(a) Quasi-Static Method for Prediction of Hurricane Surge . 

 TTiis method for determining open-coast storm surge is based on theoretical 

 approximations of the governing hydrodynamic equations originally proposed 

 by Freeman, Baer, and Jung (1957). The term quasi-static method is used 

 here to emphasize that this method should be restricted to slow-moving, 

 large-scale storm systems. This method is called the Bathys trophic Storm 

 Tide Theory and, unlike earlier one-dimensional theories, some of the 

 effects of longshore flow and the apparent Coriolis force are considered. 

 Such an approximation of the theory can be described as a quasi-static 

 method in which a numerical solution is obtained by successively integrat- 

 ing wind stresses over the Continental Shelf from its seaward edge to the 

 shore for a predetermined interval of time. 



This simplified method assumes that storm surge responds instanta- 

 neously to the onshore wind stresses, advection of momentum can be ignored, 

 longshore sea surface is uniform, and no flow is assumed normal to the 

 shore which is treated as a seawall. Barometric effects and precipita- 

 tion also can be neglected. Setup due to atmospheric pressure difference 

 can be estimated from another source, and added to the final design water 

 level. Based on the preceding assumptions. Equations 3-50 and 3-51 reduce 

 to 



gD — = fV + -^ (3-53) 



3x 



ay _ ^sy - '^by 

 3t p 



(3-54) 



Conservation of mass is not considered because, (1) there is no flow 

 perpendicular to shore, (2) the longshore flow is assumed independent of 

 y and, (3) the water level is assumed slowly changing. The forces (ex- 

 pressed in mass times acceleration per unit area) involved and the corres- 

 ponding response of the sea for the bathystrophic approximation are shown 

 in Figure 3-45. As indicated in the figure, the surface shear force act- 

 ing in the x-direction Xg^ and the apparent Coriolis force is balanced 

 by the hydrostatic pressure force pgA(9S/3x). Moreover, the surface shear 

 force acting in the y-direction t is balanced by the bottom shear 

 force T^jy and the inertial force p(9V/9t). 



Bretschneider and Collins (1963) developed a computational model 

 based on this Bathystrophic Theory and applied it to open- coast surge 

 problems for the region around Corpus Christi, Texas. Marinos and 

 Woodward (1968) modified the Bretschneider and Collins model and calibra- 

 ted it for various reaches along the Texas coast by using three hurricanes 

 of record, and also made parametric studies of hypo-hurricane surges for 

 the entire coast of Texas. 



In some cases the underlying assumptions made in the development of 

 this theory are not satisfied. Thus, as a consequence of assuming that 

 the onshore wind stresses cause an instantaneous change of the water level, 

 i.e., U = 0, the traverse line (the line over the Continental Shelf along 

 which computations are carried out) must always be taken perpendicular to 



3-101 



