where BG is a universal constant. The constant G was taken as

4.5 for unstable conditions and 7.0 for stable conditions (Lumley

and Panofsky, 1964). For IZ/LI > 0.1, Equation (4.37) is not valid,

but a power law equation (Csanady, 1973) can be used:

 -- u (zl

 u 1 (4.47)




where zl is an arbitrary height. The exponent a depends upon the

roughness length zo, the reference height zl and the stability.

Since the log-linear profile given by Eq. (4.46) can be assumed to

hold up to the height IZ/LG I the reference height



 z1 = (4.48)



was chosen as this value. Therefore,the reference velocity is

 LG LG
 u G+ z
 u = L* In( 10 z) +S G 1(4.49)
 Sz L
 o G




 = (zo LG) (4.50)



The gradient similarity length LG describes the stability while zo

describes the physical characteristics. The only dimensionless param-

eters that can be formed from these parameters is Zo/LG. Therefore


1