Experimental Analysis of Roll Waves in Overconcentrated Flow

Water surface instabilities have been observed as wave trains both in laboratory and in field. This phenomenon, called roll waves, is typical of steep and suciently long channels (Montuori, 1961; Brock, 1969). Moreover roll waves development concerns not only Newtonian fluid but also mud and debris flow and has been studied most of all in fixed bed condition. In the present paper the phenomenon of roll waves over mobile bed is presented. A hydraulic flume has been used to study this wave trains in presence of intense bed-load. Measurements of wave features like amplitude, wavelength and celerity have been performed. Finally a comparison with the results known for the fixed bed has been carried out. Particular attention has been dedicated to give physical explanation and interpretation of roll waves development over mobile bed with intense bed-load.