Tidal Circulation in a Sinuous Coastal Plain Estuary

H. Seim, UNC-CH

J. Blanton, S. Elston, SkIO

Tidal propagation – interaction with the shelf

Residual circulation

Overtides

•Finite Element •Nonlinear•2D (ADCIRC)•Western North Atl.•Crossshelf Amplification•Equatorward phase propagation •Latest phase along GA/FL border

•Shelf response sensitive

NC

SC

FL

GA

M2 Elevation without estuaries – tide experiences two-fold

amplitude increase and notable phase change

m

(B. Blanton)

In the SAB large sections of the coastline are backed by extensive estuaries

(K. Smith, D. Lynch)

depth (m

)

M2 Solution Elevation Difference

Amplitude Ratio Est sol’n Amp-------------------------- > 1 NoEst sol’n Amp

Phase Diff (in red) Est Phase - NoEst Phase>0

(B. Blanton)

Including estuaries increases dissipation >25%...

Strange result – inclusion of highly dissipative estuaries leads to 10% increase in tidal range.

Log10W/m2

Longitude Latitude

(B. Blanton)

Satilla River 1 m tide2-4 m mean depth50 m3/s avg riverflow0.5-1 m/s tidal currentsPristine, typically 2 channel5 km MHHW width, 1km MLW width

Depth-scaling accounts for ~25% of variance – rest due to non-linearities?

M2 phase – earlier in shallow channels, remarkable changes at triple junction

M2+M4 fit reasonable on neap,arger residuals on spring tides

Conclusions

• Damping of propagation appears weak – need to do some simple modeling

• Tidal residual flows strong, structure reminiscent of headland eddies

• Sub-basin exhibits much different behavior

• Overtide generation complex, varies spatially and with time.