Flood Variability Increases Bed Material Sediment Discharge in an Experimental River

How does water discharge variability influence sediment transport in rivers? While larger floods generally move more sediment, the effect of disequilibrium bed state on sediment transport is less understood. However, the answer to this question is important for interpreting sediment dynamics in modern rivers where discharge is increasingly regulated. To investigate the influence on discharge variability on bed material sediment discharge (Qs), we measured Qs under both equilibrium and fluctuating conditions in a stream table experiment. First, we obtained a sediment rating curve for seven constant water discharges under equilibrium conditions. Next, we ran a fluctuating experiment with 1000 floods scaled to an arid river system and drawn from a power law distribution of the same seven water discharges. The average sediment discharge over the fluctuating experiment was compared to the average discharge using the equilibrium sediment transport rating curve and was found to be 100% higher. The results from this comparison showed that fluctuations in water discharge increases sediment transport relative to a nonfluctuating baseline. We interpret this increase to be due to the constant disequilibrium of the sediment bed relative to the flows applied to it.