Modeling the temporal variability in the flux of sediment from ungauged river basins

Abstract

The suspended sediment load carried by rivers is highly variable in space and time. On a given river, the suspended sediment load is generally related to the discharge. However, at any given discharge on a specific river the suspended sediment load can vary by a couple of orders of magnitude. The temporal variations can be due to many factors including: varying water sources through a season (i.e., rain versus snowmelt), variability in the amount of easily mobilized sediment stored in the channel, changing channel morphology due to intermittent events or changing climate, and variations in erosional processes supplying sediment to the river. Many studies have looked at the causes of the temporal variability in suspended sediment load on a particular river over specific time periods and created models to simulate the variability. A review of the physical mechanisms responsible for the variability in suspended sediment load reveals the necessary components of a general suspended sediment model for ungauged (and gauged) basins. A generally applicable model is presented that accounts for the inter- and intra-annual variability of suspended sediment load of rivers. The strength of this new model is that the coefficients have strong trends between river basins that can be related to drainage basin parameters. The model accounts for basin wide characteristics through a mean exponent. A variable exponent captures the annual variability and is related to the size of the river basin. The inter-annual variability is accounted for by a variable coefficient, which has large values on small rivers. This is a result of small rivers having larger changes in the intra-annual flows and large rivers tending to have less variability.