and 



gH = 32.2 (1.99) =000368 

 U 2 (132) 2 



— = 0.0185 , 

 U 2 



the fetch is given by 



gF 



— = 1.4 . 



U 2 



F = 760 feet for the 90-mile per hour windspeed, so that the equivalent 

 fetch 



F g = 760 feet . 



The vegetation does not match any of the curves in Figure 13, but falls 

 between curves B and C. Assuming that a moderate amount of brush will 

 give a friction effect about halfway between the two curves, from curve 

 B, where d = 10 feet, ff = 0.20, and from curve C, where d = 10 feet, 

 £f = 0.485. The bottom friction is then take", in this case, as the 

 average of the two values 



- 0.20 + 0.485 . . _ 

 if = s = 0.^-+3 . 



For £f = 0.01, 



f f H i Ax 0.01 x 6 x 3,000 1 _ . 



x = ~ •■ - 1.0, 



d 2 10 2 



for ff = 0.343, 



l f 



ff Hi Ax 0.343 x 6 x 3,000 ,. _ 



— * — s = 7. ■ — = bi . / ; 



d 2 10 2 



for T = 4.5 seconds and d = 10 feet, 



2rrd = 2 JL il0 1 _ __ Q ^ 

 gT 2 g (4.5) 2 



From Figure 14, 



K f.01 = °- 80 for f f = °- 01 and f f H i Ax / d2 =1.8 

 Kf a = 0.105 for ff = 0.343 and f f H^ Ax/d 2 =61.7 



33 



