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Sediment variability and bed material sampling in gravel‐bed rivers
Author(s) -
Mosley M. P.,
Tindale D. S.
Publication year - 1985
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.3290100506
Subject(s) - sediment , sampling (signal processing) , homogeneous , grain size , geology , hydrology (agriculture) , soil science , environmental science , sample size determination , spatial variability , geotechnical engineering , geomorphology , statistics , mathematics , computer science , computer vision , filter (signal processing) , combinatorics
In a 350 m wide reach of the braided, gravel‐bed Ashley River, the surface layer of the bed material was sampled in 141 areas of homogeneous graded sediment along seven cross‐sections, and 30 kg bulk samples were collected at 86 randomly selected locations along the cross‐sections. At one location, a single 854 kg sample composed of 28 subsamples was also collected. Analysis of the single large sample indicate that accurate determination of mean grain size D at that site requires, desirably, a sample of ∼ 100 kg, but that samples in which the weight of the largest stone is less than 5 per cent of the total weight have unbiased estimates of D. Spatial variability of bulk material is such that 228 and 50 samples are needed to estimate D to ± 10 and ± 20 per cent respectively of the true value; requirements for estimating inclusive graphic standard duration are only 11 and 3 respectively. The grain‐size distribution of the surface layer is only weakly related to the bulk material beneath. The results of ‘Wolman sampling’ along 12 cross‐sections at two pace intervals (average 120 stones per cross‐section) indicate that estimation of overall surface D to ±10 and ±20 per cent would require sampling along 64 and 14 cross‐sections respectively. It is concluded that accurate characterization of bed sediment in gravel‐bed rivers is very demanding of labour and resources, and that careful planning is needed to ensure efficiency and meaningful results.