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RELATING WEIGHT AND COUNT DISTRIBUTIONS OF STREAM BED GRAVEL
Citation:
Shirazi, M A., J. M. Faustini, A. J. Waters, I. Vazquez, AND A. Osterbur. RELATING WEIGHT AND COUNT DISTRIBUTIONS OF STREAM BED GRAVEL. Presented at American Geophysical Union fall meeting, San Francisco, CA, December 6-10, 2002.
Description:
The size distribution of particles in a stream bed reflects the stream hydrology as well as its physical and chemical water quality characteristics. In environmental assessments, gravel distribution determines habitat quality for aquatic insects and stream suitability for spawning by various fish species. A common monitoring approach(e.g., Wolman count) assesses surface particles as size-count distribution. The method is convenient, but the distribution of subsurface particles, which cannot be assessed by size-count is also needed for water quality assessment. We collected surface and subsurface substrate samples from several coastal and inland streams in Oregon to develop methods of relating size-count and size-weight distributions of the surface material and their relationship with the size-weight distribution of the bulk sample. In this study, we present examples of relationships of size-count and size-weight distributions of the surface particles. These distributions differ substantially, and depending on the method of calculation, the distribution means for the same sample can differ by an order of magnitude. We converted the size-count to size-weight distribution using log-normal functions between two consecutive size groups. When used to calculate the median and the standard deviation of the distribution, the method yielded a more stable approach than two alternative calculations.