posted on 2012-06-06, 12:52authored byDavid GrahamDavid Graham, Anne-Julia Rollet, Stephen Rice, Herve Piegay
Information about the grain-size distribution of the surface layer of sediment exposed on river
beds is often critical in studies of fluvial hydraulics, geomorphology and ecology. A variety
of sampling and analysis techniques are in common usage which produce grain-size
distributions that are not directly comparable. This paper seeks to explore the appropriate
conversions between different types of surface grain-size sampling methods. This is
particularly timely in the light of increasingly widespread use of automatic and semiautomatic
image-based measurement methods, the comparability of which with conventional
measurement methods is relatively poorly constrained. For conversions between area-bynumber
(paint-and-pick) and grid-by-number (pebble count) samples, the empirically-derived
conversion factor (±2.2) was found to be greater than that predicted by the Kellerhals and
Bray model (±2), but the errors associated with using the value predicted by the model were
small (3.8% in mm). For conversions between areal samples recorded by count and weight, the empirically-derived conversion factor was approximately ±2.9, but the use of the value
predicted by the Kellerhals and Bray model (±3) resulted in only small errors (5.2% in mm).
Similarly, for conversions between image-based grain-size distributions recorded in area-bynumber
and grid-by number form, the emipirically-derived conversion factor was ±1.9, but
the using the model value of ±2 resulted in only small errors (4.1% in mm). Although these
results are specific to the datasets analysed, the variety of sedimentary conditions included
gives us confidence that the results are representative.
History
School
Social Sciences
Department
Geography and Environment
Citation
GRAHAM, D.J. ... et al, 2012. Conversions of surface grain-size samples collected and recorded using different procedures. Journal of Hydraulic Engineering, 138 (10), pp.839–849.