Figure A9 . Arnhem (Dutch) pressure -difference 

 bed-load sampler (Hubbell 1964) 



Sampler (Helley and Smith 1971; Druffel et al . 1976; Emmett 

 1976; Johnson et al . 1977; Emmett and Thomas 1978; Emmett 

 1980; Emmett 1981; Emmett, Leopold, and Myrick 1983). The 

 VUV bed-load sampler was developed in 1957 based on the 

 Goncarov and Karolyi types of samplers. The sampler 

 consists of a full metal streamlined exterior with a wire 

 mesh on the rear top part of the apparatus to facilitate 

 flow exiting the sampler. The shape of the sampler was 

 designed to compensate for the resistance of the apparatus. 

 Novak (1957) measured the hydraulic and sediment -trapping 

 efficiencies of several types of samplers, including the 

 VUV, S (mesh), Karolyi, Nesper (Figure A7), and Ehren- 

 berger . Hydraulic efficiencies of the VUV and Karolyi 

 samplers were calculated at 1.0 and 0.8, respectively. 

 Ambient sediment trapping efficiencies were measured in a 

 flume using a pit sampler. Conclusions from the experiment 

 were as follows: (a) sediment trapping efficiency of the 

 VUV sampler may increase slightly with grain size; (b) all 

 samplers retain representative samples; (c) efficiency may 

 increase slightly as flow increases; and (d) the hydraulic 

 efficiency only gives a qualitative measure of sediment- 

 trapping efficiency. Sediment- trapping efficiencies for 

 the samplers were as follows: VUV sampler, 0.70; S(mesh) 

 sampler, 0.65; Karolyi, 0.45; Nesper, 0.40; and Ehren- 

 berger, 0.60. Lee (1975) and Pickrill (1986) used the VUV 

 sampler in the coastal environment, and their studies are 

 discussed in the coastal section. The Helley-Smith 

 sampler, perhaps the most extensively studied sediment 



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