Effect of Flume Width on Bed-Form Characteristics

The dimensions of bed-forms developed in laboratory channels are found to be a function of channel width. A 10-30% reduction is observed in the size of irregularities, (wavelength ~ 4 ft; height ~ 0.2 ft) displayed by a self-formed bed of 0.6 mm diameter sand in a channel of 1.5 ft width, compared to that in a 5.0 ft-wide channel, under closely similar water and sediment discharge conditions. Emphasis is placed on the need to standardize parameters for the dimensional description of bed-form profile, and the adoption of significant form height and the average distance between alternate zero-crossings is advised. The distribution of bed elevations conforms reasonably well with accepted theoretical distributions for water waves provided allowance is made for the greater spectral width values that characterize the bed-form profiles. Because sediment movement occurs as surface creep in this case, the transport, calculated from bed-form celerity and a form height parameter proposed by Mercer, is in close agreement with the measured total transport.