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Measuring and defining bimodal sediments: Problems and implications
Author(s) -
Smith G. H. Sambrook,
Nicholas A. P.,
Ferguson R. I.
Publication year - 1997
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 - 10.1029/97wr00365
Subject(s) - bimodality , flume , grain size , geology , bedform , deposition (geology) , geotechnical engineering , sediment , statistics , statistical physics , soil science , flow (mathematics) , sediment transport , geomorphology , mathematics , geometry , physics , quantum mechanics , galaxy
Gravel bed rivers close to the transition to a sand bed often have bimodal grain size distributions. These can be quantified in several ways, giving wide differences in derived statistics and calculations. Problems associated with measuring, summarizing, and defining bimodality are examined using evidence from flume experiments and a simple numerical simulation of sand deposition. No single index of bimodality serves all purposes; alternatives are suggested. Measured near‐bed hydraulic properties relate more closely to grain size statistics calculated by area than by volume; this has implications for the abrupt downstream transition often found from gravel to sand bed.