Streambed gravel sampling and frequency base conversion: A solution to data set sharing

The analysis of streambed particle size distribution is fundamental to geology, geomorphology, engineering, ecology, and hydrology. There is a continued need for standard analytical methods to accommodate different practices in sample collection, particle size characterization, frequency analysis, and frequency base conversion. We focus upon two related topics: (1) quantitative description of size of irregular particles and (2) frequency base conversion procedures. The first is needed to accurately determine physical particle properties (diameter, surface area, volume, and weight), and the second to determine the statistical influence on one or more of these properties of each particle in a mixture. We collected natural streambed particles, measured various calipered diameters including a nominal diameter using each particle volume, and calculated a shape factor for each diameter that converts it to an equivalent sieved diameter. Next, we extended a model originally derived in 1929 for a lognormal distribution to a streambed particle size distribution that severely deviated from a lognormal distribution. After successfully converting from number to weight frequency (and the reverse) of samples collected by grid, area, and volume, we extended the conversion to apply across these collection methods. These results make streambed frequency analysis independent of the particular diameter used, the observed frequency base, and the sample collection procedure. The immediate utility of our analysis is to facilitate data sharing among disciplines. The ultimate benefit is to free researchers to select the most convenient diameter measurement, size frequency classification, frequency base, and sample collection procedure from the many alternative strategies available.