35 



4. TIDAL RANGE EFFECTS 



4.1 INTRODUCTION 



The effect of sea level rise on the open coast and estuarine tidal 

 ranges is a matter of significance as far as the dynamics of shoreline 

 response is concerned, including such processes as coastal flooding, 

 salinity intrusion and sediment transport. An obvious question is whether 

 a rise in the range, should it occur, would overshadow the effect of the 

 mean sea level rise itself. The phenomenon is strongly site-specif ic , 

 depending upon local morphological and meteorological conditions, and also 

 on remote forcing due to macro -scale oceanographic phenomena. 



Astronomical tides are shallow water waves even in the deepest ocean, 

 and therefore "feel the bottom." Conversely, therefore, the bottom 

 topography and frictional resistance influence tide propagation in the sea. 

 Since shorelines define the boundaries of the offshore shelf which is 

 usually quite "shallow," nearshore tides are strongly influenced by the 

 shelf topography. The distinction between tide measured "along the open 

 coast" and, for example, at a bay entrance therefore becomes somewhat 

 blurred. With reference to tide measured inside a bay as opposed to 

 outside, Mehta and Philip (1986) noted that "the definition of 'outside' 

 remains somewhat obscure in physiographic terms...." However, they added 

 that "restrictive dimensions of bays compared to the sea impose water level 

 oscillations whose range and frequency may be partially unrelated to 

 oscillations outside." Furthermore, from the point of view of organizing 

 data, the distinction between open coast tide and bay or estuarine tide may 

 be retained, as in the following description. 



4.2 LITERATURE REVIEW 



The principal tide -generating forces arise from the gravitational pull 

 exerted on the earth's surficial water mass (and to a much smaller extent 

 on the entire mass of earth; see, for example, Hendershott, 1972) by the 

 moon and the sun. Darwin (1898) presented an "Equilibrium Theory of the 

 Tides," which rovides a useful qualitative description of some of the main 

 features of the tide phenomenon based on a force balance involving 



