174 



Samples of the sediment-water mixture, approximately 1 I in volume, were 

 obtained once per day during the 2-week period that the OSU team was at 

 SUPERTANK; however, two of the samples were lost in transport from the 

 wave channel. Particle size distribution was measured using three 5-rai 

 aliquots from each of the samples using the HIAC Model PC-320 Automatic 

 Particle Size Analyzer. As samples are channeled through a narrow tube past 

 a light emitter-detector pair, particles within the sample occlude a portion of 

 the light detected by a photo sensor and decrease the light intensity detected, 

 which results in a lower output voltage and is expressed as a function of 

 particle diameter. The particle size analyzer is calibrated with polystyrene 

 beads of known size distributions. The device contains a counter with 12 

 voltage threshold values; thus, as a particular sensor voltage is detected, the 

 event increments one of the 12 values. The particle counts in each of these 

 voltage ranges can then be plotted, yielding a grain size distribution for the 

 grab sample. One limitation of using this particle size analyzer is that it can 

 only reliably interpret particle diameters within the range of 1 to 100 vm, 

 losing resolution of larger sizes. 



A total solids analysis was performed with the remaining portion of the 

 grab samples. The samples were divided into three 200- to 250-m^ aliquots 

 and analyzed using the method for determining total solids prescribed in Stan- 

 dard Methods for the Examination of Water and Wastewater (American Public 

 Health Association 1989). Table 9-4 shows the results of the analysis. 



The converted sediment concentration profiles obtained from the model are 

 averaged over the time that was required to take each grab sample, as well as 

 over the number of range bins of the profile that the sampler covered in 

 space. For example, the grab sample took about 1 min to complete and was 

 taken with a 32-cm by 14-cm-diam cylindrical Niskin bottle that was 

 suspended with its axis arranged vertically at 33 to 65 cm above the bottom, 

 the corresponding range bins are 54 to 82, where the higher-numbered range 

 bins are closer to the bottom. Thus, sixty 1-sec partial profiles, from bins 54 

 to 82, were averaged together, and the resulting concentration in mgli was 

 compared to that of the averaged grab sample concentration. The ratio repre- 

 sents a scale factor, which every model-calculated range bin concentration 

 value in a profile is multiplied by. 



A sample profile for a 15-min averaging time is shown in Figure 9-10. 

 The concentration profile depicted in the figure is from the wave run num- 

 bered A0608A, and the 15-min average is taken at nearly the same time as the 

 10-min average raw intensity shown in Figure 9-8. The figure shows the 

 mean of the concentration, the mean plus and minus one standard deviation 

 for each range bin, and the maximum and minimum concentration values in 

 each bin. The sample profile was taken at a time during the wave run when a 

 time trace from any one bin would not show large changes over time in the 

 concentration; i.e., an equilibrium period some time after any "spin up" 

 effects have ceased. 



Chapter 9 The Ohio State University Measurements 



