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The Residual Currents

The residual current is commonly defined as the tidal-cycle average of tidal current. This definition could not be simply applied to the case with inclusion of M2, S2, N2, K1 and O1 tides since their tidal periods are different. Neither could it be applied to the intertidal salt marsh area due to alternative dry and wet periods over one tidal cycle. For this reason, the residual current described here is the sub-tidal flow that is separated from the tidal current using Foreman's harmonic analysis program and only exists in the estuarine channel.

Fig. 1: Distribution of the model-predicted residual currents in the Satilla River Estuary. Click here for larger image.


In the case with the M2, S2, N2, K1 and O1 tidal forcings, the residual current in the main channel of the Satilla River estuary is characterized by multiple eddy-like convergent and divergent zones. The figure on this page shows two eddy circulations, one is anti-cyclonic gyre, another is cyclonic. The FVCOM-predicted multiple eddy-like residual circulation cells in the Satilla River Estury were demonstrated by the towed ADCP measurements. They are very similar to the ADCP depth-averaged subtidal current vectors (on March 11, 1999, not shown here).

Fig. 2: Distribution of the ADCP-derived residual currents in the Satilla River Estuary. Figure was provided by scientists at Skidaway Institute of Oceanography. Click here to view the full size figure



  Dr. Changsheng Chen

  School for Marine Science
  and Technology
  University of Massachusetts   Dartmouth


  Dr. Mac V. Rawson
  Georgia Sea Grant College   Program
  University of Georgia
  Athens, GA 30602


  Dr. Randal L. Walker
  Marine Extension Service
  University of Georgia
  Athens, GA 30602-3636



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