为满足泥沙沉降和起动相似，河工模型试验一般采用轻质模型沙。轻质模型沙引起的河床冲淤时间比尺与水流运动时间比尺不一致，使得模型水流运动过程发生扭曲、河道槽蓄及泥沙传播发生偏离，从而导致模型河床冲淤变形不相似。结合长江防洪模型试验分析了长河段河工模型时间变态对水流运动和河床冲淤变形的影响，探讨了时间变态影响改进措施，提出的模型进口提前、出口滞后的水沙过程控制方式，可供类似河工模型借鉴。

In order to meet the similarity of sediment settlement and starting motion, light model sediments are commonly adopted in river model test. The inconformity of the erosion time scale with the flow time scale generated by light model sediments causes distortion in the flow movement and deviation in the river storage tank and sediment transmission, which lead to the dissimilarity of river-bed deformation. Based on the Changjiang Flood Protection Physical Model Test, the paper analyzes the influence of time scale distortion on the flow movement and on the riverbed deformation. The paper also discusses the improvement approach to solving the distortion influence. The control mode of watersediment process that is ahead of time at inlet and lags at outlet of the physical model may be used in similar models.