引用水力学中单个潜水球体起动平衡时的阻力系数试验曲线，结合颗粒土料的渗流阻力试验中孔隙率的关系，提出了鉴别堤坝下游地基各土层发生管涌的临界流速和渗水量观测方法。为方便计算还给出了阻力系数试验曲线的不同流态（达西流和非达西流）经验公式。为应用方便，又算出常规土层的管涌临界流速和渗水量的对照表格，供汛期防洪查用。现场实施只要在局部渗水地面围以圆环观测渗出水量即可判别是否会发生管涌险情。

 During flood season, piping risk in the downstream of embankment is the most dangerous hidden trouble. The discrimination of piping in the past was generally based on seepage gradient which is not only limited theoretically by Darcy ' s flow but also inconvenient in practice. In view of this, a method of identifying piping below embankment, which can be called critical velocity or unit seepage discharge observation method, is suggested in this paper. It is based on the experimental curve of drag coefficients for single immersed spherical body moving steadily in water as well as the seepage experimental results for porosity relationship of grained soil mass. Furthermore, the empirical formulas for different flow patterns (Darcy and non-Darcy ' s flow) of the experimental curve are given to calculate the critical velocity. A table for the critical velocity and seepage discharge of different kinds of soil mass is also given. In practice, it only needs to measure the seepage discharge per unit by surrounding a suitable ring on the permeable surface to determine whether piping will happen or not.