(Beard, I966). However, the results obtained indicated that forward 

 speed of the hurricane had only a negligible effect on the open-coast 

 surge buildup. This, of course, contradicts the more sophisticated 

 analytical schemes for predicting the open-coast surge height, and also 

 disobeys the laws of motion. 



The author first believed that the method of defining the forward 

 speed as the average speed, two hours before and two hours after landfall, 

 was causing the difficulty. Therefore, based on the time histories of 

 the 19 hurricanes used in this report , a study was made by defining the 

 forward speed as the average speed over the Continental Shelf and these 

 speeds were estimated. These average forward speeds were used instead 

 of the ones given in the above reference; the results of this analysis, 

 however, indicated the same contradiction that had obtained before. It 

 was concluded that the discrepancy must be due to data acquired from 

 Texas hurricanes; therefore, five Louisiana hurricanes and the 13 Texas 

 hurricanes used for deriving the open-coast surge frequency at Galveston, 

 Texas, were used in a separate regression analysis. Again, the results 

 indicated that forward speed has little significance on the open-coast 

 surge buildup. Consequently, it was assumed that the limited data did 

 not provide the necessary information for carrying out this type of 

 analysis . 



In all three investigations using multiple correlation analyses, 

 it was found that the surge -height may be estimated approximately by 



H = 0.26 (AP x R) 



where H = Surge height in feet, AP = 29-92 - CPI = the difference between 

 the normal pressure and central pressure index in inches of H„, and R = 

 Radius of maximum winds in nautical miles. The coefficient of correlation 

 for this relation is approximately 0.75, as found by the three attempted 

 investigations . 



Section V. MY SURGE FREQUENCIES 



1. General 



Surge height frequencies within a semienclosed bay system are more 

 difficult to predict than those on the open coast. Virtually no surge 

 height records are available for the Texas estuaries and adjoining low- 

 lying terrain; the available records at a few locations do not give any 

 indication of the actual surge heights experienced at other positions in 

 the system. The water surface may vary throughout the entire spatial 

 range, and the vertical departure of the free surface is dependent upon 

 the magnitude of the forcing functions involved. The water level ele- 

 vations reached at various positions in the system are also affected by 

 direct rainfall on the water surface, and rainfall runoff entering the 

 bay from the surrounding terrain and local streams. Siirge heights at 

 each position are also dependent upon basin configuration, basin depths. 



28 



