Sediment-wave development in subcritical water flow

A power law relating bed-form magnitudes (lengths or heights) to time, with all parameters normalized by equilibrium values, is promoted to describe ripple or dune growth with time from plane-bed to equilibrium conditions. In order to use this relation for prediction purposes, new expressions are presented herein for both the times required for ripples and dunes to achieve equilibrium magnitudes, and also the respective growth exponents for the development of bed-form heights and lengths. These new relations have been determined based on 15 new and 76 previously published laboratory experiments covering ranges of sands and flow strengths, although additional work is warranted to confirm these expressions for field scales. The power-law relation for bed-form growth from a plane bed is also extended in concept herein to describe changes in bed-form size from nonzero initial magnitudes. In preliminary tests, this modified power-law expression was found to provide reasonable descriptions of trends in increasing and decreasing bed-form heights and lengths with changes in flow strength. At this stage, application of this modified expression is principally conceptual in nature, with further work required to facilitate prediction for changes in flow of both times to achieve equilibrium magnitudes and also height and length growth exponents.