32 



The net rate of sand transportation in the form of ripples can be 

 -ascertained once the distance traveled by the ripple and the area of 

 the vertical section of the ripple is known. Let Qr denote the weight 

 of sand transported per hour per foot of width. Denoting the dis- 

 tance traveled by a sand ripple per hour by D and the sectional area 

 MA, 



Qr=ysDA (15) 



where 7s is the specific weight of sand. For the sand ripples in test 51 



A=OMhl (16) 



where h is the height of the ripple mark and I the length of the base, 

 both quantities being expressed in feet. Accordingly, 



Qr=OMhlDys 



(17) 



Table 2 lists the dimensions of some thirteen sand ripples of test 

 51 together with their rate of travel. The first ripple mark was 

 located at station 2, and the remainder covered the distance between 

 the bar and that station. See figure 14. It can be seen from the 

 table that with a few exceptions the ripples have nearly equal sizes 

 and travel with nearly equal velocities. This can be explained on 

 the basis that the depth of water over the ripples is constant and the 

 displacement of the surface uniform during the passage of waves. 

 On the average the rate of transportation of each is Qr=l.21 pounds 

 per hour per foot of width. Comparing this with the data of figure 

 15 it is obvious that sand transportation in the form of ripples is 

 imuch smaller than the sand movement under initial conditions. 



Table II. — Transportation of Sand by Ripples 



