where 



is the average windspeed at height z 



is the friction velocity (U^ = /t/p , t is the horizontal 

 shear stress and p is air density) 



K = 0.4 (the von Karman constant) 



z is height above ground 



D is the zero-plane displacement 



r r 



z^ is the roughness length. 



The values for D and z were taken from the works of Cowan (1968) and Stanhill 

 o o 



(1969). Figure 1, taken from Stanhill, shows a plot of versus vegetation height. 

 The plot agrees with the relationship = 0.64H derived by Cowan, where H is the vege- 

 tation height. The derived relationship was based on z = 0,13H as found by Tanner 

 and Pelton (1960). ° 



o 



<: 



Q_ 

 1/1 



< 

 Q_ 



o 



LlJ 



M 



20 

 10 



5 



2 

 1 



0.5 



0.2 



0.1 



0. 05 



0. 01 



' ' 1 





1 1 iiii| 



1 ' ' 



|iiii| 



1 ' 



1 















































































/ • 









Illllll 













illllll 







• 



• 













✓ * • 





































































1 1 1 



III! 1 1 1 



1 , M.I 



\ i 1 



hiiil 



1 1 





0.02 0.05 0.1 0.2 0.5 1 2 5 

 VEGETATION HEIGHT (M) 



10 20 



50 



Fig-. 1. — Relationship between zevo-plane displaaement Dq and vegeta- 

 tion height H for different vegetation types (after Stanhill 1969). 



2 



