Figure A12 . 



Birkbeck bed -load sampler (from Reid, Layman, 

 and Frostick 1980) 



consists of a wedge-shaped pan that can be inserted into 

 the bed by divers during low to moderate flows. The 

 sampler induces flow separation at the leading edge of the 

 pan; a sieve -mesh screen contains sediment as flow exits 

 the trap. The trap was installed in a section of the 

 Ottawa River, Ottawa, Canada. Sediment transport rates 

 inferred from use of the sampler were compared with the 

 dune -tracking method of calculating sediment transport. 

 Values compared well at two of three stations. The author 

 contributes discrepancies at the other station to (a) the 

 cyclic nature of sediment transport and the short sampling 

 times inherent in this type of sampler, and (b) the non- 

 angularity of dunes at that station, an assumption in the 

 dune -tracking method. Laboratory experiments were con- 

 ducted in two flumes. The first flume was exactly the 

 width of the sampler and indicated that the trap had a 

 sediment- trapping efficiency equal to or greater than 0.85. 

 The ambient rate of sediment transport was calculated using 

 the weight of sediment in the tail water without the 

 sampler in use . The width of the second flume was twice 

 that of the sampler; therefore, for a sediment -trapping 

 efficiency of 1.0, the weight of material caught by the 

 sampler would equal the weight of material in the tail 



A18 



