Table 2: Filter max. D15-distribution in relation to performance history of internal erosion.DF >= 1.4 mm1.4 < DF < 0.7DF <= 0.7 mm

13 1 0 No. of 1-dams (probable occurrence of internal erosion.
11 25 23 No. of dams without internal erosion (2 and 3-dams)
54% 4% 0% Proportion of dams with probable occurence of internal erosion