The theoretical frame of a new two-dimensional sediment mathematical model is established on the basis of the resent research achievements about the sediment transport law of the Yellow River. The formulas of sediment carrying capacity of flow, which reflect the features of the Yellow River, are applied to it. The finite element scheme is employed to deduce the discretized equations of the model. Verifications of the model are carried out with the flood occurring on Jinan reach of the Yellow Rive during the flood season in 1976. The calculation results with the model are in good agreement with the measured data. The programs calculating indicates that the Jinanyan's constructing will be of great benefit to Jinan city's flood protecting and water supply.

The experimental study of comparison of local scour depthes at bridge piers under both steady and unsteady flows in fine sand river beds is carried out in the paper. The result shows that the maximum local scour depth at bridge piers under unsteady flows is generally less than the balance depth of that from steady flows with equal flood peak discharges to the unsteady ones, but larger than the balance depth of that from unsteady flows with equal average flood discharges. The correlation of local scour depthes at bridge piers between steady and unsteady flows is established through the experiment, at the same time, calculation method for local scour depthes at bridge piers under unsteady floods in fine sand river beds is obtained.