Study on a Generalized Mathematical Model of Sand Wave Morphology and Migration Characteristics

Upstream damming can alter significantly the flow and sediment regime in the reach downstream. The bed load discharge would decrease greatly, and the suspended load discharge would account for the main part of sediment transport. During the continuous channel degradation, the sand wave migration gradually changes from a predominantly transport of bed load to the combined transport of bed load and suspended load. In this study, a one-dimensional generalized mathematical model of sand wave morphology and migration characteristics was established, and the migration characteristics based on bed load and suspended load were compared based on the model predictions. Then the sand wave morphology and migration rate were verified by comparing the results of bed load model with the existing formulas. The effects of different parameters on the sand wave migration were finally discussed. Simulative results indicate that:(1)Sand wave based on the bed load transport migrates downstream while the rate is positively correlated with the bed elevation. Sediment erodes on the stoss side and deposits on the lee side, which leads to an asymmetrical morphology. The critical time for the sand wave migration is 31.78h and the relative error with the existing analytical solution is only 1.5%. Sand wave based on the suspended load transport does not migrate downstream. Sediment erodes vertically mainly while the erosion intensity is positively correlated with the bed elevation and the wave height decreases gradually. The sand wave morphology is basically symmetrical and tends to wash out; (2)The calculated migration rate of crest and trough based on the bed load transport is 51m/d and 17m/d respectively, and the maximum relative errors are less than 26% compared with the calculated values of existing three formulas. The average relative errors of morphology curve calculated by this model and existing three formulas are less than 19%. Therefore, the calculated results can generally reflect the characteristics of sand wave migration; (3)Effects of flow and sediment parameters on sand wave are more significant than initial morphological parameters. The migration intensity of sand wave can be enhanced by increasing the discharge per width or decreasing the flow depth, while it is more sensitive to the variation of flow depth.