What is the difference of movement of solids in large sewers and small sewers?

For solids in large sewers, forces on solids position them at different flow heights depending on their specific gravity.

There are generally two modes of movement of solids in small sewers, namely, floating and sliding dam. The floating mechanism operates when the size of solid is small when compared with the diameter of sewer. Solids move with the wave of sewage. On the other hand, the sliding mechanism functions when the size of solid is large when compared with the diameter of sewer. The sewage waves build up behind the solids which act as a barrier at the base of sewer. When the waves store sufficient energy to overcome the friction between solids and sewer invert, the solid would move along the sewer.

This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.