According to DIN EN 14654-1 deposits are "material deposited by gravity in the pipe invert or the bottom of a section of the drainage system" [DIN EN 14654-1]]. According to [ASTM D4410-16], “deposits of sediment within a channel, partly or completely filling the channel. Such materials accumulate where the transporting capacity has been insufficient to remove it as rapidly as it has been delivered”.

The solids sink and form deposits only when the critical velocity of the waste water falls bellow a target value. This is influenced by the following parameters [KA30]:

• Pipe diameter

• Slope

• Partial filling degree

• Surface roughness

• Suspended mineral solids

• Average particle diameter of the mineral solids.