pump mounted on a sled. Visual inspection indicated that 

 the sled did not increase the sediment in suspension; 

 however, if nozzle orientation was reversed, more than 

 double the concentration of sediment was collected. 

 Thornton and Morris (1977) used a series of intake nozzles 

 in the surf zone to calibrate a transmissometer , a light 

 transmission indicator (see below). Bosman, Van Der 

 Velden, and Hulsberger (1987) pumped samples at a speed 

 three times greater than ambient flow speeds, with the 

 nozzle orientation perpendicular to vertical plane of 

 orbital motion. The pumping method of collecting suspended 

 sediment works well when the nozzle is oriented vertically. 

 Disadvantages, however, include: (a) large volumes must be 

 collected to obtain significant quantities of sediment; and 

 (b) the apparatus needs a mounting system such as a pier, 

 boat, or sled. Suction and self -syphoning samplers are 

 types of pumping devices that collect a water -sediment 

 mixture using either suction or the pressure difference 

 between the water surface and nozzle location. Nielsen 

 (1983) and Nielsen et al . (1982) used a self -siphoning 

 sampler in the Eastern Beach, Gippsland, Australia, surf 

 zone that sampled at seven elevations simultaneously 

 (Figure A16). The sampler collected for 3.5 min with an 

 intake velocity of 1.5 m/sec in a 1.2-m water depth; the 

 intake velocity was limited by the pressure difference 

 between the water surface and nozzle locations. Hom-ma and 

 Horikawa (1962) used siphon samplers in the laboratory to 

 measure the vertical distribution of suspended sediment due 

 to wave action. Staub, Svendsen, and Jonsson (1983) 

 describe a rotating-wheel apparatus designed to collect 

 water -sediment mixtures in the turbulent oscillatory flow 

 over a laboratory sand bed. A siphon probe located at a 

 particular elevation above the bed feeds into a rotating 

 wheel outside of the flume with 18 cups in the circum- 

 ference. The rotation of the wheel is synchronized with 

 the oscillating flow in the flume; in this manner, the 

 concentration of sediment collected in each cup represents 

 one -eighteenth of the wave period. Kilner (1977) used 2- 

 liter preserving jars with a total internal vacuum as 

 handheld samplers for use in wading depths (surf zone). 

 For deeper water, two compressed air samplers were 

 developed using 7 -liter compressed air cylinders with a 

 trigger valve connected to an air motor. Disadvantages of 

 the suction/siphon type of sampler are: (a) the intake 

 flow speed with self -siphoning samplers depends on the 

 distance between the probe and water surface; (b) large 

 samples must be obtained to result in significant quan- 

 tities of sediment; and (c) the flow speed must be known at 

 the probe to calculate sediment transport rates . 



A26 



