added to the calibration tank and the procedure repeated until the range 
of the optical equipment was covered. Measurable concentrations ranged 
from 0).1 to 2.5 grams per liter. The logarithm of the fraction of light 
passed versus the concentration in grams per liter was plotted to give 
the calibration curve shown in Figure 4. The least squares, best fit 
equation for this curve is: 
GS (COsSeS), tan /G, =I) 5 (8) 
where 
C = concentration (in grams per liter) 
I = mean voltage from the receiver when the light beam is passed 
through the sediment-water mixture 
I, = mean voltage from the receiver when the light beam is passed 
through clear water 
I' = mean voltage from the receiver when the light beam is turned off 
The calibration curve, which was checked periodically during the experi- 
ments, did not change. 
In setting up the calibration experiments, it was found that a change 
in the focus of the optical equipment would change the resulting calibra- 
tion curve. To eliminate this problem a brace was made to hold the equip- 
ment in focus. A check of the focus was made during each concentration 
measurement by a wire-screen filter which, when placed in the light beam, 
blocked out a known and constant amount of light. If a change in focus 
was detected by the filter measurements, the concentration measurements 
were not used. 
c. Concentration Distribution Measurements. For concentration dis- 
tribution measurements in the flume, a datum elevation of the optical 
equipment had to be established. The mean elevation of the crest of the 
artificial dunes was used as the base elevation and was determined by a 
scale fixed to the flume and a pointer fixed to the optical equipment 
brace. 
The desired period and eccentricity were selected and the flume link- 
age adjusted to give a symmetric oscillation. The flume was filled with 
deaerated water to the elevation of the wave suppressent board (12 inches 
above the lowest point of the bed), and the asymmetric end roughnesses 
were positioned. Depending on the flow conditions chosen, 100 to 500 
grams of sediment was cleaned and deposited in the flume. The flume was 
then oscillated until the distribution of sediment in the flume was at 
equilibrium. The equilibrium condition was determined by periodically 
measuring the concentration of sediment at a fixed point in space until 
the concentration did not change with time. 
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