Shields versus Isbash.

The Shields and the Isbash equations for predicting the stability of rocks exposed to a turbulent flow were both proposed in 1936, and since then, both equations have been used widely in the analysis of transport thresholds for coarse sediment. These two equations were obtained using two very different approaches, but as demonstrated in this paper, the equation developed by Isbash is consistent with the relation formulated by Shields for predicting the motion of sediments either in the flume or in the field. Comparison of the two equations suggests that standard approaches tend to oversize riprap in mountain streams. [ABSTRACT FROM AUTHOR]