Sediment transportation, like many another engineering problem, has long been studied in a purely empirical manner in the attempt to develop useful working rules from a limited supply of measured data. Since formulas for predicting the sediment load of a stream are generally based upon past records for similar types of flow, they can be depended upon to yield satisfactory results only
within this range of flow conditions. Nevertheless, any empirical formula is almost certain to be extrapolated far beyond its limit of validity--a procedure leading sooner or later to serious error, for it is practically impossible to obtain and evaluate enough field measurements to establish empirically a truly general transport law
