...
The answer is "Yes" if D50 < 200 μm or D15 < 100 μm averaged over a thickness of 5 m between the water line and the toe of the channel slope.
Question 7: Is unstable breaching possible?
...
- a slope with or without flat banks
- for sand with D50 > 250 μm and D15 > 100 μm
- for sand with D50 > 500 μm and D15 > 250 μm
- for sand finer than 250 μm , there is no rule
NOTE: D50 and D15 are determined in the same way as in question 6.
Table A.4.2a from CUR113b, profile without flat berms:
...