Experiments on Downstream Fining of Gravel. II: Wide and Sandy Runs

This is the second of two papers about experiments on downstream fining of gravel. Here we briefly summarize the complete series of runs described in the first paper, where the influence of sediment feed rate was evaluated in a narrow channel. We then present results for variation in two more conditions: sand content and channel width. The experiments were carried out in a long flume with an effective 40-m-long test section, with two different widths of 0.3 and 2.7 m. In addition, two sediment mixtures were used with different sand contents (i.e., 33 and 55%) with the remainder being gravel. The following results were obtained. The increase in channel width allowed the formation of transverse topography, enhanced the development of sediment patches, and increased the fining rate of gravel for D₅₀ and finer percentiles. Increasing sand content rendered the long profile of the bed much more concave, caused marked patch development, and most notably increased the fining rate for all percentiles of gravel-sized bed material.