The same results were obtained more recently by Kennedy .and Lacher 
(1972). Their investigation examined the behavior of the mean sediment 
concentration and the periodic sediment concentration fluctuations. The 
experiments were conducted in a stationary flume with a fixed bed on which 
a limited amount of loose sediment was distributed. Turbulence for sedi- 
ment suspension was caused by surface waves generated by a wave generator. 
The sediment concentrations were measured with optical equipment which 
incorporates the same theoretical principles as the equipment used in the 
swing-flume experiments but of a much smaller size. The smaller size and 
configuration of the equipment allowed measurements very near the bed and 
sampled a much smaller volume of flow. 
Kennedy and Locher's (1972) experiments in mean sediment concentra- 
tion distribution were limited to a wave height of 0.24 foot, a wave 
period of 1.0 second, and a mean water depth of 0.82 foot. The mean 
sediment concentration was measured at various elevations along five 
evenly spaced verticals in the flow. The spacing of the verticals was 
selected to cover one wavelength of the bed dune shape. A total of 78 
data points was measured, and when the logarithm of the mean concentra- 
tion was plotted against elevation above the bed a well-defined linear 
relationship of C = C, exp(-36.5 Y) was obtained. This relationship is 
identical to that obtained in the swing-flume experiments, with the ex- 
ception of the high rate of decay of sediment concentration, (-36.5). 
Kennedy and Locher used a quartz sediment of 0.14-millimeter mean dia- 
meter in their experiments. The settling velocity of this sediment was 
not reported; it was probably about 0.050 foot per second, which is 43 
percent greater than that of the principal plastic sediment (settling 
velocity of 0.035 foot per second) used in the swing-flume experiments. 
Swing-flume measurements, using sediments of different settling velocities, 
are discussed later in this section. For a given flow velocity a higher 
rate of decay of concentration is expected, as settling velocity increases. 
Much of the analysis of data by Kennedy and Locher dealt with the 
periodic sediment concentration fluctuations. Although no specific con- 
clusions were obtained regarding these fluctuations, the data did indi- 
cate the fluctuations were only apparent near the bed (within about 0.05 
foot of the bed). This explains the lack of periodicity in concentration 
fluctuations for the swing-flume measurements, in that 0.05 foot is near 
the lower limit where the much larger optical equipment of the swing 
flume could be used. 
Similar exponential concentration curves were obtained for the two 
different methods used in simulating sediment suspension in an oscillat- 
ing flow; i.e., an oscillating flow over a fixed bed as used by Shinohara, 
et al. (1958) and Kennedy and Locher (1972), and an oscillating bed under 
a ''stationary" body of water as used in the swing-flume experiments. 
Figure 7 shows the relationship between M and Uj, _ for two condi- 
tions. One set of data represents the condition that the optical equip- 
ment is stationary in space; the other data points are for the optical 
28 
