Auxiliary Material for “Signal shredding of environmental signals by sediment transport” by D.J. Jerolmack and C. Paola
The rice pile experimental setup (see figure) was based on the experiments of Frette et al. . Sediment was long-grain brown rice with an average length of 8 mm, width of 1.5 mm and weight of 0.03 g/grain. The plexiglass channel was 20 mm wide and 300 mm long, and was closed at the upslope end and open at the downslope end to allow grains to flow out. Rice was fed to the upslope end of the channel using a rotating gear that delivered about 1 grain/tooth. Sediment feed rate for the experiment presented here was steady at q0 = 20 grain/minute with a measured error of +/- 10%. Sediment efflux was almost entirely by collective grain motion in avalanches. Efflux went directly to a scale that logged cumulative weight onto a computer at a rate of 1 Hz, with an error comparable to the weight of one grain. The time series of cumulative weight was differenced to create a record of flux. Flux time series for all physical and numerical experiments were split into 5-10 pieces of equal length, the power spectrum of each length was computed, and then these spectra were ensemble-averaged to produce results in Figs 2-4. Cross over time Tx was determined as the inflection point that minimized cumulative error of two independent least-square linear regressions to the left and right.
See the full paper at http://onlinelibrary.wiley.com/doi/10.1029/2010GL044638/full.
Note that the paper includes only numerical simulations. Experiments described above inspired this work, however technical yet to be resolved prevented analysis of the data sets.