Note on Lag in Bedload Discharge

It is postulated that movable sediment beds comprise of two types of grains, termed undisturbed and disturbed grains. The probability of entrainment by flow of the latter is higher than that of the former. The lag in bedload transport is due to the difference in the entrainment probabilities of the two types of grains. A model is developed to predict lag in bedload transport. The spatial‐ and temporal‐lag coefficients are functions of both the inner and outer variables. The 50% of the equilibrium bedload discharge is attained within about 26% of the total lag distance or lag time. The lag model was verified by conducting laboratory experiments and using experimental data of Bagnold. The proposed model agrees with the experimental data. Both the lag distance and lag time decrease with increasing equilibrium bedload discharge. The findings of the model can be used to improve the Einstein formula for the equilibrium bedload discharge.