Experimental Characterization of Bed-load Dunes in a Closed Conduit: Size, Period, and Migration Celerity

Results are presented for dune development and migration in a closed conduit with rectangular cross section. While dunes were not clearly formed with the lowest flow rates (exceeding only slightly the threshold flow rate for sediment transport), these bed-forms regularly developed for higher transport intensities. Furthermore, the development of dunes required a certain length. Spatial and temporal measurements of the bed elevation enabled several statistical analyses to be exploited: Cumulative Frequency Distributions, auto- and cross-correlation functions, and spectra were used to characterize the properties of the bed-load dunes. The dune height was an increasing function of the flow rate and, in turn, of the transport conditions. The same held for the dune celerity, while the integral scale of auto-correlation and the dune period were decreasing functions of the flow rate. The dune length did not show any evident trend with the transport conditions. The results for the present dunes in a closed conduit are tentatively compared to predictors for dunes in open channels.