BED-FORM DEVELOPMENT

Based upon the results of a series of 47 bed-development experiments, the evolution of bed features subsequent to their initial generation from flat bed conditions is examined. For each such experiment, bed profiles were measured at frequent time intervals as sand-wave configurations developed under the action of open-channel water flow. The two sediments used for these experiments were of geometric mean size 0.20 mm and 0.82 mm, respectively. In line with the bed-form unification model of bed development postulated by Saudkivi and Witte in 1990, the principle of bed-form propagation speed decreasing with increasing bed-form height and the mechanisms of bed-form coalescence and bed-form through passing are all found to be central to bed evolution processes. A quantitative relation between bed-form speed and bed-form height is presented. Bed-development predictions based upon bed-form unification models can be seen to clearly parallel the present experimental results. Stability analyses based upon potential flow theory, while not adequately describing the mechanics of bed-form development, nevertheless correctly predict the periods of accelerated growth recorded for the present experiments.