A comparison between flume and field bedload transport data and consequences for surface-based bedload transport prediction

Overview & Synopsis

The ability of simple equations to predict bedload transport with limited knowledge of the bed surface material was investigated. This was done using a data set consisting of 7,636 bedload transport values from the flume (1,317 data) and from 84 river reaches (6,319 field data). It was possible to collapse field and flume data by correcting the ratio between the Shields number and its critical value with a very simple hiding function proposed as a power law of the D84/D50 ratio. Doing so, a surface-based bedload transport formula was proposed. It was successfully tested on an independent data set (comprising sand and gravel bed rivers with slope in the range 0.00020.08), with 86% of the values predicted within a precision of one order of magnitude. Moreover, the formula reproduced the low transport rates well, contrary to the usual surface-based formulas also tested, and is particularly well suited for estimating low transport rates associated with near bankfull flow discharge. This new formula is neither time- (no fractionwise calculation) nor data-consuming (the required parameters are the flow discharge, the active width, the slope, and the surface grain diameters D50 and D84).