Premium
Pebble Counts and The Role of User‐Dependent Bias in Documenting Sediment Size Distributions
Author(s) -
Marcus W. Andrew,
Ladd Scott C.,
Stoughton Julie A.,
Stock Joseph W.
Publication year - 1995
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/95wr02171
Subject(s) - replicate , pebble , statistics , sediment , standard deviation , percentile , calibration , sampling (signal processing) , mathematics , environmental science , soil science , geology , physics , geomorphology , optics , detector
Replicate subaqueous pebble counts show that measurement and selection bias can significantly affect sediment size distribution data. The standard deviation about replicate means increases linearly with sediment size and is independent of the sediment percentile (e.g., d 50 , d 84 , etc.). For samples collected by one person, sampling error varies from 2 ± 2.6 mm to 300 ± 35.4 mm within one standard deviation. For samples collected by different individuals, sampling bias increases the error from 2 ± 4.2 mm to 300 ± 63.8 mm. Whenever possible, only one individual should select and measure pebbles, which improves the ability of the pebble count to delineate trends between sites or over time (although the absolute size values may be in error due to bias). Bias can be reduced by rigorous training of individuals, by using templates to measure sediment size, and by using grids on the stream bottom to select particles. If two or more individuals collect samples, they should conduct replicate samples to provide a basis for later calibration of results.