the tides along the Gulf Coast are diurnal while those on the East Coast 

 are semidiurnal. For some locations, the tide may be the principal 

 component of the total rise at shore during a hurricane. 



Coriolis effect also plays an important role in the fluid motion 

 beneath the storm system. Coriolis acceleration exists only when a mass 

 has velocity relative to the earth's surface. The effect acts to the 

 right in the Northern Hemisphere and to the left in the Southern Hemi- 

 sphere. For large basins such as the ocean, and for fluid motion propa- 

 gating at relatively slow speeds, the Coriolis acceleration becomes quite 

 important . 



Section III, THEORETICAL ASPECTS 



Bathystrophic Storm- Tide theory can be described as a quasi-two- 

 dimensional method for evaluating the change of water level along a 

 single traverse line over the Continental Shelf. Unlike the older one- 

 dimensional schemes, it takes into account some of the effects of the 

 earth's rotation. However, Bathystrophic theory is only an approxima- 

 tion to the complete storm- generation process, and its usefulness in 

 predicting actual storm surge depends upon the problem being considered. 

 For some situations, the Bathystrophic approximation appears to give a 

 reasonable estimate of the open- coast surge, but for others the estimate 

 could be in error by a factor of two or more. Usefulness of this theory 

 requires some knowledge of its underlying assumptions and the hydrodynamic 

 processes neglected in its development. To display the underlying prin- 

 ciples of the approximation, the initial conditions imposed and basic 

 hydrodynamic relations appropriate to the problem follow. 



1. Preliminary Conditions Imposed 



Although the basic equations which govern storm surge generation will 

 not be derived here, it is important to mention the conditions imposed at 

 the outset of their development. A knowledge of these conditions gives a 

 better understanding of the resulting equations. The conditions are: 



a. It is assumed for a disturbance of intermediate horizontal scale 

 that L >> D and L <^ Rg, where L is the wave length; D is the fluid depth; 

 and Rg is the radius of the earth. This also implies that: 



(1) The vertical components of velocity and acceleration can 

 be neglected. Thus the vertical pressure gradient is 

 hydrostatic, and vertical Coriolis effects can be ignored. 



(2) The curvature of the earth can be neglected. 



b. The acceleration due to earth's rotation is a constant. 



c. The fluid is homogenous and incompressible, thus the water 

 density p is a constant. 



