Even with today's design standards, the formation of deposits cannot be prevented. The reasons include:

• In the theoretical principles, the contact and adhesion effects of the transported particles were not considered (the observations were carried out largely with cohesion less, uniform material)

• Objects and obstacles that are not intended to be in the sewer system sometimes do enter and form blockages which are impossible or very difficult to transport

• Reduced flow rate due to backups, over filling and flooding events [Stein98h].