hudson Neap

Hudson Spring

Vertically Sheared

Figure 3) Schematic showing movement of Hudson and James river estuary through

Kevlin/Ekman number space over the spring neap cycle. Laterally sheared estuaries lie

in the upper right quadrant, while vertically sheared estuaries lie in the lower left quadrant

U2,V2

U1,V1

s1s

s2s

s1b

Full mooring deployment (Lerczak et al. 2006) and locations of

Data used in afternoon experiment