A procedure for classifying textural facies in gravel-bed rivers

Vol. 35, pp. 1903-1915

Textural patches (i.e., grain-size facies) are commonly observed in gravel-bed
channels and are of significance for both physical and biological processes at subreach
scales. We present a general framework for classifying textural patches that allows
modification for particular study goals, while maintaining a basic degree of
standardization. Textures are classified using a two-tier system of ternary diagrams that
identifies the relative abundance of major size classes and subcategories of the dominant
size. An iterative procedure of visual identification and quantitative grain-size
measurement is used. A field test of our classification indicates that it affords reasonable
statistical discrimination of median grain size and variance of bed-surface textures. We
also explore the compromise between classification simplicity and accuracy. We find that
statistically meaningful textural discrimination requires use of both tiers of our
classification. Furthermore, we find that simplified variants of the two-tier scheme are less
accurate but may be more practical for field studies which do not require a high level of
textural discrimination or detailed description of grain-size distributions. Facies maps
provide a natural template for stratifying other physical and biological measurements and
produce a retrievable and versatile database that can be used as a component of channel
monitoring efforts.


Buffington, J.M., Montgomery, D.R.