247 



Jacobus van de Kreeke 



University of Miami 



Rosenstiel School of Marine and Atmospheric Science 



4600 Rickenbacker Causeway 



Miami, FL 33149 



SECT. 4. TIDAL RANGE EFFECTS 



The Effect of Sea Level Rise on Tides in Estuaries and Bays 



The tidal motion in estuaries and bays is forced by the ocean tide at 

 the open boundary. Therefore, in addition to the increase in depth, the 

 effect of sea level rise on the tide in the estuary enters through the 

 ocean boundary tide. The report suggests that sea level rise will be 

 accompanied by an increase in tidal range in the ocean. This is not 

 necessarily true, as the response of the water masses in the ocean and 

 coastal seas to the various frequencies contained in the tidal forcing 

 strongly depends on the resonance frequency. Without carrying out more 

 detailed calculations, it will be difficult to make a definite statement 

 whether the offshore tidal range will increase or decrease with a rise in 

 sea level. 



Preliminary calculations pertaining to co- oscillating undamped tides 

 and presented in the report suggest that sea level rise can considerably 

 alter the response of the estuary to those ocean tide components having 

 frequencies close to the natural frequency of the estuary. These 

 calculations asstime zero friction, an assumption which for most estuaries 

 is not justified. When including friction, it is expected that the effect 

 of sea level rise on the tide will be less dramatic than the effects 

 predicted by the zero friction models. 



In evaluating the effects of sea level rise on tides and tidal 

 circulation, more attention should be given to the combined effect of a 

 rise in still water in the estuary and a change in ocean tidal amplitude. 

 In particular, the change in the ratio tidal amplitude/depth is important. 

 It is the magnitude of this ratio that determines the importance of the 

 "nonlinear effects," including superelevation, residual circulation, and 

 deformation of the tide. 



