Variability of bed load measurement

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Abstract
The sampling efficiencies of two slightly different Helley‐Smith‐type bed load samplers were compared under carefully controlled field conditions. The samplers were identical in all respects except for the thickness of the metal used in their construction. The test results indicate that for coarse‐grained sand bed load, the sampler with a wall thickness of 1.5 mm has a sediment trap efficiency that can be as much as two times that of the sampler with walls that are 6.3 mm thick. In a separate test, bed load transport was monitored at a single channel cross section during a 10‐hour period of steady discharge. At individual sampling stations, measurement values ranged from nearly 0 to 3 times the mean. Composite bed load transport rates for full traverses of the channel width varied by a factor of 2.