concentration distribution. The first of these sediments was the material 
which passed the 0.701-millimeter sieve and was retained on the 0.589- 
millimeter sieve. Settling-velocity measurements of 225 randomly chosen 
particles determined the mean settling velocity, the velocity range, and 
the standard deviation as 0.0626, 0.0387 to 0.113, and 0.0131 foot per 
second, respectively. The second sediment was the material which passed 
the 0.589-millimeter sieve and was retained on the 0.495-millimeter sieve. 
Settling-velocity measurements of 240 particles of this material deter- 
mined the mean settling velocity, the velocity range, and the standard 
deviation to be 0.0498, 0.0285 to 0.0754, and 0.00885 foot per second, 
respectively. 
Table 3 gives the experimental results obtained for the two sediment 
types and Figure 15 shows how these results compare with the results for 
sediment with a settling velocity of 0.035 foot per second. As expected, 
for sediment with a higher V,, the concentration of sediment decreases 
with elevation above the bed at a higher rate. Only this qualitative 
conclusion was obtained. Not enough data were obtained to define quanti- 
tatively the relationship between Vg and M. 
Table 3. So eaeae eae distribution data for 
Vs = 0.0626 and 0.0498 foot per second. 
Curve Period Amplitude 
No. 
[eS CGB se Re Na ORES (&t/s) 
0.0626 a olneeee ey ee 
Variance in 
least squares 
curve 
Slope, 
d(inc)/@ 
Ge") 
0.0327 
0.0154 
0.00497 
0.000966 
= 0.0498 ft/s 
0.00095 
0.00698 
0.00378 
0.00177 
The interesting indication of these measurements is that the increase 
in the rate of decay with elevation of the concentration for a sediment 
of higher settling velocity is not as great as predicted from the O'Brien 
(1933) equation for concentration equilibrium conditions. Consider the 
concentration equilibrium equation used in unidirectional flow for sus- 
pended sediment: 
Glvs)  E(de/dy)) = 0.) (12) 
40 
