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 V. TliE TIDE MACHINE 



The characteristic circulation in an estuary such as Bara- 

 taria Bay is directly related to the daHy and monthly sequence 

 of tides. The design and calculations of the tide machine were 

 taken from broader considerations than the tides observed in the 

 estuary itself . 



For proper representation of tidal currents in open coast- 

 line models the tide machine should be located offshore in the 

 modeled portion cf the sea. If possible it should be equidistant 

 from all parts of the model coast line so that the cotidal lines 

 of the wave will be initially parallel to the coast and there- 

 after altered by refraction as in nature. If it is known that 

 the cotidal lines lie initially at some angle to the coast or 

 are normal to it describing a progressive wave moving up or down 

 the coast line, the tide machine and barriers should be located 

 so as to simulate this approach. The more remote the position of 

 the tide machine from the modeled embayment the more changed 

 are the amplitudes of the tidal coefficients of the machine as 

 they are amended to apply at the position offshore. Fortunately 

 this amendment often allows simplification of the tide generator, 

 for seme of the important complicating constituents in the tidal 

 records near the openings to estuaries are due to the behavior 

 of a simple wave inside the estuary. Since the modeled estuary 

 will provide these complicating effects of its own accord, they 



