| A study on the development of dunes under varying streamflow conditions is presented. This study has two main objectives. The first is to develop a framework to provide the quantitative answer to the question of what is the magnitude of T. The second is to acquire a better understanding of the nature of dune changes following a sudden change in flow depth.; For the present purposes, a series of experimental runs was carried out in a 21 m-long, 0.76 m-wide sediment transport flume. The bed was formed by a silica sand having D50 = 1.1 mm. All runs started from a flat bed, having a slope S = 1/1000. The ratio h2/h1, where h 1 and h2 are the flow depths before and after the sudden change in flow depth, were varied in the runs from 0.45 to 1.78.; It is found that the dimensionless counterpart piT of the time of development can be expressed as a function of four dimensionless variables, namely the material number xi, the relative flow intensity (eta *)1, the relative flow depth Z1 (both for the stage before the sudden change in flow depth), and the ratio h2/h1. The aforementioned series of experiments is used to reveal the form of the function pi T for specified values of xi, (eta*)1 and Z1---in what is a first attempt to quantify T.; The present study suggests that the developed dunes forming from an initially undulated bed tend to acquire the same dimensions that would have occurred if they were to form from an initially flat bed. The general features of dune development, including the rate of growth of dune height and dune length, are discussed in the light of the present experiments. (Abstract shortened by UMI.)... |
