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Dear Doc Hydro: I’ve been looking
at Bunte and Abt’s publication, “Sampling Surface and Subsurface
Particle-Size Distributions in Wadable Gravel and Cobble-Bed Streams”
(RMRS GTR-74) and reading about the characterization of various
particle distribution parameters such as the mean, sorting, skewness,
kurtosis, and the various ways of computing size distribution percentiles
and statistics. It’s all pretty complicated stuff and the equations
are pretty formidable. Are there any computer programs that perform
these computations and make this task easier ?
There’s a very nice program called GRADISTAT
that should meet your needs. GRADISTAT was developed by Simon Blott
and Kenneth Pye of the Department of Geology, Royal Holloway University
of London, England to assist the wide-ranging needs of researchers
in geomorphology and sedimentology. Soil scientists may also find
the program useful to display soil particle size data.
The program, written in Microsoft Visual
Basic, is integrated into a Microsoft Excel spreadsheet to allow
for both tabular and graphical (frequency and ternary plots) output.
A sample of the types of output is shown on this page.
Users are required to input the percentage
of sediment present in a number of size fractions. Data can be
the weight retained on a series of sieves, or the percentage of
sediment detected in size classes derived from a laser granulometer,
X-ray sedigraph, or Coulter counter. Input data is limited to an
upper size limit of 90 mm, and is therefore best suited for analyzing
finer materials.
Blott and Pye also caution that although
the GRADISTAT program is extremely flexible in terms of input and
output, it remains the responsibility of the user to interpret the
results in an appropriate manner. They note that although most
sedimentologists have traditionally worked with phi units, in their
opinion, statistics expressed in metric units are preferred because
the phi scale is seldom used by biologists, soil scientists, and
engineers and metric results are easier to visualize because they
represent the actual size of the particles.
The GRADISTAT program (GRADISTAT.xls)
can be downloaded from the Earth Surface Processes and Landforms
software web site (http://www.interscience.wiley.com/jpages/0197-9337/sites.html).
Look for: “Software from 'Gradistat: a Grain Size Distribution and
Statistics Package for the Analysis of Unconsolidated Sediments'
by Simon J. Blott and Kenneth Pye, Earth Surface Processes
and Landforms, Volume 26, Issue 11, pp. 1237– 1248.”
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