By Janrik van den Berg. Channel deposits of the Yellow River (China), composed of silt and very fine sands, show in cross-section ripple lamination, even lamination and small scour-and-fill structures. Figure 4.3 is a bedform stability diagram. Explain how bedforms change with changing grain size and with changing current flow. Keep in mind that these diagrams are based on unidirectional flow experiments in the laboratory. Layering and Unidirectional Flow Bedforms. Bedform stability diagrams have also been constructed that take into account the effect of flow depth. In general, at deeper water depths, a higher velocity is required for any given bedform transition.
Bi-directional Flow and Combined-Flow Bedforms. Shown below is one attempt at a bedform stability diagram for combined flow. The axes on this figure correspond to grain diameter, velocity, and velocity asymmetry. To utilize the bedform existence diagrams for analysis of sedimentary structures, boundary lines of bedform stability regions are significant.