Evaluation of bed load transport formulae using field evidence from the Vedder River, British Columbia

Bed load transport formulae have not been tested extensively over medium spatial and temporal scales. The lack of such testing is undoubtedly due to a paucity of field data available for testing at these scales. Extensive transport, morphologic, and discharge data, available for a 10-year period along an 8-km study reach of the Vedder River, British Columbia, are used to test the predictive capabilities of bed load transport formulae at medium scales. The transport data were obtained using the morphologic approach, which is based on the premise that changes in channel morphology reflect the transfer of sediment. Such transport estimates can be made over larger spatial and temporal scales than is possible using traditional measurement techniques. This study focuses on evaluating the original and revised versions of the Bagnold stream power formula, the Meyer-Peter and Muller formula and a stream power correlation. Overall, the formulae are found to underpredict gravel transport rates for the Vedder River. The discrepancy is particularly pronounced in 1982–1983 and 1987–1990, which are periods during which significant dredging occurred. Dredging activity may have loosened the bed structure or resulted in a disequilibrium morphology, thereby increasing sediment movement. Analysis is undertaken to assess how the use of mean daily discharge vs. 15-min increment discharge series affects transport predictions. Results show that only the Meyer-Peter and Muller formula is particularly sensitive to which discharge series is used in calculations. Modification of the Shields parameter is found to significantly affect transport predictions, although it cannot explain alone the discrepancies between field data and calculated results. Predictions of total deposition in the study reach are well within an order-of-magnitude for all equations. The Bagnold-type formulae and the Meyer-Peter and Muller formula do not capture the relatively even distribution of deposition along the study reach. Surprisingly, the simple stream power correlation captured this downstream pattern of deposition. Cumulative distributions of predicted bed load transport are found to be most realistic for the original and revised Bagnold formulae. Results of this study do not suggest that one particular formula is consistently preferred.