Bed Material Sampling Error in Sand Bed Rivers

A total of 468 bed material samples were collected at cross sections of the sand bed of the South Saskatchewan River at Saskatoon to assess the random and systematic errors in the results from four commonly used samplers. Statistically significant differences in particle size distribution occur between the results obtained from different samplers at the same location, in part due to variability in retention of the small particles. The differences are greatest in silty sand and least in well-sorted, medium sand. The precision of results from repetitive samples at the same location using the same sampler depends on both the sampler and the composition of the bed material. Except in well-sorted, medium sand, a single sample at a vertical is inadequate to determine the particle size of a given size fraction to within 10% with a probability of error of 0.1. In some cases 10 or more samples may be required. The magnitude of these statistical errors at a given location is generally less than the within-reach variability in bed material particle size, and therefore the appropriate choice of sample location is critical