The variable used to describe the flow condition is the flow 
velocity; U,, defined as: 
U,= @L/T , (10) 
where L is the amplitude (in feet) and is equal to one-half the arc 
length which passes a fixed point during one-half cycle, and T is the 
period of oscillation (in seconds). The flow conditions studied ranged 
from a minimum of U, = 0.235 foot per second (minimum to allow suspension 
of sediment) to a maximum of U, = 1.18 feet per second (maximum allowed 
by flume construction). The amplitudes and periods used in these experi- 
ments ranged from 0.235 to 1.60 feet and 1.65 to 15.16 seconds, respec- 
tively. Figure 5 shows some typical concentration distribution curves 
that were obtained. 
For the 65 different flow conditions studied, the base concentration, 
C, (eq. 9), could not be correlated to any of the hydraulic parameters 
but depended on the amount of sediment in the flume. For different flow 
conditions the sediment in the flume would be distributed differently 
along the bottom of the flume, thereby giving a different and uncontrol- 
lable base concentration. 
The 65 experiments also showed that two different laws exist in two 
ranges of conditions governing sediment suspension. For amplitudes of 
0.693 foot and larger, the concentration distribution is determined by 
the flow velocity alone. For amplitudes less than 0.693 foot, the con- 
centration distribution is a function of the amplitude relative to the 
wavelength of the artificial roughness. 
Thirty-six of the 65 concentration distribution curves were deter- 
mined using amplitudes of 0.693, 0.770, 0.925, 1.25, and 1.60 feet. For 
these five amplitudes, it was found that the slope of the distribution 
curve is a function of the flow velocity, independent of amplitude. 
Figure 6 graphically illustrates the relationship between M, the slope 
of the concentration distribution curve of equation (9), and U,, the 
variable of equation (10) used to describe the flow conditions of the 
flume. These data are also tabulated in Table 1 which gives the periods, 
amplitudes, and use of the optical equipment. The least squares, best 
fit equation for this relationship is: 
Ye atIS ee GSS) Uy. (11) 
where U, is in feet per second, and M is the slope of the concentration 
distribution curve (in feet™!). There is no statistical evidence to indi- 
cate that this relationship is significantly different from a higher order 
polynomial. 
Results of experiments by Shinohara, et al. (1958) confirm the above 
results. They found the same linear relationship between the logarithm of 
concentration and elevation and qualitatively determined that as the inten- 
sity of the flow increased the slope of the concentration distribution 
curve, M, became flatter. 
24 
