Bedload transport and the stream power approach

Abstract

Bedload transport is highly variable, and we address the issue of what value(s) of the transport rate a formula is expected to predict by incorporating two metrics of variance in an elementary scale correlation between the transport rate and stream power. The first captures uncertainty in the empirical relation we develop to describe the efficiency of the bedload transport process, and the second acknowledges that different patterns of transport are experienced under similar hydraulic conditions. Our simple, generalized expression explicitly applies to rivers in which there is always a high availability of mobile sediment on the bed, and we demonstrate that it provides a realistic portrayal of the observed range of transport rates in rivers with a sporadically mobile gravel armour and a characteristic bedload size that is approximately the same as that of the substrate. Accepting that the transport rate is influenced by the nature of the material available at the bed surface which is, in turn, moderated by antecedent flows, we suggest that if effort in the field is required to apply our methodology it should be expended on characterizing the sizes available on the bed between floods, rather than observing active transport during individual events.