energy dissipation, and radiational loss of energy from the bay to the 

 sea. To estimate the surge height frequencies at various positions in 

 the system, it is necessary to take those water levels determined "by 

 numerical methods for hurricanes of prescribed parameters. This will 

 allow assigning frequencies to the surge heights reached at all positions 

 in the system because by the method presented previously the return fre- 

 quencies of the various hypothetical hurricanes can be determined. Reid 

 and Bodine (196T) presented a finite-difference scheme for predicting the 

 surge heights at discrete positions in a bay system, and based on this 

 treatment, the water level elevations were computed for various storms 

 superimposed over Galveston Bay. Parametric studies in connection with 

 the scheme allow prediction of the surge height frequencies at various 

 positions in this bay, and can be carried out for any bay system. 



2. Prediction Method 



Hurricane surge heights in a bay are influenced by the path that the 

 storm taikes with respect to the system. That is, a storm passing to the 

 left of a semienclosed body of water on the Texas Coast will cause the 

 water to pile up in the upper region of the bay, while those passing to 

 the right depress the surge. This introduces an additional complexity 

 in evaluating the bay surge frequencies, but will be disregarded in order 

 to get a more conservative surge-frequency estimate that will take into 

 account all of the -uncertainties of the problem. If one treats the 

 problem on the relative basis considering the water levels in the bay 

 change relative to those on the immediate open coast and associated with 

 identical frequency of occurrences, then a simple scheme may be devised. 

 In other words, the bay surge frequency is the adjacent open-coast surge 

 frequency shifted to correspond with a particular hiirricane frequency and 

 known computed surge height. Again the "Beta Hurricane", with parameters 

 LR and MVp, is selected for performing the shift. For example, it was 

 found from the numerical computations of the Galveston Bay system that 

 the peak surge for the above hypothetical hurricane was I6 feet above MSL 

 for a position near Baytown, Texas. Based on the known surge frequency 

 of about once in 100 years and the l6-foot elevation, a point can be 

 established on a graph with log-log probability paper. This, however, 

 would give only a single point on the graph. But if it is assumed there 

 is a relative similarity between the surge frequency curve derived on the 

 open coast and the one in the bay, then one could approximate the entire 

 surge frequency curve by considering it parallel to the one for the open 

 coast . 



Figure I8 indicates the frequency of surge heights for Baytown by 

 performing this operation. This simply implies that the curve obtain 3d 

 on Figure I8 is the curve indicated on Figure 9 shifted upward to pass 

 through the point corresponding to I6 feet on the ordinate scale and about 

 once in 100 years on the abscissa scale. Log-log probability paper must 

 be used in carrying out this scheme because it gives the lesser surge 

 heights more reasonable values for the associated frequencies. This scheme 

 will allow surge frequency relationships to be determined for all positions 

 within any bay system and the low-lying terrain if the surge heights are 

 known in advance from previous niomerical computations. 



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