Bed load transport is of fundamental importance in river engineering. Although there are many bed load transport equations, there is still no consensus on which equation is the best and how to select a particular equation for a particular river. Often there are large discrepancies in the bed load transport values yielded by different equations and between those and observed values. Further, in many practical applications empirical bed load equations are found to produce just as good bed load results as physically based equations. This study develops and tests two regression based equations for two rivers in Iran. One equation is based on hydraulic parameters and the other on geometric parameters. It is found that the Shields parameter, Froude number and shape factor are among the controlling hydraulic parameters of bed load, while the grain size distribution and the water slope are the significant geometric parameters that affect the bed load. A linear function showing more than 60% variability in bed load values seems sufficient to describe the bed load data rather than a non-linear function. The suggested equations are calibrated by laboratory data.
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