Analysis of observations

Objective:

To corroborate the following hypotheses:

1. Fortnightly switching in the residual flow direction differs with the along-estuary distribution of the density field.
2. The internal tidal Froude number (Fr0, see below)) will change along the estuary and diagnose the main flow drivers (see below).

 

Expected results

• Distinct structure of residual flows across the channel on neap and spring tides.
• Fortnightly variability of the subtidal structures along the estuary.
• Along-estuary density gradients.
• Applicability of Fr0 as a diagnostic for hydrodynamic switching.

 

Internal tidal Froude number Fr0:

The internal tidal Froude number, Fr0, compares the tidal stress to the baroclinic pressure gradient. It is defined from the tidally-averaged momentum equation:

Fr₀² = V₀² / (g’H )

where V0 is the along estuary tidal current amplitude (in m/s), g’ is the reduced gravity (m/s2) and H is the water depth (m).