A quantitative index Df, as the ratio of steady infiltration rate fp and lower layer conductivity Ks, for finger flow development was proposed, and its criticalvalue was found to be 0.02.

• 提出了以稳渗率fp与下层土饱和导水率Ks的比值Df作为判断指流产生的量化指标，并初步分析得到 Df的临界值为0.；02。