the bottom contours for valid computations. The above assumption also 

 implies that there is no flooding landward of the shore; thus, there is 

 a deficiency in the method when substantial flooding occurs. 



The bottom contours of the actual seabed are rarely straight and para- 

 llel; however, the traverse line can often be oriented so that it is nearly 

 perpendicular to the contours in an average way. For complex offshore 

 bathymetry, such an approximation would be invalid. For storms moving 

 more or less perpendicular to a coastline, the traverse line can be taken 

 through, or anywhere to the right of, the region of maximum winds, but 

 never to the left of this region. Many other factors such as the angle 

 of approach of a storm, the coastline configuration, and inertial effects, 

 limit the use of such a simple approach. 



The computation model given here is based on Bathystrophic Storm Tide 

 Theory as described by Bodine (1971). Although Bodine applied both manual 

 and digital computer calculation methods to the open coast storm surge 

 problem, only the manual method is presented. 



The bottom and surface shear stresses are assumed to vary according 

 to: 



^by KVIVI 



sx 

 ^- = kW^ cos e 



T 



~p 



T 



(bottom shear stress) (3-55) 



(wind shear stress) (3-56) 



^ = kW^ sin e 



in which K is a dimensionless bottom friction coefficient, k is a 

 dimensionless surface friction coefficient, W is the wind speed, and 

 6 is the angle between the x-axis and the local wind vector. The bottom 

 friction coefficient K is related to the coefficient of Chezy C and 

 the Darcy-Weisbach friction factor f^ as follows: 



Typical bottom conditions result in a value of K that lies in the 

 range between 2 x 10"^ and 5 x 10" ■^. For a first estimate, a value 

 of K = 2.5 x 10"^ may be assumed. This coefficient is used in cali- 

 brating the model. It not only accounts for energy dissipation at 

 the bed, but may be used to adjust for inexact modeling and deficien- 

 cies caused by ignoring some of the hydrodynamic processes involved. 



3-103 



