Quantifying the effect of hydrologic variability on sediment transport in alluvial rivers

Existing equations for predicting the time-averaged bedload sediment flux in alluvial rivers do not explicitly include variations in discharge. In this study, we develop an analytical equation for the time-averaged sediment flux in an alluvial river that incorporates the instantaneous sediment transport equation and the frequency-size distribution of flood events, taking into account both the mean and coefficient of variation of discharge for a channel with a prescribed slope and grain size distribution. Two applications of the resulting equation are then considered. First, the geomorphic effectiveness of end-member climate regimes is considered, taking into account the inverse relationship between the mean and coefficient of variation of discharge in alluvial rivers. The results indicate that an alluvial river located in a humid climate with high effective annual runoff and low variation in discharge transports more sediment per unit time than the same river located in a more arid basin. Second, the effective discharge and its corresponding return period are calculated using the analytical equation for alluvial rivers in climates that range between arid and humid end-members. Rivers in humid climates have effective discharge return periods of months to decades, while the return periods for extremely arid climates can be up to several hundred years.