Examples of secondary flows and lateral variability

U-UU-U

S1

S2

S3

S4

U+UU-U

S1

S2

S3

S4

Differential Advection in channel with deep middle andShallow flanks Producing along channel salinity gradient

U+UU-U

Salty

FreshFresh

Effects of Differential Advection on Flood TideNunes and Simpson (1985)

What’s the effect on stratification?What’s the effect on the along channel momentum balance?What happens on Ebb?

Pressure gradient centrifugal acceleration

022

zR

uU

Kalkwijk and Booij (1986)Geyer (1993)

Requires Secondary flowsto balance forcing

z

vAz

Secondary flows due to flow curvatureFrom Geyer (1993)

Pressure gradient centrifugal acceleration

022

zy

gR

uU

Baroclinic balance arrests lateral flows

Chant and Wilson (1997)Seim and Gregg (1997)

Current VectorsUpper layer

Lower layer

CTD section

NYNJ

NY

NJ

CTD section

Chant and Wilson, 1997

Red - Surface

Blue -Middle

Purple- Bottom

ADCP mooring

Average ebb-dry periodSecondary circulation

Average ebb-wet periodNo secondary circulation

Current Vectors

NOAA/NOS - PORTS mooring data.

Wet Period

Wet Period

1 m/s

1m 2 m1.5 m

Currents during Maximum ebbWet Period

Dry Period1 m/s

Tidal Range

1m 2 m1.5 m

Red Surface Blue Bottom

Max Ebb

vs.

Tidal Range

Dry Period

Tidal Range

Dep

thD

epth

Tidal Range

Along Channel Flow

Cross Channel Flow

Neap Tides

Tidal RangeD

epth

Dep

th

Tidal Range

Along Channel Flow

Cross Channel Flow

Max Ebb vs. Tidal Range Wet Period

Spring tides

Wet Period - Maximum Ebb binned vs Tidal Range

Stronger shear in alongchannel flow but weaker

cross channel flows.

Tidal Range

Str

atif

icat

ion

Moderate Strong

WeakComplex

Lateral Sloshing??

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

vdAA

1v

Lerczak and Geyer (2004)

As stratification increases Secondary flows decrease

Flood-ebb asymmetry in Secondary flows

V~1/S(z)

ranges from 1 for weaklyStratified case and approaces100 during strongly case

(represents ratio of isopycnal tiltingTo differential advection)

Tidally mean vuy+wuz

Is dominated by flood Tide.

Note where velocity maxIs on flood (red line)

0 5 10 15 20 25 30 35 40 45 50-20

-15

-10

-5

0

m

Salinity May 4th 2002

5

0 5 10 15 20 25 30 35 40 45 50-15

-10

-5

0

km north of the Battery

m

May 26th, 2002

5

10

20

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

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.

April May June

Exchange flow drops off more slowly than H&R predicts becauseH&R neglected the effect of lateral circulation that becomes moreImportant as mixing increases.

Including Coriolis produces lateral asymmetries. This would tend to transportSediment to the right (looking seaward) and thus produce a laterally asymmetricChannel such as the Hudson.

Channel Cross-section at mooring array

1 2 3 4

In the afternoon we’ll look at aspects of lateral circulation basedOn data from the Hudson

Laterally Asymmetric Channel in Hudson

James Neap

James Spring

Hudson Neap

Hudson Spring

Vertically Sheared

Laterally Sheared

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

U1,V1U2,V2

s1s

s1b

s2s

Full mooring deployment (Lerczak et al. 2006) and locations ofData used in afternoon experiment