(4) Photography 



Some researchers (e.g., Bijker 1971; Horikawa, Watanabe, 

 and Katori 1983) have used high-speed photography to docu- 

 ment and measure the movement of suspended and near -bed 

 sediment. Horikawa, Watanabe, and Katori used a motor- 

 driven 35 -mm camera and stroboscopic lamp to record the 

 suspended sediment concentration and particle advection 

 speed in the upper layer of flow in the laboratory. A 

 painted black copper plate located 1 cm into the flume was 

 used as a backdrop; grains passing between the flume wall 

 and the black copper plate were photographed. Disadvan- 

 tages with this type of measurement tool include: (a) 

 analysis of the photographic data is extremely time-consum- 

 ing; and (b) the method appears to be applicable only to 

 the laboratory environment. 



Bed -load apparatus 



14. The number of suspended -sediment instruments available far outnumber 

 the number of bed -load measuring apparatus. Direct measuring bed -load devices 

 include variations of the pit, pressure -difference, and box riverine samplers; 

 the only indirect measuring device is an acoustical instrument. 



a. Pit samplers. 



Pit samplers in the nearshore coastal zone are nearly identical 

 to those described for riverine use: some sort of collection 

 device rests in an excavated region in the bed. Inman and Bowen 

 (1963) used two pits at either end of a flume to measure the net 

 quantity of sediment transported due to oscillatory flow. The 

 pits consisted of perforated steel sheets placed over an exca- 

 vated region; sediment fell through the perforations and was 

 retained in the excavated region. 



b. Pressure -difference . 



The only pressure-difference traps used in the coastal zone have 

 been the VUV sampler, developed for riverine use and discussed 

 in the riverine pressure-difference section. Lee (1975) used an 

 array of VUV samplers through the surf zone to measure the bed- 

 load transport on the west shore of Lake Michigan in Kewaunee 

 County, Wisconsin. Pickrill (1986) used VUV traps across a 

 cross -section of Rangaunu Harbor, New Zealand. Results were 

 corrected for the sediment- trapping efficiency of 0.70, reported 

 by Novak (1957). Measured transport rates were lower than those 

 predicted with relationships presented by Yalin (1963); Pickrill 

 attributes the discrepancy to: (a) migrating bedforms and their 

 location relative to the initial placement of the traps; (b) the 

 use of only one trap; and/or (c) spillage of the samples upon 

 removal because the trap had no doors. Thornton (1969) used 

 bed -load traps at Fernandina Beach, FL. 



A31 



