Conceptual mechanics-based models for sediment transport processes in steady and unsteady turbulent boundary layer flows are derived and discussed. To the extent possible the predictions of the conceptual models are compared with accepted empirical sediment transport relationships, e.g., Shields criterion for initiation of motion and the Meyer-Peter and Mueller bedload transport formula. From the agreement between the model developed for saltating sediment grain transport and the Meyer-Peter and Mueller bedload transport formula it is concluded that this should be regarded as the bedload transport formula for use in the coastal environment.