1.5 for a nearly uniform sand 



1.8 for a naturally graded sand 



2.8 for sand with a very wide range of grain diameter 



Kawamu 



ra Formula: The rate of sand movement, q, is given by: 



q = K ^ (U* - U*t) (U* + U^^)2 (2) 



where y is the specific weight of air, U^ is the shear velocity, and U^. 

 is the threshold shear velocity, and K is a constant which must be 

 determined by experiment. 



(7) 

 O'Brien and Rindlaub Formula : O'Brien and Rindlaub proposed 



the following formula from data derived by field tests 



G = 0.036 U^"^ (for U5 > 20 ft/sec) (3) 



where G is the rate of transport in pounds per day per foot width, and 

 Uc is the wind velocity at 5 feet above the sand surface in ft/sec. How- 

 ever, the use of this formula should be limited to sand having the same 

 grain diameter of that existing in the field tests'"-' (0.195 mm). 



WIND VELOCITY ABOVE A SAND SURFACE 



The shear stress, T, proauced at the sand surface by wind is one 

 of the most important factors in investigating sand movement by wind 

 action. When the sheat stress exceeds a certain critical value, the sand 

 particles start to move. As long as there is no sand movement, the wind- 

 velocity distribution can be described adequately by the general equation 



U = C Log ^ (4) 



z 

 ^o 



in which U is the velocity at height Z above the sand surface and Zq is 

 a reference parameter. The coefficient, C, according to von Karman's 

 development, is equal to z^ U^ , wh ere K is the Karman constant, U^ is 



/~T~ 

 the shear velocity defined as w T , and p is the density of air. For 



K equals 0.40, the von Karman equation becomes 



